Inflammation is vital for host defence against invasive
pathogens. In response to an infection, a cascade of
signals leads to the recruitment of inflammatory cells,
particularly innate immune cells such as neutrophils
and macrophages. These cells, in turn, phagocytose
infectious agents and produce additional cytokines
and chemokines that lead to the activation of lympho
cytes and adaptive immune responses. Similar to
the eradication of pathogens, the inflammatory
response is also crucial for tissue and wound repair
(BOX 1). Inflammation as a result of trauma, ischaemia–
reperfusion injury or chemically induced injury typically
occurs in the absence of any microorganisms and has
therefore been termed ‘sterile inflammation’. Similar to
microbially induced inflammation, sterile inflamma
tion is marked by the recruitment of neutrophils and
macrophages and the production of proinflammatory
cytokines and chemokines, notably tumour necrosis
factor (TNF) and interleukin1 (IL1).
Although inflammation is important in tissue repair
and eradication of harmful pathogens, unresolved,
chronic inflammation that occurs when the offending
agent is not removed or contained can be detrimental
to the host. The production of reactive oxygen species
(ROS), proteases and growth factors by neutrophils and
macrophages results in tissue destruction, as well as
fibroblast proliferation, aberrant collagen accumulation
and fibrosis. There are several examples of sterile inflam
matory diseases. Chronic inhalation of sterile irritants,
such as asbestos and silica, can lead to persistent activa
tion of alveolar macrophages and result in pulmonary
interstitial fibrosis1. In ischaemia–reperfusion injury, as
seen with myocardial infarction and stroke, the restoration
of blood flow causes further tissue destruction as a
result of neutrophilic infiltration, enhanced production
of ROS and inflammatory responses to necrotic cells2.
Sterile inflammation has also been implicated in such
disease processes as gout and pseudogout, in which the
deposition of monosodium urate (MSU) and calcium
pyrophosphate dihydrate (CPPD) crystals in the joints
results in acute neutrophilic infiltration followed by
chronic inflammation, fibrosis and cartilage destruc
tion3. In Alzheimer’s disease, neurotoxicity is associated
with activated microglial cells adjacent to βamyloid
containing plaques that generate ROS in addition to
proinflammatory cytokines4. Sterile inflammation
is also an important component of atherosclerosis, as
engulfment of cholesterol crystals by macrophages
leads to the activation and recruitment of inflamma
tory cells, endothelial cell dysfunction and plaque form
ation5. Finally, immune cell infiltration in the absence
of microorganisms is also characteristic of tumours,
and these cells can influence the growth and progres
sion of cancer6. Thus, understanding the mechanisms of
sterile inflammation is important for devising treatment
strategies against various human diseases.
As the inflammation induced in response to sterile
cell death or injury is similar to that observed during
microbial infection, host receptors that mediate the
immune response to microorganisms may be involved
in the activation of sterile inflammation. In the case
of infection, the mechanisms by which the inflam
matory response is initiated have been well studied.
There are several classes of receptors that are impor
tant for sensing microorganisms and for the subse
quent induction of proinflammatory responses (for a
*Department of Internal
Cancer Center, University of
‡Department of Pathology,
Comprehensive Cancer Center,
University of Michigan,
Michigan 48109, USA.
19 November 2010
An injury in which the tissue
first suffers from hypoxia as a
result of severely decreased,
or completely arrested, blood
flow. Restoration of normal
blood flow further enhances
exacerbates tissue damage.
Reactive oxygen species
(ROS). Oxygen radicals that
are mainly produced by the
chain. In excess, they can
cause intracellular and
which promotes cell death.
Sterile inflammation: sensing and
reacting to damage
Grace Y. Chen* and Gabriel Nuñez‡
Abstract | Over the past several decades, much has been revealed about the nature of
the host innate immune response to microorganisms, with the identification of pattern
recognition receptors (PRRs) and pathogen-associated molecular patterns, which are the
conserved microbial motifs sensed by these receptors. It is now apparent that these same
PRRs can also be activated by non-microbial signals, many of which are considered as
damage-associated molecular patterns. The sterile inflammation that ensues either resolves
the initial insult or leads to disease. Here, we review the triggers and receptor pathways that
result in sterile inflammation and its impact on human health.
826 | DeCeMbeR 2010 | VOLUMe 10
© 20 Macmillan Publishers Limited. All rights reserved 10
An episode of acute cardiac
ischaemia that leads to death
of heart muscle cells. It is
usually caused by a thrombotic
A chronic disorder of the
arterial wall characterized by
endothelial cell damage that
gradually induces deposits of
cholesterol, cellular debris,
calcium and other substances.
These deposits finally lead to
plaque formation and arterial
A form of cell death that
frequently results from toxic
injury, hypoxia or stress.
Necrosis involves the loss of
cell integrity and the release
of cell contents into the
interstitium. This form of cell
death usually occurs together
with inflammation. Depending
on the context, the self
antigens that are released
by necrosis can become
review, see Ref. 7). These have been collectively termed
pattern recognition receptors (PRRs). These germline
encoded PRRs sense conserved structural moieties
that are found in microorganisms and are often called
pathogenassociated molecular patterns (PAMPs). Five
classes of PRRs have been identified to date: Tolllike
receptors (TLRs), which are transmembrane proteins
located at the cell surface or in endosomes; NODlike
receptors (NLRs), which are located in the cytoplasm;
RIGIlike receptors (RLRs), which are also located
intracellularly and are primarily involved in antiviral
responses; Ctype lectin receptors (CLRs), which are
transmembrane receptors that are characterized by
the presence of a carbohydratebinding domain; and
absence in melanoma 2 (AIM2)like receptors, which
are characterized by the presence of a pyrin domain and
a DNAbinding HIN domain involved in the detection
of intracellular microbial DNA8. Following ligand rec
ognition or cellular disruption, these receptors activate
downstream signalling pathways, such as the nuclear
factorκb (NFκb), mitogenactivated protein kinase
(MAPK) and type I interferon pathways, which result
in the upregulation of proinflammatory cytokines and
chemokines that are important in inflammatory and
It is now evident that PRRs also recognize non
infectious material that can cause tissue damage and
endogenous molecules that are released during cellu
lar injury (TABle 1). These endogenous molecules have
been termed damageassociated molecular patterns
(DAMPs), as these hostderived nonmicrobial stimuli
are released following tissue injury or cell death and
have similar functions as PAMPs in terms of their abil
ity to activate proinflammatory pathways. Here, we
discuss the nature of these instigators of inflammation
in the absence of infection, the potential mechanisms
by which they are recognized by the host to activate
inflammatory pathways and the implications for
DAMPs: indicators of tissue injury
A common feature of DAMPs is that they are endog
enous factors that are normally sequestered intracel
lularly and are therefore hidden from recognition by
the immune system under normal physiological condi
tions. However, under conditions of cellular stress or
injury, these molecules can then be released into the
extracellular environment by dying cells and trigger
inflammation under sterile conditions. The type of cell
death notably affects its immunogenicity and ability to
release immunostimulatory DAMPs. However, in gen
eral, DAMPs can be construed as signals of a potential
danger to the host9 (BOX 2). Necrosis usually occurs under
conditions of extreme damage (for example, ischaemia
or trauma) when apoptosis fails to occur. An important
consequence of necrotic cell death is the loss of plasma
membrane integrity, thereby allowing escape of intra
cellular material from the cell. Prototypical DAMPs
derived from necrotic cells include the chromatin
associated protein high-mobility group box 1 (HMGb1)10,
heat shock proteins (HSPs)11, and purine metabolites,
such as ATP12 and uric acid13 (TABle 1). In addition to
DAMPs from an intracellular source, there are also
extracellularly located DAMPs. These are typically
released by extracellular matrix degradation during
tissue injury. extracellular matrix fragments, such as
hyaluronan, heparan sulphate and biglycan, are gener
ated as a result of proteolysis by enzymes released from
dying cells or by proteases activated to promote tissue
repair and remodelling14. Similarly, in addition to intra
cellular molecules, intracellular stores of biologically
active proinflammatory cytokines and chemokines,
such as IL1α15 and IL33 (Ref. 16), may be released by
necrotic cells. Although these factors are not conven
tionally considered as DAMPs, they can mediate sterile
inflammatory responses (see below).
DAMPs have been identified by their ability
to induce inflammatory responses in vitro and/or
in vivo when purified and by the observed reduction
in inflammation when they are selectively depleted17.
However, in addition to the concern that the stimula
tory activity of some DAMPs is attributed to contami
nation of purified preparations with bacterial products,
important questions remain unanswered. It is unclear,
for example, whether some of the DAMPs that have
been identified based on their ability to stimulate
proinflammatory cytokine production in vitro have
a role in inducing sterile inflammation in vivo, as is
the case for HSPs11,18, S100 calciumbinding proteins19
and ATP20. Furthermore, many DAMPs, such as HSPs
and HMGb1, seem to interact with several receptors
(TABle 1) and, therefore, the significance of these inter
actions during sterile inflammation and disease patho
genesis remains to be fully elucidated. Also unknown
is the relative importance of individual DAMPs — that
Box 1 | Inflammation and wound repair
The acute inflammatory response has an integral role in normal wound healing and
tissue repair to eradicate the offending agent, regenerate the parenchyma and heal
any sustained damage. In response to injury that disrupts the parenchyma and causes
blood vessel damage, the coagulation system is activated, which begins the initial
stages of healing with the release of chemical mediators that promote vascular
permeability and leukocyte adhesion and recruitment. Activated platelets also
produce growth factors such as transforming growth factor‑β (TGFβ) and
platelet‑derived growth factor (PDGF), which activate fibroblasts and act as
chemoattractants for leukocytes116. The infiltration of leukocytes — first neutrophils,
followed by macrophages — allows the removal of dead cells and cellular debris. More
importantly, these cells secrete chemokines and cytokines, such as tumour necrosis
factor (TNF) and interleukin‑1 (IL‑1), that upregulate leukocyte adhesion molecules to
increase immune cell recruitment and induce the production of additional growth
factors and proteases by macrophages117. The release of proteases including matrix
metalloproteases leads to the degradation of the extracellular matrix to allow for
tissue remodelling. In addition to IL‑1 and TNF, growth factors and inflammatory
mediators produced by macrophages, such as fibroblast growth factor (FGF), PDGF,
prostaglandins and thrombospondin 1, promote new blood vessel growth, fibroblast
proliferation and collagen deposition117. Tissue remodelling is accompanied by
parenchymal regeneration or regrowth of the epithelial cell layer with resolution of
the healing process. Under conditions in which complete healing does not occur,
as in the setting of chronic infection or prolonged exposure to injurious agents, the
inflammatory response remains unresolved. Macrophages and neutrophils persist and
continue to secrete inflammatory cytokines, proteases and growth factors that lead to
inappropriate tissue destruction and scarring or fibrosis.
