C-reactive protein inhibits plasmacytoid dendritic cell interferon responses to autoantibody immune complexes

Redefining CRP in tissue injury and repair: more than an acute pro-inflammatory mediator

Most early studies investigating the role of C-reactive protein (CRP) in tissue damage determined it supported pro-hemostatic and pro-inflammatory activities. However, these findings were not universal, as other data suggested CRP inhibited these same processes. A potential explanation for these disparate observations finally emerged with the recognition that CRP undergoes context-dependent conformational changes in vivo, and each of its three isoforms - pentameric CRP (pCRP), modified pentameric CRP (pCRP*), and monomeric CRP (mCRP) - have different effects. In this review, we consider this new paradigm and re-evaluate the role of CRP and its isoforms in the tissue repair process. Indeed, a growing body of evidence points toward the involvement of CRP not just in hemostasis and inflammation, but also in the resolution of inflammation and in tissue regeneration. Additionally, we briefly discuss the shortcomings of the currently available diagnostic tests for CRP and highlight the need for change in how CRP is currently utilized in clinical practice.

Vitamin D3 mitigates autoimmune inflammation caused by activation of myeloid dendritic cells in SLE

Systemic lupus erythematosus (SLE) is an autoimmune disease in which defective T cells, immune complex deposition and other immune system alterations contribute to pathological changes of multiple organ systems. The vitamin D metabolite c is a critical immunomodulator playing pivotal roles in the immune system. Epidemiological evidence indicates that vitamin D deficiency is correlated with the severity of SLE. Our aim is to investigate the effects of 1,25(OH)2D3 (VitD3) on the activation of myeloid dendritic cells (mDCs) by autologous DNA-containing immune complex (DNA-ICs), and the effects of VitD3 on immune system balance during SLE. We purified DNA-ICs from the serum of SLE patients and isolated mDCs from normal subjects. In vitro studies showed that DNA-ICs were internalized and consumed by mDCs. VitD3 blocked the effects of DNA-ICs on RelB, IL-10 and TNF-α in mDCs. Further analysis indicated that DNA-ICs stimulated histone acetylation in the RelB promoter region, which was inhibited by VitD3. Knockdown of the histone deacetylase 3 gene (HDAC3) blocked these VitD3-mediated effects. Co-culture of mDCs and CD4+ T cells showed that VitD3 inhibited multiple processes mediated by DNA-ICs, including proliferation, downregulation of IL-10, TGF-β and upregulation of TNF-α. Moreover, VitD3 could also reverse the effects of DNA-IC-induced imbalance of CD4+  CD127-  Foxp3+ T cells and CD4+  IL17+ T cells. Taken together, our results indicated that autologous DNA-ICs stimulate the activation of mDCs in the pathogenesis of SLE, and VitD3 inhibits this stimulatory effects of DNA-ICs by negative transcriptional regulation of RelB gene and maintaining the Treg/Th17 immune cell balance. These results suggest that vitamin D may have therapeutic value for the treatment of SLE.

Conformational state of C-reactive protein is critical for reducing immune complex-triggered type I interferon response: Implications for pathogenic mechanisms in autoimmune diseases imprinted by type I interferon gene dysregulation

Presence of autoantibodies targeting nuclear constituents, i.e., double-stranded DNA and small nuclear ribonucleoproteins (snRNPs), remain a cornerstone in systemic lupus erythematosus (SLE). Fcγ receptor IIa (FcγRIIa) dependent uptake of nucleic acid containing immune complexes (ICs) by plasmacytoid dendritic cells (PDCs) can activate toll-like receptors (TLRs) such as TLR7 and TLR9 resulting in type I interferon (IFN) production. Previously, the classical liver-derived acute-phase reactant C-reactive protein (CRP) has been suggested to reduce IC-induced type I IFN production, whereas monomeric (mCRP) vs. pentameric (pCRP) mediated effects have not yet been unraveled. Herein, peripheral blood mononuclear cells (PBMCs) or enriched blood DCs from healthy volunteers were stimulated with SLE sera, snRNP-IgG (ICs), or TLR ligands with or without pCRP, mCRP, or anti-FcγRIIa antibody. Type I IFNs and cytokine responses were investigated using quantitative PCR, ELISA, and flow cytometry. pCRP inhibited IFN gene expression in PBMCs and enriched DCs after incubation with ICs, compared to ICs alone, whereas mCRP had significantly less inhibitory effect. The effect was independent on the order in which IC or CRP was added to the cells. In addition, pCRP inhibited IFN induced by other TLR stimulators, implicating broader inhibitory effects induced by pCRP. We demonstrate pronounced immunoregulatory functions of CRP whereas the inhibitory properties were evidently dependent on CRP's intact conformational state. The inhibition of type I IFNs was not due to competition of FcγRs, or binding of CRP to the ICs. Our findings have implications for autoimmune IC-mediated conditions imprinted by type I IFN gene dysregulation.

