Immune complexes in syphilis sera

Four hundred and forty-nine syphilis sera, positive in VDRL and FTA-ABS tests, were studied for the presence of circulating immune complexes (CIC) by means of anti-antibody (AA) neutralization test. Ninety-three (20.7%) sera had demonstrable CIC. Subsequently, dispersion of CIC by saline suspension of cardiolipin and by extract of rabbit testicular syphiloma was examined. Of 40 CIC-containing sera tested with cardiolipin, dispersion of CIC was noted in 16 instances; of 32 CIC-containing sera examined with syphiloma extract, dispersion was noted in 16 cases. Significantly, CIC that showed definite dispersion by cardiolipin were not dispersed by syphiloma extract and vice versa. Some studies were also performed on lepromatous leprosy and SLE. None of 27 cIC-containing lepromatous leprosy sera were affected by cardiolipin, but in 2 of 9 CIC-containing SLE sera, cardiolipin dispersed the complexes. Cardiolipin-anti-cardiolipin complexes that neutralized AA were frequently observed when cardiolipin was added to sera containing its corresponding antibodies but not CIC. Similar reactions were noted between the syphiloma extract and anti-treponemal antibodies.