Abnormal costimulatory phenotype and function of dendritic cells before and after the onset of severe murine lupus

Immunological Involvement of MicroRNAs in the Key Events of Systemic Lupus Erythematosus

Systemic lupus erythematosus (SLE) is an archetype autoimmune disease characterized by a myriad of immunoregulatory abnormalities that drives injury to multiple tissues and organs. Due to the involvement of various immune cells, inflammatory cytokines, and related signaling pathways, researchers have spent a great deal of effort to clarify the complex etiology and pathogenesis of SLE. Nevertheless, current understanding of the pathogenesis of SLE is still in the early stages, and available nonspecific treatment options for SLE patients remain unsatisfactory. First discovered in 1993, microRNAs (miRNAs) are small RNA molecules that control the expression of 1/3 of human genes at the post-transcriptional level and play various roles in gene regulation. The aberrant expression of miRNAs in SLE patients has been intensively studied, and further studies have suggested that these miRNAs may be potentially relevant to abnormal immune responses and disease progression in SLE. The aim of this review was to summarize the specific miRNAs that have been observed aberrantly expressed in several important pathogenetic processes in SLE, such as DCs abnormalities, overactivation and autoantibody production of B cells, aberrant activation of CD4⁺ T cells, breakdown of immune tolerance, and abnormally increased production of inflammatory cytokines. Our summary highlights a novel perspective on the intricate regulatory network of SLE, which helps to enrich our understanding of this disorder and ignite future interest in evaluating the molecular regulation of miRNAs in autoimmunity SLE.

Inhibition of fatty acid metabolism by etomoxir or TOFA suppresses murine dendritic cell activation without affecting viability

Objective: Dendritic cells (DCs) are important players in immunity against pathogens, but overactive DCs have been implicated in autoimmune diseases, like lupus, in which a paucity of targeted therapies remains. Recent research shows that DCs upregulate their immunometabolism when activating. We explored whether modulating fatty acid (FA) metabolism needed for oxidative phosphorylation can affect the activation of two main DC subsets. Material and methods: Sorted murine plasmacytoid DCs (pDCs) and conventional DCs (cDCs), generated in FLT3-L medium, were treated with etomoxir, an inhibitor of FA oxidation, or TOFA, an inhibitor of FA synthesis, then stimulated with TLR9 agonist CpGA. Surface activation markers and viability were analyzed by flow cytometry, cytokine, and chemokine production and were measured by ELISA. Results: Modulation of FA metabolism suppressed the upregulation of costimulatory molecules and the production of proinflammatory cytokine IL-6 and type I Interferon-dependent chemokine CXCL10 by both subsets of DCs, without affecting DC viability, neither of resting DCs or upon activation. Etomoxir inhibited pDCs at lower doses than cDCs, suggesting that pDCs may be more susceptible to FA metabolic modulation. Conclusions: Both cDCs, the primary antigen presenting cell, and pDCs, the primary type I IFN producer, exhibit a suppressed ability to activate but normal viability when their FA metabolism is inhibited by etomoxir or TOFA. Our findings indicate that FA metabolism plays an important role in the activation of both pDCs and cDCs and suggest that its modulation is an exploitable therapeutic target to suppress DC activation in inflammation or autoimmunity.

Genetic association between CD86 polymorphisms and the risk of sepsis in a Chinese Han population

BACKGROUND

Sepsis is a clinical syndrome that is frequently observed after injury or infection, representing a leading cause of mortality worldwide. CD86 (B7-2) is a co-stimulatory molecule on antigen-presenting cells, and plays critical roles in immune responses.

METHODS

A total of 135 sepsis patients and 151 healthy controls were recruited in the current case-control study. Hardy-Weinberg equilibrium (HWE) conformity was examined to assess the representativeness of the study population. CD86 gene polymorphisms were genotyped using the polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) method. The relative expression of CD86 mRNA was estimated via quantitative real-time PCR (qRT-PCR). Chi-square test was performed to estimate the associations between CD86 gene polymorphisms and sepsis risk, and the results were presented through odds ratio (OR) and 95% confidence intervals (CI).

RESULTS

The genotype distributions of CD86 polymorphisms in the case and control groups conformed to HWE. The GA genotype of the polymorphism rs1129055 was significantly correlated with an increased risk of sepsis (OR = 2.540, 95%CI = 1.288-5.008). The TT genotype of rs1915087 was a risk factor for sepsis (OR = 2.769, 95%CI = 1.292-5.935). High linkage disequilibrium was observed between the two polymorphisms (D' = 1.0, r² = 0.955). However, no significant association was observed between CD86 polymorphisms and its gene expressions (P > 0.05 for all).

CONCLUSION

CD86 gene polymorphisms rs1129055 and rs1915087 may increase the risk of sepsis.

Conventional DCs from Male and Female Lupus-Prone B6.NZM Sle1/Sle2/Sle3 Mice Express an IFN Signature and Have a Higher Immunometabolism That Are Enhanced by Estrogen

Type I interferons (IFN) are pathogenic in systemic lupus erythematosus (SLE) and were proposed to control the immunometabolism of dendritic cells (DCs). We previously reported that DCs from female lupus-prone mice constitutively overexpress IFN-responsive genes resembling the IFN signature found in SLE patients. As SLE has higher incidence in women than men, more so in women of reproductive age, estrogens are suggested to affect lupus pathogenesis. We investigated the effects of sex and estrogens on the IFN signature in conventional GM-CSF-bone marrow-derived DCs (cDCs), from male and female Triple Congenic B6.NZM.Sle1/Sle2/Sle3 (TCSle) lupus-prone mice or from wild-type C57BL/6 mice, generated with titrations of 17-beta-estradiol (E2). We found that cDCs from prediseased TCSle male mice express the IFN signature as female TCSle cDCs do. Estrogens are necessary but not sufficient to express this IFN signature, but high doses of E2 can compensate for other steroidal components. E2 stimulation, regardless of sex, modulates type I IFN-dependent and type I IFN-independent activation of cDCs in response to TLR stimulation. Finally, we found that TCSle cDCs from both sexes have elevated markers of immunometabolism and estrogens enhance the metabolic pathways in cDCs, suggesting a mechanistic link between estrogens, immunometabolism, and the IFN signature in lupus.

