Cutting edge: a T-bet-independent role for IFN-alpha/beta in regulating IL-2 secretion in human CD4+ central memory T cells

Homeostasis of Naive and Memory T Lymphocytes

Conventional CD4+ and CD8+ T lymphocytes comprise a mixture of naive and memory cells. Generation and survival of these T-cell subsets is under strict homeostatic control and reflects contact with self-major histocompatibility complex (MHC) and certain cytokines. Naive T cells arise in the thymus via T-cell receptor (TCR)-dependent positive selection to self-peptide/MHC complexes and are then maintained in the periphery through self-MHC interaction plus stimulation via interleukin-7 (IL-7). By contrast, memory T cells are largely MHC-independent for their survival but depend strongly on stimulation via cytokines. Whereas typical memory T cells are generated in response to foreign antigens, some arise spontaneously through contact of naive precursors with self-MHC ligands; we refer to these cells as memory-phenotype (MP) T cells. In this review, we discuss the generation and homeostasis of naive T cells and these two types of memory T cells, focusing on their relative interaction with MHC ligands and cytokines.

Relationship Between T-Cell Exosomes and Cellular Subsets in SLE According to Type I IFN-Signaling

Objective: To quantify the levels of circulating exosomes derived from T-cells and monocytes and their possible associations with leukocyte subpopulations and cytokine milieu in Systemic Lupus Erythematosus (SLE).

Methods: Total circulating exosomes (CD9⁺-Ex) and those derived from T-cells (CD3⁺-Ex) and monocytes (CD14⁺-Ex) were quantified by flow cytometry in 82 SLE patients and 32 controls. Leukocyte subsets and serum cytokines were analyzed by flow cytometry or by immunoassays. IFN-score was evaluated by real time RT-PCR in whole blood samples from a subgroup of 73 patients and 24 controls.

Results: Activation markers (IFNR1 and BLyS) on monocytes, neutrophils and B-cells correlated inversely with circulating exosomes (CD9⁺-Ex, CD3⁺-Ex, and CD14⁺-Ex) in controls but directly with CD3⁺-Ex in patients (all p < 0.05). Although CD9⁺-Ex were increased in SLE, no differences were found in CD3⁺-Ex, supporting that exosome content accounts for this opposite role. Interestingly, CD4⁺CD28^null cells correlated with CD3⁺-Ex in patients and controls, and displayed similar associations with leukocyte subsets in both groups. Additionally, CD3⁺-Ex correlated in patients with the expression of CD25 in CD4⁺CD28^null cells. Furthermore, the activated status of this senescent subset was related to IFNα serum levels in controls and to IFN-score in SLE patients. Finally, patients presenting high IFN-score, in addition to elevated CD25⁺CD28^null cells associated with the activation of myeloid cells, displayed higher levels of inflammatory cytokines and chemokines.

Conclusion: Our results support a relationship between T-cell exosomes and cellular subsets in SLE according to type I IFN-signaling, which could amplify chronic immune activation and excessive cytokine/chemokine response.

Immune response modulation upon sequential heterogeneous co-infection with Tetracapsuloides bryosalmonae and VHSV in brown trout (Salmo trutta)

Simultaneous and sequential infections often occur in wild and farming environments. Despite growing awareness, co-infection studies are still very limited, mainly to a few well-established human models. European salmonids are susceptible to both Proliferative Kidney Disease (PKD), an endemic emergent disease caused by the myxozoan parasite Tetracapsuloides bryosalmonae, and Viral Haemorrhagic Septicaemia (VHS), an OIE notifiable listed disease caused by the Piscine Novirhabdovirus. No information is available as to how their immune system reacts when interacting with heterogeneous infections. A chronic (PKD) + acute (VHS) sequential co-infection model was established to assess if the responses elicited in co-infected fish are modulated, when compared to fish with single infections. Macro- and microscopic lesions were assessed after the challenge, and infection status confirmed by RT-qPCR analysis, enabling the identification of singly-infected and co-infected fish. A typical histophlogosis associated with histozoic extrasporogonic T. bryosalmonae was detected together with acute inflammation, haemorrhaging and necrosis due to the viral infection. The host immune response was measured in terms of key marker genes expression in kidney tissues. During T. bryosalmonae/VHSV-Ia co-infection, modulation of pro-inflammatory and antimicrobial peptide genes was strongly influenced by the viral infection, with a protracted inflammatory status, perhaps representing a negative side effect in these fish. Earlier activation of the cellular and humoral responses was detected in co-infected fish, with a more pronounced upregulation of Th1 and antiviral marker genes. These results reveal that some brown trout immune responses are enhanced or prolonged during PKD/VHS co-infection, relative to single infection.

