fig2

Figure 2. Differences in recognition and downstream processes between CD8⁺ and CD4⁺ T cells. CD8⁺ T cells recognize pMHC-I complexes, where the peptide is a fragment from an endogenous protein typically 8 to 11 AAs in length, which occupies a groove that is closed on both ends. CD4⁺ T cells recognize pMHC-II complexes, where the peptide is derived from cells or antigens engulfed by the APC and is typically longer, 12 to 25 AAs in length. The MHC-II groove is open on both ends. After activation, CD8⁺ T cells differentiate into cytotoxic T lymphocytes (CTLs), whereas CD4⁺ T cells differentiate e.g. into T helper cells, depending on receipt of further cytokine signals. APC: antigen-presenting cell; MHC: major histocompatibility complex; TCR: T cell receptor