Fig. 4: Immunocompetence and self-tolerance in FlipFlop mice.

a, Intracellular staining for Foxp3 in TCRβ⁺ LN T cells from B6 and FlipFlop mice (left). Numbers in histograms indicate frequency of cells in that box. Numbers (mean ± s.e.m.) of Foxp3⁺ cells among CD4 and CD8 LN T cells in B6 (gray bar) and FlipFlop (black bar) mice are shown in bar graphs (right). (n = 5 per strain, representative of 5 independent experiments). b, Expression of T_reg proteins on T_reg cells (Foxp3⁺) and non-T_reg cells (Foxp3^–) among B6 CD4 or FlipFlop CD8 TCRβ⁺ LN T cells (n = 5 per strain, representative of 5 independent experiments); mean ± s.e.m. c, LNs (top) and H&E stain of tissue sections (bottom) from FlipFlop and FlipFlop^sfy male mice (4 weeks old). Arrows indicate regions of lymphocytic cell infiltration (n = 4 per strain, representative of 4 independent experiments). d, In vitro T_reg suppression assay. Purified naive CD4 TCRβ⁺ LN T cells from B6 mice were stimulated in vitro for 3 days with immobilized anti-CD3ε monoclonal antibodies and titrated doses of either B6 CD4 T_reg (CD4⁺Foxp3-GFP⁺) or FlipFlop CD8 T_reg (CD8⁺Foxp3-GFP⁺) cells sorted from LNs. After 3 days, cultures were assessed for [H³]thymidine incorporation (mean ± s.e.m.). Data are representative of three independent experiments. **P < 0.01, ***P < 0.001 (two-tailed unpaired t-test); mean + s.e.m. e, Skin allograft rejection. Tail skins from BALB/c mice were grafted onto the flanks of indicated host mice. Graph indicates graft survival over time on B6 (blue line, n = 8), FlipFlop (red line, n = 9), and CB6 (black line, n = 4) host mice (log-rank (Mantel–Cox) test, P = 0.15 between B6 and FlipFlop host mice, 3 independent experiments). Median survival times (MSTs) on B6 and FlipFlop mice were 14 and 17 days, respectively. n.s., not significant.