Immune complexes in experimental syphilis: a methodologic evaluation.

Sustained antigenic stimulation following intravenous infection of rabbits with Treponema pallidum results in antibody responses and the formation of immune complexes. Complexes in greater than 300 sera from normal rabbits and from animals with experimental syphilis were measured by Raji cell and polyethylene glycol-complement consumption assays. Profound increases in both the incidence and levels of immune complexes were seen between the third and seventh weeks of infection. Single radial immunodiffusion studies revealed moderate increases in immunoglobulin levels and depression of C3 levels during the third and fourth weeks of infection. Penicillin treatment was followed by normalization of C3 levels and clearance of immune complexes. Lower levels of complexes in the sera of intradermally infected rabbits and the absence of immune complexes in intratesticularly infected animals suggest that immune complexes in the circulation may be related to the extent and severity of cutaneous involvement.