Anti-Streptokinase IgG Immunoassay
Background The BioResearch Ireland Assay
Intra thrombolytic therapy has now become the standard therapeutic approach for patients with acute myocardial infraction (AMI). The reduction in short and long term mortality caused by thrombolytic therapy has been demonstrated in several large clinical trials and the greatest therapeutic effect is seen when the patient is treated during the early phase of AMI, i.e. within the first 12 hours from the initial onset of symptoms.
Streptokinase (SK), a 47kD protein produced by Group C β hemolytic streptococci, is a widely used thrombolytic agent because of its ability to indirectly activate plasminogen. Anti-SK antibodies can arise as a result of therapeutic administration of SK and these have been shown to persist for up to 4 years after SK administration in some patients. There is great individual variation in the antibody response to SK treatment. However, since it is probable that AMI patients who were previously treated with SK have circulating anti-SK antibodies, it is current practise to avoid re-administration of SK in all cases. Anti-SK antibodies are also found in a significant proportion of the general population (up to 10 % in some studies), arising, most likely, following natural infection with streptococci.
BRI, in collaboration with the Royal College of Surgeons' Medical School, have developed a simple ELISA for the detection and/or quantification of anti-SK IgG in human serum. The assay has been thoroughly validated against a highly sensitive SK neutralisation assay, thus indicating that the assay is largely detecting neutralising activity. Anti-SK IgM antibodies which may be present in the early days after treatment with SK will not be detected.
SK coated plates capture anti-SK antibodies if present in a dilution of patient's serum and anti-human IgG horseradish peroxidase conjugate detects the captured antibodies.
Clinical application of the BioResearch Ireland
Where thrombolytic therapy is indicated, the BRI test will detect anti-stretokinase IgG within 2 hours if present in the patient's serum and thereby facilitate selection of an appropriate therapeutic regime.