Early Syphilis: Immunoglobulins Reactive in Immunofluorescence and other Serologic Tests

Abstract

Sera and serum fractions from 41 patients with darkfield-positive untreated primary and secondary syphilis were studied to reveal the immunoglobulins that are reactive in immunogluorescence and other serologic tests for syphilis. A monospecific indirect fluorescent antibody (IFA) assay revealed that IgG is the major immunoglobulin class reactive with Treponema pallidum, and that smaller amounts of IgM and IgA antibodies may also react. IgG is the principal immunoglobulin operative in the fluorescent treponemal antibody-absorption (FTA-ABS) test, and in its predecessor tests, the fluorescent treponemal antibody 1:5 (FTA-1:5), and the fluorescent treponemal antibody-200 (FTA-200). “Sorbent,” or a sonicate of Reiter treponemes, which is used in the FTA-ABS test to distinguish syphilitic from nonsyphilitic sera, operationally acts mainly to prevent “natural” IgG antibodies in nonsyphilitic serum from reacting with T. pallidum. It does not prevent syphilitic IgG antibodies from reacting, and apparently it enhances their role relative to IgM and IgA antibodies. Reactivity in the Treponema pallidum immobilization (TPI) test and the Reiter protein complement-fixation (RPCF) test was found mainly in the 7 S fractions of sera as compared to the 19 S fractions. Absorbing a syphilitic serum with T. pallidum did not produce a measurable decrease in total levels of IgG, IgM, or IgA. Antilipoidal antibodies detectable in the VDRL slide test were found in both the 19 S and 7 S fractions of sera; the antibodies associated with primary syphilis were not confined to the IgM class. In the course of these studies, 19 S and 3.5 S IgG-related substances were noted to possess anti-T. pallidum reactivity, and IgA in the 7 S fraction of serum was observed to be functionally silent in contrast to IgA of higher weight.