House Dust Mite Induces Bone Marrow IL-33-Responsive ILC2s and TH Cells

Dampening type 2 properties of group 2 innate lymphoid cells by a gammaherpesvirus infection reprograms alveolar macrophages

Immunological dysregulation in asthma is associated with changes in exposure to microorganisms early in life. Gammaherpesviruses (γHVs), such as Epstein-Barr virus, are widespread human viruses that establish lifelong infection and profoundly shape host immunity. Using murid herpesvirus 4 (MuHV-4), a mouse γHV, we show that after infection, lung-resident and recruited group 2 innate lymphoid cells (ILC2s) exhibit a reduced ability to expand and produce type 2 cytokines in response to house dust mites, thereby contributing to protection against asthma. In contrast, MuHV-4 infection triggers GM-CSF production by those lung ILC2s, which orders the differentiation of monocytes (Mos) into alveolar macrophages (AMs) without promoting their type 2 functions. In the context of γHV infection, ILC2s are therefore essential cells within the pulmonary niche that imprint the tissue-specific identity of Mo-derived AMs and shape their function well beyond the initial acute infection.

Rapamycin Dampens Inflammatory Properties of Bone Marrow ILC2s in IL-33-Induced Eosinophilic Airway Inflammation

The alarmin cytokine interleukin (IL)-33 plays an important proinflammatory role in type 2 immunity and can act on type 2 innate lymphoid cells (ILC2s) and type 2 T helper (T_H2) cells in eosinophilic inflammation and asthma. The mechanistic target of rapamycin (mTOR) signaling pathway drives immune responses in several inflammatory diseases, but its role in regulating bone marrow responses to IL-33 is unclear. The aim of this study was to determine the role of the mTORC1 signaling pathway in IL-33-induced bone marrow ILC2 responses and its impact on IL-33-induced eosinophilia. Wild-type mice were intranasally exposed to IL-33 only or in combination with the mTORC1 inhibitor, rapamycin, intraperitoneally. Four groups were included in the study: saline-treated (PBS)+PBS, rapamycin+PBS, PBS+IL-33 and rapamycin+IL-33. Bronchoalveolar lavage fluid (BALF), serum and bone marrow cells were collected and analyzed by differential cell count, enzyme-linked immunosorbent assay and flow cytometry. IL-33 induced phosphorylation of the mTORC1 protein rpS6 in bone marrow ILC2s both ex vivo and in vivo. The observed mTOR signal was reduced by rapamycin treatment, indicating the sensitivity of bone marrow ILC2s to mTORC1 inhibition. IL-5 production by ILC2s was reduced in cultures treated with rapamycin before stimulation with IL-33 compared to IL-33 only. Bone marrow and airway eosinophils were reduced in mice given rapamycin before IL-33-exposure compared to mice given IL-33 only. Bone marrow ILC2s responded to IL-33 in vivo with increased mTORC1 activity and rapamycin treatment successfully decreased IL-33-induced eosinophilic inflammation, possibly by inhibition of IL-5-producing bone marrow ILC2s. These findings highlight the importance of investigating specific cells and proinflammatory pathways as potential drivers of inflammatory diseases, including asthma.

Single-cell RNA transcriptomic analysis identifies Creb5 and CD11b-DCs as regulator of asthma exacerbations

Immune responses that result in asthma exacerbation are associated with allergen or viral exposure. Identification of common immune factors will be beneficial for the development of uniformed targeted therapy. We employed a House Dust Mite (HDM) mouse model of asthma and challenged allergic HDM mice with allergens (HDM, cockroach extract (CRE)) or respiratory syncytial virus (RSV). Purified lung immune cells underwent high-dimensional single-cell RNA deep sequencing (scRNA-seq) to generate an RNA transcriptome. Gene silencing with siRNA was employed to confirm the efficacy of scRNA-seq analysis. scRNA-seq UMAP analysis portrayed an array of cell markers within individual immune clusters. SCENIC R analysis showed an increase in regulon number and activity in CD11b^- DC cells. Analysis of conserved regulon factors further identified Creb5 as a shared regulon between the exacerbation groups. Creb5 siRNAs attenuated HDM, CRE or RSV-induced asthma exacerbation. scRNA-seq multidimensional analysis of immune clusters identified gene pathways that were conserved between the exacerbation groups. We propose that these analyses provide a strong framework that could be used to identify specific therapeutic targets in multifaceted pathologies.

Children With Asthma Have Impaired Innate Immunity and Increased Numbers of Type 2 Innate Lymphoid Cells Compared With Healthy Controls

Background

Asthma is the most frequent cause of hospitalisation among children; however, little is known regarding the effects of asthma on immune responses in children.

Objective

The present study aimed to evaluate cytokine responses of peripheral blood mononuclear cells (PBMCs), PBMC composition and lung function in children with and without asthma.

Methods

Using a case-control design, we compared 48 children with asthma aged 3-11 years with 14 age-matched healthy controls. PBMC composition and cytokine production including interferon (IFN)-γ, interleukin (IL)-1β, IL-5 and lL-6 following stimulation with rhinovirus-1B (RV1B), house dust mite (HDM) and lipopolysaccharide (LPS) were measured. Lung function was assessed using impulse oscillometry and nitrogen multiple breath washout.

