Which immunoglobulin class is associated with a secretory component?

Immunoglobulin A (IgA) is the immunoglobulin class associated with a secretory component. This is particularly significant in its role as a primary antibody found in mucosal areas such as the respiratory and gastrointestinal tracts, as well as in secretions like saliva, tears, and breast milk.

The secretory component is a polypeptide that attaches to IgA in its dimeric form, aiding in the transport of the antibody across epithelial cells. This transport protects IgA from proteolytic degradation in the lumen, allowing it to maintain its functional integrity and providing important immune protection at mucosal surfaces. This feature underscores the role of IgA in the first line of defense against pathogens that enter through the mucosal routes.

Other immunoglobulin classes—such as IgM, IgG, and IgE— do not have this specific association with a secretory component, which distinguishes IgA in terms of its function and structural adaptations for mucosal immunity.