Role of circulating immune complexes in human secondary syphilis

Studies in animal models and in the glomerulonephritis of human secondary syphilis and results from in vitro assays have suggested a role for circulating immune complexes (CICs) in human secondary syphilis. Nine adult subjects with early secondary syphilis were studied. All patients tested had CICs on C1q-binding or Raji cell assays. Proteins previously described as Treponema pallidum-specific antigens were detected by radioimmunoblot techniques in CICs from all five subjects tested. Biopsy of early cutaneous lesions revealed immunoreactants (IgG, C3, and/or C1q) in three of nine subjects and treponemal antigen in six of eight subjects tested. Histamine was injected intradermally as a trap for CICs, and biopsy of these injection sites revealed immunoreactants in four of nine subjects and treponemal antigen in five of eight subjects tested. A neutrophilic vascular reaction consistent with CIC-mediated vessel damage was seen in three of nine lesions and six of nine histamine injection sites. Normal controls did not show these changes.