Cell-specific type I Interferon signatures in autoimmunity and viral infection: what makes the difference? Chieko Kyogoku 1, Biljana Smiljanovic 1, Joachim R Grün 1, Robert Biesen 2, Falk Hiepe 2, Thomas Häupl 2, Tobias Alexander 2, Andreas Radbruch 1, Andreas Grützkau 1 1 German Rheumatism Research Centre (DRFZ) Berlin, An Institute of the Leibniz Association, Berlin, Germany; 2 Department of Rheumatology and Clinical Immunology, Charité University Medicine Berlin, Humboldt University of Berlin, Berlin, Germany Poster Patients and Methods Gene expression profiling experiments using peripheral blood mononuclear cells (PBMCs) revealed a crucial role of type I interferon (IFN) in the pathogenesis of systemic lupus erythematosus (SLE). However, it is almost unknown how particular leukocyte subsets contribute to the overall type I IFN signature described for PBMCs. Furthermore, a detailed analysis of how IFN signatures differ in autoimmune disease from that observed after viral infection is missing so far. Therefore, we compared expression levels of IFN interferon-related genes in peripheral CD4 + T helper cells, CD16-negative inflammatory and CD16-positive resident monocytes (Mo) isolated from patients with SLE, healthy donors (ND) and ND vaccinated against yellow fever by global gene expression profiling.  Peripheral blood from below age- and gender-matched patients and ND were recruited. Same ND were examined before and 7 days after immunization by yellow fever vaccine. SLE patients showed disease activity scores (SLEDAI) ranged from 2~22.  CD3+CD4+ T cells, CD14+CD16- Mo and CD14+CD16+ Mo were sorted by FACS.  RNA were isolated and applied to Affymetrix Human Genome U133 Plus 2.0 Arrays.  Data analysis was done using BioRetis database ( analysis.de), Genesis Software and Ingenuity Pathway Analysis (IPA).  A reference list of IFN-related genes was obtained from recent publications (Ramos PS et al. Arthritis Rheum 2011, Smiljanovic B et al. J Mol Med 2012) and used to estimate IFN imprints.  SLE and immunized ND were compared against unimmunized ND; therefore 6 comparisons were made.  Significantly differentially expressed probe sets were chosen by BioRetis database and filtered based on the list of IFN signature genes. A cutoff of fold change (FC) >=2, <=-2 was applied. CD4+ T cells CD16 - Mo CD16 + Mo 6 SLE 4 ND 4 immunized ND 4 SLE 4 ND 4 immunized ND 4 SLE 3 ND 3 immunized ND Background and aim of the study  When compared absolute number of differentially expressed probe sets, 9 / 3 / 2 (CD4+ T cells/CD16-negative Mo/CD16-positive Mo, respectively) times more number of probes were detected in patients with SLE compared to immunized ND.  The contribution of IFN-related transcrips to total number of differentially expressed probe-sets was 20.7 / 23.3 / 23.3 % in patients with SLE, whereas 48.6 / 35.2 / 30.5 % in immunized ND.  98 / 165 / 173 probe sets (FC >=2, <=-2) were detected as a “common” IFN signature observed both in autoimmunity and in immunized ND.  111 / 164 / 120 probe sets were detected as an “autoimmune-specific” IFN signature, whereas only 0 / 8 / 5 probe sets were detected to be specific for the “virus-induced” IFN signature.  Expression pattern of these IFN signature genes clearly distinguished patients with SLE from immunized ND by hierarchical cluster analysis. SLE ND Immunized ND SLE ND Immunized ND SLE ND Immunized ND Results I  The increased expression levels of LAMP3 (lysosomal-associated membrane protein 3) in CD4+ T cells, CCL2 (chemokine (C-C motif) ligand 2) in CD16-negative Mo, and SIGLEC1 (sialic acid binding Ig-like lectin 1) in both CD16-negative and CD16-positive Mo were the most significant cell- specific IFN surrogate markers.  Although major IFN signature genes were commonly expressed in CD4+ T cells and Mo of patients with SLE and immunized ND, expression magnitudes of them were higher in patients with SLE compared to immunized ND.  In SLE, in addition to the typical “viral-induced” IFN signature, genes that are involved in apoptosis signaling, antiviral PKR signaling, Fcγ receptor- mediated phagocytosis and IL-10- / IL-9- / IL-15-mediated JAK/Stat signaling pathways were identified by IPA gene enrichment analyses. Results II CD4+ T cells CD16- Mo CD16+ Mo Fold change CD4+ T cells CD16- Mo CD16+ Mo This study demonstrated for the first time that IFN signature in autoimmunity and in viral infection are quite different quantitatively in the number of IFN-related genes activated and qualitatively in their expression magnitudes. Autoimmunity is characterized by a much stronger expression of IFN signature genes and is obviously modulated by a separate set of co- regulated genes defining the “autoimmune-specific” IFN signature. CD4+ T cells and Mo respond to IFN in a cell-specific manner. Mo show more complex IFN response than CD4+ T cells. “Common” and “autoimmune-specific” IFN signature genes can be applied as a clinical biomarker to diagnose SLE flare discriminating from viral infection. Conclusion Funding