Innate Lymphoid Cells Play a Pathogenic Role in Pericarditis.

We find that cardiac group 2 innate lymphoid cells (ILC2s) are essential for the development of IL-33-induced eosinophilic pericarditis. We show a pathogenic role for ILC2s in cardiac inflammation, in which ILC2s activated by IL-33 drive the development of eosinophilic pericarditis in collaboration with cardiac fibroblasts. ILCs, not T and B cells, are required for the development of pericarditis. ILC2s transferred to the heart of Rag2-/-Il2rg-/- mice restore their susceptibility to eosinophil infiltration. Moreover, ILC2s direct cardiac fibroblasts to produce eotaxin-1. We also find that eosinophils reside in the mediastinal cavity and that eosinophils transferred to the mediastinal cavity of eosinophil-deficient ΔdblGATA1 mice following IL-33 treatment migrate to the heart. Thus, the serous cavities may serve as a reservoir of cardiac-infiltrating eosinophils. In humans, patients with pericarditis show higher amounts of ILCs in pericardial fluid than do healthy controls and patients with other cardiac diseases. We demonstrate that ILCs play a critical role in pericarditis.

Presence and Concentrations of Select Bacterial Vaginosis-Associated Bacteria Are Associated With Increased Risk of Pelvic Inflammatory Disease.

In a vaginal 16S ribosomal RNA gene quantitative PCR study of 17 pelvic inflammatory disease (PID) cases and 17 controls who tested positive for Chlamydia trachomatis, women who additionally tested positive for Atopobium vaginae, Sneathia spp., Megasphaera spp., Eggerthella-like bacterium or Prevotella amnii were more likely to develop PID.

The Cardiac Microenvironment Instructs Divergent Monocyte Fates and Functions in Myocarditis.

Two types of monocytes, Ly6Chi and Ly6Clo, infiltrate the heart in murine experimental autoimmune myocarditis (EAM). We discovered a role for cardiac fibroblasts in facilitating monocyte-to-macrophage differentiation of both Ly6Chi and Ly6Clo cells, allowing these macrophages to perform divergent functions in myocarditis progression. During the acute phase of EAM, IL-17A is highly abundant. It signals through cardiac fibroblasts to attenuate efferocytosis of Ly6Chi monocyte-derived macrophages (MDMs) and simultaneously prevents Ly6Clo monocyte-to-macrophage differentiation. We demonstrated an inverse clinical correlation between heart IL-17A levels and efferocytic receptor expressions in humans with heart failure (HF). In the absence of IL-17A signaling, Ly6Chi MDMs act as robust phagocytes and are less pro-inflammatory, whereas Ly6Clo monocytes resume their differentiation into MHCII+ macrophages. We propose that MHCII+Ly6Clo MDMs are associated with the reduction of cardiac fibrosis and prevention of the myocarditis sequalae.

Non-cytotoxic Cardiac Innate Lymphoid Cells Are a Resident and Quiescent Type 2-Commited Population.

Innate lymphoid cells (ILC) are a subset of leukocytes with lymphoid properties that lack antigen specific receptors. They can be stimulated by and exert their effect via specific cytokine axes, whereas Natural Killers (NK) cells are the only known cytotoxic member of this family. ILCs are considered key in linking the innate and adaptive response in physiologic and pathologic environments. In this study, we investigated the properties of non-cytotoxic cardiac ILCs in physiologic, inflammatory, and ischemic conditions. We found that in healthy humans and mice, non-cytotoxic cardiac ILCs are predominantly a type 2-committed population with progenitor-like features, such as an absence of type-specific immunophenotype, intermediate GATA3 expression, and capacity to transiently express Pro-myelocytic Leukemia Zinc Finger protein (PLZF) upon activation. During myocarditis and ischemia, in both human and mice, cardiac ILCs differentiated into conventional ILC2s. We found that cardiac ILCs lack IL-25 receptor and cannot become inflammatory ILC2s. We found a strong correlation between IL-33 production in the heart and the ability of cardiac ILCs to become conventional ILC2s. The main producer of IL-33 was a subset of CD29+Sca-1+ cardiac fibroblasts. ILC2 expansion and fibroblast-derived IL-33 production were significantly increased in the heart in mouse models of infarction and myocarditis. Despite its progenitor-like status in healthy hearts, cardiac ILCs were unable to become ILC1 or ILC3 in vivo and in vitro. Using adoptive transfer and parabiosis, we demonstrated that the heart, unlike other organs such as lung, cannot be infiltrated by circulating ILCs in adulthood even during cardiac inflammation or ischemia. Thus, the ILC2s present during inflammatory conditions are derived from the heart-resident and quiescent steady-state population. Non-cytotoxic cardiac ILCs are a resident population of ILC2-commited cells, with undifferentiated progenitor-like features in steady-state conditions and an ability to expand and develop pro-inflammatory type 2 features during inflammation or ischemia.

