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.

Networking between helminths, microbes, and mammals

Just as mammals have coevolved with the intestinal bacterial communities that are part of the microbiota, intestinal helminths represent an important selective force on their mammalian host. The complex interaction between helminths, microbes, and their mammalian host is likely an important determinant of mutual fitness. The host immune system in particular is a critical interface with both helminths and the microbiota, and this crosstalk often determines the balance between tolerance and resistance against these widespread parasites. Hence, there are many examples of how both helminths and the microbiota can influence tissue homeostasis and homeostatic immunity. Understanding these processes at a cellular and molecular level is an exciting area of research that we seek to highlight in this review and that will potentially guide future treatment approaches.

Social association predicts immunological similarity in rewilded mice

Environmental influences on immune phenotypes are well-documented, but our understanding of which elements of the environment affect immune systems, and how, remains vague. Behaviors, including socializing with others, are central to an individual's interaction with its environment. We tracked behavior of rewilded laboratory mice of three inbred strains in outdoor enclosures and examined contributions of behavior, including social associations, to immune phenotypes. We found that the more associated two individuals were, the more similar their immune phenotypes were. Social association was particularly predictive of similar memory T and B cell profiles and was more influential than sibling relationships or worm infection status. These results highlight the importance of social networks for immune phenotype and reveal important immunological correlates of social life.

Gut microbiome of helminth-infected indigenous Malaysians is context dependent

BACKGROUND

While microbiomes in industrialized societies are well characterized, indigenous populations with traditional lifestyles have microbiomes that are more akin to those of ancient humans. However, metagenomic data in these populations remains scarce, and the association with soil-transmitted helminth infection status is unclear. Here, we sequenced 650 metagenomes of indigenous Malaysians from five villages with different prevalence of helminth infections.

RESULTS

Individuals from villages with higher prevalences of helminth infections have more unmapped reads and greater microbial diversity. Microbial community diversity and composition were most strongly associated with different villages and the effects of helminth infection status on the microbiome varies by village. Longitudinal changes in the microbiome in response to albendazole anthelmintic treatment were observed in both helminth infected and uninfected individuals. Inference of bacterial population replication rates from origin of replication analysis identified specific replicating taxa associated with helminth infection.

CONCLUSIONS

Our results indicate that helminth effects on the microbiota were highly dependent on context, and effects of albendazole on the microbiota can be confounding for the interpretation of deworming studies. Furthermore, a substantial quantity of the microbiome remains unannotated, and this large dataset from an indigenous population associated with helminth infections is a valuable resource for future studies. Video Abstract.

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.

Interactions between the Environment and Genetics determines immune variation in rewilded mice

Immune responses to pathogens and vaccination can be varied with some individuals inducing optimal responses while others do not. The host genetic profile, environment and previous microbial experience could influence an individual’s response, but the relative contribution, and interactions of these different factors remains largely unknown. Here, using various multi-omics, ecological and single cell approaches, we show that release of genetic inbred strains of mice, 129-SL, PWK and C57/B6 mice, to a rewilded environment and exposure of these rewilded and laboratory specific pathogen free control mice to a helminth parasite, Trichuris muris allowed us to assess the contribution and interaction of host genotype and environment to the immune cell landscape in the blood and secondary lymphoid organs. Critically, we find that the environment has the greatest effect on circulating blood immune cells while the genetic profile has the greatest effect on the mesenteric lymph node. We also observed significant interactions between the host genetic profile, environment, and infection status in their contribution to immune cell composition, with most of the effect driven by the cells of the adaptive immune system. These findings provide a model for contribution and interactions between genetics, environment, and helminth infection in the inter-individual variation of immune responses.

Redefining inflammatory macrophage phenotypes across stages and tissues by single-cell transcriptomics

Single-cell transcriptomic data identifies major activation paths of monocyte-derived macrophages as a framework for inflammatory tissue macrophages.

Helminth infections and cardiovascular diseases: A role for the microbiota and Mϕs?

Cardiovascular diseases are rising in developing countries with increasing urbanization and lifestyle changes and remains a major cause of death in the developed world. In this mini review, we discuss the possibility that the effect of helminth infections on the immune system and the microbiota may affect risk factors in cardiovascular diseases such as atherosclerosis, as part of the hygiene hypothesis. The effects of Type 2 immune responses induced by helminths and helminth derived molecules on regulating metabolism and Mϕ function could be a mechanistic link for further investigation. We emphasize the complexity and difficulties in determining indirect or direct and causal relationships between helminth infection status and cardiovascular diseases. New experimental models, such as rewilding laboratory mice, whereby different aspects of the environment and host genetics can be carefully dissected may provide further mechanistic insights and therapeutic strategies for treating cardiovascular diseases.

Correction: Helminth Colonization Is Associated with Increased Diversity of the Gut Microbiota

[This corrects the article DOI: 10.1371/journal.pntd.0002880.].

Microbial genetic and transcriptional contributions to oxalate degradation by the gut microbiota in health and disease

Over-accumulation of oxalate in humans may lead to nephrolithiasis and nephrocalcinosis. Humans lack endogenous oxalate degradation pathways (ODP), but intestinal microbes can degrade oxalate using multiple ODPs and protect against its absorption. The exact oxalate-degrading taxa in the human microbiota and their ODP have not been described. We leverage multi-omics data (>3000 samples from >1000 subjects) to show that the human microbiota primarily uses the type II ODP, rather than type I. Furthermore, among the diverse ODP-encoding microbes, an oxalate autotroph, Oxalobacter formigenes, dominates this function transcriptionally. Patients with inflammatory bowel disease (IBD) frequently suffer from disrupted oxalate homeostasis and calcium oxalate nephrolithiasis. We show that the enteric oxalate level is elevated in IBD patients, with highest levels in Crohn's disease (CD) patients with both ileal and colonic involvement consistent with known nephrolithiasis risk. We show that the microbiota ODP expression is reduced in IBD patients, which may contribute to the disrupted oxalate homeostasis. The specific changes in ODP expression by several important taxa suggest that they play distinct roles in IBD-induced nephrolithiasis risk. Lastly, we colonize mice that are maintained in the gnotobiotic facility with O. formigenes, using either a laboratory isolate or an isolate we cultured from human stools, and observed a significant reduction in host fecal and urine oxalate levels, supporting our in silico prediction of the importance of the microbiome, particularly O. formigenes in host oxalate homeostasis.

