Systemic lupus erythematosus (SLE) is a prototype systemic autoimmune disease characterized by flares of high morbidity. Using oligonucleotide microarrays, we now show that active SLE can be distinguished by a remarkably homogeneous gene expression pattern with overexpression of granulopoiesis-related and interferon (IFN)-induced genes. Using the most stringent statistical analysis (Bonferroni correction), 15 genes were found highly up-regulated in SLE patients, 14 of which are targets of IFN and one, defensin DEFA-3, a major product of immature granulocytes. A more liberal correction (Benjamini and Hochberg correction) yielded 18 additional genes, 12 of which are IFN-regulated and 4 granulocyte-specific. Indeed immature neutrophils were identified in a large fraction of SLE patients white blood cells. High dose glucocorticoids, a standard treatment of disease flares, shuts down the interferon signature, further supporting the role of this cytokine in SLE. The expression of 10 genes correlated with disease activity according to the SLEDAI. The most striking correlation (P < 0.001, r = 0.55) was found with the formyl peptide receptor-like 1 protein that mediates chemotactic activities of defensins. Therefore, while the IFN signature confirms the central role of this cytokine in SLE, microarray analysis of blood cells reveals that immature granulocytes may be involved in SLE pathogenesis.

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Interferon and Granulopoiesis Signatures in Systemic Lupus Erythematosus Blood

Human and mouse plasmacytoid dendritic cells have been shown to correspond to a specialized cell population that produces large amounts of type I interferons in response to viruses, the so-called natural interferon-producing cells. As a result, intensive investigation is now focused on the potential functions of plasmacytoid dendritic cells in both innate and adaptive immunity. Here we review recent progress on the characterization of plasmacytoid dendritic cell origin, development, migration and function in immunity and tolerance, as well as their effect on human diseases.

Plasmacytoid dendritic cells in immunity.

▪ Abstract Type 1 interferon-(α, β, ω)-producing cells (IPCs), also known as plasmacytoid dendritic cell precursors (pDCs), represent 0.2%–0.8% of peripheral blood mononuclear cells in both humans and mice. IPCs display plasma cell morphology, selectively express Toll-like receptor (TLR)-7 and TLR9, and are specialized in rapidly secreting massive amounts of type 1 interferon following viral stimulation. IPCs can promote the function of natural killer cells, B cells, T cells, and myeloid DCs through type 1 interferons during an antiviral immune response. At a later stage of viral infection, IPCs differentiate into a unique type of mature dendritic cell, which directly regulates the function of T cells and thus links innate and adaptive immune responses. After more than two decades of effort by researchers, IPCs finally claim their place in the hematopoietic chart as the most important cell type in antiviral innate immunity. Understanding IPC biology holds future promise for developing cures for infectious...

IPC: professional type 1 interferon-producing cells and plasmacytoid dendritic cell precursors.

Dendritic cells (DCs) are important in regulating both immunity and tolerance. Hence, we hypothesized that systemic lupus erythematosus (SLE), an autoimmune disease characterized by autoreactive B and T cells, may be caused by alterations in the functions of DCs. Consistent with this, monocytes from SLE patients' blood were found to function as antigen-presenting cells, in vitro. Furthermore, serum from SLE patients induced normal monocytes to differentiate into DCs. These DCs could capture antigens from dying cells and present them to CD4-positive T cells. The capacity of SLE patients' serum to induce DC differentiation correlated with disease activity and depended on the actions of interferon-alpha (IFN-alpha). Thus, unabated induction of DCs by IFN-alpha may drive the autoimmune response in SLE.

https://science.sciencemag.org/content/sci/294/5546/1540.full.pdf

Induction of Dendritic Cell Differentiation by IFN-α in Systemic Lupus Erythematosus

Systemic lupus erythematosus (SLE) is a systemic autoimmune disease characterized by a breakdown of tolerance to nuclear antigens and the development of immune complexes. Genomic approaches have shown that human SLE leukocytes homogeneously express type I interferon (IFN)–induced and neutrophil-related transcripts. Increased production and/or bioavailability of IFN-α and associated alterations in dendritic cell (DC) homeostasis have been linked to lupus pathogenesis. Although neutrophils have long been shown to be associated with lupus, their potential role in disease pathogenesis remains elusive. Here, we show that mature SLE neutrophils are primed in vivo by type I IFN and die upon exposure to SLE-derived anti-ribonucleoprotein antibodies, releasing neutrophil extracellular traps (NETs). SLE NETs contain DNA as well as large amounts of LL37 and HMGB1, neutrophil proteins that facilitate the uptake and recognition of mammalian DNA by plasmacytoid DCs (pDCs). Indeed, SLE NETs activate pDCs to produce high levels of IFN-α in a DNA- and TLR9 (Toll-like receptor 9)–dependent manner. Our results reveal an unsuspected role for neutrophils in SLE pathogenesis and identify a novel link between nucleic acid–recognizing antibodies and type I IFN production in this disease.

