Fig. 4. Direct interaction between iNKT cells and activated CD8⁺ T cells enhances IFN-γ production by iNKT cells.

a Purified CD1d^WT OT-1 or CD1d^KO OT-1 CD8⁺ T cells were stimulated with K^bOVA in the presence of iNKT cells. The percentages of IFN-γ- or IL-4-producing iNKT cells were examined using intracellular FACS analysis. b Naïve OT-1 CD8⁺ T cells were stimulated with K^bOVA for 18 h. iNKT cells were cocultured with preactivated or naïve OT-1 cells. The levels of IFN-γ in iNKT cells were evaluated after 2 h of culture using intracellular FACS analysis (b). c Purified OT-1 CD8⁺ T cells and iNKT cells were cocultured with CD1d^KO DCs in the presence or absence of OVA_257–264. After 18 h of activation, the surface expression of CD69 on iNKT cells was measured by FACS. iNKT cells were gated on the α-GalCer-CD1d dimer⁺ TCR-β⁺ cell population. All data are representative of at least three independent experiments. Data are presented as the mean ± SEM. *p < 0.05, **p < 0.01, and ***p < 0.001. Unpaired t tests (a, c). One-way ANOVA with Bonferroni’s multiple comparison test was used for statistical analysis (b)