Association of B7-1 co-stimulation with the development of graft arterial disease. Studies using mice lacking B7-1, B7-2, or B7-1/B7-2

ACTH treatment promotes murine cardiac allograft acceptance

Heart transplantation is the optimal therapy for patients with end-stage heart disease, but its long-term outcome remains inadequate. Recent studies have highlighted the importance of the melanocortin receptors (MCRs) in inflammation, but how MCRs regulate the balance between alloreactive T cells and Tregs, and whether they impact chronic heart transplant rejection, is unknown. Here, we found that Tregs express MC2R, and MC2R expression was highest among all MCRs by Tregs. Our data indicate that adrenocorticotropic hormone (ACTH), the sole ligand for MC2R, promoted the formation of Tregs by increasing the expression of IL-2Rα (CD25) in CD4⁺ T cells and activation of STAT5 in CD4⁺CD25⁺ T cells. ACTH treatment also improved the survival of heart allografts and increased the formation of Tregs in CD28KO mice. ACTH treatment synergized with the tolerogenic effect of CTLA-4–Ig, resulting in long-term survival of heart allografts and an increase in intragraft Tregs. ACTH administration also demonstrated higher prolongation of heart allograft survival in transgenic mouse recipients with both complete KO and conditional KO of PI3Kγ in T cells. Finally, ACTH treatment reduced chronic rejection markedly. These data demonstrate that ACTH treatment improved heart transplant outcomes, and this effect correlated with an increase in Tregs.

T cell co-stimulation and co-inhibition in cardiovascular disease: a double-edged sword

The role of inflammation in cardiovascular disease (CVD) is now widely accepted. Immune cells, including T cells, are influenced by inflammatory signals and contribute to the onset and progression of CVD. T cell activation is modulated by T cell co-stimulation and co-inhibition pathways. Immune checkpoint inhibitors (ICIs) targeting T cell inhibition pathways have revolutionized cancer treatment and improved survival in patients with cancer. However, ICIs might induce cardiovascular toxicity via T cell re-invigoration. With the rising use of ICIs for cancer treatment, a timely overview of the role of T cell co-stimulation and inhibition molecules in CVD is desirable. In this Review, the importance of these molecules in the pathogenesis of CVD is highlighted in preclinical studies on models of CVD such as vein graft disease, myocarditis, graft arterial disease, post-ischaemic neovascularization and atherosclerosis. This Review also discusses the therapeutic potential of targeting T cell co-stimulation and inhibition pathways to treat CVD, as well as the possible cardiovascular benefits and adverse events after treatment. Finally, the Review emphasizes that patients with cancer who are treated with ICIs should be monitored for CVD given the reported association between the use of ICIs and the risk of cardiovascular toxicity.

Expression of CD80 and CD86 on B cells during coxsackievirus B3-induced acute myocarditis

Introduction

The pathogenesis of viral myocarditis (VMC) is unclear, but many studies have shown that VMC is associated with an excessive immune response. CD80 and CD86 are important costimulatory molecules that play a critical role in autoimmunity. However, whether CD80+/CD86+ B cells participate in the pathogenesis of acute VMC is unknown.

Material and methods

Male C57BL/6 mice were infected by intraperitoneal injection with coxsackievirus B3 (CVB3) to establish a VMC model. Control mice were administered phosphate-buffered saline intraperitoneally. At one week and two weeks post injection, histopathological changes in heart tissue were assessed with haematoxylin and eosin staining. The frequency of splenic CD80+/CD86+ B cells was measured with flow cytometry.

Results

The frequency of CD80+ B cells was significantly increased in VMC, while the frequency of CD86+ B cells was significantly decreased. Furthermore, the frequency of CD80+ B cells related to the severity of VMC.

Conclusions

These data show that CD80+/CD86+B cells are involved in the pathogenesis of VMC, with CD80+B cells being more important than CD86+B cells.

The role of CD27-CD70-mediated T cell co-stimulation in vasculogenesis, arteriogenesis and angiogenesis

BACKGROUND

T cells have a distinctive role in neovascularization, which consists of arteriogenesis and angiogenesis under pathological conditions and vasculogenesis under physiological conditions. However, the role of co-stimulation in T cell activation in neovascularization has yet to be established. The aim of this study was to investigate the role T cell co-stimulation and inhibition in angiogenesis, arteriogenesis and vasculogenesis.

METHODS AND RESULTS

Hind limb ischemia was induced by double ligation of the left femoral artery in mice and blood flow recovery was measured with Laser Doppler Perfusion Imaging in control, CD70^-/-, CD80/86^-/-, CD70/80/86^-/- and CTLA4^+/- mice. Blood flow recovery was significantly impaired in mice lacking CD70 compared to control mice, but was similar in CD80/86^-/-, CTLA4^+/- and control mice. Mice lacking CD70 showed impaired vasculogenesis, since the number of pre-existing collaterals was reduced as observed in the pia mater compared to control mice. In vitro an impaired capability of vascular smooth muscle cells (VSMC) to activate T cells was observed in VSMC lacking CD70. Furthermore, CD70^-/-, CD80/86^-/- and CD70/80/86^-/- mice showed reduced angiogenesis in the soleus muscle 10 days after ligation. Arteriogenesis was also decreased in CD70^-/- compared to control mice 10 and 28 days after surgery.

