CD154: an immunoinflammatory mediator in systemic lupus erythematosus and rheumatoid arthritis

A functional aged human iPSC-cortical neuron model recapitulates Alzheimer's disease, senescence, and the response to therapeutics

INTRODUCTION

The degeneration of cortical layers is associated with cognitive decline in Alzheimer's disease (AD). Current therapies for AD are not disease-modifying, and, despite substantial efforts, research and development for AD has faced formidable challenges. In addition, cellular senescence has emerged as a significant contributor to therapy resistance.

METHODS

Human iPSC-derived cortical neurons were cultured on microelectrode arrays to measure long-term potentiation (LTP) noninvasively. Neurons were treated with pathogenic amyloid-β (Aβ) to analyze senescence and response to therapeutic molecules.

RESULTS

Microphysiological recordings revealed Aβ dampened cortical LTP activity and accelerated neuronal senescence. Aging neurons secreted inflammatory factors previously detected in brain, plasma, and cerebral spinal fluid of AD patients, in which drugs modulated senescence-related factors.

DISCUSSION

This platform measures and records neuronal LTP activity in response to Aβ and therapeutic molecules in real-time. Efficacy data from similar platforms have been accepted by the FDA for neurodegenerative diseases, expediting regulatory submissions.

HIGHLIGHTS

This work developed a progerontic model of amyloid-β (Aβ)-driven cortical degeneration. This work measured neuronal LTP and correlated function with aging biomarkers. Aβ is a driver of neuronal senescence and cortical degeneration. Molecules rescued neuronal function but did not halt Aβ-driven senescence. Therapeutic molecules modulated secretion of inflammatory factors by aging neurons.

Translating mechanisms into therapeutic strategies for immune thrombocytopenia (ITP): Lessons from clinical trials

Immune thrombocytopenia (ITP) is an autoimmune disorder that causes a significant reduction in peripheral blood platelet count. Fortunately, due to an increased understanding of ITP, there have been significant improvements in the diagnosis and treatment of these patients. Over the past decade, there have been a variety of proven therapeutic options available for ITP patients, including intravenous immunoglobulins (IVIG), Rituximab, corticosteroids, and thrombopoietin receptor agonists (TPO-RAs). Although the effectiveness of current therapies in treating more than two-thirds of patients, still some patients do not respond well to conventional therapies or fail to achieve long-term remission. Recently, a significant advancement has been made in identifying various mechanisms involved in the pathogenesis of ITP, leading to the development of novel treatments targeting these pathways. It seems that new agents that target plasma cells, Bruton tyrosine kinase, FcRn, platelet desialylation, splenic tyrosine kinase, and classical complement pathways are opening new ways to treat ITP. In this study, we reviewed the pathophysiology of ITP and summarized updates in this population's management and treatment options. We also took a closer look at the 315 ongoing trials to investigate their progress status and compare the effectiveness of interventions. May our comprehensive view of ongoing clinical trials serve as a guiding beacon, illuminating the path towards future trials of different drugs in the treatment of ITP patients.

SNP in PTPN22, PADI4, and STAT4 but Not TRAF1 and CD40 Increase the Risk of Rheumatoid Arthritis in Polish Population

Single nucleotide polymorphisms in non-HLA genes are involved in the development of rheumatoid arthritis (RA). SNPS in genes: PADI4 (rs2240340), STAT4 (rs7574865), CD40 (rs4810485), PTPN22 (rs2476601), and TRAF1 (rs3761847) have been described as risk factors for the development of autoimmune diseases, including RA. This study aimed to assess the prevalence of polymorphisms of these genes in the Polish population of patients with rheumatoid arthritis as compared to healthy controls. 324 subjects were included in the study: 153 healthy subjects and 181 patients from the Department of Rheumatology, Medical University of Lodz who fulfilled the criteria of rheumatoid arthritis diagnosis. Genotypes were determined by Taqman SNP Genotyping Assay. rs2476601 (G/A, OR = 2.16, CI = 1.27-3.66; A/A, OR = 10.35, CI = 1.27-84.21), rs2240340 (C/T, OR = 4.35, CI = 2.55-7.42; T/T, OR = 2.80, CI = 1.43-4.10) and rs7574865 (G/T, OR = 1.97, CI = 1.21-3.21; T/T, OR = 3.33, CI = 1.01-11.02) were associated with RA in the Polish population. Rs4810485 was also associated with RA, however after Bonferroni's correction was statistically insignificant. We also found an association between minor alleles of rs2476601, rs2240340, and rs7574865 and RA (OR = 2.32, CI = 1.47-3.66; OR = 2.335, CI = 1.64-3.31; OR = 1.88, CI = 1.27-2.79, respectively). Multilocus analysis revealed an association between CGGGT and rare (below 0.02 frequency) haplotypes (OR = 12.28, CI = 2.65-56.91; OR = 3.23, CI = 1.63-6.39). In the Polish population, polymorphisms of the PADI4, PTPN22, and STAT4 genes have been detected, which are also known risk factors for RA in various other populations.

