Question

Identify major class of antibody present in saliva, tears and intestinal mucus

• A. Ig G
• B. Ig M
• C. Ig E
• D. Ig A

Hint:

Antibody Distribution:
IgA $\rightarrow$ Mucosal secretions (saliva, tears, colostrum, gut mucus).
IgG $\rightarrow$ Major serum antibody ($80\%$, crosses placenta).
IgM $\rightarrow$ Primary response (pentamer).
IgE $\rightarrow$ Allergy & parasites.

Answer 1

The Correct Option is D

Step 1: Understanding the Concept:
Secretory immunoglobulins provide primary mucosal immune defense at epithelial surfaces and external exocrine secretions.

Step 2: Detailed Explanation:
Immunoglobulin A (IgA) is the predominant antibody isotype found in external mucosal secretions:
- In mucosal linings (saliva, tears, colostrum, bronchial mucus, and gastrointestinal fluids), IgA exists as dimeric Secretory IgA (sIgA) linked by a J-chain and enveloped by a protective Secretory Component (SC) that prevents enzymatic proteolysis.
- It neutralizes mucosal pathogens and toxins through immune exclusion.

Step 3: Final Answer:
Hence, the major antibody class present is IgA, matching option (D).