CONCLUSIONS

The present study is the first to describe an important role for T cell activation via co-stimulation in angiogenesis, arteriogenesis and vasculogenesis, where the CD27-CD70 T cell co-stimulation pathway appears to be the most important co-stimulation pathway in pre-existing collateral formation and post-ischemic blood flow recovery, by arteriogenesis and angiogenesis.

CD80 Regulates Th17 Cell Differentiation in Coxsackie Virus B3-Induced Acute Myocarditis

The cluster of differentiation protein complex, CD80/CD86, regulates Th1/Th2 differentiation in autoimmune disease. In order to establish the effects of CD80/CD86 on Th17 cell differentiation in acute viral myocarditis (VMC), we infected C57BL/6 mice with Coxsackie virus B3 (CVB3) and examined the effects of the treatment with anti-CD80/CD86 monoclonal antibodies (mAbs) on Th17 cell differentiation in vivo. The effects of anti-CD80/CD86 mAbs on Th17 cell differentiation were further evaluated in vitro. The treatment with anti-CD80 mAb induced marked suppression of Th17 cell differentiation and ROR-γt mRNA expression, whereas anti-CD86 mAb alone had no effect, both in vivo and in vitro. Our finding that CD80 regulates Th17 differentiation supports the potential utility of anti-CD80 mAb as an effective new immunotherapeutic target in acute VMC.

The human blood DNA methylome identifies crucial role of β-catenin in the pathogenesis of Kawasaki disease

Kawasaki disease (KD) is a type of acute febrile vasculitis syndrome and is the most frequent cause of cardiac illness in children under the age of five years old. Although the etiology of KD remains largely unknown, some recent genome-wide studies have indicated that epigenetic factors may be important in its pathogenesis. We enrolled 24 KD patients and 24 non-KD controls in this study to access their DNA methylation status using HumanMethylation450 BeadChips. Another 34 KD patients and 62 control subjects were enrolled for expression validation. Of the 3193 CpG methylation regions with a methylation difference ≥ 20% between KD and controls, 3096 CpG loci revealed hypomehtylation, with only 3% being hypermethylated. Pathway buildup identified 11 networked genes among the hypermethylated regions, including four transcription factors: nuclear factor of activated T-cells 1, v-ets avian erythroblastosis virus E26 oncogene homolog 1, runt related transcription factor 3, and retinoic acid receptor gamma, as well as the activator β-catenin. Ten of these network-selected genes demonstrated a significant decrease in mRNA in KD patients, whereas only CTNNB1 significantly decreased in correlation with coronary artery lesions in KD patients. Furthermore, CTNNB1-silenced THP-1 monocytic cells drastically increased the expression of CD40 and significantly increased the expression of both CD40 and CD40L in cocultured human coronary artery endothelial cells. This study is the first to identify network-based susceptible genes of hypermethylated CpG loci, their expression levels, and the functional impact of β-catenin, which may be involved in both the cause and the development of KD.

Co-stimulatory molecules in and beyond co-stimulation – tipping the balance in atherosclerosis?

A plethora of basic laboratory and clinical studies has uncovered the chronic inflammatory nature of atherosclerosis. The adaptive immune system with its front-runner, the T cell, drives the atherogenic process at all stages. T cell function is dependent on and controlled by a variety of either co-stimulatory or co-inhibitory signals. In addition, many of these proteins enfold T cell-independent pro-atherogenic functions on a variety of cell types. Accordingly they represent potential targets for immune- modulatory and/or anti-inflammatory therapy of atherosclerosis. This review focuses on the diverse role of co-stimulatory molecules of the B7 and tumour necrosis factor (TNF)-superfamily and their downstream signalling effectors in atherosclerosis. In particular, the contribution of CD28/CD80/CD86/CTLA4, ICOS/ICOSL, PD-1/PDL-1/2, TRAF, CD40/CD154, OX40/OX40L, CD137/CD137L, CD70/CD27, GITR/GITRL, and LIGHT to arterial disease is reviewed. Finally, the potential for a therapeutic exploitation of these molecules in the treatment of atherosclerosis is discussed.

