The determination of TGF-β1 revealed similar differences as those observed for IL-17 as higher percentage of RA or SpA patients had detectable levels of TGF-β1 in their SF (P < 0.0001 compared with OA for both comparisons) and the median values of this cytokine were higher in SF from both RA and SpA patients (P < 0.0001 RA vs OA, and P < 0.01 SpA vs OA) (Fig. 1c). Here, TGFB1 is linked to rheumatoid arthritis.