Although the enhanced IL-6 level in synovial fluids has been suggested and IL-6 is considered to be an important biomarker in RA (Kokebie et al., 2011), the pathogenesis of RA with a focus on cytotoxic edema remains unclear, and the role of NKCC1 and volume homeostasis in FLS remains to be defined. This evidence concerns the gene SLC12A2 and rheumatoid arthritis.