An inflammatory link in atherosclerosis and obesity. Co-stimulatory molecules

Atherosclerosis and obesity-induced metabolic dysfunction are lipid-driven inflammatory pathologies responsible for a major part of cardiovascular complications. Immune cell activation as well as interactions between the different immune cells is dependent on and controlled by a variety of co-stimulatory signals. These co-stimulatory signals can either aggravate or ameliorate the disease depending on the stage of the disease, the cell-types involved and the signal transduction cascades initiated. This review focuses on the diverse roles of the most established co-stimulatory molecules of the B7 and Tumor Necrosis Factor Receptor (TNFR) families, ie the CD28/CTLA4-CD80/CD86 and CD40L/CD40 dyads in the pathogenesis of atherosclerosis and obesity. In addition, we will explore their potential as therapeutic targets in both atherosclerosis and obesity.

Upregulation of Programmed Death-1 and Its Ligand in Cardiac Injury Models: Interaction with GADD153

Purpose

Programmed Death-1 (PD-1) and its ligand, PD-L1, are regulators of immune/ inflammatory mechanisms. We explored the potential involvement of PD-1/PD-L1 pathway in the inflammatory response and tissue damage in cardiac injury models.

Experimental Design

Ischemic-reperfused and cryoinjured hearts were processed for flow cytometry and immunohistochemical studies for determination of cardiac PD-1 and PD-L1 in the context of assessment of the growth arrest- and DNA damage-inducible protein 153 (GADD153) which regulates both inflammation and cell death. Further, we explored the potential ability of injured cardiac cells to influence proliferation of T lymphocytes.

Results

The isolated ischemic-reperfused hearts displayed marked increases in expression of PD-1 and PD-L1 in cardiomyocytes; however, immunofluorescent studies indicate that PD-1 and PD-L1 are not primarily co-expressed on the same cardiomyocytes. Upregulation of PD-1/PD-L1 was associated with a) marked increases in GADD153 and interleukin (IL)-17 but a mild increase in IL-10 and b) disruption of mitochondrial membrane potential (ψ_m) as well as apoptotic and necrotic cell death. Importantly, while isotype matching treatment did not affect the aforementioned changes, treatment with the PD-L1 blocking antibody reversed those effects in association with marked cardioprotection. Further, ischemic-reperfused cardiac cells reduced proliferation of T lymphocytes, an effect partially reversed by PD-L1 antibody. Subsequent studies using the cryoinjury model of myocardial infarction revealed significant increases in PD-1, PD-L1, GADD153 and IL-17 positive cells in association with significant apoptosis/necrosis.

Conclusions

The data suggest that upregulation of PD-1/PD-L1 pathway in cardiac injury models mediates tissue damage likely through a paracrine mechanism. Importantly, inhibition of T cell proliferation by ischemic-reperfused cardiac cells is consistent with the negative immunoregulatory role of PD-1/PD-L1 pathway, likely reflecting an endogenous cardiac mechanism to curtail the deleterious impact of infiltrating immune cells to the damaged myocardium. The balance of these countervailing effects determines the extent of cardiac injury.

CD80+ and CD86+ B cells as biomarkers and possible therapeutic targets in HTLV-1 associated myelopathy/tropical spastic paraparesis and multiple sclerosis

Background

Human T-cell lymphotropic virus (HTLV-1) is the causative agent of the incapacitating, neuroinflammatory disease HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP). Currently, there are no disease-modifying therapies with long-term clinical benefits or validated biomarkers for clinical follow-up in HAM/TSP. Although CD80 and CD86 costimulatory molecules play prominent roles in immune regulation and reflect disease status in multiple sclerosis (MS), data in HAM/TSP are lacking.

Methods

Using flow cytometry, we quantified ex vivo and in vitro expression of CD80 and CD86 in PBMCs of healthy controls, HTLV-1-infected individuals with and without HAM/TSP, and MS patients. We hypothesized ex vivo CD80 and CD86 expressions and their in vitro regulation by interferon (IFN)-α/β mirror similarities between HAM/TSP and MS and hence might reveal clinically useful biomarkers in HAM/TSP.

Results

Ex vivo expression of CD80 and CD86 in T and B cells increased in all HTLV-1 infected individuals, but with a selective defect for B cell CD86 upregulation in HAM/TSP. Despite decreased total B cells with increasing disease duration (p = 0.0003, r = −0.72), CD80⁺ B cells positively correlated with disease severity (p = 0.0017, r = 0.69) in HAM/TSP. B cell CD80 expression was higher in women with HAM/TSP, underscoring that immune markers can reflect the female predominance observed in most autoimmune diseases. In contrast to MS patients, CD80⁺ (p = 0.0001) and CD86⁺ (p = 0.0054) lymphocytes expanded upon in vitro culture in HAM/TSP patients. The expansion of CD80⁺ and CD86⁺ T cells but not B cells was associated with increased proliferation in HTLV-1 infection. In vitro treatment with IFN-β but not IFN-α resulted in a pronounced increase of B cell CD86 expression in healthy controls, as well as in patients with neuroinflammatory disease (HAM/TSP and MS), similar to in vivo treatment in MS.

