Minor histocompatibility antigen expression by the hematopoietic compartment results in cutaneous chronic GVHD. (a–d) Sclerotic dermis of skin from [BALB.B→B6] chimeric recipients, harvested day 90 after HCT, was distinguished by thickened dermis (vertical line, a) containing randomly oriented and tightly compacted bundles of collagen (c). In contrast, skin from [B6→B6] syngeneic controls had a normal dermal thickness (vertical line, b) and contained mostly horizontally oriented, loosely packed bundles of collagen (d). Original magnification: a and b, ×200; c and d, ×400. (e) Mean dermal thickness ± SEM, in millimeters. n = 5 for both groups.