NATURe ReVIewS | Immunology
VOLUMe 10 | DeCeMbeR 2010 | 827
© 20 Macmillan Publishers Limited. All rights reserved10
A common form of cell death
that is defined by specific
morphological changes and by
the involvement of caspases.
The morphological features
include chromatin condensation,
plasma membrane blebbing
and DNA fragmentation into
segments of ~180 base pairs.
eventually, the cell breaks up
into many membrane-bound
‘apoptotic bodies’, which are
phagocytosed by neighbouring
High-mobility group box 1
(HMGB1; also known as
amphoterin). A nuclear protein
that binds DNA in a non-
sequence-specific manner and
modulates transcription and
chromatin remodelling by
bending DNA and facilitating
the binding of transcription
factors and nucleosomes,
A substance that stimulates the
immune system to enhance
the immunogenicity of antigens
or vaccines and enhance
is, whether they have redundant roles or whether a pre
dominant DAMP (the expression of which may depend
on the inciting event) triggers sterile inflammation. For
example, a reduction of uric acid, which is released
from dying cells and has adjuvant activity in vivo21,
was associated with substantially reduced neutrophil
recruitment in the liver after acetaminopheninduced
injury in two different mouse models13. by contrast,
in particulateinduced sterile inflammation, uric acid
depletion had no effect, suggesting that uric acid may
be a major proinflammatory DAMP that is specifically
involved in cell deathrelated sterile inflammation13.
However, uric acid depletion does not completely
eliminate acetaminopheninduced liver inflammation or
the adjuvant activity of damaged cells, which may reflect
residual uric acid following depletion or redundant
activities by other DAMPs.
The context of cellular injury leading to sterile
inflammation may also be important. In one study,
treatment of mice with HMGb1specific antibod
ies during acetaminopheninduced liver necrosis
ameliorated inflammatory cell recruitment10. However,
in a peritoneal model of sterile inflammation, there was
no difference between wildtype and HMGb1deficient
necrotic cells in their ability to promote neutrophilic
recruitment22. Thus, although substantial progress
has been made in identifying potential DAMPs that
can elicit inflammatory responses, much remains
to be learnt, such as the different biological func
tions of the various DAMPs during sterile inflamma
tion, which would be important for identifying new
Mechanisms of sterile inflammation
Despite the growing list of sterile immune stimuli, the
mechanisms by which these stimuli trigger an inflam
matory response are still not fully understood. even
though endogenously generated DAMPs are struc
turally heterogeneous, the outcome of inflamma
tory responses to these stimuli is generally uniform.
Moreover, inflammatory responses during infection
are very similar to responses induced by sterile stimuli,
Table 1 | Sterile stimuli
Putative sensor Associated pathologyRefs*
TLR2, TLR4, TLR9, RAGE and CD24Cellular injury and necrosis 26,93,98,106
HSPs TLR2, TLR4, CD91, CD24, CD14 and CD40Cellular injury and necrosis11,25,106,122
S100 proteins RAGECellular injury and necrosis 19
SAP130CLEC4E Cellular injury and necrosis72
RNA TLR3Cellular injury and necrosis 39,123
DNATLR9 and AIM2Cellular injury and necrosis40,48–50
Uric acid and MSU crystalsNLRP3Gout 13,55
ATPNLRP3 Cellular injury and necrosis 20,60
Hyaluronan TLR2, TLR4 and CD44 Cellular injury and necrosis31,32,103
Biglycan TLR2 and TLR4 Cellular injury and necrosis14,33
Versican TLR2Cellular injury and necrosis 34
Heparan sulphateTLR4 Cellular injury and necrosis124
FPR1 Cellular injury and necrosis125
DNA (mitochondrial)TLR9 Cellular injury and necrosis125
NLRP3, CD36 and RAGEAlzheimer’s disease56,94,105
NLRP3 and CD36Atherosclerosis59,105
IL-1RCellular injury and necrosis15,22,41
ST2 Cellular injury and necrosis16,86
NLRP3 Silicosis and pulmonary
AsbestosNLRP3 Asbestosis and pulmonary
AIM2, absent in melanoma 2; CLEC4E, C-type lectin 4E; CPPD, calcium pyrophosphate dihydrate; DAMP, damage-associated
molecular pattern; FPR1, formyl peptide receptor 1; HMGB1, high-mobility group box 1; HSP, heat shock protein; IL, interleukin;
MSU, monosodium urate; IL-1R, IL-1 receptor; NLRP3, NOD-, LRR- and pyrin domain-containing 3; RAGE, receptor for advanced
glycation end products; SAP130, spliceosome-associated protein 130; TLR, Toll-like receptor. *References may not be all inclusive.
828 | DeCeMbeR 2010 | VOLUMe 10
© 20 Macmillan Publishers Limited. All rights reserved10
including the recruitment of neutrophils and macro
phages, the production of inflammatory cytokines
and chemokines, and the induction of T cellmediated
adaptive immune responses23. This suggests that both
infectious and sterile stimuli may function through
common receptors and pathways. based on our cur
rent understanding, we propose three, not necessar
ily mutually exclusive, mechanisms by which sterile
endogenous stimuli trigger inflammation: activation of
PRRs by mechanisms similar to those used by micro
organisms and PAMPs; release of intracellular cytokines
and chemokines, such as IL1α, that activate common
pathways downstream of PRRs; and direct activation
by receptors that are not typically associated with
microbial recognition (fIG. 1).
Role of PRRs: recognition of endogenous DAMPs by
TLRs. There is mounting evidence that TLRs sense
endogenous molecules in addition to microbial PAMPs.
The possibility that mammalian TLRs recognize non
microbial structures is not unexpected, because the evo
lutionarily conserved Toll receptor originally identified
in Drosophila melanogaster binds to the endogenous
ligand Spätzle24. Indeed, several endogenous molecules
that are released from necrotic cells or are present in
the extracellular matrix have been reported to activate
TLRs. These include intracellular proteins, such as
HSPs, S100 proteins, uric acid, HMGb1 and endog
enous nucleic acids, as well as components of the extra
cellular matrix, such as hyaluronan, heparan sulphate
Although several of the purified endogenous mol
ecules, including HSPs, HMGb1 and uric acid, can
induce the production of proinflammatory cytokines
through TLR2 and/or TLR4 in vitro25–27, the relevance
of these observations has previously been questioned
because of the possibility of microbial contamination:
several of these proteins, including HSPs and HMGb1,
bind lipopolysaccharide (LPS), making the interpreta
tion of proinflammatory responses by these molecules
difficult28–30. because mice lacking TLR2 and TLR4
have only a slight reduction in the peritoneal inflam
matory response to sterile dead cells in vivo22, a reason
able conclusion is that TLR2–TLR4 signalling is not the
main mechanism by which intracellular factors induce
inflammatory responses to necrotic cell death. However,
this does not exclude a role for TLR signalling in other
models of sterile inflammation. For example, there is
evidence for a role of TLR2 and/or TLR4 in the induc
tion of cytokine and chemokine production in response
to extracellular matrix components, including hyaluro
nan fragments or soluble proteoglycan components,
in vitro and in vivo31–34. Tlr2 and Tlr4 doubleknockout
mice exhibit impaired transepithelial recruitment of
inflammatory cells and decreased survival in response
to lung injury31. Deficiency in either TLR2 or TLR4
signalling also reduced atherosclerotic disease in mouse
models35–37, and TLR4, specifically, has been shown
to mediate inflammatory responses to free fatty acids,
which are elevated in obesity and are associated with
insulin resistance38. Similarly, TLR3 can sense endogenous
RNA derived from necrotic neutrophils, which contrib
utes to the inflammatory response elicited by necrosis
in the bowel39. In the liver, which is normally devoid of
microbial exposure, TLR9 has been implicated in trig
gering cytokine production and hepatocyte toxicity
in acetaminopheninduced injury40. In this model of
sterile inflammation, activation of TLR9 is presum
ably mediated by genomic DNA released from necrotic
hepatocytes40. Collectively, the evidence suggests that
endogenous stimuli can induce a sterile inflammatory
response through TLRs, although the precise molecules
that engage TLRs remain poorly defined. Furthermore,
TLRs seem to function redundantly with other signal
ling pathways, so the contribution of TLRs to the overall
sterile inflammatory response remains unclear.
Role of PRRs: generation of IL‑1β by inflammasomes.
IL1, which includes both IL1α and IL1β, is a key
mediator of sterile inflammation that acts through
the IL1 receptor (IL1R)22,41. IL1β is a potent pro
inflammatory cytokine that is produced mainly by
macrophages and has many biological functions that are
important in sterile inflammation, such as the upregu
lation of those adhesion molecules on endothelial cells
that are important for the recruitment of neutrophils
and monocytes42 and for the induction of additional
proinflammatory mediators43. Compared with wild
type mice, IL1Rdeficient mice had decreased neutro
philic infiltration and inflammation in the liver after
acetaminopheninduced liver injury22 and in the lungs
after exposure to silica44.
Box 2 | Immunogenic cell death
Sterile stimuli — specifically, damage‑associated molecular patterns (DAMPs) —
are generally intracellular factors that are normally hidden from recognition by
the host immune system, and this ‘hiding’ effectively prevents pathological
inflammation and autoimmunity. Sterile inflammation occurs when DAMPs are
released into the extracellular environment. This occurs mostly when a cell
undergoes necrotic, as opposed to apoptotic, cell death. Indeed, necrotic cells are
normally immunostimulatory and lead to inflammatory cell infiltration and cytokine
production10,18. Apoptosis involves an orchestrated caspase signalling cascade that
ultimately leads to cell rounding and shrinkage (pyknosis), chromatin condensation,
non‑random DNA fragmentation or laddering, plasma membrane blebbing and
nuclear fragmentation (karyorrhexis). The apoptotic bodies that form can be
cleared effectively by phagocytes. This death process is therefore self‑contained,
and immunogenic endogenous molecules are not released to a significant extent
into the extracellular environment.
