HO-1 protects ECs against complement-mediated injury. HUVECs were infected with Adv-HO-1 () or Ad0 (■) (MOI 200); and 24 hours after infection, ECs were harvested and (A) opsonized with mAb RMAC8 before exposure to NHS or heat-inactivated NHS (HIHS) for up to 3 hours. To inhibit DAF, mAb 1H4 was added to the assay with RMAC8. C3 deposition was analyzed by flow cytometry using FITC-conjugated anti–human C3, and results are RFI (mean ± SEM; n = 4 experiments). *P < .05. (B) To measure complement-mediated lysis, ECs were opsonized and exposed to NHS or HIHS. Propidium iodide (PI; 50 μg/mL) was added to the cell suspension, and analysis was by flow cytometry. Percentage EC lysis was calculated as the number of PI-positive cells expressed as a percentage of the total number of cells (mean ± SEM, n = 4 experiments). *P < .05.