Urs Eriksson

Dendritic cell–induced autoimmune heart failure requires cooperation between adaptive and innate immunity

Genetic susceptibility and autoimmunity triggered by microbial infections are factors implicated in the pathogenesis of dilated cardiomyopathy, the most common cause of heart failure in young patients. Here we show that dendritic cells (DCs) loaded with a heart-specific self peptide induce CD4+ T-cell-mediated myocarditis in nontransgenic mice. Toll-like receptor (TLR) stimulation, in concert with CD40 triggering of self peptide–loaded dendritic cells, was shown to be required for disease induction. After resolution of acute myocarditis, DC-immunized mice developed heart failure, and TLR stimulation of these mice resulted in relapse of inflammatory infiltrates. Injection of damaged, syngeneic cardiomyocytes also induced myocarditis in mice if TLRs were activated in vivo. DC–induced myocarditis provides a unifying theory as to how tissue damage and activation of TLRs during infection can induce autoimmunity, relapses and cardiomyopathy.

T-bet negatively regulates autoimmune myocarditis by suppressing local production of interleukin 17

Experimental autoimmune myocarditis (EAM) appears after infectious heart disease, the most common cause of dilated cardiomyopathy in humans. Here we report that mice lacking T-bet, a T-box transcription factor required for T helper (Th)1 cell differentiation and interferon (IFN)-γ production, develop severe autoimmune heart disease compared to T-bet −/− control mice. Experiments in T-bet −/− IL-4−/− and T-bet −/− IL-4Rα−/− mice, as well as transfer of heart-specific Th1 and Th2 cell lines, showed that autoimmune heart disease develops independently of Th1 or Th2 polarization. Analysis of T-bet −/− IL-12Rβ1−/− and T-bet −/− IL-12p35−/− mice then identified interleukin (IL)-23 as critical for EAM pathogenesis. In addition, T-bet −/− mice showed a marked increase in production of the IL-23–dependent cytokine IL-17 by heart-infiltrating lymphocytes, and in vivo IL-17 depletion markedly reduced EAM severity in T-bet −/− mice. Heart-infiltrating T-bet −/− CD8+ but not CD8− T cells secrete IFN-γ, which inhibits IL-17 production and protects against severe EAM. In contrast, T-bet −/− CD8+ lymphocytes completely lost their capacity to release IFN-γ within the heart. Collectively, these data show that severe IL-17–mediated EAM can develop in the absence of T-bet, and that T-bet can regulate autoimmunity via the control of nonspecific CD8+ T cell bystander functions in the inflamed target organ.

Abnormal High-Density Lipoprotein Induces Endothelial Dysfunction via Activation of Toll-like Receptor-2

Endothelial injury and dysfunction (ED) represent a link between cardiovascular risk factors promoting hypertension and atherosclerosis, the leading cause of death in Western populations. High-density lipoprotein (HDL) is considered antiatherogenic and known to prevent ED. Using HDL from children and adults with chronic kidney dysfunction (HDL(CKD)), a population with high cardiovascular risk, we have demonstrated that HDL(CKD) in contrast to HDL(Healthy) promoted endothelial superoxide production, substantially reduced nitric oxide (NO) bioavailability, and subsequently increased arterial blood pressure (ABP). We have identified symmetric dimethylarginine (SDMA) in HDL(CKD) that causes transformation from physiological HDL into an abnormal lipoprotein inducing ED. Furthermore, we report that HDL(CKD) reduced endothelial NO availability via toll-like receptor-2 (TLR-2), leading to impaired endothelial repair, increased proinflammatory activation, and ABP. These data demonstrate how SDMA can modify the HDL particle to mimic a damage-associated molecular pattern that activates TLR-2 via a TLR-1- or TLR-6-coreceptor-independent pathway, linking abnormal HDL to innate immunity, ED, and hypertension.

