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Purification of Toxoplasma Antigen for Hemagglutination Tests
Toxoplasma hemagglutination (HA) antigen was fractionated and purified by means of differential centrifugation, Sephadex G-200 gel-filtration, ammonium sulfate precipitation, and sucrose density-gradient centrifugation (SDGC). The HA activity was found in the supernatant fluid from centrifugation at 100,000 × G, the initial peak of gelfiltration, precipitates from 60% saturation with ammonium sulfate, and in the 6.9S fraction obtained by SDGC. A low recovery of antigen activity was obtained by ammonium sulfate precipitation of the initial peak of gel-filtration. Thereafter gel-filtration was omitted from the preparation system. The active fraction obtained by SDGC showed 230 times greater specific activity than the starting material, which was the supernatant fluid obtained by centrifuging French press-disrupted Toxoplasma trophozoites at 13,000 × G. A good recovery of antigen activity was obtained by this procedure. The protein nature of the antigen was demonstrated by tryptic digestion.