Reduced acute GVHD severity of TLR4−/− mouse donor-derived BMT or TLR4−/− mice as BMT recipients receiving cells from BALB/c mice. (▴) indicates TLR4+/+ recipient, (▪) indicates TLR4−/− recipient BALB/c mice. TLR4−/−→BALB/c allogeneic BMT experiment. (a) Mean GVHD index score: (▴) vs. (▪), P=0.004. (b) Mean body weight: (▴) vs. (▪), P<0.001. (c) Percentage of survival: donor TLR4+/+ (▴) vs. donor TLR4−/− (▪), P=0.01. Results of the subsequent reverse-direction allogeneic BMT experiments with BALB/c→TLR4+/+ mice. (d) Mean GVHD index score: (▴) vs. (▪), P=0.002. Compared to BALB/c→TLR4−/− mice, BALB/c→TLR4+/+ mice developed obvious symptoms of GVHD 14 days after BMT. (e) Mean body weight: (▴) vs. (▪), P=0.002. (f) The survival curves of TLR4+/+ recipients (▴) compared with TLR4−/− recipients (▪) indicates no significant difference. Data shown are derived from at least two independent experiments. BMT, bone marrow transplantation; GVHD, graft-versus-host disease; TLR4, Toll-like receptor 4.