WHY DO PATIENTS DEVELOP REACTIONS TO STREPTOKINASE

Minor reactions to streptokinase are not uncommon, although the etiolo gy is unknown. It is widely presumed, however, that these, like the mo re serious immune reactions, are antibody-mediated. We measured specif ic anti-streptokinase IgG, subclasses IgG1, IgG2, IgG3, IgG4 and IgE b y ELISAs, haemagglutination, indirect Coombs' test and immunoblotting in six patients who developed reactions to streptokinase. Evidence of complement activation by streptokinase was sought by a haemolytic comp lement assay and by measurement of C3, C4 and C3d. The patients who re acted to streptokinase presented with low titres of anti-streptokinase IgG (median = 5; range 0-32) and IgG1 (median=3; range 0-14). No evid ence of any other IgG subclass was found, nor of specific anti-strepto kinase IgE. Anti-streptokinase IgG1 was found to fix complement; patie nts who reacted to streptokinase were found to have low levels of tota l complement 1 year post reaction. Probable aggregates and fragments o f human albumin (added stabiliser) were found in the streptokinase pre paration and proved to be antigenic in some patients, but were not fou nd to be related to the development of reactions. The findings suggest that patients who develop reactions to streptokinase cannot be predic ted on the basis of antibody titres at presentation. Minor reactions t o streptokinase would not appear to be antibody-mediated, although com plement activation may be involved.