Conclusions

We propose two novel biomarkers, ex vivo CD80⁺ B cells positively correlating to disease severity and CD86⁺ B cells preferentially induced by IFN-β, which restores defective upregulation in HAM/TSP. This study suggests a role for B cells in HAM/TSP pathogenesis and opens avenues to B cell targeting (with proven clinical benefit in MS) in HAM/TSP but also CD80-directed immunotherapy, unprecedented in both HAM/TSP and MS.

PD-1 blockage delays murine squamous cell carcinoma development

Engagement of programmed death-1 (PD-1) with its two ligands [programmed death ligand-1 (PD-L1) and PD-L2] has been associated with the suppression of tumor-reactive T cells; however, the underlying mechanism for this T-cell dysfunction is not clear. We hypothesized that PD-1 and PD-L1 signals are, in part, responsible for squamous cell carcinoma (SCC) escape from immune antitumor regulation by modulation of the tumor environment. In the present study, we used a multistage model of SCC to examine the role of PD-1/PD-L1 activation during tumor development. Tumor sites presented an increased percentage of CD4(+) and CD8(+) T cells expressing PD-1 when compared with non-tumorigenic control mice, whereas the expression of PD-L1 was particularly increased in F4/80(+) macrophages in tumor sites. Further, the systemic immune neutralization of PD-1 resulted in a decreased number and delayed incidence rate of papillomas followed by a differential expression of cytokeratins, suggesting that the PD-1-PD-L1 interaction contributes to the progression of SCC by downregulation of antitumor responses. In fact, blocking PD-1 increased the percentage of CD8(+) and CD4(+) T cells, and the levels of interferon-γ in the tumor sites. Our results indicated involvement of PD-1(+) T cells in SCC development and in the modulation of the inflammatory immune response.

Adaptive immunity and atherosclerosis: mouse tales in the AJP

Chronic inflammation driven by immune responses to lipid deposition in the arterial wall is now understood to be fundamental to the pathogenesis of atherosclerosis. The frequent presence of T lymphocytes in human atherosclerotic lesions was first described in the 1980s, but experiments to test whether adaptive immunity influences lesion development and phenotype required animal models. The American journal of pathology has published many research articles focused on the role of inflammation and adaptive immunity in diet-induced and genetically manipulated murine models of atherosclerosis. Seminal articles in the 1990s were the first to describe the presence of T cells in mouse atherosclerotic lesions; other articles demonstrated the effects of defective adaptive immunity on lesion development in mice.

Transcriptomic analysis of peritoneal cells in a mouse model of sepsis: confirmatory and novel results in early and late sepsis

BACKGROUND

The events leading to sepsis start with an invasive infection of a primary organ of the body followed by an overwhelming systemic response. Intra-abdominal infections are the second most common cause of sepsis. Peritoneal fluid is the primary site of infection in these cases. A microarray-based approach was used to study the temporal changes in cells from the peritoneal cavity of septic mice and to identify potential biomarkers and therapeutic targets for this subset of sepsis patients.

RESULTS

We conducted microarray analysis of the peritoneal cells of mice infected with a non-pathogenic strain of Escherichia coli. Differentially expressed genes were identified at two early (1 h, 2 h) and one late time point (18 h). A multiplexed bead array analysis was used to confirm protein expression for several cytokines which showed differential expression at different time points based on the microarray data. Gene Ontology based hypothesis testing identified a positive bias of differentially expressed genes associated with cellular development and cell death at 2 h and 18 h respectively. Most differentially expressed genes common to all 3 time points had an immune response related function, consistent with the observation that a few bacteria are still present at 18 h.

CONCLUSIONS

Transcriptional regulators like PLAGL2, EBF1, TCF7, KLF10 and SBNO2, previously not described in sepsis, are differentially expressed at early and late time points. Expression pattern for key biomarkers in this study is similar to that reported in human sepsis, indicating the suitability of this model for future studies of sepsis, and the observed differences in gene expression suggest species differences or differences in the response of blood leukocytes and peritoneal leukocytes.

PD-1 protects against inflammation and myocyte damage in T cell-mediated myocarditis

PD-1, a member of the CD28 family of immune regulatory molecules, is expressed on activated T cells, interacts with its ligands, PD-L1/B7-H1 and PD-L2/B7-DC, on other cells, and delivers inhibitory signals to the T cell. We studied the role of this pathway in modulating autoreactive T cell responses in two models of myocarditis. In a CD8(+) T cell-mediated adoptive transfer model, we found that compared with Pd1(+/+) CD8(+) T cells, Pd1(-/-) CD8(+) T cells cause enhanced disease, with increased inflammatory infiltrate, particularly rich in neutrophils. Additionally, we show enhanced proliferation in vivo and enhanced cytotoxic activity of PD-1-deficient T lymphocytes against myocardial endothelial cells in vitro. In experimental autoimmune myocarditis, a disease model dependent on CD4(+) T cells, we show that mice lacking PD-1 develop enhanced disease compared with wild-type mice. PD-1-deficient mice displayed increased inflammation, enhanced serum markers of myocardial damage, and an increased infiltration of inflammatory cells, including CD8(+) T cells. Together, these studies show that PD-1 plays an important role in limiting T cell responses in the heart.

