ACTIVATION OF SYNOVIAL FIBROBLASTS BY BACTERIAL PEPTIDOGLYCAN IS DEPENDENT ON TOLL-LIKE RECEPTOR 2

Background: Rheumatoid arthritis (RA) is characterized by synovial activation and inflammatory cell infiltrates. The triggering events leading to the inflammatory changes in the joints are not known. Infectious organisms have been suspected but attempts to isolate a specific virus or bacteria have failed. However in joints of RA patients bacterial products such as cell wall components and DNA have been detected. Bacterial products stimulate the innate immune system by binding to Toll-like receptors (TLR) which mediate activation of genes involved in inflammtory processes.Objectives: To assess the stimulatory capacity of bacterial peptidoglycan (PGN) on human synovial fibroblasts from RA patients.Methods: Cultured RA-SF were stimulated by staphylococcal PGN or left untreated. Surface expression of CD54 (ICAM-1) was assessed by FACS. Messenger RNA expression of matrix metalloproteinases (MMP) 1, 3, 9, 13 and 14 was determined by real time PCR. ELISA was used to measure IL-6 levels in the culture supernatants.Results: CD54 expression of cultured RA-SF increased between 40 and 150% depending on the individual cultures upon stimulation with bacterial PGN. Significant upregulation of MMP mRNA production was found for MMPs 1 and 3, up to several hundred fold. Moreover, IL-6 levels were significantly higher (at least 20-fold) in the culture supernatants after stimulation with bacterial PGN. The addition of anti-TLR2 antibodies to cultured RA-SF prior to PGN stimulation resulted in a partial inhibition of CD54 upregulation and IL-6 production.Conclusion: As previous reports have shown PGN stimulates the innate immune system by binding to pattern recognition receptors of the Toll-like receptor family. Our results suggest that staphylococcal PGN activates synovial fibroblasts in a TLR2 dependent fashion. Based on our findings TLRs represent possible targets for antiinflammatory treatment with inhibitory agents.Citation: , volume , supplement , year 2002, page Session: Cell receptor-ligand interaction signalling and activation