T cell receptor specificities of Toxoplasma gondii-reactive mouse CD4+ T lymphocytes and Th1 clones.

The Toxoplasma gondii-directed CD4+ T cell response in chronically infected mice was studied with respect to both T cell receptor diversity and antigen specificities. T cell receptor chains V beta 4, 6, 8, 10, and 14 were predominantly found on toxoplasma-reactive CD4+ splenocytes. This repertoire was also detected among T. gondii-specific CD4+ T cell clones. Analysis of clonotypic cytokine profiles revealed typical Th1 clones secreting interleukin-2, interferon-gamma and tumour necrosis factor activity and Th2 clones producing interleukin-4 and interleukin-10. Five distinct toxoplasma antigens (p26, p40, p55, p58 and p60) were detected in electrophoretically separated toxoplasma lysate by five individual Th1 clones. Parallel testing of CD4+ T lymphocytes from infected mice confirmed that these specificities constitute the peak immunogenic fractions of toxoplasma lysate. The expression patterns of two clonotypic, T cell-stimulatory parasite antigens were studied in detail. While p55 was expressed by mouse-virulent and avirulent T. gondii isolates and in both the tachyzoite and bradyzoite stages, p58 was detected only in virulent strains from intraspecies subgroup I. Thus, we describe the heterogeneity of toxoplasmic immunodominant T cell antigens including a 58-kDa group I-restricted molecule which may provide a marker for virulent isolates.