Figure 7. Th1 polarization is dependent on IFN-γ production by NKT cells.

(A) A schematic for the NKT cell-transfer experiment showing purification of NKT cells from WT or IFN-γ–KO mice and adoptive transfer 1 day prior to DENV2 infection in CD1d-KO mice. (B) DENV genome copies in dLNs on day 3 after infection. FP skin and dLNs were collected for intracellular staining of IL-4 and IFN-γ at 3 days after infection. Frequencies of (C) IL-4–producing CD4⁺ and (D) IFN-γ–producing CD4⁺ and CD8⁺ T cells in the dLNs after infection. (E) Frequencies of activated CD4⁺ and CD8⁺ T cells in the dLNs after infection. Frequencies of (F) IL-4– and (G) IFN-γ–producing CD4⁺ and CD8⁺ T cells in the FP skin after infection. (H) Frequencies of total CD8 in the FP skin after infection. n = 7–8 mice per group. *P < 0.05; **P < 0.01; ***P < 0.001; ****P < 0.0001. For all panels, Student’s unpaired t tests were used, including for D–G, where CD4⁺ or CD8⁺ T cells were compared between groups. IFN-γ produced by NKT cells is required for optimal Th1 immunity.