AP BIOLOGY

Detailed explanation-1: -IgE is not believed to play an important role in defense against bacterial infections, since it does not activate complement or participate in opsonization [5]. IgE plays a key role in the pathogenesis of allergic diseases, especially mast cell/basophil activation, and in antigen presentation.

Detailed explanation-2: -Immunoglobulins of IgD, IgE and IgA isotypes do not have the capacity to activate complement through the classical pathway (2). Among IgG subtypes, IgG1 and IgG3 are strong, IgG2 moderate activator of complement and IgG4 has no complement-activating properties at all (2).

Detailed explanation-3: -Complement activation does not occur in systemic anaphylaxis because IgE immune complexes do not activate complement. In this immediate hypersensitivity reaction, the antigen binds to an IgE antibody on mast cells or basophils, causing release of mediators that produce life-threatening symptoms.

Detailed explanation-4: -It is well known that both IgG and IgM can activate complement via the classical pathway by binding of C1q to the Fc regions of these immunoglobulins. Recent advances have shown that also IgA is capable of activating the complement system.

Detailed explanation-5: -IgM activates the immune complement system only after binding to cell-surface antigens.