CD80/86 expression is required for skin cGVHD. Combined data from 3 experiments are shown. On day 0 recipient mice were lethally irradiated and reconstituted with 8 × 10⁶ BM cells WT BM or CD80/86^-/- [CD80/86] BM) alone or with 2 × 10⁶ WT CD4 cells (BM + CD4). All BM controls (ctrls): WT or CD80/86^-/- recipients of WT or CD80/86^-/- BM (n = 20); WT recipients of WT BM + CD4 (n = 17); WT recipients of CD80/86^-/- BM + CD4 (n = 8); CD80/86^-/- recipients of WT BM + CD4 (n = 28); CD80/86^-/- recipients of CD80/86^-/- BM + CD4 (n = 16). (A) Incidence of cGVHD. †P < .01 for CD80/86^-/- recipients of WT BM + CD4 as compared with all other experimental groups. (B) Average clinical disease score for mice affected with cGVHD (unaffected mice are excluded). †P < .01 for CD80/86^-/- recipients of CD80/86^-/- BM + CD4 as compared with all other CD4 recipients. BM control mice and CD80/86^-/- recipients of CD80/86^-/- BM + CD4 did not get cGVHD and are represented on the graph as scoring “0.” (C) Pathology scores for representative mice. Mean score is indicated by a horizontal bar. †P < .01 for CD80/86^-/- recipients of CD80/86^-/- BM + CD4 as compared with all other CD4 recipients. P = .1715 for CD80/86^-/- recipients of CD80/86^-/- BM + CD4 as compared with BM control recipients.