IgA helps prevent colonization by pathogens at mucosal surfaces.

• A. True
• B. False
• C. Only in the bloodstream
• D. Only in bone marrow

Answer: (A)

Secretory IgA is a key player in mucosal immunity. It is produced by plasma cells in mucosa-associated lymphoid tissue and transported into mucosal secretions as secretory IgA. In the lumen, it binds pathogens and toxins, preventing their adhesion to epithelial cells and neutralizing them before they can invade. This immune exclusion and agglutination help keep microbes from colonizing mucosal surfaces while minimizing inflammation. While IgA can be present in serum, its main protective role is at mucosal surfaces, aligning with the statement. The other options imply a restricted role to the bloodstream or bone marrow, which doesn’t reflect how IgA functions to defend mucosal barriers.