T cell costimulatory and coinhibitory pathways in vascular inflammatory diseases

A broad array of evidence indicates that T lymphocytes make significant contributions to vascular inflammation in the setting of atherosclerotic disease, hypertension, autoimmune vasculitis, and other disorders. Experimental data show that costimulatory and coinhibitory pathways involving molecules of the B7-CD28 and TNF–TNFR families regulate T cell responses that promote vascular disease. Antigen presenting cells (APCs) display both peptide–major histocompatibility complex antigen and costimulators or coinhibitors to T cells. Two major types of APCs, dendritic cells (DCs) and macrophages, are present in significant numbers in the walls of arteries affected by atherosclerosis and arteritis, and some DCs are present in normal arteries. Costimulatory and coinhibitory molecules expressed by these vascular APCs can contribute to the activation or inhibition of effector T cells within the arterial wall. Vascular DCs may also be involved in transport of antigens to secondary lymphoid organs, where they activate or tolerize naïve T cells, depending on the balance of costimulators and coinhibitors they express. Costimulatory blockade is already an approved therapeutic approach to treat autoimmune disease and prevent transplant rejection. Preclinical models suggest that costimulatory blockade may also be effective in treating vascular disease. Experiential data in mice show that DCs pulsed with the appropriate antigens and treated in a way that reduces costimulatory capacity can reduce atherosclerotic disease, presumably by inducing T cell tolerance. Progress in treating vascular disease by immune modulation will require a more complete understanding of the functions of different costimulatory and coinhibitory pathways and the different subsets of vascular APCs involved.

Treatment with telmisartan attenuates graft arteriosclerosis in murine cardiac allografts

BACKGROUND

Chronic rejection remains the most prominent cause of graft failure after transplantation. Recently, it was reported that telmisartan can function as a partial agonist of peroxisome proliferator-activated receptor gamma (PPARgamma) in addition to a blocker of angiotensin II receptor. We investigated the effect of telmisartan on chronic rejection.

METHODS

Hearts from Bm12 mice were transplanted into C57BL/6 mice (Class II mismatch), and allografts were harvested at 8 weeks after transplantation. Recipient mice were fed either control chow or chow containing telmisartan (10 mg/kg/day) from 1 day before transplantation. Proliferation assays of smooth muscle cells (SMCs), which were isolated from the aorta of B/6 mice, was performed.

RESULTS

Although severe neo-intimal hyperplasia developed in allografts from control mice fed chow (luminal occlusion 70.9 +/- 6.1%), neo-intimal hyperplasia was significantly attenuated in allografts from mice fed chow containing telmisartan (30.0 +/- 10%, p < 0.001). Expression of interferon (IFN)-gamma and interleukin (IL)-15 mRNAs and matrix metalloproteinase (MMP)-2 in allografts was significantly lower in telmisartan-treated mice than in control mice. Proliferation of smooth muscle cells (SMCs) in response to fetal bovine serum was suppressed significantly by telmisartan (10 micromol/liter). The PPARgamma antagonist blocked telmisartan-induced suppression of SMC proliferation.

CONCLUSIONS

Telmisartan attenuates SMC proliferation via PPARgamma activity and suppresses neo-intimal hyperplasia after transplantation. Telmisartan may be useful for suppressing chronic allograft rejection.

Paradoxical functions of B7: CD28 costimulation in a MHC class II-mismatched cardiac transplant model

Blockade of the B7: CD28 costimulatory pathway has emerged as a promising therapy to prevent allograft rejection. However, this pathway has also been demonstrated to be important for the generation and maintenance of regulatory T cells. In this study, we investigated the role of the B7: CD28 pathway in the 'bm12 into B6' MHC class II-mismatched vascularized cardiac transplant model of chronic rejection. Allograft rejection was remarkably accelerated in B6 background B7DKO and CD28KO recipients compared with B6 wild-type (WT) recipients. Allograft rejection was associated with a significantly enhanced Th1/Th2 alloreactivity and marked reduction in the ratio of regulatory T cells to CD4(+) effector/memory cells. We noted that administration of anti-B7-1 and anti-B7-2 mAb prior to transplantation also accelerated allograft rejection. Furthermore, depleting CD25(+) cells in B6 WT recipients of bm12 hearts prior to transplant also precipitated rejection at a similar rate. Neither B7/CD28 deficiency nor CD25 depletion affected graft survival in single MHC class I-mismatched (bm1 into B6) recipients. This study highlights the paradoxical functions of B7: CD28 costimulation in a MHC class II-mismatched model, in which the B7: CD28 pathway is demonstrated to be important in preventing rejection through the generation and maintenance of Tregs.

