Interferon-alpha promotes survival of human primary B-lymphocytes via phosphatidylinositol 3-kinase

Type I interferon and cancer

Type I interferon (IFN) is a class of proinflammatory cytokines with a dual role on malignant transformation, tumor progression, and response to therapy. On the one hand, robust, acute, and resolving type I IFN responses have been shown to mediate prominent anticancer effects, reflecting not only their direct cytostatic/cytotoxic activity on (at least some) malignant cells, but also their pronounced immunostimulatory functions. In line with this notion, type I IFN signaling has been implicated in the antineoplastic effects of various immunogenic therapeutics, including (but not limited to) immunogenic cell death (ICD)-inducing agents and immune checkpoint inhibitors (ICIs). On the other hand, weak, indolent, and non-resolving type I IFN responses have been demonstrated to support tumor progression and resistance to therapy, reflecting the ability of suboptimal type I IFN signaling to mediate cytoprotective activity, promote stemness, favor tolerance to chromosomal instability, and facilitate the establishment of an immunologically exhausted tumor microenvironment. Here, we review fundamental aspects of type I IFN signaling and their context-dependent impact on malignant transformation, tumor progression, and response to therapy.

Type I IFN Receptor Signaling on B Cells Promotes Antibody Responses to Polysaccharide Antigens

We previously reported monophosphoryl lipid A (MPL) and synthetic cord factor trehalose-6,6'-dicorynomycolate (TDCM) significantly increase Ab responses to T cell-independent type 2 Ags (TI-2 Ags) in a manner dependent on B cell-intrinsic TLR4 expression, as well as MyD88 and TRIF proteins. Given the capacity of MPL to drive type I IFN production, we aimed to investigate the extent to which type I IFN receptor (IFNAR) signaling was required for TI-2 responses and adjuvant effects. Using Ifnar1-/- mice and IFNAR1 Ab blockade, we found that IFNAR signaling is required for optimal early B cell activation, expansion, and Ab responses to nonadjuvanted TI-2 Ags, including the pneumococcal vaccine. Further study demonstrated that B cell-intrinsic type I IFN signaling on B cells was essential for normal TI-2 Ab responses. In particular, TI-2 Ag-specific B-1b cell activation and expansion were significantly impaired in Ifnar1-/- mice; moreover, IFNAR1 Ab blockade similarly reduced activation, expansion, and differentiation of IFNAR1-sufficient B-1b cells in Ifnar1-/- recipient mice, indicating that B-1b cell-expressed IFNAR supports TI-2 Ab responses. Consistent with these findings, type I IFN significantly increased the survival of TI-2 Ag-activated B-1b cells ex vivo and promoted plasmablast differentiation. Nonetheless, MPL/TDCM adjuvant effects, which were largely carried out through innate B cells (B-1b and splenic CD23- B cells), were independent of type I IFN signaling. In summary, our study highlights an important role for B-1b cell-expressed IFNAR in promoting responses to nonadjuvanted TI-2 Ags, but it nonetheless demonstrates that adjuvants which support innate B cell responses may bypass this requirement.

Antiviral response within different cell types of the CNS

The central nervous system (CNS) is a constitutive structure of various cell types conserved by anatomical barriers. Many of the major CNS cell-type populations distributed across the different brain regions are targets for several neurotropic viruses. Numerous studies have demonstrated that viral susceptibility within the CNS is not absolute and initiates a cell-type specific antiviral defence response. Neurons, astrocytes, and microglial cells are among the major resident cell populations within the CNS and are all equipped to sense viral infection and induce a relative antiviral response mostly through type I IFN production, however, not all these cell types adopt a similar antiviral strategy. Rising evidence has suggested a diversity regarding IFN production and responsiveness based on the cell type/sub type, regional distinction and cell`s developmental state which could shape distinct antiviral signatures. Among CNS resident cell types, neurons are of the highest priority to defend against the invading virus due to their poor renewable nature. Therefore, infected and uninfected glial cells tend to play more dominant antiviral roles during a viral infection and have been found to be the major CNS IFN producers. Alternatively, neuronal cells do play an active part during antiviral responses but may adopt differential strategies in addition to induction of a typical type I IFN response, to minimize the chance of cellular damage. Heterogeneity observed in neuronal IFN responsiveness may be partially explained by their altered ISGs and/or lower STATS expression levels, however, further in vivo studies are required to fully elucidate the specificity of the acquired antiviral responses by distinct CNS cell types.

IFN-I signaling in cancer: the connection with dysregulated Insulin/IGF axis

Type I interferons (IFN-Is) are prototypical inflammatory cytokines produced in response to stress. IFN-Is have a critical role in antitumor immunity by driving the activation of leukocytes and favoring the elimination of malignant cells. However, IFN-I signaling in cancer, specifically in the tumor microenvironment (TME), can have opposing roles. Sustained IFN-I stimulation can promote immune exhaustion or enable tumor cell-intrinsic malignant features. Herein, we discuss the potential impact of the insulin/insulin-like growth factor system (I/IGFs) and of metabolic disorders in aberrant IFN-I signaling in cancer. We consider the possibility that targeting I/IGFs, especially in patients with cancer affected by metabolic disorders, contributes to an effective strategy to inhibit deleterious IFN-I signaling, thereby restoring sensitivity to various cancer therapies, including immunotherapy.

B Cell Activation and Plasma Cell Differentiation Are Promoted by IFN-λ in Systemic Lupus Erythematosus

Type I IFN is essential for viral clearance but also contributes to the pathogenesis of autoimmune diseases, such as systemic lupus erythematosus (SLE), via aberrant nucleic acid-sensing pathways, leading to autoantibody production. Type III IFN (IFN-λ) is now appreciated to have a nonredundant role in viral infection, but few studies have addressed the effects of IFN-λ on immune cells given the more restricted expression of its receptor primarily to the epithelium. In this study, we demonstrate that B cells display a prominent IFN gene expression profile in patients with lupus. Serum levels of IFN-λ are elevated in SLE and positively correlate with B cell subsets associated with autoimmune plasma cell development, including CD11c+T-bet+CD21- B cells. Although B cell subsets express all IFN receptors, IFNLR1 strongly correlates with the CD11c+CD21- B cell expansion, suggesting that IFN-λ may be an unappreciated driver of the SLE IFN signature and B cell abnormalities. We show that IFN-λ potentiates gene transcription in human B cells typically attributed to type I IFN as well as expansion of T-bet-expressing B cells after BCR and TLR7/8 stimulation. Further, IFN-λ promotes TLR7/8-mediated plasmablast differentiation and increased IgM production. CD11c+ B cells demonstrate IFN-λ hyperresponsive signaling compared with other B cell subsets, suggesting that IFN-λ accelerates plasma cell differentiation through this putative extrafollicular pathway. In summary, our data support type III IFN-λ as a cytokine promoting the Ab-secreting cell pool in human viral and autoimmune disease.

