Absence of nonhematopoietic MHC class II expression protects mice from experimental autoimmune myocarditis

Are fetal microchimerism and circulating fetal extracellular vesicles important links between spontaneous preterm delivery and maternal cardiovascular disease risk?

Trafficking and persistence of fetal microchimeric cells (fMCs) and circulating extracellular vesicles (EVs) have been observed in animals and humans, but their consequences in the maternal body and their mechanistic contributions to maternal physiology and pathophysiology are not yet fully defined. Fetal cells and EVs may help remodel maternal organs after pregnancy-associated changes, but the cell types and EV cargos reaching the mother in preterm pregnancies after exposure to various risk factors can be distinct from term pregnancies. As preterm delivery-associated maternal complications are rising, revisiting this topic and formulating scientific questions for future research to reduce the risk of maternal morbidities are timely. Epidemiological studies report maternal cardiovascular risk as one of the major complications after preterm delivery. This paper suggests a potential link between fMCs and circulating EVs and adverse maternal cardiovascular outcomes post-pregnancies, the underlying mechanisms, consequences, and methods for and how this link might be assessed.

IFITM3 mediates inflammation induced myocardial injury through JAK2/STAT3 signaling pathway

Myocarditis is an inflammation of the heart muscle often associated with viral infections and can lead to dilated cardiomyopathy. Interferon-induced transmembrane protein 3 (IFITM3) is a small endosomal membrane protein with anti-viral activity against multiple viruses and is also implicated in non-infectious diseases such as cancer and Alzheimer's Disease. Since the IFITM3 proteins are expressed both in T cells and in cardiomyocytes, it is reasonable to hypothesize that these molecules could affect myocarditis either through their effect on the autoimmune response or through direct modulation of cardiomyocyte damage. The aim of this study was to investigate the role of IFITM3 in experimental autoimmune myocarditis (EAM)-mediated myocardial injury. Immunization of rats with cardiac myosin results in substantial cardiac inflammation and is associated with increased expression of IFITM3 after 21 days. In vivo IFITM3 shRNA knockdown using the lentivirus transfection method reduced cardiac injury while restoring IFITM3 expression reversed the protective effect of IFITM3 RNA interference. To determine the direct impact of IFITM3, the rat ventricular cell line, H9c2, was treated with palmitic acid which causes apoptosis in these cells. Suppressing IFITM3 expression protects H9c2 cells while overexpressing IFITM3 enhances cell injury. JAK inhibitors reduced IFITM3-mediated myocardial cell injury. In conclusion, IFITM3 may mediate myocardial injury in EAM rats and palmitic acid-induced damage to H9c2 cells through the JAK2/STAT3 pathway.

TGF-β Signaling Prevents MHC Class II-Expressing Lymphatic Endothelial Cells from Reactivating Human Allogenic Memory CD4+ T Cells

Lymphatic endothelial cells (LECs) express MHC class II (MHC-II) upon IFN-γ stimulation, yet recent evidence suggests that LECs cannot activate naive or memory CD4+ T cells. In this article, we show that IFN-γ-activated human dermal LECs can robustly reactivate allogeneic human memory CD4+ T cells (hCD4+ TMs), but only when TGF-β signaling is inhibited. We found that in addition to upregulating MHC-II, IFN-γ also induces LECs to upregulate glycoprotein A repetitions predominant, which anchors latent TGF-β to the membrane and potentially inhibits T cell activation. Indeed, hCD4+ TM proliferation was substantially increased when LEC-CD4+ TM cultures were treated with a TGF-β receptor type 1 inhibitor or when glycoprotein A repetitions predominant expression was silenced in LECs. Reactivated hCD4+ TMs were characterized by their proliferation, CD25 expression, and cytokine secretion. CD4+ TM reactivation was dependent on LEC expression of MHC-II, confirming direct TCR engagement. Although CD80 and CD86 were not detected on LECs, the costimulatory molecules OX40L and ICOSL were upregulated upon cytokine stimulation; however, blocking these did not affect CD4+ TM reactivation by LECs. Finally, we found that human dermal LECs also supported the maintenance of Foxp3-expressing hCD4+ TMs independently of IFN-γ-induced MHC-II. Together, these results demonstrate a role for LECs in directly modulating CD4+ TM reactivation under inflammatory conditions and point to LEC-expressed TGF-β as a negative regulator of this activation.

