The assay showed significantly elevated IL-6 levels in the culture medium of RA synovial fibroblast cells in the presence of 100 μM UDP, but the concentrations of IL-2, IL-4, IL-10, TNF-α and IFN-γ were not significantly changed compared with those in the PBS-treated controls (Figure 4A). Here, IL4 is linked to rheumatoid arthritis.