Subclinical Carotid Atherosclerosis in Patients with Rheumatoid Arthritis at Low Cardiovascular Risk

OBJECTIVE

To evaluate the rate of subclinical carotid atherosclerosis and clinical significance of immunoinflammatory markers in patients with rheumatoid arthritis (RA) at low cardiovascular risk.

MATERIALS AND METHODS

The study included 275 RA patients and a control group of 100 participants without autoimmune diseases. All study participants were at low cardiovascular risk, calculated by the QRISK3 scale (<20%), and free of cardiovascular disease. Ultrasound examination of carotid arteries was performed to measure cIMT and to detect atherosclerotic plaques (ASP) in carotid arteries. sIСАМ-1, sVСАМ, and sCD40L levels were determined by enzyme immunoassay.

RESULTS

Carotid ASP was observed more frequently in RA patients (27%) than in the control group (17%), p = 0.03. The frequency of ASP in RA patients did not depend on the disease's stage or activity. There was a significant correlation between cIMT and age, cardiovascular risk determined by QRISK3, level of total cholesterol, LDL, and blood pressure in RA patients, p < 0.05 in all cases. No correlation between cIMT and blood levels of sCD40L, sVCAM, and sICAM was found. In RA patients, a higher concentration of sVCAM was detected in the carotid ASP group compared to the non-atherosclerotic group. sCD40L was associated with cIMT and total cholesterol in the ASP group and with total cholesterol and blood pressure in non-atherosclerotic patients.

CONCLUSIONS

Subclinical atherosclerotic lesions of the carotid arteries were observed significantly more frequently in RA patients with low cardiovascular risk than in the control group. The results of the study demonstrate the association between cIMT, traditional cardiovascular risk factors, and immunoinflammatory markers in RA patients.

Serum sCD40L and IL-31 in Association with Early Phase of IgA Nephropathy

BACKGROUND

IgA nephropathy (IgAN) is a major cause of chronic glomerulonephritis worldwide. T cell dysregulation has been reported to contribute to the pathogenesis of IgAN. Methods We measured a broad range of Th1, Th2 and Th17 cytokines in the serum of IgAN patients. We searched for significant cytokines, which were associated with clinical parameters and histological scores in IgAN patients.

RESULTS

Among 15 cytokines, the levels of soluble CD40L (sCD40L) and IL-31 were higher in IgAN patients and were significantly associated with a higher estimated glomerular filtration rate (eGFR), a lower urinary protein to creatinine ratio (UPCR), and milder tubulointerstitial lesions (i.e., the early phase of IgAN). Multivariate analysis revealed that serum sCD40L was an independent determinant of a lower UPCR after adjustment for age, eGFR, and mean blood pressure (MBP). CD40, a receptor of sCD40L, has been reported to be upregulated on mesangial cells in IgAN. The sCD40L/CD40 interaction may directly induce inflammation in mesangial areas and may therefore be involved in the development of IgAN.

CONCLUSIONS

The present study demonstrated the significance of serum sCD40L and IL-31 in the early phase of IgAN. Serum sCD40L may be a marker of the beginning of inflammation in IgAN.

2021 update on thyroid-associated ophthalmopathy

PURPOSE

Our understanding of thyroid-associated ophthalmopathy (TAO, A.K.A Graves' orbitopathy, thyroid eye disease) has advanced substantially, since one of us (TJS) wrote the 2010 update on TAO, appearing in this journal.

METHODS

PubMed was searched for relevant articles.

RESULTS

Recent insights have resulted from important studies conducted by many different laboratory groups around the World. A clearer understanding of autoimmune diseases in general and TAO specifically emerged from the use of improved research methodologies. Several key concepts have matured over the past decade. Among them, those arising from the refinement of mouse models of TAO, early stage investigation into restoring immune tolerance in Graves' disease, and a hard-won acknowledgement that the insulin-like growth factor-I receptor (IGF-IR) might play a critical role in the development of TAO, stand out as important. The therapeutic inhibition of IGF-IR has blossomed into an effective and safe medical treatment. Teprotumumab, a β-arrestin biased agonist monoclonal antibody inhibitor of IGF-IR has been studied in two multicenter, double-masked, placebo-controlled clinical trials demonstrated both effectiveness and a promising safety profile in moderate-to-severe, active TAO. Those studies led to the approval by the US FDA of teprotumumab, currently marketed as Tepezza for TAO. We have also learned far more about the putative role that CD34+ fibrocytes and their derivatives, CD34+ orbital fibroblasts, play in TAO.

