The light and dark sides of intestinal intraepithelial lymphocytes. Nat Rev Immunol. 2011;11:445-456. [PMID: 21681197 DOI: 10.1038/nri3007]

Intravital Imaging of Intestinal Intraepithelial Lymphocytes

Intestinal intraepithelial lymphocytes (IEL) are a numerous population of T cells located within the epithelium of the small and large intestines, being more numerous in the small intestine (SI). They surveil this tissue by interacting with epithelial cells. Intravital microscopy is an important tool for visualizing the patrolling activity of IEL in the SI of live mice. Most IEL express CD8α; therefore, here we describe an established protocol of intravital imaging that tracks lymphocytes labeled with a CD8α-specific monoclonal antibody in the SI epithelium of live mice. We also describe data acquisition and quantification of the movement metrics, including mean speed, track length, displacement length, and paths for each CD8α+ IEL using the available software. The intravital imaging technique for measuring IEL movement will provide a better understanding of the role of IEL in homeostasis and protection from injury or infection in vivo.

Colonization during a key developmental window reveals microbiota-dependent shifts in growth and immunity during undernutrition

Childhood undernutrition is a major global health challenge with devastating lifelong consequences. Linear growth stunting due to undernutrition has been linked to poor outcomes, and mothers who experience stunting are more likely to give birth to stunted children. Murine models that capture the intergenerational and multifactorial nature of undernutrition are critical to understanding the underlying biology of this disorder. Here we report a gnotobiotic mouse model of undernutrition using microbiota from human infants with healthy or stunted growth trajectories. Intergenerational transmission of microbiota from parents to offspring leads to the development of growth and immune features of undernutrition and enteropathy, including reduced linear growth, intestinal villus blunting and accumulation of intraepithelial lymphocytes. In contrast, colonization after weaning reduces sensitivity to detect changes driven by distinct microbial communities. Overall, these results suggest intergenerational colonization is a useful approach with which to investigate microbiota-dependent growth and immunity in early life.

Gut microbial fatty acid isomerization modulates intraepithelial T cells

The human gut microbiome constantly converts natural products derived from the host and diet into numerous bioactive metabolites1-3. Dietary fats are essential micronutrients that undergo lipolysis to release free fatty acids (FAs) for absorption in the small intestine4. Gut commensal bacteria modify some unsaturated FAs-for example, linoleic acid (LA)-into various intestinal FA isomers that regulate host metabolism and have anticarcinogenic properties5. However, little is known about how this diet-microorganism FA isomerization network affects the mucosal immune system of the host. Here we report that both dietary factors and microbial factors influence the level of gut LA isomers (conjugated LAs (CLAs)) and that CLAs in turn modulate a distinct population of CD4+ intraepithelial lymphocytes (IELs) that express CD8αα in the small intestine. Genetic abolition of FA isomerization pathways in individual gut symbionts significantly decreases the number of CD4+CD8αα+ IELs in gnotobiotic mice. Restoration of CLAs increases CD4+CD8αα+ IEL levels in the presence of the transcription factor hepatocyte nuclear factor 4γ (HNF4γ). Mechanistically, HNF4γ facilitates CD4+CD8αα+ IEL development by modulating interleukin-18 signalling. In mice, specific deletion of HNF4γ in T cells leads to early mortality from infection by intestinal pathogens. Our data reveal a new role for bacterial FA metabolic pathways in the control of host intraepithelial immunological homeostasis by modulating the relative number of CD4+ T cells that were CD4+CD8αα+.

The intestinal γδ T cells: functions in the gut and in the distant organs

Located in the frontline against the largest population of microbiota, the intestinal mucosa of mammals has evolved to become an effective immune system. γδ T cells, a unique T cell subpopulation, are rare in circulation blood and lymphoid tissues, but rich in the intestinal mucosa, particularly in the epithelium. Via rapid production of cytokines and growth factors, intestinal γδ T cells are key contributors to epithelial homeostasis and immune surveillance of infection. Intriguingly, recent studies have revealed that the intestinal γδ T cells may play novel exciting functions ranging from epithelial plasticity and remodeling in response to carbohydrate diets to the recovery of ischemic stroke. In this review article, we update regulatory molecules newly defined in lymphopoiesis of the intestinal γδ T cells and their novel functions locally in the intestinal mucosa, such as epithelial remodeling, and distantly in pathological setting, e.g., ischemic brain injury repair, psychosocial stress responses, and fracture repair. The challenges and potential revenues in intestinal γδ T cell studies are discussed.

Single-cell profiling identifies a novel human polyclonal unconventional T cell lineage

In the human thymus, a CD10+ PD-1+ TCRαβ+ differentiation pathway diverges from the conventional single positive T cell lineages at the early double-positive stage. Here, we identify the progeny of this unconventional lineage in antigen-inexperienced blood. These unconventional T cells (UTCs) in thymus and blood share a transcriptomic profile, characterized by hallmark transcription factors (i.e., ZNF683 and IKZF2), and a polyclonal TCR repertoire with autoreactive features, exhibiting a bias toward early TCRα chain rearrangements. Single-cell RNA sequencing confirms a common developmental trajectory between the thymic and blood UTCs and clearly delineates this unconventional lineage in blood. Besides MME+ recent thymic emigrants, effector-like clusters are identified in this heterogeneous lineage. Expression of Helios and KIR and a decreased CD8β expression are characteristics of this lineage. This UTC lineage could be identified in adult blood and intestinal tissues. In summary, our data provide a comprehensive characterization of the polyclonal unconventional lineage in antigen-inexperienced blood and identify the adult progeny.

Distant antimetastatic effect of enterotropic colon cancer-derived α4β7+CD8+ T cells

Despite the high prognostic value of immune infiltrates in colorectal cancer (CRC), metastatic disease remains resistant to immunotherapy by immune checkpoint blockade (ICB). Here, we show, in metastatic CRC preclinical models, that orthotopically implanted primary colon tumors exert a colon-specific antimetastatic effect on distant hepatic lesions. Enterotropic α4β7 integrin-expressing neoantigen-specific CD8 T cells were key components of the antimetastatic effect. Accordingly, the presence of concomitant colon tumors improved control of liver lesions by anti-PD-L1 proof-of-concept immunotherapy and generated protective immune memory, whereas partial depletion of α4β7⁺ cells abrogated control of metastases. Last, in patients with metastatic CRC, response to ICB was associated with expression of α4β7 integrin in metastases and with circulating α4β7⁺ CD8 T cells. Our findings identify a systemic cancer immunosurveillance role for gut-primed tumor-specific α4β7⁺ CD8 T cells.

