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Mast cells (MCs) are a key structural and functional component of both the innate and the adaptive immune systems. They are involved in many different processes, but play a major role in the response to infections and in inflammatory reactions. In addition, MCs are the main effector cells in allergy. MC biology is far more complex than initially believed. Thus, MCs may act directly or indirectly against pathogens and show a wide variety of membrane receptors with the ability to activate cells in response to various stimuli. Depending on where MCs complete the final stages of maturation, the composition of their cytoplasmic granules may vary considerably, and the clinical symptoms associated with tissue MC activation and degranulation may be also different. MCs are activated by complex signalling pathways characterized by multimolecular activating and inhibitory interactions. This article provides a comprehensive overview of MC biology, focusing predominantly on mechanisms of MC activation and the role of MCs in the pathogenesis of allergic diseases.
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J Investig Allergol Clin Immunol 2018; Vol. 28(6): 365-378© 2018 Esmon Publicidad
doi: 10.18176/jiaci.0327
REVIEWS
Mast Cells as Key Players in Allergy
and Inammation
González-de-Olano D1*, Álvarez-Twose I2,3*
1Department of Allergy, Hospital Universitario Ramón y Cajal, Madrid, Spain
2Instituto de Estudios de Mastocitosis de Castilla La Mancha (CLMast), Hospital Virgen del Valle, Toledo, Spain
3Spanish Network on Mastocytosis (REMA)
*Both authors contributed equally to the manuscript and should be considered rst authors.
Abstract
Mast cells (MCs) are a key structural and functional component of both the innate and the adaptive immune systems. They are involved
in many different processes, but play a major role in the response to infections and in inammatory reactions. In addition, MCs are the
main effector cells in allergy.
MC biology is far more complex than initially believed. Thus, MCs may act directly or indirectly against pathogens and show a wide variety
of membrane receptors with the ability to activate cells in response to various stimuli. Depending on where MCs complete the nal stages
of maturation, the composition of their cytoplasmic granules may vary considerably, and the clinical symptoms associated with tissue MC
activation and degranulation may be also different. MCs are activated by complex signalling pathways characterized by multimolecular
activating and inhibitory interactions.
This article provides a comprehensive overview of MC biology, focusing predominantly on mechanisms of MC activation and the role of
MCs in the pathogenesis of allergic diseases.
Key words: Allergy. Inammation. KIT. Mast cell. Signalling. Activation. IgE.
Resumen
Actualmente el mastocito (MC) es considerado como un componente estructural y funcional clave del sistema inmunitario, tanto innato
como adquirido. El MC está involucrado en muchos procesos biológicos diferentes, pero juega un papel primordial en la respuesta inmune
frente a infecciones y en las reacciones inamatorias. Además, el MC es la principal célula efectora en los procesos alérgicos.
La biología mastocitaria es mucho más compleja de lo que se podía pensar en un principio. Así, los MCs pueden actuar frente a patógenos
tanto de forma directa como indirecta, y presentan una amplia variedad de receptores de membrana capaces de inducir la activación de
la célula en respuesta a diferentes estímulos. Dependiendo del lugar donde los MCs completan los estadíos nales de su maduración,
la composición de sus gránulos citoplasmáticos puede variar considerablemente, y los síntomas clínicos asociados a la activación y
desgranulación de los MCs tisulares pueden ser también diferentes. La activación mastocitaria se produce como consecuencia de complejas
vías de señalización caracterizadas por interacciones multimoleculares activadoras e inhibidoras.
Este artículo muestra una revisión integral de la biología mastocitaria, predominantemente enfocado a los mecanismos de activación
mastocitaria y en el papel que los MCs desempeñan en la patogenia de las enfermedades alérgicas.
Palabras clave: Alergia. Inamación. KIT. Mastocito. Señalización. Activación. IgE.
J Investig Allergol Clin Immunol 2018; Vol. 28(6): 365-378
doi: 10.18176/jiaci.0327
González-de-Olano D, et al.
J Investig Allergol Clin Immunol 2018; Vol. 28(6): 365-378 © 2018 Esmon Publicidad
doi: 10.18176/jiaci.0327
Introduction
Recent major advances in the ontogeny, physiology,
metabolism, proteomics, and genetics of mast cells (MCs)
have improved our understanding of their impact on health and
disease. MCs are a key structural and functional component
of both the innate and the adaptive immune systems and are
involved in many biological processes. They play a pivotal role
in the immune response to infection by pathogenic parasites
and in inammatory reactions; at the same time, MCs are the
main eector cells in allergic diseases.
The mechanisms that regulate MC function have been
extensively investigated and include complex multimolecular
pathways that control the activation and inhibition of cell
signalling. Among the wide number of molecules involved
in these pathways, 2 transmembrane receptors on the surface
of MCs are particularly relevant: (1) the tyrosine-kinase
(TK) receptor of the stem cell factor (SCF), known as KIT,
which plays major roles in the proliferation, dierentiation,
and survival of MCs: and (2) the high-anity IgE receptor
(FcεRI), which is involved in the underlying mechanisms of
IgE-mediated MC activation and typically occurs in immediate
hypersensitivity reactions (type I).
In this review, we provide a comprehensive picture of MC
biology, with emphasis on its role in the inammatory response
and allergic diseases.
Structure and Function of Mast Cells
MCs are eector cells of the immune system that were rst
identied in 1878 by Paul Ehrlich, who showed their unique
tinctorial properties [1], for example, metachromasia, which
consists in the ability to stain a dierent color from that of the
stain used. In morphological terms, normal MCs are 7-12 μm
in diameter and round to ovoid in shape with a central round
nucleus and numerous granules lling the cytoplasm, often
hiding the nucleus completely [2] (Figure 1).
Functionally, MCs are derived from pluripotent
hematopoietic progenitors in the bone marrow [3-6],
from where MCs migrate through the bloodstream as
immature cells to reach the peripheral tissues [4,7]. Here,
they nish their dierentiation under the inuence of the
microenvironment [8,9]. Once complete functionality is
achieved, MCs become one of the most important cells in
the immune system, playing a key role in the mechanisms
underlying the initiation and perpetuation of the inammatory
response [10-14].
Despite being a minority cell population compared with
all the other cells in the immune system, MCs are present in
practically all human tissues, particularly those that act as
physical barriers against external microorganisms such as the
skin and the gastrointestinal and respiratory tracts [15]. This
strategic distribution of MCs, together with the existence of a
large number of membrane receptors with the ability to induce
cell activation in response to various stimuli, enables MCs to
be the rst line of defense against pathogens, allergens, and
other potentially harmful environmental agents. Therefore,
specific bacterial compounds can directly activate MCs
through interactions with membrane receptors such as Toll-
like receptors [13,16,17] and CD48 [18-20]. MCs also express
IgG receptors (FcγR) and complement receptors, which can
recognize previously opsonized microorganisms [21-23]. The
microorganisms MCs act against mostly include parasites
(helminths, nematodes, and protozoa), as well as some bacteria
(particularly gram-negative bacteria), viruses, and fungi. Once
the pathogen is recognized, MCs act directly either through
their phagocytic ability under specic circumstances [20,24]
or via the production of antimicrobial peptides such as
cathelicidin (LL37) [25]. MCs also act indirectly against
microorganisms through the release of potent inammatory
mediators, some of which are preformed and stored within the
cytoplasmic granules, whereas others are synthesized de novo.
The process of MC mediator release has mainly been
studied in anaphylactic reactions, in which the MC participates
as the main eector cell. In such reactions, activation of MCs
results from an interaction between FcεRI on the membrane
surface and specific allergens to which patients have
previously been sensitized [26,27]. Furthermore, MCs have
been involved in the pathogenesis of several inammatory
diseases, such as rheumatoid arthritis [28,29], scleroderma
[30,31], interstitial cystitis [32,33], multiple sclerosis [34,35],
and irritable bowel disease [36-39], as well as in processes
366
Figure 1. Cytomorphological appearance of normal mast cells (arrows)
in bone marrow smears. A, Blue toluidine stain (×60); B, May-Grünwald-
Giemsa stain (×100).