RuvB-Like Protein 2 Interacts with the NS1 Protein of Influenza A Virus and Affects Apoptosis That Is Counterbalanced by Type I Interferons

The NS1 protein of influenza A virus (IAV) plays important roles in viral pathogenesis and host immune response. Through a proteomic approach, we have identified RuvB-like proteins 1 and 2 (RuvBL1 and RuvBL2) as interacting partners of the NS1 protein of IAVs. Infection of human lung A549 cells with A/PR/8/34 (PR8) virus resulted in reductions in the protein levels of RuvBL2 but not RuvBL1. Further studies with RuvBL2 demonstrated that the NS1-RuvBL2 interaction is RNA-independent, and RuvBL2 binds the RNA-binding domain of the NS1. Infection of interferon (IFN)-deficient Vero cells with wild-type or delNS1 PR8 virus reduced RuvBL2 protein levels and induced apoptosis; delNS1 virus caused more reductions in RuvBL2 protein levels and induced more apoptosis than did wild-type virus. Knockdown of RuvBL2 by siRNAs induced apoptosis and overexpression of RuvBL2 resulted in increased resistance to infection-induced apoptosis in Vero cells. These results suggest that a non-NS1 viral element or elements induce apoptosis by suppressing RuvBL2 protein levels, and the NS1 inhibits the non-NS1 viral element-induced apoptosis by maintaining RuvBL2 abundance in infected cells in the absence of IFN influence. In contrast to Vero cells, infection of IFN-competent A549 cells with PR8 virus caused reductions in RuvBL2 protein levels but did not induce apoptosis. Concomitantly, pretreatment of Vero cells with a recombinant IFN resulted in resistance to infection-induced apoptosis. These results demonstrate that the infection-induced, RuvBL2-regulated apoptosis in infected cells is counterbalanced by IFN survival signals. Our results reveal a novel mechanism underlying the infection-induced apoptosis that can be modulated by the NS1 and type I IFN signaling in IAV-infected cells.

Interferon α Enhances B Cell Activation Associated With FOXM1 Induction: Potential Novel Therapeutic Strategy for Targeting the Plasmablasts of Systemic Lupus Erythematosus

Systemic lupus erythematosus (SLE) is an autoimmune disease. It is characterized by the production of various pathogenic autoantibodies and is suggested to be triggered by increased type I interferon (IFN) signature. Previous studies have identified increased plasmablasts in the peripheral blood of SLE patients. The biological characteristics of SLE plasmablasts remain unknown, and few treatments that target SLE plasmablasts have been applied despite the unique cellular properties of plasmablasts compared with other B cell subsets and plasma cells. We conducted microarray analysis of naïve and memory B cells and plasmablasts (CD38+CD43+ B cells) that were freshly isolated from healthy controls and active SLE (n = 4, each) to clarify the unique biological properties of SLE plasmablasts. The results revealed that all B cell subsets of SLE expressed more type I IFN-stimulated genes. In addition, SLE plasmablasts upregulated the expression of cell cycle-related genes associated with higher FOXM1 and FOXM1-regulated gene expression levels than that in healthy controls. This suggests that a causative relationship exists between type I IFN priming and enhanced proliferative capacity through FOXM1. The effects of pretreatment of IFNα on B cell activation and FOXM1 inhibitor FDI-6 on B cell proliferation and survival were investigated. Pretreatment with IFNα promoted B cell activation after stimulation with anti-IgG/IgM antibody. Flow cytometry revealed that pretreatment with IFNα preferentially enhanced the Atk and p38 pathways after triggering B cell receptors. FDI-6 inhibited cell division and induced apoptosis in activated B cells. These effects were pronounced in activated B cells pretreated with interferon α. This study can provide better understanding of the pathogenic mechanism of interferon-stimulated genes on SLE B cells and an insight into the development of novel therapeutic strategies.

Type I interferons promote the survival and proinflammatory properties of transitional B cells in systemic lupus erythematosus patients

A hallmark of systemic lupus erythematosus (SLE) is the breaking of B-cell tolerance with the generation of high-affinity autoantibodies; however, the antibody-independent features of the B-cell compartment in SLE are less understood. In this study, we performed an extensive examination of B-cell subsets and their proinflammatory properties in a Chinese cohort of new-onset SLE patients. We observed that SLE patients exhibited an increased frequency of transitional B cells compared with healthy donors and rheumatoid arthritis patients. Plasma from SLE patients potently promoted the survival of transitional B cells in a type I IFN-dependent manner, which can be recapitulated by direct IFN-α treatment. Furthermore, the effect of IFN-α on enhanced survival of transitional B cells was associated with NF-κB pathway activation and reduced expression of the pro-apoptotic molecule Bax. Transitional B cells from SLE patients harbored a higher capacity to produce proinflammatory cytokine IL-6, which was also linked to the overactivated type I IFN pathway. In addition, the frequency of IL-6-producing transitional B cells was positively correlated with disease activity in SLE patients, and these cells were significantly reduced after short-term standard therapies. Thus, the current study provides a direct link between type I IFN pathway overactivation and the abnormally high frequency and proinflammatory properties of transitional B cells in active SLE patients, which contributes to the understanding of the roles of type I IFNs and B cells in the pathogenesis of SLE.

Role of cellular metabolism in regulating type I interferon responses: Implications for tumour immunology and treatment

Type I interferons (IFN) are increasingly recognized for their role in regulating anti-tumour immune responses. However, chronic activation of these pathways can result in immunosuppression and has been linked to poor responses to genotoxic and radiotoxic therapies. Emerging evidence suggests energy, lipid and amino acid metabolism play an important role in regulating and fine tuning type I IFN responses. Further, dysregulation of these processes has been implicated in the pathogenesis of chronic viral infections and autoimmune disorders. Systematic evaluation of these interrelationships in cancer models and patients may have important implications for the development of targeted IFN based anti-cancer therapeutics with minimal toxicity and limited off target effects.

Interferon alpha gene expression and serum level association with low vitamin D levels in Egyptian female patients with systemic lupus erythematosus

Background Patients with systemic lupus erythematosus (SLE) are prone to develop vitamin D (25(OH) D3) deficiency, due to several factors and there is an association between lower vitamin D levels and higher SLE disease activity. The aim of this research was to assess the prevalence of vitamin D deficiency in Egyptian female patients with SLE. Furthermore, we analyzed the potential relationship between this deficiency and SLE manifestations, disease activity, and its effect on interferon alpha (IFN-α) gene expression and serum level. Methods We evaluated the serum levels of vitamin D 25(OH)D3 and IFN-α by enzyme-linked immunosorbent assay (ELISA). IFN-α gene expression was measured by real-time polymerase chain reaction (PCR) assay in 123 Egyptian female patients with SLE and in 100 females as a healthy control group. Results Vitamin D deficiency was prevalent in 20.30%, while insufficiency was prevalent in 42.40% of the total group of patients. Serum levels of 25(OH)D3 were significantly decreased in the group of severe disease, and in the group of patients with lupus nephritis. 25(OH)D3 showed highly significant negative correlation with the SLE Disease Activity Index (SLEDAI) in the high activity group and lupus nephritis group. There was a significant negative correlation between 25(OH)D3 and IFN-α serum level and gene expression in all patients; more significant in the group with lupus nephritis. Conclusions The deficiency of 25(OH)D3 has a direct relationship with increase disease activity and nephritis in Egyptian SLE patients, suggesting the need for vitamin D supplementation in these patients. Also, it is directly correlated with increased secretion and gene expression of IFN-α, suggesting its role in pathogenesis of lupus nephritis, to be confirmed by further longitudinal observational studies.