C-Reactive Protein Is an Indicator of the Immunosuppressive Microenvironment Fostered by Myeloid Cells in Hepatocellular Carcinoma

BACKGROUND

C-reactive protein (CRP) is a widely used marker of systemic inflammation and predicts poor clinical outcomes in patients with hepatocellular carcinoma (HCC); however, its significance in the local immune response at the tumor site is not clear.

METHODS

Serum CRP levels of 329 HCC patients were detected before resection. Paired paraffin-embedded tumor samples were used to quantify immune cell populations, such as CD11b+ myeloid cells, CD68+ macrophages (Mφs), CD15+ neutrophils, CD8+ T cells, and CD206+, CD204+, CD163+ and CD169+ Mφs, by immunohistochemistry. Enrichment scores for 34 types of immune cells based on transcriptome data from 24 HCC samples were calculated by xCell. Overall survival of patients was analyzed using the Kaplan-Meier method.

RESULTS

Serum CRP levels were correlated with liver functions and tumor stages in patients with HCC. The densities of CD68+ tumor-associated macrophages (TAMs) and CD15+ tumor-associated neutrophils (TANs) were significantly higher in patients with elevated serum CRP levels than in those with low CRP levels (both p < 0.0001). Further analysis of TAM subtypes revealed that serum CRP levels were associated with CD204+ and CD163+ Mφ densities (p < 0.0001 and p = 0.0003, respectively). Moreover, transcriptome data showed that CRP expression was associated with the expression of myeloid cell infiltration-related genes in HCC tumors. The combination of serum CRP with TAMs or TANs in both the nontumor and intratumor regions could represent a powerful criterion for predicting patient prognoses.

CONCLUSION

Serum CRP could serve as an indicator of an immunosuppressive TME in HCC, which could be of potential clinical application for treatment strategies targeting the TME.

The Complex Role of C-Reactive Protein in Systemic Lupus Erythematosus

C-reactive protein (CRP) is well-known as a sensitive albeit unspecific biomarker of inflammation. In most rheumatic conditions, the level of this evolutionarily highly conserved pattern recognition molecule conveys reliable information regarding the degree of ongoing inflammation, driven mainly by interleukin-6. However, the underlying causes of increased CRP levels are numerous, including both infections and malignancies. In addition, low to moderate increases in CRP predict subsequent cardiovascular events, often occurring years later, in patients with angina and in healthy individuals. However, autoimmune diseases characterized by the Type I interferon gene signature (e.g., systemic lupus erythematosus, primary Sjögren’s syndrome and inflammatory myopathies) represent exceptions to the general rule that the concentrations of CRP correlate with the extent and severity of inflammation. In fact, adequate levels of CRP can be beneficial in autoimmune conditions, in that they contribute to efficient clearance of cell remnants and immune complexes through complement activation/modulation, opsonization and phagocytosis. Furthermore, emerging data indicate that CRP constitutes an autoantigen in systemic lupus erythematosus. At the same time, the increased risks of cardiovascular and cerebrovascular diseases in patients diagnosed with systemic lupus erythematosus and rheumatoid arthritis are well-established, with significant impacts on quality of life, accrual of organ damage, and premature mortality. This review describes CRP-mediated biological effects and the regulation of CRP release in relation to aspects of cardiovascular disease and mechanisms of autoimmunity, with particular focus on systemic lupus erythematosus.

RNA-Containing Immune Complexes Formed by Anti-Melanoma Differentiation Associated Gene 5 Autoantibody Are Potent Inducers of IFN-α

Objective

Anti-melanoma differentiation-associated gene 5 (MDA5) autoantibody is a distinctive serology hallmark of dermatomyositis (DM). As an autoantigen, MDA5 is a cytoplasmic RNA recognition receptor. The aim of this study was to address the question of whether the RNA-containing immune complex (IC) formed by MDA5 and anti-MDA5 could activate type I interferon (IFN) response.

