Plasminogen inhibits complement-mediated hemolysis only when artificially activated and present at disproportionately high concentration.

A: Inhibition of erythrocyte lysis in highly diluted (1.5%) serum with increasing concentrations of added plasmin. Data for plasminogen, urokinase (used in preparation of plasmin), and the negative control BSA are also shown. The assay was done six times. B: Loss of plasmin-mediated inhibition of sheep erythrocytes (Es) with increasing concentration of serum. The concentration of plasmin was kept at 20% of the physiological plasma level. The assay was done six times. C: In addition to plasmin, hemolysis was inhibited with the proteases α-chymotrypsin and trypsin. The assay was done three times in triplicate. (Data shown are mean values ± SD. *, P < 0.05; **, P < 0.01; ***, P < 0.001; ns, not significant).