Q.10 Which of the following statements are correct regarding Immunoglobulin A (IgA)?

1. IgA is the main class of antibody in secretions such as tears and saliva.
2. IgA is also found in secretions of lungs and intestine.
3. IgA is the first line of defense against infection at these sites.
4. IgA is the main immunoglobulin in the bloodstream late in the primary immune response.

Choose the correct answer from the options given below:

1. (A), (B) and (D) only
2. (A), (B) and (C) only
3. (A), (B), (C) and (D)
4. (B), (C) and (D) only

   Immunoglobulin A (IgA) is the primary antibody in mucosal secretions like tears and saliva, as well as in lungs and intestines, serving as the first line of defense there, but it is not the main immunoglobulin in bloodstream during late primary response—that role belongs to IgG.

   Question Breakdown

   The statements test IgA’s roles in mucosal immunity versus systemic circulation. IgA exists as secretory IgA (sIgA) in external fluids and monomeric form in serum.​

   • (A) Correct: IgA dominates secretions like tears, saliva, colostrum.​

   • (B) Correct: Found in respiratory (lungs) and gastrointestinal (intestine) secretions.​

   • (C) Correct: sIgA neutralizes pathogens at mucosal entry points, blocking adhesion.​

   • (D) Incorrect: Late primary response in blood features IgG; IgA is minor in serum (~10-15%).​

   Option Analysis

   Option	Statements Included	Correct?	Reason
   First	(A), (B), (D)	No	Includes wrong (D) ​.
   Second	(A), (B), (C)	Yes	All accurate on mucosal role .
   Third	(A), (B), (C), (D)	No	Adds false (D) ​.
   Fourth	(B), (C), (D)	No	Misses true (A), includes wrong (D) ​.

   Immunoglobulin A IgA statements focus on its mucosal immunity role, vital for GATE Life Sciences exams covering immunology basics. This guide solves a key PYQ identifying correct facts about IgA in secretions and defense.

   IgA Structure and Locations

   IgA, as dimeric sIgA, protects mucosal surfaces with secretory component resisting proteases. Predominant in tears, saliva, lung mucus, intestinal fluids—unlike serum where IgG prevails.

   Key Functions Explained

   • Neutralizes microbes in secretions without inflammation.

   • First barrier at entry sites like respiratory/gut tracts.​

   • Not dominant in blood; IgM starts, IgG peaks late primary response.​

   Solved PYQ

   Correct: (A), (B), (C) only—IgA excels in external secretions as frontline mucosal defender.​

   Exam Strategy

   Memorize: sIgA for mucosa; serum order IgM → IgG → IgA. Practice PYQs for immunology scoring in GATE.