MHC class II antigen presentation by intestinal epithelial cells fine-tunes bacteria-reactive CD4 T-cell responses

Although intestinal epithelial cells (IECs) can express major histocompatibility complex class II (MHC II), especially during intestinal inflammation, it remains unclear if antigen presentation by IECs favors pro- or anti-inflammatory CD4+ T-cell responses. Using selective gene ablation of MHC II in IECs and IEC organoid cultures, we assessed the impact of MHC II expression by IECs on CD4+ T-cell responses and disease outcomes in response to enteric bacterial pathogens. We found that intestinal bacterial infections elicit inflammatory cues that greatly increase expression of MHC II processing and presentation molecules in colonic IECs. Whilst IEC MHC II expression had little impact on disease severity following Citrobacter rodentium or Helicobacter hepaticus infection, using a colonic IEC organoid-CD4+ T cell co-culture system, we demonstrate that IECs can activate antigen-specific CD4+ T cells in an MHC II-dependent manner, modulating both regulatory and effector Th cell subsets. Furthermore, we assessed adoptively transferred H. hepaticus-specific CD4+ T cells during intestinal inflammation in vivo and report that IEC MHC II expression dampens pro-inflammatory effector Th cells. Our findings indicate that IECs can function as non-conventional antigen-presenting cells and that IEC MHC II expression fine-tunes local effector CD4+ T-cell responses during intestinal inflammation.

Tolerance Induction in Vascularized Composite Allotransplantation-A Brief Review of Preclinical Models

Pre-clinical studies are an obligatory tool to develop and translate novel therapeutic strategies into clinical practice. Acute and chronic rejection mediated by the recipient's immune system remains an important limiting factor for the (long-term) survival of vascularized composite allografts (VCA). Furthermore, high intensity immunosuppressive (IS) protocols are needed to mitigate the immediate and long-term effects of rejection. These IS regiments can have significant side-effects such as predisposing transplant recipients to infections, organ dysfunction and malignancies. To overcome these problems, tolerance induction has been proposed as one strategy to reduce the intensity of IS protocols and to thereby mitigate long-term effects of allograft rejection. In this review article, we provide an overview about animal models and strategies that have been used to induce tolerance. The induction of donor-specific tolerance was achieved in preclinical animal models and clinical translation may help improve short and long-term outcomes in VCAs in the future.

The Roles of Cardiac Fibroblasts and Endothelial Cells in Myocarditis

In myocarditis caused by various etiologies, activated immune cells and the immune regulatory factors released by them play important roles. But in this complex microenvironment, non-immune cells and non-cardiomyocytes in the heart, such as cardiomyocytes (CMs), cardiac fibroblasts (CFs) and endothelial cells (ECs), play the role of “sentinel”, amplify inflammation, and interact with the cardiomyocytes. The complex interactions between them are rarely paid attention to. This review will re-examine the functions of CFs and ECs in the pathological conditions of myocarditis and their direct and indirect interactions with CMs, in order to have a more comprehensive understanding of the pathogenesis of myocarditis and better guide the drug development and clinical treatment of myocarditis.

A genetic screen in macrophages identifies new regulators of IFNγ-inducible MHCII that contribute to T cell activation

Cytokine-mediated activation of host immunity is central to the control of pathogens. Interferon-gamma (IFNγ) is a key cytokine in protective immunity that induces major histocompatibility complex class II molecules (MHCII) to amplify CD4⁺ T cell activation and effector function. Despite its central role, the dynamic regulation of IFNγ-induced MHCII is not well understood. Using a genome-wide CRISPR-Cas9 screen in murine macrophages, we identified genes that control MHCII surface expression. Mechanistic studies uncovered two parallel pathways of IFNγ-mediated MHCII control that require the multifunctional glycogen synthase kinase three beta (GSK3β) or the mediator complex subunit 16 (MED16). Both pathways control distinct aspects of the IFNγ response and are necessary for IFNγ-mediated induction of the MHCII transactivator Ciita, MHCII expression, and CD4⁺ T cell activation. Our results define previously unappreciated regulation of MHCII expression that is required to control CD4⁺ T cell responses.

