Immunoglobulin A IgA

Immunoglobulin A IgA

Immunoglobulin A IgA

Immunoglobulin A is present predominantly in extracellular secretions. It circulates in the plasma in the form of a four peptide monomer (MWI60,000) or a drimer (MW 320,000) or a trimer (MW480,OOO). Each four peptide unit consists of two kappa(k) or two lambda λ light chains and two alpha heavy chains.

The heavy, chains each contain about 450 amino acid residues. Two subclasses of the heavy chain have been found, α1' and α2' Polymers of IgA contain, inter heavy chain disulphide linkages between monomers. IgA polymers also contain two acceseory polypeptides, a joining link (j) and a secretory component(T)

The joining link (MW 15,000) apparently promotes the association of two or three monomers to form dimers and trimers. The secretary components (MW 60,000) are synthesized within mucosal cells and migrate to the cell membrane. Here they combine with IgA, dimers, or trimers to form a complex which is released from free cell surface into the lumen. The secretory components appear to enhance the section of IgA into, the extracellular fluids. The function of IgA is to provide defence against entry of organisms through the surface cell membrane.

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