Adoptive transfer of autoimmune splenic dendritic cells to lupus-prone mice triggers a B lymphocyte humoral response

Systemic lupus erythematosus (SLE) is an autoimmune disease characterized by increased autoantibody production that leads to multiple tissue injuries. Dendritic cells (DCs) are important orchestrators of immune responses and key components in fine-tuning the balance between tolerance and immunity. However, their role in autoimmune disorders such as SLE remains uncertain. We analyzed the contribution of DCs in triggering SLE by adoptively transferring splenic DCs from aged autoimmune [NZB×NZW]F1 (BWF1) mice to young healthy BWF1 mice. We observed that the transfer of DCs from autoimmune mice to pre-autoimmune mice induced high autoantibody titers in the serum of recipient mice. Moreover, autoimmune DCs from aged BWF1 mice were crucial for the expansion and differentiation of plasmablasts and CD5⁺ B cells or B1-like cells in the peripheral blood, and spleen of recipient BWF1 mice, a phenomenon that is observed in autoimmune BWF1 mice. On the other hand, DCs from aged BWF1 mice participated in the expansion and differentiation of DCs and IFN-γ-producing T cells. These results reveal that DCs from autoimmune BWF1 mice exhibit functional and phenotypic characteristics that allow them to trigger B cell hyperactivation, as well as DC and T cell expansion and differentiation, thereby promoting an exacerbated humoral response in lupus-prone mice.

Plasmacytoid dendritic cell distribution and maturation are altered in lupus prone mice prior to the onset of clinical disease

Plasmacytoid dendritic cells (pDCs) and their production of type I interferons (IFN) are key pathogenic mediators of systemic lupus erythematosus (SLE). Despite the key role of pDCs in SLE, the mechanism by which pDCs promote disease is not well understood. The first objective for this study was to assess the number and maturation state of pDCs in pre-disease NZM2410 lupus prone mice compared to control mice. Second, we sought to identify mechanisms responsible for the alteration in pDCs in NZM mice prior to onset of clinical disease. We compared the number and percent of pDCs in the spleens and bone marrow (BM) of pre-disease NZM24010 (NZM) mice to C57BL/6 (B6) control mice. In the spleens of pre-disease NZM mice, pDC percent and number were increased. This increase occurs in parallel with a decrease in BM pDC number and percent in the NZM mice. The decrease in BM pDC number suggests the increase in spleen pDCs is a result of altered pDC distribution and not increased production of pDCs in the BM. To determine if pDC developmental potential is altered in lupus prone mice, we cultured BM from NZM and B6 mice in vitro. We found a reduced percentage/number of pDCs developing from the BM of NZM mice compared to B6 mice, which further supports that the increase in pDC number is a result of altered pDC distribution rather than increased pDC production. To better characterize the pDC population, we compared the percentage of mature pDCs in the spleens and BM of NZM mice to controls. In the NZM mice, there is a dramatic reduction in the number of mature pDCs in the BM of NZM mice, suggesting that mature pDCs exit the BM at a higher rate/earlier maturation time compared to healthy mice. We conclude that pDCs contribution to disease pathogenesis in NZM mice may include the alteration of pDC distribution to increase the number of pDCs in the spleen prior to disease onset.

MicroRNA-155 Mediates Augmented CD40 Expression in Bone Marrow Derived Plasmacytoid Dendritic Cells in Symptomatic Lupus-Prone NZB/W F1 Mice

Systemic lupus erythematosus (SLE) is a chronic multi-organ autoimmune disease characterized by hyperactivated immune responses to self-antigens and persistent systemic inflammation. Previously, we reported abnormalities in circulating and bone marrow (BM)-derived plasmacytoid dendritic cells (pDCs) from SLE patients. Here, we aim to seek for potential regulators that mediate functional aberrations of pDCs in SLE. BM-derived pDCs from NZB/W F1 mice before and after the disease onset were compared for toll-like receptor (TLR) induced responses and microRNA profile changes. While pDCs derived from symptomatic mice were phenotypically comparable to pre-symptomatic ones, functionally they exhibited hypersensitivity to TLR7 but not TLR9 stimulation, as represented by the elevated upregulation of CD40, CD86 and MHC class II molecules upon R837 stimulation. Upregulated induction of miR-155 in symptomatic pDCs following TLR7 stimulation was observed. Transfection of miR-155 mimics in pre-symptomatic pDCs induced an augmented expression of Cd40, which is consistent with the increased CD40 expression in symptomatic pDCs. Overall, our results provide evidence for miR-155-mediated regulation in pDC functional abnormalities in SLE. Findings from this study contribute to a better understanding of SLE pathogenesis and ignite future interests in evaluating the molecular regulation in autoimmunity.