TGF-β controls development of TCRγδ+CD8αα+ intestinal intraepithelial lymphocytes

γδ intestinal intraepithelial lymphocytes (IELs) constitute the majority of IELs with unique CD8αα⁺ homodimers that are distinct from γδT cells in other tissues. However, it remains largely unclear how those cells develop. Here we show that transforming growth factor beta (TGF-β) signaling controls the development of TCRγδ⁺CD8αα⁺ IELs. Deletion of TGF-β receptors or Smad3 and Smad2 in bone marrow stem cells caused a deficiency of TCRγδ⁺CD8αα⁺ IELs in mixed bone marrow chimeric mice. Mechanistically, TGF-β is required for the development of TCRγδ⁺CD8αα⁺ IELs thymic precursors (CD44^-CD25^- γδ thymocytes). In addition, TGF-β signaling induced CD8α in thymic γδT cells and maintained CD8α expression and survival in TCRγδ⁺CD8αα⁺ IELs. Moreover, TGF-β also indirectly controls TCRγδ⁺CD8αα⁺ IELs by modulating the function of intestinal epithelial cells (IECs). Importantly, TGF-β signaling in TCRγδ⁺CD8αα⁺ IELs safeguarded the integrity of the intestinal barrier in dextran sulfate sodium (DSS)-induced colitis.

Intestinal cell type-specific communication networks underlie homeostasis and response to Western diet

The small intestine plays a key role in immunity and mediates inflammatory responses to high fat diets. We have used single-cell RNA-sequencing (scRNA-seq) and statistical modeling to examine gaps in our understanding of the dynamic properties of intestinal cells and underlying cellular mechanisms. Our scRNA-seq and flow cytometry studies of different layers of intestinal cells revealed new cell subsets and modeled developmental trajectories of intestinal intraepithelial lymphocytes, lamina propria lymphocytes, conventional dendritic cells, and enterocytes. As compared to chow-fed mice, a high-fat high-sucrose (HFHS) "Western" diet resulted in the accumulation of specific immune cell populations and marked changes to enterocytes nutrient absorption function. Utilizing ligand-receptor analysis, we profiled high-resolution intestine interaction networks across all immune cell and epithelial structural cell types in mice fed chow or HFHS diets. These results revealed novel interactions and communication hubs among intestinal cells, and their potential roles in local as well as systemic inflammation.

Repression of the aryl-hydrocarbon receptor prevents oxidative stress and ferroptosis of intestinal intraepithelial lymphocytes

The aryl-hydrocarbon receptor (AHR) is a ligand-activated transcription factor that buoys intestinal immune responses. AHR induces its own negative regulator, the AHR repressor (AHRR). Here, we show that AHRR is vital to sustaining intestinal intraepithelial lymphocytes (IELs). AHRR deficiency reduced IEL representation in a cell-intrinsic fashion. Single-cell RNA sequencing revealed an oxidative stress profile in Ahrr-/- IELs. AHRR deficiency unleashed AHR-induced expression of CYP1A1, a monooxygenase that generates reactive oxygen species, increasing redox imbalance, lipid peroxidation, and ferroptosis in Ahrr-/- IELs. Dietary supplementation with selenium or vitamin E to restore redox homeostasis rescued Ahrr-/- IELs. Loss of IELs in Ahrr-/- mice caused susceptibility to Clostridium difficile infection and dextran sodium-sulfate-induced colitis. Inflamed tissue of inflammatory bowel disease patients showed reduced Ahrr expression that may contribute to disease. We conclude that AHR signaling must be tightly regulated to prevent oxidative stress and ferroptosis of IELs and to preserve intestinal immune responses.

Treg specialization and functions beyond immune suppression

The actions of the immune system are finely tuned, involving complex communication and coordination between diverse immune and non-immune cells across the tissues of the body. A healthy immune system requires a precise balance between immunity and tolerance. Regulatory T cells (Tregs) have long been appreciated as one of the master regulators of this balance; their importance is underscored by the autoimmunity that develops in mice and humans when Tregs are missing or dysfunctional. In addition to the immunoregulatory roles of Tregs in suppressing autoimmunity and inflammation via control of adaptive and innate immune responses, several non-immune modulatory functions of Tregs have been identified in recent years. In this review, we have highlighted the growing literature on the action of Tregs in metabolism, stem cell maintenance, tissue repair, and angiogenesis. Alongside Tregs' immune suppressive role, these non-suppressive activities comprise a key function of Tregs in regulating health and disease. As Tregs receive increasing attention as therapeutic targets, understanding their non-canonical functions may become an important feature of Treg-directed interventions.

Levels of Genetic Variants Among Symptomatic Blastocystis Subtypes and their Relationship to Mucosal Immune Surveillance in the Precancerous Colons of Experimentally Infected Rats

PURPOSE

The relationship between the genetic diversity of Blastocystis and immune surveillance in precancerous colons with blastocystosis is still under investigation. This study aimed to identify the genetic Blastocystis variants among 54 symptomatic human isolates and their relationship to mucosal immune surveillance in the precancerous polyps of experimentally infected rats.

METHODS

Polymerase chain reaction and high-resolution melting (PCR/HRM) curves discriminated human symptomatic Blastocystis isolates into subtypes (STs)/intrasubtypes, which were orally administered to rats to induce experimental infection. Then, the mucosal immune responses of the infected colons were evaluated in relation to polyp formation through immunostaining to identify mucus MUC2 and determine mucosal immune cell (goblet, lymphocyte and mast) counts, secretory IgA levels and parasitic intestinal invasion.

