CSF1R and rheumatoid arthritis: In addition, the anti-CSF-1R mAb had an antagonistic effect on IL-6 production when FLS were preincubated with anti-CSF-1R mAb (25 ng/ml) in the presence of IL-34 (50 ng/ml) for 0, 12, 24, 48, and 72 h (Figure 2(c)), which suggests that the interaction of IL-34 with CSF-1R promoted IL-6 production by RA FLS.