Question

Amino acid variation among MHC class II alleles that present antigens to CD4 T cells is

concentrated:

A. where MHC contacts the co-receptors CD4 or CD8
B. in the β chain, because the α chain is monomorphic
C. where the MHC molecule contacts peptide and the T-cell receptor
D. in the α chain, because the β chain is monomorphic
E. throughout both the α and β chains in all domains

Answer 1

Amino acid variation among MHC class II alleles is mainly found where the molecule binds to the peptide and T-cell receptor, allowing the immune system to recognize a wide array of antigens.

Step-by-step explanation:

Amino acid variation among MHC class II alleles that present antigens to CD4 T cells is concentrated where the MHC molecule contacts peptide and the T-cell receptor. This is because the main function of the MHC class II molecules is to present processed antigens to helper T cells (CD4 T cells).

MHC class II molecules are composed of two protein chains (α and β chains), both of which span the plasma membrane and fold into two separate domains. The antigen-binding cleft, which is the most variable part, is formed by domains α₁ and β₁. This variability is crucial for the immune system to recognize a wide array of antigens presented by different MHC molecules.

The diversity of the antigen-binding sites provided by genetic rearrangement in MHC molecules is analogous to the diversity in T cell receptors and B cell receptors (BCRs), which also undergo genetic rearrangement to recognize a vast array of antigens.