Syphilitic immunofluorescence in experimental relapsing fever.

Immunological cross-reactivity has been shown between related genera of the family Treponemataceae. Extracts of Borrelia cross-react with antibodies in syphilitic serum (Saurino and De Lamater, 1952) and produce positive skin tests in the later stages of syphilis (Ranque, Quilici, and Assadourian, 1967). The fluorescent treponemal antibody absorption test (FTA-ABS) is at present considered to be specific, as its name implies, for treponemal disease. However, we have found that Borrelia infection in mice also induces an antibody that reacts in the FTA-ABS test, which would suggest that Treponema and Borrelia share a common antigen.