The gene regulatory basis of bystander activation in CD8+ T cells

CD8+ T cells are classically recognized as adaptive lymphocytes based on their ability to recognize specific foreign antigens and mount memory responses. However, recent studies indicate that some antigen-inexperienced CD8+ T cells can respond to innate cytokines alone in the absence of cognate T cell receptor stimulation, a phenomenon referred to as bystander activation. Here, we demonstrate that neonatal CD8+ T cells undergo a robust and diverse program of bystander activation, which corresponds to enhanced innate-like protection against unrelated pathogens. Using a multi-omics approach, we found that the ability of neonatal CD8+ T cells to respond to innate cytokines derives from their capacity to undergo rapid chromatin remodeling, resulting in the usage of a distinct set of enhancers and transcription factors typically found in innate-like T cells. We observed that the switch between innate and adaptive functions in the CD8+ T cell compartment is mediated by changes in the abundance of distinct subsets of cells. The innate CD8+ T cell subset that predominates in early life was also present in adult mice and humans. Our findings provide support for the layered immune hypothesis and indicate that the CD8+ T cell compartment is more functionally diverse than previously thought.

Exposure to lung-migrating helminth protects against murine SARS-CoV-2 infection through macrophage-dependent T cell activation

Helminth endemic regions report lower COVID-19 morbidity and mortality. Here, we show that lung remodeling from a prior infection with a lung-migrating helminth, Nippostrongylus brasiliensis, enhances viral clearance and survival of human-ACE2 transgenic mice challenged with SARS-CoV-2 (SCV2). This protection is associated with a lymphocytic infiltrate, including increased accumulation of pulmonary SCV2-specific CD8+ T cells, and anti-CD8 antibody depletion abrogated the N. brasiliensis-mediated reduction in viral loads. Pulmonary macrophages with a type 2 transcriptional and epigenetic signature persist in the lungs of N. brasiliensis-exposed mice after clearance of the parasite and establish a primed environment for increased CD8+ T cell recruitment and activation. Accordingly, depletion of macrophages ablated the augmented viral clearance and accumulation of CD8+ T cells driven by prior N. brasiliensis infection. Together, these findings support the concept that lung-migrating helminths can limit disease severity during SCV2 infection through macrophage-dependent enhancement of antiviral CD8+ T cell responses.

Basophil responses in susceptible AKR mice upon infection with the intestinal helminth parasite Trichuris muris

Intestinal helminth infection promotes a Type 2 inflammatory response in resistant C57BL/6 mice that is essential for worm clearance. The study of inbred mouse strains has revealed factors that are critical for parasite resistance and delineated the role of Type 1 versus Type 2 immune responses in worm clearance. In C57BL/6 mice, basophils are key innate immune cells that promote Type 2 inflammation and are programmed via the Notch signalling pathway during infection with the helminth Trichuris muris. However, how the host genetic background influences basophil responses and basophil expression of Notch receptors remains unclear. Here we use genetically susceptible inbred AKR/J mice that have a Type 1-skewed immune response during T. muris infection to investigate basophil responses in a susceptible host. Basophil population expansion occurred in AKR/J mice even in the absence of fulminant Type 2 inflammation during T. muris infection. However, basophils in AKR/J mice did not robustly upregulate expression of the Notch2 receptor in response to infection as occurred in C57BL/6 mice. Blockade of the Type 1 cytokine interferon-γ in infected AKR/J mice was not sufficient to elicit infection-induced basophil expression of the Notch2 receptor. These data suggest that the host genetic background, outside of the Type 1 skew, is important in regulating basophil responses during T. muris infection in susceptible AKR/J mice.

Helminth exposure protects against murine SARS-CoV-2 infection through macrophage dependent T cell activation

Helminth endemic regions report lower COVID-19 morbidity and mortality. Here, we show that lung remodeling from a prior infection with a lung migrating helminth, Nippostrongylus brasiliensis , enhances viral clearance and survival of human-ACE2 transgenic mice challenged with SARS-CoV-2 (SCV2). This protection is associated with a lymphocytic infiltrate including an increased accumulation of pulmonary SCV2-specific CD8+ T cells and anti-CD8 antibody depletion abrogated the N. brasiliensis -mediated reduction in viral loads. Pulmonary macrophages with a type-2 transcriptional signature persist in the lungs of N. brasiliensis exposed mice after clearance of the parasite and establish a primed environment for increased antigen presentation. Accordingly, depletion of macrophages ablated the augmented viral clearance and accumulation of CD8+ T cells driven by prior N. brasiliensis infection. Together, these findings support the concept that lung migrating helminths can limit disease severity during SCV2 infection through macrophage-dependent enhancement of anti-viral CD8+ T cell responses.