An activating mutation of interferon regulatory factor 4 (IRF4) in adult T-cell leukemia

The human T-cell leukemia virus-1 (HTLV-1) oncoprotein Tax drives cell proliferation and resistance to apoptosis early in the pathogenesis of adult T-cell leukemia (ATL). Subsequently, probably as a result of specific immunoediting, Tax expression is down-regulated and functionally replaced by somatic driver mutations of the host genome. Both amplification and point mutations of interferon regulatory factor 4 (IRF4) have been previously detected in ATL., K59R is the most common single-nucleotide variation of IRF4 and is found exclusively in ATL. High-throughput whole-exome sequencing revealed recurrent activating genetic alterations in the T-cell receptor, CD28, and NF-κB pathways. We found that IRF4, which is transcriptionally activated downstream of these pathways, is frequently mutated in ATL. IRF4 RNA, protein, and IRF4 transcriptional targets are uniformly elevated in HTLV-1-transformed cells and ATL cell lines, and IRF4 was bound to genomic regulatory DNA of many of these transcriptional targets in HTLV-1-transformed cell lines. We further noted that the K59R IRF4 mutant is expressed at higher levels in the nucleus than WT IRF4 and is transcriptionally more active. Expression of both WT and the K59R mutant of IRF4 from a constitutive promoter in retrovirally transduced murine bone marrow cells increased the abundance of T lymphocytes but not myeloid cells or B lymphocytes in mice. IRF4 may represent a therapeutic target in ATL because ATL cells select for a mutant of IRF4 with higher nuclear expression and transcriptional activity, and overexpression of IRF4 induces the expansion of T lymphocytes in vivo.

STAT4-mediated transcriptional repression of the IL5 gene in human memory Th2 cells

Type I interferon (IFN-α/β) plays a critical role in suppressing viral replication by driving the transcription of hundreds of interferon-sensitive genes (ISGs). While many ISGs are transcriptionally activated by the ISGF3 complex, the significance of other signaling intermediates in IFN-α/β-mediated gene regulation remains elusive, particularly in rare cases of gene silencing. In human Th2 cells, IFN-α/β signaling suppressed IL5 and IL13 mRNA expression during recall responses to T-cell receptor (TCR) activation. This suppression occurred through a rapid reduction in the rate of nascent transcription, independent of de novo expression of ISGs. Further, IFN-α/β-mediated STAT4 activation was required for repressing the human IL5 gene, and disrupting STAT4 dimerization reversed this effect. This is the first demonstration of STAT4 acting as a transcriptional repressor in response to IFN-α/β signaling and highlights the unique activity of this cytokine to acutely block the expression of an inflammatory cytokine in human T cells.

Activated T cells enhance interferon-α production by plasmacytoid dendritic cells stimulated with RNA-containing immune complexes

OBJECTIVES

Patients with systemic lupus erythematosus (SLE) have an ongoing interferon-α (IFN-α) production by plasmacytoid dendritic cells (pDCs). We investigated whether T cells can promote IFN-α production by pDCs.