Method

Patients with anti-MDA5⁺ DM (n = 217), anti-MDA5⁻ DM (n = 68), anti-synthase syndrome (ASyS, n = 57), systemic lupus erythematosus (SLE, n = 245), rheumatoid arthritis (RA, n = 89), and systemic sclerosis (SSc, n = 30) and healthy donors (HD, n = 94) were enrolled in our studies. Anti-MDA5 antibody was detected by line blotting, enzyme-linked immunosorbent assay (ELISA), immunoprecipitation, and Western blotting. Cytokine profiling was determined by multiplex flow cytometry, and IFN-α was further measured by ELISA. Type I IFN-inducible genes were detected by quantitative PCR (qPCR). RNA–IC binding was analyzed by RNA immunoprecipitation. Plasmacytoid dendritic cells (pDCs) derived from healthy donors were cultivated and stimulated with MDA5 ICs with or without RNase and Toll-like receptor 7 (TLR-7) agonist. The interaction between MDA5 ICs and TLR7 was evaluated by immunoprecipitation and confocal microscopy.

Results

According to our in-house ELISA, the presence of anti-MDA5 antibody in 76.1% of DM patients, along with 14.3% of SLE patients who had a lower titer yet positive anti-MDA5 antibody, was related to the high level of peripheral IFN-α. ICs formed by MDA5 and anti-MDA5 were potent inducers of IFN-α via TLR-7 in an RNA-dependent manner in vitro.

Conclusion

Our data provided evidence of the mechanistic relevance between the anti-MDA5 antibody and type I IFN pathway.

C-Reactive Protein Suppresses the Th17 Response Indirectly by Attenuating the Antigen Presentation Ability of Monocyte Derived Dendritic Cells in Experimental Autoimmune Encephalomyelitis

Experimental autoimmune encephalomyelitis (EAE) is a classical murine model for Multiple Sclerosis (MS), a human autoimmune disease characterized by Th1 and Th17 responses. Numerous studies have reported that C-reactive protein (CRP) mitigates EAE severity, but studies on the relevant pathologic mechanisms are insufficient. Our previous study found that CRP suppresses Th1 response directly by receptor binding on naïve T cells; however, we did not observe the effect on Th17 response at that time; thus it remains unclear whether CRP could regulate Th17 response. In this study, we verified the downregulation of Th17 response by a single-dose CRP injection in MOG-immunized EAE mice in vivo while the direct and indirect effects of CRP on Th17 response were differentiated by comparing its actions on isolated CD4⁺ T cells and splenocytes in vitro, respectively. Moreover, the immune cell composition was examined in the blood and CNS (Central Nervous System), and a blood (monocytes) to CNS (dendritic cells) infiltration pathway is established in the course of EAE development. The infiltrated monocyte derived DCs (moDCs) were proved to be the only candidate antigen presenting cells to execute CRP’s function. Conversely, the decrease of Th17 responses caused by CRP disappeared in the above in vivo and in vitro studies with FcγR2B^−/− mice, indicating that FcγR2B expressed on moDCs mediates CRP function. Furthermore, peripheral blood monocytes were isolated and induced to establish moDCs, which were used to demonstrate that the antigen presenting ability of moDCs was attenuated by CRP through FcγR2B, and then NF-κB and ERK signaling pathways were manifested to be involved in this regulation. Ultimately, we perfected and enriched the mechanism studies of CRP in EAE remission, so we are more convinced that CRP plays a key role in protecting against EAE development, which may be a potential therapeutic target for the treatment of MS in human.

C-Reactive Protein Levels in Systemic Lupus Erythematosus Are Modulated by the Interferon Gene Signature and CRP Gene Polymorphism rs1205

Objectives

Patients with systemic lupus erythematosus (SLE) often display modest elevations of C-reactive protein (CRP) despite raised disease activity and increased interleukin (IL-) 6. We asked to what extent IL-6 levels, the CRP polymorphism rs1205, and the type I interferon (IFN) gene signature affects the basal CRP levels in patients with SLE during a quiescent phase of the disease.

Methods

CRP and IL-6 were analyzed in plasma from 57 patients meeting established classification criteria for SLE. The CRP polymorphism rs1205 was assessed and gene expression analyzed including four type I IFN-regulated genes (IGS).

Results

CRP was increased in patients with detectable IL-6 levels (p=0.001) and decreased among IGS-positive subjects (p=0.033). A multiple linear regression model revealed IL-6 to have a positive association with CRP levels, whereas both IGS-positivity and CRP genotype (rs1205) AA/GA were negatively associated with CRP-levels.