Metabolic Reprogramming Commits Differentiation of Human CD27+IgD+ B Cells to Plasmablasts or CD27-IgD- Cells

B cells play a crucial role in the pathogenesis of autoimmune diseases, such as systemic lupus erythematosus (SLE). However, the relevance of the metabolic pathway in the differentiation of human B cell subsets remains unknown. In this article, we show that the combination of CpG/TLR9 and IFN-α markedly induced the differentiation of CD27⁺IgD⁺ unswitched memory B cells into CD27^hiCD38^hi plasmablasts. The response was accompanied by mammalian target of rapamycin complex 1 (mTORC1) activation and increased lactate production, indicating a shift to glycolysis. However, CpG alone induced the differentiation of unswitched memory B cells into CD27^-IgD^- memory B cells with high cytokine production, but such differentiation was suppressed by IFN-α. AMP-activated protein kinase activation enhanced the differentiation to CD27^-IgD^- B cells, but it attenuated mTORC1 activation and differentiation into plasmablasts. High mTORC1 activation was noted in CD19⁺ B cells of patients with SLE and correlated with plasmablast differentiation and disease activity. Taken together, differential metabolic reprogramming commits the differentiation of human unswitched memory B cells into plasmablasts (the combination of CpG and IFN-α amplifies mTORC1-glycolysis pathways) or CD27^-IgD^- memory B cells (CpG alone amplifies the AMP-activated protein kinase pathway). The former metabolic pathway may play a pivotal role in SLE.

Adjuvant activity of fish type I interferon shown in a virus DNA vaccination model

There is a need for more efficient vaccines to combat viral diseases of Atlantic salmon and other farmed fish. DNA vaccines are highly effective against salmonid rhabdoviruses, but have shown less effect against other viruses. In the present work we have studied if type I IFNs might be used as adjuvants in fish DNA vaccines. For this purpose we chose a DNA vaccine model based on the hemagglutinin-esterase (HE) gene of infectious salmon anemia virus (ISAV) as antigen. Salmon presmolts were injected with a plasmid encoding HE alone or together with a plasmid encoding Atlantic salmon type I IFN (IFNa1, IFNb or IFNc). Sera were harvested after 7-10 weeks for measurements of antibody against ISAV and the fish were challenged with ISAV to measure protective effects of the vaccines. The results showed that all three IFN plasmids delivered together with HE plasmid potently enhanced protection of salmon against ISAV mediated mortality and stimulated an increase in IgM antibodies against the virus. In contrast, HE plasmid alone gave low antibody titers and a minor protection against ISAV. This demonstrates that type I IFNs stimulate adaptive immune responses in fish, which may be a benefit also in other fish DNA vaccines. Quantitative RT-PCR studies showed that the salmon IFNs caused an increased influx of B-cells and cytotoxic T-cells at the muscle injection site, which may in part explain the adjuvant effect of the IFNs.

Modulation of the sensitivity of Jurkat T-cells to inhibition of protein synthesis by tumor necrosis factor α-related apoptosis-inducing ligand

Tumor necrosis factor α-related apoptosis-inducing ligand (TRAIL) is a potent inducer of apoptosis in Jurkat T lymphoma cells. One of the characteristics of the phase preceding overt apoptosis is the marked downregulation of protein synthesis. We have investigated factors that can influence this response and have explored some of the signaling pathways involved. We show that interferon-α (IFNα) pretreatment desensitizes Jurkat cells to TRAIL-induced inhibition of protein synthesis, such that the concentration of TRAIL required for 50% inhibition is increased by 10-fold. The inhibition of translation is characterized by dephosphorylation of the eIF4E-binding protein 4E-BP1 and IFNα desensitizes Jurkat cells to this effect. IFNα also inhibits TRAIL-mediated dephosphorylation of the growth-promoting protein kinase B (Akt). Since Jurkat cells are defective for phosphatase and tensin homolog deleted on chromosome 10 (PTEN) and therefore have constitutive phosphoinositide 3-kinase (PI3K) activity, we investigated the consequences for protein synthesis of inhibiting PI3K using LY294002. Inhibition of PI3K partially inhibits translation, but also enhances the effect of a suboptimal concentration of TRAIL. However, LY294002 does not block the ability of IFNα to protect protein synthesis from TRAIL-induced inhibition. Data are presented suggesting that IFNα impairs the process of activation of caspase-8 within the TRAIL death-inducing signaling complex.

New function of type I IFN: induction of autophagy

Autophagy is a highly conserved cellular process responsible for recycling of intracellular material. It is induced by different stress signals, including starvation, cytokines, and pathogens. Type I interferons (IFN) are proteins with pleiotropic functions, such as antiviral, antiproliferative, and immunomodulatory activities. Several recent studies showed type I IFN-induced autophagy in multiple cancer cell lines as evidenced by autophagic markers, for example, the conversion of microtubule-associated protein 1 light chain 3 beta (MAP1LC3B, also known as LC3-I) to LC3-II and the formation of autophagosomes by electron microscopy. In addition, studies suggest the involvement of Janus kinase (JAK)/signal transducer and activator of transcription (STAT) and phosphatidylinositol-4,5-bisphosphate 3-kinase (PI3K)/v-akt murine thymoma viral oncogene homolog (AKT) and mechanistic target of rapamycin, serine/threonine kinase (mTOR) pathways in the induction of autophagy. This review highlights a new function of type I IFN as an inducer of autophagy. This new function of type I IFN may play an important role in viral clearance, antigen presentation, inhibition of proliferation, as well as a positive feedback loop for the production of type I IFN.

Innate immunity in pluripotent human cells: attenuated response to interferon-β

Type I interferon (IFN-α/β) binds to cell surface receptors IFNAR1 and IFNAR2 and triggers a signaling cascade that leads to the transcription of hundreds of IFN-stimulated genes. This response is a crucial component in innate immunity in that it establishes an "antiviral state" in cells and protects them against further damage. Previous work demonstrated that, compared with their differentiated counterparts, pluripotent human cells have a much weaker response to cytoplasmic double-stranded RNA (dsRNA) and are only able to produce a minimal amount of IFN-β. We show here that human embryonic stem cells (hESCs) and human induced pluripotent stem cells (hiPSCs) also exhibit an attenuated response to IFN-β. Even though all known type I IFN signaling components are expressed in these cells, STAT1 phosphorylation is greatly diminished upon IFN-β treatment. This attenuated response correlates with a high expression of suppressor of cytokine signaling 1 (SOCS1). Upon differentiation of hESCs into trophoblasts, cells acquire the ability to respond to IFN-β, and this is accompanied by a significant induction of STAT1 phosphorylation as well as a decrease in SOCS1 expression. Furthermore, SOCS1 knockdown in hiPSCs enhances their ability to respond to IFN-β. Taken together, our results suggest that an attenuated cellular response to type I IFNs may be a general feature of pluripotent human cells and that this is associated with high expression of SOCS1.