Wnt signaling enhances macrophage responses to IL-4 and promotes resolution of atherosclerosis

Atherosclerosis is a disease of chronic inflammation. We investigated the roles of the cytokines IL-4 and IL-13, the classical activators of STAT6, in the resolution of atherosclerosis inflammation. Using Il4-/-Il13-/- mice, resolution was impaired, and in control mice, in both progressing and resolving plaques, levels of IL-4 were stably low and IL-13 was undetectable. This suggested that IL-4 is required for atherosclerosis resolution, but collaborates with other factors. We had observed increased Wnt signaling in macrophages in resolving plaques, and human genetic data from others showed that a loss-of-function Wnt mutation was associated with premature atherosclerosis. We now find an inverse association between activation of Wnt signaling and disease severity in mice and humans. Wnt enhanced the expression of inflammation resolving factors after treatment with plaque-relevant low concentrations of IL-4. Mechanistically, activation of the Wnt pathway following lipid lowering potentiates IL-4 responsiveness in macrophages via a PGE2/STAT3 axis.

Strong effects of lab-to-field environmental transitions on the bacterial intestinal microbiota of Mus musculus are modulated by Trichuris murisinfection

Studies of controlled lab animals and natural populations represent two insightful extremes of microbiota research. We bridged these two approaches by transferring lab-bred female C57BL/6 mice from a conventional mouse facility to an acclimation room and then to an outdoor enclosure, to investigate how the gut microbiota changes with environment. Mice residing under constant conditions served as controls. Using 16S rRNA sequencing of fecal samples, we found that the shift in temperature and humidity, as well as exposure to a natural environment, increased microbiota diversity and altered community composition. Community composition in mice exposed to high temperatures and humidity diverged as much from the microbiota of mice housed outdoors as from the microbiota of control mice. Additionally, infection with the nematode Trichuris muris modulated how the microbiota responded to environmental transitions: The dynamics of several families were buffered by the nematodes, while invasion rates of two taxa acquired outdoors were magnified. These findings suggest that gut bacterial communities respond dynamically and simultaneously to changes within the host's body (e.g. the presence of nematodes) and to changes in the wider environment of the host.

Targeting leukocidin-mediated immune evasion protects mice from Staphylococcus aureus bacteremia

Staphylococcus aureus is responsible for various diseases in humans, and recurrent infections are commonly observed. S. aureus produces an array of bicomponent pore-forming toxins that target and kill leukocytes, known collectively as the leukocidins. The contribution of these leukocidins to impair the development of anti–S. aureus adaptive immunity and facilitate reinfection is unclear. Using a murine model of recurrent bacteremia, we demonstrate that infection with a leukocidin mutant results in increased levels of anti–S. aureus antibodies compared with mice infected with the WT parental strain, indicating that leukocidins negatively impact the generation of anti–S. aureus antibodies in vivo. We hypothesized that neutralizing leukocidin-mediated immune subversion by vaccination may shift this host-pathogen interaction in favor of the host. Leukocidin-immunized mice produce potent leukocidin-neutralizing antibodies and robust Th1 and Th17 responses, which collectively protect against bloodstream infections. Altogether, these results demonstrate that blocking leukocidin-mediated immune evasion can promote host protection against S. aureus bloodstream infection.

The helminth glycoprotein omega-1 improves metabolic homeostasis in obese mice through type 2 immunity-independent inhibition of food intake

Type 2 immunity plays an essential role in the maintenance of metabolic homeostasis and its disruption during obesity promotes meta-inflammation and insulin resistance. Infection with the helminth parasite Schistosoma mansoni and treatment with its soluble egg antigens (SEA) induce a type 2 immune response in metabolic organs and improve insulin sensitivity and glucose tolerance in obese mice, yet, a causal relationship remains unproven. Here, we investigated the effects and underlying mechanisms of the T2 ribonuclease omega-1 (ω1), one of the major S mansoni immunomodulatory glycoproteins, on metabolic homeostasis. We show that treatment of obese mice with plant-produced recombinant ω1, harboring similar glycan motifs as present on the native molecule, decreased body fat mass, and improved systemic insulin sensitivity and glucose tolerance in a time- and dose-dependent manner. This effect was associated with an increase in white adipose tissue (WAT) type 2 T helper cells, eosinophils, and alternatively activated macrophages, without affecting type 2 innate lymphoid cells. In contrast to SEA, the metabolic effects of ω1 were still observed in obese STAT6-deficient mice with impaired type 2 immunity, indicating that its metabolic effects are independent of the type 2 immune response. Instead, we found that ω1 inhibited food intake, without affecting locomotor activity, WAT thermogenic capacity or whole-body energy expenditure, an effect also occurring in leptin receptor-deficient obese and hyperphagic db/db mice. Altogether, we demonstrate that while the helminth glycoprotein ω1 can induce type 2 immunity, it improves whole-body metabolic homeostasis in obese mice by inhibiting food intake via a STAT6-independent mechanism.

Identification of a nerve-associated, lung-resident interstitial macrophage subset with distinct localization and immunoregulatory properties

Tissue-resident macrophages are a diverse population of cells that perform specialized functions including sustaining tissue homeostasis and tissue surveillance. Here, we report an interstitial subset of CD169⁺ lung-resident macrophages that are transcriptionally and developmentally distinct from alveolar macrophages (AMs). They are primarily localized around the airways and are found in close proximity to the sympathetic nerves in the bronchovascular bundle. These nerve- and airway-associated macrophages (NAMs) are tissue resident, yolk sac derived, self-renewing, and do not require CCR2⁺ monocytes for development or maintenance. Unlike AMs, the development of NAMs requires CSF1 but not GM-CSF. Bulk population and single-cell transcriptome analysis indicated that NAMs are distinct from other lung-resident macrophage subsets and highly express immunoregulatory genes under steady-state and inflammatory conditions. NAMs proliferated robustly after influenza infection and activation with the TLR3 ligand poly(I:C), and in their absence, the inflammatory response was augmented, resulting in excessive production of inflammatory cytokines and innate immune cell infiltration. Overall, our study provides insights into a distinct subset of airway-associated pulmonary macrophages that function to maintain immune and tissue homeostasis.

