Given that correlation analysis showed that claudin-1 stool levels inversely correlate with both IL-6 and C-reactive protein (CRP) serum levels, our data are consistent with this statement since IL-6 is a marker of systemic inflammation, while CRP, stimulated by IL-6 [50], is a routine inflammation marker in RA [51,52]. Here, CLDN1 is linked to rheumatoid arthritis.