Preparation of a Toxoplasma gondii agar gel immunodiffusion test antigen from ovine fetal kidney cell cultures.

A toxoplasma gondii antigen prepared from the cell-free supernatant of ovine fetal kidney (OFK) cell cultures produced a sharp precipitation line against anti-Toxoplasma serum in an agar-gel immunodiffusion (AGID) test. Results obtained from the AGID and indirect hemagglutination (IHA) tests on 46 human and nine rabbit sera were compared. Thirty-three percent of the serum samples, which were negative for the Toxoplasma IHA test, were positive when assayed by the AGID method. The AGID test appears to be superior to the IHA test for detecting low titers of antibodies against T. gondii. After 70 generations of serial passages through the OFK cell cultures, T. gondii still produced the AGID test antigen.