Page "Mast cell" Paragraph 10

In allergic reactions, mast cells remain inactive until an allergen binds to IgE already in association with the cell ( see above ).

Other membrane activation events can either prime mast cells for subsequent degranulation or can act in synergy with FceRI signal transduction.

Allergens are generally proteins or polysaccharides.

The allergen binds to the antigen-binding sites, which are situated on the variable regions of the IgE molecules bound to the mast cell surface.

It appears that binding of two or more IgE molecules ( cross-linking ) is required to activate the mast cell.

The clustering of the intracellular domains of the cell-bound Fc receptors, which are associated with the cross-linked IgE molecules, causes a complex sequence of reactions inside the mast cell that lead to its activation.

Although this reaction is most well understood in terms of allergy, it appears to have evolved as a defense system against intestinal worm infestations ( tapeworms, etc.

).