Netting Neutrophils Are Major Inducers of Type I IFN Production in Pediatric Systemic Lupus Erythematosus

Patients with systemic lupus erythematosus (SLE) have a circulating inducer of interferon-alpha (IFN-alpha) production acting on leucocytes resembling immature dendritic cells

Systemic lupus erythematosus (SLE) patients have increased levels of interferon-alfa (IFN-alpha) in the circulation but a reduced number of functionally intact natural IFN-alpha producing cells (IPC) in peripheral blood. In search for tissue localisation of activated IPC, we investigated skin biopsies from SLE patients for the occurrence of such cells. Eleven SLE patients with inflammatory skin lesions and six healthy controls were biopsied. An immunohistochemical technique (IH) and in situ hybridisation (ISH) were used to detect intracellular IFN-alpha protein and IFN-alpha mRNA, respectively. In all 11 biopsies from SLE lesions, a high number of IPC were detected by IH. In the nonlesional SLE biopsies we could also demonstrate IPC in 10/11 patients. In 6/11 SLE patients, IFN-alpha mRNA containing cells could be detected in the specimens. A low number of IPC were detected in 1/6 healthy controls by IH, but no ISH positive cells were seen. Our results demonstrate that SLE patients have active IPC in both dermal lesions and in noninflammatory skin. A recruitment of IPC from blood to peripheral tissues may explain the low number of circulating natural IPC in SLE patients. Because the type I IFN system is involved in the SLE disease process, these results are of interest for the understanding of the pathogenesis in SLE.

Presence of cutaneous interferon-a producing cells in patients with systemic lupus erythematosus

Patients with systemic lupus erythematosus have reduced numbers of circulating natural interferon-alpha-producing cells

Human peripheral blood mononuclear cells (PBMC) were stimulated to produce interferon-alpha (IFN-alpha) by glutaraldehyde-fixed Herpes simplex virus type 1 (HSV)-infected WISH amnion cells in vitro. Different cytokines were included during the stimulation and tested for their ability to enhance the IFN-alpha response which occurs in the natural IFN-alpha producing (NIP) leucocytes. The total production of IFN-alpha and the numbers of IFN-alpha producing cells (IPCs) were increased by interleukin-3 (IL-3) or granulocyte-macrophage colony-stimulating factor (GM-CSF). Their most marked effect was to reduce the time required for induction of the IPC by the HSV-infected cells, thereby causing both an earlier peak of IPC numbers and secretion of IFN-alpha. Addition of IFN-alpha 2b did not alter the kinetics of the IFN-alpha response in the same way as the two CSFs, but instead generally increased the IPC numbers and the production of IFN-alpha. The IL-3 and GM-CSF, especially in combination with IFN-alpha, had the most pronounced enhancing effects on IPC numbers when PBMC were induced at low cell concentrations. The cytokines IL-1, IL-2, IL-4, IL-6 or tumour necrosis factor-alpha (TNF-alpha) had no detectable effects on the IFN-alpha response. The results suggest that cytokines such as the CSFs and IFNs may be involved in the regulation of NIP cell functions.

Interferons and the Colony‐Stimulating Factors IL‐3 and GM‐CSF Enhance the IFN‐α Response in Human Blood Leucocytes Induced by Herpes Simplex Virus

The ability of peripheral blood mononuclear cells (PBMC) from newborn infants, gestational age 24-42 wk, to produce interferon-α (IFN-α) on the first day after birth was studied in vitro. Human amnion cells (WISH) coated with herpes simplex virus type I and fixed by glutaraldehyde were used as IFN-α inducers. Individual IFN-α producing cells (IPC) among PBMC were determined by an immunoplaque assay. The frequency of IPC was low in all premature (≤36 wk) infants (median 0.3 IPC/104 PBMC, range 0.0-2.6), and significantly higher (median 2.0 IPC/104 PBMC, range 0.0-16.4) in term infants (>37 wk). The frequencies were lower in both groups of infants than in adults (7.3 IPC/104 PBMC, range 2.0- 23.7). When a conditioned medium from cultures of herpes simplex virus type I-stimulated PBMC from adults was added to the IFN induction cultures, the frequencies of IPC increased in PBMC from both preterm and term infants, and in the latter group did not differ significantly from adult levels. The median production of IFN-α per IPC was 1.1 U (range 0.0-2.8) in premature infants, 1.0 U (range 0.0-8.8) in term infants and 3.2 U (range 1.5-8.0) were decreased, a decline of IPC frequencies occurred. This decline was more marked and started at higher PBMC concentrations in infants than in adults, and was prevented by addition of conditioned medium from herpes simplex virus type I-stimulated cultures of PBMC from adults. The results suggest that PBMC of preterm infants on the first day after birth are deficient both with respect to the proportion of actual IPC and to accessory mechanisms necessary for a normal IFN-αresponse. In contrast, IPC frequencies in term infants approach levels of adults, but accessory functions may still be deficient.

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B. Cederblad

Papers

Patients with systemic lupus erythematosus (SLE) have a circulating inducer of interferon-alpha (IFN-alpha) production acting on leucocytes resembling immature dendritic cells

Presence of cutaneous interferon-a producing cells in patients with systemic lupus erythematosus

Patients with systemic lupus erythematosus have reduced numbers of circulating natural interferon-alpha-producing cells

Interferons and the Colony‐Stimulating Factors IL‐3 and GM‐CSF Enhance the IFN‐α Response in Human Blood Leucocytes Induced by Herpes Simplex Virus

Deficient Herpes Simplex Virus-Induced Interferon-α Production by Blood Leukocytes of Preterm and Term Newborn Infants