RESULTS

ST1, ST3, and ST4 were found in 18.5% (10/54), 54.7% (29/54), and 27.8% (15/54) of the samples, respectively. Then, the HRM curve discriminated ST3 into the wild, mutant, and heterozygous [17/54 (31.5%), 5/54 (9.3%), and 7/54 (12.9%)] intrasubtypes. ST1 and ST4 had no genetic variations. Precancerous polyps were detected in the colons of 40.5% of the infected rats. ST1 constituted 14.7% of these cases, while the wild, mutant, and heterozygous intrasubtypes of ST3 showed polyps in 12.9%, 5.5%, and 5.5% of cases, respectively. Only 1.9% of the polyps were related to ST4. MUC2 showed weak immunostaining in 44.5% of the infected colons, and 38.9% were polyp inducers. Low goblet cell numbers and high interepithelial lymphocyte counts were significantly associated with polyp formation, particularly with ST1 and wild ST3. Among the polyp inducers, high numbers of mast cells were detected in wild ST3 and ST4, while a low number was found with heterozygous ST3. The level of secretory IgA was low in polyp-inducing STs. Most of the results were statistically significant.

CONCLUSION

Immunosurveillance showed a potential relationship between ST1 and the ST3 intrasubtypes and precancerous polyps. This relationship may provide insight into the prevention and/or development of new immunotherapeutic strategies to combat colorectal cancer.

Glutamine alleviates intestinal injury in a murine burn sepsis model by maintaining intestinal intraepithelial lymphocyte homeostasis

Intestinal intraepithelial lymphocytes (IELs) play a sentinel role in the mucosal immune system because of their unique anatomical location in the epithelial layer. The disruption of IEL homeostasis is implicated in driving the intestinal injury of many typical inflammatory disorders, such as inflammatory bowel disease (IBD) and sepsis. Therefore, it is meaningful to alleviate intestinal injury by restoring IEL homeostasis in disease conditions. This study explores the effects of glutamine on intestinal IEL homeostasis in a murine model of burn sepsis. We report that glutamine inhibits inflammatory response and reduces injury in the small intestine of burn septic mice. This effect is attributed to the maintaining of IEL homeostasis by suppressing apoptosis and restoring the disrupted subpopulation balance induced by burn sepsis. Mechanistically, we show that glutamine does not affect the IL-15 dependent mechanisms that drive the maintenance and differentiation of IELs. Instead, glutamine sustains IEL homeostasis by upregulate aryl hydrocarbon receptor (AHR) and interleukin (IL)-22 transcription and expression. Consistently, the protective roles of glutamine in burn septic mice were repressed by further supplement with an AHR antagonist CH-223191. Collectively, our study reveals a new role of glutamine to maintain IEL homeostasis by activating the AHR signaling pathway, which in turn ameliorates intestinal injury in burn sepsis.

Intestinal location- and age-specific variation of intraepithelial T lymphocytes and mucosal microbiota in pigs

Intraepithelial T lymphocytes (T-IELs) are T cells located within the epithelium that provide a critical line of immune defense in the intestinal tract. In pigs, T-IEL abundances and phenotypes are used to infer putative T-IEL functions and vary by intestinal location and age, though investigations regarding porcine T-IELs are relatively limited. In this study, we expand on analyses of porcine intestinal T-IELs to include additional phenotypic designations not previously recognized in pigs. We describe non-conventional CD8α⁺CD8β^- αβ T-IELs that were most prevalent in the distal intestinal tract and primarily CD16⁺CD27^-, a phenotype suggestive of innate-like activation and an activated cell state. Additional T-IEL populations included CD8α⁺CD8β⁺ αβ, CD2⁺CD8α⁺ γδ, and CD2⁺CD8α^- γδ T-IELs, with increasing proportions of CD16⁺CD27^- phenotype in the distal intestine. Thus, putative non-conventional, activated T-IELs were most abundant in the distal intestine within multiple γδ and αβ T-IEL populations. A comparison of T-IEL and respective mucosal microbial community structures across jejunum, ileum, and cecum of 5- and 7-week-old pigs revealed largest community differences were tissue-dependent for both T-IELs and the microbiota. Between 5 and 7 weeks of age, the largest shifts in microbial community compositions occurred in the large intestine, while the largest shifts in T-IEL communities were in the small intestine. Therefore, results indicate different rates of community maturation and stabilization for porcine T-IELs and the mucosal microbiota for proximal versus distal intestinal locations between 5 and 7 weeks of age. Collectively, data emphasize the intestinal tract as a site of location- and age-specific T-IEL and microbial communities that have important implications for understanding intestinal health in pigs.

Stromal regulation of the intestinal barrier

The intestinal barrier is a complex structure that allows the absorption of nutrients while ensuring protection against intestinal pathogens and balanced immunity. The development and maintenance of a functional intestinal barrier is a multifactorial process that is only partially understood. Here we review novel findings on the emerging role of mesenchymal cells in this process using insights gained from lineage tracing approaches, Cre-based gene deletion, and single-cell transcriptomics. The current evidence points toward a key organizer role for distinct mesenchymal lineages in intestinal development and homeostasis, regulating both epithelial and immune components of the intestinal barrier. We further discuss recent findings on functional mesenchymal heterogeneity and implications for intestinal regeneration and inflammatory intestinal pathologies.

Activated regulatory T-cells promote duodenal bacterial translocation into necrotic areas in severe acute pancreatitis

OBJECTIVE

In acute pancreatitis (AP), bacterial translocation and subsequent infection of pancreatic necrosis are the main risk factors for severe disease and late death. Understanding how immunological host defence mechanisms fail to protect the intestinal barrier is of great importance in reducing the mortality risk of the disease. Here, we studied the role of the T_reg/Th17 balance for maintaining the intestinal barrier function in a mouse model of severe AP.

DESIGN

AP was induced by partial duct ligation in C57Bl/6 or DEREG mice, in which regulatory T-cells (T_reg) were depleted by intraperitoneal injection of diphtheria toxin. By flow cytometry, functional suppression assays and transcriptional profiling we analysed T_reg activation and characterised T-cells of the lamina propria as well as intraepithelial lymphocytes (IELs) regarding their activation and differentiation. Microbiota composition was examined in intestinal samples as well as in murine and human pancreatic necrosis by 16S rRNA gene sequencing.

