Although there is experimental evidence that IL-34 expressed by T regulatory cells can induce a suppressive phenotype in leukocytes [69], the cytokine has also been implicated in pro-inflammatory processes associated with rheumatoid arthritis ([73]), where IL-34 expression has been recently shown to be inhibited by TGF-β1 [74], which induces an immunosuppressive effect within the synovium. The gene discussed is TGFB1; the disease is rheumatoid arthritis.