Signaling at neuro/immune synapses.
ABSTRACT Immunological and neural synapses share properties such as the synaptic cleft, adhesion molecules, stability, and polarity. However, the mismatch in scale has limited the utility of these comparisons. The discovery of phosphatase micro-exclusion from signaling elements in immunological synapses and innate phagocytic synapses define a common functional unit at a common sub-micron scale across synapse types. Bundling of information from multiple antigen receptor microclusters by an immunological synapse has parallels to bundling of multiple synaptic inputs into a single axonal output by neurons, allowing integration and coincidence detection. Bonafide neuroimmune synapses control the inflammatory reflex. A better understanding of the shared mechanisms between immunological and neural synapses could aid in the development of new therapeutic modalities for immunological, neurological, and neuroimmunological disorders alike.
- SourceAvailable from: Isaac Cano[Show abstract] [Hide abstract]
ABSTRACT: Background and hypothesis: Heterogeneity in clinical manifestations and disease progression in Chronic Obstructive Pulmonary Disease (COPD) lead to consequences for patient health risk assessment, stratification and management. Implicit with the classical "spill over" hypothesis is that COPD heterogeneity is driven by the pulmonary events of the disease. Alternatively, we hypothesized that COPD heterogeneities result from the interplay of mechanisms governing three conceptually different phenomena: 1) pulmonary disease, 2) systemic effects of COPD and 3) co-morbidity clustering, each of them with their own dynamics. Objective and method: To explore the potential of a systems analysis of COPD heterogeneity focused on skeletal muscle dysfunction and on co-morbidity clustering aiming at generating predictive modeling with impact on patient management. To this end, strategies combining deterministic modeling and network medicine analyses of the Biobridge dataset were used to investigate the mechanisms of skeletal muscle dysfunction. An independent data driven analysis of co-morbidity clustering examining associated genes and pathways was performed using a large dataset (ICD9-CM data from Medicare, 13 million people). Finally, a targeted network analysis using the outcomes of the two approaches (skeletal muscle dysfunction and co-morbidity clustering) explored shared pathways between these phenomena. Results: (1) Evidence of abnormal regulation of skeletal muscle bioenergetics and skeletal muscle remodeling showing a significant association with nitroso-redox disequilibrium was observed in COPD; (2) COPD patients presented higher risk for co-morbidity clustering than non-COPD patients increasing with ageing; and, (3) the on-going targeted network analyses suggests shared pathways between skeletal muscle dysfunction and co-morbidity clustering. Conclusions: The results indicate the high potential of a systems approach to address COPD heterogeneity. Significant knowledge gaps were identified that are relevant to shape strategies aiming at fostering 4P Medicine for patients with COPD.Journal of Translational Medicine 11/2014; 12(Suppl 2:S3). · 3.99 Impact Factor
Article: Synaptic view of eukaryotic cell[Show abstract] [Hide abstract]
ABSTRACT: Synapses are stable adhesive domains between two neighbouring cells of the multicellular organisms which serve for cell–cell communication as well as for information processing and storing. The synaptic concept was developed over more than 100 years specifically for neuronal cell–cell communication. In the last ten years, this concept was adapted to embrace other cell–cell communication phenomena. Here, we focus on the recently emerged phagocytic synapse and propose new endosymbiotic synapses and “intracellular organellar synapses”. All these synapses of eukaryotic cells are in a good position to explain the high capacity of eukaryotic cells for integration of diverse signalling inputs into coherent cellular behaviour.International Journal of General Systems 10/2014; 43(7). · 0.79 Impact Factor
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ABSTRACT: Malignancy is associated with altered expression of glycans and glycoproteins that contribute to the cellular glycocalyx. We constructed a glycoprotein expression signature, which revealed that metastatic tumours upregulate expression of bulky glycoproteins. A computational model predicted that these glycoproteins would influence transmembrane receptor spatial organization and function. We tested this prediction by investigating whether bulky glycoproteins in the glycocalyx promote a tumour phenotype in human cells by increasing integrin adhesion and signalling. Our data revealed that a bulky glycocalyx facilitates integrin clustering by funnelling active integrins into adhesions and altering integrin state by applying tension to matrix-bound integrins, independent of actomyosin contractility. Expression of large tumour-associated glycoproteins in non-transformed mammary cells promoted focal adhesion assembly and facilitated integrin-dependent growth factor signalling to support cell growth and survival. Clinical studies revealed that large glycoproteins are abundantly expressed on circulating tumour cells from patients with advanced disease. Thus, a bulky glycocalyx is a feature of tumour cells that could foster metastasis by mechanically enhancing cell-surface receptor function.Nature 07/2014; 511(7509):319-25. · 42.35 Impact Factor
?The?Journal?of?Clinical?Investigation http://www.jci.org Volume 122 Number 4 April 2012
Signaling at neuro/immune synapses
Michael L. Dustin
The Helen L. and Martin S. Kimmel Center for Biology and Medicine, Skirball Institute of Biomolecular Medicine,
New York University School of Medicine, New York, New York, USA.