Mast Cells in Allergy and Inammation
J Investig Allergol Clin Immunol 2018; Vol. 28(6): 365-378© 2018 Esmon Publicidad
doi: 10.18176/jiaci.0327
367
such as wound healing [40-42], angiogenesis [43,44], and the
development of tumors [45,46].
Ontogeny and Development of Mast
Cells
MCs derive from progenitor cells in bone marrow [3-6],
where they start their maturation under the inuence of a variety
of growth factors and cytokines such as SCF, interleukins
(eg, IL-4, IL-6, IL-9, IL-10, IL-12, IL-15, and IL-18), nerve
growth factor, transforming growth factor beta (TGF-β), and
thrombopoietin [47]. In contrast to other hematopoietic cells
that complete their dierentiation within the bone marrow,
MCs migrate as immature cells through the bloodstream
to peripheral tissues where they complete their maturation.
Mature MCs in peripheral tissues then exert their eects under
the inuence of SCF and other microenvironmental molecules
including adhesion molecules (eg, integrins and cadherins) and
diverse chemokines [47].
Once in peripheral tissues, the MC acquires a specic
phenotype, which is shared by all MCs independently of the
tissue where they reside. The phenotype is characterized by
strong expression of 3 dierent molecules [48-50]: (1) the
antigen CD117 (KIT), which is the receptor for SCF; (2) FcεRI,
the high-anity serum IgE receptor; and (3) intracytoplasmic
tryptase, which is the most abundant protein stored in the
granules of MCs. According to the pattern of expression
of cytoplasmic tryptase and other MC proteases, 3
main phenotypically different subtypes of MCs can be
distinguished [51,52], as follows: (1) MCs that only contain
tryptase (MCT), which are located in the alveoli of the lung and
in the small intestinal mucosa; (2) MCs containing tryptase,
chymase, carboxypeptidase A (CPA), and cathepsin G (MCTC),
which predominate in the skin and in the small intestinal
submucosa; and (3) MCs that contain chymase, CPA, and
cathepsin G in the absence of tryptase (MCC), which mainly
reside in the intestinal and nasal submucosa.
The pattern of cytokines expressed by the dierent subtypes
of MCs described above is considerably heterogeneous. Thus,
whereas IL-4 is found preferentially in MCTC, production
of IL-5 and IL-6 is limited to MCT [53]. Other dierential
characteristics among the phenotypic MC subtypes include the
dependence on helper T (CD4+) lymphocytes of MCT and the
expression of the receptor for the C5a complement activation
fragment (CD88) on MCTC [54]. Altogether, these ndings
show that the pattern of synthesis and release of cytokines by
MCs varies depending on the tissue where they reside, thus
suggesting dierent biological functions for each subtype
of MC. Furthermore, MCs are able to reversibly modify the
expression of certain molecules in response to environmental
or infectious factors [55]. In itself, this ability constitutes an
adaptive mechanism of the immune response.
Immunophenotypic Features of Mast Cells
From an immunophenotypical perspective, normal
MCs display dierent antigenic proles depending on their
maturation stage and the tissue where they reside. Several in
vitro models of dierentiation have shown that MCs arise from
pluripotent hematopoietic progenitor cells, which typically
express CD34, CD45, CD117, CD116, CD38, CD13, CD33
(Siglec-3), CD123, and, to a lesser extent, CD203c [3,4,56].
By contrast, expression of molecules associated with more
mature MCs, such as CD327 (Siglec-6), CD329 (Siglec-8),
and FcεRI, and expression of intracytoplasmic proteases and
mediators such as tryptase, CPA, chymase, and histamine are
typically absent in bone marrow MC precursors [4,57,58].
During maturation, MC precursors in bone marrow
progressively lose expression of markers associated with
early stages of dierentiation such as CD34, CD38, CD123,
and CD116; at the same time, the intensity of expression of
other antigens such as CD117, CD45, CD33, and CD203c
gradually increases, remaining high until the end of the
dierentiation process [59]. As they mature, MCs start to
express proteins associated with the inammatory response
(eg, FcεRI), cytoplasmic mediators (eg, CPA, tryptase,
chymase, and histamine), integrins (eg, CD49b and CD49c),
and immunomodulatory molecules (eg, Siglec-6 and
Siglec-8) [4,57,58]. Unlike these markers, antigens such as
CD58, CD63, CD147, CD151, CD172a, CD182, and CD184
show relatively constant levels of expression during the
dierent stages of MC maturation [59].
Finally, during the last stage of cell dierentiation in
peripheral tissues, the MC acquires the expression of a number
of functional proteins involved in MC activation, such as
CD69 [60] and HLA-DR [61]; at the same time, the MC
increases the expression of other molecules that were already
present at early stages of dierentiation including CD63,
CD84, and CD203c [49,59].
Although MCs represent only a small fraction of all
hematopoietic cells in bone marrow under normal conditions,
it is relatively easy to identify and count them using
multiparametric ow cytometry [48-50,62,63]. According to
their antigenic features, the vast majority of MCs found in
bone marrow are mature resting cells, which strongly express
CD117, CD203c, and FcεRI, although none of these markers
are specic to the MC lineage. Thus, in bone marrow, CD117
is also expressed by hematopoietic precursors, dendritic
cells, CD56+ natural killer cells, some plasma cells, and
nonhematopoietic tumor cells [49]; in turn, CD203c and FcεRI
are also systematically expressed by basophils [9,64]. For this
reason, the identication of MCs by ow cytometry is based
on the use of a rational combination of monoclonal antibodies
against dierent antigens; therefore, the expression of CD117,
CD203c, FcεRI, CD45, and CD33, together with the absence
of expression of CD34, CD38, and CD138, constitutes a
unique antigenic prole associated with mature MCs, which
enables them to be identied and dierentiated from other cell
populations in bone marrow.
Structure and Function of the KIT
Receptor
The SCF receptor, which is known as KIT, is one of the
most relevant receptors of MCs. Despite the fact that it is
also present in hematopoietic precursor cells, melanocytes,
interstitial cells of Cajal, and germline cells [65-69], in none
González-de-Olano D, et al.
J Investig Allergol Clin Immunol 2018; Vol. 28(6): 365-378 © 2018 Esmon Publicidad
doi: 10.18176/jiaci.0327
of these cells are the levels of expression of KIT as high as
those found in MCs. The importance of KIT and the processes
regulated by this receptor have been largely established based
upon genetically modied animal models. Thus, c-kit–decient
and SCF-decient mice lack mature MCs and suer from
hypoplastic anemia, hypopigmentation, and sterility [70,71].
In contrast to other protein receptors expressed by MCs
whose function is usually restricted to advanced stages of
dierentiation, the KIT receptor exerts its function throughout
the development of MCs, playing a crucial role in their
proliferation, dierentiation, migration, and survival [72-75].
The KIT receptor (CD117) is a transmembrane glycoprotein
that belongs to the type III TK family of receptors, which is
coded by c-kit, a gene located in the pericentromeric region
of the long arm of chromosome 4 (4q11-q12) [76,77]. The
KIT receptor is composed of 976 amino acids distributed
over 21 exons, with a total molecular weight of 145 kDa [78].
