To test this, we differentiated monocytes from mononuclear cells of buffy coats in blood from HD, and peripheral blood and synovial fluid from patients with RA with CSF-1 (CSF-1 Mφ), IL-34 (IL-34 Mφ) or GM-CSF (GM-CSF Mφ). Here, CSF1 is linked to rheumatoid arthritis.