By contrast, necrotic cell death involves cellular and organelle swelling (oncosis)
and, most importantly, rupture of the plasma membrane, resulting in the release of
intracellular molecules that can elicit an inflammatory response. Reactive oxygen
species production, lysosomal membrane destabilization, activation of proteases
(including cathepsins) and ionic flux changes are all associated with necrosis and
can activate sterile inflammatory pathways in addition to the release of DAMPs118.
Necrosis predominates in conditions such as toxin‑ or ischaemia‑induced injury.
Although typically not associated with immunogenicity and inflammation,
apoptosis can become inflammatory under conditions in which there is delayed
clearance of apoptotic cells, as can occur with high levels of apoptosis, resulting in
secondary necrosis with loss of plasma membrane integrity119. Signalling through
death receptors that classically lead to apoptosis, such as FAS (also known as CD95),
has also been associated with inflammatory responses, although whether this is
actually correlated with the extent of apoptotic cell death is unclear120.
NATURe ReVIewS | Immunology
VOLUMe 10 | DeCeMbeR 2010 | 829
© 20 Macmillan Publishers Limited. All rights reserved10
A multiprotein complex that
contains a pattern recognition
receptor (PRR), typically a
member of the NOD-like
receptor (NlR) family, that, on
sensing its cognate agonist,
oligomerizes and recruits
the adaptor protein ASC
protein containing a CARD)
through protein domain
interactions. ASC can recruit
caspase 1 through its CARD,
thereby linking the PRR to
caspase 1 activation and
interleukin-1 production. There
are currently four characterized
inflammasomes, named by
the PRRs that form them: the
NRlP1 (NOD-, lRR- and pyrin
domain-containing 1), NlRP3,
NlRC4 (NOD-, lRR- and
CARD-containing 4) and
absence in melanoma 2 (AIM2)
IL1β has been implicated in various nonmicrobial
proinflammatory diseases. In atherosclerosis, engulfment
of cholesterol by macrophages leads to IL1β production,
which can stimulate the production of plateletderived
growth factor, promotion of smooth muscle cell and
fibroblast proliferation, arterial wall thickening and plaque
formation5,45. Crystalinduced arthropathies, such as gout,
are associated with elevated IL1β production, which leads
to joint inflammation and destruction5. elevated levels of
IL1β are also observed in the pancreatic islet cells from
patients with type 2 diabetes46, which is increasingly
being recognized as having a strong inflammatory com
ponent47. The secretion of IL1β by inflammatory cells is
largely dependent on a multiprotein complex termed the
inflammasome, of which the hallmark activity is the acti
vation of caspase 1. Following activation, caspase 1 pro
teolytically cleaves IL1β into its biologically active form.
Caspase 1 also cleaves the IL1 family member IL18 into
its active form and, therefore, IL18 may potentially be
involved in sterile responses, but its relevance in sterile
inflammation has not been well studied. There are sev
eral inflammasomes that have been described to date, and
each is named after the specific PRR contained in it. Of
these inflammasomes, two have been described that can
sense nonmicrobial molecules: the NLRP3 (NOD, LRR
and pyrin domaincontaining 3) inflammasome and the
The AIM2 inflammasome has been recently shown to
recognize cytoplasmic doublestranded DNA (dsDNA)
that is not necessarily microbial in origin, resulting in
caspase 1 activation and IL1β secretion48–50. Although
distinct from NLRs, AIM2 has a pyrin domain that allows
it to interact with the adaptor protein ASC (apoptosis
associated specklike protein containing a CARD) to
form the inflammasome50. AIM2 has a demonstrated
role in immune responses directed against both bacteria51
and DNA viruses52, but it will be important to determine
whether there is a physiological role for AIM2 in sterile
inflammation, especially in autoimmune diseases such as
systemic lupus erythematosus, which is associated with
elevated circulating levels of dsDNA.
Our understanding of how IL1β production is
induced during sterile inflammation has been advanced
by studies of the NLRP3 inflammasome. NRLP3 was
initially identified as an important mediator of chronic
inflammation owing to its association with auto
inflammatory disorders (BOX 3). Since then, NLRP3
has been implicated in various sterile inflammatory
diseases. NLRP3 signalling has been shown to involve
at least two steps, the first involving PRR or cytokine
dependent transcriptional upregulation of NLRP3 and
the second involving activation of the NLRP3 inflam
masome, which leads to IL1β production53,54 (BOX 4).
A unique feature of NLRP3 is its ability to sense various
Figure 1 | mechanisms for inducing sterile inflammation. Sterile stimuli that include damage-associated molecular
patterns (DAMPs), sterile particulates and intracellular cytokines released from necrotic cells can activate the host
immune system to induce sterile inflammation through at least three pathways that are not mutually exclusive. DAMPs
and sterile particulates can active host pathogen recognition receptors (PRRs), such as the Toll-like receptors (TLRs) and
the nucleotide-binding oligomerization domain (NOD)-like receptor NLRP3 (NOD-, LRR- and pyrin domain-containing 3),
which are also used by the host to sense microorganisms. Activation of these receptors results in the upregulation of
cytokines and chemokines, such as interleukin-1β (IL-1β), which are released to recruit and activate additional
inflammatory cells (1). Intracellular cytokines such as IL-1α and IL-33 that are released by damaged, necrotic cells activate
signalling pathways downstream of PRRs (2). Endogenous DAMPs signal directly through host receptors that are not
typically considered to be PRRs or to be involved in microbial detection (3). HMGB1, high-mobility group box 1;
IL-1R, IL-1 receptor; RAGE, receptor for advanced glycation end-products.
830 | DeCeMbeR 2010 | VOLUMe 10
© 20 Macmillan Publishers Limited. All rights reserved 10
structurally diverse stimuli. Therefore, it is posited that
NLRP3 does not recognize each stimulus individually,
but senses a common downstream event. NLRP3 has
been shown to respond to sterile stimuli, including
asbestos, silica, MSU and CPPD crystals55, cholesterol
crystals and βamyloid fibrils56. Consistently, in mouse
models of sterile injury, such as gout, asbestosis and
silicosis, NLRP3deficient mice exhibited decreased
inflammation with reduced levels of tissue infiltration
by neutrophils or macrophages55,57,58. Lowdensity lipo
protein (LDL) receptordeficient mice, which are prone
to developing atherosclerotic lesions, had lower IL1β
levels, smaller atherosclerotic lesions and less neutro
philic infiltration than wildtype mice when lethally
irradiated and infused with NLRP3deficient bone mar
row59. NLRP3deficient mice were also less susceptible
to renal ischaemia–reperfusion injuries induced by bilat
eral renal artery ligation and to acetaminopheninduced
hepatotoxicity40,60. A potential role for NLRP3 in pro
moting elevated levels of IL1β in type 2 diabetes was
also implied by the observation of NLRP3dependent
IL1β secretion by mouse bone marrowderived macro
phages and dendritic cells in response to islet amyloid
polypeptide (IAPP), which is deposited in the pancreas
and associated with loss of βcell function in type 2 dia
betes61. Interestingly, the antidiabetic drug glyburide
(Glibenclamide; Roche/SanofiAventis) has been shown
to block glucosemediated secretion of IL1β by mouse
pancreatic islets62, as well as IL1β production by macro
phages in response to IAPP61, and NLRP3deficient
mice were more glucose tolerant than wildtype mice62.
However, whether NLRP3 is directly involved in the
pathogenesis of type 2 diabetes in humans remains to
be determined. Regardless, understanding how NLRP3
senses diverse sterile stimuli is important for under
standing the pathogenesis of possibly many sterile
inflammatory disorders and for identifying potential
therapeutic targets. There are three main pathways
that have been proposed to mediate sterile activation
of NLRP3 (fIG. 2). These can be categorized as ATP,
lysosomal damage or ROSmediated activation.
In vitro, robust activation of the NLRP3 inflam
masome in phagocytic cells that were pretreated with
microbial products or cytokines such as TNF is depend
ent on the presence of ATP20. However, the amounts of
ATP necessary for NLRP3mediated caspase 1 activa
tion to be detected in macrophages in vitro are greater
than physiological concentrations63 and, therefore, the
relevance of this pathway in vivo is uncertain. ATP binds
to purinergic receptor P2X7 (P2RX7), which leads to the
opening of an ATPgated cation channel that induces
K+ efflux and the formation of a large pore mediated by
the hemichannel protein pannexin 1 (RefS 64,65). Thus,
it has been suggested that NLRP3 senses intracellular
K+ depletion, which may act as a surrogate marker of
cellular injury that is sensed by NLRP3. Consistently,
inhibition of K+ efflux by high extracellular K+ concen
trations prevents NLRP3dependent caspase 1 activation
in response to ATP, asbestos, silica and MSU crystals58,66.
Also, necrotic cells can activate NLRP3, which is partly
dependent on actively respiring mitochondria and the
physiological release of ATP60. However, IL1β secre
tion was only partially dependent on P2RX7, suggesting
that the release of ATP may be only one mechanism by
which necrotic cells can activate NLRP3. It is probable
that additional factors besides ATP have a role60.
Box 3 | Role of NLRP3 in autoinflammatory syndromes
Autoinflammatory syndromes are a group of rare monogenic inherited disorders that
are characterized by episodic occurrences of fever, sterile inflammation and other
more variable inflammatory manifestations in the absence of clinical and laboratory
markers of autoimmunity or infection. These syndromes include familial cold
autoinflammatory syndrome, Muckle–Wells syndrome and neonatal‑onset
multisystemic inflammatory disease (NOMID; also known as CINCA syndrome) and
are caused by missense mutations in the nucleotide‑binding oligomerization domain
(NOD)‑like receptor family member NLRP3 (NOD‑, LRR‑ and pyrin domain‑containing 3;
also known as cryopyrin). Clinical features of these dominantly inherited disorders,
which are commonly referred as cryopyrin‑associated periodic syndromes, include
recurring episodes of fever, urticarial skin rash and arthropathy. These disease‑
asssociated missense NLRP3 mutations result in enhanced activation of caspase 1 and
secretion of interleukin‑1β (IL‑1β) by causing constitutive activation of the NLRP3
inflammasome. Notably, treatment of these patients with an IL‑1 receptor antagonist
or IL‑1β‑specific blocking antibody reverses clinical symptoms, which suggests a
cause–effect relationship between IL‑1β production and the development of disease.
