Which molecule presents endogenous peptides to CD8+ cytotoxic T cells?

Which molecule presents endogenous peptides to CD8+ cytotoxic T cells?

• A. MHC class I
• B. MHC class II
• C. CD28
• D. B7

Answer: (A)

Endogenous peptides are presented by MHC class I molecules to CD8+ cytotoxic T cells. Proteins synthesized inside the cell are degraded in the cytosol by the proteasome, their fragments are transported into the endoplasmic reticulum by TAP transporters, loaded onto MHC class I, and then displayed on the cell surface. CD8+ T cells recognize these peptide–MHC I complexes via the T cell receptor, initiating cytotoxic responses against infected or abnormal cells. MHC class II, in contrast, presents exogenous peptides to CD4+ helper T cells, after uptake and processing of extracellular proteins. CD28 and B7 are costimulatory molecules that provide a second activation signal, not the peptide-presenting molecule themselves.

Endogenous peptides are presented by MHC class I molecules to CD8+ cytotoxic T cells. Proteins synthesized inside the cell are degraded in the cytosol by the proteasome, their fragments are transported into the endoplasmic reticulum by TAP transporters, loaded onto MHC class I, and then displayed on the cell surface. CD8+ T cells recognize these peptide–MHC I complexes via the T cell receptor, initiating cytotoxic responses against infected or abnormal cells. MHC class II, in contrast, presents exogenous peptides to CD4+ helper T cells, after uptake and processing of extracellular proteins. CD28 and B7 are costimulatory molecules that provide a second activation signal, not the peptide-presenting molecule themselves.