Question

Which of the following statements is true about the assembly and loading of peptides to MHC class II molecules?

a. The alpha & beta chains of MHC class II assemble with the invariant chain.
b. Li, a protein, prohibits peptides from binding to MHC class II within the ER.
c. In a proteasome, the degradation of intracellular antigen will produce short peptides (8-10 amino acids) to be loaded on the MHC II.
d. A & B
e. A, B & C

Answer 1

The true statements regarding the process of peptide loading onto MHC class II are that the alpha and beta chains of MHC class II assemble with the invariant chain and that the invariant chain blocks binding of peptides within the ER. These facts exclude the proteasome producing peptides for MHC class II, as it is associated with MHC class I.

Step-by-step explanation:

The correct statement about the assembly and loading of peptides to MHC class II molecules is that the alpha and beta chains of MHC class II assemble with the invariant chain. Specifically:

• The alpha and beta chains of the MHC class II molecule assemble in the endoplasmic reticulum (ER) with a molecule known as the invariant chain. This chain blocks the antigen-binding site to prevent peptides from binding to MHC class II in the ER.
• The invariant chain is later degraded, and the resulting peptides from extracellular antigens processed by lysosomes are loaded onto the MHC class II molecules.
• The degradation of intracellular antigen within a proteasome results in short peptides that are subsequently loaded onto MHC class I, not MHC class II molecules.

Therefore, the true statements about MHC class II molecules are 'a' and 'b' (Option d: A & B).