Which antibody isotype is primarily secreted at mucosal surfaces and provides local protection?

• A. IgG is the main mucosal antibody.
• B. IgA is secreted at mucosal surfaces and provides local protection.
• C. IgM is primarily responsible for mucosal immunity.
• D. IgE is the major mucosal antibody.

Answer: (B)

Secretory IgA is the antibody most abundant at mucosal surfaces and provides local protection. It is produced as a dimer by plasma cells in mucosa-associated lymphoid tissues and is transported across the epithelium by the polymeric immunoglobulin receptor, which adds a protective secretory component. This form resists proteolysis in the harsh mucosal environment and acts to neutralize pathogens and toxins in the lumen, preventing adherence and entry—a process known as immune exclusion. While other isotypes like IgG, IgM, and IgE play important roles elsewhere, IgA’s specialization for mucosal secretions makes it the primary defender at these surfaces.