Background/Purpose:

Plasmacytoid dendritic cells (pDC) are considered the main source of type-I interferon (IFN-I). The interferon signature has been widely associated to systemic lupus erythematosus (SLE). Among these over-expressed genes, interferon regulatory factors (IRF) have been proposed as key regulators of the increased IFN-I production in SLE patients and murine models. Many genetic association studies have found association between many IRF-5 polymorphisms with increased susceptibility to SLE in different ethnic groups, however these studies have been done with total mononuclear cells, which may not reflect specific DC alterations. The aim of the present study was to address the expression of IRF-3 and 5 on different DC subsets from SLE patients, as well as their association to IFN-I production.

Methods:

In this work we included 35 patients with SLE (20 with SLEDAI=0, 15 with SLEDAI>6) according to the classification criteria of the American College of Rheumatology as well as 35 healthy age and gender matched controls. Peripheral blood mononuclear cells were isolated by density gradient. Monocytes were purified by positive selection with magnetic beads. mDC were generated by culturing monocytes for 6 days in presence of GM-CSF, IL-4 and for 2 additional days in presence of LPS to induce maturation. The expression of CD80, CD86, HLA-DR, CD40 was evaluated by flow cytometry. IRF3 and IRF5 expression was assessed by qPCR, flow cytometry and western blot in mDC and pDC from peripheral blood and monocyte derived DC. IFN-I serum levels were measured by ELISA. Data were analyzed by the Student t test. In all cases, an informed consent was obtained, and the ethics committee approved this study.

Results:

We found increased expression of IRF-3(4331.6±794 vs 2400.8±225.9, p=0.038) and 5 (2724.6±335.9 vs 1785±115.2, p=0.031) by flow cytometry (mean fluorescence intensity) on pDCs from SLE patients vs healthy controls. This finding was associated to increased IFN-I serum levels in SLE patients vs healthy controls (160.2±21 vs 106.1±14, p=0.036).  We found as well that monocyte derived DC from SLE patients showed decreased levels of CD40 after maturation with LPS.  However no other differences were observed on the other DC phenotype markers. Interestingly, differences between IRF-3 and 5 expression were restricted to pDC subset. Moreover, these findings were present regardless of disease activity. 

Conclusion: Our findings suggest that increased levels of IFN-I  in SLE patients are associated to increased expression of IRF-3 and 5, which is restricted to pDC subset. Furthermore, the abnormal expression of these factors might be an intrinsic defect in SLE, since it is present regardless of disease activity.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/interferon-regulatory-factors-3-and-5-as-key-elements-of-the-interferon-signature-on-plasmacytoid-dendritic-cells-from-systemic-lupus-erythematosus-patients/