Q.56 Match the immunoglobulin class in Group I with its properties in Group II

Group I                   Group II
P. IgG                   1. Major antibody in external secretions such as bronchial mucus
Q. IgA                  2. Protects against parasites
R. IgE                  3. Antibody that appears first in serum after exposure to an antigen
S. IgM                 4. Antibody present in highest concentration in serum
(A) P-4, Q-1, R-2, S-3         (B) P-3, Q-2, R-1, S-4
(C) P-4, Q-3, R-1, S-2         (D) P-1, Q-4, R-3, S-2

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Immunoglobulins (antibodies) represent the cornerstone of humoral immunity, with each class exhibiting distinct structural, functional, and distributional characteristics. This article solves a classic immunology matching question appearing frequently in competitive exams like NEET PG, CSIR NET, and university entrance tests.

Correct Answer: Option (A) P-4, Q-1, R-2, S-3

Why Option A is Correct – Property-by-Property Matching

P. IgG → 4. Antibody present in highest concentration in serum
IgG constitutes 75-80% of total serum immunoglobulins (10-15 mg/mL), making it the most abundant antibody class in blood. Its long half-life (21-23 days) and efficient transplacental transport further elevate its serum dominance.

Q. IgA → 1. Major antibody in external secretions such as bronchial mucus
Secretory IgA (sIgA) dominates mucosal surfaces including saliva, tears, bronchial mucus, and gastrointestinal secretions. Produced by plasma cells beneath epithelial layers, sIgA neutralizes pathogens at entry points through immune exclusion.

R. IgE → 2. Protects against parasites
IgE mediates Type I hypersensitivity and provides anti-parasitic defense. It binds to FcεRI receptors on mast cells and eosinophils, triggering degranulation that expels helminths (e.g., Ascaris, Schistosoma). Serum levels remain low (nanogram range) except during allergy/parasitic infections.

S. IgM → 3. Antibody that appears first in serum after exposure to an antigen
IgM is the primary response antibody, appearing within 3-5 days of first antigen exposure. As a pentamer with 10 antigen-binding sites, it provides high-avidity binding despite low affinity of individual monomers. IgM peaks first, then declines as class switching produces IgG.

Why Other Options Are Incorrect

Option B (P-3, Q-2, R-1, S-4) – Completely Wrong

• IgG ≠ first serum antibody (IgM appears first)

• IgA ≠ parasite protection (IgE role)

• IgE ≠ external secretions (IgA role)

• IgM ≠ highest serum concentration (IgG dominates)

Option C (P-4, Q-3, R-1, S-2) – Two Major Errors

• IgA ≠ first serum antibody (IgM primary response)

• IgE ≠ external secretions (IgA in bronchial mucus)

• Gets IgG (highest serum) and IgM (parasites? ❌ IgE) wrong

Option D (P-1, Q-4, R-3, S-2) – Multiple Errors

• IgG ≠ external secretions (IgA role)

• IgA ≠ highest serum (IgG dominates)

• IgE ≠ first serum antibody (IgM primary)

Quick Reference Table: Immunoglobulin Properties Summary

Clinical Relevance for Exams

• IgM positivity = acute/recent infection

• IgG positivity = past infection/immunity

• Elevated IgE = allergy/parasitic infection

• sIgA deficiency = recurrent sinopulmonary infections

Master this matching pattern – it appears consistently across immunology sections in competitive exams!