The JAK/STAT signaling pathways mediate the effects of many cytokines/interferons and growth factors important in RA (e.g., IL-2, IL-6, IL-7, IL-10, IL-12, IL-15, IL-21, IL-23, interferons (IFNs), granulocyte macrophage colony-stimulating factor (GM-CSF)) and regulate the activity of hemopoietic and joint resident cells. The gene discussed is CSF2; the disease is rheumatoid arthritis.