Nd CD4+ T cells were found to contribute to such expansion67. Finally, it has been reported that certain MC progenitors can proliferate in vitro66, however, whether they can also proliferate within mucosal tissues remains to be proven.Author Manuscript Author Manuscript Author Manuscript Author ManuscriptMucosal 3-Methyladenine molecular weight Immunol. Author manuscript; available in PMC 2016 February 03.Reber et al.PageMast cell activationMCs ordinarily express on their surface large numbers of the high affinity IgE receptor, FcRI. During IgE-dependent immune responses, the antigen-dependent cross-linking of antigen-specific IgE bound to FcRI induces the aggregation of FcRI, promoting the activation of downstream signaling events that lead to the secretion of biologically active products implicated in allergic reactions6, 68, 69. The IgE-dependent stimulation of MCs has been extensively reviewed6, 69?2. It was recently reported that perivascular MCs can “order SC144 sample” circulating IgE directly in the blood by extending cell processes across the vessel wall73. Moreover, MC FcRI were shown to be able to distinguish between high- or lowaffinity stimuli, permitting the MCs to respond differentially to such signals by releasing distinct spectra of secretory products in vitro and by orchestrating distinct in vivo outcomes74. Our group recently reported a beneficial role for IgE, FcRI, and FcRI in defense against honeybee venom-induced mortality in mice75. Together with evidence that expression of the FcRI chain is important for full expression of acquired resistance to the hypothermiainducing effect of honeybee venom-derived phospholipase A276, these findings support the hypothesis that IgE, which contributes to allergic disorders, also has an important function in protection of the host against noxious substances77, 78. MCs can respond to many stimuli beside IgE. MCs can respond to various pathogens though activation of TLRs, including TLR-2 and TLR-479, 80 and, via GPCRs, to certain peptides found in venoms81?3, or can be activated by various complement peptides84, 85 and plateletactivation factor86. There is evidence that MCs also can be directly or indirectly activated by some plant products, including aqueous pollen extracts from birch87, and by products of the coagulation system, including Factor Xa88 and thrombin receptor activating peptide (TRAP)89. MCs also can respond to certain chemokines and cytokines (including IL-3325?7, 90, 91 and TSLP92), or be activated through the aryl hydrocarbon receptor93, 94, the CD40 ligand95 or the OX40 ligand96?8 or by immune complexes of IgG99, 100. MC activation (e.g., via the FcRI) can also be modulated by various mechanisms, including interactions with other cells such as granulocytes101, regulatory T cells102 and other lymphocytes103, via a variety of negative regulatory receptors expressed on their surface8, 104?06, or by exposure to certain cytokines, including the KIT ligand SCF8, 12?4, 107, 108, IL-3325?7, 109 and IFN-56, 110.Author Manuscript Author Manuscript Author Manuscript Author ManuscriptMast cell-derived mediatorsMCs store preformed mediators in their granules and can release some of them almost instantly upon degranulation. These stored mediators include vasoactive amines such as histamine111, 112 (although MCs are considered the main source of histamine outside of the CNS, other cells also can produce histamine, including basophils113 and neutrophils114, 115), and, in rodents, serotonin112. MC granules also contain man.Nd CD4+ T cells were found to contribute to such expansion67. Finally, it has been reported that certain MC progenitors can proliferate in vitro66, however, whether they can also proliferate within mucosal tissues remains to be proven.Author Manuscript Author Manuscript Author Manuscript Author ManuscriptMucosal Immunol. Author manuscript; available in PMC 2016 February 03.Reber et al.PageMast cell activationMCs ordinarily express on their surface large numbers of the high affinity IgE receptor, FcRI. During IgE-dependent immune responses, the antigen-dependent cross-linking of antigen-specific IgE bound to FcRI induces the aggregation of FcRI, promoting the activation of downstream signaling events that lead to the secretion of biologically active products implicated in allergic reactions6, 68, 69. The IgE-dependent stimulation of MCs has been extensively reviewed6, 69?2. It was recently reported that perivascular MCs can “sample” circulating IgE directly in the blood by extending cell processes across the vessel wall73. Moreover, MC FcRI were shown to be able to distinguish between high- or lowaffinity stimuli, permitting the MCs to respond differentially to such signals by releasing distinct spectra of secretory products in vitro and by orchestrating distinct in vivo outcomes74. Our group recently reported a beneficial role for IgE, FcRI, and FcRI in defense against honeybee venom-induced mortality in mice75. Together with evidence that expression of the FcRI chain is important for full expression of acquired resistance to the hypothermiainducing effect of honeybee venom-derived phospholipase A276, these findings support the hypothesis that IgE, which contributes to allergic disorders, also has an important function in protection of the host against noxious substances77, 78. MCs can respond to many stimuli beside IgE. MCs can respond to various pathogens though activation of TLRs, including TLR-2 and TLR-479, 80 and, via GPCRs, to certain peptides found in venoms81?3, or can be activated by various complement peptides84, 85 and plateletactivation factor86. There is evidence that MCs also can be directly or indirectly activated by some plant products, including aqueous pollen extracts from birch87, and by products of the coagulation system, including Factor Xa88 and thrombin receptor activating peptide (TRAP)89. MCs also can respond to certain chemokines and cytokines (including IL-3325?7, 90, 91 and TSLP92), or be activated through the aryl hydrocarbon receptor93, 94, the CD40 ligand95 or the OX40 ligand96?8 or by immune complexes of IgG99, 100. MC activation (e.g., via the FcRI) can also be modulated by various mechanisms, including interactions with other cells such as granulocytes101, regulatory T cells102 and other lymphocytes103, via a variety of negative regulatory receptors expressed on their surface8, 104?06, or by exposure to certain cytokines, including the KIT ligand SCF8, 12?4, 107, 108, IL-3325?7, 109 and IFN-56, 110.Author Manuscript Author Manuscript Author Manuscript Author ManuscriptMast cell-derived mediatorsMCs store preformed mediators in their granules and can release some of them almost instantly upon degranulation. These stored mediators include vasoactive amines such as histamine111, 112 (although MCs are considered the main source of histamine outside of the CNS, other cells also can produce histamine, including basophils113 and neutrophils114, 115), and, in rodents, serotonin112. MC granules also contain man.
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