Abstract Figure

Effects of helminths on the human immune response and the microbiome

Helminths have evolved sophisticated immune regulating mechanisms to prevent rejection by their mammalian host. Our understanding of how the human immune system responds to these parasites remains poor compared to mouse models of infection and this limits our ability to develop vaccines as well as harness their unique properties as therapeutic strategies against inflammatory disorders. Here, we review how recent studies on human challenge infections, self-infected individuals, travelers, and endemic populations have improved our understanding of human type 2 immunity and its effects on the microbiome. The heterogeneity of responses between individuals and the limited access to tissue samples beyond the peripheral blood are challenges that limit human studies on helminths, but also provide opportunities to transform our understanding of human immunology. Organoids and single-cell sequencing are exciting new tools for immunological analysis that may aid this pursuit. Learning about the genetic and immunological basis of resistance, tolerance, and pathogenesis to helminth infections may thus uncover mechanisms that can be utilized for therapeutic purposes.

The Influence of Genetic and Environmental Factors and Their Interactions on Immune Response to Helminth Infections

Helminth infection currently affect over 2 billion people worldwide, with those with the most pathologies and morbidities, living in regions with unequal and disproportionate access to effective healthcare solutions. Host genetics and environmental factors play critical roles in modulating and regulating immune responses following exposure to various pathogens and insults. However, the interplay of environment and genetic factors in influencing who gets infected and the establishment, persistence, and clearance of helminth parasites remains unclear. Inbred strains of mice have long been used to investigate the role of host genetic factors on pathogenesis and resistance to helminth infection in a laboratory setting. This review will discuss the use of ecological and environmental mouse models to study helminth infections and how this could be used in combination with host genetic variation to explore the relative contribution of these factors in influencing immune response to helminth infections. Improved understanding of interactions between genetics and the environment to helminth immune responses would be important for efforts to identify and develop new prophylactic and therapeutic options for the management of helminth infections and their pathogenesis.

E-Protein Inhibition in ILC2 Development Shapes the Function of Mature ILC2s during Allergic Airway Inflammation

E-protein transcription factors limit group 2 innate lymphoid cell (ILC2) development while promoting T cell differentiation from common lymphoid progenitors. Inhibitors of DNA binding (ID) proteins block E-protein DNA binding in common lymphoid progenitors to allow ILC2 development. However, whether E-proteins influence ILC2 function upon maturity and activation remains unclear. Mice that overexpress ID1 under control of the thymus-restricted proximal Lck promoter (ID1^tg/WT) have a large pool of primarily thymus-derived ILC2s in the periphery that develop in the absence of E-protein activity. We used these mice to investigate how the absence of E-protein activity affects ILC2 function and the genomic landscape in response to house dust mite (HDM) allergens. ID1^tg/WT mice had increased KLRG1^- ILC2s in the lung compared with wild-type (WT; ID1^WT/WT) mice in response to HDM, but ID1^tg/WT ILC2s had an impaired capacity to produce type 2 cytokines. Analysis of WT ILC2 accessible chromatin suggested that AP-1 and C/EBP transcription factors but not E-proteins were associated with ILC2 inflammatory gene programs. Instead, E-protein binding sites were enriched at functional genes in ILC2s during development that were later dynamically regulated in allergic lung inflammation, including genes that control ILC2 response to cytokines and interactions with T cells. Finally, ILC2s from ID1^tg/WT compared with WT mice had fewer regions of open chromatin near functional genes that were enriched for AP-1 factor binding sites following HDM treatment. These data show that E-proteins shape the chromatin landscape during ILC2 development to dictate the functional capacity of mature ILC2s during allergic inflammation in the lung.

