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

Arthritis Res Ther. 2010;12(3):R90. doi: 10.1186/ar3017. Epub 2010 May 18.


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 Fcgamma receptors (FcgammaRs), chemokine receptors, and activation markers were analyzed with flow cytometry in whole blood from patients with SLE and healthy controls. FcgammaR 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 FcgammaRI (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.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adrenal Cortex Hormones / therapeutic use
  • Adult
  • Antigens / metabolism
  • Antigens, Surface / metabolism
  • Biomarkers / metabolism
  • Case-Control Studies
  • Cells, Cultured
  • Cytoskeletal Proteins / metabolism
  • Dose-Response Relationship, Drug
  • Female
  • GPI-Linked Proteins / metabolism
  • GTP-Binding Proteins / metabolism
  • Humans
  • Interferon Type I / metabolism*
  • Leukocytes, Mononuclear / metabolism*
  • Lupus Erythematosus, Systemic / drug therapy
  • Lupus Erythematosus, Systemic / immunology
  • Lupus Erythematosus, Systemic / metabolism*
  • Male
  • Myxovirus Resistance Proteins
  • Receptors, IgG / metabolism*


  • Adrenal Cortex Hormones
  • Antigens
  • Antigens, Surface
  • Biomarkers
  • Cytoskeletal Proteins
  • GPI-Linked Proteins
  • IFI44 protein, human
  • Interferon Type I
  • LY6E protein, human
  • Myxovirus Resistance Proteins
  • Receptors, IgG
  • GTP-Binding Proteins