All complement activation pathways are involved in serum-mediated MSC cytotoxicity. MSCs (5 × 10⁵) were subjected to the same BCECF leakage-based cytotoxicity assays with 10, 20, and 30 μL of NHS, C1q-depleted sera (classic pathway-deficient), fB-depleted sera (alternative pathway-deficient), MBL-depleted (lectin pathway-deficient) or C4-depleted sera (both classic and lectin pathways deficient) in 100 μL of GVB⁺⁺ buffer. After incubation at 37°C for 30 minutes, MSCs cytotoxicity was assessed by measuring BCECF leaked into the supernatants. Representative results of 3 individual experiments. Data are mean ± SD, *P < .05;