Conclusion

Our data offer an explanation to the modest CRP levels seen in viral infections and IFN-α driven autoimmunity and corroborate prior observations showing an IFN-α dependent downregulation of CRP. The latter observation, together with the fact that the CRP-lowering polymorphism rs1205 is overrepresented in human SLE, could explain low basal CRP and inadequate CRP-responses among patients with active SLE.

Toll-like receptor signalling in B cells during systemic lupus erythematosus

B lymphocytes have a central role in autoimmune diseases, which are often defined by specific autoantibody patterns and feature a loss of B cell tolerance. A prototypic disease associated with B cell hyperactivity is systemic lupus erythematosus (SLE). In patients with SLE, the loss of B cell tolerance to autoantigens is controlled in a cell-intrinsic manner by Toll-like receptors (TLRs), which sense nucleic acids in endosomes. TLR7 drives the extrafollicular B cell response and the germinal centre reaction that are involved in autoantibody production and disease pathogenesis. Surprisingly, TLR9 seems to protect against SLE, even though it is required for the production of autoantibodies recognizing double-stranded DNA-associated antigens, which are abundant in SLE and are a hallmark of this disease. The protective function of TLR9 is at least partly mediated by its capacity to limit the stimulatory activity of TLR7. The roles of TLR7 and TLR9 in the effector function of B cells in lupus-like disease and in patients with SLE, and the unique features of TLR signalling in B cells, suggest that targeting TLR signalling in SLE might be therapeutically beneficial.

Loss of B cell tolerance to autoantigens in systemic lupus erythematosus (SLE) is driven by TLR7, whereas TLR9 appears to protect against SLE by limiting the stimulatory activity of TLR7. The unique features of Toll-like receptor signalling in B cells implicate it as a therapeutic target in SLE.

Intrinsic TLR7 and TLR9 signalling in B cells plays an important role in the development and pathogenesis of systemic lupus erythematosus (SLE).

In patients with SLE, effector plasma cells are generated via the extrafollicular response and via the formation of spontaneous germinal centres.

TLR7 plays key roles in the extrafollicular response and the response mediated by germinal centres.

Some plasma cells produce IL-10 and can have protective roles in lupus-like disease.

Pentraxins and Fc Receptor-Mediated Immune Responses

C-reactive protein (CRP) is a member of the pentraxin family of proteins. These proteins are highly conserved over the course of evolution being present as far back as 250 million years ago. Mammalian pentraxins are characterized by the presence of five identical non-covalently linked subunits. Each subunit has a structurally conserved site for calcium-dependent ligand binding. The biological activities of the pentraxins established over many years include the ability to mediate opsonization for phagocytosis and complement activation. Pentraxins have an important role in protection from infection from pathogenic bacteria, and regulation of the inflammatory response. It was recognized early on that some of these functions are mediated by activation of the classical complement pathway through C1q. However, experimental evidence suggested that cellular receptors for pentraxins also play a role in phagocytosis. More recent experimental evidence indicates a direct link between pentraxins and Fc receptors. The Fc receptors were first identified as the major receptors for immunoglobulins. The avidity of the interaction between IgG complexes and Fc receptors is greatly enhanced when multivalent ligands interact with the IgG binding sites and activation of signaling pathways requires Fc receptor crosslinking. Human pentraxins bind and activate human and mouse IgG receptors, FcγRI and FcγRII, and the human IgA receptor, FcαRI. The affinities of the interactions between Fc receptors and pentraxins in solution and on cell surfaces are similar to antibody binding to low affinity Fc receptors. Crystallographic and mutagenesis studies have defined the structural features of these interactions and determined the stoichiometry of binding as one-to-one. Pentraxin aggregation or binding to multivalent ligands increases the avidity of binding and results in activation of these receptors for phagocytosis and cytokine synthesis. This review will discuss the structural and functional characteristics of pentraxin Fc receptor interactions and their implications for host defense and inflammation.

Discovery of tear biomarkers in children with chronic non-infectious anterior uveitis: a pilot study

BACKGROUND

Biomarkers in easily obtained specimens that accurately predict uveitis in children with juvenile idiopathic arthritis (JIA) are needed. Aqueous humor has been studied for biomarkers, but is not routinely available. We evaluated tears from children with chronic anterior uveitis (CAU) for biomarkers reported in aqueous humor. In this pilot study, we used Schirmer strips to collect tears from seven children (nine eyes); three children had JIA- associated uveitis (JIA-U) and four had idiopathic disease (I-CAU). Liquid chromatography-tandem mass spectrometry was used to identify and quantify tear proteins. The Mann-Whitney U test identified differential tear protein expression between children with JIA-U and those with I-CAU.