RESULTS

The prophylactic T_reg-depletion enhanced the proinflammatory response in an experimental mouse model of AP but stabilised the intestinal immunological barrier function of Th17 cells and CD8⁺/γδTCR⁺ IELs. T_reg depleted animals developed less bacterial translocation to the pancreas. Duodenal overgrowth of the facultative pathogenic taxa Escherichia/Shigella which associates with severe disease and infected necrosis was diminished in T_reg depleted animals.

CONCLUSION

T_regs play a crucial role in the counterbalance against systemic inflammatory response syndrome. In AP, T_reg-activation disturbs the duodenal barrier function and permits translocation of commensal bacteria into pancreatic necrosis. Targeting T_regs in AP may help to ameliorate the disease course.

Gut immune cells and intestinal niche imprinting

The intestine comprises the largest proportion of immune cells in the body. It is continuously exposed to new antigens and immune stimuli from the diet, microbiota but also from intestinal pathogens. In this review, we describe the main populations of immune cells present along the intestine, both from the innate and adaptive immune system. We later discuss how intestinal niches significantly impact the phenotype and function of gut immune populations at steady state and upon infection.

Regulator of G-protein signaling 1 critically supports CD8+ TRM cell-mediated intestinal immunity

Members of the Regulator of G-protein signaling (Rgs) family regulate the extent and timing of G protein signaling by increasing the GTPase activity of Gα protein subunits. The Rgs family member Rgs1 is one of the most up-regulated genes in tissue-resident memory (T_RM) T cells when compared to their circulating T cell counterparts. Functionally, Rgs1 preferentially deactivates Gαq, and Gαi protein subunits and can therefore also attenuate chemokine receptor-mediated immune cell trafficking. The impact of Rgs1 expression on tissue-resident T cell generation, their maintenance, and the immunosurveillance of barrier tissues, however, is only incompletely understood. Here we report that Rgs1 expression is readily induced in naïve OT-I T cells in vivo following intestinal infection with Listeria monocytogenes-OVA. In bone marrow chimeras, Rgs1 ^-/- and Rgs1 ^+/+ T cells were generally present in comparable frequencies in distinct T cell subsets of the intestinal mucosa, mesenteric lymph nodes, and spleen. After intestinal infection with Listeria monocytogenes-OVA, however, OT-I Rgs1 ^+/+ T cells outnumbered the co-transferred OT-I Rgs1^{- /-} T cells in the small intestinal mucosa already early after infection. The underrepresentation of the OT-I Rgs1 ^-/- T cells persisted to become even more pronounced during the memory phase (d30 post-infection). Remarkably, upon intestinal reinfection, mice with intestinal OT-I Rgs1 ^+/+ T_RM cells were able to prevent the systemic dissemination of the pathogen more efficiently than those with OT-I Rgs1 ^-/- T_RM cells. While the underlying mechanisms are not fully elucidated yet, these data thus identify Rgs1 as a critical regulator for the generation and maintenance of tissue-resident CD8⁺ T cells as a prerequisite for efficient local immunosurveillance in barrier tissues in case of reinfections with potential pathogens.

Myo1f has an essential role in γδT intraepithelial lymphocyte adhesion and migration

γδT intraepithelial lymphocyte represents up to 60% of the small intestine intraepithelial compartment. They are highly migrating cells and constantly interact with the epithelial cell layer and lamina propria cells. This migratory phenotype is related to the homeostasis of the small intestine, the control of bacterial and parasitic infections, and the epithelial shedding induced by LPS. Here, we demonstrate that Myo1f participates in the adhesion and migration of intraepithelial lymphocytes. Using long-tailed class I myosins KO mice, we identified the requirement of Myo1f for their migration to the small intestine intraepithelial compartment. The absence of Myo1f affects intraepithelial lymphocytes' homing due to reduced CCR9 and α4β7 surface expression. In vitro, we confirm that adhesion to integrin ligands and CCL25-dependent and independent migration of intraepithelial lymphocytes are Myo1f-dependent. Mechanistically, Myo1f deficiency prevents correct chemokine receptor and integrin polarization, leading to reduced tyrosine phosphorylation which could impact in signal transduction. Overall, we demonstrate that Myo1f has an essential role in the adhesion and migration in γδT intraepithelial lymphocytes.

Dihydromyricetin Attenuates High-Intensity Exercise-Induced Intestinal Barrier Dysfunction Associated with the Modulation of the Phenotype of Intestinal Intraepithelial Lymphocytes

BACKGROUND

Exercise-induced gastrointestinal syndrome (GIS) has symptoms commonly induced by strenuous sports. The study aimed to determine the effect of dihydromyricetin (DHM) administration on high-intensity exercise (HIE)-induced intestinal barrier dysfunction and the underlying mechanism involved with intestinal intraepithelial lymphocytes (IELs).

METHODS

The HIE model was established with male C57BL/6 mice using a motorized treadmill for 2 weeks, and DHM was given once a day by oral gavage. After being sacrificed, the small intestines of the mice were removed immediately.

RESULTS

We found that DHM administration significantly suppressed HIE-induced intestinal inflammation, improved intestinal barrier integrity, and inhibited a HIE-induced increase in the number of IELs and the frequency of CD8αα⁺ IELs. Meanwhile, several markers associated with the activation, gut homing and immune functions of CD8αα⁺ IELs were regulated by DHM. Mechanistically, luciferase reporter assay and molecular docking assay showed DHM could activate the aryl hydrocarbon receptor (AhR).

CONCLUSIONS

These data indicate that DHM exerts a preventive effect against HIE-induced intestinal barrier dysfunction, which is associated with the modulation of the quantity and phenotype of IELs in the small intestine. The findings provide a foundation to identify novel preventive strategies based on DHM supplementation for HIE-induced GIS.

Intraepithelial lymphocytes in the pig intestine: T cell and innate lymphoid cell contributions to intestinal barrier immunity

Intraepithelial lymphocytes (IELs) include T cells and innate lymphoid cells that are important mediators of intestinal immunity and barrier defense, yet most knowledge of IELs is derived from the study of humans and rodent models. Pigs are an important global food source and promising biomedical model, yet relatively little is known about IELs in the porcine intestine, especially during formative ages of intestinal development. Due to the biological significance of IELs, global importance of pig health, and potential of early life events to influence IELs, we collate current knowledge of porcine IEL functional and phenotypic maturation in the context of the developing intestinal tract and outline areas where further research is needed. Based on available findings, we formulate probable implications of IELs on intestinal and overall health outcomes and highlight key findings in relation to human IELs to emphasize potential applicability of pigs as a biomedical model for intestinal IEL research. Review of current literature suggests the study of porcine intestinal IELs as an exciting research frontier with dual application for betterment of animal and human health.