Multiomic analysis defines the first microRNA atlas across all small intestinal epithelial lineages and reveals novel markers of almost all major cell types

MicroRNA-mediated regulation is critical for the proper development and function of the small intestinal (SI) epithelium. However, it is not known which microRNAs are expressed in each of the cell types of the SI epithelium. To bridge this important knowledge gap, we performed comprehensive microRNA profiling in all major cell types of the mouse SI epithelium. We used flow cytometry and fluorescence-activated cell sorting with multiple reporter mouse models to isolate intestinal stem cells, enterocytes, goblet cells, Paneth cells, enteroendocrine cells, tuft cells, and secretory progenitors. We then subjected these cell populations to small RNA-sequencing. The resulting atlas revealed highly enriched microRNA markers for almost every major cell type (https://sethupathy-lab.shinyapps.io/SI_miRNA/). Several of these lineage-enriched microRNAs (LEMs) were observed to be embedded in annotated host genes. We used chromatin-run-on sequencing to determine which of these LEMs are likely cotranscribed with their host genes. We then performed single-cell RNA-sequencing to define the cell type specificity of the host genes and embedded LEMs. We observed that the two most enriched microRNAs in secretory progenitors are miR-1224 and miR-672, the latter of which we found is deleted in hominin species. Finally, using several in vivo models, we established that miR-152 is a Paneth cell-specific microRNA.NEW & NOTEWORTHY In this study, first, microRNA atlas (and searchable web server) across all major small intestinal epithelial cell types is presented. We have demonstrated microRNAs that uniquely mark several lineages, including enteroendocrine and tuft. Identification of a key marker of mouse secretory progenitor cells, miR-672, which we show is deleted in humans. We have used several in vivo models to establish miR-152 as a specific marker of Paneth cells, which are highly understudied in terms of microRNAs.

PGD2 and CRTH2 counteract Type 2 cytokine-elicited intestinal epithelial responses during helminth infection

Type 2 inflammation is associated with epithelial cell responses, including goblet cell hyperplasia, that promote worm expulsion during intestinal helminth infection. How these epithelial responses are regulated remains incompletely understood. Here, we show that mice deficient in the prostaglandin D2 (PGD2) receptor CRTH2 and mice with CRTH2 deficiency only in nonhematopoietic cells exhibited enhanced worm clearance and intestinal goblet cell hyperplasia following infection with the helminth Nippostrongylus brasiliensis. Small intestinal stem, goblet, and tuft cells expressed CRTH2. CRTH2-deficient small intestinal organoids showed enhanced budding and terminal differentiation to the goblet cell lineage. During helminth infection or in organoids, PGD2 and CRTH2 down-regulated intestinal epithelial Il13ra1 expression and reversed Type 2 cytokine-mediated suppression of epithelial cell proliferation and promotion of goblet cell accumulation. These data show that the PGD2-CRTH2 pathway negatively regulates the Type 2 cytokine-driven epithelial program, revealing a mechanism that can temper the highly inflammatory effects of the anti-helminth response.

Prostaglandin regulation of type 2 inflammation: From basic biology to therapeutic interventions

Type 2 immunity is critical for the protective and repair responses that mediate resistance to parasitic helminth infection. This immune response also drives aberrant inflammation during atopic diseases. Prostaglandins are a class of critical lipid mediators that are released during type 2 inflammation and are integral in controlling the initiation, activation, maintenance, effector functions, and resolution of Type 2 inflammation. In this review, we explore the roles of the different prostaglandin family members and the receptors they bind to during allergen‐ and helminth‐induced Type 2 inflammation and the mechanism through which prostaglandins promote or suppress Type 2 inflammation. Furthermore, we discuss the potential role of prostaglandins produced by helminth parasites in the regulation of host–pathogen interactions, and how prostaglandins may regulate the inverse relationship between helminth infection and allergy. Finally, we discuss opportunities to capitalize on our understanding of prostaglandin pathways to develop new therapeutic options for humans experiencing Type 2 inflammatory disorders that have a significant prostaglandin‐driven component including allergic rhinitis and asthma.