Alternative Activation of Macrophages Is Accompanied by Chromatin Remodeling Associated with Lineage-Dependent DNA Shape Features Flanking PU.1 Motifs

IL-4 activates macrophages to adopt distinct phenotypes associated with clearance of helminth infections and tissue repair, but the phenotype depends on the cellular lineage of these macrophages. The molecular basis of chromatin remodeling in response to IL-4 stimulation in tissue-resident and monocyte-derived macrophages is not understood. In this study, we find that IL-4 activation of different lineages of peritoneal macrophages in mice is accompanied by lineage-specific chromatin remodeling in regions enriched with binding motifs of the pioneer transcription factor PU.1. PU.1 motif is similarly associated with both tissue-resident and monocyte-derived IL-4-induced accessible regions but has different lineage-specific DNA shape features and predicted cofactors. Mutation studies based on natural genetic variation between C57BL/6 and BALB/c mouse strains indicate that accessibility of these IL-4-induced regions can be regulated through differences in DNA shape without direct disruption of PU.1 motifs. We propose a model whereby DNA shape features of stimulation-dependent genomic elements contribute to differences in the accessible chromatin landscape of alternatively activated macrophages on different genetic backgrounds that may contribute to phenotypic variations in immune responses.

Distinct Features of Human Myeloid Cell Cytokine Response Profiles Identify Neutrophil Activation by Cytokines as a Prognostic Feature during Tuberculosis and Cancer

Myeloid cells are a vital component of innate immunity and comprise monocytes, macrophages, dendritic cells, and granulocytes. How myeloid cell lineage affects activation states in response to cytokines remains poorly understood. The cytokine environment and cellular infiltrate during an inflammatory response may contain prognostic features that predict disease outcome. In this study, we analyzed the transcriptional responses of human monocytes, macrophages, dendritic cells, and neutrophils in response to stimulation by IFN-γ, IFN-β, IFN-λ, IL-4, IL-13, and IL-10 cytokines to better understand the heterogeneity of activation states in inflammatory conditions. This generated a myeloid cell-cytokine-specific response matrix that can infer representation of myeloid cells and the cytokine environment they encounter during infection, in tumors and in whole blood. Neutrophils were highly responsive to type 1 and type 2 cytokine stimulation but did not respond to IL-10. We identified transcripts specific to IFN-β stimulation, whereas other IFN signature genes were upregulated by both IFN-γ and IFN-β. When we used our matrix to deconvolute blood profiles from tuberculosis patients, the IFN-β-specific neutrophil signature was reduced in tuberculosis patients with active disease, whereas the shared response to IFN-γ and IFN-β in neutrophils was increased. When applied to glioma patients, transcripts of neutrophils exposed to IL-4/IL-13 and monocyte responses to IFN-γ or IFN-β emerged as opposing predictors of patient survival. Hence, by dissecting how different myeloid cells respond to cytokine activation, we can delineate biological roles for myeloid cells in different cytokine environments during disease processes, especially during infection and tumor progression.

Regulatory T Cells License Macrophage Pro-Resolving Functions During Atherosclerosis Regression

RATIONALE

Regression of atherosclerosis is an important clinical goal; however, the pathways that mediate the resolution of atherosclerotic inflammation and reversal of plaques are poorly understood. Regulatory T cells (Tregs) have been shown to be atheroprotective, yet the numbers of these immunosuppressive cells decrease with disease progression, and whether they contribute to atherosclerosis regression is not known.

OBJECTIVE

We investigated the roles of Tregs in the resolution of atherosclerotic inflammation, tissue remodeling, and plaque contraction during atherosclerosis regression.

METHODS AND RESULTS

Using multiple independent mouse models of atherosclerosis regression, we demonstrate that an increase in plaque Tregs is a common signature of regressing plaques. Single-cell RNA-sequencing of plaque immune cells revealed that unlike Tregs from progressing plaques that expressed markers of natural Tregs derived from the thymus, Tregs in regressing plaques lacked Nrp1 expression, suggesting that they are induced in the periphery during lipid-lowering therapy. To test whether Tregs are required for resolution of atherosclerotic inflammation and plaque regression, Tregs were depleted using CD25 monoclonal antibody in atherosclerotic mice during apolipoprotein B antisense oligonucleotide-mediated lipid lowering. Morphometric analyses revealed that Treg depletion blocked plaque remodeling and contraction, and impaired hallmarks of inflammation resolution, including dampening of the T helper 1 response, alternative activation of macrophages, efferocytosis, and upregulation of specialized proresolving lipid mediators.

CONCLUSIONS

Our data establish essential roles for Tregs in resolving atherosclerotic cardiovascular disease and provide mechanistic insight into the pathways governing plaque remodeling and regression of disease.

Intestinal Macrophages in Resolving Inflammation

Macrophages not only regulate intestinal homeostasis by recognizing pathogens to control enteric infections but also employ negative feedback mechanisms to prevent chronic inflammation. Hence, macrophages are intriguing targets for immune-mediated therapies, especially when barrier function in the gut is compromised to trigger aberrant inflammatory responses, most notably during inflammatory bowel diseases. Recently, there has been considerable progress in our understanding of human macrophage biology in different tissues, including the intestines. In this review, we discuss some new findings on the properties of distinct populations of intestinal macrophages, how resolution of inflammation and tissue repair by macrophages could be promoted by type 2 cytokines as well as other therapeutic interventions, and highlight some challenges for translating these findings into the future for this exciting area of immunology research.

Altered Immunity of Laboratory Mice in the Natural Environment Is Associated with Fungal Colonization

Free-living mammals, such as humans and wild mice, display heightened immune activation compared with artificially maintained laboratory mice. These differences are partially attributed to microbial exposure as laboratory mice infected with pathogens exhibit immune profiles more closely resembling that of free-living animals. Here, we examine how colonization by microorganisms within the natural environment contributes to immune system maturation by releasing inbred laboratory mice into an outdoor enclosure. In addition to enhancing differentiation of T cell populations previously associated with pathogen exposure, outdoor release increased circulating granulocytes. However, these "rewilded" mice were not infected by pathogens previously implicated in immune activation. Rather, immune system changes were associated with altered microbiota composition with notable increases in intestinal fungi. Fungi isolated from rewilded mice were sufficient in increasing circulating granulocytes. These findings establish a model to investigate how the natural environment impacts immune development and show that sustained fungal exposure impacts granulocyte numbers.

