Toxoplasma gondii: kinetics of lymphocyte subsets in blood and spleen of perorally infected mice.

The blood and spleen lymphocyte subsets and parasite burdens in blood, lungs, and brain were determined serially in C57B1/6 mice infected with an avirulent strain of Toxoplasma gondii. Five mice were sacrificed at various time points after infection; Thy1-2+, Ly5+, CD4+, CD8+, and Ly6c+ lymphocyte subsets and macrophages were determined in blood and spleen by cytofluorometry and parasite burdens were quantified in blood, lungs, and brain by means of a tissue culture method. In infected mice, a large increase in the percentage of CD8+ lymphocytes in blood was observed from Day 14, peaking at Day 21; the percentage of CD4+ lymphocytes was not significantly modified compared with uninfected controls. Analysis of Ly6 antigen expression on T lymphocytes showed that CD8+Ly6c+ cells were largely predominant at the different stages of infection. Similar results were obtained for spleen cells. The marked increase in CD8+Ly6c+ cells in the early phase of infection was associated with the clearance of parasites from the lungs. Furthermore, the proportion of CD8+Ly-6c+ remained high until Day 162, when the infection was at the chronic stage. These results suggest that CD8+Ly6c+ lymphocytes may be involved in the control of toxoplasmosis in the acute phase and in the containment of the infection in the chronic stage.