Cell-cell communication systems in the immune and nervous sys-
tems share several features, which has led to the adoption of the
common term “synapse” to describe the close cell-cell contacts in
each. Chemical synapses in the nervous system can be defined as
sites of stability, polarity, and vectoral communication, where two
cells may adhere without fusion (1). The concept of the immune
synapse was first applied to cells of the adaptive immune system,
T and B cells, but has since expanded to include interactions
involving innate immune cells such as NK cells and, more recently,
phagocytes (2–7). Herein we refer to data from phagocytic, T cell,
B cell, and NK cell synapses as specific subtypes of immunologi-
cal synapses. Among all synapses, phagocytic synapses might serve
as an ancestral template. Phagocytosis evolved in early single-cell
organisms and allowed them to more efficiently compete for nutri-
ents in the environment; the phagocytosis receptor system utilized
by soil amoeba is similar to that employed by innate immune cells
of mammals (8). While the term “phagocytic synapse” could be
used in a general sense based on early studies of junctions driven
by phagocytic receptors (9), the first effort to address how phago-
cytosis is selectively triggered by particulate, but not polyvalent,
soluble ligands engaging the same receptors led to the proposal of
a phagocytic synapse (ref. 7 and Figure 1, A and B). The threshold is
a diameter of approximately 0.5 μm, which is similar to the size of
T cell antigen receptor (TCR) microclusters that drive signaling in
T cells (ref. 10 and Figure 1, C and D), and is the characteristic size
of the neural synaptic connections (ref. 11 and Figure 1, E and F).
In this review I discuss the molecular basis of the convergence on a
submicron scale for basic elements, consider signal integration by
immune cells and neurons, and discuss central control of inflam-
mation through neuroimmune synapses.
A synaptic relay race with the pathogen
In the nervous system, even simple activities require the serial and
parallel function of multiple synaptic connections. Similarly, the
immune response is a relay race against the pathogen in which the
baton is passed from innate to adaptive immune cells (Figure 2).
Recent research suggests that multiple immune cell types employ
similar molecular strategies, based on phosphatase exclusion,
to target pathogens (7, 10, 12). Immature DCs phagocytose cell
fragments greater than 0.5 μm in diameter, an innate immune
function (innate leg in Figure 2A and ref. 13). This takes a matter
of seconds, and detection of components associated with a live
infection, such as microbial RNA, leads to maturation of the DCs
and their migration to lymph nodes (14). Partial proteolytic deg-
radation of the phagocytosed material allows for association of
component peptides with MHC class II molecules that are routed
to the cell’s surface for priming of helper T cell precursors, the
afferent phase of adaptive immunity (afferent leg in Figure 2A
and ref. 15). DCs can also divert peptides to the MHC class I sys-
tem in the endoplasmic reticulum for priming of cytotoxic T cell
precursors (16). T and B cells utilize diverse repertoires of antigen
receptors that are generated by somatic gene rearrangement, and
the MHC-peptide complex–bearing DCs need to search through
this repertoire to find T cells with the appropriate receptors. The
DCs form dense networks in secondary lymphoid tissues and
contact approximately 5,000 T cells per hour as the T cells move
over reticular networks (17–19). Within a day, rare antigen-spe-
cific T cells locate these DCs and initiate clonal expansion as well
as conditions for an immune response through the formation of
provisionally stable T cell–DC interactions lasting on the order of
24 hours (20); by comparison, neural synapses may be stable for
years (21). Nonetheless, in the absence of these stable interactions,
the generation of long-lived memory T cells fails (22). After clonal
expansion, the MHC class I restricted T cells can use a synapse to
kill target cells, the efferent phase of adaptive immunity (efferent
leg in Figure 2A and ref. 23), whereas the MHC class II restricted
cells may use a synapse to help B cells generate neutralizing anti-
bodies (efferent leg in Figure 2A and ref. 24).
B cells use synapses to gather intact viral antigens from
macrophages, DCs, or follicular DCs in proportion to the affinity
of their antigen receptor and process the antigens to make MHC
class II peptide complexes to obtain help from T cells. Obtaining
T cell help is a competitive process, and B cells with the highest-
affinity receptors switch to producing the IgG isotype and differ-
entiate into antigen-secreting plasma cells with T cell help (25).
NK cells are innate immune cells that work in concert with
cytotoxic T cells to defend against viruses by using inhibitory
receptors that bind MHC class I antigens and host-derived or
virally encoded activating receptors to control the outcome of
synapse formation (26). Loss of inhibition when a virus down-
Conflict?of?interest: The author has declared that no conflict of interest exists.
Citation?for?this?article: J Clin Invest. 2012;122(4):1149–1155. doi:10.1172/JCI58705.
1150?The?Journal?of?Clinical?Investigation http://www.jci.org Volume 122 Number 4 April 2012
regulates MHC class I molecules as an evasion strategy, so called
“missing-self” recognition, or increased activation due to expres-
sion of virally encoded activating ligands, will trigger the NK
cells to kill (27).
The common element in all of these immune synapses is that
the key triggering signals are accompanied by phosphatase exclu-
sion from the site of interaction at a submicron scale as a means of
enabling activation of kinases by the removal of an inhibitor. The
submicron scale is important because it allows triggering to hap-
pen fast — in less than a second (28) — whereas large areas would
require many seconds or even minutes, which is too slow to win
the race with a pathogen.
Phosphatase exclusion from microclusters
Tyrosine phosphatase inhibition with chemical agents such as
vanadate rapidly triggers T cell signaling, supporting the notion
that tyrosine phosphatase exclusion could be used as a trigger for
tyrosine kinase cascades (29, 30). Phosphatase exclusion models
for immune cell triggering typically focus on the hematopoietic
phosphatase CD45, which is a type I transmembrane protein with a
large extracellular domain and a cytoplasmic tyrosine phosphatase
domain (31, 32). TCRs and NK cells activating receptors all utilize
the Src family tyrosine kinase Lck to mediate early phosphory-
lation events (33, 34). CD45 maintains Lck in an active state by
removing a C-terminal inhibitory phosphate. However, CD45 also
deactivates several targets of Lck at antigen receptors, and thus
it was proposed, first as speculation by Springer (31) and later
with experimental support by van der Merwe and my group (10,
35), that CD45 exclusion is a key initial event in TCR triggering.
