Interferon-γ induces Fas-dependent apoptosis of Peyer's patch T cells following peroral infection of mice with Toxoplasma gondii

Our recent observation of a remarkable decrease in the numbers of T cells in the Peyer's patches of the small intestines of genetically susceptible C57BL/6 but not of genetically resistant BALB/c mice following peroral infection with Toxoplasma gondii, led us to examine the mechanism(s) whereby this decrease occurs. We found that apoptotic cell death of CD4+ and CD8+ αβ T cells occurred in Peyer's patches of C57BL/6 but not BALB/c mice following infection. Upregulation of Fas expression was observed in the T cells of infected C57BL/6 but not of infected BALB/c mice. C57BL/6-background mutant mice which lack functional Fas antigen did not develop apoptosis in their Peyer's patches following infection. Treatment of infected C57BL/6 mice with anti-IFN-γmAb prevented upregulation of Fas on their Peyer's patch T cells and inhibited occurrence of apoptosis of these T cells. These results indicate that IFN-γ induces Fas-dependent apoptosis in CD4⁺ and CD8⁺ αβ T cells in Peyer's patches following peroral infection with T. gondii and that these events correlate with susceptibility to the infection.