FCGR1A(CD64) expression on monocyte subsets and FIL1Z(IL-37) serum level as biomarkers of rheumatoid arthritis activity: A case controlled study and in silico analysis

Rheumatoid arthritis (RA) is one of the most common chronic autoimmune diseases. Chronic joint inflammation and bone destruction were shown to be caused by expanded monocytes in RA affected individuals. Interleukin-37 which known as FIL1Z(IL-37) is a well-known anti-inflammatory cytokine that plays a negative regulatory role of inflammation in RA. A total of 48 RA patients were divided equally into active RA group and stable RA group using the Disease Activity score (DAS)-28 score. Twenty-four age-and sex-matched healthy subjects were enrolled as controls. The expression level of Fc gamma receptor IA (FCGR1A(CD64)) on monocytes and their subsets in peripheral blood were assessed by flow cytometry (FC) and serum levels of FIL1Z(IL-37) were measured by ELISA. The mean fluorescence intensity (MFI) of FCGR1A(CD64) expressing classical and intermediate monocyte subsets and serum levels of FIL1Z(IL-37) were significantly elevated in RA patients compared to the control and positively correlated with erythrocyte sedimentation rate (ESR), C-reactive protein (CRP), rheumatoid factor (RF), anti-cyclic citrullinated peptide (anti-CCP) and DAS-28 scores. The MFI of FCGR1A(CD64) expressing classical monocyte and serum levels of FIL1Z(IL-37) were significantly elevated in the active RA group compared to the stable RA group. The serum concentration of FIL1Z(IL-37) revealed very high specificity but limited sensitivity in discriminating between active and stable RA patients. Our results demonstrate a strong correlation between serum levels of FIL1Z(IL-37) and FCGR1A(CD64) expression on activated monocytes and their subsets in peripheral blood of RA patients. The results also depict that activated monocytes and their subsets may contribute to the elevated levels of FIL1Z(IL-37) during an active disease status to counter-act the inflammatory process.