Box 4 | NLRP3 activation
The assembly and activation of the NLRP3 (NOD‑, LRR‑ and pyrin domain‑containing 3) inflammasome results in the
cleavage of pro‑caspase 1 to its active form, which in turn, cleaves pro‑interleukin‑1β (pro‑IL‑1β) and pro‑IL‑18 into
their mature, biologically active forms. In vitro studies have led to a model of NLRP3‑mediated IL‑1β production that
requires two separate signals. The first signal is the nuclear factor‑κB (NF‑κB)‑dependent transcription of pro‑IL‑1β
and NLRP3, either through the activation of Toll‑like receptors (TLRs) or nucleotide‑binding oligomerization
domain 2 (NOD2), and therefore, in vitro, this signal can be provided by various TLR or NOD2 agonists, such as
lipopolysaccharide20,53,121. In the case of sterile inflammation, certain cytokines that induce NF‑κB, such as tumour
necrosis factor or IL‑1, can provide the first signal for NLRP3 activation54. In addition, during sterile inflammation,
endogenous molecules that signal through TLRs, such as low‑density lipoprotein, may be the first signal to prime the
activation of the NLRP3 inflammasome, resulting in cooperative signalling through separate pathways14,40,61,105.
The second signal is provided by stimuli that specifically activate NLRP3 and leads to caspase 1 activation. In vitro,
this second signal is typically provided by the addition of ATP or certain bacterial toxins, which results in pore
formation and K+ depletion that may be sensed by NLRP3, leading to caspase 1 activation and pro‑IL‑1β cleavage.
As intracellular pro‑IL‑1β levels are usually low, the first signal has been considered to be a ‘priming’ event to allow for
subsequent NLRP3 activation and IL‑1β release, which otherwise could not occur. The two step model would allow
for an additional level of regulation of caspase 1 activation.
NATURe ReVIewS | Immunology
VOLUMe 10 | DeCeMbeR 2010 | 831
© 20 Macmillan Publishers Limited. All rights reserved10
Caspase 1 activation
and IL-1β production
An enzyme system that
consists of several cytoplasmic
subunits. The complex is
assembled in activated
phagocytic cells mainly on
NADPH oxidase uses electrons
from NADPH to reduce
molecular oxygen to form
superoxide anions. Superoxide
anions are enzymatically
converted to hydrogen
peroxide, which is converted
by myeloperoxidase to
hypochloric acid, a highly toxic
and microbicidal agent.
P2RX7dependent pore formation is not a prerequi
site for NLRP3 activation by all stimuli. Urate and choles
terol crystals, as well as sterile particulates, for example,
can bypass the requirement for ATP and P2RX7 for
IL1β production55,59. For these sterile particulates to
activate NLRP3, they must be internalized, as block
ade of endocytosis by the actindepolymerizing drug
cytochalasin D inhibited NLRP3dependent IL1β pro
duction58,59. Importantly, NLRP3dependent caspase 1
activation was associated with destabilization of the lyso
somal membrane and activation of lysosomal proteases
(specifically, cathepsin b)44. Lysosomal damage can
occur during cellular injury and necrosis, and has also
been associated with other sterile activators of NLRP3,
such as cholesterol59 and silica crystals44. Therefore, it is
possible that divergent upstream danger signals that are
sensed by NLRP3 may converge on lysosomal damage
and cathepsin b activation. evidence to support this are
the observations that artificial lysosomal rupture alone
can activate NLRP3 and that pharmacological inhibi
tion or genetic depletion of cathepsin b results in inhi
bition of caspase 1 activation, although this inhibition
was only partial44,56,59. However, cathepsin bdeficient
macrophages have no impairment in IL1β production
in response to certain NLRP3 agonists, including LPS
plus ATP, or MSU crystals, despite the impairment in
their response to silica44,56,59,67. Furthermore, there is
only partial inhibition of the neutrophil infiltration and
IL1β production associated with sterile inflammation
in response to cholesterol crystals44,56,59,67.
An additional damage signal that has been associ
ated with NLRP3 stimulation and caspase 1 activation
is ROS. During sterile inflammation, the production
of ROS by neutrophils (for example, through an oxida
tive burst) is important for the destruction of pathogens
but, during excessive cellular stress, high levels of ROS
can lead to oxidative stress with ensuing cell death and
necrosis. ROS levels can be controlled by neutralization
by enzymes with antioxidant activities. Therefore, the
detrimental effect of ROS during sterile inflammation
depends on the balance between ROS producers and
ROS inactivators. Silica58,68, asbestos57 and ATP69 have all
been associated with ROS production, and ROS inhibi
tion in vitro resulted in impairment of caspase 1 activation
and IL1β production by these stimuli57,58,69. How ROS
production is sensed by NLRP3 is unknown, but it was
recently shown in one study that NLRP3 interacts in a
ROSdependent manner with thioredoxininteracting
protein (TXNIP), which dissociates from the antioxi
dant enzyme thioredoxin during oxidative stress62. In this
study, TXNIPdeficient mice had impaired IL1β produc
tion and neutrophil influx after intraperitoneal injection
of MSU crystals, and TXNIPdeficient macrophages had
decreased IL1β production in response to a range of
known NLRP3 activators, including MSU crystals, silica,
and ATP62. Thus, the sensing of ROS may be a unifying
mechanism by which NLRP3 senses its various activa
tors. However, the role of TXNIP and ROS in NLRP3
activation has been challenged. In a separate study, no
differences in IL1β secretion were observed between
wildtype and TXNIPdeficient bone marrowderived
macrophages in response to several NLRP3 stimuli,
including MSU crystals and ATP61. Furthermore, mouse
macrophages that are deficient in p22phox (L. Franchi and
G.N., unpublished observations) or the Gp91phox subunit
of NADPH oxidase cytochrome b, which is a major genera
tor of ROS in the cell, had normal, rather than decreased,
levels of caspase 1 activation in response to ATP, silica or
MSU crystals44. Thus, the relevance of ROS generation in
NLRP3 activation in vivo remains unclear. Collectively,
there is still controversy regarding the roles of the indi
vidual model pathways for NLRP3 activation, and it
remains to be determined whether there is a common
mechanism by which numerous heterogeneous stimuli
converge on NLRP3.
Role of PRRs: an emerging role for CLRs. CLRs are an
increasingly recognized category of PRRs that are
important in host defence. This class of PRRs contains
a carbohydratebinding domain that recognizes carbo
hydrates on viruses, bacteria and fungi. In general, the
ligands of these CLRs are unknown70. Stimulation of
CLRs typically results in the induction of signalling
Figure 2 | Proposed pathways for nlRP3 activation. The activation of the NLRP3
(NOD-, LRR- and pyrin domain-containing 3) inflammasome has been associated with
three separate phenomena. ATP can bind to purinergic receptor P2X7 (P2RX7), which
then opens a cation channel and a large pore through pannexin 1 that, in turn, can lead
to ionic fluxes, including intracellular K+ depletion, and other events that are poorly
understood. Endocytosis of sterile particulates, such as silica, asbestos and cholesterol
crystals, results in lysosomal damage and membrane destabilization, leading to
activation of the protease cathepsin B. The generation of reactive oxygen species (ROS)
during cellular stress or death has been associated with NLRP3 activation, although the
role of ROS in NLRP3 activation remains controversial. DAMPs, damage-associated
molecular patterns; IL-1β, interleukin-1β.
832 | DeCeMbeR 2010 | VOLUMe 10
© 20 Macmillan Publishers Limited. All rights reserved 10
pathways that, in some cases, can synergize with TLR
signalling pathways to upregulate cytokine and chemo
kine production. In antigenpresenting cells, they are
involved in antigen uptake and trafficking for antigen
presentation71. Although their primary importance is in
host defence against pathogens, CLRs can sense necrotic
cell death72. In particular, Ctype lectin 4e (CLeC4e;
also known as MINCLe) can detect the DAMP
spliceosomeassociated protein 130 (SAP130), which
is a component of a small nuclear ribonucleo protein
that can be released by necrotic but not apoptotic cells,
resulting in upregulation of proinflammatory media
tors such as CXCchemokine ligand 2 (CXCL2) and
in neutrophil recruitment73. In a model of high levels
of cell death in the thymus by wholebody irradiation,
CXCL2 production by thymic macrophages, as well
as neutrophil infiltration into the thymus, was sig
nificantly suppressed in mice treated with a blocking
antibody to CLeC4e73. whether CLeC4e contributes
to sterile inflammationrelated diseases is unknown.
Interestingly, Clec4e mRNA is upregulated in patients
with rheumatoid arthritis73,74.
CLeC9A (also known as DNGR1), which is
expressed by CD8α+ dendritic cells, is also involved
in the recognition of necrotic cells. CLeC9A has been
shown to recognize necrotic cells and induce the cross
presentation of dead cellassociated antigens to CD8+
T cells. Therefore, it may be involved in regulating
sterile immune responses, although the specific ligand
recognized in this case is still unknown73,75. Similar to
CLeC4e, the ability of CLeC9A to recognize necrotic
cells makes it a potential receptor that is important for
sterile inflammatory responses. Determining whether
CLeC9A contributes to sterile inflammation in vivo
should be possible, as transgenic mice deficient in this
receptor have been made75.
Release of intracellular cytokines. The passive release
of biologically active cytokines during sterile injury
associated cell death is an important mechanism to alert
the immune system of tissue damage and to initiate the
healing response. There is evidence that the passive
release of cytokines during sterile cell injury has a role
in disease. Two cytokines of the IL1 family, IL1α and
IL33, are particularly relevant. In the case of IL1α, its
release from injured endothelial cells promotes allogeneic
T cell infiltration in a mouse–human chimeric model of
artery allograft rejection76. In addition, IL1α released
during hepatocyte necrosis contributes to carcinogen
induced liver tumorigenesis in mice77. Unlike its related
family members IL1β and IL18, IL1α is synthesized
as a biologically active cytokine in its fulllength precur
sor form and does not require processing for signalling
through IL1R78,79. when cells die by necrosis, such as
during injury, this precursor form of IL1α is released,
leading to activation of its cognate receptor and rapid
recruitment of inflammatory cells into the surrounding
injured tissue22,78. This is in contrast with apoptotic cells,
in which IL1α is sequestered intracellularly78, or with
intact cells, in which the secretion of mature IL1α is
partially dependent on caspase 1 activity80–82.