From a structural perspective, KIT shows a unique topology
shared by other receptors of the type III TK family, such as
the platelet-derived growth factor receptor (PDGFR), the
macrophage colony-stimulating factor receptor (CSF-1), and
the Fl cytokine receptor (Flt3). The extracellular region of
KIT contains 5 immunoglobulin-like domains and constitutes
the binding site for the SCF [79,80]. The transmembrane
portion of the receptor connects the extracellular domain
to the intracellular part of the molecule, which comprises
1 juxtamembrane domain and 2 TK domains including an
adenosine triphosphate (ATP)–binding site (TK1 domain)
and a phosphotransferase region (TK2 domain) linked by a
kinase insert domain. The catalytic activity of KIT resides in
the TK domains and is related to phosphorylation of proteins
through the transfer of phosphate groups obtained from ATP;
in turn, the juxtamembrane domain has a regulatory role in the
receptor through the inhibition of its activity in the absence of
SCF [81,82] (Figure 2).
SCF is a glycoprotein encoded in chromosome 12
(12q22-q24) [83], which is produced by stromal cells,
fibroblasts, and endothelial cells [69]. The 2 currently
recognized biologically active isoforms of SCF are a
transmembrane form (mSCF) and a soluble form (sSCF).
These isoforms are formed by alternative splicing of the same
RNA transcript that either include exon 6 (sSCF) or exclude
exon 6 (mSCF) in the mature mRNA; thus, SCF is initially
synthesized as a membrane-bound polypeptide (mSCF) which
would be proteolytically cleaved within the sequences encoded
by exon 6 to release a soluble protein (sSCF) [83].
The interaction between SCF and KIT plays a key role in
MC biology. This interaction results from non–covalent binding
of SCF homodimers to the immunoglobulin-like domains in
the extracellular region of KIT, which induces dimerization
of the receptor [74,84,85]; as a consequence, the intrinsic
TK activity in the intracellular region of KIT is stimulated,
catalyzing phosphorylation of tyrosine residues by transferring
phosphate groups obtained from ATP bound to the receptor [86].
Once phosphorylated, these tyrosine residues serve as binding
sites for proteins containing Src-homology 2 (SH2) domains,
and binding of these proteins generates activation signals
through signaling pathways such as rat sarcoma/extracellular
signal-regulated kinase (Ras/ERK) [87], Janus kinase/signal
transducers and activators of transcription (JAK/STAT) [88-90],
phosphatidylinositol triphosphate [91,92], and several kinases
of the Src family [93]. These signaling pathways induce the
activation of transcription factors and the synthesis of proteins
involved in the modulation of proliferation, dierentiation,
migration, adhesion, secretion, and survival of MCs [94].
Given the importance of the processes mediated by the
activation of KIT, strong regulatory mechanisms that exist under
normal conditions prevent disproportionate hyperactivation
states of the receptor and ensure the development of normal
mastopoiesis. One such regulatory mechanism is the
monoubiquitination of KIT by the action of ubiquitin ligases
immediately after KIT-SCF binding, which results in the
internalization of the receptor and its subsequent degradation
in lysosomes [95-97]. In addition, several molecules that are
activated during the intracellular transduction of signaling
generated by the KIT/SCF interaction, such as SHP-1 (“Src-
homology region 2 domain containing phosphatase-1”),
protein kinase C (PKC) or suppressor of cytokine signaling-1
(SOCS-1), are also involved in the regulation of the process.
Thus, SHP-1 catalyzes the dephosphorylation of KIT by
interacting with a tyrosine residue in the juxtramembrane
domain, negatively modulating the activity of the receptor [98].
By contrast, PKC promotes the phosphorylation of serine
residues in the kinase insert region of KIT, thereby inhibiting its
activity. The activation of PKC is mediated by diacylglycerol,
which is generated from phosphatidic acid by the action of
the enzyme phospholipase D, which is in turn activated by
phosphatidylinositol 3-kinase (PI3K) [99]. Finally, SOCS-1
exerts its regulatory eect via selective suppression of KIT-
induced mitogenesis [100].
368
Figure 2. Structure of the KIT receptor.
Exon
N-terminal
C-terminal
Domain
(codon)
Extracellular
(1-520)
Kinase domain 1 (TK1)
(582-684)
Kinase domain 2 (TK2)
(762-937)
Juxtamembrane
(544-581)
Transmembrane
(521-543)
C-terminal
(938-976)
Kinase insert
(685-761)
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J Investig Allergol Clin Immunol 2018; Vol. 28(6): 365-378© 2018 Esmon Publicidad
doi: 10.18176/jiaci.0327
369
Mutations in the KIT receptor–encoding proto-oncogene
(c-kit) have been extensively reported in the literature. These
mutations are associated with diseases characterized by
neoplastic cell growth in cell lines expressing KIT, which
include MCs, stromal cells, germline cells, melanocytes,
hematopoietic progenitors in bone marrow, and a wide variety
of neoplastic cells from various tumors. Thus, although
KIT-driven disorders mostly include mastocytosis and
gastrointestinal stromal tumors, where KIT mutations are
detected in ~95% and ~75% of cases, respectively [101-103],
KIT mutations have also been described in a subset of patients
with seminoma [104], germinoma [65], melanoma [105], small
cell lung cancer [106], colon cancer [107], neuroblastoma [108],
and breast cancer [109], as well as in hematologic malignancies
such as acute leukemia [110], myelodysplastic syndrome [111],
and myeloproliferative neoplasm [112]. Most KIT mutations
tend to cluster in small regions of the protein, especially at
exons 11 and 17, although mutations involving other exons
have been also reported. In mastocytosis, the most common
KIT mutation is a somatic activating point mutation caused
by the substitution of adenine with thymine at nucleotide
sequence 2447 in the c-kit gene, which results in the
replacement of aspartic acid by valine at codon 816 (exon 17)
of the KIT receptor [112]. By contrast, the most common site
of KIT mutations in gastrointestinal stromal tumors is exon 11,
which encodes the juxtamembrane domain of the molecule;
these mutations mostly consist of deletions or substitutions
involving codons 550-560 [103]. Of note, the specic site
where KIT mutations arise in KIT-driven diseases is of
critical importance when deciding on therapy; thus, mutations
involving exon 17 of KIT are resistant to imatinib mesylate
[113,114], whereas most of those arising outside exon 17 are
sensitive to this TK inhibitor [115,116].
Mast Cell Activation Mechanisms
MCs express a wide variety of membrane receptors
involved in both the innate and the acquired immune responses.
Although FcεRI, Toll-like receptors, complement receptors
(CR1-5), and the IgG receptors FcγRI (CD64) and FcγRII
(CD32) are the main receptors involved in the activation of
MCs, they can be also activated by neuropeptides, cytokines,
chemokines, and other inammatory substances [117], as
well as by physical stimuli such as pressure or heat [118].
The most clinically relevant MC activation mechanism is
that involved in type I hypersensitivity allergic reactions,
which are mediated by cross-linking of antigen-specic IgE
immune complexes and FcεRI receptors on the membrane
surface of MCs (Figure 3). Although FcεRI is typically
expressed by MCs, other cells such as basophils and, to a
lesser extent, Langerhans cells, a subpopulation of monocytes
and eosinophil granulocytes can also express this receptor.
Structurally, FcεRI is a tetramer composed of the following:
(1) an α chain, whose extracellular domain constitutes the IgE
binding site; (2) a β chain, which enhances binding stability
and amplies signal transduction; and (3) a homodimer of γ
chains, which is involved in the conduction of the signal to
the interior of the cell [27,119]. The process of intracellular
signalling is necessary for the activation and further eector
response of MCs and depends mainly on the phosphorylation
of immunoreceptors containing activation sequences based
on tyrosine (ITAMs, immunoreceptor tyrosine-based
activation motifs), which are present in both β and γ chains
of the FcεRI [120]. Phosphorylation of ITAM domains in
FcεRI occurs in a stepwise fashion through the action of
dierent proteins with TK activity (Figure 4). Initially, an
Src family TK called Lyn, which is located adjacent to FcεRI,
phosphorylates the β chain, thus inducing the subsequent
phosphorylation of the γ chain, which in turn promotes the
activation of a ZAP-70 family TK protein called Syk. This
protein is capable of phosphorylating dierent substrates,
including the linker for activation of T cells (LAT), SLP-76,
Vav, and phospholipase Cγ (PLCγ). Once activated, these
molecules determine the development of intracellular stimuli,
which are essential for the release of mediators stored inside
MC cytoplasmic granules and for the synthesis of cytokine
and the activation of phospholipase A2, with the subsequent
generation of arachidonic acid (AA) from phospholipids in the
cell membrane. The activation process is complemented by
the phosphorylation of the adaptor protein Gab2 via the action
of another Src family TK called Fyn. The phosphorylation
of Gab2 promotes the generation of phosphatidylinositol
triphosphate, which in turn leads to the recruitment of
molecules such as Btk and PLCγ towards the cell membrane.