Rewilding Nod2 and Atg16l1 Mutant Mice Uncovers Genetic and Environmental Contributions to Microbial Responses and Immune Cell Composition

The relative contributions of genetic and environmental factors to variation in immune responses are poorly understood. Here, we performed a phenotypic analysis of immunological parameters in laboratory mice carrying susceptibility genes implicated in inflammatory bowel disease (IBD) (Nod2 and Atg16l1) upon exposure to environmental microbes. Mice were released into an outdoor enclosure (rewilded) and then profiled for immune responses in the blood and lymph nodes. Variations of immune cell populations were largely driven by the environment, whereas cytokine production elicited by microbial antigens was more affected by the genetic mutations. We identified transcriptional signatures in the lymph nodes associated with differences in T cell populations. Subnetworks associated with responses against Clostridium perfringens, Candida albicans, and Bacteroides vulgatus were also coupled with rewilding. Therefore, exposing laboratory mice with genetic mutations to a natural environment uncovers different contributions to variations in microbial responses and immune cell composition.

Temporal changes in gut microbiota profile in children with acute lymphoblastic leukemia prior to commencement-, during-, and post-cessation of chemotherapy

BACKGROUND

Alteration in gut microbiota has been recently linked with childhood leukemia and the use of chemotherapy. Whether the perturbed microbiota community is restored after disease remission and cessation of cancer treatment has not been evaluated. This study examines the chronological changes of gut microbiota in children with acute lymphoblastic leukemia (ALL) prior to the start-, during-, and following cessation of chemotherapy.

METHODOLOGY

We conducted a longitudinal observational study in gut microbiota profile in a group of paediatric patients diagnosed with ALL using 16 s ribosomal RNA sequencing and compared these patients' microbiota pattern with age and ethnicity-matched healthy children. Temporal changes of gut microbiota in these patients with ALL were also examined at different time-points in relation to chemotherapy.

RESULTS

Prior to commencement of chemotherapy, gut microbiota in children with ALL had larger inter-individual variability compared to healthy controls and was enriched with bacteria belonging to Bacteroidetes phylum and Bacteroides genus. The relative abundance of Bacteroides decreased upon commencement of chemotherapy. Restitution of gut microbiota composition to resemble that of healthy controls occurred after cessation of chemotherapy. However, the microbiota composition (beta diversity) remained distinctive and a few bacteria were different in abundance among the patients with ALL compared to controls despite completion of chemotherapy and presumed restoration of normal health.

CONCLUSION

Our findings in this pilot study is the first to suggest that gut microbiota profile in children with ALL remains marginally different from healthy controls even after cessation of chemotherapy. These persistent microbiota changes may have a role in the long-term wellbeing in childhood cancer survivors but the impact of these changes in subsequent health perturbations in these survivors remain unexplored.

Serum Amyloid A Proteins Induce Pathogenic Th17 Cells and Promote Inflammatory Disease

Lymphoid cells that produce interleukin (IL)-17 cytokines protect barrier tissues from pathogenic microbes but are also prominent effectors of inflammation and autoimmune disease. T helper 17 (Th17) cells, defined by RORγt-dependent production of IL-17A and IL-17F, exert homeostatic functions in the gut upon microbiota-directed differentiation from naive CD4⁺ T cells. In the non-pathogenic setting, their cytokine production is regulated by serum amyloid A proteins (SAA1 and SAA2) secreted by adjacent intestinal epithelial cells. However, Th17 cell behaviors vary markedly according to their environment. Here, we show that SAAs additionally direct a pathogenic pro-inflammatory Th17 cell differentiation program, acting directly on T cells in collaboration with STAT3-activating cytokines. Using loss- and gain-of-function mouse models, we show that SAA1, SAA2, and SAA3 have distinct systemic and local functions in promoting Th17-mediated inflammatory diseases. These studies suggest that T cell signaling pathways modulated by the SAAs may be attractive targets for anti-inflammatory therapies.

IFN-I and IL-22 mediate protective effects of intestinal viral infection

Products derived from bacterial members of the gut microbiota evoke immune signalling pathways of the host that promote immunity and barrier function in the intestine. How immune reactions to enteric viruses support intestinal homeostasis is unknown. We recently demonstrated that infection by murine norovirus (MNV) reverses intestinal abnormalities following depletion of bacteria, indicating that an intestinal animal virus can provide cues to the host that are typically attributed to the microbiota. Here, we elucidate mechanisms by which MNV evokes protective responses from the host. We identify an important role for the viral protein NS1/2 in establishing local replication and a type I interferon (IFN-I) response in the colon. We further show that IFN-I acts on intestinal epithelial cells to increase the proportion of CCR2-dependent macrophages and interleukin (IL)-22-producing innate lymphoid cells, which in turn promote pSTAT3 signalling in intestinal epithelial cells and protection from intestinal injury. In addition, we demonstrate that MNV provides a striking IL-22-dependent protection against early-life lethal infection by Citrobacter rodentium. These findings demonstrate novel ways in which a viral member of the microbiota fortifies the intestinal barrier during chemical injury and infectious challenges.

Specialized dendritic cells induce tumor-promoting IL-10+IL-17+ FoxP3neg regulatory CD4+ T cells in pancreatic carcinoma

The drivers and the specification of CD4+ T cell differentiation in the tumor microenvironment and their contributions to tumor immunity or tolerance are incompletely understood. Using models of pancreatic ductal adenocarcinoma (PDA), we show that a distinct subset of tumor-infiltrating dendritic cells (DC) promotes PDA growth by directing a unique TH-program. Specifically, CD11b+CD103- DC predominate in PDA, express high IL-23 and TGF-β, and induce FoxP3neg tumor-promoting IL-10+IL-17+IFNγ+ regulatory CD4+ T cells. The balance between this distinctive TH program and canonical FoxP3+ TREGS is unaffected by pattern recognition receptor ligation and is modulated by DC expression of retinoic acid. This TH-signature is mimicked in human PDA where it is associated with immune-tolerance and diminished patient survival. Our data suggest that CD11b+CD103- DC promote CD4+ T cell tolerance in PDA which may underscore its resistance to immunotherapy.

