These cytokines trigger the initiation of diverse mechanisms that play a part in the development of RA, including essential pathogenesis events such as the increase in the cell population of RA synovial fibroblasts (RASFs), the generation of enzymes that breakdown bone and cartilage, colony-forming factors including granulocyte macrophage colony-stimulating factor (GM-CSF), and production of cytokines such as IL-8 (Sweeney and Firestein 2004) (Fig. 1). Here, CSF2 is linked to rheumatoid arthritis.