In RA, cytokines such as tumor necrosis factor alpha (TNF-α), interleukin-6 (IL-6), IL-17a, IL-22, IL-23, IL-1β, IL-8, interferon-γ (IFN-γ), granulocyte/macrophage colony-stimulating factor (GM-CSF), granulocyte colony-stimulating factor (G-CSF), IL-15, IL-18, IL-33, and IL-37 [11, 13, 18–36] are all detected either in the serum or in the synovial fluids of these patients. Here, IL17A is linked to rheumatoid arthritis.