Staphylococcus aureus Leukocidins Target Endothelial DARC to Cause Lethality in Mice

The pathogenesis of Staphylococcus aureus is thought to depend on the production of pore-forming leukocidins that kill leukocytes and lyse erythrocytes. Two leukocidins, Leukocidin ED (LukED) and γ-Hemolysin AB (HlgAB), are necessary and sufficient to kill mice upon infection and toxin challenge. We demonstrate that LukED and HlgAB cause vascular congestion and derangements in vascular fluid distribution that rapidly cause death in mice. The Duffy antigen receptor for chemokines (DARC) on endothelial cells, rather than leukocytes or erythrocytes, is the critical target for lethality. Consistent with this, LukED and HlgAB injure primary human endothelial cells in a DARC-dependent manner, and mice with DARC-deficient endothelial cells are resistant to toxin-mediated lethality. During bloodstream infection in mice, DARC targeting by S. aureus causes increased tissue damage, organ dysfunction, and host death. The potential for S. aureus leukocidins to manipulate vascular integrity highlights the importance of these virulence factors.

Enrichment of gut-derived Fusobacterium is associated with suboptimal immune recovery in HIV-infected individuals

We explored the gut microbiota profile among HIV-infected individuals with diverse immune recovery profiles following long-term suppressive ART and investigated the relationship between the altered bacteria with markers of immune dysfunction. The microbiota profile of rectal swabs from 26 HIV-infected individuals and 20 HIV-uninfected controls were examined. Patients were classified as suboptimal responders, sIR (n = 10, CD4 T-cell <350 cells/ul) and optimal responders, oIR (n = 16, CD4 T-cell >500 cells/ul) after a minimum of 2 years on suppressive ART. Canonical correlation analysis(CCA) and multiple regression modelling were used to explore the association between fecal bacterial taxa abundance and immunological profiles in optimal and suboptimal responders. We found Fusobacterium was significantly enriched among the HIV-infected and the sIR group. CCA results showed that Fusobacterium abundance was negatively correlated with CD4 T-cell counts, but positively correlated with CD4 T-cell activation and CD4 Tregs. Multiple linear regression analysis adjusted for age, baseline CD4 T-cell count, antibiotic exposure and MSM status indicated that higher Fusobacterium relative abundance was independently associated with poorer CD4 T-cell recovery following ART. Enrichment of Fusobacterium was associated with reduced immune recovery and persistent immune dysfunction following ART. Modulating the abundance of this bacterial taxa in the gut may be a viable intervention to improve immune reconstitution in our setting.

Assessing the Mouse Intestinal Microbiota in Settings of Type-2 Immune Responses

The microbial communities that reside within the mammalian host play important roles in the development of a robust host immune system. With the advent of sequencing technology and barcoding strategy of the bacterial 16S ribosomal RNA (rRNA) gene, microbiota studies are becoming more economical but also more important in many immunology studies. Here, we described a representative study protocol to characterize how the microbiota changes during an intestinal helminth infection, with emphasis on subtle aspects of the experimental design that are critical for data interpretation.

A Commensal Protozoan Strikes a Balance in the Gut

Gut commensals profoundly affect host immunity and intestinal homeostasis, but the impact of commensal eukaryotic protozoans is poorly understood. In a recent Cell paper, Chudnovskiy et al. (2016) identify a commensal protozoan, Tritrichomonas musculis, that can enhance anti-bacterial defenses, but at the cost of increasing intestinal inflammation.

Inflammatory Ly6Chi monocytes and their conversion to M2 macrophages drive atherosclerosis regression

Atherosclerosis is a chronic inflammatory disease, and developing therapies to promote its regression is an important clinical goal. We previously established that atherosclerosis regression is characterized by an overall decrease in plaque macrophages and enrichment in markers of alternatively activated M2 macrophages. We have now investigated the origin and functional requirement for M2 macrophages in regression in normolipidemic mice that received transplants of atherosclerotic aortic segments. We compared plaque regression in WT normolipidemic recipients and those deficient in chemokine receptors necessary to recruit inflammatory Ly6Chi (Ccr2-/- or Cx3cr1-/-) or patrolling Ly6Clo (Ccr5-/-) monocytes. Atherosclerotic plaques transplanted into WT or Ccr5-/- recipients showed reduced macrophage content and increased M2 markers consistent with plaque regression, whereas plaques transplanted into Ccr2-/- or Cx3cr1-/- recipients lacked this regression signature. The requirement of recipient Ly6Chi monocyte recruitment was confirmed in cell trafficking studies. Fate-mapping and single-cell RNA sequencing studies also showed that M2-like macrophages were derived from newly recruited monocytes. Furthermore, we used recipient mice deficient in STAT6 to demonstrate a requirement for this critical component of M2 polarization in atherosclerosis regression. Collectively, these results suggest that continued recruitment of Ly6Chi inflammatory monocytes and their STAT6-dependent polarization to the M2 state are required for resolution of atherosclerotic inflammation and plaque regression.

Can Helminth Infection Reverse Microbial Dysbiosis?

There is growing interest in treating inflammatory conditions with helminth infection. Recently, Loukas and colleagues have reported promising results from using experimental hookworm infection to reduce gluten sensitivity in celiac disease patients. Analysis of microbiota samples from the trial is contributing to our understanding of the complexity underlying helminth–microbiota–host relationships.

