Development and evaluation of a monoclonal antibody inhibition enzyme linked immunosorbent assay to diagnose syphilis

A highly specific inhibition enzyme linked immunosorbent assay (ELISA) using murine monoclonal antibodies to treponemes has been developed to diagnose syphilis. The monoclonal antibodies used in this study were reactive to antigens of both Treponema pallidum and Treponema pertenue and not to antigens of non-pathogenic treponemes. Inhibition of the binding of monoclonal antibody to the treponemal antigens was successful with serum antibodies of patients with syphilis in an inhibition ELISA using monoclonal antibodies raised against T pallidum antigens with molecular weights of 42 and 47 kilodaltons. In contrast, the binding of monoclonal antibodies obtained by immunising mice with treponemal membrane protein TmpB, derived from recombinant DNA was not inhibited by serum antibodies from patients with syphilis. The sensitivity of the inhibition ELISA using monoclonal antibody against the 47 kilodalton T pallidum antigen was 93% in 58 serum samples from patients with untreated syphilis. The sensitivity was 79% if the monoclonal antibody against the 42 kilodalton T pallidum antigen was used. By a combination of the test results obtained in these two inhibition assays a sensitivity of 97% in the 58 serum samples from untreated patients and 64% in 64 from treated patients was obtained. The specificity of the inhibition ELISA performed with either monoclonal antibody was 100% in 500 serum samples from non-infected people. The specificity in 432 non-infected patients attending a sexually transmitted disease clinic was 98.8% for the monoclonal antibody against the 42 kilodalton antigen, 99.5% for the monoclonal antibody against the 47 kilodalton antigen, and 98.4% for the combined antibodies. The sensitivity and specificity of the inhibition ELISA using the combination of test results obtained by the application of the monoclonal antibodies against the 42 kilodalton treponemal membrane protein, TmpA, and against the 47 kilodalton T pallidum antigen were comparable with those of the Treponema pallidum haemagglutination assay (TPHA) and the fluorescent treponemal antibody absorption (FTA-ABS) test for diagnosing early untreated disease. The inhibition ELISA offers the potential for additional confirmation of early untreated syphilis. Its use for confirming late untreated syphilis is still under investigation. The test is highly specific for pathogenic treponemes and does not need sorbens.