STAT3 and rheumatoid arthritis: We observed a weak, but significant positive correlation between STAT3 expression and serum IL-6 levels in RA patients (r = 0.4, p = 0.05, Figure 9S in Supplementary Files), and between SMAD2 expression and serum IL-35 levels in OA patients (r = 0.47, p = 0.05, Figure 9S in Supplementary Files).