Expansion of Treg after infection with F-MuLV. C57BL/6 mice were infected with F-MuLV and sacrificed 8 or 10 days after infection. Then, suspensions of spleen cells were prepared. Flow cytometry was used to quantify the numbers of CD8+ T cells specific for the H-2Db-restricted F-MuLV glycosylated gag epitope (MHC I Tetramer+), and CD4+ T cells specific for the Ab-restricted FV-H19-Env epitope (MHC II Tetramer+) in the spleen. A. Numbers of CD8+ MHC I Tetramer+ T cells per one million spleen cells. B. Numbers of CD4+ MHC II Tetramer+ T cells per one million spleen cells. C. Numbers of CD4+ Foxp3+ T cells per one million spleen cells. D. Numbers of CD4+Foxp3+ T cells expressing Ki-67 per one million spleen cells. E. A representative dot plot shows the gating-strategy to identify CD4+ Foxp3+ that were Npn-1+ or Npn-1-. Upper graph, numbers of CD4+Foxp3+Npn-1+ cells per one million nucleated cells. Lower panel, numbers of CD4+Foxp3+Npn-1-cells per one million nucleated cells. F. A representative dot plot shows the expression of Helios and Ki67 on gated CD4+Foxp3+Npn-1+ nTregs (upper panel) and on gated CD4+Foxp3+Npn-1-iTregs (lower panel). The numbers in the upper quadrants represent the percentages of Helios+ cells. Data was pooled from three independent experiments with similar results. Differences between naïve mice and mice infected for 10 days with F-MuLV were analyzed by an unpaired t-test. Statistically significant differences between the groups are indicated in the figure.