Eosinophils are granulocytes which can stain intensely with the dye eosin. The cytoplasm is filled with granules of basic substances such as histamine. Eosinophils are motile, phagocytic agents against parasites, but are also partly responsible for allergies. Basophils are granulocytes stained by basic dyes such as toluidine blue, carrying IgE receptors. As they mature, they settle into fixed tissue locations and become mast cells.
Mast cells are tissue-resident granule containing cells with IgE receptors.
Granules contain stored mediators of inflammation such as histamine, proteases, and proteoglycans such as heparin. Degranulation is stimulated by physical trauma, toxins or venoms, tissue proteases, binding of allergens to IgE or binding complement factor C5a. Unlike histamine, which is stored, SRS-A is produced at the time of IgE stimulation. SRS-A was found to consist of the products of glutathione conjugation to LTA 4 . Simple addition of glutathione to C-6, which opens the epoxide ring, gives Leukotriene C, LTC 4 .