Question

MHC class II molecules first travel to ___ where they bind peptides produced by lysosomal degradation of extracellular pathogens before move to cell surface

Answer 1

MHC class II molecules bind peptides in the endomembrane system, following lysosomal degradation of extracellular pathogens, before being presented on the cell surface.

Step-by-step explanation:

MHC class II molecules first travel to the endomembrane system of the cell where they bind peptides produced by lysosomal degradation of extracellular pathogens before moving to the cell surface. More specifically, after extracellular antigens are taken into the cell via receptor-mediated endocytosis, the resulting vesicle containing the antigen fuses with a vesicle from the Golgi complex that contains pre-formed MHC class II molecules. This fusion allows for the association of the antigen with MHC class II molecules, and subsequently, the new vesicle transports these complexes to the cell surface for immune surveillance.

'Professional' antigen-presenting cells such as macrophages, dendritic cells, and B cells exclusively express MHC class II molecules. They play a crucial role in immune defense by presenting extracellular pathogen-derived antigens to helper T-cells which, upon activation, mediate a variety of immune responses.