MHC class I molecules present endogenous peptides to which T cell population?

MHC class I molecules present endogenous peptides to which T cell population?

• A. CD4+ helper T cells
• B. CD8+ cytotoxic T cells
• C. B cells
• D. NK cells

Answer: (B)

Endogenous peptides are displayed by MHC class I on nearly all nucleated cells so CD8+ cytotoxic T cells can survey them. Proteins made inside the cell are chopped up by the proteasome, and these peptides are transported into the endoplasmic reticulum by TAP, where they are loaded onto MHC class I molecules. The peptide–MHC I complex travels to the cell surface and is recognized by the CD8 co-receptor on cytotoxic T cells, activating them to kill the presenting cell if the peptide is foreign. MHC class II presents exogenous peptides to CD4+ helper T cells on professional antigen-presenting cells; B cells present antigens via MHC II to helper T cells as well; NK cells are innate lymphocytes that respond to stress signals and altered MHC expression rather than presenting peptides to T cells.

Endogenous peptides are displayed by MHC class I on nearly all nucleated cells so CD8+ cytotoxic T cells can survey them. Proteins made inside the cell are chopped up by the proteasome, and these peptides are transported into the endoplasmic reticulum by TAP, where they are loaded onto MHC class I molecules. The peptide–MHC I complex travels to the cell surface and is recognized by the CD8 co-receptor on cytotoxic T cells, activating them to kill the presenting cell if the peptide is foreign. MHC class II presents exogenous peptides to CD4+ helper T cells on professional antigen-presenting cells; B cells present antigens via MHC II to helper T cells as well; NK cells are innate lymphocytes that respond to stress signals and altered MHC expression rather than presenting peptides to T cells.