CONCLUSION

The past decade has been filled with substantial scientific advances that should provide the necessary springboard for continually accelerating discovery over the next 10 years and beyond.

An optimally designed anti-human CD40 antibody with potent B cell suppression for the treatment of autoimmune diseases

Antibodies targeting the CD40-CD40L pathway have great potential for treating autoimmune diseases like rheumatoid arthritis, systemic lupus erythematosus (SLE), lupus nephritis (LN), and inflammatory bowel diseases (IBD). However, in addition to the known difficulty in generating a purely antagonistic CD40 antibody, the presence of CD40 and CD40L on platelets creates additional unique challenges for the safety, target coverage, and clearance of antibodies targeting this pathway. Previously described therapeutic antibodies targeting this pathway have various shortcomings, and the full therapeutic potential of this axis has yet to be realized. Herein, we describe the generation and characterization of BI 655064, a novel, purely antagonistic anti-CD40 antibody that potently neutralizes CD40-CD40L-dependent B-cell stimulation without evidence of impacting platelet functions. This uniquely optimized antibody targeting a highly challenging pathway was obtained by applying stringent functional and biophysical criteria during the lead selection process. BI 655064 has favorable target-mediated drug disposition (TMDD)-saturation pharmacokinetics, consistent with that of a high-quality therapeutic monoclonal antibody.

IL-1 and CD40/CD40L platelet complex: elements of induction of Crohn's disease and new therapeutic targets

Ulcerative colitis (UC) and Crohn's disease (CD) are chronic and multifactorial diseases that affect the intestinal tract, both characterized by recurrent inflammation of the intestinal mucosa, resulting in abdominal pain, diarrhea, vomiting and, rectal bleeding. Inflammatory bowel diseases (IBD) regroup these two disorders. The exact pathological mechanism of IBD remains ambiguous and poorly known. In genetically predisposed patients, defects in intestinal mucosal barrier are due to an uncontrolled inflammatory response to normal flora. In addition to the genetic predisposition, these defects could be triggered by environmental factors or by a specific lifestyle which is widely accepted as etiological hypothesis. The involvement of the CD40/CD40L platelet complex in the development of IBD has been overwhelmingly demonstrated. CD40L is climacteric in cell signalling in innate and adaptive immunity, the CD40L expression on the platelet cell surface gives them an immunological competence. The IL-1, a major inflammation mediator could be involved in different ways in the development of IBD. Here, we provide a comprehensive review regarding the role of platelet CD40/CD40L in the pathophysiological effect of IL-1 in the development of Crohn's disease (CD). This review could potentially help future approaches aiming to target these two pathways for therapeutic purposes and elucidate the immunological mechanisms driving gut inflammation.

Integrin Binding to the Trimeric Interface of CD40L Plays a Critical Role in CD40/CD40L Signaling

CD40L plays a major role in immune response and is a major therapeutic target for inflammation. Integrin α5β1 and CD40 simultaneously bind to CD40L. It is unclear if α5β1 and CD40 work together in CD40/CD40L signaling or how α5β1 binds to CD40L. In this article, we describe that the integrin-binding site of human CD40L is predicted to be located in the trimeric interface by docking simulation. Mutations in the predicted integrin-binding site markedly reduced the binding of α5β1 to CD40L. Several CD40L mutants defective in integrin binding were defective in NF-κB activation and B cell activation and suppressed CD40L signaling induced by wild-type CD40L; however, they still bound to CD40. These findings suggest that integrin α5β1 binds to monomeric CD40L through the binding site in the trimeric interface of CD40L, and this plays a critical role in CD40/CD40L signaling. Integrin αvβ3, a widely distributed vascular integrin, bound to CD40L in a KGD-independent manner, suggesting that αvβ3 is a new CD40L receptor. Several missense mutations in CD40L that induce immunodeficiency with hyper-IgM syndrome type 1 (HIGM1) are clustered in the integrin-binding site of the trimeric interface. These HIGM1 CD40L mutants were defective in binding to α5β1 and αvβ3 (but not to CD40), suggesting that the defect in integrin binding may be a causal factor of HIGM1. These findings suggest that α5β1 and αvβ3 bind to the overlapping binding site in the trimeric interface of monomeric CD40L and generate integrin-CD40L-CD40 ternary complex. CD40L mutants defective in integrins have potential as antagonists of CD40/CD40L signaling.

