Apoptotic cells reduce T-cell proliferation in vitro and in vivo. (A) In vitro, T-cell proliferation is significantly reduced in MLR cultures of whole splenocytes, cultured with or without apoptotic cells for 48 hours, irradiated with 30 cGy and followed by coculture with CFSE-labeled allogeneic T cells for 96 hours at a ratio 2:1. FACS histogram of CFSE dilution profile (left) and bar graphs displaying the proportions of unproliferated T cells (right) are shown. (B) In vivo, Quantification of T-cell proliferation shows significant reduction in ECP-treated mice. BLI on day +4 (left, upper panel) shows a significant reduction in T-cell proliferation among ECP-treated mice, no difference in BLI signal is observed at day +7 between both groups (left, lower panel). Quantification of photons per second per mouse (middle; P = .001) and relative weight loss (right; P = .0003) of transplanted mice at day +4 is shown. (C) Ex vivo, Proportion of T-cell proliferation in reisolated CFSE-labeled Tcon at day +4 is shown. CD4⁺ and CD8⁺ T cells show lower proliferation index in ECP-treated mice. Results were done in triplicates (A) and represent 3 independent experiments or (B) are a composite of 2 independent experiments or (C) are representative for 2 individual experiments with a total of 8 to 11 mice per group. Error bars indicate mean ± SEM and significance was assessed by 2-tailed Student t test.