Which is the correct order of activities showcased by exogenous pathway? i) Generation of MHC class II molecules ii) MHC-peptide transport iii) Class II MHC peptide loading iv) Generation of Peptide from proteolysis
Correct Answer: iv—i—iii—ii
Processing and presentation of antigens require 4 major activities. Firstly, there is generation of peptides in the endosomes which is carried out by proteases to degrade antigens into peptide fragments. Meanwhile, MHC class II molecules are generated in other vesicles with the help of a protein named invariant chain. Class II MHC molecules along with invariant chain are then transported to endosomes where processed peptides are present. The peptides are then loaded on to the MHC class II molecules and are transported into membrane bound vesicles to the plasma membrane.