An investigation of the antigenic structure of Toxoplasma gondii.

Mechanical fragmentation has been the prime method for preparing soluble Toxoplasma gondii antigens for use in serodiagnosis. The three methods most commonly used (lysis-in-water, sonication and freeze-thawing) all yielded three antigenic peaks (4, 5 and 6) on crossed immunoelectrophoresis. Antigen 6 has been shown to be heat stable (56 degrees C/1 h) and appears to be a major antigen in the indirect haemagglutination test (IHAT). Saponin and octyl glucoside were found to be the most effective detergents for solubilization when used in combination, yielding between 7 and 11 antigens. Using a new triple-staining technique, antigen 3 has been characterized as a glycoprotein, antigen 7 as a lipopolysacchiaride and antigens 1, 2, 4, 5, 6 and 8 to 11 as proteins. Molecular weight determination by gel filtration has been carried out and the majority of the antigens have a mol. wt of 10(5) to 1.5 x 10(5) daltons. Crossed immunoelectrofocusing has shown that all the antigens are isoelectric at acidic pH. The findings of this preliminary investigation into the basic antigenic structure of T. gondii are discussed in relation to future work and the rational development of serodiagnostic tests.