Unlike Drd2−/− CIA mice, Drd1-null CIA mice did not manifest either more severe inflammation of limbs as determined by clinical arthritis score, ankle joint width, and hind paw thickness or higher serum anti-CII IgG level, in comparison with wild-type CIA mice (Figures 3(d) and 3(e)). Here, DRD1 is linked to arthritic joint disease.