Attenuation of GVHD by blockade of IL-6 signaling does not require an intact thymus. Lethally irradiated (900 cGy) thymectomized Balb/c mice received a transplant of Foxp3^EGFP BM (10 × 10⁶) and 0.4 × 10⁶ Foxp3^EGFP spleen cells. Cohorts of mice were then treated with either rat IgG isotype control (n = 12) or anti–IL-6R antibody (n = 12) once weekly for 4 weeks beginning on the day of transplantation. Animals were then killed 46 to 48 days after transplantation. (A) The percentage of original body weight of mice over time from both groups is depicted. (B) Pathological damage in the colon, liver, and lung using a semiquantitative scoring system as detailed in “Histologic analysis.” (C) Total spleen cellularity, (D) absolute number of splenic CD4⁺ T cells, and (E) absolute number of splenic Tregs are depicted. Data are presented as the mean (± SEM) and are the cumulative results from 3 independent experiments. (Statistics: *P ≤ .05, **P < .01.)