Expression of Toll‐like receptors 2 and 4 in rheumatoid synovial tissue and regulation by proinflammatory cytokines interleukin‐12 and interleukin‐18 via interferon‐γ

Abstract

Objective To study the expression of Toll-like receptor 2 (TLR-2) and TLR-4 and its association with proinflammatory cytokines in synovial tissue from patients with rheumatoid arthritis (RA), osteoarthritis (OA), and healthy individuals. Methods Synovial tissue specimens from 29 RA patients were stained for TLR-2, TLR-4, and proinflammatory cytokines (interleukin-1β [IL-1β], IL-12, IL-17, IL-18, and tumor necrosis factor α [TNFα]). The expression of TLR-2, TLR-4, and cytokines as well as the degree of inflammation in synovial tissue were compared between patients with RA, patients with OA (n = 5), and healthy individuals (n = 3). Peripheral blood mononuclear cells (PBMCs) were incubated with IL-12 and IL-18, and TLR expression was assessed using fluorescence-activated cell sorter analysis. Production of TNFα and IL-6 was measured using Luminex bead array technology. Results In RA synovial tissue, the expression of TLR-2 was slightly higher than that of TLR-4. Interestingly, both TLR-2 and TLR-4 were expressed at higher levels in moderately inflamed synovium, as compared with synovial tissue with no or severe inflammation. TLR expression in both the lining and the sublining was associated with the presence of IL-12 and IL-18, but no other cytokines, in the lining. The expression of both TLRs was low in synovial tissue from OA patients and healthy donors. Stimulation of PBMCs with IL-12 and IL-18 resulted in increased expression of both TLR-2 and TLR-4; this could be blocked with anti–interferon-γ (anti-IFNγ) antibodies, suggesting a role for IFNγ. Lipopolysaccharide- or lipoteichoic acid–mediated triggering of PBMCs incubated with IL-12/IL-18 or IFNγ led to an increased production of both TNFα and IL-6, indicating the functionality of TLR-2 and TLR-4. Conclusion TLR-2 and TLR-4 are expressed in synovial tissue of patients with clinically active disease and are associated with the levels of both IL-12 and IL-18. The synergistic effect of IL-12 and IL-18 on T cell IFNγ production seems to regulate expression of TLR-2 and TLR-4 in the synovial tissue of RA patients.