During mannan-induced arthritis, there were increased numbers of both GPR15+ RORγt-expressing Tregs and RORγt+FoxP3–CD4+ T cells but not of total GPR15+ Tregs in both popliteal lymph nodes and ankles of Ptpn2-haploinsufficient SKG mice. The gene discussed is GPR15; the disease is arthritic joint disease.