Which antibody plays a crucial role in gut mucosal immunity against poliovirus?

• A. Secretory IgA
• B. Serum IgG
• C. IgM
• D. IgE

Answer: (A)

Secretory IgA at the gut mucosa is the key defender against poliovirus in the intestinal lumen. It is produced as a dimer by mucosal plasma cells and transported across the epithelium into the lumen as secretory IgA, where its secretory component helps it withstand digestive enzymes. This form of antibody neutralizes poliovirus right where it first replicates, preventing the virus from attaching to and entering intestinal cells, thus blocking infection and reducing person-to-person transmission. Serum IgG works mainly in the bloodstream and doesn’t concentrate in the gut lumen to provide strong mucosal protection. IgM can appear early but is less specialized for long-term mucosal defense, and IgE is not involved in antiviral gut immunity. For this reason, secretory IgA is the crucial antibody in gut mucosal immunity against poliovirus, and vaccines that induce mucosal IgA (like oral polio vaccine) are particularly effective at generating this protective barrier.