STAT1 and rheumatoid arthritis: Upregulated expression of STAT1 protein and its phosphorylated form has been studied in RA synoviocytes [52], and its activation in the cell, primarily stimulated by different pro-inflammatory cytokines (IFNγ, IL-2, IL-6, IL-7, and IL-21), has been reported to promote cartilage degradation [53].