Development and function of natural TCR+ CD8αα+ intraepithelial lymphocytes

The complexity of intestinal homeostasis results from the ability of the intestinal epithelium to absorb nutrients, harbor multiple external and internal antigens, and accommodate diverse immune cells. Intestinal intraepithelial lymphocytes (IELs) are a unique cell population embedded within the intestinal epithelial layer, contributing to the formation of the mucosal epithelial barrier and serving as a first-line defense against microbial invasion. TCRαβ⁺ CD4^- CD8αα⁺ CD8αβ^- and TCRγδ⁺ CD4^- CD8αα⁺ CD8αβ^- IELs are the two predominant subsets of natural IELs. These cells play an essential role in various intestinal diseases, such as infections and inflammatory diseases, and act as immune regulators in the gut. However, their developmental and functional patterns are extremely distinct, and the mechanisms underlying their development and migration to the intestine are not fully understood. One example is that Bcl-2 promotes the survival of thymic precursors of IELs. Mature TCRαβ⁺ CD4^- CD8αα⁺ CD8αβ^- IELs seem to be involved in immune regulation, while TCRγδ⁺ CD4^- CD8αα⁺ CD8αβ^- IELs might be involved in immune surveillance by promoting homeostasis of host microbiota, protecting and restoring the integrity of mucosal epithelium, inhibiting microbiota invasion, and limiting excessive inflammation. In this review, we elucidated and organized effectively the functions and development of these cells to guide future studies in this field. We also discussed key scientific questions that need to be addressed in this area.

Leukemia inhibitory factor protects against graft-versus-host disease while preserving graft-versus-leukemia activity

Graft-versus-host disease (GVHD) remains a major complication after allogeneic hematopoietic stem cell transplantation, a widely used therapy for hematologic malignancies and blood disorders. Here, we report an unexpected role of cytokine leukemia inhibitory factor (LIF) in protecting against GVHD development. Administrating recombinant LIF protein (rLIF) protects mice from GVHD-induced tissue damage and lethality without compromising the graft-versus-leukemia activity, which is crucial to prevent tumor relapse. We found that rLIF decreases the infiltration and activation of donor immune cells and protects intestinal stem cells to ameliorate GVHD. Mechanistically, rLIF downregulates IL-12-p40 expression in recipient dendritic cells after irradiation through activating STAT1 signaling, which results in decreased major histocompatibility complex II levels on intestinal epithelial cells and decreased donor T-cell activation and infiltration. This study reveals a previously unidentified protective role of LIF for GVHD-induced tissue pathology and provides a potential effective therapeutic strategy to limit tissue pathology without compromising antileukemic efficacy.

Lactoferrin Alleviates Lipopolysaccharide-Induced Infantile Intestinal Immune Barrier Damage by Regulating an ELAVL1-Related Signaling Pathway

As the most important intestinal mucosal barrier of the main body, the innate immune barrier in intestinal tract plays especially pivotal roles in the overall health conditions of infants and young children; therefore, how to strengthen the innate immune barrier is pivotal. A variety of bioactivities of lactoferrin (LF) has been widely proved, including alleviating enteritis and inhibiting colon cancer; however, the effects of LF on intestinal immune barrier in infants and young children are still unclear, and the specific mechanism on how LF inhibits infantile enteritis by regulating immune signaling pathways is unrevealed. In the present study, we firstly performed pharmacokinetic analyses of LF in mice intestinal tissues, stomach tissues and blood, through different administration methods, to confirm the metabolic method of LF in mammals. Then we constructed in Vitro and in Vivo infantile intestinal immune barrier damage models utilizing lipopolysaccharide (LPS), and evaluated the effects of LF in alleviating LPS-induced intestinal immune barrier damage. Next, the related immune molecular mechanism on how LF exerted protective effects was investigated, through RNA-seq analyses of the mouse primary intestinal epithelial cells, and the specific genes were analyzed and screened out. Finally, the genes and their related immune pathway were validated in mRNA and protein levels; the portions of special immune cells (CD4⁺ T cells and CD8⁺ T cells) were also detected to further support our experimental results. Pharmacokinetic analyses demonstrated that the integrity of LF could reach mice stomach and intestine after oral gavage within 12 h, and the proper administration of LF should be the oral route. LF was proven to down-regulate the expression levels of inflammatory cytokines in both the primary intestinal epithelial cells and mice blood, especially LF without iron (Apo-LF), indicating LF alleviated infantile intestinal immune barrier damage induced by LPS. And through RNA-seq analyses of the mouse primary intestinal epithelial cells treated with LPS and LF, embryonic lethal abnormal vision Drosophila 1 (ELAVL1) was selected as one of the key genes, then the ELAVL1/PI3K/NF-κB pathway regulated by LF was verified to participate in the protection of infantile intestinal immune barrier damage in our study. Additionally, the ratio of blood CD4⁺/CD8⁺ T cells was significantly higher in the LF-treated mice than in the control mice, indicating that LF distinctly reinforced the overall immunity of infantile mice, further validating the strengthening bioactivity of LF on infantile intestinal immune barrier. In summary, LF was proven to alleviate LPS-induced intestinal immune barrier damage in young mice through regulating ELAVL1-related immune signaling pathways, which would expand current knowledge of the functions of bioactive proteins in foods within different research layers, as well as benefit preclinical and clinical researches in a long run.

A microbiota-derived antigen drives CD4+ intraepithelial lymphocyte (CD4IEL) development

CD4⁺ intraepithelial lymphocytes (CD4IEL) are tissue-resident T cells with cytotoxic and regulatory properties; together with peripheral regulatory T cells, they control intestinal inflammation. Recently, Bousbaine and colleagues identified a microbiota-derived conserved antigen that induces CD4IEL differentiation and promotes their regulatory function, attenuating the severity of murine colitis.