METHODS

Human pDCs were stimulated with immune complexes (ICs) containing U1 small nuclear ribonucleic proteins particles and SLE-IgG (RNA-IC) in the presence of T cells or T cell supernatants. T cells were activated by anti-CD3/CD28 antibodies or in a mixed leucocyte reaction. IFN-α and other cytokines were determined in culture supernatants or patient sera with immunoassays. The effect of interleukin (IL) 3 and granulocyte-macrophage-colony-stimulating factor (GM-CSF) on pDCs was examined by the use of antibodies, and the expression of CD80/CD86 was determined using flow cytometry.

RESULTS

Activated T cells and supernatants from activated T cells increased IFN-α production by >20-fold. The stimulatory effect of T cell supernatants was reduced after depletion of GM-CSF (81%) or by blocking the GM-CSF receptor (55%-81%). Supernatant from activated T cells, furthermore, increased the frequency of CD80 and CD86 expressing pDCs stimulated with RNA-IC from 6% to 35% (p<0.05) and from 10% to 26% (p<0.01), respectively. Activated SLE T cells enhanced IFN-α production to the same extent as T cells from healthy individuals and a subset of patients with SLE had increased serum levels of GM-CSF.

CONCLUSIONS

Activated T cells enhance IFN-α production by RNA-IC stimulated pDCs via GM-CSF and induce pDC maturation. Given the increased serum levels of GM-CSF in a subset of patients with SLE, these findings suggest that activated T cells may upregulate type I IFN production in SLE.

CpG ODN nanorings induce IFNα from plasmacytoid dendritic cells and demonstrate potent vaccine adjuvant activity

CpG oligodeoxynucleotides (ODN) are short single-stranded synthetic DNA molecules that activate the immune system and have been found to be effective for preventing and treating infectious diseases, allergies, and cancers. Structurally distinct classes of synthetic ODN expressing CpG motifs differentially activate human immune cells. K-type ODN (K-ODN), which have progressed into human clinical trials as vaccine adjuvants and immunotherapeutic agents, are strong activators of B cells and trigger plasmacytoid dendritic cells (pDCs) to differentiate and produce tumor necrosis factor-α (TNFα). In contrast, D-type ODN (D-ODN) stimulate large amounts of interferon-α (IFNα) secretion from pDCs. This activity depends on the ability of D-ODN to adopt nanometer-sized G quadruplex-based structures, complicating their manufacturing and hampering their progress into the clinic. In search of a D-ODN substitute, we attempted to multimerize K-ODN into stable nanostructures using cationic peptides. We show that short ODN with a rigid secondary structure form nuclease-resistant nanorings after condensation with the HIV-derived peptide Tat(47-57). The nanorings enhanced cellular internalization, targeted the ODN to early endosomes, and induced a robust IFNα response from human pDCs. Compared to the conventional K-ODN, nanorings boosted T helper 1-mediated immune responses in mice immunized with the inactivated foot and mouth disease virus vaccine and generated superior antitumor immunity when used as a therapeutic tumor vaccine adjuvant in C57BL/6 mice bearing ovalbumin-expressing EG.7 thymoma tumors. These results suggest that the nanorings can act as D-ODN surrogates and may find a niche for further clinical applications.

Interferon and interferon-inducible gene activation in patients with type 1 diabetes

Type 1 diabetes (T1D) is an autoimmune disease that is thought to be triggered by environmental factors in genetically susceptible individuals. Enteroviruses have been mentioned as the most probable induction component of the disease. Nevertheless, the literature is controversial regarding the association of T1D with viral infection and first-line antiviral defence components, for example type I interferons (IFNs). Our aim was to test the hypothesis that an abnormality in IFN-stimulated gene patterns may cause a failure in immunological tolerance and, thereby, initiate T1D as an autoimmune disorder. We studied material from 64 T1D and 36 control subjects, divided into two age groups: <10 years and ≥10 years old. Using a relative gene expression method, we observed a lower expression of interferon-induced helicase 1 (IFIH1) and other type I IFN-induced genes in the blood cells of T1D subjects, especially subjects under 10 years old, in spite of their higher IFN levels as measured by the pSTAT1-inducing capacity of their sera. Likewise, freshly purified CpG-stimulated cells from T1D patients showed significantly lower upregulation of IFN-induced genes, that is IFIH1 and CXCL10, compared to cells from the control group. The identified dysregulation in the IFN-α-induced antiviral response in T1D patients, especially in early childhood, could be one of the factors affecting T1D development.

