Increased levels of IL-34 have been reported in serum and synovial fluid of RA patients, and the levels of IL-34 correlate well with that of IL-6, receptor activator of nuclear factor kappa-B ligand (RANKL), rheumatoid factor (RF) and anti-cyclic citrullinated peptide antibody (ACPA) [117]. This evidence concerns the gene IL34 and rheumatoid arthritis.