Lin28b promotes innate functions in CD8+ T cells through rapid chromatin remodeling

Lin28b serves as a master regulator of fetal lymphopoiesis and promotes the development of more innate-like lymphocytes in early life. However, it is still unclear how Lin28b alters the function of CD8+ T cells and protects the host against infection. In this report we examined how Lin28b transcriptionally and epigenetically programs neonatal CD8+ T cells for innate immune defense. We found that murine neonatal CD8+ T cells possess innate-like transcriptomes, are more responsive to innate cytokines in the absence of antigen and produce a broader spectrum of cytokines compared to their adult counterparts. This unique program of bystander activation in early life corresponded with enhanced innate-like protection against irrelevant strains of bacterial, helminth and virus infections. To understand how this diversity of immune function is mediated, we used flow cytometry and scRNAseq and discovered that the neonatal CD8+ T cell pool is composed of many subsets of cells expressing distinct cytokines. ATACseq analysis revealed that neonatal CD8+ T cells are programmed to display innate-like properties and produce a diverse array of cytokines, which may be due to their ability to undergo extensive chromatin remodeling upon cytokine stimulation. These unique properties may be driven by high Lin28b expression in fetal progenitor cells, as adult cells expressing Lin28b initiated a program of bystander activation and immune protection that was analogous to neonates. Collectively, our data suggests that Lin28b enables neonatal CD8+ T cells to undergo a more diverse program of bystander activation, allowing them to deploy a bet-hedging immune strategy and protect the host against a rapidly changing pathogenic environment.

Astrocytes promote a protective immune response to brain Toxoplasma gondii infection via IL-33-ST2 signaling

It is of great interest to understand how invading pathogens are sensed within the brain, a tissue with unique challenges to mounting an immune response. The eukaryotic parasite Toxoplasma gondii colonizes the brain of its hosts, and initiates robust immune cell recruitment, but little is known about pattern recognition of T. gondii within brain tissue. The host damage signal IL-33 is one protein that has been implicated in control of chronic T. gondii infection, but, like many other pattern recognition pathways, IL-33 can signal peripherally, and the specific impact of IL-33 signaling within the brain is unclear. Here, we show that IL-33 is expressed by oligodendrocytes and astrocytes during T. gondii infection, is released locally into the cerebrospinal fluid of T. gondii-infected animals, and is required for control of infection. IL-33 signaling promotes chemokine expression within brain tissue and is required for the recruitment and/or maintenance of blood-derived anti-parasitic immune cells, including proliferating, IFN-γ-expressing T cells and iNOS-expressing monocytes. Importantly, we find that the beneficial effects of IL-33 during chronic infection are not a result of signaling on infiltrating immune cells, but rather on radio-resistant responders, and specifically, astrocytes. Mice with IL-33 receptor-deficient astrocytes fail to mount an adequate adaptive immune response in the CNS to control parasite burden–demonstrating, genetically, that astrocytes can directly respond to IL-33 in vivo. Together, these results indicate a brain-specific mechanism by which IL-33 is released locally, and sensed locally, to engage the peripheral immune system in controlling a pathogen.

Toxoplasma gondii is a highly successful parasite, estimated to infect one-third of the world’s human population and many warm-blooded vertebrates. T. gondii traffics to the brain of its hosts where it persists for their lifetime. Immune pressure is required to control T. gondii in brain tissue, as evidenced by destruction of brain tissue in T. gondii-infected immunosuppressed patients. But how T. gondii presence is sensed by brain cells to orchestrate immune responses is not well understood. Here, we show that a host protein, IL-33, typically sequestered within brain cells in the healthy state, is released as a damage signal during brain T. gondii infection and can induce local changes to the brain environment to recruit immune cells. We show that astrocytes, specifically, are capable of directly responding to IL-33, thus illustrating a local mechanism by which brain-resident cells are alerted to pathogen entry.