IFN-α suppresses GATA3 transcription from a distal exon and promotes H3K27 trimethylation of the CNS-1 enhancer in human Th2 cells

CD4(+) Th2 development is regulated by the zinc finger transcription factor GATA3. Once induced by acute priming signals, such as IL-4, GATA3 poises the Th2 cytokine locus for rapid activation and establishes a positive-feedback loop that maintains elevated GATA3 expression. Type I IFN (IFN-α/β) inhibits Th2 cells by blocking the expression of GATA3 during Th2 development and in fully committed Th2 cells. In this study, we uncovered a unique mechanism by which IFN-α/β signaling represses the GATA3 gene in human Th2 cells. IFN-α/β suppressed expression of GATA3 mRNA that was transcribed from an alternative distal upstream exon (1A). This suppression was not mediated through DNA methylation, but rather by histone modifications localized to a conserved noncoding sequence (CNS-1) upstream of exon 1A. IFN-α/β treatment led to a closed conformation of CNS-1, as assessed by DNase I hypersensitivity, along with enhanced accumulation of H3K27me3 mark at this CNS region, which correlated with increased density of total nucleosomes at this putative enhancer. Consequently, accessibility of CNS-1 to GATA3 DNA binding activity was reduced in response to IFN-α/β signaling, even in the presence of IL-4. Thus, IFN-α/β disrupts the GATA3-autoactivation loop and promotes epigenetic silencing of a Th2-specific regulatory region within the GATA3 gene.

Type I IFN-mediated regulation of IL-1 production in inflammatory disorders

Although contributing to inflammatory responses and to the development of certain autoimmune pathologies, type I interferons (IFNs) are used for the treatment of viral, malignant, and even inflammatory diseases. Interleukin-1 (IL-1) is a strongly pyrogenic cytokine and its importance in the development of several inflammatory diseases is clearly established. While the therapeutic use of IL-1 blocking agents is particularly successful in the treatment of innate-driven inflammatory disorders, IFN treatment has mostly been appreciated in the management of multiple sclerosis. Interestingly, type I IFNs exert multifaceted immunomodulatory effects, including the reduction of IL-1 production, an outcome that could contribute to its efficacy in the treatment of inflammatory diseases. In this review, we summarize the current knowledge on IL-1 and IFN effects in different inflammatory disorders, the influence of IFNs on IL-1 production, and discuss possible therapeutic avenues based on these observations.

IKZF1: a critical role in the pathogenesis of systemic lupus erythematosus?

Ikaros family zinc finger 1, encoded by IKZF1, are lymphoid-restricted zinc finger transcription factors that share common N-terminal Kruppel-like zinc finger DNA-binding domain. IKZF1 play multiple important roles on regulators of lymphocyte differentiation and hematological tumor suppressor. Our genome-wide association (GWA) studies in systemic lupus erythematosus (SLE) independently identified genetic variants in IKZF1 associated with SLE, which are supported by other studies. Previous studies found that lower expression of IKZF1 may play critical roles in activating some signal pathways involved in SLE, such as signal transducers and activators of transcription (STAT)4 and interferon pathways. In addition, IKZF1 has been implicated in roles involved in some hematologic traits or abnormalities, such as erythrocyte measures, myelofibrosis, and acute lymphoblastic leukemia (ALL), which may be common clinical manifestations or co-occurrence hematological diseases of patients with SLE. All these findings suggest that IKZF1 may play a critical role in the pathogenesis of SLE. In this article, we discuss the existing understanding of the role of IKZF1 on the physiological and pathological functions associated with SLE, providing insights that may assist in the development of new therapeutic strategies based on IKZF1 for patients with SLE.

