Which immunoglobulin is most involved in mucosal immunity?

• A. IgG
• B. IgM
• C. IgA
• D. IgE

Answer: (C)

Secretory IgA is the primary defender at mucosal surfaces. It’s produced by plasma cells in mucosa-associated lymphoid tissue and secreted as a dimer linked by a J chain. The polymeric immunoglobulin receptor transports it across the epithelium and adds a secretory component, which protects it from proteolysis in harsh secretions like mucus and gut fluid. Once in the lumen, secretory IgA neutralizes viruses and toxins, and prevents microbes from sticking to and invading epithelial cells—doing so without provoking strong inflammatory responses, which is ideal for constantly exposed mucosal tissues. Other immunoglobulins have different main roles: IgG is mainly systemic and can reach mucosa but isn’t specialized for it; IgM is an early responder and is great at clumping pathogens; IgE is involved in allergic reactions and antiparasitic defenses. IgA’s unique presence in secretions and its immune-exclusion function make it the key immunoglobulin in mucosal immunity.