['Interleukin-32 (IL-32) is a recently described cytokine that is a strong inducer of pro-inflammatory cytokines such as tumor necrosis factor (TNF)-α, IL-1β, IL-6, and IL-8. The expression of this cytokine is highly increased in the rheumatoid synovium and correlated with the severity of joint inflammation. Little is known regarding the innate immune-related regulation of IL-32 by fibroblast-like synoviocytes (FLSs). We therefore investigated the effect of innate immune stimulation by ligands of Toll-like receptor (TLR)2, TLR3, and TLR4, and cytokines such as TNF-α and interferon (IFN)-γ, on IL-32 expression by FLSs.', 'FLSs were isolated from patients with rheumatoid arthritis (RA) according to the ACR criteria. Quantitative RT-PCR, confocal analysis, and ELISA were performed to evaluate IL-32 mRNA induction and IL-32 release by FLSs stimulated with TLR2 (BLP), TLR3 (poly I:C), and TLR4 (lipopolysaccharide) ligands, TNF-α and IFN-γ.', 'TLR2, -3, and -4 ligands as well as IFN-γ and TNF-α induced IL-32 β, γ and δ mRNA expression by RA FLSs. Mature IL-32 was expressed intracellularly and released by cells stimulated with the various activators. The IL-32α isoform was expressed intracellularly in response to TNF-α and poly I:C and not released in culture supernatants. Stimulation of FLS with TNF-α, BLP, lipopolysaccharide, or poly I:C concomitant with IFN-γ increased IL-32 expression compared with stimulation with IFN-γ alone.'] Does innate immunity trigger IL-32 expression by fibroblast-like synoviocytes in rheumatoid arthritis?