Differential expansion and time course of STAT1 expression on CD4 and CD8 T cells during the course of infection. For these experiments, populations were prepared from uninfected or day 5, 6, 7, and 8 LCMV-infected mice. Splenic leukocytes were counted using a hemocytometer. Percentages of CD4 and CD8 T cells were obtained by FACS analysis. The intracellular staining for expression of STAT1 protein was analyzed by FACS, electronically gating on total splenic leukocytes, CD8 or CD4 T cells. The numbers in the histograms represent percentages of STAT1-positive cells, compared with the isotype controls.