Question

List the 5 classes of antibodies (immunoglobulins), explain the structure of each, and state a role that each plays in the immune system.

Answer 1

Answere : Five classes of antibodies are :

IgM : They form about 5-13% of antibodies in the blood & lymph. They are also attached to surfaces of B cells.

It has Pentameric structure having 10 antigen-binding sites (cross links effectively). The large size prevents it from crossing from the bloodstream into tissues.

The main role of IgM is to control bloodstream infections. It is most efficient class in triggering the classical pathway of complement system activation.

IgG : It is first and most abundant antibody. They are about 80-85% of all antibodies in the blood

They are present in blood, lymph, & intestinal wall.
It provides longest term protection.

It has monomeric structure.

It is transported across the placenta into the fetus's bloodstream, so it protects the developing fetus against infections.

IgA : They make up about 10-13% of antibodies in the blood. It is found in two forms :

I. Serum IgA : It has monomeric structure(basic four chain structure). It is found in blood. It is found in blood.

II. Secretory IgA : It has dimeric structure (2 or more molecules). These antibodies qre found in mucous secretion and secretion from gastro-intestinal tract.

They protects breastfed infants against intestinal pathogens. They provide localized protection of mucous membranes.

IgD : They form about less than 1% of antibodies in blood and lymph, mainly attached to surfaces of B cells.

It has monomeric structure.

It involved with the development and maturation of the antibody response.

IgE : They form about less than 0.01%. They are attached to surfaces of basophils, mast cells and B cells.

It has monomeric structure.

It involved in some allergic reactions. They are important in eliminating parasites, particularly parasitic worms.

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