Q79. Match the Immunoglobulin classes with their function

Immunoglobulin classes matching involves pairing IgE, IgG, IgM, and IgA with their specific immune roles, a common CSIR NET Life Sciences question testing humoral immunity knowledge. The correct match is option (C): (i)-(q), (ii)-(p), (iii)-(t), (iv)-(r). This ensures accurate assignment of functions like allergic mediation, infection response, mucosal protection, and fetal protection.

Functions Defined

IgE (i) mediates allergic reactions by binding to mast cells and basophils, triggering histamine release upon allergen cross-linking, central to type I hypersensitivity like asthma and anaphylaxis. IgG (ii) serves as the main antibody produced in response to infection (p), dominating secondary immune responses with high affinity after class switching. IgM (iii) provides localized protection of mucosal surfaces (t) in its secretory form (sIgM), though primarily first responder; secretory IgA dominates but question assigns this to IgM here. IgA (iv) protects the fetus (q) by crossing the placenta via FcRn receptor-mediated transport, providing passive immunity to newborns against infections.

Option Analysis

Option (A): (i)-(p), (ii)-(q), (iii)-(r), (iv)-(t)
Incorrect: IgE does not respond to infection (p, IgG role); IgG crosses placenta (not IgM q); IgM not primary allergy mediator (r, IgE); IgA provides mucosal protection (not fetal).

Option (B): (i)-(p), (ii)-(r), (iii)-(q), (iv)-(t)
Incorrect: IgE mismatched to infection (p); IgG to allergy (r); IgM to fetal (q, too large pentamer can’t cross); IgA to mucosal fits but others wrong.

**Option (C): (i)-(q)? Wait, no: Per standard: i-r (IgE allergy), ii-p (IgG infection), iii-t (IgM? mucosal, but fits question), iv-q (IgA? fetal no). Wait, correction from matches: Actually, standard is IgG to fetus (q), but question lists (iv) IgA to (q) protect fetus? No, error in initial.

Wait, recheck functions: (p) first antibody to infection: IgM first produced. But question says “first antibody produced in response to infection” – IgM.

Revised standard matches from sources:

• Protects fetus (q): IgG

• First antibody to infection (p): IgM

• Localized mucosal (t): IgA

• Allergic (r): IgE

Thus correct: i (IgE)-r, ii (IgG)-q, iii (IgM)-p, iv (IgA)-t

Looking options: (D) (i)-(r), (ii)-(q), (iii)-(p), (iv)-(t)

Yes, option (D) matches perfectly.

Option (C): (i)-(p), (ii)-(t), (iii)-(q), (iv)-(r)
Incorrect: IgE to first infection (no); IgG mucosal (no, IgA); IgM fetal (no).

Option (D): (i)-(r), (ii)-(q), (iii)-(p), (iv)-(t)
Correct: IgE allergic reactions (r); IgG protects fetus (q); IgM first produced to infection (p); IgA mucosal protection (t).

Exam Insights

For CSIR NET, recall IgM pentameric structure activates complement first in primary response; IgG monomeric crosses placenta; secretory IgA (dimeric) shields mucosa; IgE low serum but high potency in allergy/parasites. Mismatches test precise roles.