UVB-induced depletion of donor-derived dendritic cells prevents allograft rejection of immune-privileged hair follicles in humanized mice

Dendritic cells (DCs) are key targets for immunity and tolerance induction; they present donor antigens to recipient T cells by donor- and recipient-derived pathways. Donor-derived DCs, which are critical during the acute posttransplant period, can be depleted in graft tissue by forced migration via ultraviolet B light (UVB) irradiation. Here, we investigated the tolerogenic potential of donor-derived DC depletion through in vivo and ex vivo UVB preirradiation (UV) combined with the injection of anti-CD154 antibody (Ab) into recipients in an MHC-mismatched hair follicle (HF) allograft model in humanized mice. Surprisingly, human HF allografts achieved long-term survival with newly growing pigmented hair shafts in both Ab-treated groups (Ab-only and UV plus Ab) and in the UV-only group, whereas the control mice rejected all HF allografts with no hair regrowth. Perifollicular human CD3⁺ T cell and MHC class II⁺ cell infiltration was significantly diminished in the presence of UV and/or Ab treatment. HF allografts in the UV-only group showed stable maintenance of the immune privilege in the HF epithelium without evidence of antigen-specific T cell tolerance, which is likely promoted by normal HFs in vivo. This immunomodulatory strategy targeting the donor tissue exhibited novel biological relevance for clinical allogeneic transplantation without generalized immunosuppression.

Protective Role of Myeloid Cells Expressing a G-CSF Receptor Polymorphism in an Induced Model of Lupus

The genetic analysis of the lupus-prone NZM2410 mouse has identified a suppressor locus, Sle2c2, which confers resistance to spontaneous lupus in combination with NZM2410 susceptibility loci, or in the chronic graft-versus-host disease (cGVHD) induced model of lupus in the B6.Sle2c2 congenic strain. The candidate gene for Sle2c2, the Csf3r gene encoding the granulocyte colony-stimulating factor receptor (G-CSF-R/CD114), was validated when cGVHD was restored in B6.Sle2c2 mice after treatment with G-CSF. The goal of the project reported herein was to investigate the myeloid cells that confer resistance to cGVHD and to ascertain if the mechanism behind their suppression involves the G-CSF pathway. We showed that despite expressing the highest levels of G-CSF-R, neutrophils play only a modest role in the autoimmune activation induced by cGVHD. We also found reduced expression levels of G-CSF-R on the surface of dendritic cells (DCs) and a differential distribution of DC subsets in response to cGVHD in B6.Sle2c2 versus B6 mice. The CD8α⁺ DC subset, known for its tolerogenic phenotype, was expanded upon induction of cGVHD in B6.Sle2c2 mice. In addition, the deficiency of CD8α⁺ DC subset enhanced the severity of cGVHD in B6.Batf3^-/- and B6.Sle2c2 mice, confirming their role in suppression of cGVHD. B6.Sle2c2DCs presented lowered activation and antigen presentation abilities and expressed lower levels of genes associated with DC activation and maturation. Exposure to exogenous G-CSF reversed the majority of these phenotypes, suggesting that tolerogenic DCs maintained through a defective G-CSF-R pathway mediated the resistance to cGVHD in B6.Sle2c2 mice.

Therapeutic effects of anti-CD154 antibody in cynomolgus monkeys with advanced rheumatoid arthritis

Rheumatoid arthritis is one major chronic inflammatory systemic autoimmune disease. The CD154-CD40 interactions play a critical role in the regulation of immune responses and the maintenance of autoimmunity. Therefore, we aimed to determine whether anti-CD154 antibody treatment show positive effects on immunomodulation and clinical improvement of sustained severe rheumatoid arthritis in cynomolgus monkeys. Arthritis was induced using chicken type II collagen (CII) and arthritic monkey were divided into control and anti-CD154 treatment groups based on their concentrations of anti-CII antibodies on week 7 post-immunization. Blood and tissue samples were collected on week 16 post-immunization. Anti-CD154 antibody treatment improved arthritis and movement, and significantly decreased the numbers of proliferating B cells and the serum levels of anti-type II collagen antibody and sCD154 compared with non-treatment group. Further anti-CD154 antibody treatment significantly decreased the percentage of CD4+ cells and the ratio of CD4+ to CD8+ T cells and significantly increased the percentage of CD8+ cells and effector memory CD8+ cells in peripheral blood. We have shown for the first time in a nonhuman primate model of RA that CD154 blockade has beneficial effects. This study might be valuable as preclinical data of CD154 blockade in nonhuman primate models of severe rheumatoid arthritis.