The mechanism by which necrotic cells and IL1α
induce sterile inflammation remains poorly understood.
Using a model of peritonitis triggered by necrotic cells,
IL1α was shown to be important for the recruitment of
neutrophils, which was caspase 1 independent, and this
response was impaired in mice lacking IL1R expression
by nonmyeloid cells22. Subsequently, it was shown that
IL1α released by necrotic cells was crucial for the pro
duction of CXCL1, which recruits neutrophils, by non
haematopoietic cells such as mesothelial cells15. However,
the mechanism by which necrotic cells induce acute
inflammatory responses seems to be more complex
in vivo. For example, necrotic dendritic cells, but not
necrotic macrophages, heart cells or liver cells, rely
on IL1α to recruit neutrophils, at least in a peritonitis
model41. In the case of necrotic liver tissue, IL1α and
IL1β derived from resident macrophages, but not the
necrotic cells themselves, seem to have a crucial role in
eliciting the neutrophilic response41. Thus, the release of
IL1α from certain cells, such as dendritic cells, contributes
to sterile inflammation, but macrophages seem to be the
primary sentinel cells that mediate the sensing of necrotic
cells through the production of mature IL1α and IL1β41.
The mechanism by which resident macro phages produce
mature IL1α and IL1β in response to necrotic cells to
mediate neutrophilic recruitment remains unclear, but
it is caspase 1 independent22, suggesting that in the case
of IL1β other proteases may be responsible for cleaving
proIL1β to its active form83,84. These studies suggest that
the precursor form of IL1α that is released by necrotic
cells contributes to the initial neutrophilic response, but
resident macrophages are the main source of mature
IL1α and IL1β, which are needed for cell deathinduced
sterile inflammation (fIG. 3). Locally produced IL1 then
mediates neutrophil recruitment within the peritoneal
cavity through IL1R signalling and induction of CXCL1
production (fIG. 3).
Similar to IL1α, IL33 is active as a precursor pro
tein. extracellular IL33 that is released during necrosis
also functions as an alarmin to alert cells, such as mast
cells and other innate immune cells, to tissue damage85,86.
Although it was initially thought that the IL33 precur
sor was processed by caspase 1 to produce biologically
active IL33, it is now clear that its processing by the
executioner caspases caspase 3 and caspase 7 during
apoptosis inactivates IL33 (RefS 85,86). Thus, IL33,
which is expressed at high levels by endothelial cells and
some epithelial cells, is expected to be active when it is
released during necrosis, but not apoptosis, which is asso
ciated with executioner caspase activation. IL33 is highly
expressed within endothelial cells in the synovium of
patients with rheumatoid arthritis87, and IL33deficient
mice have reduced neutrophil migration in an experi
mental model of rheumatoid arthritis88, but the actual
role of this cytokine in the pathogenesis of rheumatoid
arthritis or other sterile inflammatory diseases remains
to be determined. Collectively, the evidence suggests that
the precursor forms of IL1α and IL33 (both of which
are biologically active) are preferentially released dur
ing necrosis to alert the immune system to cell damage,
leading to the initiation of the healing response.
NATURe ReVIewS | Immunology
VOLUMe 10 | DeCeMbeR 2010 | 833
© 20 Macmillan Publishers Limited. All rights reserved 10
Non‑PRR‑mediated recognition of DAMPs. In addi
tion to PRRs, DAMPs are recognized by DAMPspecific
receptors. The prototypical DAMPspecific receptor
is receptor for AGes (RAGe). RAGe is a transmembrane
receptor that is expressed by immune cells, endothe
lial cells, cardiomyocytes and neurons89–91. It detects
advanced glycation endproducts (AGes) that arise from
nonenzymatic glycation and oxidation of proteins and
lipids. These products can accumulate under conditions
of high oxidant stress and are found at elevated levels
in chronic inflammatory disease states such as type 1
In addition to AGes, RAGe also recognizes HMGb193
and the S100 family members19, which are released dur
ing cellular stress and necrotic cell death, and βamyloid94,
the accumulation of which is pathogenic in Alzheimer’s
disease. Activation of RAGe by its ligands results
in the upregulation of several inflammatory signal
ling pathways, including, but not limited to, NFκb,
phospho inositide 3kinase, Janus kinase (JAK)–signal
transducer and activator of transcription (STAT) and
MAPK signalling pathways, which lead to induction
of proinflammatory cytokines such as TNF19,91,95,96.
The mechanism by which RAGe activates these pro
inflammatory signalling pathways is unclear. The protein
contains no obvious signalling domains90, although
extracellular signalregulated kinase (eRK) was shown
to directly interact with the cytoplasmic tail of RAGe97.
In certain cases, RAGe may transduce signals by acting
cooperatively with TLRs. Specifically, HMGb1bound
DNA can form a complex with TLR9 and RAGe to
induce proinflammatory cytokines98, which may be
important for promoting inflammation in patients with
systemic lupus erythematosus who have elevated cir
culating levels of DNAcontaining immune complexes.
The mechanistic detail of RAGe signalling and the
importance of its various ligands in disease pathology
continue to be areas of investigation.
RAGe has been implicated in both diabetes and
obesityrelated atherosclerosis using apolipoprotein e
(APOe)deficient mice, which are susceptible to devel
oping atherosclerosis99,100. Furthermore, blockade of
RAGe by using a soluble competitive inhibitor sup
pressed diabetesassociated atherosclerosis in mouse
models92. Apoe–/–Rage–/– mice also exhibited a reduc
tion in atherosclerosis101, as shown by a reduction in
both atherosclerotic plaque formation and production
of proinflammatory mediators within the aorta. In
addition, the binding of βamyloid to RAGe results in
activated microglial cells94, and RAGe expression by
microglial cells contributed to neuroinflammation in a
mouse model of Alzheimer’s disease89. whether RAGe
has a direct role in the pathogenesis of these diseases
in humans and what pathways are specifically activated
remain to be elucidated.
Several other nonPRRs have been shown to inter
act with certain DAMPs, although their precise roles
during sterile inflammation in vivo have not been veri
fied. As in the case of TLR9 and RAGe, some of these
receptors engage TLRs to form coreceptor complexes,
which then induce inflammatory responses through
TLRdependent pathways. Hyaluronan fragments, for
example, can signal through CD44, leading to MAPK
activation102. Hyaluronan is also directly recognized
by TLR2 and TLR4, and this interaction was shown
to have a role in mediating inflammatory responses
in a mouse model of sterile bleomycininduced lung
injury102. How CD44 signalling contributes to sterile
inflammation is unclear, but it has been shown to phys
ically interact with TLR4 in vitro and function as an
accessory molecule for TLR4 signalling in response to
hyaluronan102,103. Similarly, CD36 is a scavenger recep
tor that binds oxidized LDL and βamyloid, which are
associated with sterile inflammation related to athero
sclerosis and Alzheimer’s disease, respectively. CD36
mediates heterodimer formation of TLR4 and TLR6
(Ref. 104), and this coreceptor complex upregulates the
production of chemokines and cytokines such as pro
IL1β through the activation of NFκb. Induction of
NFκb signalling through this coreceptor complex to
produce IL1β may serve as a priming event for subse
quent NLRP3 activation105 (the first signal; see BOX 1)
or provide additional signals to mediate inflammation
in atherosclerosis and Alzheimer’s disease.
It has also been shown that DAMPspecific recep
tors can negatively regulate inflammatory responses.
Specifically, CD24, which can bind to both HMGb1
and HSPs, negatively regulates sterile inflammatory
Figure 3 | model for Il‑1‑mediated neutrophil
recruitment in response to necrotic cell death. Necrotic
cells release the precursor form of interleukin-1α (IL-1α),
which is biologically active and stimulates neighbouring
parenchymal cells, through IL-1 receptor (IL-1R), to secrete
the chemokine CXC-chemokine ligand 1 (CXCL1). In
addition, IL-1α can stimulate resident macrophages to
produce additional IL-1α and IL-1β through a caspase 1-
independent mechanism that further boosts CXCL1
secretion. In turn, CXCL1 functions through CXC-chemokine
receptor 2 (CXCR2) on neutrophils to recruit them to the site
of injury. This figure is based on published studies using a
peritoneal model of sterile inflammation15,22,41.
834 | DeCeMbeR 2010 | VOLUMe 10
© 20 Macmillan Publishers Limited. All rights reserved10
responses. CD24mediated inhibition was associated
with increased proinflammatory cytokine production
by HMGb1 and decreased survival following aceta
minopheninduced liver injury106. This may provide
one mechanism by which the host immune system can
modulate responses to DAMPs and distinguish DAMPs
from PAMPs107. whether there are other examples of
this phenomenon remains to be determined. Thus,
although there are nonPRRs that can sense sterile
stimuli, most notably RAGe, whether these receptors
have a primary or secondary role (for example through
regulation of TLR responses) in sterile inflammation
and their relevance in the pathogenesis of human
disease remain unknown.
Implications for therapy
Given the crucial role for IL1 in sterile inflamma
tory responses, blockade of IL1R has been tested as a
therapeutic target for sterile inflammatory disorders in
humans. Promising results have been obtained with the
use of IL1β blockade using anakinra (Kineret; Amgen/
biovitrum), a recombinant IL1R antagonist. Anakinra
was shown to be highly effective in the treatment of
patients with gout who could not tolerate or did not
respond to previous therapy108. Although the clini
cal study was small, with only ten patients evaluated,
all ten patients treated with anakinra had significant
relief from symptoms108. However, the effect of IL1R
antagonism in other inflammatory joint diseases, such
as osteoarthritis and rheumatoid arthritis, has not been
as promising, with little or no clinical benefit shown in
human clinical trials43.
A benefit for anakinra was also shown in a small,
randomized trial of 70 patients with type 2 diabetes109.
