Absence of γδ T cells in the host reduces acute GVHD pathology. γδ^-/- (▥, n = 4), wt (▪, n = 4), and syn BM transplant recipients (□, n = 4) underwent transplantation as in Figure 1 and the gastrointestinal tract was analyzed on day 7 after BMT as described in “Materials and methods.” Damage to syn small bowel was minimal (A), whereas wt exhibited severe villous blunting, crypt destruction changes and atrophy, and increased lymphocytic infiltrates (B). γδ^-/- small bowel showed significantly less damage (C). Original magnification, ×100. Images were visualized using an Olympus Bx 40 microscope (Olympus, Melville, NY) equipped with an 10 ×/0.65 aperture objective lens. Image acquisition was performed with a JVC digital camera GC-Qx 5HDU (JVC, Wayne, NJ). Coded slides were scored for pathologic damage (D) as described in “Materials and methods.” Serum was obtained on day 7 after BMT and analyzed for LPS (E) and TNF-α (F). γδ^-/- vs wt, ^*P < .05 (D-F). Error bars represent standard error.