Type I interferons induce autophagy in certain human cancer cell lines

Autophagy is an evolutionarily conserved cellular recycling mechanism that occurs at a basal level in all cells. It can be further induced by various stimuli including starvation, hypoxia, and treatment with cytokines such as IFNG/IFNγ and TGFB/TGFβ. Type I IFNs are proteins that induce an antiviral state in cells. They also have antiproliferative, proapoptotic and immunomodulatory activities. We investigated whether type I IFN can also induce autophagy in multiple human cell lines. We found that treatment with IFNA2c/IFNα2c and IFNB/IFNβ induces autophagy by 24 h in Daudi B cells, as indicated by an increase of autophagy markers MAP1LC3-II, ATG12–ATG5 complexes, and a decrease of SQSTM1 expression. An increase of MAP1LC3-II was also detected 48 h post-IFNA2c treatment in HeLa S3, MDA-MB-231, T98G and A549 cell lines. The presence of autophagosomes in selected cell lines exposed to type I IFN was confirmed by electron microscopy analysis. Increased expression of autophagy markers correlated with inhibition of MTORC1 in Daudi cells, as well as inhibition of cancer cell proliferation and changes in cell cycle progression. Concomitant blockade of either MTOR or PI3K-AKT signaling in Daudi and T98G cells treated with IFNA2c increased the level of MAP1LC3-II, indicating that the PI3K-AKT-MTORC1 signaling pathway may modulate IFN-induced autophagy in these cells. Taken together, our findings demonstrated a novel function of type I IFN as an inducer of autophagy in multiple cell lines.

Activation and regulation of interferon-β in immune responses

Interferons (IFNs) were discovered more than half a century ago, and extensive research has since identified multifarious roles for type I IFN in human immune responses. Here, we review the functions of IFN-β in innate and adaptive immunity. We also discuss the activation and influence of IFN-β on myeloid cell types, including monocytes and dendritic cells, as well as address the effects of IFN-β on T cells and B cells. Findings from our own laboratory, which explores the molecular mechanisms of IFN-β activation by LPS and viruses, as well as from other groups investigating the regulation of IFN-β by viral proteins and endogenous factors are described. The effects of post-translational modifications of the interferon regulatory factor (IRF)-3 on IFN-β induction are also highlighted. Many unanswered questions remain concerning the regulation of the type I IFN response in inflammation, especially the role of transcription factors in the modulation of inflammatory gene expression, and these questions will form the basis for exciting avenues of future research.

Apoptosis and NET formation in the pathogenesis of SLE

Systemic Lupus Erythematosus is an autoimmune disease characterized by the formation of anti-nuclear autoantibodies, particularly anti-chromatin. Although the aetiology of the disease has not yet been fully elucidated, several mechanisms have been proposed to be involved. Due to an aberrant apoptosis or decreased removal of apoptotic cells, apoptotic blebs containing chromatin are released. During apoptosis, chromatin is modified that increases its immunogenicity. Myeloid dendritic cells (myDC) can take up apoptotic blebs and stimulate autoreactive T helper cells, and subsequently the formation of autoantibodies by autoreactive B cells. Immune complexes formed by anti-chromatin autoantibodies and modified chromatin deposit on basal membranes, and incite a local inflammation, but can also stimulate plasmacytoid dendritic cells to produce IFN-α. In addition to apoptotic blebs, neutrophil extracellular traps released by dying neutrophils, in a process called NETosis, may serve as a source of autoantigens as well. In this review, we describe the role of both apoptosis and NETosis in the pathogenesis of SLE, and show how both processes may interact with each other.

Cytokine disturbances in systemic lupus erythematosus

The pathogenesis of systemic lupus erythematosus (SLE) is complex, and the resulting disease manifestations are heterogeneous. Cytokine dysregulation is pervasive, and their protein and gene expression profiles may serve as markers of disease activity and severity. Importantly, biologic agents that target specific cytokines may represent novel therapies for SLE. Four cytokines (IL-6, TNFα, IFNα, and BLyS) are being evaluated as therapeutic targets in SLE. The present review will examine the roles of each of these cytokines in murine and human SLE, and will summarize results from clinical trials of agents that target these cytokines.

IFN-α produced by human plasmacytoid dendritic cells enhances T cell-dependent naïve B cell differentiation

The development and quality of a humoral immune response are largely influenced by the environment that supports the activation of naïve B cells. Human PDCs, through their unique capacity to produce high levels of IFN-α, have been shown earlier to enhance B cell responses stimulated by selected TLR ligands. In this study, we investigated whether PDCs also promote B cell activation induced by Th cell interactions and BCR ligation. Sorted human naive CD19(+) CD27(-) B cells were activated in vitro with anti-Ig and irradiated CD4(+) T cells. Under these conditions, the presence of supernatants from TLR-stimulated PDCs increased B cell proliferation, the frequency of B cells that differentiated to CD27(high) CD38(high) cells, and secretion of IgM. Similar results were observed when the B cells were activated in the presence of purified IFN-α. In contrast, supernatants from stimulated MDCs did not augment these functions. Also, IFN-α treatment of B cells up-regulated the expression of costimulatory molecule CD86 but not CD40, CD80, MHC class II, or CD25. Although direct IFN-α exposure of T cells suppressed their proliferative capacity, IFN-α treatment of B cells led to a small increase in their capacity to induce superantigen-driven activation of autologous CD4(+) T cells. In summary, PDCs, via their production of IFN-α, may render B cells more responsive to T cell contact, which in turn, facilitates B cell proliferation and differentiation to antibody-producing cells.

Interferon-β induces apoptosis in human SH-SY5Y neuroblastoma cells through activation of JAK-STAT signaling and down-regulation of PI3K/Akt pathway

Type I interferons (IFNs) are known to cause neuropsychiatric side effects, which have been proposed to be mediated by either peripheral actions or activation of glial cells. In the present study, we have investigated whether these cytokines could act directly on neuronal cells and regulate signaling pathways involved in cell death. In human SH-SY5Y neuroblastoma cells, type I IFNs rapidly stimulated tyrosine phosphorylation of Janus kinase and signal transducer and activator of transcription (STAT) through type I IFN receptor. Prolonged exposure to IFN-β induced apoptotic cell death accompanied by cytochrome C release, cleavage of caspases 9, 7, 3 and poly-(ADP ribose) polymerase and DNA fragmentation. Janus kinase inhibition reduced IFN-β-stimulated TyK2 and STAT1 phosphorylation, STAT1 transcriptional activity, induction of double-stranded RNA-activated protein kinase (PKR) and caspase cleavage. PKR induction was associated with enhanced PKR activity and chemical inhibition of PKR reduced IFN-stimulated caspase activation. Moreover, long-term IFN-β treatment led to down-regulation of phosphatidylinositol 3-kinase/Akt signaling and IFN-β-induced apoptosis was attenuated in cells expressing constitutively active Akt. Similarly, in mouse primary neurons IFN-β induced STAT phosphorylation, caspase 3 cleavage and inhibition of Akt signaling. Thus, type I IFNs can directly impair neuronal survival by regulating multiple signaling molecules promoting the intrinsic apoptotic pathway. This effect may contribute to the cytokine neurotoxicity.

Interferon alpha in systemic lupus erythematosus

The pleiotropic cytokine interferon alpha is involved in multiple aspects of lupus etiology and pathogenesis. Interferon alpha is important under normal circumstances for antiviral responses and immune activation. However, heightened levels of serum interferon alpha and expression of interferon response genes are common in lupus patients. Lupus-associated autoantibodies can drive the production of interferon alpha and heightened levels of interferon interfere with immune regulation. Several genes in the pathways leading to interferon production or signaling are associated with risk for lupus. Clinical and cellular manifestations of excess interferon alpha in lupus combined with the genetic risk factors associated with interferon make this cytokine a rare bridge between genetic risk and phenotypic effects. Interferon alpha influences the clinical picture of lupus and may represent a therapeutic target. This paper provides an overview of the cellular, genetic, and clinical aspects of interferon alpha in lupus.

