Protein mast cell activation

This chapter highlights the mechanisms responsible for mast cell activation during anaphylactic responses to environmental substances. In addition to discussing in detail the activation of mast cells and basophils by IgE and antigen, we also will describe how mouse models have been used to analyze the importance of various proteins, cells, mediators and activation mechanisms in the expression of anaphylaxis in that species. 

While the majority of attention has focused on peptides contained within the nervous system, two other important methods for delivering peptides to the vicinity of the mast cell have been established (1) peptides produced and secreted by other cells of inflammation that may affect mast-cell function and (2) the local generation of mast-cell-active peptides by secreted enzymes acting on circulating protein precursors. Examples of the former include several, as yet ill-defined, peptide factors and cationic proteins from other immunocompetent cells [66-69], defined lymphokines such as the interleukin-1 [70] and interleukin-3 [71], and tumour necrosis factor [70], Examples of the latter include bradykinin [72] and a recently identified peptide produced by the action of acid proteinases on albumin [73, 74]. 

IL-5 also enhances the expression of IL-2R on B cells and stimulates basophils. Proeosinophilic and/or proallergic Th2 cytokines, originally described as T lymphocyte products, have been ascribed to mast cells as weU, and these cells are probably analogous to T cells in the requirement of costimuli for the production of IL-5 protein. Moreover, the rapid kinetics of IgE-mediated IL-5 transcription and protein elaboration are consistent with a primary role for mast cell activation, directly leading to late phase airway eosinophilia. ... 

Thrombin and factor Xa that have escaped into the blood flow are both inhibited by serpins, anti-thrombin III (ATIII) and heparin cofactor II (HCII). These proteins bind to heparin sulfate or dermatan sulfate (Sect. 6.3.1), glycosaminoglycans which are secreted onto the luminal surface of healthy endothelial cells and also released into the blood from mast cells activated by an injury. Among the heparin molecules is a pentaglycan sequence... 

Recruitment of the Syk kinase and subsequent phosphorylation activation steps involving Lyn lead to mast cell activation demonstrating the importance of protein tyrosine kinases in the pathways that result in allergic inflammation and anaphylaxis. 

There may be substantial variation both within and among species (e.g., in mice vs. humans) in the expression of various proteins, receptors and/or ligands that influence the activation of mast cells (or basophils or other potential effector cell types), or that can regulate the responsiveness of end organ target cells (e.g., bronchial or gastrointestinal smooth muscle cells, vascular endothelial cells) to potential mediators of anaphylaxis derived from mast cells. 

Like all immunoreceptor family members, FceRI lacks intrinsic tyrosine kinase activity. IgE and antigen-induced crosshnking of FceRI initiates a complex series of phosphate transfer events via the activation of non-receptor Src, Syk and Tec family protein tyrosine kinases (fig. 1). The Src family kinase Lyn, which associates with the FceRI p subunit in mast cells, transphosphorylates neighboring FceRI ITAMs after receptor aggregation [7, 26]. Once phosphorylated, the p chain ITAM binds to the SH2 domain of additional Lyn molecules, while the phosphorylated y chain ITAM recruits Syk to the receptor complex, where it is activated by both autophosphorylation and phosphorylation by Lyn [2, 7,15, 26]. 

Sander LE. Frank SP, Bolat S, Blank U, Galli T. Bigalke H. Bischoff SC, Lorentz A Vesicle-associated membrane protein (VAMP)-7 and VAMP-8, but not VAMP-2 or VAMP-3, are required for activation-induced degranulation of mature human mast cells. Eur J Immunol 2008 38 855-863. 

Perret D, Shields M, Saxon A, Kehry MR A mouse Fey Fee protein that inhibits mast cells through activation of FcyRIIB, SH2 domain-containing inositol SS phosphatase 1, and SH2 domain-containing protein tyrosine phosphatases. J Allergy Chn Immunol 2008 121 441-447. 

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