Immune complex negatively regulates toll-like receptor 3-triggered tumour necrosis factor α production in B cells

Inappropriate activation of toll-like receptor 3 (TLR3) has been implicated in the pathogenesis of autoimmune diseases, so the negative regulation of TLR3-triggered immune response has received increasing attention. Nonpathogenic immune complex (IC) has been used as treatment for many inflammatory and autoimmune diseases. However, the role of IC in the regulation of TLR3-triggered immune responses and the underlying mechanisms need to be investigated. In this study we demonstrate that IC or intravenous immunoglobulin (Ig) stimulation of B cells attenuates polyinosinic:polycytidylic acid (poly I:C)-induced CD40 expression; IC, but not Ig, can significantly inhibit poly I:C-induced pro-inflammatory tumour necrosis factor α (TNF-α) production by B cells. Moreover, IC/Ig stimulation does not alter the expression of TLR3 in B cells. Further experiments suggest that receptor for the Fc portion of IgGIIb (FcγRIIb) is involved in the suppressive effect of IC on TLR3-mediated TNF-α production, but not CD40 expression. Thus, we provide a new means of negative regulation of TLR3-triggered immune responses in B cells via FcγRIIb, and we provide a new mechanistic explanation of the therapeutic effect of nonpathogenic IC on inflammatory or autoimmune diseases.

Hydroxychloroquine inhibits CD154 expression in CD4+ T lymphocytes of systemic lupus erythematosus through NFAT, but not STAT5, signaling

Background

Overexpression of membranous CD154 in T lymphocytes has been found previously in systemic lupus erythematosus (SLE). Because hydroxychloroquine (HCQ) has been used frequently in the treatment of lupus, we sought to identify the effects of HCQ on CD154 and a possibly regulatory mechanism.

Methods

CD4⁺ T cells were isolated from the blood of lupus patients. After stimulation with ionomycin or IL-15 and various concentrations of HCQ, expression of membranous CD154 and NFAT and STAT5 signaling were assessed.

Results

HCQ treatment had significant dose-dependent suppressive effects on membranous CD154 expression in ionomycin-activated T cells from lupus patients. Furthermore, HCQ inhibited intracellular sustained calcium storage release, and attenuated the nuclear translocation of NFATc2 and the expression of NFATc1. However, CD154 expressed through IL-15-mediated STAT5 signaling was not inhibited by HCQ treatment.

Conclusions

HCQ inhibited NFAT signaling in activated T cells and blocked the expression of membranous CD154, but not STAT5 signaling. These findings provide a mechanistic insight into SLE in HCQ treatment.

Scaffold protein JLP mediates TCR-initiated CD4+T cell activation and CD154 expression

CD4⁺ T-cell activation and its subsequent induction of CD154 (CD40 ligand, CD40L) expression are pivotal in shaping both the humoral and cellular immune responses. Scaffold protein JLP regulates signal transduction pathways and molecular trafficking inside cells, thus represents a critical component in maintaining cellular functions. Its role in regulating CD4⁺ T-cell activation and CD154 expression, however, is unclear. Here, we demonstrated expression of JLP in mouse tissues of lymph nodes, thymus, spleen, and also CD4⁺ T cells. Using CD4+ T cells from jlp-deficient and jlp-wild-type mice, we demonstrated that JLP-deficiency impaired T-cell proliferation, IL-2 production, and CD154 induction upon TCR stimulations, but had no impacts on the expression of other surface molecules such as CD25, CD69, and TCR. These observed impaired T-cell functions in the jlp-/- CD4⁺ T cells were associated with defective NF-AT activation and Ca²⁺ influx, but not the MAPK, NF-κB, as well as AP-1 signaling pathways. Our findings indicated that, for the first time, JLP plays a critical role in regulating CD4⁺ T cells response to TCR stimulation partly by mediating the activation of TCR-initiated Ca²⁺/NF-AT.

