Ligation of TLR7/8 induces transient expression of IDO in the colon and reduces GVHD lethality. (A) B6 Mice were lethally irradiated and 5 hours later injected intravenous with PBS or 200 μg of 3M-011. On day 0, 48 hours later, some mice were killed and colons, and spleens were assessed for IDO mRNA. The remaining mice were infused with BALB/c BM and 3 × 10⁶ T cells. On days 2 and 4 after BM transplantation, IDO mRNA was again assessed from colons and spleens. For colon IDO on D0, *P = .05; for spleen on D4, *P = .02. n = 4 mice/group, D0 colon data are representative of 2 identical experiments. (B) Wt (left) or IDO^−/− (right) mice were pretreated with PBS (■) or 3M-011 (□) and transplanted 48 hours later as in panel A. Survival is shown. Data are pooled from 2 identical experiments, n = 7-8 mice/group. P = .03. (C) Mice were treated and transplanted as in panels A and B. At 37 days after transplantation, colons were harvested, sectioned, and stained by hematoxylin and eosin. Sections were scored for pathology. n = 5 mice/group. *P < .05. (D) Sections taken from day 37 tissues in panel C were stained for CD4 by IHC. Representative sections are on the left, quantification of CD4⁺ cells is shown on the right. n = 5 mice/group. *P = .01.