Alpha 1 Antitrypsin Inhibits Dendritic Cell Activation and Attenuates Nephritis in a Mouse Model of Lupus

Systemic lupus erythematosus (SLE) is an autoimmune disorder with a worldwide distribution and considerable mortality and morbidity. Although the pathogenesis of this disease remains elusive, over-reactive dendritic cells (DCs) play a critical role in the disease development. It has been shown that human alpha-1 antitrypsin (hAAT) has protective effects in type 1 diabetes and rheumatoid arthritis mouse models. In the present study, we tested the effect of AAT on DC differentiation and functions, as well as its protective effect in a lupus-prone mouse model. We showed that hAAT treatment significantly inhibited LPS (TLR4 agonist) and CpG (TLR9 agonist) -induced bone-marrow (BM)-derived conventional and plasmacytoid DC (cDC and pDC) activation and reduced the production of inflammatory cytokines including IFN-I, TNF-α and IL-1β. In MRL/lpr mice, hAAT treatment significantly reduced BM-derived DC differentiation, serum autoantibody levels, and importantly attenuated renal pathology. Our results for the first time demonstrate that hAAT inhibits DC activation and function, and it also attenuates autoimmunity and renal damage in the MRL/lpr lupus model. These results imply that hAAT has a therapeutic potential for the treatment of SLE in humans.

Dendritic Cells in Systemic Lupus Erythematosus: From Pathogenic Players to Therapeutic Tools

System lupus erythematosus (SLE) is a multifactorial systemic autoimmune disease with a wide variety of presenting features. SLE is believed to result from dysregulated immune responses, loss of tolerance of CD4 T cells and B cells to ubiquitous self-antigens, and the subsequent production of anti-nuclear and other autoreactive antibodies. Recent research has associated lupus development with changes in the dendritic cell (DC) compartment, including altered DC subset frequency and localization, overactivation of mDCs and pDCs, and functional defects in DCs. Here we discuss the current knowledge on the role of DC dysfunction in SLE pathogenesis, with the focus on DCs as targets for interventional therapies.

Breakdown of Immune Tolerance in Systemic Lupus Erythematosus by Dendritic Cells

Dendritic cells (DC) play an important role in the pathogenesis of systemic lupus erythematosus (SLE), an autoimmune disease with multiple tissue manifestations. In this review, we summarize recent studies on the roles of conventional DC and plasmacytoid DC in the development of both murine lupus and human SLE. In the past decade, studies using selective DC depletions have demonstrated critical roles of DC in lupus progression. Comprehensive in vitro and in vivo studies suggest activation of DC by self-antigens in lupus pathogenesis, followed by breakdown of immune tolerance to self. Potential treatment strategies targeting DC have been developed. However, many questions remain regarding the mechanisms by which DC modulate lupus pathogenesis that require further investigations.

The Role of MicroRNAs and Human Epidermal Growth Factor Receptor 2 in Proliferative Lupus Nephritis

OBJECTIVE

To understand the roles of microRNAs (miRNAs) in proliferative lupus nephritis (LN).

METHODS

A high-throughput analysis of the miRNA pattern of the kidneys of LN patients and controls was performed by molecular digital detection. Urinary miRNAs were measured by quantitative reverse transcription-polymerase chain reaction (qRT-PCR). Target gene expression in human mesangial cells was evaluated by arrays and qRT-PCR. Human epidermal growth factor receptor 2 (HER-2) was analyzed by immunohistochemistry in kidney samples from LN patients and in a murine model of lupus. Urinary levels of HER-2, monocyte chemotactic protein 1 (MCP-1), and vascular cell adhesion molecule 1 (VCAM-1) were measured by enzyme-linked immunosorbent assay.

RESULTS

Levels of the miRNAs miR-26a and miR-30b were decreased in the kidneys and urine of LN patients. In vitro these miRNAs controlled mesangial cell proliferation, and their expression was regulated by HER-2. HER-2 was overexpressed in lupus-prone NZM2410 mice and in the kidneys of patients with LN, but not in other mesangioproliferative glomerulonephritides. HER-2 was found to be up-regulated by interferon-α and interferon regulatory factor 1. Urinary HER-2 was increased in LN and reflected disease activity, and its levels correlated with those of 2 other recognized LN biomarkers, MCP-1 and VCAM-1.

CONCLUSION

The kidney miRNA pattern is broadly altered in LN, which contributes to uncontrolled cell proliferation. Levels of the miRNAs miR-26a and miR-30b are decreased in the kidneys and urine of LN patients, and they directly regulate the cell cycle in mesangial cells. The levels of these miRNAs are controlled by HER-2, which is overexpressed in NZM2410 mice and in the kidneys and urine of LN patients. HER-2, miR-26a, and miR-30b are thus potential LN biomarkers, and blocking HER-2 may be a promising new strategy to decrease cell proliferation and damage in this disease.

Estrogen Receptor α Deficiency Modulates TLR Ligand-Mediated PDC-TREM Expression in Plasmacytoid Dendritic Cells in Lupus-Prone Mice

Female lupus-prone NZM2410 estrogen receptor α (ERα)-deficient mice are protected from renal disease and have prolonged survival compared with wild-type littermates; however, the mechanism of protection is unknown. Plasmacytoid dendritic cells (pDCs) and type I IFN drive lupus pathogenesis. Estrogen acting via ERα enhances both pDC development and IFN production. The objectives for this study were to determine if ERα modulates pDC function and IFN activity in predisease NZM2410 mice as a possible protective mechanism of ERα deficiency in lupus-prone mice. We measured the effect of ERα deficiency on spleen pDC frequency, number, maturation, and activation state. ERα deficiency reduced type I IFN activity and the frequency of MHC class II(+) pDCs in the spleen without altering overall pDC frequency, number, or maturation state. Additionally, ERα-deficient NZM2410 mice had a significantly decreased frequency of pDCs expressing PDC-TREM, a modulator of TLR-mediated IFN production. After in vitro TLR9 stimulation, ERα deficiency significantly reduced the expression of PDC-TREM on pDCs from both NZM2410 and C57BL/6 mice. Thus, we have identified a significant effect of ERα deficiency on pDCs in predisease NZM2410 mice, which may represent a mechanism by which ERα deficiency protects NZM2410 mice from lupuslike disease.