Heart non-specific effector CD4+ T cells protect from postinflammatory fibrosis and cardiac dysfunction in experimental autoimmune myocarditis

Heart-specific CD4⁺ T cells have been implicated in development and progression of myocarditis in mice and in humans. Here, using mouse models of experimental autoimmune myocarditis (EAM) we investigated the role of heart non-specific CD4⁺ T cells in the progression of the disease. Heart non-specific CD4⁺ T cells were obtained from DO11.10 mice expressing transgenic T cell receptor recognizing chicken ovalbumin. We found that heart infiltrating CD4⁺ T cells expressed exclusively effector (T_eff) phenotype in the EAM model and in hearts of patients with lymphocytic myocarditis. Adoptive transfer experiments showed that while heart-specific T_eff infiltrated the heart shortly after injection, heart non-specific T_eff effectively accumulated during myocarditis and became the major heart-infiltrating CD4⁺ T cell subset at later stage. Restimulation of co-cultured heart-specific and heart non-specific CD4⁺ T cells with alpha-myosin heavy chain antigen showed mainly Th1/Th17 response for heart-specific T_eff and up-regulation of a distinct set of extracellular signalling molecules in heart non-specific T_eff. Adoptive transfer of heart non-specific T_eff in mice with myocarditis did not affect inflammation severity at the peak of disease, but protected the heart from adverse post-inflammatory fibrotic remodelling and cardiac dysfunction at later stages of disease. Furthermore, mouse and human T_eff stimulated in vitro with common gamma cytokines suppressed expression of profibrotic genes, reduced amount of α-smooth muscle actin filaments and decreased contraction of cardiac fibroblasts. In this study, we provided a proof-of-concept that heart non-specific T_eff cells could effectively contribute to myocarditis and protect the heart from the dilated cardiomyopathy outcome.

Myocarditis in Humans and in Experimental Animal Models

Myocarditis is defined as an inflammation of the cardiac muscle. In humans, various infectious and non-infectious triggers induce myocarditis with a broad spectrum of histological presentations and clinical symptoms of the disease. Myocarditis often resolves spontaneously, but some patients develop heart failure and require organ transplantation. The need to understand cellular and molecular mechanisms of inflammatory heart diseases led to the development of mouse models for experimental myocarditis. It has been shown that pathogenic agents inducing myocarditis in humans can often trigger the disease in mice. Due to multiple etiologies of inflammatory heart diseases in humans, a number of different experimental approaches have been developed to induce myocarditis in mice. Accordingly, experimental myocarditis in mice can be induced by infection with cardiotropic agents, such as coxsackievirus B3 and protozoan parasite Trypanosoma cruzi or by activating autoimmune responses against heart-specific antigens. In certain models, myocarditis is followed by the phenotype of dilated cardiomyopathy and the end stage of heart failure. This review describes the most commonly used mouse models of experimental myocarditis with a focus on the role of the innate and adaptive immune systems in induction and progression of the disease. The review discusses also advantages and limitations of individual mouse models in the context of the clinical manifestation and the course of the disease in humans. Finally, animal-free alternatives in myocarditis research are outlined.

Infectious myocarditis: the role of the cardiac vasculature

Infectious myocarditis is the result of an immune response to a microbial infection of the heart. The blood vessels of the heart, both the intramyocardial microvasculature and the large epicardial coronary arteries, play an important role in the pathogenesis of infectious myocarditis. First of all, in addition to cardiomyocytes, endothelial cells of the cardiac (micro)vasculature are direct targets for infection. Moreover, through the expression of adhesion molecules and antigen presenting Major Histocompatibility Complex molecules, the blood vessels assist in shaping the cellular immune response in infectious myocarditis. In addition, damage and dysfunction of the cardiac (micro)vasculature are associated with thrombus formation as well as aberrant regulation of vascular tone including coronary vasospasm. These in turn can cause cardiac perfusion abnormalities and even myocardial infarction. In this review, we will discuss the role of the cardiac (micro)vasculature in the pathogenesis of infectious myocarditis.