Addressing this issue at present requires the use of a reductionist
model to enable sufficiently high-resolution imaging. Antibodies
to the TCR complex and to CD28, a co-stimulatory receptor that
is engaged by CD80 or CD86 when DCs are strongly activated by
signs of infection, are very effective at activating T cells. Substrates
coated with these antibodies completely exclude CD45 (36, 37),
but this is not likely to be the physiological situation. Presenta-
Role of submicron receptor complexes in immunological and neural synapses. (A) Phagocytosis is triggered when CD45 and CD148 are excluded
from a region more than 0.5 μm in diameter in which Syk is phosphorylated. (B) Micrograph of a phagocytic synapse. Scale bar: 4 μm. Arrow
indicates the exclusion zone. Reproduced with permission from Nature (7). (C) T cell synapses are larger interfaces in which TCR microclusters
that exclude CD45 are formed. These are linked by mysosin II–based contractility to augment signaling and trigger effector functions. Linkage of
microclusters through myosin II ensures that T cells respond to multiple coincident MHC-peptide signals. Inset: TCR/MHC-peptide interactions
with the support of adhesion molecules form microclusters that exclude CD45 and trigger robust tyrosine phosphorylation. TCR microclusters
are short lived. (D) Micrograph of a T cell synapse. Scale bar: 4 μm. Arrow points to an example of a microcluster. Reproduced with permission
from Nature (10). (E) Neural synapses are stabilized by adhesion molecules and can recruit receptor tyrosine kinases. More restrained signaling
may promote a longer-lived junction than can then be used to process action potentials into chemical synapse and compute one output from
many inputs. Eph, Eph family tyrosine kinase; PTP, protein tyrosine phosphatase; NT, neurotransmitter. (F) Microgaph of a neural synapse.
Green indicates receptor-type protein tyrosine phosphatase ρ, red indicates neuroligin, blue indicates PSD-95. Scale bar: 4 μm. Arrows indicate
examples of RPTPρ colocalization with neuroligin. Reproduced with permission from EMBO Journal (43).
?The?Journal?of?Clinical?Investigation http://www.jci.org Volume 122 Number 4 April 2012
tion of MHC-peptide ligands and the adhesion ligand ICAM-1
on supported planar bilayers activates T cells (4, 38), but accurate
assessment of CD45 exclusion from TCR microclusters requires
total internal reflection fluorescence microscopy (TIRFM) (10).
With the use of TIRFM, it became evident that TCR microclusters
exclude CD45 (10). Clusters of B cell antigen receptors (BCRs) also
excluded CD45 in the same spatially restricted fashion (12). TIRFM
is required for this observation because when analyzed by confocal
and deconvolution microscopy, the two layers of actin-rich protru-
sions on flat surfaces (lamellipodia) are closely apposed, making
it appear as if CD45 levels are 2-fold higher than they actually are
(39). The exclusion of CD45 from Dectin-1–rich clusters in the cells
phagocytosing yeast cell walls was observed by confocal microscopy
(7). Dectin-1, a β-glucan receptor, has kinase recruitment motifs
similar to those of the TCR and BCR. The CD45 exclusion zones
in this study were defined by contacts with β-glucan–rich yeast cell
walls of approximately 5 μm diameter, which generated regions of
CD45 exclusion larger than 2 μm. These results are exciting and
suggest a unifying mechanism for triggering synapses, but further
study of how Dectin-1 forms signaling complexes using systems
that enable TIRFM or super-resolution imaging methods would
be of great value in more precisely determining the relationship
of Dectin-1 to CD45. In contrast, neural synapses are stabilized
by receptor tyrosine kinases (40, 41) but actually recruit tyrosine
phosphatases into the synaptic adhesion complexes. For example,
protein tyrosine phosphatase, receptor type, M (PTPRμ) under-
goes homophilic interactions in the context of cadherin-depen-
dent adhesions (42), and other members of this family undergo
heterophilic interactions with synaptic adhesion molecules (43,
44). The balance of phosphatase and kinase activity may allow for
the much longer lifespan of neural synapses (years) compared with
immunoreceptor microclusters (minutes).
The prototypic neural synapse has a scale of approximately 0.2–0.3
μm2, which means that they have a diameter of only 0.5–0.6 μm,
Immunological relay race. (A) The immune response is based on a series of immunological synapses with a common mechanism based on
phosphatase exclusion. Innate leg: An intracellular pathogen infects cells, activating innate sensing mechanisms and leading to phagocytosis by
an immature DC (iDC). This phagocytic synapse contributes to maturation of the DC (mDC). If the pathogen downregulates MHC class I in the
infected cell, then the infected cell can be directly recognized by NK cells. Afferent leg: The mDC presents antigens on MHC class I to cytotoxic
T cell precursors (CD8), on MHC class II to helper T cell precursors (CD4), and as intact complexes to B cells. Efferent leg: CTLs can directly kill
MHC class I–positive infected cells, and the infected target induces cytokine production by the CD8 T cell. Helper T cells allow selection of high-
affinity activated B cells and help B cells to generate an appropriate type of antibody. The B cell provides costimulatory molecules that promote
cytokine production by the helper T cell. (B) The inflammatory reflex is based on innervation of a subset of helper T cells that express choline
acetyltransferase. The vagus nerve relays signals to adrenergic neurons in the celiac ganglion that form neuroimmune synapses with the helper
T cells. Adrenergic receptors on the T cell trigger production of acetylcholine (ACh), which interacts with cholinergic receptors on macrophages
to suppress production of inflammatory cytokines such as TNF.