RESULTS

S100A9, LAP3, TTR, MIF, sCD14, S100A8, and SAA1 were detected in tears of all children; the same cytokines have been reported in aqueous humor of children with JIA-U. Tears from children with JIA-U had higher expression of proteins associated with inflammatory arthritis (SEMA3G, TIMP1, HEXB, ERN1, and SAA1) than tears from those with I-CAU. In addition, we found higher expression of sCD14, S100A8, and SAA1, but lower expression of S100A9, LAP3, TTR, and MIF, in tears from children with JIA-U compared to tears from those with I-CAU.

CONCLUSIONS

Tears contain similar cytokine profiles to aqueous humor in children with CAU and may be a clinically useful source of disease biomarkers. Tears from children with JIA-U also contain cytokines associated with inflammatory arthritis; furthermore, differential expression of other tear proteins as well may provide clues to intrinsic differences between JIA-U and I-CAU, despite their similar clinical phenotypes.

C-Reactive Protein Impairs Dendritic Cell Development, Maturation, and Function: Implications for Peripheral Tolerance

C-reactive protein (CRP) is the prototypical acute phase reactant, increasing in blood concentration rapidly and several-fold in response to inflammation. Recent evidence indicates that CRP has an important physiological role even at low, baseline levels, or in the absence of overt inflammation. For example, we have shown that human CRP inhibits the progression of experimental autoimmune encephalomyelitis (EAE) in CRP transgenic mice by shifting CD4+ T cells away from the TH1 and toward the TH2 subset. Notably, this action required the inhibitory Fcγ receptor IIB (FcγRIIB), but did not require high levels of human CRP. Herein, we sought to determine if CRP's influence in EAE might be explained by CRP acting on dendritic cells (DC; antigen presenting cells known to express FcγRIIB). We found that CRP (50 µg/ml) reduced the yield of CD11c+ bone marrow-derived DCs (BMDCs) and CRP (≥5 μg/ml) prevented their full expression of major histocompatibility complex class II and the co-stimulatory molecules CD86 and CD40. CRP also decreased the ability of BMDCs to stimulate antigen-driven proliferation of T cells in vitro. Importantly, if the BMDCs were genetically deficient in mouse FcγRIIB then (i) the ability of CRP to alter BMDC surface phenotype and impair T cell proliferation was ablated and (ii) CD11c-driven expression of a human FCGR2B transgene rescued the CRP effect. Lastly, the protective influence of CRP in EAE was fully restored in mice with CD11c-driven human FcγRIIB expression. These findings add to the growing evidence that CRP has important biological effects even in the absence of an acute phase response, i.e., CRP acts as a tonic suppressor of the adaptive immune system. The ability of CRP to suppress development, maturation, and function of DCs implicates CRP in the maintenance of peripheral T cell tolerance.

Activated neuro-oxidative and neuro-nitrosative pathways at the end of term are associated with inflammation and physio-somatic and depression symptoms, while predicting outcome characteristics in mother and baby

OBJECTIVES

To examine oxidative & nitrosative stress (O&NS) biomarkers at the end of term in relation to perinatal affective symptoms, neuro-immune biomarkers and pregnancy-related outcome variables.

METHODS

We measured plasma advanced oxidation protein products (AOPP), nitric oxide metabolites (NOx), total radical trapping antioxidant parameter (TRAP), -sulfhydryl (-SH), peroxides (LOOH) and paraoxonase (PON)1 activity in pregnant women with and without prenatal depression and non-pregnant controls.

RESULTS

Pregnancy is accompanied by significantly increased AOPP and NOx, and lowered TRAP, -SH and LOOH. Increased O&NS and lowered LOOH and -SH levels are associated with prenatal depressive and physio-somatic symptoms (fatigue, pain, dyspepsia, gastro-intestinal symptoms). Increased AOPP and NOx are significantly associated with lowered -SH, TRAP and zinc, and with increased haptoglobin and C-reactive protein levels. Increased O&NS and lowered TRAP and PON 1 activity, at the end of term predict mother (e.g. hyperpigmentation, labor duration, caesarian section, cord length, breast milk flow) and baby (e.g. sleep and feeding problems) outcome characteristics.

