Myocarditis can develop into inflammatory cardiomyopathy through chronic stimulation of myosin heavy chain 6–specific T helper (TH)1 and TH17 cells. However, mechanisms governing the cardiotoxicity programming of heart-specific T cells have remained elusive. Using a mouse model of spontaneous autoimmune myocarditis, we show that progression of myocarditis to lethal heart disease depends on cardiac myosin–specific TH17 cells imprinted in the intestine by a commensal Bacteroides species peptide mimic. Both the successful prevention of lethal disease in mice by antibiotic therapy and the significantly elevated Bacteroides-specific CD4+ T cell and B cell responses observed in human myocarditis patients suggest that mimic peptides from commensal bacteria can promote inflammatory cardiomyopathy in genetically susceptible individuals. The ability to restrain cardiotoxic T cells through manipulation of the microbiome thereby transforms inflammatory cardiomyopathy into a targetable disease.

The cytoplasmic C terminus of the ␤ 2 -adrenergic receptor and many other G protein-coupled receptors contains a dileucine sequence that has been implicated in endosome͞lysosome targeting of diverse proteins. In the present study, we provide evidence for an essential role of this motif in the agonist-induced internalization of the ␤ 2 -adrenergic receptor. Mutation of Leu-339 and͞or Leu-340 to Ala caused little changes in surface expression, ligand binding, G protein coupling, and signaling to adenylyl cyclase, when these receptors were transiently or stably expressed in CHO or HEK-293 cells. However, agonist-induced receptor internalization was markedly impaired in the L 339,340 A double mutant and reduced in the two single mutants. This impairment in receptor internalization was seen by using various approaches to determine internalization: binding of hydrophobic vs. hydrophilic ligands, loss of surface ␤ 2 -adrenergic receptor immunoreactivity, and immunof luorescence microscopy. The selective effects of these mutations suggest that the C-terminal dileucine motif is involved in agonist-induced internalization of the ␤ 2 -adrenergic receptor.Many types of membrane-bound receptors undergo a dynamic trafficking between the cell surface and intracellular compartments. Such trafficking may be involved both in the transmission of receptor signals and in the termination of such signaling (1). For the ␤ 2 -adrenergic receptor, a prototypical G proteincoupled receptor, the most remarkable trafficking process is agonist-induced receptor internalization. This internalization is part of a whole spectrum of adaptive processes triggered by agonist stimulation (2, 3).Agonist-induced translocation of these receptors to an intracellular compartment has been established by several approaches: (i) After agonist stimulation, a certain (and variable) proportion of the receptors becomes inaccessible for hydrophilic ligands but remains accessible for hydrophobic ligands; this process is usually termed sequestration (4). (ii) Upon cell fractionation and sucrose density centrifugation, these receptors can be recovered in a fraction lighter than the plasma membrane fraction (5). (iii) Immunofluorescence studies show that agonist treatment results in the appearance of receptors in intracellular aggregates that might represent endosomes; these data thus provide evidence for true internalization (6-8).Whereas earlier studies assumed that internalization of ␤ 2 -adrenergic receptors was essentially a mechanism of receptor desensitization (9, 10), more recent studies have assigned it a recycling and sorting function. According to these models, receptor internalization may occur subsequent to receptor phosphorylation and desensitization and may serve to either dephosphorylate the receptors and recycle them back to the cell surface or-particularly in the case of prolonged receptor stimulation-to direct the receptors to lysosomes for degradation (8, 11-13).The mechanism of ␤ 2 -adrenergic receptor internalization is ill-defined at the...

Background— Monocytes and macrophages are indispensable in the healing process after myocardial infarction (MI); however, the spatiotemporal distribution of monocyte infiltration and its correlation to prognostic indicators of reperfused MI have not been well described. Methods and Results— With combined fluorine 19/proton ( 1 H) magnetic resonance imaging, we noninvasively visualized the spatiotemporal recruitment of monocytes in vivo in a rat model of reperfused MI. Blood monocytes were labeled by intravenous injection of 19 F-perfluorocarbon emulsion 1 day after MI. The distribution patterns of monocyte infiltration were correlated to the presence of microvascular obstruction (MVO) and intramyocardial hemorrhage. In vivo, 19 F/ 1 H magnetic resonance imaging performed in series revealed that monocyte infiltration was spatially inhomogeneous in reperfused MI areas. In the absence of MVO, monocyte infiltration was more intense in MI regions with serious ischemia-reperfusion injuries, indicated by severe intramyocardial hemorrhage; however, monocyte recruitment was significantly impaired in MVO areas accompanied by severe intramyocardial hemorrhage. Compared with MI with isolated intramyocardial hemorrhage, MI with MVO resulted in significantly worse pump function of the left ventricle 28 days after MI. Conclusions— Monocyte recruitment was inhomogeneous in reperfused MI tissue. It was highly reduced in MVO areas defined by magnetic resonance imaging. The impaired monocyte infiltration in MVO regions could be related to delayed healing and worse functional outcomes in the long term. Therefore, monocyte recruitment in MI with MVO could be a potential diagnostic and therapeutic target that could be monitored noninvasively and longitudinally by 19 F/ 1 H magnetic resonance imaging in vivo.

AimsA novel concept for the treatment of heart failure is the neutralization of antibodies against the b 1 -adrenergic receptor (anti-b 1 AR-ab). In a rat model of autoimmune cardiomyopathy, the cyclic peptide COR-1 (given i.v. once monthly) neutralized anti-b 1 AR-abs and prevented anti-b 1 AR-ab-induced myocardial damage, and completely reverted cardiac dysfunction over 3-6 months. Methods and resultsA clinical phase I trial was designed as a single-blinded, placebo-controlled study. Fifty human volunteers received COR-1 or matching placebo as a single i.v. administration with ascending doses (10 -240 mg). Primary endpoints were safety and tolerability, while the pharmacokinetic profile of COR-1 was assessed as a secondary endpoint. All five investigated dose groups were well tolerated; no drug-related side effects occurred. Pharmacokinetics revealed a favourable profile with an almost complete plasma clearance within 60 min after administration. Pharmacodynamic investigation showed dose-dependent efficacy with almost complete scavenging of pathological antib 1 AR-abs ex vivo at the two highest doses. No anti-COR-1 autoantibodies occurred. No other effects on the immune system (such as an increase of crucial cytokines) were observed up to 43 days after drug administration, nor upon incubation of anti-b 1 AR-ab-positive patient blood samples with COR-1 ex vivo. ConclusionsCOR-1 was shown to be safe after i.v. administration in vivo; no relevant side effects occurred. Efficacy was estimated from ex vivo investigation of the potency to neutralize specific anti-b 1 -AR-abs.