1152?The?Journal?of?Clinical?Investigation http://www.jci.org Volume 122 Number 4 April 2012
similar to the scale of the microclusters in immunological synapses
(11). The axon-based presynaptic structure includes secretory
vesicles, and such structures can be triggered by adhesion to any
surface such that restricting the formation of these structures
to appropriate locations may be an important process in neural
development (45). Presynaptic axonal terminals and postsynaptic
dendritic spines transduce action potentials, moving along the
axon into a chemical signal that generates a membrane poten-
tial change in the dendritic membrane through regulation of
neurotransmitter secretion that involves Ca2+-regulated snare
proteins (46). In neurons, postsynaptic potentials, which can be
activating or inhibitory, are integrated in the dendritic tree to gen-
erate (or not) an output action potential — effectively acting as
analog-digital converters (47). Thus, in some respects, the T cell
synapse, which integrates input from many microclusters, some
of which may be activating and others inhibitory, is more akin
to the dendritic tree of a neuron than any single neural synapse.
Tetanus toxin–sensitive snare proteins deliver vesicles to the T cell
synapse in response these signals (48).
Force-dependent coincidence detection
in T cell synapses
In neural networks, reliability is ensured, in part, by coincidence
detection (49). In the immune synapse, the exclusion of CD45 from
activating receptor microclusters is a key process for signaling, but
this is not sufficient. In T, B, and NK cell synapses the signaling
from the early microclusters rapidly triggers an expansion of the
contact area to 50–100 μm2, even in the absence of other adhesion
systems (50). The first evidence that microclusters on their own are
insufficient to fully activate T cells came from studies examining
activation of T cells by polystyrene beads of different sizes. These
studies defined a bead size threshold of over 3 μm in diameter for
stimulation of cytotoxic function by purified MHC class I–peptide
complexes (51). These studies are the basis for current clinical-grade
culture systems for T cell expansion in adoptive immunotherapy
(52, 53). One way to interpret this basic result is that CTLs require
activation through at least 2 microclusters spaced a few microns
apart. T cell receptor signaling is dependent on an intact f-actin
cytoskeleton (54). One molecular ruler that operates on this length
scale in concert with f-actin is the myosin II thick filament, which
requires at least 1 μm of space between sites to generate tension
(55). Myosin IIA is the major myosin II isoform in T cells, and its
activity is required for full T cell signaling (56). In some contexts,
externally applied forces can also be used to trigger T cell signaling
(57, 58). It has been unclear why T cells would integrate mechano-
transduction modules into the activation process, given that it is
not obvious how innate and adaptive signals would be converted
into physical forces. One way to avoid errors in activation in a sys-
tem with single-molecule sensitivity is to require that that same sig-
nal be received from physically distinct points on the T cell surface
at the same time to trigger a response. Thus, making part of the
T cell activation process dependent upon forces exerted by
myosin II ensures that at least two MHC-peptide complexes need
to trigger signaling events from locations at least 1 μm apart in
order to develop force. Even the most sensitive signaling processes
in which MHC-peptide counting studies have been performed
required at least 3 MHC-peptide complexes to sustain T cell activa-
tion (59). Thus, while innate immunity may activate phagocytosis
with a single microcluster-based signal, adaptive immunity led by
T cells requires multiple, spatially distinct microclusters.
Organizing information in synapses
Both the nervous system and immune system utilize several types
of receptors in synapses. In the immune system there are at least
2 types of microclusters into which these receptors are distrib-
uted. Kupfer first described the bullseye pattern of the T-B syn-
apses with a ring of LFA-1, an integrin family adhesion molecule,
surrounding a central cluster of TCR (60). Parallel studies with
MHC-peptide complexes and LFA-1 ligand ICAM-1 presented
in a supported planar bilayer with CD2 as an early marker for
TCR-rich domains demonstrated that active processes in the
T cells generate the pattern (4, 61). Kupfer described the LFA-1–
rich ring as a peripheral supramolecular activation cluster
(pSMAC) and the central TCR-rich cluster as a central supra-
molecular activation cluster (cSMAC). The initial contact area
is formed by a rapid, f-actin–driven spreading that is mediated
by the Rac effector WAVE2 to activate the Arp2/3 complex and
formins (62, 63). Cdc42 and Wiscott-Aldrich syndrome protein
also play a role in this process but are not needed for this initial
spreading phase (64). TIRFM on the bilayer system has revealed
that the SMACs are assembled by centripetal transport of LFA-1
and TCR microclusters (10, 65). The LFA-1 microclusters may
include other integrin family adhesion molecules, although this
has not been extensively studied. The TCR microclusters are well
established to incorporate both the CD2-CD58 adhesion system
and the CD28-CD80 costimulatory pathway. Negative regulators
such as CTLA4 and PD-1 may also be incorporated into these
microclusters in a ligand-dependent manner. Although segre-
gated spatially, the LFA-1/ICAM-1 interaction improves the sen-
sitivity of the TCR for ligand by 100-fold and increases the dura-
tion of Ca2+ signaling (66–68). These two microclusters may thus
work as a synergistic functional unit that would be composed of
a TCR microcluster surrounded by LFA-1 microclusters. Such a
radial organization may exist in neural synapse with different
receptors to initiate (neurexin) and limit (polysialated NCAM)
the synapse (69, 70). Synaptogenesis has been reconstituted by
incorporation of neuroligin into supported planar bilayers (71),
but nonspecific adhesive contacts have also been shown to trig-
ger presynaptic structures (45). Since neural synapse survival is
dependent upon electrical activity and growth factors, synapse
initiation may be less dependent upon specific recognition than
the immunological counterpart (72). Furthermore, activation of
immunoreceptor-like tyrosine kinase cascades in neurons leads
to synapse pruning (73, 74).