Those treated with anakinra had improved glucose lev
els and reduced systemic inflammation, as suggested
by lower circulating levels of inflammatory markers,
such as IL6 and Creactive protein. This treatment
approach for type 2 diabetes is promising, as the
improvement in levels of glucose and inflammatory
markers was longlasting110. However, the clinical study
was still small and was not designed to determine opti
mal dosing, duration of use or longterm outcomes in
Chronic inflammation is also important for carcino
genesis, as proinflammatory cytokines, including IL1β,
can be tumour promoting6,111. Thus, IL1R may also be a
potential target for the treatment of patients with cancer.
However, inflammatory responses are equally important
for mounting an effective antitumour response against
chemotherapyinduced, immunogenic tumour cell
death. Dying tumour cells release ATP and, indeed, the
ability of dendritic cells to prime tumourspecific T cells
required NLRP3 and P2RX7 (Ref. 112). Furthermore,
chemotherapytreated tumour cells injected into wild
type mice inhibited tumour development when the
mice were rechallenged with tumour cells, but this effect
was abrogated in NLRP3deficient and P2RX7deficient
mice112, suggesting that NLRP3mediated IL1β produc
tion through the ATP–P2RX7 pathway is important for
immune surveillance against tumours. Consistently, a
lossoffunction P2RX7 allele was also associated with
poorer prognosis (decreased metastasisfree survival) in
earlystage breast cancer patients treated with chemo
therapy112. Thus, an approach to treating patients with
cancer hinges on an improved understanding of how to
balance the tumoursuppressive and tumourpromoting
functions of IL1β.
Similarly, as TLRs also mediate sterile inflam
mation, they could be another potential therapeutic
target. Mice deficient in both TLR2 and TLR4 or in
myeloid differentiation primaryresponse protein 88
(MYD88), an adaptor protein for TLR and IL1R sig
nalling, were protected against bleomycininduced
lung injury related to the generation of hyaluronan
fragments, and administration of a hyaluronan
blocking peptide to wildtype mice provided similar,
although incomplete, protection31. TLR signalling is
also implicated in the pathogenesis of atherosclerotic
disease35–37. Furthermore, it was shown that TLR2
signalling by the endogenous extracellular matrix
derived proteoglycan versican can promote tumour
metastasis34. However, as TLR signalling is important
for tissue repair113,114, caution must also be taken in
devising a therapeutic strategy against TLRmediated
sterile inflammation. Indeed, mice deficient in TLR2
and TLR4 expression had increased mortality in
response to hypoxiainduced lung injury, which was
associated with decreased integrity of the lung epi
thelium31. TLR signalling during sterile inflammation
in the tumour microenvironment also has important
clinical implications. TLR4 signalling was found to be
important for dendritic cellmediated crosspresentation
of tumour antigens from dying, chemotherapytreated
tumour cells and involved HMGb1 release from the
dying cells115. The clinical importance of this finding
was suggested by the fact that, in earlystage breast
cancer patients who were treated with chemotherapy,
lower metastasisfree survival was associated with a
TLR4 polymorphism that affects binding of HMGb1
to TLR4 (Ref. 115). Thus, as inflammation is impor
tant not only in disease pathogenesis but also in tis
sue repair mechanisms and immune surveillance,
challenges remain in identifying optimal targets
and appropriate contexts for the treatment of sterile
Much progress has been made in identifying some of
the triggers of sterile inflammation. Many questions
remain, including the relative importance of the dif
ferent DAMPs in their biological activity, whether
they differentially activate downstream signalling
pathways and the molecular basis for their recog
nition. whether there are additional unidentified
endogenous DAMPs that may be implicated in disease
is also unknown. Finally, further studies are needed
to understand how the different inflammatory signal
ling pathways (mediated by TLRs, inflammasomes
and IL1R) interact to mediate the sterile inflamma
tory response and how they may be modulated for the
benefit of the host.
NATURe ReVIewS | Immunology
VOLUMe 10 | DeCeMbeR 2010 | 835
© 20 Macmillan Publishers Limited. All rights reserved10
Mossman, B. T. & Churg, A. Mechanisms in the
pathogenesis of asbestosis and silicosis. Am. J. Respir.
Crit. Care Med. 157, 1666–1680 (1998).
Cotran, R. S., Kumar, V. & Robbins, S. in Robbins
Pathologic Basis of Disease (ed. Schoen, F. J.) 6–11
(W. B. Saunders Company, Philadelphia, 1994).
Cotran, R. S., Kumar, V. & Robbins, S. in Robbins
Pathologic Basis of Disease (ed. Schoen, F. J.)
1255–1259 (W. B. Saunders Company, Philadelphia,
Weiner, H. L. & Frenkel, D. Immunology and
immunotherapy of Alzheimer’s disease. Nature Rev.
Immunol. 6, 404–416 (2006).
Ross, R. Atherosclerosis — an inflammatory disease.
N. Engl. J. Med. 340, 115–126 (1999).
Coussens, L. M. & Werb, Z. Inflammation and cancer.
Nature 420, 860–867 (2002).
Takeuchi, O. & Akira, S. Pattern recognition receptors
and inflammation. Cell 140, 805–820 (2010).
Unterholzner, L. et al. IFI16 is an innate immune
sensor for intracellular DNA. Nature Immunol.
11, 997–1004 (2010).
Matzinger, P. Tolerance, danger, and the extended
family. Annu. Rev. Immunol. 12, 991–1045 (1994).
10. Scaffidi, P., Misteli, T. & Bianchi, M. E. Release of
chromatin protein HMGB1 by necrotic cells triggers
inflammation. Nature 418, 191–195 (2002).
11. Quintana, F. J. & Cohen, I. R. Heat shock proteins
as endogenous adjuvants in sterile and septic
inflammation. J. Immunol. 175, 2777–2782
12. Bours, M. J., Swennen, E. L., Di Virgilio, F.,
Cronstein, B. N. & Dagnelie, P. C. Adenosine
5ʹ-triphosphate and adenosine as endogenous
signaling molecules in immunity and inflammation.
Pharmacol. Ther. 112, 358–404 (2006).
13. Kono, H., Chen, C. J., Ontiveros, F. & Rock, K. L.
Uric acid promotes an acute inflammatory response
to sterile cell death in mice. J. Clin. Invest. 120,
14. Babelova, A. et al. Biglycan, a danger signal that
activates the NLRP3 inflammasome via Toll-like and
P2X receptors. J. Biol. Chem. 284, 24035–24048
15. Eigenbrod, T., Park, J. H., Harder, J., Iwakura, Y. &
Nunez, G. Cutting edge: critical role for mesothelial
cells in necrosis-induced inflammation through the
recognition of IL-1α released from dying cells.
J. Immunol. 181, 8194–8198 (2008).
This paper shows that the passive release of
IL‑1α from necrotic cells, in particular necrotic
dendritic cells, is important for the recruitment of
neutrophils in the sterile inflammatory response
through the production of CXCL1 by cells
responsive to IL‑1α.
16. Moussion, C., Ortega, N. & Girard, J. P. The IL-1-like
cytokine IL-33 is constitutively expressed in the
nucleus of endothelial cells and epithelial cells in vivo:
a novel ‘alarmin’? PLoS ONE 3, e3331 (2008).
17. Kono, H. & Rock, K. L. How dying cells alert the
immune system to danger. Nature Rev. Immunol.
8, 279–289 (2008).
18. Basu, S., Binder, R. J., Suto, R., Anderson, K. M. &
Srivastava, P. K. Necrotic but not apoptotic cell death
releases heat shock proteins, which deliver a partial
maturation signal to dendritic cells and activate the
NF-κB pathway. Int. Immunol. 12, 1539–1546
19. Hofmann, M. A. et al. RAGE mediates a novel
proinflammatory axis: a central cell surface receptor
for S100/calgranulin polypeptides. Cell 97, 889–901
20. Mariathasan, S. et al. Cryopyrin activates the
inflammasome in response to toxins and ATP.
Nature 440, 228–232 (2006).
21. Shi, Y., Evans, J. E. & Rock, K. L. Molecular identification
of a danger signal that alerts the immune system to
dying cells. Nature 425, 516–521 (2003).
22. Chen, C. J. et al. Identification of a key pathway
required for the sterile inflammatory response triggered
by dying cells. Nature Med. 13, 851–856 (2007).
This paper demonstrates a crucial role for IL‑1α in
sterile inflammation and, in particular, neutrophil
recruitment induced by necrotic cells.
23. Mbitikon-Kobo, F. M. et al. Characterization of a
CD44/CD122int memory CD8 T cell subset generated
under sterile inflammatory conditions. J. Immunol.
182, 3846–3854 (2009).
24. Weber, A. N. et al. Binding of the Drosophila cytokine
Spatzle to Toll is direct and establishes signaling.
Nature Immunol. 4, 794–800 (2003).
25. Vabulas, R. M. et al. Endocytosed HSP60s use Toll-like
receptor 2 (TLR2) and TLR4 to activate the Toll/
interleukin-1 receptor signaling pathway in innate
immune cells. J. Biol. Chem. 276, 31332–31339
26. Yu, M. et al. HMGB1 signals through Toll-like receptor
(TLR) 4 and TLR2. Shock 26, 174–179 (2006).
27. Liu-Bryan, R., Scott, P., Sydlaske, A., Rose, D. M. &
Terkeltaub, R. Innate immunity conferred by Toll-like
receptors 2 and 4 and myeloid differentiation factor
88 expression is pivotal to monosodium urate
monohydrate crystal-induced inflammation.
Arthritis Rheum. 52, 2936–2946 (2005).
28. Gao, B. & Tsan, M. F. Endotoxin contamination in
recombinant human heat shock protein 70 (Hsp70)
preparation is responsible for the induction of tumor
necrosis factor α release by murine macrophages.
J. Biol. Chem. 278, 174–179 (2003).
29. Rouhiainen, A., Tumova, S., Valmu, L., Kalkkinen, N.
& Rauvala, H. Pivotal advance: analysis of
proinflammatory activity of highly purified eukaryotic
recombinant HMGB1 (amphoterin). J. Leukoc. Biol.
81, 49–58 (2007).
