Fig. 5.

CD4⁺ effector T cell differentiation requires host-derived IL-15 (A) Male skin graft survival was delayed in the absence of IL-15. Ml γ_c⁺ thymocytes were adoptively transferred to female Rag2^−/−γ_c^−/− (filled triangles; n = 5) or female Rag2^−/−IL-15^−/− (open squares; n = 4) recipients, and male skin grafts were placed 1 day later. We observed normal proliferation of Ml T cells in the spleen at day 10 (0.8 ± 0.23 × 10⁶ cells recovered) in the absence of host IL-15. (B) At 10 days after transplant, skin-infiltrating cells were isolated and analyzed by FACS. CD44, CD62L, CD27, Ly6C, and NKG2D expression are shown on electronically gated CD4⁺Vβ6⁺ T cells in the presence (black lines) or absence of host-derived IL-15 (shaded histograms). (C) FACS analysis of granzyme B (grzB) versus CD62L expression on gated CD4⁺ T cells is shown. (D) IFN-γ production from CD4⁺ T cells was analyzed after overnight restimulation of skin-infiltrating T cells with male APC. Between two and four recipient mice of each genotype were analyzed.