Abstract 1: Atherosclerosis Regression is Dependent Upon Newly Recruited Ly6c high Circulating Monocytes and Their STAT6-Mediated M2 Polarization

Inflammatory M1 macrophages (Mø) are a hallmark of progressing atherosclerotic lesions. Reversal of dyslipidemia reduces Mø burden in plaques, a process termed regression. In addition to significant Mø loss, we have shown that regressing plaque Møs are characterized by an M2 phenotype normally associated with activation by type 2 cytokines such as IL-4 and IL-13. However the origin of these M2 Møs remain unknown. We report here that M2 Møs derive from circulating monocytes, rather than a switch from M1 to M2 in situ. Using an aortic transplant model, we show that plaques transplanted from hyperlipidemic Apoe -/- mice into normolipidemic CD68-GFP reporter mice contained approximately 60% GFP+ CD11b+ F4/80+ (recipient origin) Møs 5 days post-surgery, indicating monocyte recruitment is active in regressing plaques. To determine the origin of M2 Møs in regressing plaques, arches from hyperlipidemic Apoe -/- mice (baseline) were transplanted into normolipidemic Ccr2 -/- ( chemokine receptor necessary for Ly6c high Mø recruitment to inflammatory sites), Ccr5 -/- (chemokine receptor necessary for Ly6c lo Mø recruitment), as well as WT and Apoe -/- control mice. Immunostaining of plaques 5 days post-transplant showed that WT and Ccr5 -/- mice had a 57% reduction (p<0.01) in total CD68+ Mø area and a 2.5 fold increase in M2 Mø (Arginase-1 and Mannose Receptor+) area (p <0.01) compared to baseline, whereas plaques from Ccr2 -/- mice failed to regress, as there was no change in total Mø or M2 Mø area compared to baseline. These data indicate that recruitment of inflammatory Ly6c high circulating monocytes is required for plaque regression and M2 Mø enrichment. To determine whether M2 Mø polarization of newly recruited monocytes is regulated by the canonical STAT6 signaling pathway via IL-4 and IL-13, a similar approach was taken. Notably, arches from hyperlipidemic Apoe -/- mice transplanted into normolipidemic Stat6 -/- or Il-4 -/- mice showed no significant reduction in total Mø or M2 Mø area compared to baseline. Collectively, our studies indicate that recruitment of Ly6c high monocytes into plaques and their differentiation into M2 Mø via the IL-4-STAT6 pathway are required for plaque regression.

Helminth infection promotes colonization resistance via type 2 immunity

Increasing incidence of inflammatory bowel diseases, such as Crohn's disease, in developed nations is associated with changes to the microbial environment, such as decreased prevalence of helminth colonization and alterations to the gut microbiota. We find that helminth infection protects mice deficient in the Crohn's disease susceptibility gene Nod2 from intestinal abnormalities by inhibiting colonization by an inflammatory Bacteroides species. Resistance to Bacteroides colonization was dependent on type 2 immunity, which promoted the establishment of a protective microbiota enriched in Clostridiales. Additionally, we show that individuals from helminth-endemic regions harbor a similar protective microbiota and that deworming treatment reduced levels of Clostridiales and increased Bacteroidales. These results support a model of the hygiene hypothesis in which certain individuals are genetically susceptible to the consequences of a changing microbial environment.

Monocyte-mediated defense against bacteria, fungi, and parasites

Circulating blood monocytes are a heterogeneous leukocyte population that contributes critical antimicrobial and regulatory functions during systemic and tissue-specific infections. These include patrolling vascular tissue for evidence of microbial invasion, infiltrating peripheral tissues and directly killing microbial invaders, conditioning the inflammatory milieu at sites of microbial tissue invasion, and orchestrating the activation of innate and adaptive immune effector cells. The central focus of this review is the in vivo mechanisms by which monocytes and their derivative cells promote microbial clearance and immune regulation. We include an overview of murine models to examine monocyte functions during microbial challenges and review our understanding of the functional roles of monocytes and their derivative cells in host defense against bacteria, fungi, and parasites.

Helminths and the microbiota: parts of the hygiene hypothesis

In modern societies, diseases that are driven by dysregulated immune responses are increasing at an alarming pace, such as inflammatory bowel diseases and diabetes. There is an urgent need to understand these epidemiological trends, which are likely to be driven by the changing environment of the last few decades. There are complex interactions between human genetic factors and this changing environment that is leading to the increasing prevalence of metabolic and inflammatory diseases. Alterations to human gut bacterial communities (the microbiota) and lowered prevalence of helminth infections are potential environmental factors contributing to immune dysregulation. Helminths have co-evolved with the gut microbiota and their mammalian hosts. This three-way interaction is beginning to be characterized, and the knowledge gained may enable the design of new therapeutic strategies to treat metabolic and inflammatory diseases. However, these complex interactions need to be carefully investigated in the context of host genetic backgrounds to identify optimal treatment strategies. The complex nature of these interactions raises the possibility that only with highly personalized treatment, with knowledge of individual genetic and microbiota communities, will therapeutic interventions be successful for a majority of the individuals suffering from these complex diseases of immune dysregulation.

Effect of ethnicity and socioeconomic variation to the gut microbiota composition among pre-adolescent in Malaysia

Gut microbiota plays an important role in mammalian host metabolism and physiological functions. The functions are particularly important in young children where rapid mental and physical developments are taking place. Nevertheless, little is known about the gut microbiome and the factors that contribute to microbial variation in the gut of South East Asian children. Here, we compared the gut bacterial richness and composition of pre-adolescence in Northern Malaysia. Our subjects covered three distinct ethnic groups with relatively narrow range of socioeconomic discrepancy. These included the Malays (n = 24), Chinese (n = 17) and the Orang Asli (indigenous) (n = 20). Our results suggested a strong ethnicity and socioeconomic-linked bacterial diversity. Highest bacterial diversity was detected from the economically deprived indigenous children while the lowest diversity was recorded from the relatively wealthy Chinese children. In addition, predicted functional metagenome profiling suggested an over-representation of pathways pertinent to bacterial colonisation and chemotaxis in the former while the latter exhibited enriched gene pathways related to sugar metabolism.