In the immunological synapse, the LFA-1 accumulates in a ring
associated with the adapter protein talin, whereas TCR microclu-
sters translocate through spaces in this ring to the center of the
synapse. This is dependent upon TSG101, an early component in
the endosomal sorting complexes required for transport (ESCRTs)
(75). TSG101 recognizes receptors with mono-ubiquitin groups.
The TCR is ubiquitinated by c-Cbl and Cbl-b ubiquitin ligases that
are recruited and activated under stimulation with agonist MHC-
peptide complexes (76, 77). In fact, the very robust tyrosine phos-
phorylation due to CD45 exclusion may paradoxically promote
TCR ubiquitination and rapid signal termination. TCR signaling
is terminated by the TSG101-dependent step, which also sorts out
the CD28-CD80 interactions into a distinct signaling structure rich
in PKC-θ (75, 78). Long-term maintenance of neural synapses also
depends upon correct function of endosomal sorting complexes
required for transports (79, 80). Indeed, mutations in these com-
ponents are linked to frontotemporal dementia (81).
? The?Journal?of?Clinical?Investigation http://www.jci.org Volume 122 Number 4 April 2012
TCR microclusters are continuously being buffeted by centripe-
tal actin flow and myosin IIA–dependent contractions as discussed
above. Theses effects decrease the duration of the TCR–MHC-
peptide interaction by 10-fold, and at the same time are required
to achieve full signaling activity (56, 82). The stable immunologi-
cal synapse is dependent upon a continual centripetal actin flow,
and the synapse breaks and relocates whenever the symmetry of
the pSMAC structure is broken (64, 83). While most of these obser-
vations have been made using the supported planar bilayer model
system, there is evidence for similar events in T cell–DC synapses
in vivo and in vitro (64, 84). DCs add another dimension to the
T cell synapse, as the DC cytoskeleton plays an important role in
T cell activation (85–87). Each element in the multifocal T cell–DC
immunological synapse appears to be a SMAC-like assembly of
multiple microclusters, rather than single microclusters (84, 88).
The actin cytoskeleton is also critical for pathfinding in axons (89)
and in the shape of dendritic spines (90).
Neuroimmune synapses and the inflammatory reflex
The “inflammatory reflex” links vagus nerve activity to inhibition
of pro-inflammatory cytokine production by macrophages in the
spleen (91). This is important for control of immune homeostasis
and to prevent immunopathology during infection. However, such
reflexes can also become dysregulated and contribute to infection
following injury to the brain (92). The vagus nerve suppresses
TNF-α production by spleen through acetylcholine receptors on
TNF-producing cells. However, the vagus nerve connection to the
spleen is via adrenergic neurons from the celiac ganglion, thus it
was unclear what cell produces acetylcholine. Work from Kevin
Tracey’s group determined that these adrenergic neurons synapse
with choline acetyltransferase–expressing T cells in the spleen (91).
Adrenergic stimulation of these T cells causes them to release ace-
tylcholine, which then acts on nearby TNF-α–producing cells (Fig-
ure 2). These neuroimmune synapses have been documented by
electron microscopy (93, 94) and the synaptic cleft is close enough,
at 6 nm, to exclude CD45 and potentially induce arrest of motile
T cells. In addition, neuroimmune synapses with mast cells that
involve N-cadherin expression on the mast cells may be impor-
tant in allergy (95). It will be interesting to evaluate the status of
phosphatases in these neuroimmune synapses. Are phosphatases
efficiently excluded, potentially leading to short-lived synapses
due to negative feedback, or do T cells that express choline acet-
yltransferase also express RPTPs to engage in long-lived synapses
with adrenergic termini? These are exciting therapeutic targets for
inflammatory diseases and allergy.
Advances in the study of neural and immune synapses allow a
more refined view of parallels and differences in these systems
than was possible a few years ago. Recent studies of different
types of immune synapses have emphasized the critical role of
submicron structures more similar in scale to neural synapses.
The ancestral phagocytic synapse serves as the simplest protoype.
Actin-dependent immunoreceptor microclusters operate in part
through a principle of receptor tyrosine phosphatase exclusion
and coordination of signaling pathways by scaffold proteins.
High-order integration through myosin II–dependent mecha-
nisms verifies the presence of multiple agonist MHC-peptide
complexes to improve fidelity of T cell signaling. Individual neural
synapses are dependent on actin and scaffold proteins. The den-
dritic tree of a neuron has parallels to the immunological synapse,
in that it integrates signaling from multiple submicron elements
to generate a unified output. However, the much greater lifetime
of neural synapses compared with immunological microclusters
may require more sustainable signaling strategies that require
recruitment of RPTPs, which can also contribute directly to syn-
aptic adhesion. A better understanding of immunological and
neural synapses has clear therapeutic value. The synaptic basis of
neuroimmune communication is also coming into focus, and this
area is particularly exciting due to the potential to execute rapid
changes in immune status.
This work was supported by NIH grants R37AI543542 and
Address correspondence to: Michael Dustin, New York Univer-
sity School of Medicine, 540 First Avenue, SKI2-4, New York,
New York 10016, USA. Phone: 212.263.3207; Fax: 212.263.5711;
1. Dustin ML, Colman DR. Neural and immunological
synaptic relations. Science. 2002;298(5594):785–789.
2. Norcross MA. A synaptic basis for T-lymphocyte acti-
vation. Ann Immunol (Paris). 1984;135D(2):113–134.
3. Paul WE, Seder RA. Lymphocyte responses and
cytokines. Cell. 1994;76(2):241–251.
4. Grakoui A, et al. The immunological synapse: A
molecular machine controlling T cell activation.
5. Davis DM, Chiu I, Fassett M, Cohen GB, Man-
delboim O, Strominger JL. The human natural
killer cell immune synapse. Proc Natl Acad Sci U S A.
