Given the extraordinary number of neutrophils and PMN-MDSCs in the SF of RA patients (87, 88) and the destructive ability of neutrophils in joints (89), it is important to consider whether PMN-MDSCs consistently remain in a steady immunosuppressive state or grow and mature under the presence of factors, such as G-CSF, within inflamed joints to transform into neutrophils and promote arthritis development. Here, CSF3 is linked to rheumatoid arthritis.