Sca-1+ cardiac fibroblasts promote development of heart failure.

The causative effect of GM-CSF produced by cardiac fibroblasts to development of heart failure has not been shown. We identified the pathological GM-CSF-producing cardiac fibroblast subset and the specific deletion of IL-17A signaling to these cells attenuated cardiac inflammation and heart failure. We describe here the CD45- CD31- CD29+ mEF-SK4+ PDGFRα+ Sca-1+ periostin+ (Sca-1+ ) cardiac fibroblast subset as the main GM-CSF producer in both experimental autoimmune myocarditis and myocardial infarction mouse models. Specific ablation of IL-17A signaling to Sca-1+ periostin+ cardiac fibroblasts (PostnCre Il17rafl/fl ) protected mice from post-infarct heart failure and death. Moreover, PostnCre Il17rafl/fl mice had significantly fewer GM-CSF-producing Sca-1+ cardiac fibroblasts and inflammatory Ly6Chi monocytes in the heart. Sca-1+ cardiac fibroblasts were not only potent GM-CSF producers, but also exhibited plasticity and switched their cytokine production profiles depending on local microenvironments. Moreover, we also found GM-CSF-positive cardiac fibroblasts in cardiac biopsy samples from heart failure patients of myocarditis or ischemic origin. Thus, this is the first identification of a pathological GM-CSF-producing cardiac fibroblast subset in human and mice hearts with myocarditis and ischemic cardiomyopathy. Sca-1+ cardiac fibroblasts direct the type of immune cells infiltrating the heart during cardiac inflammation and drive the development of heart failure.

Regulation of autoimmune myocarditis by host responses to the microbiome.

The extensive, diverse communities that constitute the microbiome are increasingly appreciated as important regulators of human health and disease through inflammatory, immune, and metabolic pathways. We sought to elucidate pathways by which microbiota contribute to inflammatory, autoimmune cardiac disease. We employed an animal model of experimental autoimmune myocarditis (EAM), which results in inflammatory and autoimmune pathophysiology and subsequent maladaptive cardiac remodeling and heart failure. Antibiotic dysbiosis protected mice from EAM and fibrotic cardiac dysfunction. Additionally, mice derived from different sources with different microbiome colonization profiles demonstrated variable susceptibility to disease. Unexpectedly, it did not track with segmented filamentous bacteria (SFB)-driven Th17 programming of CD4+ T cells in the steady-state gut. Instead, we found disease susceptibility to track with presence of type 3 innate lymphoid cells (ILC3s). Ablating ILCs by antibody depletion or genetic tools in adoptive transfer variants of the EAM model demonstrated that ILCs and microbiome profiles contributed to the induction of CCL20/CCR6-mediated inflammatory chemotaxis to the diseased heart. From these data, we conclude that sensing of the microbiome by ILCs is an important checkpoint in the development of inflammatory cardiac disease processes through their ability to elicit cardiotropic chemotaxis.

Macrophages and cardiac fibroblasts are the main producers of eotaxins and regulate eosinophil trafficking to the heart.

