Taken together, this mechanism of action study indicates that blocking of the p40 subunit shared by IL-12 and IL-23 by ustekinumab suppresses synovial inflammation in PsA through modulation of MAPK-ERK, Wnt and potentially also PI3K-Akt-mTOR signaling pathways rather than by directly impacting the IL-17 pathway. This evidence concerns the gene MAPK1 and inflammation.