Dendritic cells and macrophages in the kidney: a spectrum of good and evil

Renal dendritic cells (DCs) and macrophages represent a constitutive, extensive and contiguous network of innate immune cells that provide sentinel and immune-intelligence activity; they induce and regulate inflammatory responses to freely filtered antigenic material and protect the kidney from infection. Tissue-resident or infiltrating DCs and macrophages are key factors in the initiation and propagation of renal disease, as well as essential contributors to subsequent tissue regeneration, regardless of the aetiological and pathogenetic mechanisms. The identification, and functional and phenotypic distinction of these cell types is complex and incompletely understood, and the same is true of their interplay and relationships with effector and regulatory cells of the adaptive immune system. In this Review, we discuss the common and distinct characteristics of DCs and macrophages, as well as key advances that have identified the renal-specific functions of these important phagocytic, antigen-presenting cells, and their roles in potentiating or mitigating intrinsic kidney disease. We also identify remaining issues that are of priority for further investigation, and highlight the prospects for translational and therapeutic application of the knowledge acquired.

TLR ligands up-regulate Trex1 expression in murine conventional dendritic cells through type I Interferon and NF-κB-dependent signaling pathways

Mutations in the Trex1 are associated with a spectrum of type I IFN-dependent autoimmune diseases. Trex1 plays an essential role in preventing accumulation of excessive cytoplasmic DNA, avoiding cell-intrinsic innate DNA sensor activation and suppressing activation of type I IFN-stimulated and -independent antiviral genes. Trex1 also helps HIV to escape cytoplasmic detection by DNA sensors. However, regulation of Trex1 in innate immune cells remains elusive. We report that murine cDCs have high constitutive expression of Trex1 in vitro and in vivo in the spleen. In resting bone marrow-derived cDCs, type I IFNs up-regulate Trex1 expression via the IFNAR-mediated signaling pathway (STAT1- and STAT2-dependent). DC activation induced by TLR3, -4, -7, and -9 ligands also augments Trex1 expression through autocrine IFN-β production and triggering of the IFN signaling pathway, whereas TLR4 ligand LPS also stimulates an early expression of Trex1 through IFN-independent NF-κB-dependent signaling pathway. Furthermore, retroviral infection also induces Trex1 up-regulation in cDCs, as we found that a gene therapy HIV-1-based lentiviral vector induces significant Trex1 expression, suggesting that Trex1 may affect local and systemic administration of gene-therapy vehicles. Our data indicate that Trex1 is induced in cDCs during activation upon IFN and TLR stimulation through the canonical IFN signaling pathway and suggest that Trex1 may play a role in DC activation during infection and autoimmunity. Finally, these results suggest that HIV-like viruses may up-regulate Trex1 to increase their ability to escape immunosurveillance.

Hyperactivated MyD88 signaling in dendritic cells, through specific deletion of Lyn kinase, causes severe autoimmunity and inflammation

Deletion of lyn, a Src-family tyrosine kinase expressed by B, myeloid, and dendritic cells (DCs), triggers lupus-like disease in mice, characterized by autoantibody production and renal immune complex deposition leading to chronic glomerulonephritis. B cells from these mice are hyperactive to antigen-receptor stimulation owing to a loss of inhibitory signaling mediated by Lyn kinase. The hyperactive B-cell responses are thought to underlie the development of autoimmunity in this model. Lyn-deficient mice also manifest significant myeloexpansion. To test the contribution of different immune cell types to the lupus-like disease in this model, we generated a lyn(flox/flox) transgenic mouse strain. To our surprise, when we crossed these mice to Cd11c-cre animals, generating DC-specific deletion of Lyn, the animals developed spontaneous B- and T-cell activation and subsequent production of autoantibodies and severe nephritis. Remarkably, the DC-specific Lyn-deficient mice also developed severe tissue inflammatory disease, which was not present in the global lyn(-/-) strain. Lyn-deficient DCs were hyperactivated and hyperresponsive to Toll-like receptor agonists and IL-1β. To test whether dysregulation of these signaling pathways in DCs contributed to the inflammatory/autoimmune phenotype, we crossed the lyn(f/f) Cd11c-cre(+) mice to myd88(f/f) animals, generating double-mutant mice lacking both Lyn and the adaptor protein myeloid differentiation factor 88 (MyD88) in DCs, specifically. Deletion of MyD88 in DCs alone completely reversed the inflammatory autoimmunity in the DC-specific Lyn-mutant mice. Thus, we demonstrate that hyperactivation of MyD88-dependent signaling in DCs is sufficient to drive pathogenesis of lupus-like disease, illuminating the fact that dysregulation in innate immune cells alone can lead to autoimmunity.