Genetic associations in type I interferon related pathways with autoimmunity

Type I interferons play an outstanding role in innate and adaptive immunity by enhancing functions of dendritic cells, inducing differentiation of monocytes, promoting immunoglobulin class switching in B cells and stimulating effector functions of T cells. The increased production of IFNα/β by plasmacytoid dendritic cells could be responsible for not only efficient antiviral defence, but it also may be a pathological factor in the development of various autoimmune disorders. The first evidence of a genetic link between type I interferons and autoimmune diseases was the observation that elevated IFNα activity is frequently detected in the sera of patients with systemic lupus erythematosus, and that this trait shows high heritability and familial aggregation in their first-degree healthy relatives. To date, a number of genes involved in interferon signalling have been associated with various autoimmune diseases. Patients with systemic lupus erythematosus, Sjögren's syndrome, dermatomyositis, psoriasis, and a fraction of patients with rheumatoid arthritis display a specific expression pattern of interferon-dependent genes in their leukocytes, termed the interferon signature. Here, in an attempt to understand the role of type I interferons in the pathogenesis of autoimmunity, we review the recent advances in the genetics of autoimmune diseases focusing on the association of genes involved in type I interferon pathways.

Role of Natural Interferon-α Producing Cells (Plasmacytoid Dendritic Cells) in Autoimmunity

The type I interferons (IFNs) have antiviral, cytostatic and prominent immunomodulatory effects, which all are of great importance during viral infections. However, prolonged exposure of the immune system to type I IFN can break tolerance and initiate an autoimmune reaction, eventually leading to autoimmune disease. Recent observations in patients with systemic lupus erythematosus (SLE) have revealed that such individuals have endogenous IFN-alpha inducers, causing an ongoing IFN-alpha production and consequently a continuous stimulation of the immune system. These IFN-alpha inducers consist of small immune complexes (IC) containing DNA or RNA and act on the principal IFN-alpha producing cell, the natural IFN-alpha producing cell (NIPC), also termed the plasmacytoid dendritic cell (PDC). The NIPC/PDC is a key cell in both the innate and adaptive immune response but can also, either directly or via produced IFN-alpha, have a pivotal role in autoimmunity. In this review we summarize recent data concerning NIPC/PDC, including their activation, regulation, function and possible role in autoimmune diseases, especially SLE.

Regulation of apoptosis by type III interferons

OBJECTIVE

Two types of interferons (IFNs), type I (IFN-alpha/beta) and type III (IFN-lambdas), utilize distinct receptor complexes to induce similar signalling and biological activities, including recently demonstrated for IFN-lambdas antitumour activity. However, ability of type III IFNs to regulate cell population growth remains largely uncharacterized.

MATERIALS AND METHODS

Intact and modified human colorectal adenocarcinoma HT29 cells were used to study regulation of apoptosis by IFN-lambdas.

RESULTS AND CONCLUSIONS

We report that the IFN-lambdaR1 chain of the type III IFN receptor complex possesses an intrinsic ability to trigger apoptosis in cells. Signalling induced through the intracellular domain of IFN-lambdaR1 resulted in G(1)/G(0) phase cell cycle arrest, phosphatidylserine surfacing and chromosomal DNA fragmentation. Caspase-3, caspase-8 and caspase-9 were activated; however, pancaspase inhibitor Z-VAD-FMK did not prevent apoptosis. In addition, the extent of apoptosis correlated with the level of receptor expression and was associated with prolonged IFN-lambda signalling. We also demonstrated that the ability to trigger apoptosis is a unique intrinsic function of all IFN receptors. However, more robust apoptosis was induced by signalling through type III IFN receptor than through type I or type II (IFN-gamma) receptors, suggesting higher cytotoxic potential of type III IFNs. In addition, we observed that IFN-gamma treatment sensitized HT29 cells to IFN-lambda-mediated apoptosis. These results provide evidence that type III IFNs, alone or in combination with other stimuli, have the potential to induce apoptosis.

Dual regulatory roles of phosphatidylinositol 3-kinase in IFN signaling

PI3K is activated by the type I and II IFN receptors, but its precise role in the generation of IFN responses is not well understood. In the present study we used embryonic fibroblasts from mice with targeted disruption of the genes encoding for both the p85alpha and p85beta regulatory subunits of PI3'-kinase (p85alpha(-/-)beta(-/-)) to precisely define the role of PI3K in the control of IFN-induced biological responses. Our data demonstrate that PI3K plays dual regulatory roles in the induction of IFN responses by controlling both IFN-alpha- and IFN-gamma-dependent transcriptional regulation of IFN-sensitive genes and simultaneously regulating the subsequent initiation of mRNA translation for such genes. These processes include the Isg15, Cxcl10, and/or Irf7 genes, whose functions are important in the generation of the biological effects of IFNs. Consistent with this, the induction of IFN antiviral responses is defective in double p85alpha/p85beta knockout cells. Thus, integration of signals via PI3K is a critical event during engagement of the IFN receptors that complements both the transcriptional activity of Jak-STAT pathways and controls initiation of mRNA translation.

Interferon-alpha prevents apoptosis of endothelial cells after short-term exposure but induces replicative senescence after continuous stimulation

Although the antiangiogenic activity of type I interferons (IFN) is well known, the mechanism by which it occurs is unclear. In the present study, we have investigated effects of short-term and long-term IFN-alpha exposure on different types of endothelial cells (EC). Short-term IFN-alpha treatment resulted in a distinct reduction of apoptosis of serum and growth factor starved HUVEC and HDMEC. This was accompanied by a strong upregulation of the IFN inducible guanylate binding protein-1 (GBP-1) whereas no consistent regulation of several known antiapoptotic proteins was evident. Stable transfection of HUVEC with an expression vector for GBP-1 mimicked the protective effect of IFN-alpha, suggesting that GBP-1 may contribute to the inhibition of apoptosis. When IFN-alpha, together with serum and EC growth factors, was present continuously a decrease of population doublings by more than 40% was observed in both HDMEC and HCAEC. In addition, the cells displayed a senescent phenotype significantly earlier than control cells and showed an increased adherence for monocytes. Our findings suggest that the antiangiogenic effect of IFN-alpha is mediated by inducing EC senescence rather than EC apoptosis. Furthermore IFN-alpha released in chronic inflammatory conditions might contribute via its prosenescent activity to the pathogenesis of atherosclerosis.

Complex Modulation of Cell Type-Specific Signaling in Response to Type I Interferons

The type I interferons (IFNs) are pleiotropic cytokines that regulate many different cellular functions. The major signaling pathway activated by type I IFNs involves sequential phosphorylation of the tyrosine residues of the Janus kinase (JAK) and signal transducers and activators of transcription (STAT) proteins, providing the primary mechanism through which gene expression is induced. Recent work has shown that the responses are quite complex, as shown by different responses to specific subtypes of type I IFN, activation of kinases in addition to JAKs, patterns of activation of all seven STATs in different cells, and activation of transcription factors other than STATs. The type I IFNs use this complexity to regulate many different biological functions in different types of cells, by activating different specific signals and patterns of gene expression.

