FLG and rheumatoid arthritis: Rheumatoid arthritis (RA) is an autoimmune disease, and serum from RA patients contains a spectrum of autoantibodies including rheumatoid factor, anti-filaggrin autoantibody, anti-keratin antibody (AKA), anti-perinuclear factor, anti-vimentin and anti-cyclic citrullinated peptide antibody (anti-CCP) [1]–[5].