Investigation of the immunogenicity of, and characterisation of the immune response to streptokinase

Streptokinase (SK) is a naturally occurring bacterial protein. It is used to lyse blood clots and restore blood flow to the heart during acute myocardial infarction (AMI) by initiating the conversion of plasminogen to plasmin.;SK is substantially cheaper than most alternative thrombolytic drugs but is immunogenic in humans. Natural antibodies specific for SK are present at low levels in most people due to streptococcal infections. Following SK treatment, anti-SK antibody levels increase in a manner consistent with a secondary immune response. These anti-SK antibodies may neutralise a subsequent dose of SK before activation of plasmin can occur (SK resistance). Individuals who have received SK treatment are treated for a second infarct with a more expensive, and possibly less safe thrombolytic drug.;In this thesis, in vitro responsiveness to SK of lymphocytes isolated from SK-treated AMI patients before and for several years after treatment was determined. Secondly, a system for the production of recombinant SK fragments, the detection of their fibrinolytic activity and evaluation of their immunogenicity was optimised.;A fibrinolytically active recombinant SK fusion protein and nine non-overlapping recombinant peptide fragments of SK were produced. Two peptides were preferentially recognised in vitro by lymphocytes isolated from 5 out of 7 volunteers tested.;The in vitro peripheral T cell response to SK was shown to increase significantly in the first week after SK treatment, but return to control levels within 12 months. Significantly elevated total anti-SK IgG levels were detected in the serum of SK-treated AMI patients for up to 93 months after SK treatment.;These data provide support for the possibility of effective T cell epitope modification to produce an immunologically silent form of SK. In addition, they suggest that the acquired immune response to SK may persist for up to 93 months after SK treatment for AMI.