CD4+-mediated colitis in mice is independent of the GPR183 and GPR18 pathways

Colitis is characterized by an exacerbated intestinal immune response, but the genetic and other mechanisms regulating immune activation remain incompletely understood. In order to identify new pathways leading to colitis, we sought to identify genes with increased expression in the colons of patients that also are near loci identified by genome wide association studies (GWAS) associated with IBD risk. One such SNP, rs9557195 was of particular interest because it is within an intron of G-protein-coupled receptor (GPR) 183, known to be important for lymphocyte migration. Furthermore, this SNP is in close proximity to the gene encoding another G-protein coupled receptor, GPR18. Analyzing publicly available datasets, we found transcripts of GPR183 and GPR18 to be increased in colon biopsies from ulcerative colitis and Crohn's disease patients, and GPR183 was even more increased in patients resistant to TNF treatment. Expression of both genes also was increased in mouse models of colitis. Therefore, our aim was to understand if increased expression of these GPRs in the intestine is related to disease severity in colitis models. Here we investigated the role of these receptors in the T cell transfer model and the dextran sulfate sodium model. In the T cell transfer model, GPR183 expression on donor T cells, as well as on other cell types in the Rag-/- recipients, was not essential for severe colitis induction. Furthermore, deficiency in Rag-/- mice for the enzyme that synthesizes a cholesterol metabolite that is a major ligand for GPR183 also did not affect disease. Similarly, lack of GPR18 expression in T cells or other cell types did not affect colitis pathogenesis in the T cell transfer or in the dextran sulfate sodium model. Therefore, despite increased expression of transcripts for these genes in the intestine during inflammation in humans and mice, they are not required for disease severity in mouse models of colitis induced by chemical injury or T cell cytokines, perhaps due to redundancy in mechanisms important for homing and survival of lymphocytes to the inflamed intestine.

Divergent roles for the gut intraepithelial lymphocyte GLP-1R in control of metabolism, microbiota, and T cell-induced inflammation

Gut intraepithelial lymphocytes (IELs) are thought to calibrate glucagon-like peptide 1 (GLP-1) bioavailability, thereby regulating systemic glucose and lipid metabolism. Here, we show that the gut IEL GLP-1 receptor (GLP-1R) is not required for enteroendocrine L cell GLP-1 secretion and glucose homeostasis nor for the metabolic benefits of GLP-1R agonists (GLP-1RAs). Instead, the gut IEL GLP-1R is essential for the full effects of GLP-1RAs on gut microbiota. Moreover, independent of glucose control or weight loss, the anti-inflammatory actions of GLP-1RAs require the gut IEL GLP-1R to selectively restrain local and systemic T cell-induced, but not lipopolysaccharide-induced, inflammation. Such effects are mediated by the suppression of gut IEL effector functions linked to the dampening of proximal T cell receptor signaling in a protein-kinase-A-dependent manner. These data reposition key roles of the L cell-gut IEL GLP-1R axis, revealing mechanisms linking GLP-1R activation in gut IELs to modulation of microbiota composition and control of intestinal and systemic inflammation.

The multifunctional nature of CD103 (αEβ7 integrin) signaling in tissue-resident lymphocytes

Intestinal tissue-resident lymphocytes are critical for maintenance of the mucosal barrier and to prevent enteric infections. The activation of these lymphocytes must be tightly regulated to prevent aberrant inflammation and epithelial damage observed in autoimmune diseases, yet also ensure that antimicrobial host defense remains uncompromised. Tissue-resident lymphocytes express CD103, or αE integrin, which dimerizes with the β7 subunit to bind to E-cadherin expressed on epithelial cells. Although the role of CD103 in homing and retention of lymphocytes to and within peripheral tissues has been well characterized, the molecular signals activated following CD103 engagement remain understudied. Here, we highlight recent studies that elucidate the functional contribution of CD103 in various lymphocyte subpopulations, either as an independent signaling molecule or in the context of TCR co-stimulation. Finally, we will discuss the gaps in our understanding of CD103 biology and the therapeutic potential of targeting CD103 on tissue-resident lymphocytes.

The γδ IEL effector API5 masks genetic susceptibility to Paneth cell death

Loss of Paneth cells and their antimicrobial granules compromises the intestinal epithelial barrier and is associated with Crohn's disease, a major type of inflammatory bowel disease^1-7. Non-classical lymphoid cells, broadly referred to as intraepithelial lymphocytes (IELs), intercalate the intestinal epithelium^8,9. This anatomical position has implicated them as first-line defenders in resistance to infections, but their role in inflammatory disease pathogenesis requires clarification. The identification of mediators that coordinate crosstalk between specific IEL and epithelial subsets could provide insight into intestinal barrier mechanisms in health and disease. Here we show that the subset of IELs that express γ and δ T cell receptor subunits (γδ IELs) promotes the viability of Paneth cells deficient in the Crohn's disease susceptibility gene ATG16L1. Using an ex vivo lymphocyte-epithelium co-culture system, we identified apoptosis inhibitor 5 (API5) as a Paneth cell-protective factor secreted by γδ IELs. In the Atg16l1-mutant mouse model, viral infection induced a loss of Paneth cells and enhanced susceptibility to intestinal injury by inhibiting the secretion of API5 from γδ IELs. Therapeutic administration of recombinant API5 protected Paneth cells in vivo in mice and ex vivo in human organoids with the ATG16L1 risk allele. Thus, we identify API5 as a protective γδ IEL effector that masks genetic susceptibility to Paneth cell death.

P2X7 receptor as the regulator of T-cell function in intestinal barrier disruption

The intestinal mucosa is a highly compartmentalized structure that forms a direct barrier between the host intestine and the environment, and its dysfunction could result in a serious disease. As T cells, which are important components of the mucosal immune system, interact with gut microbiota and maintain intestinal homeostasis, they may be involved in the process of intestinal barrier dysfunction. P2X7 receptor (P2X7R), a member of the P2X receptors family, mediates the effects of extracellular adenosine triphosphate and is expressed by most innate or adaptive immune cells, including T cells. Current evidence has demonstrated that P2X7R is involved in inflammation and mediates the survival and differentiation of T lymphocytes, indicating its potential role in the regulation of T cell function. In this review, we summarize the available research about the regulatory role and mechanism of P2X7R on the intestinal mucosa-derived T cells in the setting of intestinal barrier dysfunction.

