IgA

IgA is an immunoglobulin that plays a key role in defending mucosal surfaces against attack by infectious microorganisms. It is the second most prevalent circulating immunoglobulin after IgG. IgA is present in both serum and external secretions such as those that bathe mucosal surfaces, where it is the predominant immunoglobulin. Secretory IgA, a dimer, provides the primary defense mechanism against local infections because of its abundance in mucosal secretions (e.g., saliva and tears) . The principal function of secretory IgA may be not to destroy antigens but to prevent the passage of foreign substances into the circulatory system.