Splenic CD8 T cells derived from day 5 LCMV-infected mice continue to expand ex vivo. Total splenic leukocytes were prepared, CFSE-labeled, and cultured for 1 to 5 days. Histograms of CFSE dilution within electronically gated CD8 and CD4 populations are shown. The marker in the histogram shows percentage of proliferating cells based on CFSE dilution. The averages of different samples had SD between 0% and 2% for the splenic leukocytes, 0% and 5% for the CD4 T cells, and 0% and 4% for the CD8 T cells. Expressed on the graphs are percentages, as well as number of total and proliferating CD4 (○) and CD8 (•) T cells. The bars denote deviations of the means. The experiment has been repeated more than 2 times, obtaining similar results.