Phosphoinositide 3-Kinase γ–Deficient Mice Are Protected From Isoproterenol-Induced Heart Failure

Background—We have recently shown that genetic inactivation of phosphoinositide 3-kinase &ggr; (PI3K&ggr;), the isoform linked to G-protein–coupled receptors, results in increased cardiac contractility with no effect on basal cell size. Signaling via the G-protein–coupled &bgr;-adrenergic receptors has been implicated in cardiac hypertrophy and heart failure, suggesting that PI3K&ggr; might play a role in the pathogenesis of heart disease. Methods and Results—To determine the role for PI3K&ggr; in hypertrophy induced by G-protein–coupled receptors and cardiomyopathy, we infused isoproterenol, a &bgr;-adrenergic receptor agonist, into PI3K&ggr;-deficient mice. Compared with controls, isoproterenol infusion in PI3K&ggr;-deficient mice resulted in an attenuated cardiac hypertrophic response and markedly reduced interstitial fibrosis. Intriguingly, chronic &bgr;-adrenergic receptor stimulation triggered impaired heart functions in wild-type mice, whereas PI3K&ggr;-deficient mice retained their increased heart function and did not develop heart failure. The lack of PI3K&ggr; attenuated the activation of Akt/protein kinase B and extracellular signal-regulated kinase 1/2 signaling pathways in cardiac myocytes in response to isoproterenol. &bgr;1- and &bgr;2-adrenergic receptor densities were decreased by similar amounts in PI3K&ggr;-deficient and control mice, suggesting that PI3K&ggr; isoform plays no role in the downregulation of &bgr;-adrenergic receptors after chronic &bgr;-adrenergic stimulation. Conclusions—Our data show that PI3K&ggr; is critical for the induction of hypertrophy, fibrosis, and cardiac dysfunction function in response to &bgr;-adrenergic receptor stimulation in vivo. Thus, PI3K&ggr; may represent a novel therapeutic target for the treatment of decreased cardiac function in heart failure.

Activation of Dendritic Cells through the Interleukin 1 Receptor 1 Is Critical for the Induction of Autoimmune Myocarditis

Dilated cardiomyopathy, resulting from myocarditis, is the most common cause of heart failure in young patients. We here show that interleukin (IL)-1 receptor type 1–deficient (IL-1R1−/−) mice are protected from development of autoimmune myocarditis after immunization with α-myosin-peptide(614–629). CD4+ T cells from immunized IL-1R1−/− mice proliferated poorly and failed to transfer disease after injection into naive severe combined immunodeficiency (SCID) mice. In vitro stimulation experiments suggested that the function of IL-1R1−/−CD4+ T cells was not intrinsically defect, but their activation by dendritic cells was impaired in IL-1R1−/− mice. Accordingly, production of tumor necrosis factor (TNF)-α, IL-1, IL-6, and IL-12p70 was reduced in dendritic cells lacking the IL-1 receptor type 1. In fact, injection of immature, antigen-loaded IL-1R1+/+ but not IL-1R1−/− dendritic cells into IL-1R1−/− mice fully restored disease susceptibility by rendering IL-1R1−/− CD4+ T cells pathogenic. Thus, IL-1R1 triggering is required for efficient activation of dendritic cells, which is in turn a prerequisite for induction of autoreactive CD4+ T cells and autoimmunity.

Dual Role of the IL-12/IFN-γ Axis in the Development of Autoimmune Myocarditis: Induction by IL-12 and Protection by IFN-γ

IL-12 and IFN-γ positively regulate each other and type 1 inflammatory responses, which are believed to cause tissue damage in autoimmune diseases. We investigated the role of the IL-12/IFN-γ (Th1) axis in the development of autoimmune myocarditis. IL-12p40-deficient mice on a susceptible background resisted myocarditis. In the absence of IL-12, autospecific CD4+ T cells proliferated poorly and showed increased Th2 cytokine responses. However, IFN-γ-deficient mice developed fatal autoimmune disease, and blockade of IL-4R signaling did not confer susceptibility to myocarditis in IL-12p40-deficient mice, demonstrating that IL-12 triggers autoimmunity by a mechanism independent of the effector cytokines IFN-γ and IL-4. In conclusion, our results suggest that the IL-12/IFN-γ axis is a double-edged sword for the development of autoimmune myocarditis. Although IL-12 mediates disease by induction/expansion of Th1-type cells, IFN-γ production from these cells limits disease progression.

Interleukin-6–Deficient Mice Resist Development of Autoimmune Myocarditis Associated With Impaired Upregulation of Complement C3

Background—Interleukin (IL)-6 regulates various aspects of the immune response. In the context of heart diseases, it has been recognized as a prognostic factor for dilated cardiomyopathy, which often results from myocarditis. Methods and Results—Using IL-6–deficient mice, we studied the role of IL-6 in a model of autoimmune myocarditis resulting from immunization with a peptide derived from cardiac &agr;-myosin. Prevalence and severity of myocarditis were markedly reduced in the absence of IL-6. CD4+ T cells from immunized IL-6–deficient mice proliferated poorly on restimulation with specific antigen in vitro and did not mediate disease on adoptive transfer into IL-6–competent RAG-2–deficient mice, which otherwise lack B cells and T cells. Production of complement C3, a crucial factor for the development of myocarditis, was strongly upregulated in IL-6+/+ but not in IL-6–deficient mice after immunization. Conclusions—Our results demonstrate that IL-6 is required for the expansion of autoimmune CD4+ T cells and the pathogenesis of autoimmune myocarditis, possibly by upregulation of complement C3.

