TNFRSF11B and rheumatoid arthritis: We stimulated TNFα-pretreated OA- and RA-SF with 10–11 to 10–14 M PK2 and measured the cell culture medium concentration of the arthritis-aggravating factors IL-6 and MMP-3 and arthritis-inhibiting factors TIMP-1 and OPG (Fig. 6).