Which immunoglobulin is the secretory antibody found on mucosal surfaces?

• A. IgA
• B. IgM
• C. IgG
• D. IgE

Answer: (A)

Secretory IgA is the antibody found on mucosal surfaces. It is produced in mucosal tissues and released into secretions as a dimer linked by a J chain and associated with a secretory component. This secretory component protects IgA from being degraded in the harsh mucosal environment and helps it remain stable in secretions like saliva, tears, and intestinal fluids. The main job of secretory IgA is immune exclusion: it binds pathogens and toxins before they can attach to or invade mucosal cells, helping to prevent infection while keeping inflammation low. Other immunoglobulins aren’t the primary secretory antibody on mucosal surfaces: IgM can be secreted but mainly as a pentamer; IgG is abundant in serum and can be transported across mucosa in some contexts but isn’t the main secretory antibody; IgE is involved in allergic responses and parasite defense, not mucosal secretory defense.