IgA is predominantly found in mucosal secretions. Which immunoglobulin option lists its correct representative?

• A. IgG
• B. IgM
• C. IgE
• D. IgA

Answer: (D)

IgA is the antibody class specialized for mucosal immunity and is the main immunoglobulin found in mucosal secretions such as saliva, tears, mucus, and intestinal secretions. It often exists as secretory IgA, a dimer that includes a secretory component allowing it to be released into mucosal surfaces where it neutralizes pathogens and toxins without triggering inflammation. This positioning makes IgA the most representative immunoglobulin at mucosal barriers.

In contrast, IgG is the dominant antibody in blood and tissues and can cross the placenta; IgM is the first antibody produced during a primary response and is primarily a pentamer in serum; IgE is involved in allergic responses and defense against certain parasites. Their primary roles and localizations do not match mucosal secretions as directly as IgA, which is why IgA is the correct choice here.