Detection of toxoplasma IgM antibody by passive latex agglutination reaction

Three major components (designated Sp-1, -2 and -3) of the microsomal pellet of Toxoplasma gondii (Tp) were isolated by Ultragel AcA 44 gel filtration chromatography from the microsomal pellet solubilized with detergents. Of these, Sp-2 proved to be most reactive with anti-Tp antibodies and its reactivity with IgM and IgG antibodies varied with the concentration at which it was used for sensitizing latex particles. Sp-2 antigen reacted with IgM antibody alone when latex particles were sensitized with less than or equal to 100 micrograms of this antigen/mg of particles, and its reactivity with IgG antibody appeared and increased progressively with increasing sensitizing concentrations of this antigen. Based on this finding, a method of direct measurement of anti-Tp IgM antibody in serum by passive latex agglutination has been developed. Polyacrylamide disc gel electrophoretic analysis of Sp-2 antigen in the presence of SDS revealed four constituents of 43, 35, 28 and 14 kDa. All these components reached with both IgM and IgG when tested by immunoblotting.