CD37 and rheumatoid arthritis: The treatment of both OA and RA cells with the CD37-blocker AMPCP resulted in significantly increased IL-6 concentrations compared to untreated control cells (OA: 10−6 M p = 0.036, 10−5 M p = 0.013, 10−4 M p < 0.001; RA: 10−6 M p < 0.001, 10−5 M p < 0.001, 10−4 M p < 0.001) (Figure 4A).