Rabbit model of disseminated syphilis: immunoblot and immunohistologic evidence for a role of specific immune complexes in lesion pathogenesis.

Circulating immune complexes (CIC) containing Treponema pallidum proteins have been preliminarily implicated as inducers of a neutrophilic vascular reaction in early human cutaneous lesions of secondary syphilis. To clarify the role of specific CIC in producing cutaneous and renal lesions, 12 rabbits were studied at the following intervals after induction of disseminated syphilis: 20 days (4 rabbits: biopsies of normal and lesional skin for direct immunofluorescence (IMF) for (IgG, IgM, IgA, Clq, C3, C4), fibrin, and T. pallidum proteins; routine histology; and immunoblots of serum for CIC containing T. pallidum proteins); 21 days (4 rabbits: as at 20 days without IMF for T. pallidum protein); 23 days (4 rabbits: as at 20 days without IMF); 30 days (same 12 rabbits restudied with routine histology of normal and lesional skin; kidneys from 4 rabbits removed for routine, IMF, and electron microscopy (EM). Treponemal polypeptide antigen (MW-87 kd) was demonstrated in CIC from rabbits. Routine cutaneous histology showed evolution of lesions from an early neutrophilic vascular reaction to the typical lymphoplasmacytic reaction. IMF showed vessel-based immunoreactants in 3 of the 4 rabbits tested at 20 days and 1 of 4 at 21 days, and T. pallidum proteins in 3 of 4 rabbits at 20 days. Routine histology, IMF, and EM studies of glomeruli showed glomerular abnormalities, but no evidence of immune deposits containing specific T. pallidum protein. Skin and kidney studies of 4 controls were all negative. These data indicate a role for specific immune complexes in the pathogenesis of cutaneous lesions in this rabbit model.