The Prostaglandin D2 Receptor CRTH2 Promotes IL-33-Induced ILC2 Accumulation in the Lung

Group 2 innate lymphoid cells (ILC2s) are rare innate immune cells that accumulate in tissues during allergy and helminth infection, performing critical effector functions that drive type 2 inflammation. ILC2s express ST2, the receptor for the cytokine IL-33, and chemoattractant receptor-homologous molecule expressed on Th2 cells (CRTH2), a receptor for the bioactive lipid prostaglandin D2 (PGD2). The IL-33-ST2 and the PGD2-CRTH2 pathways have both been implicated in promoting ILC2 accumulation during type 2 inflammation. However, whether these two pathways coordinate to regulate ILC2 population size in the tissue in vivo remains undefined. In this study, we show that ILC2 accumulation in the murine lung in response to systemic IL-33 treatment was partially dependent on CRTH2. This effect was not a result of reduced ILC2 proliferation, increased apoptosis or cell death, or differences in expression of the ST2 receptor in the absence of CRTH2. Rather, data from adoptive transfer studies suggested that defective accumulation of CRTH2-deficient ILC2s in response to IL-33 was due to altered ILC2 migration patterns. Whereas donor wild-type ILC2s preferentially accumulated in the lungs compared with CRTH2-deficient ILC2s following transfer into IL-33-treated recipients, wild-type and CRTH2-deficient ILC2s accumulated equally in the recipient mediastinal lymph node. These data suggest that CRTH2-dependent effects lie downstream of IL-33, directly affecting the migration of ILC2s into inflamed lung tissues. A better understanding of the complex interactions between the IL-33 and PGD2-CRTH2 pathways that regulate ILC2 population size will be useful in understanding how these pathways could be targeted to treat diseases associated with type 2 inflammation.

Elevated circulating Th2 but not group 2 innate lymphoid cell responses characterize canine atopic dermatitis

Atopic dermatitis (AD) is an allergic skin disease that causes significant morbidity and affects multiple species. AD is highly prevalent in companion dogs, and the clinical management of the disease remains challenging. An improved understanding of the immunologic and genetic pathways that lead to disease could inform the development of novel treatments. In allergic humans and mouse models of AD, the disease is associated with Th2 and group 2 innate lymphoid cell (ILC2) activation that drives type 2 inflammation. Type 2 inflammation also appears to be associated with AD in dogs, but gaps remain in our understanding of how key type 2-associated cell types such as canine Th2 cells and ILC2s contribute to the pathogenesis of canine AD. Here, we describe previously uncharacterized canine ILC2-like cells and Th2 cells ex vivo that produced type 2 cytokines and expressed the transcription factor Gata3. Increased circulating Th2 cells were associated with chronic canine AD. Single-cell RNA sequencing revealed a unique gene expression signature in T cells in dogs with AD. These findings underline the importance of pro-allergic Th2 cells in orchestrating AD and provide new methods and pathways that can inform the development of improved therapies.

Enteroendocrine Progenitor Cell-Enriched miR-7 Regulates Intestinal Epithelial Proliferation in an Xiap-Dependent Manner

BACKGROUND & AIMS

The enteroendocrine cell (EEC) lineage is important for intestinal homeostasis. It was recently shown that EEC progenitors contribute to intestinal epithelial growth and renewal, but the underlying mechanisms remain poorly understood. MicroRNAs are under-explored along the entire EEC lineage trajectory, and comparatively little is known about their contributions to intestinal homeostasis.

METHODS

We leverage unbiased sequencing and eight different mouse models and sorting methods to identify microRNAs enriched along the EEC lineage trajectory. We further characterize the functional role of EEC progenitor-enriched miRNA, miR-7, by in vivo dietary study as well as ex vivo enteroid in mice.

RESULTS

First, we demonstrate that miR-7 is highly enriched across the entire EEC lineage trajectory and is the most enriched miRNA in EEC progenitors relative to Lgr5+ intestinal stem cells. Next, we show in vivo that in EEC progenitors miR-7 is dramatically suppressed under dietary conditions that favor crypt division and suppress EEC abundance. We then demonstrate by functional assays in mouse enteroids that miR-7 exerts robust control of growth, as determined by budding (proxy for crypt division), EdU and PH3 staining, and likely regulates EEC abundance also. Finally, we show by single-cell RNA sequencing analysis that miR-7 regulates Xiap in progenitor/stem cells and we demonstrate in enteroids that the effects of miR-7 on mouse enteroid growth depend in part on Xiap and Egfr signaling.

CONCLUSIONS

This study demonstrates for the first time that EEC progenitor cell-enriched miR-7 is altered by dietary perturbations and that it regulates growth in enteroids via intact Xiap and Egfr signaling.

