TJP1 and rheumatoid arthritis: Several studies report possible increased intestinal permeability in at-risk and established RA individuals through use of indirect measures, including increased circulation of the tight junction stabilizing protein zonulin, LPS, lipopolysaccharide-binding protein (LBP), and soluble CD14 (sCD14), alongside decreased colonic expression of the tight junction protein ZO-1 (82, 92–94).