IFN-alpha sensitizes daudi B lymphoma cells to anti-IgM induced loss of mitochondrial membrane potential through activation of c-Jun NH(2)-terminal kinase

Interferon-alpha (IFN-alpha) regulates multiple biologic functions, including antiviral activity, immune regulation, cell differentiation, and cell survival or death, in a variety of cell types. We and others have recently demonstrated that IFN-alpha induces cell death through activation of c-Jun NH(2)-terminal kinase (JNK) in human Daudi B lymphoma and U266 myeloma cells. Moreover, the IFN-alpha-induced signaling pathway has been shown to cross talk with the antigen receptor-mediated signaling cascade. In the present study, we examined whether IFN-alpha affects cell death after engagement of membrane immunoglobulin (mIg) using anti-IgM. Daudi cells pretreated with low concentrations of IFN-alpha (25 or 250 U/mL) for 24 h were stimulated with anti-IgM (1-10 microg/mL) for 24 h. The cells were assayed for JNK activation, mitochondrial membrane potential (DeltaPsim) by Western blotting, and DiOC(6) staining, respectively. The IFN-alpha-primed Daudi cells showed an increased sensitivity to subsequent stimulation with anti-IgM, as assessed by JNK activation and DeltaPsim. Moreover, Daudi cells overexpressing the constitutively active or dominant-negative form of JNK were substantially susceptible or resistant to anti-IgM-induced DeltaPsim, respectively, compared with cells overexpressing the control vector alone. Taken together, these results indicate that IFN-alpha renders Daudi B lymphoma cells susceptible to anti-IgM-induced apoptosis, probably through upregulation of JNK activation.

Alternative signaling pathways regulating type I interferon-induced apoptosis

Type I interferons (IFNs) are pleiotropic cytokines that exert multiple effects on normal and tumor cells. These effects are supposedly mediated through the stimulation of several signal transduction pathways by type I IFNs. These include the well-studied canonical Jak-Stat pathway, largely responsible for the antiviral and growth-inhibitory activities of IFNs, as well as the phosphatidylinositol 3-kinase (PI3K) and mitogen-activated protein kinase (MAPK) pathways, whose importance in IFN-induced biologic outcomes has not been precisely established. One of the effects of type I IFNs on tumor cells is the induction of programmed cell death, apoptosis, which has been studied extensively over the last decade and has been suggested to be an important effector mechanism for IFN's antitumor effects in the treatment of cancer. The aim of this review is to summarize and discuss the recent data in the field of type I IFN-induced apoptosis, with special emphasis on the molecular mechanisms of apoptosis and on the role of alternative noncanonical signaling pathways stimulated by type I IFNs in this process.

Cutting Edge: Enhancement of Antibody Responses Through Direct Stimulation of B and T Cells by Type I IFN

Type I IFN (IFN-alphabeta) is induced rapidly by infection and plays a key role in innate antiviral defense. IFN-alphabeta also exerts stimulatory effects on the adaptive immune system and has been shown to enhance Ab and T cell responses. We have investigated the importance of B and T cells as direct targets of IFN-alphabeta during IFN-alpha-mediated augmentation of the Ab response against a soluble protein Ag. Strikingly, the ability of IFN-alpha to stimulate the Ab response and induce isotype switching was markedly reduced in mice in which B cells were selectively deficient for the IFN-alphabetaR. Moreover, IFN-alpha-mediated enhancement of the Ab response was also greatly impaired in mice in which T cells were selectively IFN-alphabetaR-deficient. These results indicate that IFN-alphabetaR signaling in both B and T cells plays an important role in the stimulation of Ab responses by IFN-alphabeta.

The PI3' Kinase Pathway in Interferon Signaling

Interferons (IFNs) are pleiotropic cytokines with important immunomodulatory, antitumor, antiviral, and growth inhibitory properties. Consistent with the multiplicity of their effects, the IFNs activate several cellular cascades after they bind to their receptors. Although the Jak-Stat pathway is the most studied pathway, it appears that additional signaling cascades play roles in IFN signaling. The phosphatidylinositol 3'-kinase (PI3'K) pathway has emerged as one of the critical players in IFN signal transduction and is the focus of this review. This pathway is activated distinctively from the Stat pathway but plays important roles in the regulation of IFN-dependent gene transcription and initiation of mRNA translation.

Uncoupled anti-HIV and immune-enhancing effects when combining IFN-alpha and IL-7

Cytokine-based therapies have been examined for purging viral reservoirs and immunomodulation in HIV infection. However, single cytokines did not result in either HIV eradication or an efficient HIV-specific immune response. We hypothesize that cytokines with distinct biologic effects need to be combined for immunotherapy of HIV infection. In this study, we investigated the anti-HIV activity and immune-enhancing effects of the combination of IFN-alpha and IL-7. In human lymphocyte aggregate cultures infected ex vivo with the X4 HIV strain NL4-3, IFN-alpha/IL-7 potently inhibited HIV replication and preserved CD4(+) T cells, probably by up-regulating Bcl-2. IFN-alpha/IL-7 also strongly inhibited R5 HIV replication. Furthermore, in allogeneic MLRs, IFN-alpha/IL-7 increased T cell proliferation and IFN-gamma production. IFN-alpha alone also had strong anti-HIV activity, but neither preserved CD4(+) T cells nor increased T cell responses in MLRs. IL-7 alone maintained T cells and enhanced T cell activation in MLRs, but only moderately inhibited or increased HIV replication. Thus, coadministration of IFN-alpha/IL-7 combines the potent anti-HIV activity of IFN-alpha with the beneficial effects of IL-7 on T cell survival and function. We speculate that IFN-alpha will block viral replication, activate APCs, and up-regulate MHC molecules, thus allowing IL-7 to display its effects for generating an efficient immune response. In this scenario, the known reactivation of latent HIV by IL-7 may be advantageous.

Alpha/beta interferon protects against lethal West Nile virus infection by restricting cellular tropism and enhancing neuronal survival

West Nile virus (WNV) is a mosquito-borne flavivirus that is neurotropic in humans, birds, and other animals. While adaptive immunity plays an important role in preventing WNV spread to the central nervous system (CNS), little is known about how alpha/beta interferon (IFN-alpha/beta) protects against peripheral and CNS infection. In this study, we examine the virulence and tropism of WNV in IFN-alpha/beta receptor-deficient (IFN- alpha/betaR-/-) mice and primary neuronal cultures. IFN-alpha/betaR-/- mice were acutely susceptible to WNV infection through subcutaneous inoculation, with 100% mortality and a mean time to death (MTD) of 4.6 +/- 0.7 and 3.8+/- 0.5 days after infection with 10(0) and 10(2) PFU, respectively. In contrast, congenic wild-type 129Sv/Ev mice infected with 10(2) PFU showed 62% mortality and a MTD of 11.9 +/- 1.9 days. IFN-alpha/betaR-/- mice developed high viral loads by day 3 after infection in nearly all tissues assayed, including many that were not infected in wild-type mice. IFN-alpha/betaR-/- mice also demonstrated altered cellular tropism, with increased infection in macrophages, B cells, and T cells in the spleen. Additionally, treatment of primary wild-type neurons in vitro with IFN-beta either before or after infection increased neuronal survival independent of its effect on WNV replication. Collectively, our data suggest that IFN-alpha/beta controls WNV infection by restricting tropism and viral burden and by preventing death of infected neurons.

