IL-17A mediates cutaneous GVHD IL-17A mediates cutaneous GVHD. Lethally irradiated (A) B6D2F1 (n = 6) or (B) B6 mice (n = 5 or 6) were transplanted with G-CSF–mobilized grafts from WT or IL-17A−/− B6 donors or WT or IL-17A−/− BALB/c donors, respectively. IL-17A mediates cutaneous GVHD. Lethally irradiated (A) B6D2F1 (n = 6) or (B) B6 mice (n = 5 or 6) were transplanted with G-CSF–mobilized grafts from WT or IL-17A−/− B6 donors or WT or IL-17A−/− BALB/c donors, respectively. Non-GVHD controls (n = 3) received T-cell–depleted G-CSF WT grafts. Tissue injury expressed as a mean composite score was determined by semiquantitative histology as described in “Histology and immunostaining of GVHD target organs.” **P < .01, WT vs IL-17A−/−. (C) Representative images (original magnification ×400) of hematoxylin and eosin–stained paraffin sections of tissues taken 28 days after transplantation. Geoffrey R. Hill et al. Blood 2010;116:819-828 ©2010 by American Society of Hematology