Toll-like receptor 2 and 4 combination engagement upregulate IL-15 synergistically in human rheumatoid synovial fibroblasts.
Toll-like receptors (TLRs) are pattern-recognition receptors that connect innate and adaptive immunity. Interleukin-15 (IL-15) is a proinflammatory, innate response cytokine that mediates pleiotropic effector functions in inflammatory synovitis of rheumatoid arthritis (RA). The aim of this study was to clarify whether stimulation of TLR2 and TLR4 by their specific ligands induces the production of IL-15 in fibroblast-like synoviocytes (FLS) from RA patients. FLS were isolated from RA synovial tissues and stimulated with the TLR2 ligand bacterial peptidoglycan (PGN) and the TLR4 ligand lipopolysaccharide (LPS). IL-15 in the culture supernatants was measured by ELISA, and mRNA levels were assessed by RT-PCR and real time PCR. The expression of TLR2, TLR4, and IL-15 in the RA synovium was quantified by immunohistochemistry and compared with values obtained in osteoarthritis synovium. IL-15 production increased in culture supernatants of RA FLS stimulated with PGN or PGN plus LPS, and this was upregulated at the transcriptional level. In contrast, LPS did not increase the level of IL-15 although it augmented the stimulatory effect of PGN on IL-15 production. Inhibition of nuclear factor (NF)-kappaB with a specific inhibitor abrogated the stimulatory effect of PGN or PGN plus LPS on IL-15. Neutralization of TLR2 with a blocking monoclonal antibody significantly reduced IL-15 production (P<0.05), reflecting the functional relevance of TLR2 activation in the induction of IL-15 production. These data suggest that TLR2 activation in RA FLS by microbial constituents is involved in the induction of IL-15 and that TLR2 promotes inflammation through NF-kappaB. TLR4 augmented the stimulatory effect of TLR2 on IL-15, possibly contributing to the maintenance of synovitis in patients with RA.
Jung
Young Ok
YO
Department of Internal Medicine, Division of Rheumatology, Hallym University Kang-Nam Sacred Heart Hospital, Seoul, Republic of Korea.
Cho
Mi-La
ML
Kang
Chang-Min
CM
Jhun
Joo-Yeon
JY
Park
Jin-Sil
JS
Oh
Hye-Joa
HJ
Min
Jun-Ki
JK
Park
Sung-Hwan
SH
Kim
Ho-Youn
HY
D000906:Antibodies / Q000276:immunology / Q000494:pharmacology; D001172:Arthritis, Rheumatoid / Q000276:immunology* / Q000378:metabolism / Q000473:pathology; D005347:Fibroblasts / Q000276:immunology / Q000378:metabolism / Q000473:pathology; D006801:Humans; D019409:Interleukin-15 / Q000096:biosynthesis* / Q000235:genetics / Q000276:immunology; D016328:NF-kappa B / Q000037:antagonists & inhibitors; D012717:Sesquiterpenes / Q000494:pharmacology; D013583:Synovial Membrane / Q000276:immunology* / Q000378:metabolism / Q000473:pathology; D051195:Toll-Like Receptor 2 / Q000037:antagonists & inhibitors / Q000096:biosynthesis / Q000276:immunology* / Q000378:metabolism; D051197:Toll-Like Receptor 4 / Q000037:antagonists & inhibitors / Q000096:biosynthesis / Q000276:immunology* / Q000378:metabolism; D015854:Up-Regulation
D000906:Antibodies; D019409:Interleukin-15; D016328:NF-kappa B; D012717:Sesquiterpenes; D051195:Toll-Like Receptor 2; D051197:Toll-Like Receptor 4; C002669:parthenolide