Pro-remodeling effect of autoantibody against β1-adrenoceptor on cardiomyocytes involves T cells dysfunction under the pathological condition of heart failure

Autoantibody against β₁-adrenoceptor (β₁-AA) has been shown to be closely linked to the aggravation of heart failure. Removal of β₁-AA remarkably attenuated patients' cardiac dysfunction. We found that β₁-AA induced rat heart failure with increased CD4⁺ T cells. However, whether or not β₁-AA interacts with T cells isolated from heart failure patients remains unknown. Twenty-one β₁-AA-negative heart failure patients were divided into those taking β-adrenergic blocker and those not. The effects of β₁-AA monoclonal antibodies (β₁-AAmAb) on T cells proliferation were detected using the CCK-8 assay. IFN-γ and IL-4 production by human T cells were measured by after the administration of β₁-AAmAb. The levels of cardiomyocyte apoptosis and hypertrophy were detected after co-cultured with the supernatant of T cells pre-stimulated by β₁-AAmAb. It was found that β₁-AAmAb promoted T cell proliferation via the β₁-AR/cAMP/PKA pathway in patients who not take β-blocker. β₁-AAmAb inhibited the characteristic cytokine secretion of Th1, IFN-γ, but had no significant effect on the Th2 cytokine IL-4. Supernatant resulted from the T cells pre-treated with β₁-AAmAb induced cardiomyocytes remodeling, as evidenced by increased levels of cardiomyocytes apoptosis and hypertrophy. We propose that heart failure is likely to be an interference factor for Th-mediated immunity, and the presence of β₁-AAmAb may aggravate this effect and deteriorate concomitant inflammatory injury in cardiomyocytes, partially via β₁-AR/cAMP/PKA pathway.

Absence of MHC-II expression by lymph node stromal cells results in autoimmunity

MHCII-restricted antigen presentation by lymph node stromal cells is essential for regulatory T-cell proliferation and functions, and for the regulation of autoimmunity.

How lymph node stromal cells (LNSCs) shape peripheral T-cell responses remains unclear. We have previously demonstrated that murine LNSCs, lymphatic endothelial cells (LECs), blood endothelial cells (BECs), and fibroblastic reticular cells (FRCs) use the IFN-γ–inducible promoter IV (pIV) of the MHC class II (MHCII) transactivator CIITA to express MHCII. Here, we show that aging mice (>1 yr old) in which MHCII is abrogated in LNSCs by the selective deletion of pIV exhibit a significant T-cell dysregulation in LNs, including defective Treg and increased effector CD4⁺ and CD8⁺ T-cell frequencies, resulting in enhanced peripheral organ T-cell infiltration and autoantibody production. The proliferation of LN-Tregs interacting with LECs increases following MHCII up-regulation by LECs upon aging or after exposure to IFN-γ, this effect being abolished in mice in which LECs lack MHCII. Overall, our work underpins the importance of LNSCs, particularly LECs, in supporting Tregs and T-cell tolerance.

Cardiac morbidity in HIV infection is associated with checkpoint inhibitor LAG-3 on CD4 T cells

Recent findings point to a role of Checkpoint Inhibitor (CPI) receptors at the tissue level in immune homeostasis. Here we investigated the role of CPI molecules on immune cells in relation to cardiac function. Participants recruited in Chennai, India consisted of HIV+ ART naive viremic (Gp1 n = 102), HIV+ on ART, virologically suppressed (Gp2, n = 172) and HIV negative healthy controls (Gp3, n = 64). A cross-sectional analysis of cardiac function, arterial resistance and immunologic assessment of CPI expressing T cells was performed. Data indicate that ART naive exhibited cardiac function impairment and greater arterial stiffness than the other groups. Frequencies of CD4+ T cells expressing LAG-3 and PD1 were higher in ART naïve while TIGIT and TIM3 were similar among the patient groups. LAG-3+, PD1+ and dual LAG-3+PD1+ CD4 T cells were inversely correlated with cardiac function and arterial elasticity and directly with arterial stiffness in ART naïve participants and with arterial elasticity in virally suppressed group on ART. We conclude that HIV induced upregulation of LAG-3 singly or in combination with PD1 in immune cells may regulate cardiac health and warrant mechanistic investigations. The implications of these findings have bearing for the potential utility of anti-LAG-3 immunotherapy for cardiac dysfunction in chronic HIV infection.