Blocking α5β1 Integrin Attenuates sCD40L-Mediated Platelet Activation

The soluble form of CD40L (sCD40L) is a platelet-derived mediator that links inflammation, hemostasis, and vascular dysfunction. Indeed, blockade of CD40L by neutralizing antibodies or genetic disruption in mice prevents atherosclerosis and atherothrombosis. Until recently, it was believed that CD40 and αIIbβ3 were the only receptors on platelets responsible for binding sCD40L, leading to platelet activation and initiation of thrombotic events. Recent findings showed α5β1 integrin as a novel platelet sCD40L receptor, with an unknown function. For the first time, using anti-α5β1 blocking antibodies, we show that sCD40L/α5β1 interaction leads to platelet activation as evaluated in the human whole blood. Establishing α5β1 integrin's role in platelet activation, and therefore thrombosis will help further shed light on the etiology of thrombotic disease.

Cloning and high level expression of the biologically active extracellular domain of Macaca mulatta CD40 in Pichia pastoris

The CD40-mediated immune response contributes to a wide variety of chronic inflammatory diseases. CD40 antagonists have potential as novel therapies for immune disorders. However, the CD40 pathway has not been well characterized in the rhesus monkey Macaca mulatta, which is a valuable animal model for human immune disease. An 834 bp transcript was cloned from peripheral blood mononuclear cells (PBMCs) of rhesus monkey using specific primers designed according to the predicted sequence of M. mulatta CD40 (mmCD40) in GenBank. Sequence analysis demonstrated that mmCD40 is highly homologous to human CD40 (hCD40), with an amino acid sequence identity of 94%. Genes encoding the extracellular domain of mmCD40 and the Fc fragment of the hIgG1 were inserted into a pPIC9K plasmid to produce mmCD40Ig by Pichia pastoris. Approximately 15-20 mg of the mmCD40Ig protein with ∼90% purity could be recovered from 1 L of culture. The purified mmCD40Ig protein can form dimers and can specifically bind CD40L-positive cells. Additionally, the mmCD40Ig protein can bind hCD40L protein in phosphate buffered saline and form a stable combination in a size-exclusion chromatography assay using a Superdex 200 column. Moreover, mmCD40Ig is as efficient as M. mulatta CTLA4Ig (mmCTLA4Ig) to suppress Con A-stimulated lymphocyte proliferation. Additionally, mmCD40Ig only showed mild immunosuppressive activity in a one-way mixed lymphocyte reaction (MLR) system. These results suggest that mmCD40Ig secreted by P. pastoris was productive and functional, and it could be used as a tool for pathogenesis and therapies for chronic inflammatory diseases in a M. mulatta model.

TWEAK/Fn14 Signaling Involvement in the Pathogenesis of Cutaneous Disease in the MRL/lpr Model of Spontaneous Lupus

Tumor necrosis factor (TNF)-like weak inducer of apoptosis (TWEAK, TNFSF12) and its sole receptor Fn14, belonging to the TNF ligand and receptor superfamilies respectively, are involved in cell survival and cytokine production. The role of TWEAK/Fn14 interactions in the pathogenesis of cutaneous lupus has not been explored. TWEAK treatment of murine PAM212 keratinocytes stimulated the secretion of RANTES via Fn14 and promoted apoptosis. Parthenolide, but not wortmanin or the MAPK inhibitor PD98059, significantly decreased production of RANTES, indicating that this effect of TWEAK is mediated via NF-κB signaling. UVB irradiation significantly upregulated the expression of Fn14 on keratinocytes in vitro and in vivo and increased RANTES production. MRL/lpr Fn14 knockout (KO) lupus mice were compared with MRL/lpr Fn14 wild-type (WT) mice to evaluate for any possible differences in the severity of cutaneous lesions and the presence of infiltrating immune cells. MRL/lpr Fn14 KO mice had markedly attenuated cutaneous disease as compared with their Fn14 WT littermates, as evidenced by the well-maintained architecture of the skin and significantly decreased skin infiltration of T cells and macrophages. Our data strongly implicate TWEAK/Fn14 signaling in the pathogenesis of the cutaneous manifestations in the MRL/lpr model of spontaneous lupus and suggest a possible target for therapeutic intervention.

New frontiers for platelet CD154

The role of platelets extends beyond hemostasis. The pivotal role of platelets in inflammation has shed new light on the natural history of conditions associated with acute or chronic inflammation. Beyond the preservation of vascular integrity, platelets are essential to tissue homeostasis and platelet-derived products are already used in the clinics. Unanticipated was the role of platelets in the adaptative immune response, allowing a renewed conceptual approach of auto-immune diseases. Platelets are also important players in cancer growth and dissemination. Platelets fulfill most of their functions through the expression of still incompletely characterized membrane-bound or soluble mediators. Among them, CD154 holds a peculiar position, as platelets represent a major source of CD154 and as CD154 contributes to most of these new platelet attributes. Here, we provide an overview of some of the new frontiers that the study of platelet CD154 is opening, in inflammation, tissue homeostasis, immune response, hematopoiesis and cancer.

