Which characteristic best distinguishes IgA1 from IgA2 structurally, and which is the predominant form in secretions such as colostrum and saliva?
- A IgA2 has a disulphide-bonded heavy-light chain linkage; IgA2 predominates in gut secretions but IgA1 predominates overall in serum ✓
- B IgA2 lacks the hinge region; IgA1 predominates in secretions
- C IgA1 lacks the hinge region; IgA2 predominates in secretions
- D IgA1 has a longer hinge region and is the predominant subclass in all secretions
Explanation
IgA2 differs from IgA1 in having a shorter hinge region and, uniquely, a non-covalent (non-disulphide) heavy–light chain linkage (the L chains are linked to each other). IgA1 predominates in serum (~80%) whereas IgA2 is relatively more abundant in colonic and urogenital secretions. Both subclasses are found in secretory IgA (sIgA), but IgA1 is still the majority in most external secretions like saliva and colostrum. Understanding this helps explain why IgA1 protease-producing bacteria (Neisseria, Streptococcus pneumoniae) can effectively evade mucosal immunity.
Reference: Ananthanarayan & Paniker's Textbook of Microbiology, 11th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.