TJP1 and rheumatoid arthritis: Tajik et al. [20] reported that the serum levels of proteins such as ZO-1, occludin-1, and claudin are elevated in the early stages of RA and established RA while the intestinal fatty-acid binding protein 2 (IFABP2) serum levels increased in RA patients without pharmacologic treatment and have been related to the clinical activity [18].