Isolation and cytokine analysis of lamina propria lymphocytes from mucosal biopsies of the human colon

Much of our understanding of gut-microbial interactions has come from mouse models. Intestinal immunity is complex and a combination of host genetics and environmental factors play a significant role in regulating intestinal immunity. Due to this complexity, no mouse model to date gives a complete and accurate representation of human intestinal diseases, such as inflammatory bowel diseases. However, intestinal tissue from patients undergoing bowel resection reflects a condition of severe disease that has failed treatment; hence a more dynamic perspective of varying inflammatory states in IBD could be obtained through the analyses of pinch biopsy material. Here we describe our protocol for analyzing mucosal pinch biopsies collected predominantly during colonoscopies. We have optimized flow cytometry panels to analyze up to 8 cytokines produced by CD4+ and CD8+ cells, as well as for characterizing nuclear proteins and transcription factors such as Ki67 and Foxp3. Furthermore, we have optimized approaches to analyze the production of cytokines, including TGF-beta from direct ex vivo cultures of pinch biopsies and LPMCs isolated from biopsies. These approaches are part of our workflow to try and understand the role of the gut microbiota in complex and dynamic human intestinal diseases.

Inferred metagenomic comparison of mucosal and fecal microbiota from individuals undergoing routine screening colonoscopy reveals similar differences observed during active inflammation

The mucosal microbiota lives in close proximity with the intestinal epithelium and may interact more directly with the host immune system than the luminal/fecal bacteria. The availability of nutrients in the mucus layer of the epithelium is also very different from the gut lumen environment. Inferred metagenomic analysis for microbial function of the mucosal microbiota is possible by PICRUSt. We recently found that by using this approach, actively inflamed tissue of ulcerative colitis (UC) patients have mucosal communities enriched for genes involved in lipid and amino acid metabolism, and reduced for carbohydrate and nucleotide metabolism. Here, we find that the same bacterial taxa (e.g. Acinetobacter) and predicted microbial pathways enriched in actively inflamed colitis tissue are also enriched in the mucosa of subjects undergoing routine screening colonoscopies, when compared with paired samples of luminal/fecal bacteria. These results suggest that the mucosa of healthy individuals may be a reservoir of aerotolerant microbial communities expanded during colitis.

Experimental cerebral malaria pathogenesis--hemodynamics at the blood brain barrier

Cerebral malaria claims the lives of over 600,000 African children every year. To better understand the pathogenesis of this devastating disease, we compared the cellular dynamics in the cortical microvasculature between two infection models, Plasmodium berghei ANKA (PbA) infected CBA/CaJ mice, which develop experimental cerebral malaria (ECM), and P. yoelii 17XL (PyXL) infected mice, which succumb to malarial hyperparasitemia without neurological impairment. Using a combination of intravital imaging and flow cytometry, we show that significantly more CD8(+) T cells, neutrophils, and macrophages are recruited to postcapillary venules during ECM compared to hyperparasitemia. ECM correlated with ICAM-1 upregulation on macrophages, while vascular endothelia upregulated ICAM-1 during ECM and hyperparasitemia. The arrest of large numbers of leukocytes in postcapillary and larger venules caused microrheological alterations that significantly restricted the venous blood flow. Treatment with FTY720, which inhibits vascular leakage, neurological signs, and death from ECM, prevented the recruitment of a subpopulation of CD45(hi) CD8(+) T cells, ICAM-1(+) macrophages, and neutrophils to postcapillary venules. FTY720 had no effect on the ECM-associated expression of the pattern recognition receptor CD14 in postcapillary venules suggesting that endothelial activation is insufficient to cause vascular pathology. Expression of the endothelial tight junction proteins claudin-5, occludin, and ZO-1 in the cerebral cortex and cerebellum of PbA-infected mice with ECM was unaltered compared to FTY720-treated PbA-infected mice or PyXL-infected mice with hyperparasitemia. Thus, blood brain barrier opening does not involve endothelial injury and is likely reversible, consistent with the rapid recovery of many patients with CM. We conclude that the ECM-associated recruitment of large numbers of activated leukocytes, in particular CD8(+) T cells and ICAM(+) macrophages, causes a severe restriction in the venous blood efflux from the brain, which exacerbates the vasogenic edema and increases the intracranial pressure. Thus, death from ECM could potentially occur as a consequence of intracranial hypertension.

Bacterial sensor Nod2 prevents inflammation of the small intestine by restricting the expansion of the commensal Bacteroides vulgatus

Nod2 has been extensively characterized as a bacterial sensor that induces an antimicrobial and inflammatory gene expression program. Therefore, it is unclear why Nod2 mutations that disrupt bacterial recognition are paradoxically among the highest risk factors for Crohn's disease, which involves an exaggerated immune response directed at intestinal bacteria. Here, we identified several abnormalities in the small-intestinal epithelium of Nod2(-/-) mice including inflammatory gene expression and goblet cell dysfunction, which were associated with excess interferon-γ production by intraepithelial lymphocytes and Myd88 activity. Remarkably, these abnormalities were dependent on the expansion of a common member of the intestinal microbiota Bacteroides vulgatus, which also mediated exacerbated inflammation in Nod2(-/-) mice upon small-intestinal injury. These results indicate that Nod2 prevents inflammatory pathologies by controlling the microbiota and support a multihit disease model involving specific gene-microbe interactions.

VIDEO ABSTRACT

Systemic impact of intestinal helminth infections

In this review, we examine the evidence that intestinal helminths can control harmful inflammatory responses and promote homeostasis by triggering systemic immune responses. Induction of separable components of immunity by helminths, which includes type 2 and immune regulatory responses, can both contribute toward the reduction in harmful type 1 immune responses that drive certain inflammatory diseases. Despite inducing type 2 responses, intestinal helminths may also downregulate harmful type 2 immune responses including allergic responses. We consider the possibility that intestinal helminth infection may indirectly affect inflammation by influencing the composition of the intestinal microbiome. Taken together, the studies reviewed herein suggest that intestinal helminth-induced responses have potent systemic effects on the immune system, raising the possibility that whole parasites or specific molecules produced by these metazoans may be an important resource for the development of future immunotherapies to control inflammatory diseases.