The Notch signaling pathway promotes basophil responses during helminth-induced type 2 inflammation

Basophils promote type 2 inflammation that mediates worm clearance during murine infection with the gastrointestinal helminth parasite Trichuris muris. Webb et al. show for the first time that basophil–intrinsic Notch signaling is required for basophil gene expression and a functional program that support helminth expulsion.

Type 2 inflammation drives the clearance of gastrointestinal helminth parasites, which infect over two billion people worldwide. Basophils are innate immune cells that support host-protective type 2 inflammation during murine infection with the helminth Trichuris muris. However, the mechanisms required for basophil function and gene expression regulation in this context remain unclear. We show that during T. muris infection, basophils localized to the intestine and up-regulated Notch receptor expression, rendering them sensitive to Notch signals that rapidly regulate gene expression programs. In vitro, Notch inhibition limited basophil cytokine production in response to cytokine stimulation. Basophil-intrinsic Notch signaling was required for T. muris–elicited changes in genome-wide basophil transcriptional programs. Mice lacking basophil-intrinsic functional Notch signaling had impaired worm clearance, decreased intestinal type 2 inflammation, altered basophil localization in the intestine, and decreased CD4⁺ T helper 2 cell responses following infection. These findings demonstrate that Notch is required for basophil gene expression and effector function associated with helminth expulsion during type 2 inflammation.

Cytokines and beyond: Regulation of innate immune responses during helminth infection

Parasitic helminth infection elicits a type 2 cytokine-mediated inflammatory response. During type 2 inflammation, damaged or stimulated epithelial cells exposed to helminths and their products produce alarmins and cytokines including IL-25, IL-33, and thymic stromal lymphopoietin. These factors promote innate immune cell activation that supports the polarization of CD4⁺ T helper type 2 (Th2) cells. Activated innate and Th2 cells produce the cytokines IL-4, -5, -9, and -13 that perpetuate immune activation and act back on the epithelium to cause goblet cell hyperplasia and increased epithelial cell turnover. Together, these events facilitate worm expulsion and wound healing processes. While the role of Th2 cells in this context has been heavily studied, recent work has revealed that epithelial cell-derived cytokines are drivers of key innate immune responses that are critical for type 2 anti-helminth responses. Cutting-edge studies have begun to fully assess how other factors and pathways, including lipid mediators, chemokines, Fc receptor signaling, danger-associated molecular pattern molecules, and direct cell-cell interactions, also participate in shaping innate cell-mediated type 2 inflammation. In this review, we discuss how these pathways intersect and synergize with pathways controlled by epithelial cell-derived cytokines to coordinate innate immune responses that drive helminth-induced type 2 inflammation.

Seroprevalence and risk factors of brucellosis in goats in selected states in Nigeria and the public health implications

Available reports on brucellosis in Nigeria are largely confined to cattle while it is believed that other ruminants like sheep and goats are equally exposed to the disease. To have an insight into the role of goats in the epidemiology of brucellosis in Nigeria, we conducted a cross-sectional study between June 2011 and May 2013 to determine the seroprevalence of brucellosis in goats in some selected states in Nigeria. Serum samples were collected from goats at different locations and tested for antibodies to Brucella spp using the Rose Bengal Test (RBT), samples positive by RBT were further subjected to Competitive Enzyme Linked Immunosorbent Assay (cELISA). Data collected to determine risk factors were also analysed using chi-square and logistics regression statistics. Out of a total of 2827 samples tested from the different states (Benue = 331; Borno =195; Oyo = 2155; Sokoto = 146), we recorded an overall seroprevalence of 2.83% (Benue = 17.30%; Borno = 2.05%; Oyo = 0.60% and Sokoto = 0.00%) by RBT. The cELISA further supported 9.45% (7/74) of the total RBT positive samples. Logistic regression analysis showed that the location (p = 0.004) and source (p < 0.0001); are probable risk factors to be considered in the epidemiology of brucellosis with sex (p = 0.179); age (p = 0.791) and breed (p = 0.369) not playing any major role. Our findings reveal a relatively low seroprevalence of brucellosis among goats screened except for Benue State. Since most of the goats sampled in the present study were from the abattoirs, further farm level investigations are required to determine the role of goats in the epidemiology of brucellosis in Nigeria since they share common environment with sheep and cattle that are natural hosts of Brucella species which are of major public health threat.