6. Batista FD, Iber D, Neuberger MS. B cells acquire
antigen from target cells after synapse formation.
7. Goodridge HS, et al. Activation of the innate immune
receptor Dectin-1 upon formation of a ‘phagocytic
synapse’. Nature. 2011;472(7344):471–475.
8. Allen PG, Dawidowicz EA. Phagocytosis in Acan-
thamoeba: I. A mannose receptor is responsible for
the binding and phagocytosis of yeast. J Cell Physiol.
9. Wright SD, Silverstein SC. Phagocytosing
macrophages exclude proteins from the zones
of contact with opsonized targets. Nature. 1984;
10. Varma R, Campi G, Yokosuka T, Saito T, Dustin
ML. T cell receptor-proximal signals are sustained
in peripheral microclusters and terminated in the
central supramolecular activation cluster. Immu-
11. Hayashi ML, et al. Altered cortical synaptic mor-
phology and impaired memory consolidation in
forebrain- specific dominant-negative PAK trans-
genic mice. Neuron. 2004;42(5):773–787.
12. Depoil D, et al. CD19 is essential for B cell activa-
tion by promoting B cell receptor-antigen micro-
cluster formation in response to membrane-bound
ligand. Nat Immunol. 2008;9(1):63–72.
13. Banchereau J, Steinman RM. Dendritic cells
and the control of immunity. Nature. 1998;
14. Sander LE, et al. Detection of prokaryotic mRNA
signifies microbial viability and promotes immu-
nity. Nature. 2011;474(7351):385–389.
15. Trombetta ES, Mellman I. Cell biology of antigen
processing in vitro and in vivo. Annu Rev Immunol.
16. Allan RS, et al. Migratory dendritic cells transfer
antigen to a lymph node-resident dendritic cell
population for efficient CTL priming. Immunity.
17. Lindquist RL, et al. Visualizing dendritic cell net-
works in vivo. Nat Immunol. 2004;5(12):1243–1250.
18. Miller MJ, Hejazi AS, Wei SH, Cahalan MD, Parker
I. T cell repertoire scanning is promoted by dynam-
ic dendritic cell behavior and random T cell motil-
ity in the lymph node. Proc Natl Acad Sci U S A. 2004;
19. Bajenoff M, et al. Stromal cell networks regulate
lymphocyte entry, migration, and territoriality in
lymph nodes. Immunity. 2006;25(6):989–1001.
20. Mempel TR, Henrickson SE, Von Andrian UH.
T-cell priming by dendritic cells in lymph nodes
occurs in three distinct phases. Nature. 2004;
21. Grutzendler J, Kasthuri N, Gan WB. Long-term
dendritic spine stability in the adult cortex. Nature.
22. Scholer A, Hugues S, Boissonnas A, Fetler L, Amigo-
rena S. Intercellular adhesion molecule-1-dependent
stable interactions between T cells and dendritic cells
determine CD8+ T cell memory. Immunity. 2008;
1154?The?Journal?of?Clinical?Investigation http://www.jci.org Volume 122 Number 4 April 2012
23. Stinchcombe JC, Bossi G, Booth S, Griffiths GM.
The immunological synapse of CTL contains a
secretory domain and membrane bridges. Immu-
24. Okada T, et al. Antigen-engaged B cells undergo
chemotaxis toward the T zone and form motile con-
jugates with helper T cells. PLoS Biol. 2005;3(6):e150.
25. Victora GD, et al. Germinal center dynamics revealed
by multiphoton microscopy with a photoactivatable
fluorescent reporter. Cell. 2010;143(4):592–605.
26. Kielczewska A, et al. Ly49P recognition of cytomeg-
alovirus-infected cells expressing H2-Dk and CMV-
encoded m04 correlates with the NK cell antiviral
response. J Exp Med. 2009;206(3):515–523.
27. Karre K. Natural killer cell recognition of missing
self. Nat Immunol. 2008;9(5):477–480.
28. Petersen NO, Elson EL. Measurements of diffu-
sion and chemical kinetics by fluorescence pho-
tobleaching recovery and fluorescence correlation
spectroscopy. Methods Enzymol. 1986;130:454–484.
29. Wong TW, Goldberg AR. In vitro phosphorylation
of angiotensin analogs by tyrosyl protein kinases.
J Biol Chem. 1983;258(2):1022–1025.
30. Tamura S, Brown TA, Dubler RE, Larner J. Insu-
lin-like effect of vanadate on adipocyte glycogen
synthase and on phosphorylation of 95,000 dalton
subunit of insulin receptor. Biochem Biophys Res
31. Springer TA. Adhesion receptors of the immune
system. Nature. 1990;346(6283):425–434.
32. van der Merwe PA, Davis SJ, Shaw AS, Dustin ML.
Cytoskeletal polarization and redistribution of
cell-surface molecules during T cell antigen recog-
nition. Semin Immunol. 2000;12(1):5–21.
33. Einspahr KJ, Abraham RT, Dick CJ, Leibson PJ. Pro-
tein tyrosine phosphorylation and p56lck modifica-
tion in IL-2 or phorbol ester-activated human natu-
ral killer cells. J Immunol. 1990;145(5):1490–1497.
34. Nika K, et al. Constitutively active Lck kinase in T
cells drives antigen receptor signal transduction.
35. Choudhuri K, Wiseman D, Brown MH, Gould K,
van der Merwe PA. T-cell receptor triggering is criti-
cally dependent on the dimensions of its peptide-
MHC ligand. Nature. 2005;436(7050):578–582.
36. Freiberg BA, et al. Staging and resetting T cell activa-
tion in SMACs. Nat Immunol. 2002;3(10):911–917.