Results

The frequency of group 2 innate lymphoid cells were significantly higher in asthmatics and PBMCs from asthmatics had deficient IFN-γ production in response to both RV1B and LPS compared with controls (P<0.01). RV1B-induced IL-1β response and HDM-stimulated IL-5 production was higher in asthmatics than controls (P<0.05). In contrast, IL-1β and IL-6 were significantly reduced in response to HDM and LPS in asthmatics compared to controls (P<0.05). Children with asthma also had reduced pulmonary function, indicated by lower respiratory reactance as well as higher area of-reactance and lung clearance index values compared with controls (P<0.05).

Conclusion

Our study indicates that children with asthma have a reduced lung function in concert with impaired immune responses and altered immune cell subsets. Improving our understanding of immune responses to viral and bacterial infection in childhood asthma can help to tailor management of the disease.

Sex Hormones and Lung Inflammation

Inflammation is a characteristic marker in numerous lung disorders. Several immune cells, such as macrophages, dendritic cells, eosinophils, as well as T and B lymphocytes, synthetize and release cytokines involved in the inflammatory process. Gender differences in the incidence and severity of inflammatory lung ailments including asthma, chronic obstructive pulmonary disease (COPD), pulmonary fibrosis (PF), lung cancer (LC), and infectious related illnesses have been reported. Moreover, the effects of sex hormones on both androgens and estrogens, such as testosterone (TES) and 17β-estradiol (E2), driving characteristic inflammatory patterns in those lung inflammatory diseases have been investigated. In general, androgens seem to display anti-inflammatory actions, whereas estrogens produce pro-inflammatory effects. For instance, androgens regulate negatively inflammation in asthma by targeting type 2 innate lymphoid cells (ILC2s) and T-helper (Th)-2 cells to attenuate interleukin (IL)-17A-mediated responses and leukotriene (LT) biosynthesis pathway. Estrogens may promote neutrophilic inflammation in subjects with asthma and COPD. Moreover, the activation of estrogen receptors might induce tumorigenesis. In this chapter, we summarize the most recent advances in the functional roles and associated signaling pathways of inflammatory cellular responses in asthma, COPD, PF, LC, and newly occurring COVID-19 disease. We also meticulously deliberate the influence of sex steroids on the development and progress of these common and severe lung diseases.

ILC-You in the Thymus: A Fresh Look at Innate Lymphoid Cell Development

The discovery of innate lymphoid cells (ILCs) has revolutionized our understanding of innate immunity and immune cell interactions at epithelial barrier sites. Their presence and maintenance are critical for modulating immune homeostasis, responding to injury or infection, and repairing damaged tissues. To date, ILCs have been defined by a set of transcription factors, surface antigens and cytokines, and their functions resemble those of three major classes of helper T cell subsets, Th1, Th2 and Th17. Despite this, the lack of antigen-specific surface receptors and the notion that ILCs can develop in the absence of the thymic niche have clearly set them apart from the T-cell lineage and promulgated a dogma that ILCs develop directly from progenitors in the bone marrow. Interestingly however, emerging studies have challenged the BM-centric view of adult ILC development and suggest that ILCs could arise neonatally from developing T cell progenitors. In this review, we discuss ILC development in parallel to T-cell development and summarize key findings that support a T-cell-centric view of ILC ontogeny.

Eosinophil Lineage-Committed Progenitors as a Therapeutic Target for Asthma

Eosinophilic asthma is the most prevalent phenotype of asthma. Although most asthmatics are adequately controlled by corticosteroid therapy, a subset (5-10%) remain uncontrolled with significant therapy-related side effects. This indicates the need for a consideration of alternative treatment strategies that target airway eosinophilia with corticosteroid-sparing benefits. A growing body of evidence shows that a balance between systemic differentiation and local tissue eosinophilopoietic processes driven by traffic and lung homing of bone marrow-derived hemopoietic progenitor cells (HPCs) are important components for the development of airway eosinophilia in asthma. Interleukin (IL)-5 is considered a critical and selective driver of terminal differentiation of eosinophils. Studies targeting IL-5 or IL-5R show that although mature and immature eosinophils are decreased within the airways, there is incomplete ablation, particularly within the bronchial tissue. Eotaxin is a chemoattractant for mature eosinophils and eosinophil-lineage committed progenitor cells (EoP), yet anti-CCR3 studies did not yield meaningful clinical outcomes. Recent studies highlight the role of epithelial cell-derived alarmin cytokines, IL-33 and TSLP, (Thymic stromal lymphopoietin) in progenitor cell traffic and local differentiative processes. This review provides an overview of the role of EoP in asthma and discusses findings from clinical trials with various therapeutic targets. We will show that targeting single mediators downstream of the inflammatory cascade may not fully attenuate tissue eosinophilia due to the multiplicity of factors that can promote tissue eosinophilia. Blocking lung homing and local eosinophilopoiesis through mediators upstream of this cascade may yield greater improvement in clinical outcomes.