Chemical and genetic control of IFNγ-induced MHCII expression

The cytokine interferon-γ (IFNγ) can induce expression of MHC class II (MHCII) on many different cell types, leading to antigen presentation to CD4⁺ T cells and immune activation. This has also been linked to anti-tumour immunity and graft-versus-host disease. The extent of MHCII upregulation by IFNγ is cell type-dependent and under extensive control of epigenetic regulators and signalling pathways. Here, we identify novel genetic and chemical factors that control this form of MHCII expression. Loss of the oxidative stress sensor Keap1, autophagy adaptor p62/SQSTM1, ubiquitin E3-ligase Cullin-3 and chromatin remodeller BPTF impair IFNγ-mediated MHCII expression. A similar phenotype is observed for arsenite, an oxidative stressor. Effects of the latter can be reversed by the inhibition of HDAC1/2, linking oxidative stress conditions to epigenetic control of MHCII expression. Furthermore, dimethyl fumarate, an antioxidant used for the treatment of several autoimmune diseases, impairs the IFNγ response by manipulating transcriptional control of MHCII We describe novel pathways and drugs related to oxidative conditions in cells impacting on IFNγ-mediated MHCII expression, which provide a molecular basis for the understanding of MHCII-associated diseases.

Heart macrophages and dendritic cells in sickness and in health: A tale of a complicated marriage

Heart disease is the major cause of death and it is broadly recognized that the immune system plays a central role in healthy and injured heart. Here, we focus on the contribution of various subsets of mononuclear phagocytes in the cardiac system. Macrophages and dendritic cells reside in the healthy myocardium to fulfill homeostatic functions and rapidly increase in numbers in diseases like myocardial ischemia and myocarditis to contribute to disease or resolve it. Recent experiments have revealed the extraordinary heterogeneity of cardiac mononuclear phagocytes that differ in origin, lifespan, phenotype and function. Although many studies described cardiac phagocytes in the mouse, subsets of cardiac mononuclear phagocytes can also be broadly found in the human heart, opening up the potential of selective targeting of these cells in a therapeutic setting. Before this goal can be achieved we need better understanding not only of the detrimental but also beneficial functions of these highly diverse cells in the heart.

Are the innate and adaptive immune systems setting hypertension on fire?

Hypertension is the most common chronic cardiovascular disease and is associated with several pathological states, being an important cause of morbidity and mortality around the world. Low-grade inflammation plays a key role in hypertension and the innate and adaptive immune systems seem to contribute to hypertension development and maintenance. Hypertension is associated with vascular inflammation, increased vascular cytokines levels and infiltration of immune cells in the vasculature, kidneys and heart. However, the mechanisms that trigger inflammation and immune system activation in hypertension are completely unknown. Cells from the innate immune system express pattern recognition receptors (PRR), which detect conserved pathogen-associated molecular patterns (PAMPs) and damage-associated molecular patterns (DAMPs) that induce innate effector mechanisms to produce endogenous signals, such as inflammatory cytokines and chemokines, to alert the host about danger. Additionally, antigen-presenting cells (APC) act as sentinels that are activated by PAMPs and DAMPs to sense the presence of the antigen/neoantigen, which ensues the adaptive immune system activation. In this context, different lymphocyte types are activated and contribute to inflammation and end-organ damage in hypertension. This review will focus on experimental and clinical evidence demonstrating the contribution of the innate and adaptive immune systems to the development of hypertension.