MYD88, IRAK3 and Rheumatoid Arthritis pathogenesis: Analysis of differential gene expression in CD14 + monocytes and the inflammatory cytokine levels.

Rheumatoid arthritis (RA) is a well-known chronic inflammatory disorder. Two molecular players act in the inflammation balance of the disease: MyD88 (Myeloid differentiation primary response 88) is related to TLR (Toll-like receptors) response and promotes the formation of myddosome complex resulting in increased inflammation; IRAK3 (Interleukin-1 receptor associated kinase 3) acts suppressing the myddosome complex thus decreasing inflammation. In this scenario, MYD88 and IRAK3 gene expression profile in RA patients and its correlation with clinical features is still partially known. So, we evaluated the MYD88 and IRAK3 gene expressions in CD14 + monocytes from RA patients and healthy controls and its relation with patients' clinical features and cytokine plasma levels. CD14 + monocytes were isolated using positive selection by magnetic cell separation. The MYD88 and IRAK3 gene expressions were measured through real time relative quantitative PCR with specific primers; relative quantification was normalized to ACTB, GAPDH, 18S and RPLP0 reference genes. Cytokine levels were analyzed by CBA (cytokine beads assays). CD14 + monocytes from RA patients showed lower IRAK3 expression level compared to controls although with a borderline statistical significance (Fold change (FC) = -1.63; p = 0.054). Furthermore, RA patients with high disease activity had lower levels of IRAK3 when compared to patients with low/moderate activity measured by the CDAI index (FC = -1.78; p = 0.030). No significant differences were observed for MYD88 gene expression (FC = 1.20; p = 0.294) between patients and controls analyzed. Additionally, we did not we did not observe correlation between IRAK3 and MYD88 gene expression and TNF-α, IL-6, IL-2 and IL-10 levels. We suggested that IRAK3 gene expression in CD14 + monocytes appears to be relevant to the RA etiology and clinical activity, whereas, in this study, MYD88 does not play a role in RA onset and development.