Mast cell, EM
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The granules of the mast cell contain vasoactive amines, such as histamines. Binding of the anaphylatoxins, C3a and C5a, plus a specific antigen, will result in degranulation. The mast cell also releases chemotactic factors for eosinophils, which are often found in association with tissues affected by allergic responses. Here a mast cell (upper left) is seen adjacent to a capillary containing an RBC and the nucleus of an endothelial cell.