In DBA/1J Ffa4 gene KO mice, the arthritis score increased significantly and showed similar patterns to the increase in WT mice (Figure 1D); however, CpdA treatment could not suppress the increase in the arthritis score and foot thickness (Figure 1D–F), implying that CpdA suppressed the CIA-induced increase in the arthritis score and foot thickening via FFA4 activation. Here, RPS19 is linked to arthritic joint disease.