The latter step is necessary for the increase in intracellular
calcium and the degranulation process [121].
In parallel to this multimolecular signalling process
leading to MC degranulation, several molecules with
mostly inhibitory eects are activated in order to avoid an
excessive or inappropriate response. These molecules include
receptors containing tyrosine-rich inhibition sequences,
known as (ITIMs, immunoreceptor tyrosine-based inhibition
motifs) [122], that promote the action of dephosphorylating
Figure 3. Mechanism of allergic inammation in type I hypersensitivity
reactions. After the initial exposure, an allergen is presented to TH cells
via antigen-presenting cells; this provides assistance in the regulation
of cellular immunity and promotes isotype switching and production of
specic IgE antibodies by B cells. Subsequent antigen exposure induces
cross-linking of antigen-IgE complexes and FcεRI on the surface of the
MC, which results in the activation and degranulation of MCs.
Allergen
TH cell
B cell
IgE
antibodies
Mast cell
Antigen-presenting
cell
Mast cell
degranulation
González-de-Olano D, et al.
J Investig Allergol Clin Immunol 2018; Vol. 28(6): 365-378 © 2018 Esmon Publicidad
doi: 10.18176/jiaci.0327
molecules such as SHP-1, SHP-2 (Src-homology region 2
domain containing phosphatase-2), and SHIP (Src-homology 2
containing inositol phosphatase) and also of the adaptor protein
NTAL (non–T cell activation linker), which is activated,
together with LAT, after the stimulation of FcεRI. NTAL is
believed to exert mostly inhibitory eects, as shown by the
increase in the secretory activity of MCs in NTAL-decient
mouse mutants [123]. Besides the intracellular activation and
inhibition pathways described above, the participation of other
molecules with mixed (activating and inhibitory) properties
highlights the considerable complexity of the mechanisms
involved in the regulation of the signalling process resulting
from stimulation of FcεRI during IgE-mediated allergic
reactions.
Mast Cell Mediators
The nal consequence of MC activation is the release of
a wide variety of proinammatory and vasoactive substances
into the extracellular environment, including mediators
constitutively stored inside the cytoplasmic granules of MCs
(primary MC mediators), mediators synthesized de novo
upon MC activation (secondary MC mediators), and diverse
cytokines [124,125], which results in a broad spectrum of
clinical manifestations (Table). The release of preformed
mediators from MCs occurs in the early phase of the immune
response, a few seconds or minutes after the contact with the
antigen. These preformed mediators include biogenic amines
(eg, histamine and serotonin), proteases (eg, tryptase, CPA,
and chymase), proteoglycans (eg, heparin and chondroitin
sulphate), and inflammatory cytokines (eg, TNFα). This
phase is followed by the release of diverse mediators newly
synthesised from membrane phospholipids, which include
prostaglandins (PGs), leukotrienes (LTs), and platelet-
activating factor (PAF), as well as a variety of cytokines and
chemokines that facilitate the activation and recruitment of
other cells of the immune system, leading to the late phase
of the immune response that typically occurs between 2 and
6 hours after exposure to an allergen.
370
Figure 4. Schematic representation of main protein interactions
and downstream signaling events following IgE-mediated FcεRI
activation. Ag, antigen; FcεRI, high afnity IgE receptor; STAT5, signal
transducers and activators of transcription-5; PIP3, phosphatidylinositol
triphosphate; IP3, inositol triphosphate; LAT, linker for activation of T
cells; PLCγ, phospholipase Cγ; Ras, rat sarcoma; AA, arachidonic acid;
ERK, extracellular signal-regulated kinase; MAPK, mitogen-activated
protein kinase.
Ag IgE
Degranulation
ERK/MAPK
Pathway
Synthesis of cytokines
Gab2 PIP3
STAT5
IP3
AA
LAT
Vav
Ras
SLP-76
Syk PLCγ
Fyn
Lyn
IgE
γ γ
b
a a
b
FcεRI FcεRI
Synthesis
of eicosanoids
Table. Main Symptoms and Signs Associated With the Release of Mast Cell Mediators
Type of Mediator Mediator Symptom(s)/sign(s)
Preformed mediators Histamine Headache, hypotension, urticaria with or without angioedema, pruritus,
diarrhea
Tryptase Endothelial activation with associated inammatory reaction
Chymase/CPA Hypertension, arrythmia
Proteoglycan (heparin) Bleeding diathesis
Lipid mediators PAF Abdominal cramping, pulmonary edema, urticaria, bronchoconstriction,
hypotension, arrythmia
PGD2 Mucus secretion, bronchoconstriction, vascular instability
LTC4, LTD4 and LTE4 Mucus secretion, edema formation, vascular instability
Cytokines TNF, IL1-α, IL-1β, IL-6, IL-18, Induction of inammation
GM-CSF, LIF, INF-α, IFN-β
IL-3, IL-4, IL-5, IL-9, IL-13, Type 2 helper T cytokines
IL-15, IL-16
IL-12, IFN-γ Type 1 helper T cytokines
IL-10, TGF-β, VEGF Regulation of inammation and angiogenesis
Chemokines CCL2, CCL3, CCL4, CCL5, Recruitment of eector cells (including dendritic cells), regulation of
CCL11, CCL20 the immune response
CXCL1, CXCL2, CXCL8, Recruitment of eector cells, regulation of the immune response
CXCL9, CXCL10, CXCL11
Abbreviations: CCL, CC-chemokine ligand; CPA, carboxypeptidase; CXCL, CXC-chemokine ligand; GM-CSF, granulocyte-macrophage colony-
stimulating factor; INF, interferon; IL, interleukin, LIF, leukemia inhibitory factor; LT, leukotriene; PAF, platelet-activating factor; PG, prostaglandin; TGF-β,
transforming growth factor-β; TNF, tumor-necrosis factor; VEGF, vascular endothelial growth factor.
Mast Cells in Allergy and Inammation
J Investig Allergol Clin Immunol 2018; Vol. 28(6): 365-378© 2018 Esmon Publicidad
doi: 10.18176/jiaci.0327
Histamine
Histamine is the most important vasoactive mediator
released from human MCs. Given its low molecular mass,
histamine has high diusion capacity once it is secreted
and fulfils different biological functions after binding to
specic receptors (H1, H2, H3, and H4). The most relevant
eects of histamine include contraction of smooth muscle
tissue, vasodilation, increased vascular permeability, nerve
stimulation, and increased glandular secretion [126,127].
Histamine is rapidly metabolized via methylation or oxidation,
both of which result in the generation of the metabolites
N-methyl histamine and imidazole acetic acid, which are
excreted in urine.
Neutral Proteases
The protein content of MC granules mainly comprises
neutral proteases with hydrolytic activity on tissue surface–
bound proteins, extracellular matrix proteins, inactive forms
of proenzymes, and other proinammatory peptide mediators;
thus, neutral proteases help to generate and amplify tissue
damage occurring after MC degranulation. Furthermore, these
proteases participate in the regulation of processes associated
with inammation by activating various proteins that inhibit
inammation and also by inhibiting proinammatory proteins.