Requirement of c-Jun NH2-terminal kinase activation in interferon-α-induced apoptosis through upregulation of tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) in Daudi B lymphoma cells

Interferon alpha (IFN-alpha) inhibits growth, at least in part, through induction of apoptosis. However, the molecular mechanisms underlying IFN-alpha-induced apoptosis are not completely understood. In the present study, we found that IFN-alpha induced a sustained activation of c-Jun N-terminal kinase 1 (JNK1), but not extracellular kinases (ERKs), in Daudi B lymphoma cells, as assessed by Western blotting using phospho-specific antibodies. Several lines of evidence support the notion that the IFN-alpha-induced activation of JNK is responsible for IFN-alpha-induced apoptosis, at least in part, through upregulation of TNF-related apoptosis-inducing ligand (TRAIL). First, pretreatment of Daudi cells with a JNK inhibitor reduced IFN-alpha-induced upregulation of TRAIL and loss of mitochondrial membrane potential (DeltaPsim) and annexin-positive cells, which was assessed by flow cytometry. Second, a dominant-negative form of JNK1 (dnJNK1) also reduced these apoptotic events, while a constitutively active form of JNK1, MKK7-JNK1beta, enhanced them. Finally, treatment with IFN-alpha enhanced the promoter activity of the TRAIL gene, which was partially abrogated by either JNK inhibitor or dnJNK1, while it was moderately enhanced by MKK7-JNK1beta. These findings are useful for understanding molecular mechanisms of IFN-alpha-induced apoptosis and also for development of treatment modalities of some tumors with IFN-alpha.

Mechanisms of type-I- and type-II-interferon-mediated signalling

Interferons are cytokines that have antiviral, antiproliferative and immunomodulatory effects. Because of these important properties, in the past two decades, major research efforts have been undertaken to understand the signalling mechanisms through which these cytokines induce their effects. Since the original discovery of the classical JAK (Janus activated kinase)-STAT (signal transducer and activator of transcription) pathway of signalling, it has become clear that the coordination and cooperation of multiple distinct signalling cascades - including the mitogen-activated protein kinase p38 cascade and the phosphatidylinositol 3-kinase cascade - are required for the generation of responses to interferons. It is anticipated that an increased understanding of the contributions of these recently identified pathways will advance our current thinking about how interferons work.

Expansion of bone marrow IFN-alpha-producing dendritic cells in New Zealand Black (NZB) mice: high level expression of TLR9 and secretion of IFN-alpha in NZB bone marrow

Patients with systemic lupus erythematosus have elevated IFN-alpha production. Furthermore, sera IFN-alpha levels correlate with disease activity. We have focused our attention on whether this phenotype is also seen in the New Zealand Black (NZB) mice and simultaneously addressed the underlying mechanisms. Specifically, we analyzed: 1) levels of sera IFN-alpha after type A CpG ODN 2216 injection in autoimmunity-prone NZB and control mice, and 2) levels of IFN-alpha synthesized by IFN-alpha-producing dendritic cells (IPDCs) using highly enriched populations of CD11c+B220+ IPDCs derived from NZB and control mice; IPDCs are divided into two subpopulations (CD4+CD11c+B220+ and CD4-CD11c+B220+). Our data demonstrate that NZB mice produced higher levels of sera IFN-alpha after type A CpG ODN 2216 injection when compared with control mice (p < 0.01). In addition, the cell numbers, frequency, and TLR9 mRNA levels of CD4+ and CD4- IPDC were markedly increased in the bone marrow (BM) of NZB mice. Upon in vitro stimulation with TLR9 ligand-CpG ODN 2216, higher levels of IFN-alpha were synthesized by IPDCs from the BM of NZB. The major contributor of IFN-alpha was the CD4-CD11c+B220+ IPDC subpopulation. Furthermore, NZB BM IPDCs manifest impaired expression of homing chemokine CCR7 and CD62L, and IL-12 production. These data on the functional characteristics of the IPDC lineages explain in part the mechanism of hyper-IFN-alpha production and help clarify the mechanism for the expansion of NZB BM IPDCs.

A dual role of IFN-alpha in the balance between proliferation and death of human CD4+ T lymphocytes during primary response

Type I IFNs (IFN-alphabeta) enhance immune responses, notably T cell-mediated responses, in part by promoting the functional activities of dendritic cells. In this study, we analyzed the direct impact of IFN-alpha on proliferative and apoptotic signals upon in vitro activation of human naive CD4+ T lymphocytes. We demonstrate that IFN-alpha protects T cells from the intrinsic mitochondrial-dependent apoptosis early upon TCR/CD28 activation. IFN-alpha acts by delaying entry of cells into the G1 phase of the cell cycle, as well as by increasing Bcl-2 and limiting Bax activation. Later, upon activation, T cells that were exposed to IFN-alpha showed increased levels of surface Fas associated with partially processed caspase-8, a key component of the extrinsic apoptotic pathway. Caspase-8 processing was augmented furthermore by Fas ligation. Overall, these findings support a model whereby IFN-alpha favors an enhanced clonal expansion, yet it sensitizes cells to the Ag-induced cell death occurring at the end of an immune response. These observations point to a complex role of type I IFN in regulating the magnitude of proliferation and survival of naive CD4+ T cells during primary response and underline how crucial could be the timing of exposure to this cytokine.

Reciprocal control of Forkhead box O 3a and c-Myc via the phosphatidylinositol 3-kinase pathway coordinately regulates p27Kip1 levels

B cell receptor (BCR) engagement of murine WEHI 231 immature B lymphoma cells leads sequentially to a drop in NF-kappa B and c-Myc, and induction of the p27(Kip1) cyclin-dependent kinase inhibitor, which promotes growth arrest and apoptosis. BCR engagement was recently shown to induce a drop in phosphatidylinositol 3-kinase (PI3K)/Akt signaling, preceding the increase in p27. As induction of p27 is due to an increase in gene transcription, we investigated the role of the Forkhead box O (FOXO) transcription factor family, which has been shown to potently induce p27 promoter activity. We demonstrate that pharmacologic inhibitors of PI3K or BCR engagement lead to decreased inactive cytoplasmic levels and increased active functional nuclear FOXO3a. In contrast, inhibition of PI3K/Akt signaling decreased the levels of NF-kappa B and c-Myc, which has been shown to repress p27 promoter activity. To test the effects of ectopic c-Myc on endogenous p27 levels, WEHI 231 cells stably expressing c-Myc or empty vector DNA were prepared. Ectopic c-Myc blocked the induction of p27 expression upon either inhibition of PI3K or BCR engagement. Thus, p27(Kip1) is coordinately regulated via two arms of a signaling pathway that are inversely controlled upon inhibition of PI3K: induction of the activator FOXO3a and down-regulation of the repressor c-Myc.

Induction of interferon-alpha production in plasmacytoid dendritic cells by immune complexes containing nucleic acid released by necrotic or late apoptotic cells and lupus IgG

OBJECTIVE

To investigate the release of interferon-alpha (IFN alpha)-inducing material by necrotic or apoptotic cells, its properties, and the necessity of autoantibodies from systemic lupus erythematosus (SLE) patients for the interferogenic activity.

