Antigenic evidence for host origin of exudative fluids in lesions of Treponema pallidum-infected rabbits.

Mucoid fluid accumulating within syphilitic lesions has been considered to be of Treponema pallidum origin. To test this assumption, we examined testicular exudative fluids from T. pallidum-infected rabbits for the presence of T. pallidum antigens by various sensitive immunochemical methods, including Western blot analysis. Antigenic analysis of these fluids revealed host components but not treponemal antigens. Prolonged immunization of rabbits, guinea pigs, and a goat with this material in complete Freund adjuvant elicited low titers (fluorescent-treponemal-antibody test titer, less than or equal to 10) of antitreponemal antibodies in the rabbits and guinea pigs but not in the goat. The data suggest that these mucoid fluids are of host origin. The presence of mucopolysaccharides in these fluids may be related to the infective process. The possible mechanism by which mucopolysaccharides protect T. pallidum from immune mechanisms and its potential relationship to the pathogenesis of the disease are discussed.