CD11b+ Monocytes Abrogate Th17 CD4+ T Cell-Mediated Experimental Autoimmune Myocarditis

Experimental autoimmune myocarditis (EAM) represents a Th17 T cell-mediated mouse model of postinflammatory heart disease. In BALB/c wild-type mice, EAM is a self-limiting disease, peaking 21 days after α-myosin H chain peptide (MyHC-α)/CFA immunization and largely resolving thereafter. In IFN-γR−/− mice, however, EAM is exacerbated and shows a chronic progressive disease course. We found that this progressive disease course paralleled persistently elevated IL-17 release from T cells infiltrating the hearts of IFN-γR−/− mice 30 days after immunization. In fact, IL-17 promoted the recruitment of CD11b+ monocytes, the major heart-infiltrating cells in EAM. In turn, CD11b+ monocytes suppressed MyHC-α-specific Th17 T cell responses IFN-γ-dependently in vitro. In vivo, injection of IFN-γR+/+CD11b+, but not IFN-γR−/−CD11b+, monocytes, suppressed MyHC-α-specific T cells, and abrogated the progressive disease course in IFN-γR−/− mice. Finally, coinjection of MyHC-α-specific, but not OVA-transgenic, IFN-γ-releasing CD4+ Th1 T cell lines, together with MyHC-α-specific Th17 T cells protected RAG2−/− mice from EAM. In conclusion, CD11b+ monocytes play a dual role in EAM: as a major cellular substrate of IL-17-induced inflammation and as mediators of an IFN-γ-dependent negative feedback loop confining disease progression.

Mechanisms of Cardiac Fibrosis in Inflammatory Heart Disease

Heart injury from many causes can end up in a common final pathway of pathologic remodeling and fibrosis, promoting heart failure development. Dilated cardiomyopathy is an important cause of heart failure and often results from virus-triggered myocarditis. Monocytes and monocyte-like cells represent a major subset of heart-infiltrating cells at the injury site. These bone marrow-derived cells promote not only tissue injury in the short term but also angiogenesis and collagen deposition in the long term. Thus, they are critically involved in the typical tissue fibrosis, which evolves in the dilating ventricle during the process of pathologic remodeling. Recent findings suggest that heart-infiltrating monocyte-like cells indeed contain a pool of progenitors, which represent the cellular source both for accumulation of differentiated monocytes during the acute inflammatory phase and for transforming growth factor-beta-mediated myocardial fibrosis during the later chronic stages of disease. Obviously, a delicate balance of proinflammatory and profibrotic cytokines dictates the fate of bone marrow-derived heart-infiltrating progenitors and directly influences the morphologic phenotype of the affected heart. In this minireview, we provide an update on these mechanisms and discuss their significance in pathologic remodeling and heart failure progression after myocarditis.

Lethal autoimmune myocarditis in interferon-γ receptor-deficient mice: Enhanced disease severity by impaired inducible nitric oxide synthase induction

Background—Interferon-&ggr; (IFN-&ggr;) is an essential cytokine in the regulation of inflammatory responses in autoimmune diseases. Little is known about its role in inflammatory heart disease. Methods and Results—We showed that IFN-&ggr; receptor–deficient mice (IFN-&ggr;R–/–) on a BALB/c background immunized with a peptide derived from cardiac &agr;-myosin heavy chain develop severe myocarditis with high mortality. Although myocarditis subsided in wild-type mice after 3 weeks, IFN-&ggr;R–/– mice showed persistent disease. The persistent inflammation was accompanied by vigorous in vitro CD4 T-cell responses and impaired inducible nitric oxide synthase expression, together with evidence of impaired nitric oxide production in IFN-&ggr;R–/– hearts. Treatment of wild-type mice with the nitric oxide synthetase inhibitor N-nitro-l-arginine-methyl-ester enhanced in vitro CD4 T-cell proliferation and prevented healing of myocarditis. Conclusions—Our data provide evidence that IFN-&ggr; protects mice from lethal autoimmune myocarditis by inducing the expression of inducible nitric oxide synthase followed by the downregulation of T-cell responses.