Consistent with the phenotype observed in Ptpn2+/– SKG mice subjected to mannan-induced arthritis (44), numbers of Th17 (CD4+IL-17A+FoxP3–), total Tregs, and RORγt-expressing Tregs were increased in arthritic ankles and lymph nodes of mice with established (28 days) compared with early (10 days) arthritis. Here, CD4 is linked to arthritic joint disease.