Preferential costimulation by CD80 results in IL-10-dependent TGF-beta1(+) -adaptive regulatory T cell generation

Costimulatory ligands CD80 and CD86 have different binding preferences and affinities to their receptors, CD28 and CTLA-4. Earlier, we demonstrated that CD80 binds to CTLA-4 with higher affinity and has a role in suppressing T cell response. The current study demonstrates that not only did blockade of CD86 upon Ag presentation by bone marrow-derived dendritic cells (DC) to OVA-specific T cells result in induction of hyporesponsive T cells but also that these T cells could suppress the proliferative response of effector T cells. These T cells showed TGF-beta1 on their surface and secreted TGF-beta1 and IL-10 upon restimulation. Although blockade of CTLA-4 and neutralization of IL-10 profoundly inhibited the induction of these TGF-beta1(+) T cells, their ability to suppress the effector T cell proliferation was abrogated by neutralization of TGF-beta1 alone. Induction of TGF-beta1(+) and IL-10(+) T cells was found to be independent of natural CD4(+)CD25(+) regulatory T cells, demonstrating that preferential ligation of CTLA-4 by CD80 induced IL-10 production by effector T cells, which in turn promoted the secretion of TGF-beta1. Treatment of prediabetic NOD mice with islet beta cell Ag-pulsed CD86(-/-) DCs, but not CD80(-/-) DCs, resulted in the induction of TGF-beta1- and IL-10-producing cells, significant suppression of insulitis, and delay of the onset of hyperglycemia. These observations demonstrate not only that CD80 preferentially binds to CTLA-4 but also that interaction during Ag presentation can result in IL-10-dependent TGF-beta1(+) regulatory T cell induction, reinstating the potential of approaches to preferentially engage CTLA-4 through CD80 during self-Ag presentation in suppressing autoimmunity.

Heterotopic vascularized murine cardiac transplantation to study graft arteriopathy

The development of microsurgical techniques has facilitated the establishment of fully vascularized cardiac transplantation models in small mammals. A particularly useful model that has evolved for the study of cardiac allograft vasculopathy (CAV) is a heterotopic (abdominal) vascularized murine cardiac transplantation model. Using this model has permitted the elucidation of genetic, immune and non-immune factors contributing to the development of this inexorable pathological condition, which compromises half of all human cardiac transplants. This protocol details methods for performing the transplant, histomorphometric assessment of the graft vasculature and functional evaluation of the transplanted heart. In experienced hands, the surgical procedure requires approximately 75 min to complete, and vasculopathy results are obtained at 2 months. This model entails a fully vascularized implantation technique in which the donor ascending aorta and pulmonary artery are sutured end-to-side to the recipient abdominal aorta and inferior vena cava, respectively. As this model reliably reproduces immunological and non-immunological features of CAV, investigators can thoroughly explore contributory mechanisms, diagnostic modalities and therapeutic approaches to its mitigation.

T-cell costimulatory pathways in allograft rejection and tolerance

The destiny of activated T cells is critical to the ultimate fate of immune response. After encountering antigen, naïve T cells receive signal 1 through the T-cell receptor (TCR)-major histocompatibility complex (MHC) plus antigenic peptide complex and signal 2 through "positive" costimulatory molecules leading to full activation. "Negative" T-cell costimulatory pathways, on the other hand, function to downregulate immune responses. The purpose of this article is to review the current state of knowledge and recent advances in our understanding of the functions of the positive and negative T-cell costimulatory pathways in alloimmune responses. Specifically, we discuss the functions of the CD28:B7 and the tumor necrosis factor receptor (TNFR):tumor necrosis factor (TNF) family of molecules in allograft rejection and tolerance. We address the following important questions: are T-cell costimulatory pathways merely redundant or do they provide distinct and unique functions? What are the important and unique interactions between the various pathways? And, what are the effects and mechanisms of targeting of these pathways in different types and patterns of allograft rejection and tolerance models?

Quantitative analysis of myocardial inflammation by flow cytometry in murine autoimmune myocarditis: correlation with cardiac function

Inflammation has been increasingly recognized as an important pathological component of heart failure. Existing methods of assessing myocardial infiltrate are labor-intensive and provide data that are difficult to quantify and not representative of the whole heart. As a result, little effort has been made to systematically assess the components of myocardial inflammation. We established an alternative method of quantitative assessment of myocardial inflammation by flow cytometry after enzymatic digestion of hearts to characterize the infiltrate and study the association between inflammation and cardiac function in murine experimental autoimmune myocarditis. The severity of acute myocarditis uniquely correlated with the proportion of neutrophils, but not T cells, B cells, or macrophages. Both acute and chronic phases were characterized by the presence of CD44high (activated) T cells in the heart, whereas T cells trafficking through normal hearts exhibited CD44low phenotype. During the chronic phase, the proportion of CD4+ T cells was associated with increased left-ventricular volumes and deterioration of systolic function, the hallmarks of dilated cardiomyopathy. We conclude that flow cytometry on uniformly digested mouse hearts provides sensitive and reproducible assessment of myocardial infiltrate and can be used to dissect out the specific role of individual immune components from the overall inflammatory response in the heart.