30. Youn, J. H., Oh, Y. J., Kim, E. S., Choi, J. E. & Shin, J. S.
High mobility group box 1 protein binding to
lipopolysaccharide facilitates transfer of
lipopolysaccharide to CD14 and enhances
lipopolysaccharide-mediated TNF-α production in
human monocytes. J. Immunol. 180, 5067–5074
31. Jiang, D. et al. Regulation of lung injury and repair by
Toll-like receptors and hyaluronan. Nature Med. 11,
This paper shows the dual role of TLRs in
mediating sterile inflammation in response to
hyaluronan fragments released during injury
and in promoting tissue repair.
32. Scheibner, K. A. et al. Hyaluronan fragments act
as an endogenous danger signal by engaging TLR2.
J. Immunol. 177, 1272–1281 (2006).
33. Schaefer, L. et al. The matrix component biglycan is
proinflammatory and signals through Toll-like
receptors 4 and 2 in macrophages. J. Clin. Invest.
115, 2223–2233 (2005).
34. Kim, S. et al. Carcinoma-produced factors activate
myeloid cells through TLR2 to stimulate metastasis.
Nature 457, 102–106 (2009).
35. Mullick, A. E., Tobias, P. S. & Curtiss, L. K.
Modulation of atherosclerosis in mice by Toll-like
receptor 2. J. Clin. Invest. 115, 3149–3156 (2005).
36. Michelsen, K. S. et al. Lack of Toll-like receptor 4 or
myeloid differentiation factor 88 reduces
atherosclerosis and alters plaque phenotype in mice
deficient in apolipoprotein E. Proc. Natl Acad. Sci.
USA 101, 10679–10684 (2004).
37. Bjorkbacka, H. et al. Reduced atherosclerosis in
MyD88-null mice links elevated serum cholesterol
levels to activation of innate immunity signaling
pathways. Nature Med. 10, 416–421 (2004).
38. Shi, H. et al. TLR4 links innate immunity and fatty
acid-induced insulin resistance. J. Clin. Invest. 116,
39. Cavassani, K. A. et al. TLR3 is an endogenous sensor
of tissue necrosis during acute inflammatory events.
J. Exp. Med. 205, 2609–2621 (2008).
40. Imaeda, A. B. et al. Acetaminophen-induced
hepatotoxicity in mice is dependent on Tlr9 and the
Nalp3 inflammasome. J. Clin. Invest. 119, 305–314
41. Kono, H., Karmarkar, D., Iwakura, Y. & Rock, K. L.
Identification of the cellular sensor that stimulates
the inflammatory response to sterile cell death.
J. Immunol. 184, 4470–4478 (2010).
This study shows the crucial role for macrophages
in mediating the inflammatory response to sterile
cell death, such as by IL‑1α production.
42. Wang, X., Feuerstein, G. Z., Gu, J. L., Lysko, P. G. &
Yue, T. L. Interleukin-1β induces expression of
adhesion molecules in human vascular smooth muscle
cells and enhances adhesion of leukocytes to smooth
muscle cells. Atherosclerosis 115, 89–98 (1995).
43. Gabay, C., Lamacchia, C. & Palmer, G. IL-1 pathways
in inflammation and human diseases. Nature Rev.
Rheumatol. 6, 232–241 (2010).
44. Hornung, V. et al. Silica crystals and aluminum
salts activate the NALP3 inflammasome through
phagosomal destabilization. Nature Immunol.
9, 847–856 (2008).
This study was pivotal in providing a model of
NLRP3 activation that involves lysosomal damage
and cathepsin B activation.
45. Raines, E. W., Dower, S. K. & Ross, R. Interleukin-1
mitogenic activity for fibroblasts and smooth muscle
cells is due to PDGF-AA. Science 243, 393–396
46. Boni-Schnetzler, M. et al. Increased interleukin (IL)-1β
messenger ribonucleic acid expression in β-cells of
individuals with type 2 diabetes and regulation of
IL-1β in human islets by glucose and autostimulation.
J. Clin. Endocrinol. Metab. 93, 4065–4074 (2008).
47. Shoelson, S. E., Lee, J. & Goldfine, A. B. Inflammation
and insulin resistance. J. Clin. Invest. 116,
48. Burckstummer, T. et al. An orthogonal proteomic-
genomic screen identifies AIM2 as a cytoplasmic DNA
sensor for the inflammasome. Nature Immunol. 10,
49. Fernandes-Alnemri, T., Yu, J. W., Datta, P., Wu, J. &
Alnemri, E. S. AIM2 activates the inflammasome
and cell death in response to cytoplasmic DNA.
Nature 458, 509–513 (2009).
50. Hornung, V. et al. AIM2 recognizes cytosolic dsDNA
and forms a caspase-1-activating inflammasome with
ASC. Nature 458, 514–518 (2009).
51. Fernandes-Alnemri, T. et al. The AIM2 inflammasome
is critical for innate immunity to Francisella tularensis.
Nature Immunol. 11, 385–393 (2010).
52. Rathinam, V. A. et al. The AIM2 inflammasome is
essential for host defense against cytosolic bacteria
and DNA viruses. Nature Immunol. 11, 395–402
53. Bauernfeind, F. G. et al. Cutting edge: NF-κB activating
pattern recognition and cytokine receptors license
NLRP3 inflammasome activation by regulating NLRP3
expression. J. Immunol. 183, 787–791 (2009).
54. Franchi, L., Eigenbrod, T. & Nunez, G. Cutting edge:
TNF-α mediates sensitization to ATP and silica via the
NLRP3 inflammasome in the absence of microbial
stimulation. J. Immunol. 183, 792–796 (2009).
References 53 and 54 provide evidence that the
first signal, or priming event, necessary for
activation of the NLRP3 inflammasome involves
upregulation of NLRP3 expression by NF‑κB
through the action of TLRs or pro‑inflammatory
cytokines such as TNF.
55. Martinon, F., Petrilli, V., Mayor, A., Tardivel, A. &
Tschopp, J. Gout-associated uric acid crystals activate
the NALP3 inflammasome. Nature 440, 237–241
This study is one of the first to identify an
endogenous, non‑microbial signal for NLPR3
inflammasome activation that can lead to a
non‑infectious inflammatory disease (in this
56. Halle, A. et al. The NALP3 inflammasome is involved
in the innate immune response to amyloid-β.
Nature Immunol. 9, 857–865 (2008).
57. Dostert, C. et al. Innate immune activation through
Nalp3 inflammasome sensing of asbestos and silica.
Science 320, 674–677 (2008).
This study led to the model of NLRP3 activation
that is dependent on the sensing of ROS, and
demonstrated a role for NLRP3 in asbestosis.
58. Cassel, S. L. et al. The Nalp3 inflammasome is
essential for the development of silicosis. Proc. Natl
Acad. Sci. USA 105, 9035–9040 (2008).
59. Duewell, P. et al. NLRP3 inflammasomes are required
for atherogenesis and activated by cholesterol
crystals. Nature 464, 1357–1361 (2010).
60. Iyer, S. S. et al. Necrotic cells trigger a sterile
inflammatory response through the Nlrp3
inflammasome. Proc. Natl Acad. Sci. USA 106,
61. Masters, S. L. et al. Activation of the NLRP3
inflammasome by islet amyloid polypeptide provides
a mechanism for enhanced IL-1β in type 2 diabetes.
Nature Immunol. 11, 897–904 (2010).
62. Zhou, R., Tardivel, A., Thorens, B., Choi, I. & Tschopp, J.
Thioredoxin-interacting protein links oxidative stress
to inflammasome activation. Nature Immunol. 11,
63. el-Moatassim, C. & Dubyak, G. R. A novel pathway for
the activation of phospholipase D by P2z purinergic
receptors in BAC1.2F5 macrophages. J. Biol. Chem.
267, 23664–23673 (1992).
64. Pelegrin, P. & Surprenant, A. Pannexin-1 mediates
large pore formation and interleukin-1β release by the
ATP-gated P2X7 receptor. EMBO J. 25, 5071–5082
65. Locovei, S., Wang, J. & Dahl, G. Activation of pannexin 1
channels by ATP through P2Y receptors and by
cytoplasmic calcium. FEBS Lett. 580, 239–244 (2006).
836 | DeCeMbeR 2010 | VOLUMe 10
© 20 Macmillan Publishers Limited. All rights reserved10
66. Petrilli, V. et al. Activation of the NALP3
inflammasome is triggered by low intracellular
potassium concentration. Cell Death Differ. 14,
67. Dostert, C. et al. Malarial hemozoin is a Nalp3
inflammasome activating danger signal. PLoS ONE
4, e6510 (2009).
68. Fubini, B. & Hubbard, A. Reactive oxygen species
(ROS) and reactive nitrogen species (RNS) generation
by silica in inflammation and fibrosis. Free Radic. Biol.
Med. 34, 1507–1516 (2003).
69. Cruz, C. M. et al. ATP activates a reactive oxygen
species-dependent oxidative stress response and
secretion of proinflammatory cytokines in
macrophages. J. Biol. Chem. 282, 2871–2879
70. Geijtenbeek, T. B. & Gringhuis, S. I. Signalling through
C-type lectin receptors: shaping immune responses.
Nature Rev. Immunol. 9, 465–479 (2009).
71. Figdor, C. G., van Kooyk, Y. & Adema, G. J. C-type
lectin receptors on dendritic cells and Langerhans
cells. Nature Rev. Immunol. 2, 77–84 (2002).
72. Yamasaki, S. et al. Mincle is an ITAM-coupled
activating receptor that senses damaged cells.
Nature Immunol. 9, 1179–1188 (2008).
73. Cambi, A. & Figdor, C. Necrosis: C-type lectins sense
cell death. Curr. Biol. 19, R375–R378 (2009).
74. Nakamura, N. et al. Isolation and expression profiling
of genes upregulated in bone marrow-derived
mononuclear cells of rheumatoid arthritis patients.
DNA Res. 13, 169–183 (2006).
75. Sancho, D. et al. Identification of a dendritic cell
receptor that couples sensing of necrosis to immunity.
Nature 458, 899–903 (2009).
This paper showed a role for CLEC9A in
regulating immune responses to sterile cell death,
specifically through the cross‑presentation of
dead cell‑associated antigens.
76. Rao, D. A. et al. Interleukin (IL)-1 promotes allogeneic
T cell intimal infiltration and IL-17 production in a
model of human artery rejection. J. Exp. Med. 205,
77. Sakurai, T. et al. Hepatocyte necrosis induced by
oxidative stress and IL-1α release mediate carcinogen-
induced compensatory proliferation and liver
tumorigenesis. Cancer Cell 14, 156–165 (2008).