Crosstalk between epithelium, myeloid and innate lymphoid cells during gut homeostasis and disease

The gut epithelium not only provides a physical barrier to separate a noxious outside from a sterile inside but also allows for highly regulated interactions between bacteria and their products, and components of the immune system. Homeostatic maintenance of an intact epithelial barrier is paramount to health, requiring an intricately regulated and highly adaptive response of various cells of the immune system. Prolonged homeostatic imbalance can result in chronic inflammation, tumorigenesis and inefficient antitumor immune control. Here we provide an update on the role of innate lymphoid cells, macrophages and dendritic cells, which collectively play a critical role in epithelial barrier maintenance and provide an important linkage between the classical innate and adaptive arm of the immune system. These interactions modify the capacity of the gut epithelium to undergo continuous renewal, safeguard against tumor formation and provide feedback to the gut microbiome, which acts as a seminal contributor to cellular homeostasis of the gut.

Intestinal immune responses to commensal and pathogenic protozoa

The physical barrier of the intestine and associated mucosal immunity maintains a delicate homeostatic balance between the host and the external environment by regulating immune responses to commensals, as well as functioning as the first line of defense against pathogenic microorganisms. Understanding the orchestration and characteristics of the intestinal mucosal immune response during commensal or pathological conditions may provide novel insights into the mechanisms underlying microbe-induced immunological tolerance, protection, and/or pathogenesis. Over the last decade, our knowledge about the interface between the host intestinal mucosa and the gut microbiome has been dominated by studies focused on bacterial communities, helminth parasites, and intestinal viruses. In contrast, specifically how commensal and pathogenic protozoa regulate intestinal immunity is less well studied. In this review, we provide an overview of mucosal immune responses induced by intestinal protozoa, with a major focus on the role of different cell types and immune mediators triggered by commensal (Blastocystis spp. and Tritrichomonas spp.) and pathogenic (Toxoplasma gondii, Giardia intestinalis, Cryptosporidium parvum) protozoa. We will discuss how these various protozoa modulate innate and adaptive immune responses induced in experimental models of infection that benefit or harm the host.

Single cell transcriptomic analysis of the immune cell compartment in the human small intestine and in Celiac disease

Celiac disease is an autoimmune disorder in which ingestion of dietary gluten triggers an immune reaction in the small intestine leading to destruction of the lining epithelium. Current treatment focusses on lifelong adherence to a gluten-free diet. Gluten-specific CD4⁺ T cells and cytotoxic intraepithelial CD8⁺ T cells have been proposed to be central in disease pathogenesis. Here we use unbiased single-cell RNA-sequencing and explore the heterogeneity of CD45⁺ immune cells in the human small intestine. We show altered myeloid cell transcriptomes present in active celiac lesions. CD4⁺ and CD8⁺ T cells transcriptomes show extensive changes and we define a natural intraepithelial lymphocyte population that is reduced in celiac disease. We show that the immune landscape in Celiac patients on a gluten-free diet is only partially restored compared to control samples. Altogether, we provide a single cell transcriptomic resource that can inform the immune landscape of the small intestine during Celiac disease.

Celiac disease is linked to responsiveness to dietary gluten, which manifests itself as immune cell activation and the immunopathology including destruction of the epithelium of the small intestine. Here the authors apply single cell transcriptomics to characterise the immune cell compartment of the human small intestine during active Celiac disease.

Gut immune cells—A novel therapeutical target for cardiovascular disease?

Despite scientific and clinical advances during the last 50 years cardiovascular disease continues to be the main cause of death worldwide. Especially patients with diabetes display a massive increased cardiovascular risk compared to patients without diabetes. Over the last two decades we have learned that cardiometabolic and cardiovascular diseases are driven by inflammation. Despite the fact that the gastrointestinal tract is one of the largest leukocyte reservoirs of our bodies, the relevance of gut immune cells for cardiovascular disease is largely unknown. First experimental evidence suggests an important relevance of immune cells in the intestinal tract for the development of metabolic and cardiovascular disease in mice. Mice specifically lacking gut immune cells are protected against obesity, diabetes, hypertension and atherosclerosis. Importantly antibody mediated inhibition of leukocyte homing into the gut showed similar protective metabolic and cardiovascular effects. Targeting gut immune cells might open novel therapeutic approaches for the treatment of cardiometabolic and cardiovascular diseases.

Intravital Microscopy to Visualize Murine Small Intestinal Intraepithelial Lymphocyte Migration

Intraepithelial lymphocytes (IELs) are critical sentinels involved in host defense and maintenance of the intestinal mucosal barrier. IELs expressing the γδ T-cell receptor provide continuous surveillance of the villous epithelium by migrating along the basement membrane and into the lateral intercellular space between adjacent enterocytes. Intravital imaging has furthered our understanding of the molecular mechanisms by which IELs navigate the epithelial compartment and interact with neighboring enterocytes at steady state and in response to infectious or inflammatory stimuli. Further, evaluating IEL migratory behavior can provide additional insight into the nature and extent of cellular interactions within the intestinal mucosa. Three protocols describe methodology to visualize small intestinal IEL motility in real time using fluorescent reporter-transgenic mice and/or fluorophore-conjugated primary antibodies and spinning-disk confocal microscopy. Using Imaris image analysis software, a fourth protocol provides a framework to analyze IEL migration and quantify lymphocyte/epithelial interactions. Together, these protocols for intravital imaging and subsequent analyses provide the basis for elucidating the spatiotemporal dynamics of mucosal immune cells and interactions with neighboring enterocytes under physiological or pathophysiological conditions. © 2022 The Authors. Current Protocols published by Wiley Periodicals LLC. Basic Protocol 1: Mouse preparation and laparotomy Support Protocol: Antibody labeling of cell surface markers Basic Protocol 2: Image acquisition by spinning-disk confocal microscopy Basic Protocol 3: 4D analysis of images.