Sepsis-induced changes in macrophage co-stimulatory molecule expression: CD86 as a regulator of anti-inflammatory IL-10 response

BACKGROUND

Sepsis remains a substantial risk after surgery or other trauma. Macrophage dysfunction, as a component of immune suppression seen during trauma and sepsis, appears to be one of the contributing factors to morbidity and mortality. However, whereas it is known that the ability of macrophages to present antigen and express major histocompatibility complex MHC class II molecules is decreased during sepsis, it is not known to what extent this is associated with the loss of co-stimulatory receptor expression. Our objectives in this study were, therefore, to determine if the expression of co-stimulatory molecules, such as CD40, CD80, or CD86, on peritoneal/splenic/liver macrophages were altered by sepsis (cecal ligation [CL] and puncture [CLP] or necrotic tissue injury (CL) alone; and to establish the contribution of such changes to the response to septic challenge using mice that are deficient in these receptors.

METHODS

To address our first objective, male C3H/HeN mice were subjected to CLP, CL, or sham (n = four to six mice/group), and the adherent macrophages were isolated from the peritoneum, spleen, or liver at 24 h post-insult. The macrophages were then analyzed by flow cytometry for their ex vivo expression of CD40, CD80, CD86, and/or MHC II.

RESULTS

The expression of CD86 and MHC II, but not CD40 or CD80, were significantly decreased on peritoneal macrophages after the onset of sepsis or CL alone. In addition, CD40 expression was significantly increased in Kupffer cells after sepsis. Alternatively, splenic macrophages from septic or CL mice did not show changes in the expression of CD80, CD86, or CD40. To the degree that the loss of CD86 expression might contribute to the changes reported in macrophage function in septic mice, we subsequently examined the effects of CLP on CD86 -/- mice. Interestingly, we found that, unlike the background controls, neither the serum IL-10 concentrations nor the IL-10 release capacity of peritoneal macrophages from septic CD86 -/- mice were increased.

CONCLUSION

Together, these data suggest a potential role for the co-stimulatory receptor CD86/B7-2 beyond that of simply promoting competent antigen presentation to T-cells, but also as a regulator of the anti-inflammatory IL-10 response. Such a role may implicate the latter response in the development of sepsis-induced immune dysfunction.

Tumor necrosis factor receptor -1 and -2 double deficiency reduces graft arterial disease in murine cardiac allografts

Graft arterial disease (GAD) remains the leading cause of long-term solid organ allograft failure. Tumor necrosis factor (TNF) promotes multiple aspects of allograft rejection via binding to type 1 (p55) and type 2 (p75) receptors. We used TNF type 1 receptor deficient (TNFR1KO), type 2 receptor deficient (TNFR2KO) and receptor double-deficient (TNFRDKO) mice to assess the relative roles of TNFR in acute rejection and GAD. Heterotopic cardiac transplantation was performed between C57BL/6 (B/6) and Balb/c (B/c) mice (total allomismatches) to assess the effects on graft survival; B/6 and Bm12 mice (class II mismatches) were used to assess the effects on GAD 8 weeks after transplantation. We found that graft survival in the total allomismatch combinations was the same regardless of TNFR status. In class II mismatches, wild-type (WT) combinations showed severe GAD, and GAD was not diminished when WT hearts were transplanted into TNFRDKO hosts. TNFR1KO donors or TNFR2KO donors had GAD comparable to WT donors, however, GAD was significantly diminished in B/6 TNFRDKO donor hearts. We conclude that both p55 and p75 signals on donor vascular wall cells are involved in the development of GAD, and either TNFR is capable of mediating a response that will culminate in GAD.

Induction of immunologic tolerance to cardiac allograft by simultaneous blockade of inducible co-stimulator and cytotoxic T-lymphocyte antigen 4 pathway

BACKGROUND

Inducible co-stimulator (ICOS) is one of the most recently described members of the CD28 family, and it plays an important role in immune responses. To investigate the role of ICOS in allograft rejection, the authors studied graft survival after cardiac transplantation in mice.

METHODS

Hearts from BALB/c mice were transplanted into C3H/He mice. Immunohistochemical staining and flow cytometry were performed. Monoclonal antibody to ICOS or ICOS-immunoglobulin (Ig) was injected intraperitoneally. The authors performed mixed lymphocyte reaction (MLR).

