CD4⁺ T cells that lack Il27ra are more fit than intact T cells in the Mtb lung. (A) CD4⁺ PD-1⁺ T cells were purified from congenically marked B6 (CD45.1) mice that had been Mtb infected for 26 d and then transferred into B6 and Il27ra^−/− mice that had been infected with Mtb 60–70 d previously. Recipient mice received isotype control or anti–IL-27R antibody for the period of the transfer (10 d). Antigen-specific endogenous (left two panels) and all transferred (right two panels) CD4⁺ T cells were examined for KLRG1 expression, and the impact of anti–IL-27R antibody treatment was determined in the lung and MLNs. Combined data from two experiments are shown, each with four mice per group. *, P < 0.05; **, P < 0.001; ***, P < 0.0001 by ANOVA. (B) Competitive BM chimeras were generated by transplanting BM containing equal numbers of B6.CD45.1 and Il27ra^−/−.CD45.2 into lethally irradiated TCRβδ^−/− mice that were then infected with Mtb via the aerosol route. Representative FACS analysis of the lungs of chimeric mice at day 120 after challenge shows the gating strategy. (C) The ratio of Il27ra^−/− CD45.2 to B6-CD45.1 cells within each population in the lungs of chimeric mice after challenge was determined. Data are representative of a total of three independent experiments with four to five mice per group. (D) BM chimeras reconstituted with either 100% B6, Il27ra^−/−, or mixed 50:50 B6 Il27ra^−/− were infected with Mtb, and the bacterial burden at day 60 after challenge was determined. Data are from four experiments combined. *, P < 0.05 by ANOVA. (A, C, and D) Mean and SE (A and D) or mean and SD (C) are shown.