Modulation of T-cell function by type I interferon

Production of type I interferon (IFN-α/β) is a common cellular response to virus infection. IFN-α/β has a dual role in combating infection, triggering innate antiviral mechanisms and stimulating the generation of an adaptive immune response. This review focuses on the effects of IFN-α/β on one particular immune cell type, the T cell, and the impact of IFN-α/β-mediated signalling in T cells on the immune response. The critical role of T-cell responsiveness to IFN-α/β for the generation of productive T-cell responses after infections with certain viruses in vivo is discussed in the context of in vitro experiments investigating the mechanisms by which IFN-α/β modifies T-cell function. These studies reveal complex effects of IFN-α/β on T cells, with the consequences of exposure to IFN-α/β depending on the context of other signals received by the T cell.

Type I IFN-dependent T cell activation is mediated by IFN-dependent dendritic cell OX40 ligand expression and is independent of T cell IFNR expression

Type I IFNs are important for direct control of viral infection and generation of adaptive immune responses. Recently, direct stimulation of CD4(+) T cells via type I IFNR has been shown to be necessary for the formation of functional CD4(+) T cell responses. In contrast, we find that CD4(+) T cells do not require intrinsic type I IFN signals in response to combined TLR/anti-CD40 vaccination. Rather, the CD4 response is dependent on the expression of type I IFNR (IFNαR) on innate cells. Further, we find that dendritic cell (DC) expression of the TNF superfamily member OX40 ligand was dependent on type I IFN signaling in the DC, resulting in a reduced CD4(+) T cell response that could be substantially rescued by an agonistic Ab to the receptor OX40. Taken together, we show that the IFNαR dependence of the CD4(+) T cell response is accounted for exclusively by defects in DC activation.

The type I interferon system in the etiopathogenesis of autoimmune diseases

Many patients with systemic autoimmune diseases have signs of a continuous production of type I interferon (IFN) and display an increased expression of IFN-α-regulated genes. The reason for the on-going IFN-α synthesis in these patients seems to be an activation of plasmacytoid dendritic cells (pDCs) by immune complexes (ICs), consisting of autoantibodies in combination with DNA or RNA-containing autoantigens. Such interferogenic ICs are internalized via the FcγRIIa expressed on pDCs, reach the endosome, and stimulate Toll-like receptor (TLR)-7 or -9, which subsequently leads to IFN-α gene transcription. Variants of genes involved in both the IFN-α synthesis and response have been linked to an increased risk to develop systemic lupus erythematosus (SLE) and other autoimmune diseases. Among these autoimmunity risk genes are IFN regulatory factor 5 (IRF5), which is involved in TLR signaling, and the signal transducer and activator of transcription 4 (STAT4) that interacts with the type I IFN receptor. Several other gene variants in the IFN signaling pathway also confer an increased risk to develop an autoimmune disease. The observations that IFN-α therapy can induce autoimmunity and that many autoimmune conditions have an on-going type I IFN production suggest that the type I IFN system has a pivotal role in the etiopathogenesis of these diseases. Possible mechanisms behind the dysregulated type IFNsystem in autoimmune diseases and how the IFN-α produced can contribute to the development of an autoimmune process will be reviewed.

IL-12 selectively programs effector pathways that are stably expressed in human CD8+ effector memory T cells in vivo

CD8(+) cytotoxic T lymphocytes play a major role in defense against intracellular pathogens, and their functions are specified by antigen recognition and innate cytokines. IL-12 and IFN-α/β are potent "signal 3" cytokines that are involved in both effector and memory cell development. Although the majority of effector cells are eliminated as inflammation resolves, some survive within the pool of memory cells and retain immediate effector function. In this study, we demonstrate that IL-12 instructs a unique program of effector cell differentiation that is distinct from IFN-α/β. Moreover, effector memory (T(EM)) cells within peripheral blood display many common attributes of cells differentiated in vitro in response to IL-12, including proinflammatory cytokine secretion and lytic activity. A pattern of IL-12-induced genes was identified that demarcate T(EM) from central memory cells, and the ontologies of these genes correlated precisely with their effector functions. Further, we uncovered a unique program of gene expression that was acutely regulated by IL-12 and reflected in stable gene expression patterns within T(EM), but not T central memory cells in vivo. Thus, this study directly links a selective set of IL-12-induced genes to the programming of effector functions within the stable population of human CD8(+) T(EM) cells in vivo.