The most abundant MC protease is tryptase, which is
stored in the intracytoplasmic granules of MCs (and, albeit to
a lesser extent, of basophils) as tetramers that form complexes
with heparin [128,129]. The isoforms of tryptase recognized
in serum are α-tryptase, which is constitutively secreted by
MCs as inactive enzyme, and β-tryptase, which is released
in large amounts during MC degranulation. A commercially
available assay can be used to measure total serum tryptase
levels, which are the sum of α- and β-tryptase isoforms.
Therefore, the high levels of total serum tryptase frequently
found in patients with mastocytosis are the result of increased
chronic release of α-tryptase as a consequence of an increased
total MC burden [130-132]. In contrast, increased total serum
tryptase levels detected in patients with anaphylaxis more
likely reect the acute release of β-tryptase that typically
occurs after MC degranulation in this setting [128,133]. Of
note, the measurement of total serum tryptase has proved
to be more useful than other MC mediators such as plasma
histamine or urine histamine metabolites in the diagnostic
work-up of both anaphylaxis and mastocytosis [134]. The
greater diagnostic eciency of serum tryptase over other
MC mediators relies on its high specicity, the simplicity and
speed of the assay, and slower metabolic degradation, which
enables the measurement of serum tryptase for up to 6 hours
after release without interference in the results by factors
such as ingestion of food with a high content of histamine.
The main biological eects of tryptase on the human body
include contraction of smooth muscle [135], degradation of
neuropeptides [136,137], activation of collagenase [138],
proliferation of broblasts [139], generation of C3a [140] and
bradykinin [141], and inactivation of brinogen [142]. Tryptase
is also capable of promoting the recruitment of other immune
cells (143), actively participates in remodelling processes
(144) and angiogenesis (145), and exerts a protective function
against the potential damaging eect of substances generated
during the inammation process, such as neurotensin and
endothelin (146).
Other MC proteins with enzymatic activity are chymase
and CPA, which are stored in MC granules as macromolecular
complexes with proteoglycans. The main eect of chymase
is the generation of angiotensin II through hydrolysis of
angiotensin I [147,148]; interestingly, this mechanism might
be involved in the development of the vasoconstrictive signs
and symptoms observed in some patients with MC disorders. In
addition, chymase induces mucous hypersecretion, degradation
of the extracellular matrix through cleavage of proteins such
as bronectin and collagen, activation of metalloproteases in
situ in atherosclerotic plaques and of TGF-β growth factor,
and induction of apoptosis in smooth muscle cells of blood
vessels [149-151]. In turn, although the eects of CPA in
humans remain less well understood, an important role in
innate immunity has been ascribed to this protease because of
its ability to hydrolyse certain toxins and potentially harmful
substances generated during the inammatory response such
as neurotensin and endothelin-1 [152].
Proteoglycans
The main function of proteoglycans stored in the secretory
granules of MCs such as heparin and chondroitin sulfate is
to form stable complexes with other MC mediators, thus
facilitating their storage and their transportation through
the lymphatic vessels [153]. Proteoglycans have also been
implicated in the regulation of the enzymatic activity of MC
proteases and in proapoptotic pathways [154].
Lipid Mediators
MC activation also induces the synthesis and further
release of proinammatory lipid mediators such as eicosanoids
and PAF. The process of synthesis of these mediators begins
with the activation of phospholipase A2, which promotes
the generation of AA and lysophosphatidylcholine from
phospholipids present on the MC membrane [155,156]. Once
generated, AA can be metabolized by the action of 2 enzymes,
cyclooxygenase (COX) and lipoxygenase (LO), resulting in the
production of PGs and LTs, respectively [157]. In turn, PAF
is formed by acetylation of lysophosphatidylcholine through
the action of an acetyltransferase [158].
The main PG generated upon activation of MCs is PGD2,
which has a potent vasodilatory eect, increases vascular
permeability [159], and promotes chemotaxis of eosinophils
[160,161]. In addition, in the respiratory tract, PGD2 has
bronchoconstrictive properties [162]. The action of LO on
AA produces LTA4, which can be metabolized to LTB4
through a hydroxylation process or to cysteinyl-LTs (ie,
LTC4, LTD4, LTE4) through various enzymes acting in a
stepwise fashion [163]. The main biological eect of LTB4 is
chemotaxis of neutrophils, while cysteinyl-LTs, particularly
LTC4 and LTD4, induce contraction of smooth muscle tissue,
bronchoconstriction, increased vascular permeability, and
mucous secretion [164]. In turn, PAF is a potent mediator
capable of acting at low concentrations that has a very short
half-life, as it is inactivated by an acetyl hydrolase present in
371
González-de-Olano D, et al.
J Investig Allergol Clin Immunol 2018; Vol. 28(6): 365-378 © 2018 Esmon Publicidad
doi: 10.18176/jiaci.0327
plasma and numerous tissues just a few minutes after being
released from MCs. Nevertheless, upon binding to specic
receptors, PAF produces a wide variety of symptoms such
as bronchoconstriction, mucous secretion, vasodilation,
increased vascular permeability, and platelet aggregation [165].
Besides these direct eects, PAF indirectly participates in the
inammatory response through the activation and chemotaxis
of leukocytes and through the induction of release of other
mediators by MCs and platelets such as histamine and both
thromboxanes and serotonin, respectively [166].
Cytokines and Chemokines
Similar to other cells of the immune system, MCs
produce a wide variety of cytokines and chemokines,
which are synthesized de novo after activation of MCs and
further released into the extracellular medium. Importantly,
these molecules contribute to the maintenance of the
inammatory process via recruitment of other immune cells
such as lymphocytes, neutrophils, and eosinophils and via the
induction of expression of adhesion molecules on leukocytes
and endothelial cells. The most relevant cytokines produced
by MCs include TNF-α, IL-1β, IL-4, IL-5, IL-6, IL-12, IL-
13, IL-15, IL-16, IL-18, granulocyte-macrophage colony-
stimulating factor, interferon (IFN) α, IFN-β, and IFN-γ, and
the chemokines CCL2, CCL3, CCL4, CCL5, and CXCL8
[14,124,167]. Other molecules synthesized and released by
MCs, such as TGF-β and IL-10, are involved in the regulation
of the process through anti-inammatory action [168,169]. Of
these molecules, TNF-α constitutes the most abundant cytokine
secreted by MCs; it is noteworthy that TNF-α is not only
synthesized de novo after activation of MCs but is also stored
in small amounts inside MC granules and then immediately
released together with other preformed MC mediators during
the process of exocytosis. Furthermore, TNF-α induces
expression of adhesion molecules in endothelial cells and of
integrins in leukocytes, thus facilitating binding between both
cell types. TNF-α also stimulates the release of chemokines,
thus facilitating recruitment of leukocytes to tissues where the
inammatory response is occurring [170].
Conclusions
MCs are one of the key eectors of early innate immunity
and play a central role not only in host defense against invading
pathogens and other environmental threats, but also in the
underlying mechanisms of implementation, perpetuation, and
regulation of the inammatory response. Thus, normal mature
MCs are involved in many physiological and pathological
processes such as inammation, angiogenesis, wound healing,
allergic diseases, and carcinogenesis.
The large number of molecules involved in the regulation
of MC downstream signalling pathways, along with the broad
spectrum of biological eects produced by activated MCs,
make these cells one of the most paradigmatic examples of
the fascinating complexity of the human immune system.