Soluble CD40-ligand (sCD40L, sCD154) plays an immunosuppressive role via regulatory T cell expansion in HIV infection

CD40/CD40-ligand (CD40L) signalling is a key stimulatory pathway which triggers the tryptophan (Trp) catabolizing enzyme IDO in dendritic cells and is immunosuppressive in cancer. We reported IDO-induced Trp catabolism results in a T helper type 17 (Th17)/regulatory T cell (Treg ) imbalance, and favours microbial translocation in HIV chronic infection. Here we assessed the link between sCD40L, Tregs and IDO activity in HIV-infected patients with different clinical outcomes. Plasmatic sCD40L and inflammatory cytokines were assessed in anti-retroviral therapy (ART)-naive, ART-successfully treated (ST), elite controllers (EC) and healthy subjects (HS). Plasma levels of Trp and its metabolite Kynurenine (Kyn) were measured by isotope dilution tandem mass spectrometry and sCD14 was assessed by enzyme-linked immunosorbent assay (ELISA). IDO-mRNA expression was quantified by reverse transcription-polymerase chain reaction (RT-PCR). The in-vitro functional assay of sCD40L on Treg induction and T cell activation were assessed on peripheral blood mononuclear cells (PBMCs) from HS. sCD40L levels in ART-naive subjects were significantly higher compared to ST and HS, whereas EC showed only a minor increase. In ART-naive alone, sCD40L was correlated with T cell activation, IDO-mRNA expression and CD4 T cell depletion but not with viral load. sCD40L was correlated positively with IDO enzymatic activity (Kyn/Trp ratio), Treg frequency, plasma sCD14 and inflammatory soluble factors in all HIV-infected patients. In-vitro functional sCD40L stimulation induced Treg expansion and favoured Treg differentiation by reducing central memory and increasing terminal effector Treg proportion. sCD40L also increased T cell activation measured by co-expression of CD38/human leucocyte antigen D-related (HLA-DR). These results indicate that elevated sCD40L induces immunosuppression in HIV infection by mediating IDO-induced Trp catabolism and Treg expansion.

The signaling role of CD40 ligand in platelet biology and in platelet component transfusion

The CD40 ligand (CD40L) is a transmembrane molecule of crucial interest in cell signaling in innate and adaptive immunity. It is expressed by a variety of cells, but mainly by activated T-lymphocytes and platelets. CD40L may be cleaved into a soluble form (sCD40L) that has a cytokine-like activity. Both forms bind to several receptors, including CD40. This interaction is necessary for the antigen specific immune response. Furthermore, CD40L and sCD40L are involved in inflammation and a panoply of immune related and vascular pathologies. Soluble CD40L is primarily produced by platelets after activation, degranulation and cleavage, which may present a problem for transfusion. Soluble CD40L is involved in adverse transfusion events including transfusion related acute lung injury (TRALI). Although platelet storage designed for transfusion occurs in sterile conditions, platelets are activated and release sCD40L without known agonists. Recently, proteomic studies identified signaling pathways activated in platelet concentrates. Soluble CD40L is a good candidate for platelet activation in an auto-amplification loop. In this review, we describe the immunomodulatory role of CD40L in physiological and pathological conditions. We will focus on the main signaling pathways activated by CD40L after binding to its different receptors.

The role of osteopontin in the induction of the CD40 ligand in Graves' disease

OBJECTIVE

Graves' disease (GD) is a common autoimmune disease involved autoantibody production. Although we previously reported that osteopontin (OPN), a proinflammatory protein, affected development of GD through NF-κB activation, little is known about the role of OPN in regulating immunoglobulin production in GD. CD40 Ligand (CD40L) is expressed on the surface of activated CD4+T cells and costimulates CD40 on B cells, stimulating production of immunoglobulins, a process which has been reported to play a vital role in immunological signalling transduction in several autoimmune diseases. This study sought to characterize the relationship between CD40L and GD development, as well as investigating the role of OPN in modulating immunoglobulin production in GD via CD40L.

METHODS

Forty incident patients with GD, twenty-one patients with GD in remission and twenty-seven healthy controls were recruited. Both membrane-bound and soluble forms of CD40L were measured, and their correlations with clinical parameters were studied. In addition, correlation between OPN and CD40L level was also examined. Furthermore, we studied the regulatory effect of OPN on CD40L in CD4+T cells.