Prolactin rescues and primes autoreactive B cells directly and indirectly through dendritic cells in B6.Sle3 mice

The lupus susceptibility interval Sle3/5 confers responsiveness to prolactin in C57BL/6 (B6) mice and hyperprolactinaemia induces a lupus-like phenotype in B6.Sel3/5 mice. In this study, the immunostimulatory effects of prolactin in B6 mice containing the Sle3 portion of the Sel3/5 interval (B6.Sle3 mice) were dissected. Because of the Sle3 interval's involvement in activation of myeloid cells, the effect of dendritic cells (DCs) from prolactin-treated B6.Sle3 mice on the phenotype of B6 mice was also evaluated. B cells from prolactin-treated B6 and B6.Sle3 mice and from B6 recipients of prolactin-modulated DCs from B6.Sle3 mice were tested for DNA-reactivity and resistance to B cell receptor (BCR)-mediated apoptosis. The expression of co-stimulatory molecules on lymphocytes and myeloid cells was also evaluated. In prolactin-treated B6.Sle3 mice, transitional type 2 B cells increased while type 1 B cells decreased as a consequence of prolactin-induced resistance to BCR-mediated apoptosis leading to the survival of DNA-reactive B cells. Follicular B cells from prolactin-treated mice expressed increased levels of CD40, B7·2 and IA(b), and DCs and monocytes had higher levels of CD44 and B7·2 than placebo-treated mice. Adoptive transfer of DCs from prolactin-treated B6.Sle3 mice to B6 recipients demonstrated the intrinsic ability of prolactin-modulated DCs to induce a development of lupus-like characteristics in B6 mice. Based on these results, prolactin accelerates the breakdown of immune tolerance in B6.Sle3 mice by promoting the survival, maturation and activation of autoreactive B cells, DCs and macrophages.

The dendritic cell response to classic, emerging, and homeostatic danger signals. Implications for autoimmunity

Dendritic cells (DCs) initiate and control immune responses, participate in the maintenance of immunological tolerance and are pivotal players in the pathogenesis of autoimmunity. In patients with autoimmune disease and in experimental animal models of autoimmunity, DCs show abnormalities in both numbers and activation state, expressing immunogenic levels of costimulatory molecules and pro-inflammatory cytokines. Exogenous and endogenous danger signals activate DCs to stimulate the immune response. Classic endogenous danger signals are released, activated, or secreted by host cells and tissues experiencing stress, damage, and non-physiologic cell death; and are therefore referred to as damage-associated molecular patterns (DAMPs). Some DAMPs are released from cells, where they are normally sequestered, during necrosis (e.g., heat shock proteins, uric acid, ATP, HMGB1, mitochondria-derived molecules). Others are actively secreted, like Type I Interferons. Here we discuss important DAMPs in the context of autoimmunity. For some, there is a clear pathogenic link (e.g., nucleic acids and lupus). For others, there is less evidence. Additionally, we explore emerging danger signals. These include inorganic materials and man-made technologies (e.g., nanomaterials) developed as novel therapeutic approaches. Some nanomaterials can activate DCs and may trigger unintended inflammatory responses. Finally, we will review “homeostatic danger signals,” danger signals that do not derive directly from pathogens or dying cells but are associated with perturbations of tissue/cell homeostasis and may signal pathological stress. These signals, like acidosis, hypoxia, and changes in osmolarity, also play a role in inflammation and autoimmunity.

A novel role of the scaffolding protein JLP in tuning CD40-induced activation of dendritic cells

Receptor internalization is a common mechanism underlying surface receptor down-regulation (and thus receptor signaling) upon its engagement with the cognate ligand. Tight regulation of surface CD40 expression is critical in regulating different functional properties of dendritic cell (DC). Engagement of CD40 on mature DC and the cognate CD40 ligand on T cell activates c-Jun N-terminal MAPK, p38 and ERK1/2 MAPK pathways in mature DC. JNK-associated leucine zipper protein (JLP) is a scaffolding protein that interacted with p38 and JNK. The molecular mechanism underlying CD40 internalization and its physiological impact on DC functions remained unclear. Here we reported that the engagement of CD40 on the LPS-activated DC down-regulated the surface expression of CD40. We examined the role of the JLP protein in DC differentiation, and in the regulation of DC function(s) in vitro. In contrast to the abundant JLP expression observed in immortal cell lines, primary immature DC expressed low levels of the JLP proteins. The induction of the JLP protein expression was observed in the LPS-mature DC that were activated by CD40 ligation, and also in the poly I:C stimulated DC. JLP-silenced DC was impaired in regulating CD40 surface expression upon LPS stimulation and CD40 induced receptor internalization. Such aberrant change in the regulation of surface CD40 expression was associated with an augmented capacity of the JLP-silenced DC in IL-12 production. Collectively, our data identified a novel role of a scaffolding protein JLP in the regulation of surface CD40 expression and fine-tuning of DC function.

Myeloid dendritic cells from B6.NZM Sle1/Sle2/Sle3 lupus-prone mice express an IFN signature that precedes disease onset

Patients with systemic lupus erythematosus show an overexpression of type I IFN-responsive genes that is referred to as "IFN signature." We found that B6.NZMSle1/Sle2/Sle3 (Sle1,2,3) lupus-prone mice also express an IFN signature compared with non-autoimmune C57BL/6 mice. In vitro, myeloid dendritic cells (mDCs) (GM-CSF bone marrow-derived dendritic cells; BMDCs) from Sle1,2,3 mice constitutively overexpressed IFN-responsive genes such as IFN-β, Oas-3, Mx-1, ISG-15, and CXCL10 and members of the IFN signaling pathway STAT1, STAT2, and IRF7. The IFN signature was similar in Sle1,2,3 BMDCs from young, pre-autoimmune mice and from mice with high titers of autoantibodies, suggesting that the IFN signature in mDCs precedes disease onset and is independent from the autoantibodies. Sle1,2,3 BMDCs hyperresponded to stimulation with IFN-α and the TLR7 and TLR9 agonists R848 and CpGs. We propose that this hyperresponse is induced by the IFN signature and only partially contributes to the signature, as oligonucleotides inhibitory for TLR7 and TLR9 only partially suppressed the constitutive IFN signature, and pre-exposure to IFN-α induced the same hyperresponse in wild-type BMDCs as in Sle1,2,3 BMDCs. In vivo, mDCs and to a lesser extent T and B cells from young prediseased Sle1,2,3 mice also expressed the IFN signature, although they lacked the strength that BMDCs showed in vitro. Sle1,2,3 plasmacytoid DCs expressed the IFN signature in vitro but not in vivo, suggesting that mDCs may be more relevant before disease onset. We propose that Sle1,2,3 mice are useful tools to study the role of the IFN signature in lupus pathogenesis.

