THE SIGNIFICANCE OF ANTISTREPTOKINASE ANTIBODIES

Antibodies to streptokinase (SK) are widespread in the population, but reports of their effect on the action of SK are conflicting. Specific anti-SK IgG was purified from the sera of 10 patients, five with low titres of anti-SK IgG and five with high titres. The effect of increas ing specific anti-SK IgG antibodies on the action of SK was evaluated in vitro using a fluorimetric assay for plasmin and by a fibrin plate lysis assay. The inhibition of SK by whole plasma from a further group of patients was also assessed by the fibrin plate assay. There was a positive correlation between the serum antibody concentration and the quantity of specific anti-SK eluted (r = 0.797; P < 0.005). The additi on of specific anti-SK IgG caused a dose-related decrease in SK activi ty (fluorimetric assay r = -0.93; P = 0.02; fibrin plate assay r = -0. 98; P < 0.001). The addition of patient plasma to the fibrin plate ass ay also resulted in decreased lysis, which was dependent upon antibody titre (r = -0.95; P < 0.0001). Significant in vitro reduction of the activity of SK by specific antibody was demonstrated, and this was sim ilar with plasma containing comparable amounts of antibody. The findin gs suggest that treatment with SK would be unlikely to induce an effec tive thrombolytic state when antibody titres are high (such as those s een within 2 years of an initial dose of SK).