Moreover, increasing knowledge accumulated over the years
on the biology of MCs has led to the development of drugs that
target specic molecules involved in activation of MCs such as
omalizumab. This humanized murine monoclonal antibody is
directed against the FcεRI-binding site of free serum IgE, which
prevents its binding to MCs; thus, omalizumab has proven to
be eective in several well-known IgE-driven diseases such
as chronic urticaria [171] and allergic asthma [172], and,
more recently, in allergic rhinitis [173], atopic dermatitis
[174], and clonal MC disorders [175-177]. Omalizumab has
also been administered as coadjuvant treatment in allergen
immunotherapy regimens [178,179]. The clinical benets
of omalizumab in these IgE-related disorders has led to the
exploration of the potential utility of novel anti-IgE therapies,
which have shown promising preliminary results.
Acknowledgments
We thank Proyecto Kaplan S.L. for its support in the design
and preparation of the illustrations included in this manuscript.
Funding
This work was supported by grants from the Sociedad
Española de Alergia e Inmunología Clínica 2014 (Spain),
the Asociación Española de Mastocitosis y enfermedades
relacionadas (AEDM 2017, Spain). Hospital Virgen de la Salud
Biobank (BioB-HVS) is supported by grant PT13/0010/0007
from the Instituto de Salud Carlos III (Spain).
Conflicts of Interest
The authors declare that they have no conicts of interest.
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Iván Álvarez-Twose
Instituto de Estudios de Mastocitosis de Castilla La Mancha
(CLMast)
Hospital Virgen del Valle
Toledo, Spain
E-mail: ivana@sescam.jccm.es
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... Sensitized individuals already have allergen-specific IgE bound to surface IgE receptors on mast cells. The main receptors involved in mast cell activation are: FcεRI, Toll-like receptors, complement receptors (CR1-5) and IgG receptors FcγRI (CD64) and FcγRII (CD32) [22]. Cross-linking of adjacent IgE molecules by bivalent or multivalent allergen, FcεRI aggregation initiates a complex intracellular signaling process that results in the secretion of key biologically active products: (1) mediators stored in primary cytoplasmic granules; (2) mediators formed from lipids and newly synthesized cytokines, chemokines and growth factors, as well as other products. ...
... Mediators contribute to an allergic reaction, known as an "immediate hypersensitivity reaction". Certain genes are involved in the specific immune response (i.e., HLA-D, TCR, CD14, toll-like receptor, STAT6) and Th1/Th2 cell differentiation; others are genes encoding (total) IgE response or IgE receptor functions (i.e., IL-4, IL-4R, FcɛRIβ, Fc epsilon RI) and genes involved in the inflammatory process (TNFγ, IFN-γ, IL-3) [4,21,22]. ...
... The released chemical mediators are responsible for allergic (inflammatory) processes, such as vasodilation, increased vascular permeability and increased chemotaxis of other inflammatory cells ( Figure 3). The second phase of the reaction begins with the synthesis of mediators derived from lipids through the conversion of phospholipids into arachidonic acid by phospholipase A2, followed by the conversion of arachidonic acid into leukotrienes (LT), platelet activation factor (PAF) and prostaglandins [4,21,22]. The inflammatory cascade continues with the synthesis of LTB4 and LTC4 (with their metabolic derivatives LTD4 and LTE4), prostaglandin D2 and other substances that stimulate by acting on vascular smooth muscles, connective tissue, mucous glands and inflammatory cells. ...
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The incidence of allergic diseases and their complications are increasing worldwide. Today, people increasingly use natural products, which has been termed a “return to nature”. Natural products with healing properties, especially those obtained from plants and bees, have been used in the prevention and treatment of numerous chronic diseases, including allergy and/or inflammation. Propolis is a multi-component resin rich in flavonoids, collected and transformed by honeybees from buds and plant wounds for the construction and adaptation of their nests. This article describes the current views regarding the possible mechanisms and multiple benefits of flavonoids in combating allergy and allergy-related complications. These benefits arise from flavonoid anti-allergic, anti-inflammatory, antioxidative, and wound healing activities and their effects on microbe-immune system interactions in developing host responses to different allergens. Finally, this article presents various aspects of allergy pathobiology and possible molecular approaches in their treatment. Possible mechanisms regarding the antiallergic action of propolis on the microbiota of the digestive and respiratory tracts and skin diseases as a method to selectively remove allergenic molecules by the process of bacterial biotransformation are also reported.
... In fact, increasing evidence implicates brain inflammation and cytokines in the pathogenesis of Alzheimer's disease [152,153]. Brain inflammation may be evident in the earlier stages of the disease and may constitute a more reasonable target for drug development [154,155]. Interestingly, IL-33 was also upregulated in astrocytes and peripheral leukocytes of multiple sclerosis (MS) patients [156]. Moreover, the expression of IL-33 protein and IL-33 genes was increased in patients with remitting-relapsing MS [157]. ...
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Article
Much evidence suggests autoimmunity in the etiopathogenesis of periodontal disease. In fact, in periodontitis, there is antibody production against collagen, DNA, and IgG, as well as increased IgA expression, T cell dysfunction, high expression of class II MHC molecules on the surface of gingival epithelial cells in inflamed tissues, activation of NK cells, and the generation of antibodies against the azurophil granules of polymorphonuclear leukocytes. In general, direct activation of autoreactive immune cells and production of TNF can activate neutrophils to release pro-inflammatory enzymes with tissue damage in the gingiva. Gingival inflammation and, in the most serious cases, periodontitis, are mainly due to the dysbiosis of the commensal oral microbiota that triggers the immune system. This inflammatory pathological state can affect the periodontal ligament, bone, and the entire gingival tissue. Oral tolerance can be abrogated by some cytokines produced by epithelial cells and activated immune cells, including mast cells (MCs). Periodontal cells and inflammatory–immune cells, including mast cells (MCs), produce cytokines and chemokines, mediating local inflammation of the gingival, along with destruction of the periodontal ligament and alveolar bone. Immune-cell activation and recruitment can be induced by inflammatory cytokines, such as IL-1, TNF, IL-33, and bacterial products, including lipopolysaccharide (LPS). IL-1 and IL-33 are pleiotropic cytokines from members of the IL-1 family, which mediate inflammation of MCs and contribute to many key features of periodontitis and other inflammatory disorders. IL-33 activates several immune cells, including lymphocytes, Th2 cells, and MCs in both innate and acquired immunological diseases. The classic therapies for periodontitis include non-surgical periodontal treatment, surgery, antibiotics, anti-inflammatory drugs, and surgery, which have been only partially effective. Recently, a natural cytokine, IL-37, a member of the IL-1 family and a suppressor of IL-1b, has received considerable attention for the treatment of inflammatory diseases. In this article, we report that IL-37 may be an important and effective therapeutic cytokine that may inhibit periodontal inflammation. The purpose of this paper is to study the relationship between MCs, IL-1, IL-33, and IL-37 inhibition in acute and chronic inflamed gingival tissue.
... They generate cytokines (including IL-4 and IL-9 in response to the alarmin IL-33) that promote T H 2 responses and IgE production while suppressing Treg responses. Mast cells can also stimulate growth of type 2 innate lymphoid cells (ILC2) by producing IL-33 and IL-4, thus increasing the risks of IgE-mediated anaphylaxis [109][110][111]. ...
Article
The role of the microbiome in the molecular mechanisms underlying allergy has become highly relevant in recent years. Studies are increasingly suggesting that altered composition of the microbiota, or dysbiosis, may result in local and systemic alteration of the immune response to specific allergens. In this regard, a link has been established between lung microbiota and respiratory allergy, between skin microbiota and atopic dermatitis, and between gut microbiota and food allergy. The composition of the human microbiota is dynamic and depends on host-associated factors such as diet, diseases, and lifestyle. Omics are the techniques of choice for the analysis and understanding of the microbiota. Microbiota analysis techniques have advanced considerably in recent decades, and the need for multiple approaches to explore and comprehend multifactorial diseases, including allergy, has increased. Thus, more and more studies are proposing mechanisms for intervention in the microbiota. In this review, we present the latest advances with respect to the human microbiota in the literature, focusing on the intestinal, cutaneous, and respiratory microbiota. We discuss the relationship between the microbiome and the immune system, with emphasis on allergic diseases. Finally, we discuss the main technologies for the study of the microbiome and interventions targeting the microbiota for prevention of allergy.
