Which immunoglobulin is most abundant in mucosal secretions?

• A. IgG
• B. IgM
• C. IgA (secretory IgA)
• D. IgE

Answer: (C)

Secretory IgA is the most abundant immunoglobulin in mucosal secretions. It is released mainly as a dimer linked by a J chain and is transported across mucosal epithelium by the polymeric immunoglobulin receptor. As it moves into the lumen, a secretory component remains attached, protecting it from proteolysis in the harsh mucosal environment. This form of IgA is specialized to neutralize pathogens and toxins right at the entryways of the body, preventing adherence and invasion without provoking inflammation. IgG and IgM can be present in mucosal secretions but at far lower levels, while IgE serves primarily in allergic responses and defense against parasites, not as a major mucosal defender.