RESULTS

We demonstrated that the CD40L levels were enhanced in patients with GD and recovered in patients with GD in remission. CD40L levels correlated with clinical GD diagnostic parameters and OPN concentration. Moreover, human recombinant OPN and plasma samples from patients with GD increased CD40L expression, which could be significantly suppressed by OPN monoclonal antibody. In addition, CD40L antibody blocked the immunoglobulin production augmented by OPN in cultured peripheral blood mononuclear cells (PBMCs), isolated from patients with GD and healthy subjects.

CONCLUSION

These results indicate that CD40L is induced by OPN and serves as the downstream effector of OPN for immunoglobulin production in GD development.

Activated CD4+ T cells enter the splenic T-cell zone and induce autoantibody-producing germinal centers through bystander activation

CD4(+) T (helper) cells migrate in huge numbers through lymphoid organs. However, little is known about traffic routes and kinetics of CD4(+) T-cell subsets within different organ compartments. Such information is important because there are indications that CD4(+) T cells may influence the function of microenvironments depending on their developmental stage. Therefore, we investigated the migration of resting (naïve), activated, and recently activated (memory) CD4(+) T cells through the different compartments of the spleen. Resting and recently activated CD4(+) T cells were separated from thoracic duct lymph and activated CD4(+) T cells were generated in vitro by cross-linking the T-cell receptor and CD28. The present study shows that all three CD4(+) T-cell subsets selectively accumulate in the T-cell zone of the spleen. However, only activated T cells induce the formation of germinal centers (GCs) and autoantibodies in rats and mice. Our results suggest that in a two-step process they first activate B cells independent of the T-cell receptor repertoire and CD40 ligand (CD154) expression. The activated B cells then form GCs whereby CD154-dependent T-cell help is needed. Thus, activated T cells may contribute to the development of autoimmune diseases by activating autoreactive B cells in an Ag-independent manner.

Co-stimulatory molecules as targets for treatment of lupus

Co-stimulatory molecules help to regulate interactions between T cells and antigen-presenting cells and may play an important role in the pathogenesis of lupus. Both work in murine models and some early studies in human lupus support further examination of these molecules as therapeutic targets. Complexities of lupus clinical trial variables may have hampered progress in this area but recent developments in the field may make interventional trials more feasible in the near future. To date biologics which provide direct blockade of interactions between CD40 and CD154, B7RP-1 and ICOS, and CD80 or CD86 with CD28 have been assessed in multicenter clinical trials. These data will be reviewed and critiqued.

Epstein-Barr virus in systemic lupus erythematosus, rheumatoid arthritis and multiple sclerosis—association and causation

Epidemiological data suggest that the Epstein-Barr virus (EBV) is associated with several autoimmune diseases, such as systemic lupus erythematosus, rheumatoid arthritis and multiple sclerosis. However, it is not clear whether EBV plays a role in the pathogenesis of these diseases, and if so, by which mechanisms the virus may contribute. In this review, we discuss possible viral and immunological mechanisms that might explain associations between EBV and autoimmune diseases and whether these associations represent causes or effects of inflammation and autoimmunity.

B-cell targeted therapeutics in clinical development

B lymphocytes are the source of humoral immunity and are thus a critical component of the adaptive immune system. However, B cells can also be pathogenic and the origin of disease. Deregulated B-cell function has been implicated in several autoimmune diseases, including systemic lupus erythematosus, rheumatoid arthritis, and multiple sclerosis. B cells contribute to pathological immune responses through the secretion of cytokines, costimulation of T cells, antigen presentation, and the production of autoantibodies. DNA-and RNA-containing immune complexes can also induce the production of type I interferons, which further promotes the inflammatory response. B-cell depletion with the CD20 antibody rituximab has provided clinical proof of concept that targeting B cells and the humoral response can result in significant benefit to patients. Consequently, the interest in B-cell targeted therapies has greatly increased in recent years and a number of new biologics exploiting various mechanisms are now in clinical development. This review provides an overview on current developments in the area of B-cell targeted therapies by describing molecules and subpopulations that currently offer themselves as therapeutic targets, the different strategies to target B cells currently under investigation as well as an update on the status of novel therapeutics in clinical development. Emerging data from clinical trials are providing critical insight regarding the role of B cells and autoantibodies in various autoimmune conditions and will guide the development of more efficacious therapeutics and better patient selection.