Ly6C(high) monocytes become alternatively activated macrophages in schistosome granulomas with help from CD4+ cells

Alternatively activated macrophages (AAM) that accumulate during chronic T helper 2 inflammatory conditions may arise through proliferation of resident macrophages or recruitment of monocyte-derived cells. Liver granulomas that form around eggs of the helminth parasite Schistosoma mansoni require AAM to limit tissue damage. Here, we characterized monocyte and macrophage dynamics in the livers of infected CX3CR1^GFP/+ mice. CX₃CR1-GFP⁺ monocytes and macrophages accumulated around eggs and in granulomas during infection and upregulated PD-L2 expression, indicating differentiation into AAM. Intravital imaging of CX₃CR1-GFP⁺ Ly6C^low monocytes revealed alterations in patrolling behavior including arrest around eggs that were not encased in granulomas. Differential labeling of CX₃CR1-GFP⁺ cells in the blood and the tissue showed CD4⁺ T cell dependent accumulation of PD-L2⁺ CX₃CR1-GFP⁺ AAM in the tissues as granulomas form. By adoptive transfer of Ly6C^high and Ly6C^low monocytes into infected mice, we found that AAM originate primarily from transferred Ly6C^high monocytes, but that these cells may transition through a Ly6C^low state and adopt patrolling behavior in the vasculature. Thus, during chronic helminth infection AAM can arise from recruited Ly6C^high monocytes via help from CD4⁺ T cells.

Macrophages will adopt different characteristics based on different types of inflammatory responses. During infection by parasitic helminths such as Schistosoma mansoni, macrophages adopt an “alternatively activated” or M2 phenotype (AAM). These AAM are important for protecting liver hepatocytes from damage caused by the parasite eggs. Here, we examine the cellular source of AAM in the liver of mice infected with S. mansoni. We find that AAM during S. mansoni infection come from monocytes and not from tissue resident macrophages. Monocytes can be separated into Ly6C^high and Ly6C^low monocyte subsets. We demonstrate that it is the Ly6C^high monocytes that are the precursors of AAM in the liver granulomas, but they might adopt the behavior of Ly6C^low monocytes in response to schistosome eggs. Additionally, these Ly6C^High monocytes require help from CD4⁺ T cells in order to differentiate into AAM or to maintain this phenotype.

Helminth colonization is associated with increased diversity of the gut microbiota

Soil-transmitted helminths colonize more than 1.5 billion people worldwide, yet little is known about how they interact with bacterial communities in the gut microbiota. Differences in the gut microbiota between individuals living in developed and developing countries may be partly due to the presence of helminths, since they predominantly infect individuals from developing countries, such as the indigenous communities in Malaysia we examine in this work. We compared the composition and diversity of bacterial communities from the fecal microbiota of 51 people from two villages in Malaysia, of which 36 (70.6%) were infected by helminths. The 16S rRNA V4 region was sequenced at an average of nineteen thousand sequences per samples. Helminth-colonized individuals had greater species richness and number of observed OTUs with enrichment of Paraprevotellaceae, especially with Trichuris infection. We developed a new approach of combining centered log-ratio (clr) transformation for OTU relative abundances with sparse Partial Least Squares Discriminant Analysis (sPLS-DA) to enable more robust predictions of OTU interrelationships. These results suggest that helminths may have an impact on the diversity, bacterial community structure and function of the gut microbiota.

Soil-transmitted helminths are carried by large numbers of people in developing countries. These parasites live in the gut and may interact with bacterial communities in the gut, also called the gut microbiota. To determine whether there are alterations to the gut microbiota that are associated with helminth infections, we examined the types of bacteria present in fecal samples from rural Malaysians, many of whom are helminth-positive and find it likely that helminth colonization alters the gut microbiota for rural Malaysians.

Parasites: what are they good for?

Parasitic diseases caused by helminth and protozoan infections remain one of the largest global public health problems for mankind. While natural immunity in man is rare or slow to develop for many parasites, the immune response is capable of recognizing and responding to infection by utilizing a number of different immunological mechanisms. This special topics journal issue examines many of the key findings in the recent literature regarding the immune response against helminth and protozoan infections, as well as highlighting areas in which our current knowledge falls short. The question of how we can tailor immune responses to prevent or reduce disease burden is a burning question within the field of immunoparasitology.

IL-22-producing CD4+ cells are depleted in actively inflamed colitis tissue

T helper type (Th17) cytokines such as interleukin (IL)-17A and IL-22 are important in maintaining mucosal barrier function and may be important in the pathogenesis of inflammatory bowel diseases (IBDs). Here, we analyzed cells from the colon of IBD patients and show that Crohn's disease (CD) patients had significantly elevated numbers of IL-17+, CD4+ cells compared with healthy controls and ulcerative colitis (UC) patients, but these numbers did not vary based on the inflammatory status of the mucosa. By contrast, UC patients had significantly reduced numbers of IL-22+ cells in actively inflamed tissues compared with both normal tissue and healthy controls. There was a selective increase in mono-IL-17-producing cells from the mucosa of UC patients with active inflammation together with increased expression of transforming growth factor (TGF)-β and c-Maf. Increasing concentrations of TGF-β in lamina propria mononuclear cell cultures significantly depleted Th22 cells, whereas anti-TGF-β antibodies increased IL-22 production. When mucosal microbiota was examined, depletion of Th22 cells in actively inflamed tissue was associated with reduced populations of Clostridiales and increased populations of Proteobacteria. These results suggest that increased TGF-β during active inflammation in UC may lead to the loss of Th22 cells in the human intestinal mucosa.

Chronic inflammatory liver disease in mice expressing a CD28-specific ligand (P4099)

Inflammation of the normally tolerant liver microenvironment precedes the development of chronic liver disease. Study of the pathogenesis of autoimmune liver diseases, such as autoimmune hepatitis (AIH), has been hampered by a lack of autochthonous chronic animal models. Through our studies of T cell costimulation, we generated transgenic mice expressing a ligand specific for the CD28 receptor, which normally shares ligands with the related inhibitory receptor CTLA-4. The mice spontaneously develop chronic inflammatory liver disease with several pathologies found in AIH, including elevated serum aminotransferases in the context of normal alkaline phosphatase and bilirubin levels, lymphocytic inflammation, focal necrosis, oval cell hyperplasia, and fibrosis. The prevalence of IFN-γ-producing CD8(+) T cells in the livers of transgenic mice suggests a role for autoimmune cytotoxicity in the chronic disease state. The CD28 ligand-specific transgenic mice will facilitate evaluation of CD8(+) T cell function in liver disease pathologies found in AIH.