RESUMEN
OBJECTIVES: The aim of this study was to analyse the expression and function of nucleotide-binding oligomerization domain (NOD)1 and NOD2 in isolated cells of patients with rheumatoid arthritis (RA). METHOD: mRNA expression levels of NOD1, NOD2, and receptor-interacting serine/threonine kinase 2 (RIPK2) genes were determined by quantitative polymerase chain reaction (qPCR) in peripheral blood mononuclear cells (PBMCs) and synovial fluid T cells (SFTCs) isolated from RA and osteoarthritis (OA) patients. Cytokines were measured by enzyme-linked immunosorbent assay (ELISA) in plasma and cell culture supernatants. The stimulatory effect of RA SF was assessed by an in-vitro NOD2 activation assay using nuclear factor kappa B (NF-κB) luciferase-transfected cells. RESULTS: A significantly higher level of NOD2 and RIPK2 mRNA expression, but not NOD1, was observed on PBMCs and SFTCs isolated from RA patients compared to the OA control group. In addition, the NOD2 pathway up-regulation was functional, as stimulation of PBMCs with muramyl dipeptide (MDP) induced the production of higher amounts of tumour necrosis factor (TNF)-α, interleukin (IL)-8, and IL-1ß compared with OA PBMCs. Incubation of PBMCs from healthy donors with recombinant TNF-α or RA serum induced the expression of NOD2 mRNA. Finally, SF isolated from RA patients is able to activate the NF-κB signalling pathway in HEK293T-transfected cells in a NOD2-dependent manner. CONCLUSIONS: Our findings suggest that NOD2/RIPK2 signalling is up-regulated in immune cells of RA patients. Moreover, it seems that there is a NOD2 agonist in the SF of RA patients. Therefore, NOD2/RIPK2 activation can modulate the innate immune response and may play a role in the perpetuation of the inflammatory response in RA.
