Background The majority of 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 expensive examination and time consuming. Research in the past few years has demonstrated that their relative expression on circulating monocytes/macrophages may be modified by cytokines, including interferon (IFN)-α1. Little data exist on the in vivo expression of specific FcγRI, CD64 in SLE. However, the quantitative expression of CD64 on monocytes has not been reported. For the treatment early intervention, more rapid disease activity assessment is required in SLE.
Objectives To determine whether quantitative expression of CD64 on circulating monocytes (mCD64) is associated with systemic exacerbation in SLE patients.
Methods In this study, 10 SLE patients with high disease activity (aSLE), 20 SLE patients with quiescent activity (qSLE) and 20 healthy controls (HC) were enrolled. We measured the expression level of CD64 per monocyte quantitatively by flow cytometry. Comparisons of levels within each group were analyzed, and levels of respective measurements at both pre- and post-treatment in aSLE were analyzed. The expression level of mCD64 was compared with SLE disease activity index (SLEDAI) and SLE disease activity biomarkers (anti DNA antibody and compliments titer).
Results aSLE had a mean SLEDAI of 12.1±7, and qSLE SLEDAI was 3.0±1.6. In aSLE and qSLE, mean expression level of mCD64 was 39800±16609 and 21759±7423 molecules/cell (p<0.01), respectively. Both levels were significantly higher than HC (15325±2731). Moreover, the level of mCD64 was correlated with SLEDAI (r=0.66, p<0.001), anti DNA antibody (r=0.69, p<0.01) and CH50 (r=-0.69, p<0.001). After treatment, the value of mCD64 was significantly decreased in aSLE (p<0.05).
Conclusions Our results suggest that quantitative measurement of CD64 expression on monocytes can be useful to detect disease exacerbation in SLE. Flow cytometry analysis of CD64 expression on circulating monocytes is a convenient and rapid approach for estimating IFN-α levels in SLE. Quantitative mCD64 could become a novel biomarker to replace the SLE disease activity marker from that found a correlation with markers of disease activity, and reduced by treatment advantage. Further quantitative measurement of CD64 on flow cytometry will be necessary to obtain consistency of result between facilities.
Li, Y. et al. Monocyte surface expression of FCγreceptor RI (CD64), a biomarker reflecting type-I interferon levels in systemic lupus erythematosus. Arthritis Research & Therapy 2010, 12:R90.
Disclosure of Interest None declared