Allo donor T cells directly attack renal cells. Splenic effector T cells from either syn BALB/c or allo B6 mice were activated by coculturing with irradiated whole splenocytes from BALB/c mice for 6 days. Target BALB/c-derived renal endothelial cells (end) or proximal tubular epithelial cells (epi) were cocultured with these activated effector T cells for 4 hours. Target cell apoptosis was detected by TUNEL assay. (A) Representative TUNEL-stained images of renal endothelial cells (top) and proximal tubular epithelial cells (bottom) are shown. Arrows highlight TUNEL-positive cells. TUNEL, red; DAPI, blue; wheat germ agglutinin (WGA), green. (B-C) The proportion of TUNEL-positive cells among renal endothelial cells (B) and proximal tubular epithelial cells (C) is shown; n = 3 to 4 mice per group. The bars show the mean ± SEM. Student t test was used for statistical analysis in panels B-C.