# DBT JRF 2020 — Question 106

Exam: DBT JRF 2020 · Section: B · Topic: Immunology · Difficulty: Medium

## Question

Opsonization is the process of

## Options

- **A.** none of the given options is correct
- **B.** coating of foreign substances by antibody
- **C.** coating of foreign substances by TCR
- **D.** coating of foreign substances by MHC

## Answer

Option B

## Explanation

Opsonisation is the process of coating pathogen/foreign particle surfaces with opsonins to enhance phagocytosis by professional phagocytes (neutrophils, macrophages). Major opsonins: (1) IgG antibodies — Fc region of IgG bound on pathogen surface recognised by Fcγ receptors (FcγRI, FcγRIII) on phagocytes; (2) Complement fragment C3b (covalently deposits on pathogen surface) and iC3b (its cleavage product) recognised by complement receptors CR1 and CR3 (Mac-1/CD11b). Opsonisation overcomes the phagocyte's difficulty in engulfing hydrophilic, charged bacterial surfaces — the opsonin acts as a molecular bridge. Result: enhanced phagocytosis and subsequent intracellular killing. Distinguished from complement-mediated lysis (MAC pore formation) or neutralisation (antibody blocks toxin).

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