Tolerogenic function of Blimp-1 in dendritic cells

Blimp-1 has been identified as a key regulator of plasma cell differentiation in B cells and effector/memory function in T cells. We demonstrate that Blimp-1 in dendritic cells (DCs) is required to maintain immune tolerance in female but not male mice. Female mice lacking Blimp-1 expression in DCs (DCBlimp-1(ko)) or haploid for Blimp-1 expression exhibit normal DC development but an altered DC function and develop lupus-like autoantibodies. Although DCs have been implicated in the pathogenesis of lupus, a defect in DC function has not previously been shown to initiate the disease process. Blimp-1(ko) DCs display increased production of IL-6 and preferentially induce differentiation of follicular T helper cells (T(FH) cells) in vitro. In vivo, the expansion of T(FH) cells is associated with an enhanced germinal center (GC) response and the development of autoreactivity. These studies demonstrate a critical role for Blimp-1 in the tolerogenic function of DCs and show that a diminished expression of Blimp-1 in DCs can result in aberrant activation of the adaptive immune system with the development of a lupus-like serology in a gender-specific manner. This study is of particular interest because a polymorphism of Blimp-1 associates with SLE.

Influenza vaccination responses in human systemic lupus erythematosus: impact of clinical and demographic features

OBJECTIVE

Vaccination against common pathogens, such as influenza, is recommended for patients with systemic lupus erythematosus (SLE) to decrease infections and improve health. However, most reports describing the vaccination response are limited to evaluations of SLE patients with quiescent disease. This study focuses on understanding the clinical, serologic, therapeutic, and demographic factors that influence the response to influenza vaccination in SLE patients with a broad range of disease activity.

METHODS

Blood specimens and information on disease activity were collected from 72 patients with SLE, at baseline and at 2, 6, and 12 weeks after influenza vaccination. Influenza-specific antibody responses were assessed by determining the total serum antibody concentration (B(max)), relative affinity (K(a)), and level of hemagglutination inhibition in the plasma. Using a cumulative score, the patients were evenly divided into groups of high or low vaccine responders. Autoantibody levels were evaluated at each time point using immunofluorescence tests and standard enzyme-linked immunosorbent assays.

RESULTS

Compared to high responders, low responders to the vaccine were more likely to have hematologic criteria (P = 0.009), to have more American College of Rheumatology classification criteria for SLE (P = 0.05), and to be receiving concurrent prednisone treatment (P = 0.04). Interestingly, European American patients were more likely to be low responders than were African American patients (P = 0.03). Following vaccination, low responders were more likely to experience disease flares (P = 0.01) and to have increased titers of antinuclear antibodies (P = 0.04). Serum interferon-α activity at baseline was significantly higher in patients in whom a flare occurred after vaccination compared to a matched group of patients who did not experience a disease flare (P = 0.04).

CONCLUSION

Ancestral background, prednisone treatment, hematologic criteria, and evidence of increased likelihood of disease flares were associated with low antibody responses to influenza vaccination in SLE patients.

Interferon-alpha differentially affects homeostasis of human plasmacytoid and myeloid dendritic cells

Interferon-alpha (IFN-alpha) is widely used for the treatment of malignant and viral diseases. Conflicting results of IFN-alpha-mediated effects on dendritic cell (DC) homeostasis have been reported and its impact on human blood DC is largely unknown. We investigated the phenotypic, migratory, and allostimulatory activities of plasmacytoid DCs (PDCs) and myeloid DCs (MDCs) upon in vitro exposure to IFN-alpha without the addition of exogenous DC growth factors. IFN-alpha-exposed PDCs exhibited an increase in viability but showed an immature phenotype and a diminished allostimulatory potential. Furthermore, IFN-alpha-treated PDCs displayed a dramatically augmented expression of CD54 and CD62L as well as an increased migratory response to CC chemokine ligand (CCL)19, CXC chemokine ligand (CXCL)11, and CXCL12, suggesting an enhanced ability to migrate into peripheral lymph nodes through high endothelial venules. Myeloid DCs exposed to IFN-alpha exhibited a matured phenotype with an increased propensity to migrate toward lymph node chemokines, yet without gaining an enhanced allostimulatory capacity. Our results provide new insights into the differential immunomodulatory action of IFN-alpha on distinct human blood DC subsets and thus, may present translational significance.

Dendritic cell function in lupus: Independent contributors or victims of aberrant immune regulation

Dendritic cells (DCs) represent an important component of the immune system connecting the innate and adaptive immune responses. They are able to trigger strong immunity as well as tolerance against certain antigens, and therefore it is obvious that they have a central role in the expression of immunological diseases. However, because DCs are sparse, heterogeneous and plastic, their exact role in complex autoimmune diseases, such as systemic lupus erythematosus (SLE) remains not well defined. In this review, we make an attempt to summarize critically recent knowledge on the role of conventional DCs in the expression of autoimmunity and pathology in SLE.