78. Cohen, I. et al. Differential release of chromatin-bound
IL-1α discriminates between necrotic and apoptotic
cell death by the ability to induce sterile inflammation.
Proc. Natl Acad. Sci. USA 107, 2574–2579 (2010).
79. Dinarello, C. A. IL-1: discoveries, controversies and
future directions. Eur. J. Immunol. 40, 599–606
80. Li, P. et al. Mice deficient in IL-1β-converting enzyme
are defective in production of mature IL-1β and
resistant to endotoxic shock. Cell 80, 401–411 (1995).
81. Kuida, K. et al. Altered cytokine export and apoptosis
in mice deficient in interleukin-1β converting enzyme.
Science 267, 2000–2003 (1995).
82. Keller, M., Ruegg, A., Werner, S. & Beer, H. D.
Active caspase-1 is a regulator of unconventional
protein secretion. Cell 132, 818–831 (2008).
83. Fantuzzi, G. et al. Response to local inflammation of
IL-1β-converting enzyme-deficient mice. J. Immunol.
158, 1818–1824 (1997).
84. Mayer-Barber, K. D. et al. Caspase-1 independent
IL-1β production is critical for host resistance to
Mycobacterium tuberculosis and does not require
TLR signaling in vivo. J. Immunol. 184, 3326–3330
85. Luthi, A. U. et al. Suppression of interleukin-33
bioactivity through proteolysis by apoptotic caspases.
Immunity 31, 84–98 (2009).
86. Cayrol, C. & Girard, J. P. The IL-1-like cytokine IL-33 is
inactivated after maturation by caspase-1. Proc. Natl
Acad. Sci. USA 106, 9021–9026 (2009).
87. Carriere, V. et al. IL-33, the IL-1-like cytokine ligand
for ST2 receptor, is a chromatin-associated nuclear
factor in vivo. Proc. Natl Acad. Sci. USA 104,
88. Verri, W. A. Jr et al. IL-33 induces neutrophil migration
in rheumatoid arthritis and is a target of anti-TNF
therapy. Ann. Rheum. Dis. 69, 1697–1703 (2010).
89. Fang, F. et al. RAGE-dependent signaling in microglia
contributes to neuroinflammation, Aβ accumulation,
and impaired learning/memory in a mouse model of
Alzheimer’s disease. FASEB J. 24, 1043–1055
90. Sims, G. P., Rowe, D. C., Rietdijk, S. T., Herbst, R. &
Coyle, A. J. HMGB1 and RAGE in inflammation and
cancer. Annu. Rev. Immunol. 28, 367–388 (2010).
91. Shang, L. et al. RAGE modulates hypoxia/
reoxygenation injury in adult murine cardiomyocytes
via JNK and GSK-3β signaling pathways. PLoS ONE
5, e10092 (2010).
92. Bucciarelli, L. G. et al. RAGE is a multiligand receptor
of the immunoglobulin superfamily: implications for
homeostasis and chronic disease. Cell. Mol. Life Sci.
59, 1117–1128 (2002).
93. Hori, O. et al. The receptor for advanced glycation
end products (RAGE) is a cellular binding site for
amphoterin. Mediation of neurite outgrowth and
co-expression of rage and amphoterin in the
developing nervous system. J. Biol. Chem. 270,
94. Yan, S. D. et al. RAGE and amyloid-β peptide
neurotoxicity in Alzheimer’s disease. Nature 382,
95. Huang, J. S. et al. Role of receptor for advanced
glycation end-product (RAGE) and the JAK/STAT-
signaling pathway in AGE-induced collagen production
in NRK-49F cells. J. Cell Biochem. 81, 102–113
96. Dukic-Stefanovic, S., Schinzel, R., Riederer, P. &
Munch, G. AGES in brain ageing: AGE-inhibitors as
neuroprotective and anti-dementia drugs?
Biogerontology 2, 19–34 (2001).
97. Ishihara, K., Tsutsumi, K., Kawane, S., Nakajima, M. &
Kasaoka, T. The receptor for advanced glycation end-
products (RAGE) directly binds to ERK by a D-domain-
like docking site. FEBS Lett. 550, 107–113 (2003).
98. Tian, J. et al. Toll-like receptor 9-dependent activation
by DNA-containing immune complexes is mediated by
HMGB1 and RAGE. Nature Immunol. 8, 487–496
99. Ueno, H. et al. Receptor for advanced glycation end-
products (RAGE) regulation of adiposity and
adiponectin is associated with atherogenesis in apoE-
deficient mouse. Atherosclerosis 211, 431–436
100. Soro-Paavonen, A. et al. Receptor for advanced
glycation end products (RAGE) deficiency attenuates
the development of atherosclerosis in diabetes.
Diabetes 57, 2461–2469 (2008).
101. Harja, E. et al. Vascular and inflammatory stresses
mediate atherosclerosis via RAGE and its ligands in
apoE-/- mice. J. Clin. Invest. 118, 183–194 (2008).
102. Jiang, D., Liang, J. & Noble, P. W. Hyaluronan in
tissue injury and repair. Annu. Rev. Cell Dev. Biol. 23,
103. Taylor, K. R. et al. Recognition of hyaluronan released
in sterile injury involves a unique receptor complex
dependent on Toll-like receptor 4, CD44, and MD-2.
J. Biol. Chem. 282, 18265–18275 (2007).
104. Hoebe, K. et al. CD36 is a sensor of diacylglycerides.
Nature 433, 523–527 (2005).
105. Stewart, C. R. et al. CD36 ligands promote sterile
inflammation through assembly of a Toll-like
receptor 4 and 6 heterodimer. Nature Immunol. 11,
106. Chen, G. Y., Tang, J., Zheng, P. & Liu, Y. CD24 and
Siglec-10 selectively repress tissue damage-induced
immune responses. Science 323, 1722–1725 (2009).
107. Liu, Y., Chen, G. Y. & Zheng, P. CD24-Siglec G/10
discriminates danger- from pathogen-associated
molecular patterns. Trends Immunol. 30, 557–561
108. So, A., De Smedt, T., Revaz, S. & Tschopp, J.
A pilot study of IL-1 inhibition by anakinra in acute
gout. Arthritis Res. Ther. 9, R28 (2007).
109. Larsen, C. M. et al. Interleukin-1-receptor antagonist
in type 2 diabetes mellitus. N. Engl. J. Med. 356,
110. Larsen, C. M. et al. Sustained effects of interleukin-1
receptor antagonist treatment in type 2 diabetes.
Diabetes Care 32, 1663–1668 (2009).
111. Pantschenko, A. G. et al. The interleukin-1 family of
cytokines and receptors in human breast cancer:
implications for tumor progression. Int. J. Oncol. 23,
112. Ghiringhelli, F. et al. Activation of the NLRP3
inflammasome in dendritic cells induces
IL-1β-dependent adaptive immunity against tumors.
Nature Med. 15, 1170–1178 (2009).
113. Rakoff-Nahoum, S., Paglino, J., Eslami-Varzaneh, F.,
Edberg, S. & Medzhitov, R. Recognition of
commensal microflora by Toll-like receptors is
required for intestinal homeostasis. Cell 118,
114. Brown, S. L. et al. Myd88-dependent positioning of
Ptgs2-expressing stromal cells maintains colonic
epithelial proliferation during injury. J. Clin. Invest.
117, 258–269 (2007).
115. Apetoh, L. et al. Toll-like receptor 4-dependent
contribution of the immune system to anticancer
chemotherapy and radiotherapy. Nature Med. 13,
This paper showed the importance of TLR4
signalling in response to DAMPs derived from
tumour cell death after chemotherapy or radiation
treatment during the induction of host immune
responses that are important for inhibiting tumour
116. Martin, P. & Leibovich, S. J. Inflammatory cells
during wound repair: the good, the bad and the ugly.
Trends Cell Biol. 15, 599–607 (2005).
117. DiPietro, L. A. Wound healing: the role of the
macrophage and other immune cells. Shock 4,
118. Kroemer, G. et al. Classification of cell death:
recommendations of the nomenclature committee
on cell death 2009. Cell Death Differ. 16, 3–11
119. Silva, M. T., do Vale, A. & dos Santos, N. M.
Secondary necrosis in multicellular animals: an
outcome of apoptosis with pathogenic implications.
Apoptosis 13, 463–482 (2008).
120. Miwa, K. et al. Caspase 1-independent IL-1β release
and inflammation induced by the apoptosis inducer
Fas ligand. Nature Med. 4, 1287–1292 (1998).
121. Marina-Garcia, N. et al. Pannexin-1-mediated
intracellular delivery of muramyl dipeptide induces
caspase-1 activation via cryopyrin/NLRP3
independently of Nod2. J. Immunol. 180,
122. Basu, S., Binder, R. J., Ramalingam, T. &
Srivastava, P. K. CD91 is a common receptor for heat
shock proteins gp96, hsp90, hsp70, and calreticulin.
Immunity 14, 303–313 (2001).
123. Kariko, K., Ni, H., Capodici, J., Lamphier, M. &
Weissman, D. mRNA is an endogenous ligand for Toll-
like receptor 3. J. Biol. Chem. 279, 12542–12550
124. Johnson, G. B., Brunn, G. J., Kodaira, Y. & Platt, J. L.
Receptor-mediated monitoring of tissue well-being
via detection of soluble heparan sulfate by Toll-like
receptor 4. J. Immunol. 168, 5233–5239 (2002).
125. Zhang, Q. et al. Circulating mitochondrial DAMPs
cause inflammatory responses to injury. Nature 464,
We apologize to our colleagues whose work was not cited or
was cited through others’ review articles because of space
limitations. Work in the authors’ laboratories is supported by
US National Institutes of Health grants CA133185 (G.C.),
and DK61707, AR051790, AI06331, AR059688 and
Competing interests statement
The authors declare no competing financial interests.
Gabriel Nuñez’s homepage: http://www.pathology.med.
All lInkS ARe ActIve In the onlIne Pdf
NATURe ReVIewS | Immunology
VOLUMe 10 | DeCeMbeR 2010 | 837
© 20 Macmillan Publishers Limited. All rights reserved10