Immunological responses in late syphilis.

Thirty-one serum samples from 18 patients with clinically established late syphilis and 1319 from patients at other stages of the disease were fractionated by density gradient ultracentrifugation and examined for antilipoidal and antitreponemal antibodies of the IgM and IgG classes. Sera from the patients with late syphilis always showed persistent concentrations of antilipoidal IgM and IgG and of antitreponemal IgG but never yielded detectable concentrations of antitreponemal IgM. When treated, these patients' antibody titres did not decline. Patients with secondary or latent syphilis also showed this serological picture after treatment but only transiently; their antibody titres continued to decline in a way which clearly distinguished them from the cases of late syphilis. It is suggested that patients whose sera persist in showing the stable pattern described may develop late symptomatic syphilis.