CD4 and Arthritis: We isolated GPR15+ and GPR15– Tregs from either WT or Ptpn2-haploinsufficient CD45.2 FoxP3EGFP SKG mice and cotransferred these with CD4+ effector T cells isolated from CD45.1 WT SKG mice into Rag2-KO mice, then monitored development of arthritis after injection of mannan (Figure 5E).