... Damaged skin is characterized by elevated serum IgE levels and infiltration of inflammatory cells (lymphocytes, macrophages, eosinophils and mast cells) (Barton and Sidbury, 2015). For instance, the activation of mast cell infiltration contributes to AD and is easily noticed in skin tissue with AD (Gonzalez- de-Olano and Alvarez-Twose, 2018). In addition, the MAPKs phosphorylation induces the production of inflammatory mediators and allergic inflammatory responses (Huang et al., 2019;Park et al., 2019). ...
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Background: Atopic dermatitis (AD), characterized by eczema as a chronic pruritic inflammatory skin disease, has become a serious health problem with recurrent clinical episodes. However, current clinical treatments have limited relief and are accompanied by adverse effects. Therefore, there is a necessity to develop new effective drugs for AD treatment. Angelica Yinzi (AYZ) is a classic ancient prescription for nourishing blood, moistening dryness, dispelling wind, and relieving itching. However, its mechanism for alleviating atopic dermatitis remains unknown. Therefore, this study aimed at determining the effects of AYZ and its potential mechanism in alleviating AD-like symptoms. Methods: In the present study, we used 1-chloro-2,4-dinitrobenzene (DNCB) to establish a mouse model of atopic dermatitis, where DNCB readily penetrates the epidermis to cause inflammation. Histopathological analysis was performed to examine the thickening of dorsal skin and infiltration in the inflammatory and mast cells in C57BL/6 mice. Additionally, the immunoglobulin E (IgE) levels in serum were determined by enzyme-linked immunosorbent assay (ELISA) kits. The IL-1β and TNF-α expression were detected using qRT-PCR. Next, the Western blotting and immunohistochemistry assays were performed to assess the contribution of MAPKs/NF-κB signaling pathways and the NLRP3 inflammasome in AD responses. Results: Histopathological examination revealed that AYZ reduced the epidermal thickness of AD-like lesioned skin and repressed the infiltration of mast cells into AD-like lesioned skin. AYZ significantly decreased the phosphorylation of p38 MAPK, JNK, ERK and NF-κB and downregulated serum IgE levels and IL-1β and TNF-α mRNA levels. Additionally, the NLRP3, ASC, Caspase-1, and IL-1β expression in dorsal skin were effectively down-regulated following AYZ treatment (p < 0.05 and p < 0.01). Conclusion: These findings revealed that AYZ effectively suppressed AD-induced skin inflammation by inhibiting the activation of the NLRP3 inflammasome and the MAPKs/NF-kB signaling. Therefore, AYZ is a potential therapeutic agent against AD in the clinical setting.
Article
Aims: As an essential indicator of allergic reactions, mast cell (MC) activation involves FcεRI-mediated signaling and the release of allergic mediators. In FcεRI signaling, Ca2+ is located at the intersection of multiple cellular signaling pathways. However, the effect of extracellular Ca2+ (exCa2+) on MCs during anaphylaxis remains unclear, along with its exact mechanisms. Therefore, we sought to determine whether and how elevated exCa2+ amplifies allergic reactions. Main methods: In vitro experiments used immunoglobulin E (IgE)/antigen (Ag)-induced activation of rat and mouse MCs in vitro. The levels of MC degranulation mediators were used to evaluate the effect of exCa2+. In vivo experiments used MC-mediated passive systemic anaphylaxis (PCA) Balb/c mice. After stimulation, anaphylaxis indexes such as rectal temperature and allergic symptom score were detected. Key findings: In vitro experiments revealed that exCa2+ is a stimulus signal for the aggravation of allergic reactions in MCs. When antagonists or siRNA inhibited GPRC6, MCs released fewer inflammatory mediators. Moreover, in vivo experiments confirmed in vitro results. Allergic symptoms were alleviated by antagonists NPS2143 in PCA mice, demonstrating that exCa2+ aggravates allergic reactions through GPRC6A. Significance: Our study provides an essential theoretical basis for targeting Ca2+ and GPRC6A as therapeutic options for allergies.
Article
Asthma is a heterogeneous disease related to numerous inflammatory cells, among which mast cells play an important role in the early stages of asthma. Therefore, treatment of asthma targeting mast cells is of great research value. α‐Asarone is an important anti‐inflammatory component of the traditional Chinese medicine Acorus calamus L, which has a variety of medicinal values. To investigate whether α‐asarone can alleviate asthma symptoms and its mechanism. In this study, we investigated the effect of α‐asarone on mast cell activation in vivo and in vitro. The release of chemokines or cytokines, AHR (airway hyperresponsiveness), and mast cell activation were examined in a mast cell‐dependent asthma model. Western blot was performed to determine the underlying pathway. α‐Asarone inhibited the degranulation of LAD2 (laboratory allergic disease 2) cells and decreased IL‐8, MCP‐1, histamine, and TNF‐α in vitro. α‐Asarone reduced paw swelling and leakage of Evans blue, as well as serum histamine, CCL2, and TNF‐α in vivo. In the asthma model, α‐asarone showed an inhibitory effect on AHR, inflammation, mast cells activation, infiltration of inflammatory cells, and the release of IL‐5 and IL‐13 in lung tissue. α‐Asarone decreased the levels of phosphorylated JAK2, phosphorylated ERK, and phosphorylated STAT3 induced by C48/80. Our findings suggest that α‐asarone alleviates allergic asthma by inhibiting mast cell activation through the ERK/JAK2‐STAT3 pathway.
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The article presents recommendations for the diagnosis and intensive care of DIC syndrome in massive blood loss in obstetrics. Issues of clinical, laboratory and instrumental diagnostics of DIC-syndrome in massive blood loss in obstetrics, application of allogeneic blood components (erythrocytes, plasma, cryoprecipitate, platelets) and blood coagulation factors (factor Vlla, concentrate of prothrombin complex factors) are considered. The quality criteria of medical patients with DIC-syndrome in massive blood loss are presented.
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Mast cell proteases are thought to be involved with tumor progression and neo-vascularization. However, their exact role is still unclear. The present study was undertaken to further elucidate the function of specific subtypes of recombinant mouse mast cell proteases (rmMCP-6 and 7) in neo-vascularization. SVEC4-10 cells were cultured on Geltrex® with either rmMCP-6 or 7 and tube formation was analyzed by fluorescence microscopy and scanning electron microscopy. Additionally, the capacity of these proteases to induce the release of angiogenic factors and pro and anti-angiogenic proteins was analyzed. Both rmMCP-6 and 7 were able to stimulate tube formation. Scanning electron microscopy showed that incubation with the proteases induced SVEC4-10 cells to invade the gel matrix. However, the expression and activity of metalloproteases were not altered by incubation with the mast cell proteases. Furthermore, rmMCP-6 and rmMCP-7 were able to induce the differential release of angiogenic factors from the SVEC4-10 cells. rmMCP-7 was more efficient in stimulating tube formation and release of angiogenic factors than rmMCP-6. These results suggest that the subtypes of proteases released by mast cells may influence endothelial cells during in vivo neo-vascularization.
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Mast cells are crucial effector cells in allergic reactions, where IgE is the best known mechanism to trigger their degranulation and release of a vast array of allergic mediators. However, IgE is not the only component to stimulate these cells to degranulate, while mast cell activation can also result in differential release of mediators. There is a plethora of stimuli, such as IgG, complement components, TLR ligands, neuropeptides, cytokines, chemokines and other inflammatory products, that can directly trigger mast cell degranulation, cause selective release of mediators, and stimulate proliferation, differentiation and/or migration. Moreover, some of these stimuli have a synergic effect on the IgE-mediated mast cell activation. Because of the ability to respond to a large repertoire of stimuli, mast cells may act as a versatile cell in various physiological and pathological conditions. In this review, we discuss current knowledge on non-IgE stimuli for (human) mast cells. Copyright © 2015. Published by Elsevier B.V.
