Q67.Which of the following are correct for MHC-I molecule?

A. Glycoprotein
B. Expressed by nearly all nucleated cells
C. Present antigen to Tₕ (T-helper) cells
D. Peptide-binding domain is α1 and β1

Choose the correct answer from the options given below :

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

The correct answer is option (1): A and B Only.

MHC-I Molecule Features

MHC class I molecules are transmembrane glycoproteins (A) expressed on nearly all nucleated cells (B), enabling immune surveillance by presenting short intracellular peptides (8-10 amino acids) to CD8+ cytotoxic T lymphocytes (CTLs). They feature an α-chain with α1, α2 (peptide-binding groove), and α3 domains plus β2-microglobulin, loading antigens via the cytosolic/proteasome/ER pathway.

Option Analysis

• Option (1) A and B Only: Correct—MHC-I confirmed as glycoprotein on nucleated cells; excludes erroneous presentation target (C) and domain structure (D).

• Option (2) A, B and C Only: Incorrectly includes C; MHC-I presents to CD8+ CTLs for cell killing, while T-helper (Th/CD4+) cells recognize MHC-II on APCs.

• Option (3) B, C and D Only: Fails on C (Th cells wrong) and D (peptide groove is α1/α2 domains, not α1/β1—MHC-II uses α1/β1).

• Option (4) B and C Only: Wrong by adding C; MHC-I flags infected/abnormal cells to CTLs, not Th activation.

Introduction: MHC-I Molecule Glycoprotein Expressed by Nearly All Nucleated Cells

NEET immunology MCQs test MHC-I specifics like glycoprotein nature and expression versus presentation targets/domains. Identifying MHC-I molecule glycoprotein expressed by nearly all nucleated cells as correct (A,B only) unlocks adaptive immunity scoring. This analyzes option (1), structure, and exam traps.

MHC Class I Structure and Role

MHC-I spans all nucleated cells (vs. MHC-II on APCs), with glycoprotein α-chain (HLA-A/B/C) + β2-microglobulin. Key:

• Peptide-binding: α1/α2 domains form groove for endogenous peptides (viral/cancer).

• Function: CD8+ T cell recognition triggers lysis.

Debunking C and D Errors

• C False: Th (CD4+) bind MHC-II exogenous antigens; MHC-I handles intracellular threats.​

• D False: α1/α2 groove (MHC-I); MHC-II uses α1/β1. Common mix-up.​

NEET Solution: Option (1) A and B Confirmed

Universal expression monitors “self” integrity; glycoprotein aids membrane stability. Vs. MHC-II table:

NEET Prep: MHC Mastery Tips

• Mnemonic: “I = Intracellular, Invariant nucleated, Immuno-glycoprotein.”

• Link pathways: Cytosolic (I) vs. endosomal (II).

• Practice: Virus-infected cell → MHC-I upregulation.