Host B cells attenuate the severity of acute GVHD following allogeneic BMT. (A) Survival by Kaplan-Meier analysis. Bone marrow and purified splenic T cells from Balb/c (allogeneic) donors were transplanted into lethally irradiated μMT (n = 23) or wild-type (n = 25) recipient B6 mice. B6 (syngeneic) BM and T cells were transplanted into μMT (n = 8) mice as non-GVHD controls. **P < .01 μMT versus wild-type allogeneic recipients. Data combined from 4 experiments. (B) Clinical scores as described in “Assessment of GVHD” were determined as a measure of GVHD severity in surviving animals. ***P < .001 μMT versus wild-type allogeneic recipients. (C) Histopathology of GVHD target organs. Bone marrow and purified splenic T cells from Balb/c (allogeneic) donors was transplanted into irradiated μMT (n = 7) or wild-type (n = 6) recipient B6 mice. μMT recipients (n = 4) receiving syngeneic B6 BM were non-GVHD controls. Semiquantitative histopathology as described in “Histopathology.” Data expressed as mean ± SE. #P < .01 and *P = .05 μMT allo versus wild-type allo.