Mast cells have their importance on our immunological system. They are strategically localized near blood vessels, where they fight against antigens that can invade the circulation through the tecidual liquid or epithelial discontinuity.
Mast cells function as sentries, because they have high sensibility with specific IgE of antigens that have already appeared on our body. When these antigens reappear and are realized through its specific IgE they provoke the release of chemical
mediators which are deposited on vesicles inside of mast cells. This is the basic thing of an inflammatory process. The granules of mast cells contain many important substances with physiological and pharmacological functions. Among them, heparin,
serotonine and histamine. Heparine represents 30% of the total content of mast cell. It''s a sulfated glycosaminoglycan and, for that, it presents metacromasia (see the text "A preparação de lâminas histológicas: Fixação e Coloração). It possess the capacity of avoid the coagulation, inhibiting platelets agregation.
histamine compounds more than 10% of the total content of mast cell. It''s an
amine derived from histidine and has a profound effect on visceral
sleek muscle, contracting it. Between the walls of epithelium cells that are not united by oclusion junctions, histamine separates membranes causing release of plasma. Serotonin is an amine derived from tryptofan. As well as histamine, serotonine also have properties vaso-active. Serotonine is found only in mast cells of certain species, like rat and mouse. On man, it is localized on platelets. Mast cells are responsible for liberation of other two chemical mediators on allergic reaction (anaphylaxis). One of mediators have an action equal to histamine, but its perfomance on sleek muscle and, consequently, on vascular permeability it slower. This mediators is known as SRS-A (slow-reacting substance of anaphylaxis). Another mediator is responsible for eosinophil atraction to the local of inflammation. It''s, therefore, an chemotactic agent, known as ECF-A (eosinophil chemotactic factor of anaphylaxis). It has to be observed mast cells with negative nucleus, granules of heparin, elastics fibres (thin) and colagen fibres (thick).
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