CONCLUSIONS

Pregnancy is accompanied by interrelated signs of O&NS, lowered antioxidant defenses and activated neuro-immune pathways. Increased O&NS at the end of term is associated with perinatal depressive and physio-somatic symptoms and may predict obstetric and behavioral complications in mother and baby.

IgM-mediated autoimmune responses to oxidative specific epitopes, but not nitrosylated adducts, are significantly decreased in pregnancy: association with bacterial translocation, perinatal and lifetime major depression and the tryptophan catabolite (TRYCAT) pathway

Immunoglubulin (Ig)M responses directed to oxidative specific epitopes (OSEs) and nitric oxide (NO)-adducts are significantly associated with major depression and physio-somatic symptoms. End of term serum IgM responses to OSEs and NO-adducts were assayed in pregnant women with (n = 24) and without prenatal depression (n = 25) as well as in 24 non-pregnant women. Associations of IgM/IgA responses to Gram-negative gut commensal bacteria (leaky gut index) and IgA/IgM responses to tryptophan catabolites (TRYCATs) were analyzed. IgM responses to OSEs, but not NO-adducts, were significantly reduced at the end of term. There were no significant associations between IgM responses to OSEs and perinatal depression, whilst IgM responses to NO-adducts, especially NO-cysteinyl, were significantly associated with a lifetime major depression. IgM responses to OSEs and NO-cysteinyl were significantly associated with IgA/IgM responses to Gram-negative bacteria, especially Morganella morganii, Klebsiella pneumoniae and Citrobacter koseri. IgM responses to NO-adducts and OSEs, especially malondialdehyde and myristic acid, and C-reactive protein (CRP) were inversely associated with TRYCAT pathway activity, whilst a lifetime depression and Pseudomonas putida were positively associated. The attenuation of natural IgM-mediated responses to OSEs at the end of term may indicate lowered activity of this part of the compensatory (anti-)inflammatory reflex system and may be partly explained by lowered bacterial translocation. Increased IgM responses to NO-cysteinyl is a biomarker of lifetime depression and may be induced by bacterial translocation. Natural IgM-mediated autoimmune responses, increased nitrosylation and higher CRP levels may have negative regulatory effects on the TRYCAT pathway.

Inflammation Thread Runs across Medical Laboratory Specialities

We work on the assumption that four major specialities or sectors of medical laboratory assays, comprising clinical chemistry, haematology, immunology, and microbiology, embraced by genome sequencing techniques, are routinely in use. Medical laboratory markers for inflammation serve as model: they are allotted to most fields of medical lab assays including genomics. Incessant coding of assays aligns each of them in the long lists of big data. As exemplified with the complement gene family, containing C2, C3, C8A, C8B, CFH, CFI, and ITGB2, heritability patterns/risk factors associated with diseases with genetic glitch of complement components are unfolding. The C4 component serum levels depend on sufficient vitamin D whilst low vitamin D is inversely related to IgG1, IgA, and C3 linking vitamin sufficiency to innate immunity. Whole genome sequencing of microbial organisms may distinguish virulent from nonvirulent and antibiotic resistant from nonresistant varieties of the same species and thus can be listed in personal big data banks including microbiological pathology; the big data warehouse continues to grow.

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.

Lack of Interferon and Proinflammatory Cyto/chemokines in Serologically Active Clinically Quiescent Systemic Lupus Erythematosus

OBJECTIVE

Serologically active clinically quiescent (SACQ) patients with systemic lupus erythematosus (SLE) remain clinically quiescent for prolonged periods despite anti-dsDNA antibodies and/or low complements, indicating the presence of immune complexes. The immune mechanisms leading to this quiescence are unknown. However, in addition to activating complement, immune complex uptake by various cells leads to the production of interferon (IFN)-α and other proinflammatory factors that are also involved in tissue damage. Here we investigate whether production of these factors is reduced in SACQ patients.

METHODS

The levels of 5 IFN-induced genes and 19 cyto/chemokines were measured in SACQ patients and were compared with those in serologically and clinically active (SACA) and serologically and clinically quiescent (SQCQ) patients. SACQ and SQCQ were defined as ≥ 2 years without clinical activity, with/without persistent serologic activity, respectively, and off corticosteroids/immunosuppressives. SACA was defined as disease activity compelling immunosuppression. Levels of OAS1, IFIT1, MX1, LY6E, and ISG15 were measured by quantitative real-time polymerase chain reaction (PCR) and a composite score (IFN-5) derived from this. Plasma cyto/chemokines were measured by Luminex assay. Nonparametric univariate and logistic regression analyses were conducted.

