Importance of membrane-bound antigens of Toxoplasma gondii and their fixation for serodiagnosis of toxoplasmic encephalitis in patients with acquired immunodeficiency syndrome.

Titers in a direct agglutination test using Formalin-fixed toxoplasma tachyzoites were significantly higher in patients with acquired immunodeficiency syndrome with toxoplasmic encephalitis (TE) than in those without TE. In contrast, when fresh (not fixed) tachyzoites were used, the titers did not differ from those in patients without TE. The direct agglutination test using Formalin-fixed tachyzoites better distinguished between patients with TE and those without TE than an agglutination test using latex particles coated with Formalin-fixed sonicated-tachyzoite antigens. Thus, both selective use of membrane-bound antigens and their fixation are important for serodiagnosis of TE in patients with acquired immunodeficiency syndrome.