Immunoglobulin A (IgA)- Structure, Subclasses and Functions


Immunoglobulin A (IgA) is one of the five major classes of antibodies that play a vital role in the immune system. IgA is mainly found in mucosal secretions, such as saliva, tears, breast milk, and intestinal fluids, where it protects the body from pathogens and toxins. IgA is also present in the blood serum, but at lower levels than other immunoglobulins.

IgA can exist in two subclasses: IgA1 and IgA2. These subclasses differ in their structure, distribution, and function. The subclasses are defined by the type of heavy chain they have: IgA1 has an alpha 1 (α1) heavy chain, while IgA2 has an alpha 2 (α2) heavy chain. The heavy chains are composed of four domains: variable (V), constant 1 (C1), hinge (H), and constant 2 (C2). The hinge region is a flexible segment that connects the C1 and C2 domains and allows the antibody to bend and bind to antigens.