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Mast cell leukemia (MCL) is a very rare form of systemic mastocytosis (SM) with a short median survival of 6 months. We describe a case of a 65-year-old woman with aleukaemic variant of MCL with a very high serum total tryptase level of 2255 μg/L at diagnosis, which occurred following an episode of hypotensive shock. She fulfilled the diagnostic criteria of SM, with a bone marrow smear infiltration of 50-60% of atypical mast cells (MCs). She tested negative for the KIT D816V mutation, without any sign of organ damage (no B- or C-findings) and only few mediator-related symptoms. She was treated with antihistamine alone and then with imatinib for the appearance of anemia. She maintained stable tryptase level and a very indolent clinical course for twenty-two months; then, she suddenly progressed to acute MCL with a serum tryptase level up to 12960 μg/L. The patient died due to haemorrhagic diathesis twenty-four months after diagnosis. This clinical case maybe represents an example of the chronic form of mast cell leukemia, described as unpredictable disease, in which the serum total tryptase level has confirmed itself as a reliable marker of mast cells burden regardless of the presence of other signs or symptoms.
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Tetramer-forming tryptase (hTryptase-β) was recently discovered to have a prominent role in preventing the internal accumulation of life-threatening fibrin deposits and fibrin-platelet clots. The anticoagulant activity of hTryptase-β is an explanation for the presence of hemorrhagic disorders in some patients with anaphylaxis or mastocytosis. The fragments of hFibrinogen formed by the proteolysis of this prominent protein by hTryptase-β could be used as biomarkers in the blood and/or urine for the identification and monitoring of patients with mast cell-dependent disorders. Recombinant hTryptase-β has potential to be used in clinical settings where it is desirable to inhibit blood coagulation.
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Mast cells (MCs) are active participants in blood coagulation and innate and acquired immunity. This review focuses on the development of mouse and human MCs, as well as the involvement of their granule serine proteases in inflammation and the connective tissue remodeling that occurs during the different phases of the healing process of wounded skin and other organs. The accumulated data suggest that MCs, their tryptases, and their chymases play important roles in tissue repair. While MCs initially promote healing, they can be detrimental if they are chronically stimulated or if too many MCs become activated at the same time. The possibility that MCs and their granule serine proteases contribute to the formation of keloid and hypertrophic scars makes them potential targets for therapeutic intervention in the repair of damaged skin.
Article
Mast cells may be cultured from human peripheral blood in the presence of recombinant human stem cell factor (rhSCF). The characteristics of the cells in peripheral blood that give rise to mast cells are unknown. Because mast cell precursors in human marrow are CD34+, human peripheral blood mononuclear cells from patients with mastocytosis and normal controls were sorted on the basis of CD34 expression and the positive and negative cell populations were cultured in rhSCF, recombinant human interleukin-3 (rhIL-3), or both for 6 weeks. Cell cultures were examined every 2 weeks for total and mast cell number and cell differential using Wright Giemsa and acid toluidine blue stains and antibodies to mast cell tryptase and chymase, cell-associated histamine, and expression of CD34, c-kit, Fc epsilon RI, and Fc gamma RII using flow cytometric analysis. The ultrastructural anatomy of mast cells was examined by electron microscopy. Peripheral blood CD34+ cells cultured in rhSCF with or without rhIL-3 gave rise to cell cultures consisting of greater than 80% mast cells by 6 weeks. CD34+ cells cultured in rhIL-3 alone did not give rise to mast cells, whereas rhIL- 3 plus rhSCF increased the final mast cell number eightfold when compared with cells cultured in rhSCF alone. Mast cells increased concomitantly with a decrease in large undifferentiated mononuclear cells. CD34- cells did not give rise to mast cells. Histamine content per cell at 6 weeks was approximately 5 pg. Electron microscopy of 4- week cultures showed immature mast cells containing predominantly tryptase-positive granules that were either homogeneous or contained lattice structures, partial scroll patterns, or central dense cores and mixtures of vesicles, fine granular material, and particles. The CD34+ population at day 0 expressed Kit (65%) and Fc gamma RII (95%), but not Fc epsilon RI, by fluorescence-activated cell sorter analysis. At 6 weeks, CD34+-derived mast cells exhibited Fc epsilon RI in addition to Kit and Fc gamma RII, and were negative for CD34 antigen. Patients with mastocytosis showed a higher number of mast cells per CD34+ cell cultured compared with normal controls. Thus, the mast cell precursor in human peripheral blood is CD34+/Fc epsilon RI- and gives rise to mast cells in the presence of rhSCF with or without rhIL-3, and the number of mast cells arising per CD34+ cell in culture is greater when the CD34+ cells are obtained from patients with mastocytosis compared with normal subjects.
Article
Recent studies have found the KIT D816V mutation in peripheral blood of virtually all adult systemic mastocytosis patients once highly sensitive PCR techniques were used; thus, detection of the KIT D816V mutation in peripheral blood has been proposed to be included in the diagnostic work-up of systemic mastocytosis algorithms. However, the precise frequency of the mutation, the biological significance of peripheral blood-mutated cells and their potential association with involvement of bone marrow hematopoietic cells other than mast cells still remain to be investigated. Here, we determined the frequency of peripheral blood involvement by the KIT D816V mutation, as assessed by two highly sensitive PCR methods, and investigated its relationship with multilineage involvement of bone marrow hematopoiesis. Overall, our results confirmed the presence of the KIT D816V mutation in peripheral blood of most systemic mastocytosis cases (161/190; 85%)-with an increasing frequency from indolent systemic mastocytosis without skin lesions (29/44; 66%) to indolent systemic mastocytosis with skin involvement (124/135; 92%), and more aggressive disease subtypes (11/11; 100%)-as assessed by the allele-specific oligonucleotide-qPCR method, which was more sensitive (P<.0001) than the peptide nucleic acid-mediated PCR approach (84/190; 44%). Although the presence of the KIT mutation in peripheral blood, as assessed by the allele-specific oligonucleotide-qPCR technique, did not accurately predict for multilineage bone marrow involvement of hematopoiesis, the allele-specific oligonucleotide-qPCR allele burden and the peptide nucleic acid-mediated-PCR approach did. These results suggest that both methods provide clinically useful and complementary information through the identification and/or quantification of the KIT D816V mutation in peripheral blood of patients suspected of systemic mastocytosis.Modern Pathology advance online publication, 12 June 2015; doi:10.1038/modpathol.2015.72.
Article
SM comprises a heterogeneous group of disorders, characterized by an abnormal accumulation of clonal MCs in 1 or more tissues, frequently involving the skin and BM. Despite the fact that most adult patients (>90%) carry the same genetic lesion (D816V KIT mutation), the disease presents with multiple variants with very distinct clinical and biologic features, a diverse prognosis, and different therapeutic requirements. Recent advances in the standardization of the study of BM MC by MFC allowed reproducible identification and characterization of normal/reactive MCs and their precursors, as well as the establishment of the normal MC maturational profiles. Analysis of large groups of patients versus normal/reactive samples has highlighted the existence of aberrant MC phenotypes in SM, which are essential for the diagnosis of the disease. In turn, 3 clearly distinct and altered maturation-associated immunophenotypic profiles have been reported recently in SM, which provide criteria for the distinction between ISM patients with MC-restricted and multilineage KIT mutation; thus, immunphenotyping also contributes to prognostic stratification of ISM, particularly when analysis of the KIT mutation on highly purified BM cells is not routinely available in the diagnostic work-up of the disease.