Deficiency of type I IFN receptor in lupus-prone New Zealand mixed 2328 mice decreases dendritic cell numbers and activation and protects from disease

Type I IFNs are potent regulators of innate and adaptive immunity and are implicated in the pathogenesis of systemic lupus erythematosus. Here we report that clinical and pathological lupus nephritis and serum anti-nuclear Ab levels are greatly attenuated in New Zealand Mixed (NZM) 2328 mice deficient in type I IFN receptors (IFNAR). To determine whether the inflammatory environment in NZM 2328 mice leads to IFNAR-regulated changes in dendritic cells (DC), the number, activation, and function of DC subsets were compared in 2- and 5-mo-old (clinically healthy) female NZM and NZM-IFNAR(-/-) mice. Numbers of activated CD40(high) plasmacytoid DC (pDC) were significantly increased in renal lymph nodes of 2-mo-old NZM but not NZM-IFNAR(-/-) mice, suggesting an early IFNAR-dependent expansion and activation of pDC at disease sites. Relative to NZM spleens, NZM-IFNAR(-/-) spleens in 5-mo-old mice were significantly decreased in size and contained reduced numbers of conventional DC subsets, but not pDC. Splenic and renal lymph node NZM-IFNAR(-/-) DC analyzed directly ex vivo expressed significantly less CD40, CD86, and PDL1 than did NZM DC. Upon activation with synthetic TLR9 ligands in vitro, splenic NZM-IFNAR(-/-) DC produced less IL-12p40/70 and TNF-alpha than did NZM DC. The limited IFNAR(-/-) DC response to endogenous activating stimuli correlated with reduced numbers of splenic activated memory CD4(+) T cells and CD19(+) B cells in older mice. Thus, IFNAR signaling significantly increases DC numbers, acquisition of Ag presentation competence, and proinflammatory function before onset of clinically apparent lupus disease.

Regulation of dendritic cells by female sex steroids: Relevance to immunity and autoimmunity

Dendritic cells (DCs) are critical mediators of adaptive immunity, tolerance and autoimmunity. The human immune system exhibits sexual dimorphism, which is most evident in the female predominance of autoimmune diseases such as systemic lupus erythematosus (SLE). Female sex steroids are strongly implicated in mediating immune sexual dimorphism, in part because estrogen accentuates disease in several models of lupus autoimmunity. In contrast, progesterone may prevent disease development. While much investigation has focused on the effects of estrogen and progesterone on lymphocyte functions, far less attention has been paid to the effects of these hormones on DCs. Current evidence now indicates estrogen can activate DCs, while in contrast, progesterone inhibits DC functions. Thus, we hypothesize that the opposite effects these two hormones have on lupus autoimmunity reflect opposing effects on DC functions. Thus, through direct actions on DCs, female sex steroids may influence autoimmunity, immunity and tolerance.

Direct B cell stimulation by dendritic cells in a mouse model of lupus

OBJECTIVE

Dendritic cells (DCs) play a major role in regulating lymphocytes, including B cells, and defective DC functions have been implicated in lupus. The purpose of this study was to assess the contribution of DCs to B cell hyperactivity in the B6.Sle1.Sle2.Sle3 (B6.TC) murine lupus model.

METHODS

We compared the effects of B6 and B6.TC bone marrow-derived DCs on naive B cells cocultured in the presence of lipopolysaccharide (LPS), anti-CD40, or anti-IgM. We measured the proliferation, antibody production, and expression of activation markers and chemokine receptors for the B cells, as well as DC cytokine production. B cell proliferation was also assessed in Transwell experiments and in response to activated DC supernatants or exosomes. The role of DC-produced cytokines was evaluated with blocking antibodies and transgenic mice.

RESULTS

LPS-stimulated or anti-CD40-stimulated DCs from B6.TC mice increased B cell proliferation, antibody production, and chemokine receptor expression as compared with DCs from B6 mice. Cell-to-cell contact was not necessary for the augmented effect of the lupus-prone DCs. Anti-CD40 treatment induced a higher production of interleukin-6 (IL-6), soluble IL-6 receptor (sIL-6R), IL-10, and tumor necrosis factor alpha in B6.TC DCs. Blocking these individual cytokines, however, did not abrogate the effects of B6.TC DCs. Additional experiments also ruled out involvement of BAFF, IL-12, and interferon-alpha.

CONCLUSION

Activated DCs from B6.TC mice directly increase B cell effector functions. This effect depends on soluble factors released by activated DCs, but none of the single major DC-produced cytokines known to affect B cells are necessary. Increased sIL-6R production suggests that increased sensitivity to IL-6 may be involved.

Dendritic cells and the immunopathogenesis of systemic lupus erythematosus

Over the last decade, the role of dendritic cells (DCs) in the immunopathogenesis of systemic lupus erythematosus (SLE) has become apparent. As unique mediators of both tolerance and immunity, aberrant myeloid and plasmacytoid DC function can promote autoimmune responses via a number of mechanisms and proinflammatory pathways. This review provides an overview of DC function, the potential role of DCs in promoting autoimmune responses in SLE, and how other abnormalities in lupus can lead to an enhanced engagement of DCs in immune responses. How medications used to treat SLE and other autoimmune conditions may exert effects on DCs is also explored.

Requirement for dendritic cells in the establishment of anti-phospholipid antibodies

OBJECTIVE

The cross-presentation of cell-associated autoantigens contributes to systemic autoimmune diseases, including systemic lupus erythematosus (SLE). Little is known about the regulation of the immune response against soluble autoantigens targeted in these diseases.

