Which immunoglobulin is primarily found in mucosal secretions?

• A. IgA
• B. IgG
• C. IgM
• D. IgE

Answer: (A)

Secretory IgA is the main immunoglobulin in mucosal secretions. It is produced as a dimer by plasma cells in mucosal tissues and transported across the epithelium, where it acquires a secretory component that makes it resistant to proteolysis in secretions. In tears, saliva, mucus, and intestinal secretions, secretory IgA neutralizes pathogens and toxins and prevents them from attaching to epithelial cells, providing protection at the entryways of the body without triggering strong inflammatory responses. Other isotypes like IgG are more abundant systemically and are not the primary secretory antibodies in mucosal surfaces; IgM is part of the early response but is less specialized for secretion; IgE is involved in allergic and parasitic responses.