Transfer of microbiota during cohousing confers increased susceptibility to intestinal hyper-acute GVHD. (A) PCA plot of B6.WT and B6.IL-17RA^−/− fecal microbiota sampled pre- and postcohousing (4 weeks) of mice. Data combined from 2 experiments (n = 12 per group) are shown with separately housed controls included within experiment 2 and sampled during the same period. (B) Cohoused or separately housed B6.WT or B6.IL-17RA^−/− mice (n = 18 to 26 per group) were lethally irradiated (1000 cGy) and transplanted with G-CSF mobilized BALB/c.WT grafts. Survival is represented by Kaplan-Meier analysis: ***P = .0001, BALB/c.WT → B6.WT cohoused (blue open circle) vs B6.WT separately housed (blue filled circle); ****P < .0001, BALB/c.WT → B6.WT separately housed (blue filled circle) vs IL-17RA^−/− separately housed (red filled square); ****P < .0001, BALB/c.WT → B6.WT cohoused (blue open circle) vs IL-17RA^−/− cohoused (red open square). Data combined from 3 replicate experiments are shown. (C) PCA plot of B6.WT and B6.IL-17RC^−/− fecal microbiota sampled pre- and postcohousing (4 weeks), and separately housed controls sampled during the same period. Data from a single experiment are shown (n = 5 to 10 per group). (D) Cohoused (4 weeks) or separately housed B6.WT or B6.IL-17RC^−/− mice (n = 5 to 10 per group) were lethally irradiated (1000 cGy) and transplanted with G-CSF mobilized BALB/c.WT grafts (T-cell replete or TCD). Survival is represented by Kaplan-Meier analysis: ****P < .0001, BALB/c.WT → B6.WT cohoused (red open circle) vs B6.WT separately housed (red filled circle); ****P < .0001, BALB/c.WT → B6.WT separately housed (red filled circle) vs IL-17RC^−/− separately housed (blue filled square); *P = .03, BALB/c.WT → B6.WT cohoused (red open circle) vs IL-17RC^−/− cohoused (blue open square). Data combined from 2 experiments. CH, cohoused mice; PCA, principal component analysis; SH, separately housed mice; Wk, week.