Fig. 6: Impact of different thymic MHC-I peptides on cytotoxic CD8⁺ T cells in WT mice.

a, Staining (i.c.) of Runx3 and Eomes in CD8⁺ T cells among CD24⁻TCR⁺ mature thymocytes from LM control β5t^WT (n = 4) and β5t^KO (n = 7) BALB/c mice (representative of 3–4 independent experiments). b, Numbers of CV (Runx3⁺Eomes⁻) and IM (Runx3⁺Eomes⁺) CD8⁺ T cells among CD24⁻TCR⁺ mature thymocytes from LM control β5t^WT and β5t^KO BALB/c mice (a). c, MHC-I peptide selection index showing the frequencies of β5t- and nonβ5t-selected cells among CV and IM CD8⁺ T cells in CD24⁻TCR⁺ mature BALB/c thymi. d, Staining (i.c.) of Runx3 and Eomes on CD8⁺ T cells among CD24⁻TCR⁺ mature thymocytes from LM control β5t^WT (n = 5) and β5t^KO (n = 10) B6 mice (representative of 5–8 independent experiments). e, Numbers of CV (Runx3⁺Eomes⁻) and IM (Runx3⁺Eomes⁺) CD8⁺ T cells among CD24⁻TCR⁺ mature thymocytes from LM control β5t^WT and β5t^KO B6 mice (d). f, MHC-I peptide selection index showing the frequencies of β5t- and nonβ5t-selected cells among CV CD8⁺ T cells in CD24⁻TCR⁺ mature B6 thymi. g, Schematic of CD8⁺ T cell lineage decisions induced by TCR engagements of different thymic peptides in the CD8^Dual thymus. CD8⁺ T cell lineage fates are determined by MHC-I TCR signaling duration that is regulated by Cd4/Cd8 co-receptor gene loci and by thymic MHC-I peptides. TCR engagements of β5t-peptides that are expressed exclusively in cTECs in the cortex invariably become disrupted during positive selection, which generates only cytotoxic CD8⁺ T cells. TCR engagements of nonβ5t-peptides that are expressed in the cortex and throughout the thymus might also become disrupted and generate cytotoxic CD8⁺ T cells, but these cells will reencounter nonβ5t-peptides on thymic elements outside the cortex, which will stimulate late TCR signaling that will induce cells, together with thymic IL-4, to become IM CD8⁺ T cells. However, TCR engagements with high affinity of nonβ5t-peptides expressed throughout the thymus might persist without disruption, which leads to the generation of helper CD8⁺ T cells. Numbers within profiles indicate frequency of cells in each box (a and d). ***P < 0.001, **P < 0.01, *P < 0.05 (two-tailed unpaired t-tests); mean ± s.e.m. (b and e). CMJ, corticomedullary junction.