Protection of thymocytes from apoptosis by C5a blockade in CLP-induced sepsis. Twenty-four hours after surgery, thymocytes were harvested from control, sham, CLP-treated with preimmune IgG, and anti-C5α–treated CLP rats, and evaluated for DNA fragmentation and Ax/PI staining using the same protocols described for Figures 1 and 2. (a) Effect of C5a blockade on DNA fragmentation induced by CLP, representative of three separate experiments. (b) Quantitative analysis of the effect of C5a blockade on thymocyte apoptosis by flow cytometry. The percentages of early-stage apoptotic cells (c) and late apoptotic/early necrotic cells (d) are presented as means ± SEM (n = 4 animals).