IgA is associated with immune protection of what bodily surfaces?

• A. Mucous Membranes
• B. Blood Plasma
• C. Bone Marrow
• D. Liver Tissue

Answer: (A)

IgA is specialized for protecting mucosal surfaces, the linings of the gut, respiratory tract, and other areas exposed to the outside world. It appears mainly in secretions as secretory IgA, found in saliva, tears, mucus, bile, and breast milk. This form is produced by plasma cells in mucosa-associated lymphoid tissue and is transported across the epithelium with a secretory component, which makes it resistant to digestive and enzymatic breakdown. Its main job is immune exclusion: IgA binds to pathogens and toxins in the lumen and prevents them from attaching to or entering epithelial cells, effectively neutralizing them without causing inflammation. Breast milk IgA also provides passive protection to newborns. While other antibodies like IgG or IgM are important elsewhere (primarily in blood and early responses), IgA’s role is specifically tied to mucosal surfaces.