METHODS

We immunized the offspring of New Zealand Black and New Zealand White mice (NZB x NZW F(1)) with syngeneic dendritic cells (DC) that had macropinocytosed beta2-glycoprotein 1 (beta(2)GPI) during propagation in normal mouse serum or that had phagocytosed apoptotic thymocytes with syngeneic (murine) or xenogeneic (bovine) beta(2)GPI, which was associated to plasma membrane of the cells. Mice were in parallel immunized with apoptotic thymocytes that had associated the beta(2)GPI to their membranes in the absence of DC. The development of anti-beta(2)GPI antibodies and clinical features were monitored.

RESULTS

Apoptotic cells alone, opsonized with beta(2)GPI, failed to induce anti-beta(2)GPI autoantibodies or clinical disease. In contrast, autoimmunity developed in the presence of DC. Furthermore, the syngeneic beta(2)GPI was a more effective antigen than the xenogeneic protein in re-boosted animals.

CONCLUSIONS

DC effectively initiate in NZB x NZW F(1) mice self-sustaining autoimmunity against the beta(2)GPI, either associated to apoptotic cells or macropinocytosed from the serum.

The role myeloid dendritic cells play in the pathogenesis of systemic lupus erythematosus

Dendritic cells (DC) play a pivotal role in the development of immune responses and the maintenance of peripheral tolerance. They continuously patrol tissues and sample antigens in search for the presence of inflammatory or pathogen-derived signals; they mature in accordance to signs prevalent in their environment and, by doing so, acquire certain features that will allow them to convey a precise message--either productive or regulatory--to the T cells they will encounter within regional lymph nodes. Evidence suggests that DC are involved in the pathogenesis of SLE. Their capacity to induce an antinuclear-oriented autoimmune response has been proven in animal models. Further, their maturation process is abnormal and their cytokine secretion and T cell stimulation is biased in patients with SLE. Lupus, however, is a problematic environment for their study and characterization. Sera from SLE patients contain several factors capable of inducing phenotypic and functional changes in DC. Thus, the abnormalities that have been reported may represent DC-intrinsic defects, a skewed phenotype due to an abnormal milieu, or a combination of both. In this review we discuss the available information in an attempt to reconcile these issues.

IL-6 produced by dendritic cells from lupus-prone mice inhibits CD4+CD25+ T cell regulatory functions

The B6.Sle1.Sle2.Sle3 triple congenic mouse (B6.TC) is a model of lupus coexpressing the three major NZM2410-derived susceptibility loci on a C57BL/6 background. B6.TC mice produce high titers of antinuclear nephrogenic autoantibodies and a highly penetrant glomerulonephritis. Previous studies have shown the Sle1 locus is associated with a reduced number of regulatory T cells (Treg) and that Sle3 results in intrinsic defects of myeloid cells that hyperactivate T cells. In this report, we show that B6.TC dendritic cells (DCs) accumulate in lymphoid organs and present a defective maturation process, in which bone marrow-derived, plasmacytoid, and myeloid DCs express a significantly lower level of CD80, CD86, and MHC class II. B6.TC DCs also induce a higher level of proliferation in CD4(+) T cells than B6 DCs, and B6.TC DCs block the suppressive activity of Treg. B6.TC DCs overproduce IL-6, which is necessary for the blockade of Treg activity, as shown by the effect of anti-IL-6 neutralizing Ab in the suppression assays. The overproduction of IL-6 by DCs and the blockade of Treg activity maps to Sle1, which therefore not only confers a reduced number of Treg but also blocks their ability to regulate autoreactive T cells. Taken together, these results provide a genetic and mechanistic evidence for systemic autoimmunity resulting from an impaired regulatory T cell compartment in both number and function and for Sle1-expressing DCs playing a major role in the latter defect though their production of IL-6.

Developments in lupus 2006

Published reports in 2006 on systemic lupus erythematosus are reviewed with regard to preclinical and clinical studies on disturbances of the immune system including co-stimulation, cytokines and recent insights into new therapeutic approaches. Increasing knowledge of components of the innate immune system, such as certain receptors (Toll-like receptors, Fc receptors and complement receptors) and cytokines as well as immune cells (dendritic cells, plasmacytoid cells and neutrophils) supports their immunopathogenic relevance and enhance our understanding of the pathogenic complexity of lupus. Although it remains to be shown which of those could be targets for therapy or biomarkers, lymphocyte-directed therapy is currently under promising clinical investigation.

The testis in immune privilege

The production, differentiation, and presence of male gametes represent inimitable challenges to the immune system, as they are unique to the body and appear long after the maturation of the immune system and formation of systemic self-tolerance. Known to protect germ cells and foreign tissue grafts from autoimmune attack, the 'immune privilege' of the testis was originally, and somewhat simplistically, attributed to the existence of the blood-testis barrier. Recent research has shown a previously unknown level of complexity with a multitude of factors, both physical and immunological, necessary for the establishment and maintenance of the immunotolerance in the testis. Besides the blood-testis barrier and a diminished capability of the large testicular resident macrophage population to mount an inflammatory response, it is the constitutive expression of anti-inflammatory cytokines in the testis by immune and particularly somatic cells, that represents an essential element for local immunosuppression. The role of androgens in testicular immune regulation has long been underestimated; yet, accumulating evidence now shows that they orchestrate the inhibition of proinflammatory cytokine expression and shift cytokine balance toward a tolerogenic environment. Furthermore, the role of the testicular dendritic cells in suppressing antigen-specific immunity and T-lymphocyte activation is discussed. Finally, the active role mast cells play in the induction and amplification of immune responses, both in infertile humans and in experimental models, highlights the importance of preventing mast cell activation to maintain the immune-privileged status of the testis.