CD8+ cytotoxic T cells recognize antigens presented by which MHC class?

• A. MHC class II
• B. MHC class I
• C. T cell receptor
• D. CD8 molecule

Answer: (D)

CD8+ cytotoxic T cells recognize peptide fragments that come from inside the cell and are displayed on the surface by MHC class I molecules. The CD8 protein on the T cell serves as a co-receptor that binds to MHC class I and helps the T cell receptor (TCR) signal more effectively, but the actual presenting molecule is MHC class I, not CD8 itself. In contrast, MHC class II presents extracellular-derived peptides to CD4+ helper T cells. So the correct concept is that CD8+ T cells are restricted to recognizing peptide-MHC class I complexes.