Blockade of IL-6 signaling results in a significant reduction in proinflammatory T_H1 and T_H17 cells. Lethally irradiated (900 cGy) Balb/c mice received a transplant of B6 BM (5 × 10⁶) and purified B6 CD4⁺ T cells (0.3 × 10⁶). Cohorts of mice were then administered rat IgG isotype control (n = 8) or anti–IL-6R antibody (n = 8) for 4 weekly injections as described in “Reagents.” Mice in both groups were killed 28 to 29 days after transplantation. (A) The percentage of original body weight of mice over time from both groups is depicted. (B) Absolute number of CD4⁺ T cells in the spleen, liver, and lung of animals treated with either isotype control or anti–IL-6R antibody. (C) Representative dot plot depicting the percentage of IL-17– and/or IFN-γ–secreting cells within the gated CD4⁺ T-cell population. (D-F) Absolute number of CD4⁺ IFN-γ⁺ or CD4⁺ IL-17⁺ T cells present in the spleen, liver, or lung of animals treated with either isotype control or anti–IL-6R antibody. Data are presented as the mean (± SEM) and are the cumulative results from 2 independent experiments. (Statistics: *P ≤ .05, **P < .01.)