37. Douglass AD, Vale RD. Single-molecule microscopy
reveals plasma membrane microdomains created by
protein-protein networks that exclude or trap signal-
ing molecules in T cells. Cell. 2005;121(6):937–950.
38. Johnson KG, Bromley SK, Dustin ML, Thomas ML. A
supramolecular basis for CD45 tyrosine phosphatase
regulation in sustained T cell activation. Proc Natl
Acad Sci U S A. 2000;97(18):10138–10143.
39. McCann FE, et al. The size of the synaptic cleft and
distinct distributions of filamentous actin, ezrin,
CD43, and CD45 at activating and inhibitory
human NK cell immune synapses. J Immunol. 2003;
40. Wu SH, Arevalo JC, Sarti F, Tessarollo L, Gan
WB, Chao MV. Ankyrin repeat-rich membrane
Spanning/Kidins220 protein regulates dendritic
branching and spine stability in vivo. Dev Neurobiol.
41. Vicario-Abejon C, Owens D, McKay R, Segal M. Role
of neurotrophins in central synapse formation and
stabilization. Nat Rev Neurosci. 2002;3(12):965–974.
42. Aricescu AR, et al. Structure of a tyrosine phosphatase
adhesive interaction reveals a spacer-clamp mecha-
nism. Science. 2007;317(5842):1217–1220.
43. Lim SH, et al. Synapse formation regulated by
protein tyrosine phosphatase receptor T through
interaction with cell adhesion molecules and Fyn.
EMBO J. 2009;28(22):3564–3578.
44. Bouyain S, Watkins DJ. The protein tyrosine phospha-
tases PTPRZ and PTPRG bind to distinct members of
the contactin family of neural recognition molecules.
Proc Natl Acad Sci U S A. 2010;107(6):2443–2448.
45. Lucido AL, et al. Rapid assembly of functional pre-
synaptic boutons triggered by adhesive contacts.
J Neurosci. 2009;29(40):12449–12466.
46. Chen YA, Scheller RH. SNARE-mediated membrane
fusion. Nat Rev Mol Cell Biol. 2001;2(2):98–106.
47. Clark B, Hausser M. Neural coding: hybrid ana-
log and digital signalling in axons. Curr Biol.
48. Das V, et al. Activation-induced polarized recycling
targets T cell antigen receptors to the immuno-
logical synapse; involvement of SNARE complexes.
49. Schaefer AT, Larkum ME, Sakmann B, Roth A.
Coincidence detection in pyramidal neurons is
tuned by their dendritic branching pattern. J Neu-
50. Bunnell SC, Kapoor V, Trible RP, Zhang W, Samel-
son LE. Dynamic actin polymerization drives T
cell receptor-induced spreading: a role for the
signal transduction adaptor LAT. Immunity. 2001;
51. Mescher MF. Surface contact requirements for
activation of cytotoxic T lymphocytes. J Immunol.
52. Kalos M, et al. T cells with chimeric antigen recep-
tors have potent antitumor effects and can estab-
lish memory in patients with advanced leukemia.
Sci Transl Med. 2011;3(95):95ra73.
53. Porter DL, Levine BL, Kalos M, Bagg A, June CH.
Chimeric antigen receptor-modified T cells in
chronic lymphoid leukemia. N Engl J Med. 2011;
54. Valitutti S, Dessing M, Aktories K, Gallati H, Lan-
zavecchia A. Sustained signaling leading to T cell
activation results from prolonged T cell receptor
occupancy. Role of T cell actin cytoskeleton. J Exp
55. Galbraith CG, Yamada KM, Sheetz MP. The rela-
tionship between force and focal complex develop-
ment. J Cell Biol. 2002;159(4):695–705.
56. Ilani T, Vasiliver-Shamis G, Vardhana S, Bretscher
A, Dustin ML. T cell antigen receptor signaling and
immunological synapse stability require myosin
IIA. Nat Immunol. 2009;10(5):531–539.
57. Kim ST, et al. The alphabeta T cell receptor is an
anisotropic mechanosensor. J Biol Chem. 2009;
58. Li YC, et al. Cutting Edge: mechanical forces acting on
T cells immobilized via the TCR complex can trigger
TCR signaling. J Immunol. 2010;184(11):5959–5963.
59. Purbhoo MA, Irvine DJ, Huppa JB, Davis MM. T
cell killing does not require the formation of a sta-
ble mature immunological synapse. Nat Immunol.
60. Monks CR, Freiberg BA, Kupfer H, Sciaky N, Kup-
fer A. Three-dimensional segregation of supramo-
lecular activation clusters in T cells. Nature. 1998;
61. Dustin ML, et al. A novel adapter protein orches-
trates receptor patterning and cytoskeletal polarity
in T cell contacts. Cell. 1998;94(5):667–677.
62. Nolz JC, et al. The WAVE2 complex regulates T cell
receptor signaling to integrins via Abl- and CrkL-
C3G-mediated activation of Rap1. J Cell Biol. 2008;
63. Nolz JC, et al. The WAVE2 complex regulates actin
cytoskeletal reorganization and CRAC-mediated cal-
cium entry during T cell activation. Curr Biol. 2006;
64. Sims TN, et al. Opposing effects of PKCtheta and
WASp on symmetry breaking and relocation of the
immunological synapse. Cell. 2007;129(4):773–785.
65. Yokosuka T, et al. Newly generated T cell receptor
microclusters initiate and sustain T cell activation
by recruitment of Zap70 and SLP-76. Nat Immunol.
66. Bachmann MF, et al. Distinct roles for LFA-1 and
CD28 during activation of naive T cells: adhesion
versus costimulation. Immunity. 1997;7(4):549–557.
