HDAC9 and rheumatoid arthritis: HDAC inhibitors reduce the secretion of proinflammatory cytokines, such as TNF and IL-6, in peripheral blood mononuclear cells (PBMC) of RA patients and reduce the secretion of TNF, IL-1α, IL-1β, and interferon (IFN)-γ in lipopolysaccharide (LPS)-stimulated normal PBMC [1, 24].