Antigen loading for MHC-II occurs in which compartment after removal of the invariant chain?

Antigen loading for MHC-II occurs in which compartment after removal of the invariant chain?

• A. Endoplasmic reticulum
• B. Acidified endosome
• C. Cytosol
• D. Nucleus

Answer: (B)

Antigen loading onto MHC class II happens in the acidified endosomal/lysosomal compartment after the invariant chain is removed. The invariant chain initially binds MHC II in the endoplasmic reticulum to prevent premature peptide binding and to direct the MHC II molecule into the endocytic pathway. In the acidified endosome, proteases trim the invariant chain, leaving a CLIP peptide, and ---- with the help of other molecules such as HLA-DM ---- the appropriate antigenic peptide from degraded exogenous proteins is loaded. The peptide–MHC II complex is then transported to the cell surface to present to CD4+ T cells.

Antigen loading onto MHC class II happens in the acidified endosomal/lysosomal compartment after the invariant chain is removed. The invariant chain initially binds MHC II in the endoplasmic reticulum to prevent premature peptide binding and to direct the MHC II molecule into the endocytic pathway. In the acidified endosome, proteases trim the invariant chain, leaving a CLIP peptide, and ---- with the help of other molecules such as HLA-DM ---- the appropriate antigenic peptide from degraded exogenous proteins is loaded. The peptide–MHC II complex is then transported to the cell surface to present to CD4+ T cells.