RESULTS

There were no differences in gene expression or cyto/chemokine levels between SACQ and SQCQ patients. The SACQ IFN-5 score was significantly lower than that of SACA (p = 0.003) and was driven by SACQ status, not by autoantibody profile or disease duration. Levels of granulocyte-macrophage colony-stimulating factor, interleukin (IL) 6, IL-10, IFN-γ-inducible protein 10, monocyte chemoattractant protein 1, and tumor necrosis factor-α were significantly lower in SACQ than SACA.

CONCLUSION

The levels of proinflammatory factors in SACQ mirror those of SQCQ patients, indicating reduced production of these factors despite the presence of immune complexes.

Pentraxin 3 Plasma Levels and Disease Activity in Systemic Lupus Erythematosus

SLE is an autoimmune disorder that involves polyclonal autoimmunity against multiple autoantigens. PTX3, a marker of the acute-phase inflammatory response, plays an important role in innate immunity and in modulation of the adaptive immune response. Our study tried to resolve some rather controversial aspects of the use of PTX3 as a biomarker of disease activity in SLE patients. We demonstrated that plasma PTX3 concentration of the SLE patients was significantly higher than the healthy control groups and reflected disease activity. ROC curve analysis was used to determine best cut-off point (2.8 ng/mL) with a good sensitivity and specificity. In patients with SLE, PTX3 concentrations were correlated with SLEDAI. Trend to remission (TTR) curve was created by plotting PTX3 levels and SLEDAI and we applied the curve as a model for the analysis of two patients with different follow-up. PTX3 plasma levels declined significantly and this decline occurred parallel to the clinical improvement with a complete remission of disease. In patients who experienced a clinical relapse, an increase in PTX3 levels followed the lupus flare. The proposal of PTX3 cut-off associated with TTR and monitoring of PTX3 plasma levels could be an innovative approach to follow-up of SLE patients.

Contribution of dendritic cells to the autoimmune pathology of systemic lupus erythematosus

Systemic lupus erythematosus (SLE) is a heterogeneous disease in which excessive inflammation, autoantibodies and complement activation lead to multisystem tissue damage. The contribution of the individual genetic composition has been extensively studied, and several susceptibility genes related to immune pathways that participate in SLE pathogenesis have been identified. It has been proposed that SLE takes place when susceptibility factors interact with environmental stimuli leading to a deregulated immune response. Experimental evidence suggests that such events are related to the failure of T-cell and B-cell suppression mediated by defects in cell signalling, immune tolerance and apoptotic mechanism promoting autoimmunity. In addition, it has been reported that dendritic cells (DCs) from SLE patients, which are crucial in the modulation of peripheral tolerance to self-antigens, show an increased ratio of activating/inhibitory receptors on their surfaces. This phenotype and an augmented expression of co-stimulatory molecules is thought to be critical for disease pathogenesis. Accordingly, tolerogenic DCs can be a potential strategy for developing antigen-specific therapies to reduce detrimental inflammation without causing systemic immunosuppression. In this review article we discuss the most relevant data relative to the contribution of DCs to the triggering of SLE.

Incomplete clearance of apoptotic cells in systemic lupus erythematosus: pathogenic role and potential biomarker

Systemic lupus erythematosus (SLE) is a chronic autoimmune disease with repeated inflammation against multiple organs. Although its pathophysiology is not yet unveiled, uncleared apoptotic cells and their accumulation in tissue contribute to the autoimmune disturbance in SLE. Apoptosis is a programmed cell death process, which maintains tissue homeostasis and inhibits the development of any further immune response against apoptotic remnants. Earlier studies revealed that various 'eat-me' signals on apoptotic cells, bridging molecules and their receptors on phagocytes play a role in such a complicated process. Tyro3-Axl-Mer receptors, their bridging molecules, milk fat globulin epidermal growth factor-8, T-cell immunoglobulin mucin domain protein family, scavenger receptors, C1q, and pentraxins were found to be abnormal in SLE. In this review, apoptosis and clearance of its remnants are summarized, and the molecules involved in the incomplete clearance of apoptotic cells in SLE are discussed.