67. Schmits R, et al. LFA-1-deficient mice show normal
CTL responses to virus but fail to reject immuno-
genic tumor. J Exp Med. 1996;183(4):1415–1426.
68. Wulfing C, Sjaastad MD, Davis MM. Visualizing
the dynamics of T cell activation: intracellular
adhesion molecule 1 migrates rapidly to the T cell/
B cell interface and acts to sustain calcium levels.
Proc Natl Acad Sci U S A. 1998;95(11):6302–6307.
69. Seki T, Rutishauser U. Removal of polysialic acid-
neural cell adhesion molecule induces aberrant mossy
fiber innervation and ectopic synaptogenesis in the
hippocampus. J Neurosci. 1998;18(10):3757–3766.
70. Dean C, et al. Neurexin mediates the assembly of pre-
synaptic terminals. Nat Neurosci. 2003;6(7):708–716.
71. Pautot S, Lee H, Isacoff EY, Groves JT. Neuronal
synapse interaction reconstituted between live
cells and supported lipid bilayers. Nat Chem Biol.
72. Boulanger LM, Poo MM. Presynaptic depolariza-
tion facilitates neurotrophin-induced synaptic
potentiation. Nat Neurosci. 1999;2(4):346–351.
73. Huh GS, Boulanger LM, Du H, Riquelme PA, Brotz
TM, Shatz CJ. Functional requirement for class I
MHC in CNS development and plasticity. Science.
74. Boulanger LM. Immune proteins in brain devel-
opment and synaptic plasticity. Neuron. 2009;
75. Vardhana S, Choudhuri K, Varma R, Dustin ML.
Essential role of ubiquitin and TSG101 protein in
formation and function of the central supramolecu-
lar activation cluster. Immunity. 2010;32(4):531–540.
76. Naramura M, Jang IK, Kole H, Huang F, Haines
D, Gu H. c-Cbl and Cbl-b regulate T cell respon-
siveness by promoting ligand-induced TCR down-
modulation. Nat Immunol. 2002;3(12):1192–1199.
77. Lee KH, et al. The immunological synapse balances
T cell receptor signaling and degradation. Science.
78. Yokosuka T, et al. Spatiotemporal regulation of
T cell costimulation by TCR-CD28 microclusters
and protein kinase C theta translocation. Immunity.
79. Rodal AA, Blunk AD, Akbergenova Y, Jorquera RA,
Buhl LK, Littleton JT. A presynaptic endosomal
trafficking pathway controls synaptic growth sig-
naling. J Cell Biol. 2011;193(1):201–217.
80. Uytterhoeven V, Kuenen S, Kasprowicz J, Miskie-
wicz K, Verstreken P. Loss of skywalker reveals syn-
aptic endosomes as sorting stations for synaptic
vesicle proteins. Cell. 2011;145(1):117–132.
81. Belly A, Bodon G, Blot B, Bouron A, Sadoul R,
Goldberg Y. CHMP2B mutants linked to fronto-
temporal dementia impair maturation of dendritic
spines. J Cell Sci. 2010;123(pt 17):2943–2954.
82. Huppa JB, et al. TCR-peptide-MHC interactions in
situ show accelerated kinetics and increased affin-
ity. Nature. 2010;463(7283):963–967.
83. Kaizuka Y, Douglass AD, Varma R, Dustin ML,
Vale RD. Mechanisms for segregating T cell recep-
tor and adhesion molecules during immunological
synapse formation in Jurkat T cells. Proc Natl Acad
Sci U S A. 2007;104(51):20296–20301.
84. Tseng SY, Waite JC, Liu M, Vardhana S, Dustin
ML. T cell-dendritic cell immunological synapses
contain TCR-dependent CD28-CD80 clusters that
recruit protein kinase Ctheta. J Immunol. 2008;
85. Al-Alwan MM, et al. Cutting edge: dendritic cell
actin cytoskeletal polarization during immunologi-
cal synapse formation is highly antigen-dependent.
J Immunol. 2003;171(9):4479–4483.
86. Al-Alwan MM, Rowden G, Lee TD, West KA. The
dendritic cell cytoskeleton is critical for the for-
mation of the immunological synapse. J Immunol.
?The?Journal?of?Clinical?Investigation http://www.jci.org Volume 122 Number 4 April 2012
87. Benvenuti F, et al. Requirement of Rac1 and Rac2
expression by mature dendritic cells for T cell prim-
ing. Science. 2004;305(5687):1150–1153.
88. Brossard C, et al. Multifocal structure of the T
cell - dendritic cell synapse. Eur J Immunol. 2005;
89. Lin CH, Forscher P. Growth cone advance is
inversely proportional to retrograde F-actin flow.
90. Korobova F, Svitkina T. Molecular architecture of
synaptic actin cytoskeleton in hippocampal neu-
rons reveals a mechanism of dendritic spine mor-
phogenesis. Mol Biol Cell. 2010;21(1):165–176.
91. Rosas-Ballina M, et al. Acetylcholine-synthesizing
T cells relay neural signals in a vagus nerve circuit.
92. Wong CH, Jenne CN, Lee WY, Leger C, Kubes P.
Functional innervation of hepatic iNKT cells is
immunosuppressive following stroke. Science. 2011;
93. Felten DL, et al. Noradrenergic sympathetic neural
interactions with the immune system: structure
and function. Immunol Rev. 1987;100:225–260.
94. Tournier JN, Hellmann AQ. Neuro-immune con-
nections: evidence for a neuro-immunological syn-
apse. Trends Immunol. 2003;24(3):114–115.
95. Suzuki A, Suzuki R, Furuno T, Teshima R, Nakani-
shi M. N-cadherin plays a role in the synapse-like
structures between mast cells and neurites. Biol
Pharm Bull. 2004;27(12):1891–1894.