Cardiac manifestations are a major cause of morbidity and mortality in patients with eosinophil-associated diseases. Eosinophils are thought to play a pathogenic role in myocarditis. We investigated the pathways that recruit eosinophils to the heart using a model of eosinophilic myocarditis, in which experimental autoimmune myocarditis (EAM) is induced in IFNγ-/- IL-17A-/- mice. Two conditions are necessary for efficient eosinophil trafficking to the heart: high eotaxin (CCL11, CCL24) expression in the heart and expression of the eotaxin receptor CCR3 by eosinophils. We identified cardiac fibroblasts as the source of CCL11 in the heart interstitium. CCL24 is produced by F4/80+ macrophages localized at inflammatory foci in the heart. Expression of CCL11 and CCL24 is controlled by Th2 cytokines, IL-4 and IL-13. To determine the relevance of this pathway in humans, we analyzed endomyocardial biopsy samples from myocarditis patients. Expression of CCL11 and CCL26 was significantly increased in eosinophilic myocarditis compared to chronic lymphocytic myocarditis and positively correlated with the number of eosinophils. Thus, eosinophil trafficking to the heart is dependent on the eotaxin-CCR3 pathway in a mouse model of EAM and associated with cardiac eotaxin expression in patients with eosinophilic myocarditis. Blocking this pathway may prevent eosinophil-mediated cardiac damage.

Collaborative Interferon-γ and Interleukin-17 Signaling Protects the Oral Mucosa from Staphylococcus aureus.

Infections with Staphylococcus aureus are a continuing and growing problem in community and hospital settings. Preclinical animal modeling of S. aureus relies on experimental infection, which carries some limitations. We describe here a novel, spontaneous model of oral staphylococcal infection in double knockout mice, deficient in the receptors for IL-17 (IL-17RA) and interferon (IFN)-γ (IFNγRI), beginning at 6 to 8 weeks of age. IFNγRI(-/-)IL17RA(-/-) (GRAKO) mice developed progressive oral abscesses. Cytometric methods revealed extensive neutrophilic infiltration of oral tissues in GRAKO mice; further investigation evidenced that IL-17 predominated neutrophil defects in these mice. To investigate the contribution of IFN-γ signaling to this native host defense to S. aureus, we observed perturbations of monocyte recruitment and macrophage differentiation in the oral tissues of GRAKO mice, and CXCL9/chemokine ligand receptor (CXCR)3-driven recruitment of T-cell oral tissues and draining lymph nodes. To address the former finding, we depleted macrophages and monocytes in vivo from IL17RA(-/-) mice using liposomes loaded with clodronate. This treatment elicited oral abscesses, recapitulating the phenotype of GRAKO mice. From these findings, we propose novel collaborative functions of IL-17 and IFN-γ, acting through neutrophils and macrophages, respectively, in native mucocutaneous host defenses to S. aureus.

Pathogenic IL-23 signaling is required to initiate GM-CSF-driven autoimmune myocarditis in mice.

Using a mouse model of experimental autoimmune myocarditis (EAM), we showed for the first time that IL-23 stimulation of CD4(+) T cells is required only briefly at the initiation of GM-CFS-dependent cardiac autoimmunity. IL-23 signal, acting as a switch, turns on pathogenicity of CD4(+) T cells, and becomes dispensable once autoreactivity is established. Il23a(-/-) mice failed to mount an efficient Th17 response to immunization, and were protected from myocarditis. However, remarkably, transient IL-23 stimulation ex vivo fully restored pathogenicity in otherwise nonpathogenic CD4(+) T cells raised from Il23a(-/-) donors. Thus, IL-23 may no longer be necessary to uphold inflammation in established autoimmune diseases. In addition, we demonstrated that IL-23-induced GM-CSF mediates the pathogenicity of CD4(+) T cells in EAM. The neutralization of GM-CSF abrogated cardiac inflammation. However, sustained IL-23 signaling is required to maintain IL-17A production in CD4(+) T cells. Despite inducing inflammation in Il23a(-/-) recipients comparable to wild-type (WT), autoreactive CD4(+) T cells downregulated IL-17A production without persistent IL-23 signaling. This divergence on the controls of GM-CSF-dependent pathogenicity on one side and IL-17A production on the other side may contribute to the discrepant efficacies of anti-IL-23 therapy in different autoimmune diseases.