Q.29 Which one of the following is NOT TRUE for class I MHC protein?

(A) MHC class I protein are polymorphic

(B) T-cell receptors recognizes MHC class I protein

(C) MHC class I protein are displayed on the surfaces of nucleated vertebrate cells

(D) 𝛽2 -microglobulin is covalently associated with MHC class I protein

Option (D) is NOT TRUE for class I MHC protein.​

MHC class I proteins present intracellular peptides to cytotoxic T cells on nucleated cells. This question tests key structural and functional features relevant for CSIR NET Life Sciences.​

Option Analysis

(A) MHC class I proteins are polymorphic

MHC class I genes, such as HLA-A, -B, and -C in humans, exhibit high polymorphism with numerous alleles in populations. This diversity enables presentation of varied peptides, enhancing immune response variability. Thus, this statement is true.​

(B) T-cell receptors recognize MHC class I protein

T-cell receptors (TCRs) on CD8+ cytotoxic T cells bind peptide-loaded MHC class I complexes. Recognition triggers immune responses against infected or abnormal cells. This statement holds true.​

(C) MHC class I proteins are displayed on nucleated vertebrate cells

These proteins appear on nearly all nucleated cells, including platelets in some cases, to signal intracellular status. Non-nucleated cells like mature erythrocytes lack them. This is accurate.​

(D) β2-microglobulin is covalently associated with MHC class I protein

β2-microglobulin (β2m) forms a heterodimer with the MHC class I heavy chain via non-covalent interactions. No covalent bond exists; engineered exceptions confirm natural non-covalent association. This statement is false.​

Class I MHC proteins play a vital role in immune surveillance by presenting peptides to T cells. For CSIR NET aspirants, understanding what is NOT true for class I MHC protein clarifies key misconceptions in immunology. This guide breaks down the MCQ options on class I MHC protein characteristics.

Core Features of Class I MHC Protein

Class I MHC proteins consist of a polymorphic heavy chain and non-covalently bound β2-microglobulin. They display endogenous peptides on nucleated vertebrate cells for TCR scrutiny.​

• High polymorphism in α chain genes ensures diverse peptide binding.​

• TCRs recognize peptide-MHC complexes, activating CD8+ T cells.​

• Expressed ubiquitously on nucleated cells, absent on erythrocytes.​

Why β2-Microglobulin is NOT Covalently Associated

The false statement claims covalent linkage, but β2m associates non-covalently with the heavy chain’s α3 domain. Crystal structures confirm this interaction supports stability without bonds. Dissociation occurs under stress, unlike covalent pairs.​

Exam Relevance for CSIR NET

This MCQ tests MHC structure and function, common in Unit 10 (Immunology). Polymorphism aids pathogen evasion challenges; non-covalent β2m enables dynamic assembly. Master these for competitive edges in genetics and biotech sections.​