METHODS

U937 monocytic leukemia cells or peripheral blood mononuclear cells (PBMCs) were rendered necrotic by freeze-thawing or apoptotic by treatment with ultraviolet light. Cell culture supernatants from these cells and IgG from SLE patients (SLE IgG) were added to cultures of normal PBMCs or purified plasmacytoid dendritic cells (PDCs). The importance of nucleic acids for IFN alpha induction was investigated by RNase and DNase treatment. The IFN alpha levels were measured by immunoassay.

RESULTS

Both necrotic and apoptotic U937 cells released material that, combined with SLE IgG, induced IFN alpha production in PDCs. The release from apoptotic cells occurred with a 16-hour delay, in late apoptosis. Also, normal PBMCs released IFN alpha-inducing material, but only during necrosis. The interferogenic activity of the necrotic material required the presence of RNA, while both RNA and DNA were important in the apoptotic material. In both cases, the presence of SLE IgG was necessary, and its activity correlated with the presence of antibodies to RNA-binding proteins, but not anti-DNA antibodies.

CONCLUSION

Necrotic and late apoptotic cells release material that, combined with SLE IgG, induces production of IFN alpha in PDCs. The IFN alpha inducers probably consist of immune complexes (ICs) containing RNA and possibly DNA as essential interferogenic components. The presence of such interferogenic ICs could explain the ongoing production of IFN alpha in SLE and could be of etiopathogenic importance.

Apoptosis of human primary B lymphocytes is inhibited by N-acetyl-L-cysteine

Thiols are important molecules to control apoptosis. This study examined the effect of N-acetyl-L-cysteine (NAC) on in vitro spontaneous apoptosis of human tonsillar B lymphocytes (TBL). Results show that NAC inhibits TBL apoptosis and maintains their survival in vitro. The antiapoptotic action of NAC is progressively reduced when its addition to culture is delayed, is reversible, and is not blocked by cycloheximide. The antiapoptotic activity of NAC is associated with its ability to inhibit caspase-3 and -7 proteolytic processing, DNA-fragmentation factor 45 cleavage, and DNA fragmentation. Furthermore, NAC inhibits BID cleavage and cytochrome c release from mitochondria and increases the expression of Bcl-2 and Bcl(XL) survival proteins. However, it has no effect on caspase-9 cleavage and increases that of caspase-8 and poly(adenosine 5'-diphosphate-ribose)polymerase. We conclude that NAC-induced inhibition of TBL apoptosis is associated with inhibition of caspase-3 and -7 processing and is accompanied by changes in several regulatory components of the apoptotic process. These results pose the question of whether microenvironment thiols may in part contribute to in vivo B cell survival.

Alternate interferon signaling pathways

More than a half a century ago, interferons (IFN) were identified as antiviral cytokines. Since that discovery, IFN have been in the forefront of basic and clinical cytokine research. The pleiotropic nature of these cytokines continues to engage a large number of investigators to define their actions further. IFN paved the way for discovery of Janus tyrosine kinase (JAK)-signal transducing activators of transcription (STAT) pathways. A number of important tumor suppressive pathways are controlled by IFN. Several infectious pathogens counteract IFN-induced signaling pathways. Recent studies indicate that IFN activate several new protein kinases, including the MAP kinase family, and downstream transcription factors. This review not only details the established IFN signaling paradigms but also provides insights into emerging alternate signaling pathways and mechanisms of pathogen-induced signaling interference.

Expression of the markers BDCA-2 and BDCA-4 and production of interferon-alpha by plasmacytoid dendritic cells in systemic lupus erythematosus

OBJECTIVE

To study the expression of blood dendritic cell antigen 2 (BDCA-2) and BDCA-4 molecules by plasmacytoid dendritic cells (PDCs) in the blood of patients with systemic lupus erythematosus (SLE), and to study PDC production of interferon-alpha (IFN alpha) and its inhibition by anti-BDCA-2 and anti-BDCA-4 antibodies.

METHODS

Peripheral blood mononuclear cells (PBMCs) from SLE patients (SLE PBMCs) and from healthy controls were induced to produce IFN alpha in vitro by SLE serum containing an endogenous IFN alpha-inducing factor (SLE-IIF) or by herpes simplex virus type 1 (HSV-1). The frequencies and numbers of BDCA-2-, BDCA-3-, and BDCA-4-expressing cells were analyzed by flow cytometry, and the effects of anti-BDCA-2 and anti-BDCA-4 monoclonal antibodies (mAb) on IFN alpha production were investigated.

RESULTS

IFN alpha production by SLE PBMCs induced by SLE-IIF or HSV-1 was decreased compared with that of healthy control PBMCs (P = 0.002 and P = 0.0007, respectively). The proportions of BDCA-2- and BDCA-3-expressing cells in SLE PBMCs were reduced compared with those in PBMCs from healthy controls (P = 0.01 and P = 0.004, respectively). IFN alpha producers in culture, especially among SLE PBMCs, displayed reduced BDCA-2 expression and constituted only a minority of the BDCA-2-positive cells, at least in healthy control PBMCs (median 18%). IFN alpha production by both SLE and healthy control PBMCs stimulated by SLE-IIF or HSV-1 was markedly reduced by anti-BDCA-2 mAb (median 81-98% inhibition). Anti-BDCA-4 mAb only partially inhibited SLE-IIF-induced IFN alpha production.

CONCLUSION

SLE patients had a reduced number of BDCA-2-expressing PDCs, also termed natural IFN alpha-producing cells, and their IFN alpha production could be inhibited by anti-BDCA-2/4 mAb. Such mAb may be a therapeutic option for inhibiting the ongoing IFN alpha production in SLE patients.

Interferons and apoptosis

The interferons (IFNs), in addition to their well-known antiviral activities, have important roles in the control of cell proliferation and are effective agents for the treatment of a limited number of malignant diseases. IFNs not only regulate cell growth and division but also influence cell survival through their effects on apoptosis. This review describes the current state of knowledge about the mechanisms of action of these cytokines on the apoptotic machinery, with particular emphasis on the synergism that exists between the IFNs and other proapoptotic agents, such as members of the tumor necrosis factor (TNF) family. The review also discusses the physiologic and clinical implications of the effects of the IFNs on apoptosis for regulation of viral infection and tumor growth.

Systemic lupus erythematosus and the type I interferon system

Patients with systemic lupus erythematosus (SLE) have ongoing interferon-alpha (IFN-alpha) production and serum IFN-alpha levels are correlated with both disease activity and severity. Recent studies of patients with SLE have demonstrated the presence of endogenous IFN-alpha inducers in such individuals, consisting of small immune complexes (ICs) containing IgG and DNA. These ICs act specifically on natural IFN-alpha-producing cells (NIPCs), often termed plasmacytoid dendritic cells (PDCs). Given the fact that the NIPC/PDC has a key role in both the innate and adaptive immune response, as well as the many immunoregulatory effects of IFN-alpha, these observations might be important for the understanding of the etiopathogenesis of SLE. In this review we briefly describe the biology of the type I IFN system, with emphasis on inducers, producing cells (especially NIPCs/PDCs), IFN-alpha actions and target immune cells that might be relevant in SLE. On the basis of this information and results from studies in SLE patients, we propose a hypothesis that explains how NIPCs/PDCs become activated and have a pivotal etiopathogenic role in SLE. This hypothesis also indicates new therapeutic targets in this autoimmune disease.