TNF and rheumatoid arthritis: In RA, IL-13 can inhibit the production of TNF-α by LPS-induced macrophages and reduce the expression levels of various factors, such as the proinflammatory cytokines IL-1β, TNF-α, and IL-6 in synovial tissue; macrophage inflammatory protein 1α; macrophage inflammatory protein 1β; and macrophage inflammatory protein 3.