Mast cells are found in almost all parts of the body along with the endothelial cells of the blood vessels as well as mucosal cells.
Unlike other blood cells they are sessile and differentiation of mast cells from precursor cells takes place in tissues. They are about 10-30p m in diameter with a polymorphic nucleus. Even though they are absent in circulation they are quite similar to basophiles in various aspects, such as morphology, function, surface receptors etc.
On the basis of origin and activities mast cells can be differentiated in to two different groups. One is mucosal mast cell group (MMC) and the other is connective tissue mast cells (CTMC).
Mucosal mast cells are derivative of thymus derived precursors but connective tissue mast cells arise from bone marrow. Since high affinity receptors for IgE antibodies are present on the surface of mast cells, the IgE antibodies secreted against specific allergen bind to the mast cells and induce mast cell secretions on antigen binding.
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These chemicals are harmful to the parasite and also serve as signals to other immune cells to come and join in the reaction.
The action of mast cells and the effect of their secretions are similar to the action of basophils. In addition to T cells, B cells, Phagocytes, immune system engages mast cells also in defense. The basic function of mast cells is to give protection against large external parasites entering through the skin, respiratory or intestinal tract.