CD8+ cells protect mice against reinfection with the intestinal parasite Eimeria falciformis.

We investigated cellular immune responses of mice infected with the apicomplexan parasite Eimeria falciformis in order to characterise protective immune mechanisms and effector functions. Adoptive transfer experiments with mesenterial lymph node cells (MLNC) from immune donor mice were performed, and the oocyst output monitored after challenge infection. Phenotypical analysis by fluorescence cytometry and T cell proliferation assay showed that already from day four post infection E. falciformis-specific lymphocytes were present in the MLN. The frequency of parasite-specific, IFN-gamma producing CD4+ and CD8+ cells increased in this period by 9.8% and 16.4%, respectively. Infection experiments with IFN-gamma deficient mice revealed that IFN-gamma is involved in resistance to primary and secondary infection. Transfer of total MLNC from immune donors reduced the oocyst output by 65-74%, as compared to the oocyst output of animals transferred with cells from naïve donors. Transfer of CD8+ cells inhibited parasite development resulting in a reduction of oocyst numbers by 42-64%, whereas CD4+ cells showed no influence on resistance to reinfection.