Complement system does not activate on fibrin surfaces.

A: Formation of C3a in 2.5% serum incubated in wells coated with fibrin, the known complement activators heat aggregated immunoglobulin (HAIgG) and mannan, and the negative control BSA. The assay was done three times with triplicate measurements. B: Conversion of plasminogen to plasmin by tissue-type plasminogen activator (tPA) on fibrin beads. Formation of plasmin was followed by measuring appearance of a fluorescent cleavage product. Preformed plasmin was used as a positive and human erythrocyte ghosts as a negative control. The assay was done four times with single samples. C: Formation of C3a in normal and partially plasminogen-depleted serum incubated in the presence of fibrin beads. Buffer added or not with Zymosan beads served as controls. Three independent assays were analyzed in duplicate. D: Residual hemolytic activity of normal and partially plasminogen-depleted serum incubated in the presence of fibrin beads. Buffer added or not with Zymosan beads served as controls. Three independent assays were analyzed in triplicate. (Data shown are mean values ± SD. **, P