Circulating immune complexes in experimental syphilis: identification of treponemal antigens and specific antibodies to treponemal antigens in isolated complexes.

As a prelude to characterization of the host and treponemal antigens present in purified immune complexes from the sera of rabbits with disseminated syphilis, autoradiographic and immunoenzymatic analyses of solubilized extracts of Treponema pallidum, Treponema phagedenis biotype Reiter, and Treponema refringens were performed on electroblots of polypeptides first separated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Electroblots of purified immune complexes were developed with the same panel of antisera so that protein profiles could be compared. Eight treponemal antigens were consistently present in isolated complexes; four of these cross-reacted with antisera prepared against avirulent treponemes. The average molecular weights of these antigens were 87,000, 76,000, 66,000, and 45,000. Antibodies dissociated from isolated immune complexes, when used for the development of T. pallidum electroblots, reacted with four antigens of comparable molecular weight. Antibodies to those polypeptides were also present in the sera of animals immunized with immune complexes. The demonstration of treponemal antigens in purified immune complexes convincingly argues that their occurrence in experimental syphilis is not merely due to tissue destruction and responses to endogenous host antigens.