(A) Representative images of skin sections obtained from the upper backs of mice from the indicated groups stained with H&E (top) and Masson’s Trichrome (bottom). Stars indicate regions of increased collagen density, indicative of GVHD-mediated fibrosis, in +Spl/placebo mice. Arrows indicate hair follicles, which were largely absent in +Spl/placebo mice. Scale bar: 115 μm. (B) Various skin disease criteria from all mice in each HCT group (n = 9–10/group), scored in a masked fashion by an expert pathologist specializing in GVHD-mediated skin disease. Scoring criteria were as follows: dermis (0, normal; 1, mild increased collagen density; 2, marked increased collagen density); hair follicles (0, normal number of approximately 5 per linear millimeter; 1, between 1 and 5 follicles per linear millimeter; 2, <1 follicle per linear millimeter); epidermis (0, normal; 1, interface damage in <20% of section with occasional necrotic keratinocytes; 2, widespread interface damage (>20% of section); inflammation (0, none; 1, focal infiltrates; 2, widespread infiltrates). Each symbol represents an individual mouse. Bars indicate the median ± range. Total skin score represents the sum of all above criteria for each mouse. Statistical analysis was performed by 1-way ANOVA with Tukey’s multiple comparisons test (GraphPad Prism). *P < 0.05; **P < 0.01; ***P < 0.001; ****P < 0.0001.