The plasmacytoid dendritic cell as the Swiss army knife of the immune system: molecular regulation of its multifaceted functions

Plasmacytoid dendritic cells (pDC) have been regarded as the "professional type I IFN-producing cells" of the immune system following viral recognition that relies on the expression of TLR7 and TLR9. Furthermore, pDC link the innate and adaptive immune systems via cytokine production and Ag presentation. More recently, their ability to induce tolerance and cytotoxicity has been added to their "immune skills." Such a broad range of actions, resembling the diverse functional features of a Swiss army knife, requires strong and prompt molecular regulation to prevent detrimental effects, including autoimmune pathogenesis or tumor escape. Over the last decades, we and other investigators have started to unravel some aspects of the signaling pathways that regulate the various functions of human pDC. In this article, we review aspects of the molecular regulatory mechanisms to control pDC function in light of their multifaceted roles during immunity, autoimmunity, and cancer.

Targeting dendritic cell function during systemic autoimmunity to restore tolerance

Systemic autoimmune diseases can damage nearly every tissue or cell type of the body. Although a great deal of progress has been made in understanding the pathogenesis of autoimmune diseases, current therapies have not been improved, remain unspecific and are associated with significant side effects. Because dendritic cells (DCs) play a major role in promoting immune tolerance against self-antigens (self-Ags), current efforts are focusing at generating new therapies based on the transfer of tolerogenic DCs (tolDCs) during autoimmunity. However, the feasibility of this approach during systemic autoimmunity has yet to be evaluated. TolDCs may ameliorate autoimmunity mainly by restoring T cell tolerance and, thus, indirectly modulating autoantibody development. In vitro induction of tolDCs loaded with immunodominant self-Ags and subsequent cell transfer to patients would be a specific new therapy that will avoid systemic immunosuppression. Herein, we review recent approaches evaluating the potential of tolDCs for the treatment of systemic autoimmune disorders.

Association of serum C-reactive protein levels with lupus disease activity in the absence of measurable interferon-α and a C-reactive protein gene variant

OBJECTIVE

The type I interferon (IFN) system is important in the pathogenesis of systemic lupus erythematosus (SLE). We previously demonstrated an inhibitory effect of IFNα on interleukin-6 (IL-6)-induced C-reactive protein (CRP) in vitro, hypothetically explaining the poor correlation between disease activity and CRP levels in SLE. This study was undertaken to investigate disease activity, IL-6 levels, and CRP levels in relation to a CRP gene polymorphism and IFNα.

METHODS

Sera from 155 SLE patients and 100 controls were analyzed for CRP. Patients were genotyped for a CRP single-nucleotide polymorphism (rs1205) associated with low CRP levels. Serum IFNα and IL-6 levels were quantified by immunoassays. Clinical disease activity was assessed using the SLE Disease Activity Index 2000 (SLEDAI-2K).

RESULTS

CRP levels were increased in SLE patients compared to controls, but were not associated with SLEDAI-2K or IL-6 levels. However, exclusion of patients carrying at least one rs1205 minor allele revealed an association between disease activity and CRP levels (P = 0.005). We found a strong association between disease activity and CRP levels (P < 0.0005) when patients with measurable IFNα levels as well as the minor allele of rs1205 were excluded from the analysis. Similarly, when patients with elevated IFNα levels and/or the rs1205 polymorphism were excluded, IL-6 levels were associated with CRP levels.

CONCLUSION

The present study demonstrates that the serum IFNα level as well as the CRP genotype affect the CRP response in SLE patients. Lack of correlation between serum levels of CRP and disease activity could therefore be explained by activation of the type I IFN system and polymorphisms in the CRP gene.

Pentraxins: structure, function, and role in inflammation

The pentraxins are an ancient family of proteins with a unique architecture found as far back in evolution as the Horseshoe crab. In humans the two members of this family are C-reactive protein and serum amyloid P. Pentraxins are defined by their sequence homology, their pentameric structure and their calcium-dependent binding to their ligands. Pentraxins function as soluble pattern recognition molecules and one of the earliest and most important roles for these proteins is host defense primarily against pathogenic bacteria. They function as opsonins for pathogens through activation of the complement pathway and through binding to Fc gamma receptors. Pentraxins also recognize membrane phospholipids and nuclear components exposed on or released by damaged cells. CRP has a specific interaction with small nuclear ribonucleoproteins whereas SAP is a major recognition molecule for DNA, two nuclear autoantigens. Studies in autoimmune and inflammatory disease models suggest that pentraxins interact with macrophage Fc receptors to regulate the inflammatory response. Because CRP is a strong acute phase reactant it is widely used as a marker of inflammation and infection.