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Open Access Research article

Monocyte surface expression of Fcγ receptor RI (CD64), a biomarker reflecting type-I interferon levels in systemic lupus erythematosus

Yi Li1*, Pui Y Lee12, Erinn S Kellner1, Matthew Paulus1, Juliana Switanek1, Yuan Xu1, Haoyang Zhuang1, Eric S Sobel1, Mark S Segal2, Minoru Satoh1 and Westley H Reeves1

Author Affiliations

1 Division of Rheumatology & Clinical Immunology, University of Florida, 1600 SW Archer Rd, Gainesville, FL 32610-0221, USA

2 Division of Nephrology, Hypertension and Transplantation, University of Florida, 1600 SW Archer Rd, Gainesville, FL 32610-0221, USA

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Arthritis Research & Therapy 2010, 12:R90  doi:10.1186/ar3017


See related editorial by Kirou and Kalliolias, http://arthritis-research.com/content/12/4/138

Published: 18 May 2010

Abstract

Introduction

More than half of systemic lupus erythematosus (SLE) patients show evidence of excess type I interferon (IFN-I) production, a phenotype associated with renal disease and certain autoantibodies. However, detection of IFN-I proteins in serum is unreliable, and the measurement of interferon-stimulated gene (ISG) expression is expensive and time consuming. The aim of this study was to identify a surrogate marker for IFN-I activity in clinical samples for monitoring disease activity and response to therapy.

Methods

Monocyte surface expression of Fcγ receptors (FcγRs), chemokine receptors, and activation markers were analyzed with flow cytometry in whole blood from patients with SLE and healthy controls. FcγR expression also was measured in peripheral blood mononuclear cells (PBMCs) from healthy controls cultured with Toll-like receptor (TLR) agonists, cytokines, or serum from SLE patients. Expression of ISGs was analyzed with real-time PCR.

Results

Circulating CD14+ monocytes from SLE patients showed increased surface expression of FcγRI (CD64). The mean fluorescent intensity of CD64 staining correlated highly with the ISG expression (MX1, IFI44, and Ly6E). In vitro, IFN-I as well as TLR7 and TLR9 agonists, induced CD64 expression on monocytes from healthy controls. Exposure of monocytes from healthy controls to SLE sera also upregulated the expression of CD64 in an IFN-I-dependent manner. Decreased CD64 expression was observed concomitant with the reduction of ISG expression after high-dose corticosteroid therapy.

Conclusions

Expression of CD64 on circulating monocytes is IFN-I inducible and highly correlated with ISG expression. Flow-cytometry analysis of CD64 expression on circulating monocytes is a convenient and rapid approach for estimating IFN-I levels in SLE patients.