Recipients of α₄β₇⁺ T cells have significantly increased GVHD organ pathology in intestines and liver. Lethally irradiated CBA (1300 cGy) mice received transplants as described in Figure 2. As a syngeneic BMT control for posttransplantation thymic cellularity, additional lethally irradiated (1100 cGy) B10.BR recipients received transplants. Recipients of B10.BR α₄β₇⁺ (light gray bars) and α₄β₇^– (dark gray bars) T cells were killed on days 7, 14, and 22 after BMT, and tissues were obtained for histopathologic analysis. Small intestine, large intestine, and liver were scored for established organ-specific parameters in a blinded fashion (mean score ± SEM). Skin GVHD was determined by the number of apoptotic keratinocytes per millimeter of epidermis (±SEM), and thymic GVHD was assessed by the total number (±SEM) of thymocytes and the percentage (±SEM) of double-positive CD4⁺CD8⁺ thymocytes. Group sizes are as follows: small intestine, day 7 (3-4 animals), day 14 (4-6), and day 22 (6-7); liver, day 14 (3-6) and day 22 (7-9); large intestine, day 14 (3-5) and day 22 (7-8); skin, day 14 (14) and day 22 (12); thymus, day 14 (7-8) and day 22 (9); thymus syngeneic (5). Statistical analysis is as follows: small bowel, day 7 P = .03, day 14 P = .01, day 22 P = .006; liver, day 14 P = .02; large intestine, day 14 P = .037, day 22 P = .003.