Question

What is the role of the invariant chain (Ii)?

A. To prevent peptide binding to class II in the ER
B. To assist in folding class II �� and �� chains
C. To direct class II to the endocytic compartment
D. To serve as a substrate for proteases in the lysosome
E. All of the above

Answer 1

The role of the invariant chain (Ii) includes preventing premature peptide binding to MHC class II in the ER, assisting in the folding of the MHC class II molecules, directing them to the endocytic compartment, and serving as a substrate for proteases in the lysosome; hence, the answer is E. All of the above.

Step-by-step explanation:

The role of the invariant chain (Ii) is multifaceted in relation to MHC class II molecules. It helps by preventing peptide binding to Class II MHC in the endoplasmic reticulum (ER), which is crucial because premature binding of peptides would impede the proper function of the MHC molecules. The invariant chain also assists in the folding of the MHC class II α and β chains, ensuring that they maintain the proper structure needed for their function.

Additionally, it directs the MHC class II molecules to the endocytic compartment, where they can appropriately process and present extracellular antigens. Furthermore, in the endosomes and lysosomes, the invariant chain serves as a substrate for proteases which break it down, allowing antigenic peptides to bind to the MHC class II molecule. Therefore, the correct answer is E. All of the above.