IL6 and rheumatoid arthritis: Thus, TNF-α and IL-6 are the two main cytokines thought to contribute most to the many pathogenic signalling pathways that cause RA and to determine the histological type of synovitis, and hence, response to treatment with IL-6, interferon (IFN), granulocyte-macrophage colony-stimulating factor (GM-CSF), and the common γ-chain cytokine family.