Regulation of effector and memory T-cell functions by type I interferon

Type I interferon (IFN-α/β) is comprised of a family of highly related molecules that exert potent antiviral activity by interfering with virus replication and spread. IFN-α/β secretion is tightly regulated through pathogen sensing pathways that are operative in most somatic cells. However, specialized antigen-presenting plasmacytoid dendritic cells are uniquely equipped with the capacity to secrete extremely high levels of IFN-α/β, suggesting a key role for this cytokine in priming adaptive T-cell responses. Recent studies in both mice and humans have demonstrated a role for IFN-α/β in directly influencing the fate of both CD4(+) and CD8(+) T cells during the initial phases of antigen recognition. As such, IFN-α/β, among other innate cytokines, is considered an important 'third signal' that shapes the effector and memory T-cell pool. Moreover, IFN-α/β also serves as a counter-regulator of T helper type 2 and type 17 responses, which may be important in the treatment of atopy and autoimmunity, and in the development of novel vaccine adjuvants.

Mouse and human intestinal immunity: same ballpark, different players; different rules, same score

The study of animal immune physiology and animal models of human disease have accelerated many aspects of translational research by allowing direct, definitive investigations. In particular, the use of mice has allowed genetic manipulation, adoptive transfer, immunization, and focused cell and tissue sampling, which would obviously be unthinkable for studies in humans. However, the disease relevance of some animal models may be uncertain and difficulties in interpretation may occur as a consequence of immunological differences between the two species. In this review, we will consider general differences in the structure and development of human and mouse mucosal lymphoid microenvironments and then discuss species differences in mucosal B- and T-cell biology that relate to the current concepts of intestinal immune function.

Robust interferon-α and IL-12 responses by dendritic cells are related to efficient CD4+ T-cell recovery in HIV patients on ART

Amongst HIV patients with successful virological responses to antiretroviral therapy (ART), poor CD4(+) T-cell recovery is associated with low nadir CD4(+) T-cell counts and persistent immune activation. These factors might be influenced by dendritic cell (DC) function. Interferon-α-producing plasmacytoid DC and IL-12-producing myeloid DC were quantified by flow cytometry after stimulation with agonists to TLR7/8 (CL075) or TLR9 (CpG-ODN). These were compared between patients who achieved CD4(+) T-cell counts above or below 200 cells/μL after 6 months on ART (High vs. Low groups). High Group patients had more DC producing interferon-α or IL-12 at Weeks 6 and 12 on ART than Low Group patients. The frequencies of cytokine-producing DC at Week 12 were directly correlated with CD4(+) T-cell counts at baseline and at Week 12. Patients with good recovery of CD4(+) T-cells had robust TLR-mediated interferon-α responses by plasmacytoid DC and IL-12 responses by myeloid DC during early ART (1-3 months).

Cutting edge: Type I IFN reverses human Th2 commitment and stability by suppressing GATA3

T helper 2 cells regulate inflammatory responses to helminth infections while also mediating pathological processes of asthma and allergy. IL-4 promotes Th2 development by inducing the expression of the GATA3 transcription factor, and the Th2 phenotype is stabilized by a GATA3-dependent autoregulatory loop. In this study, we found that type I IFN (IFN-alpha/beta) blocked human Th2 development and inhibited cytokine secretion from committed Th2 cells. This negative regulatory pathway was operative in human but not mouse CD4(+) T cells and was selective to type I IFN, as neither IFN-gamma nor IL-12 mediated such inhibition. IFN-alpha/beta blocked Th2 cytokine secretion through the inhibition of GATA3 during Th2 development and in fully committed Th2 cells. Ectopic expression of GATA3 via retrovirus did not overcome IFN-alpha/beta-mediated inhibition of Th2 commitment. Thus, we demonstrate a novel role for IFN-alpha/beta in blocking Th2 cells, suggesting its potential as a promising therapy for atopy and asthma.

