Effects of BMT on intestinal immune cell populations. Sublethal TBI (8 Gy) induced a time-dependent decrease in numbers of MPO-positive cells (panel A), macrophages (panel B), CD45R-positive cells (B-lymphocytes) (panel C) and CD4-positive cells (T-lymphocytes) (panel D). BMT significantly enhanced the recovery of mucosal granulocytes (P = 0.005), T-lymphocytes (P = 0.03) and B-lymphocytes (P = 0.03) by day 14. However, there was no difference in macrophage number in groups with or without BMT. Ten fields per section with a 40× objective; average ± SEM, n = 4–6.