PTPN2 and arthritic joint disease: Consistent with the abovementioned in vitro data, only mice receiving Ptpn2-haploinsufficient GPR15+ Tregs developed significantly more severe arthritis compared with the other groups (Figure 5F), whereas arthritis development in mice receiving Ptpn2-haploinsufficient GPR15– Tregs was comparable to mice receiving either WT GPR15+ or GPR15– Tregs (Figure 5F).