Characterization of the serum protein inhibitor of the V.D.R.L. test

The V.D.R.L. test for syphilis was used to evaluate the ability of various serum protein fractions to inhibit cardiolipin flocculation tests for syphilis. Serum protein fractions obtained by modifications of the method of Ecker et al. (1) were chromatographed by DEAE or gel filtration and characterized by immunodiffusion and electrophoresis. These experiments indicated that the V.D.R.L. inhibitor substance was in the IgM fraction of serum, although it has not yet been determined whether the inhibitor is an IgM antibody or another component which cofractionates with IgM.