Mucosal antibodies elicited by OPV primarily act to limit poliovirus replication in which location?

• A. In the gut, limiting poliovirus multiplication
• B. In the blood, preventing viremia
• C. In the cerebrospinal fluid
• D. In the environment, reducing shedding

Answer: (A)

Mucosal antibodies from OPV act where poliovirus first replicates after ingestion—the lining of the gut. Secretory IgA in the intestinal mucosa neutralizes the virus as it tries to infect enterocytes, blocking attachment and entry and thus limiting replication in the gut. This local, mucosal immunity is crucial because most poliovirus replication and shedding occur in the intestinal tract; by limiting replication there, it reduces fecal shedding and transmission. Systemic antibodies play a role in preventing viremia and CNS involvement, but the primary action of mucosal antibodies is at the gut surface, where replication begins.