Isolation of a heat-stable antigen from Treponema Reiter, using an immunoadsorbent with antibodies from syphilitic patients.

It was attempted to isolate antigens from Treponema Reiter, relevant to syphilis serology, by immunoadsorption with patients' antibodies coupled to CNBr--Sepharose 4B. One antigen was desorbed by 2 M KSCN in 0.05 M Tris--barbital buffer, pH 8.6. The recovery was 3% and 7% in two experiments. A small amount of human antibodies in the isolate was removed on an immunoadsorbent column with insolubilized rabbit antibodies against normal human serum proteins. The antigen thus obtained was immunologically pure when analysed by crossed immunoelectrophoresis. By electron microscopy of immunoprecipitates and by tandem crossed immunoelectrophoresis it was shown that the antigen differed from the flagellar antigen of T. Reiter, but was identical to antigen d previously described in T. Reiter. Antigen d could also be isolated from supernatants of T. Reiter cultures. The d antigen was not denatured at pH 2.8, by 8 M urea or by 3 M KSCN, and it resisted heating to 100 degrees C for 30 min. No protein could be detected in a concentrated preparation, and the antigen might be a polysaccharide. Antigen d is probably present in the sorbent used in the fluorescence treponemal antibody absorption (FTA-ABS) test and may constitute the active substance of this reagent.