RESULTS

ICOS was expressed strongly by graft-infiltrating cells during rejection of the allograft. Blockade of the ICOS pathway with anti-ICOS antibody and ICOSIg significantly prolonged graft survival time relative to that in untreated mice; however, all cardiac allografts were eventually rejected by a single treatment. Treatment with both ICOSIg and cytotoxic T-lymphocyte antigen 4 (CTLA4) Ig induced not only long-term acceptance of the cardiac allograft but also donor-specific tolerance, which was shown by acceptance of donor but not third-party skin. Graft arterial intimal hyperplasia in these cardiac allografts was remarkably less than that in cardiac allografts treated with tacrolimus. Addition of anti-ICOS antibody or ICOSIg to MLR resulted in inhibition of T-cell proliferation.

CONCLUSIONS

Inhibition of T-cell proliferation with ICOSIg and CTLA4Ig was more effective than that with ICOSIg alone. Thus, ICOS appears to be an important regulator of T-cell activation, and may be an effective therapy in clinical cardiac transplantation.

Mechanisms of targeting CD28 by a signaling monoclonal antibody in acute and chronic allograft rejection

There is increasing evidence that ongoing T-cell recognition of alloantigen and activation are key mediators of chronic allograft rejection. The CD28-B7 pathway is unique among costimulatory pathways in that two alternate ligands for B7 exist: CD28 and CTLA4. Recently, it has been suggested that CTLA4 negative signaling may be required for induction of acquired tolerance in vivo. A strategy by which the T cell is targeted at the CD28 receptor rather than its ligands would theoretically allow the inhibitory functions of the CTLA4-B7-1/2 axis to remain intact. Using a rat-specific monoclonal antibody, we investigated the effect of targeting CD28 in a model of chronic rejection without the confounding variable of immunosuppression. We also used an acute cardiac allograft rejection model to investigate CD28 stimulation-based strategies to induce donor-specific tolerance. We demonstrated that anti-CD28 monoclonal antibody was as effective as CTLA4 immunoglobulin in protecting against chronic allograft vasculopathy. In addition, a short course of cyclosporine therapy synergized with either anti-CD28 monoclonal antibody or CTLA4 immunoglobulin, suggesting that it may be clinically relevant to combine low-dose calcineurin inhibitors with CTLA4 immunoglobulin or anti-B7 antibodies. Finally, we report on the potential mechanisms of action of targeting CD28 in vivo.

The B7-CD28 superfamily

The B7-1/B7-2-CD28/CTLA-4 pathway is crucial in regulating T-cell activation and tolerance. New B7 and CD28 molecules have recently been discovered and new pathways have been delineated that seem to be important for regulating the responses of previously activated T cells. Several B7 homologues are expressed on cells other than professional antigen-presenting cells, indicating new mechanisms for regulating T-cell responses in peripheral tissues. Some B7 homologues have unknown receptors, indicating that other immunoregulatory pathways remain to be described. Here, we summarize our current understanding of the new members of the B7 and CD28 families, and discuss their therapeutic potential.

Cellular mechanisms that cause suppressed gamma interferon secretion in endotoxin-tolerant mice

Endotoxin (lipopolysaccharide [LPS]) tolerance is a state of altered immunity characterized, in part, by suppression of LPS-induced gamma interferon (IFN-gamma) expression. However, the cellular mediators regulating LPS-induced production of IFN-gamma in normal mice and the effect of LPS tolerance on these mediators has not been well characterized. Our studies show that macrophage dysfunction is the primary factor causing suppressed IFN-gamma expression in LPS-tolerant mice. Specifically, LPS-tolerant macrophages have a markedly impaired ability to induce IFN-gamma secretion by T cells and NK cells obtained from either control or LPS-tolerant mice. However, T cells and NK cells isolated from LPS-tolerant mice produce normal levels of IFN-gamma when cocultured with control macrophages or exogenous IFN-gamma-inducing factors. Assessment of important IFN-gamma-regulating factors showed that interleukin-12 (IL-12) and costimulatory signals provided by IL-15, IL-18, and CD86 are largely responsible for LPS-induced IFN-gamma expression in control mice. IL-10 is an inhibitor of IFN-gamma production in both the control and LPS-tolerant groups. Expression of IL-12 and the IL-12 receptor beta1 (IL-12Rbeta1) and IL-12Rbeta2 subunits are suppressed in the spleens of LPS-tolerant mice. LPS-tolerant splenocytes also exhibit decreased production of IL-15 and IL-15Ralpha. However, expression of IL-18 and the B7 proteins CD80 and CD86 are unchanged or increased compared to controls after induction of LPS tolerance. CD28, a major receptor for B7 proteins, is also increased in the spleens of LPS-tolerant mice. Expression of the inhibitory cytokine IL-10 and the IL-10R are sustained after induction of LPS tolerance. These data show that suppression of IFN-gamma production in LPS-tolerant mice is largely due to macrophage dysfunction and provide insight into the cellular alterations that occur in LPS tolerance. This study also better defines the factors that mediate LPS-induced IFN-gamma production in normal mice.