Influenza-induced production of interferon-alpha is defective in geriatric individuals

BACKGROUND

The majority of deaths (90%) attributed to influenza are in person's age 65 or older. Little is known about whether defects in innate immune responses in geriatric individuals contribute to their susceptibility to influenza.

OBJECTIVE

Our aim was to analyze interferon-alpha (IFN-alpha) production in peripheral blood mononuclear cells (PBMCs) isolated from young and geriatric adult donors, stimulated with influenza A or Toll-like receptor (TLR) ligands. IFN-alpha is a signature anti-viral cytokine that also shapes humoral and cell-mediated immune responses.

RESULTS

Geriatric PBMCs produced significantly less IFN-alpha in response to live or inactivated influenza (a TLR7 ligand) but responded normally to CpG ODN (TLR9 ligand) and Guardiquimod (TLR7 ligand). All three ligands activate plasmacytoid dendritic cells (pDCs). While there was a modest decline in pDC frequency in older individuals, there was no defect in uptake of influenza by geriatric pDCs.

DISCUSSION AND CONCLUSION

Influenza-induced production of IFN-alpha was defective in geriatric PBMCs by a mechanism that was independent of reduced pDC frequency or viability, defects in uptake of influenza, inability to secrete IFN-alpha, or defects in TLR7 signaling.

Potential role of IFNα in adult lupus

Patients with lupus have a continuous production of IFNα and display an increased expression of IFNα-regulated genes. The reason for the ongoing IFNα synthesis in these patients seems to be an activation of plasmacytoid dendritic cells (pDCs) by immune complexes (ICs), consisting of autoantibodies in combination with DNA-containing or RNA-containing autoantigens. The mechanisms behind the activation of pDCs by such ICs have to some extent been elucidated during the last years. Thus, interferogenic ICs are internalized via the FcγRIIa expressed on pDCs, reach the endosomes and stimulate Toll-like receptor (TLR) 7 or 9, which subsequently leads to IFNα gene transcription. Variants of genes involved in both the IFNα synthesis and response have been linked to an increased risk to develop lupus. Among these genes are interferon regulatory factor 5 (IRF5), which is involved in TLR signaling, and the signal transducer and activator of transcription 4 (STAT4) that interacts with the type I interferon receptor. Produced IFNα may at least partially be responsible for several of the observed alterations in the immune system of lupus patients and contribute to the autoimmune disease process, which will be discussed in the present review. How produced IFNα can contribute to some clinical manifestations will briefly be described, as well as the possible consequences of this knowledge in clinical practice for disease monitoring and therapy.

Type I interferon and lupus

PURPOSE OF REVIEW

Patients with lupus have signs of an ongoing production of type I interferons (IFNs) that are of importance both for the etiopathogenesis and the clinical manifestations. In this review, we summarize the latest information concerning the type I IFN system in lupus.

RECENT FINDINGS

Activated plasmacytoid dendritic cells are responsible for the IFNalpha production in lupus and can be found in target organs such as glomeruli. The plasmacytoid dendritic cells are triggered by interferogenic immune complexes, and produced IFNalpha activates the immune system and impairs T-regulatory cell function. Autoantibodies, which can form interferogenic immune complexes, are not only present in serum of lupus patients but also in the cerebrospinal fluid of patients with neuropsychiatric manifestations. There is a strong association between risk to develop lupus and gene variants connected to the production and effects of type I IFN. Risk variants can not only cause either increased serum IFNalpha activity or sensitivity but also a more severe disease phenotype. Administration of monoclonal anti-IFNalpha antibodies to lupus patients downregulates several proinflammatory pathways and reduces disease activity.

SUMMARY

Increasing evidence indicates that the activated type I IFN system in lupus is critical in the etiopathogenesis of the disease and is an important therapeutic target.