D. Naïve murine CD4+ T cells were isolated by FACS from lymph node and spleen cell suspension of USP44fl/fl CD4Cre+ mice and that of their wild type littermates (USP44fl/fl CD4Cre- mice; n=2-3/group/experiment). iTreg cells were generated from these mice as described for Fig. 1 before incubation on a microscope slide pre-coated with poly-L lysine for 1h. Adhered cells were then fixed by PFA for 0.5 followed by blocking with 1% BSA for 1h, then incubation with the specified antibodies. Representative confocal microscopy images (40X) were visualized for endogenous USP44 (red) and FOXP3 Baxter et al(). DAPI was used to visualize cell nuclei (blue); scale bar 50μm. 