CLDN1 and rheumatoid arthritis: Classifying RA patients according to inflammatory activity, defined by DAS28-ESR with cut-off point 3.2, claudin-1 levels showed no correlation with the abundance of any taxa in low-disease-activity patients, while in high-disease-activity patients, claudin-1 levels correlated with the abundance of an unknown genus of the family Lachnospiraceae (r = 0.615, p ≤ 0.01) and the genus Veillonella (r = 0.858, p ≤ 0.01) (Table S2).