Treatment of immune dysfunction in intrauterine growth restriction piglets via supplementation with dimethylglycine sodium salt during the suckling period

This study aimed to investigate the mechanism of small intestinal immune dysfunction in intrauterine growth restriction (IUGR) newborn piglets and relieve this dysfunction via dimethylglycine sodium salt (DMG-Na) supplementation during the suckling period. Thirty sows (Duroc × [Landrace × Yorkshire]) were selected, and 1 male newborn piglet with normal birth weight (NBW) and 1 male newborn piglet with IUGR were obtained from each sow. Among them, 10 NBW and 10 IUGR newborns were euthanized without suckling. The other 20 NBW newborns were allocated to the group named NCON, which means NBW newborns fed a basic milk diet (BMD) (n = 10), and the group named ND, which means NBW newborns fed BMD supplemented with 0.1% DMG-Na (n = 10); the other 20 IUGR newborns were assigned to the group named ICON, which means IUGR newborns fed BMD (n = 10), and the group named ID, which means IUGR newborns fed BMD supplemented with 0.1% DMG-Na (n = 10). The newborns were fed BMD from 7 to 21 d of age and euthanized at 21 d of age to collect serum and small intestinal samples. The growth performance, small intestinal histological morphology and sub-organelle ultrastructure, serum immunoglobulin, small intestinal digestive enzyme activity, inflammatory cytokine level, and jejunum mRNA and protein expression of the toll-like receptor 4 (TLR4)/nucleotide-binding oligomerization domain protein (NOD)/nuclear factor-κB (NF-κB) network deteriorated in the ICON group compared to that in the NCON group. The small intestinal histological morphology and sub-organelle ultrastructure, serum immunoglobulin, small intestinal digestive enzyme activity, and inflammatory cytokine level improved (P < 0.05) in the ID group compared to those in the ICON group. The jejunum mRNA and protein expression of the TLR4/NOD/NF-κB network improved (P < 0.05) in the ID group compared to that in the ICON group. In conclusion, the activity of the TLR4/NOD/NF-κB pathway was inhibited in the IUGR newborns, which in turn led to their jejunum immune dysfunction and reduced their performance. By ingesting DMG-Na, the IUGR newborns activated the TLR4/NOD/NF-κB pathway, thereby improving their unfavorable body state during the suckling period.

Epithelial HNF4A shapes the intraepithelial lymphocyte compartment via direct regulation of immune signaling molecules

Hepatocyte nuclear factor 4 α (HNF4A) is a highly conserved nuclear receptor that has been associated with ulcerative colitis. In mice, HNF4A is indispensable for the maintenance of intestinal homeostasis, yet the underlying mechanisms are poorly characterized. Here, we demonstrate that the expression of HNF4A in intestinal epithelial cells (IECs) is required for the proper development and composition of the intraepithelial lymphocyte (IEL) compartment. HNF4A directly regulates expression of immune signaling molecules including butyrophilin-like (Btnl) 1, Btnl6, H2-T3, and Clec2e that control IEC-IEL crosstalk. HNF4A selectively enhances the expansion of natural IELs that are TCRγδ+ or TCRαβ+CD8αα+ to shape the composition of IEL compartment. In the small intestine, HNF4A cooperates with its paralog HNF4G, to drive expression of immune signaling molecules. Moreover, the HNF4A-BTNL regulatory axis is conserved in human IECs. Collectively, these findings underscore the importance of HNF4A as a conserved transcription factor controlling IEC-IEL crosstalk and suggest that HNF4A maintains intestinal homeostasis through regulation of the IEL compartment.

Mechanisms of mucosal healing: treating inflammatory bowel disease without immunosuppression?

Almost all currently available treatments for inflammatory bowel disease (IBD) act by inhibiting inflammation, often blocking specific inflammatory molecules. However, given the infectious and neoplastic disease burden associated with chronic immunosuppressive therapy, the goal of attaining mucosal healing without immunosuppression is attractive. The absence of treatments that directly promote mucosal healing and regeneration in IBD could be linked to the lack of understanding of the underlying pathways. The range of potential strategies to achieve mucosal healing is diverse. However, the targeting of regenerative mechanisms has not yet been achieved for IBD. Stem cells provide hope as a regenerative treatment and are used in limited clinical situations. Growth factors are available for the treatment of short bowel syndrome but have not yet been applied in IBD. The therapeutic application of organoid culture and stem cell therapy to generate new intestinal tissue could provide a novel mechanism to restore barrier function in IBD. Furthermore, blocking key effectors of barrier dysfunction (such as MLCK or damage-associated molecular pattern molecules) has shown promise in experimental IBD. Here, we review the diversity of molecular targets available to directly promote mucosal healing, experimental models to identify new potential pathways and some of the anticipated potential therapies for IBD.

Mechanisms of mucosal healing: treating inflammatory bowel disease without immunosuppression?

Almost all currently available treatments for inflammatory bowel disease (IBD) act by inhibiting inflammation, often blocking specific inflammatory molecules. However, given the infectious and neoplastic disease burden associated with chronic immunosuppressive therapy, the goal of attaining mucosal healing without immunosuppression is attractive. The absence of treatments that directly promote mucosal healing and regeneration in IBD could be linked to the lack of understanding of the underlying pathways. The range of potential strategies to achieve mucosal healing is diverse. However, the targeting of regenerative mechanisms has not yet been achieved for IBD. Stem cells provide hope as a regenerative treatment and are used in limited clinical situations. Growth factors are available for the treatment of short bowel syndrome but have not yet been applied in IBD. The therapeutic application of organoid culture and stem cell therapy to generate new intestinal tissue could provide a novel mechanism to restore barrier function in IBD. Furthermore, blocking key effectors of barrier dysfunction (such as MLCK or damage-associated molecular pattern molecules) has shown promise in experimental IBD. Here, we review the diversity of molecular targets available to directly promote mucosal healing, experimental models to identify new potential pathways and some of the anticipated potential therapies for IBD.

Epithelial HVEM maintains intraepithelial T cell survival and contributes to host protection

Intraepithelial T cells (IETs) are in close contact with intestinal epithelial cells and the underlying basement membrane, and they detect invasive pathogens. How intestinal epithelial cells and basement membrane influence IET survival and function, at steady state or after infection, is unclear. The herpes virus entry mediator (HVEM), a member of the TNF receptor superfamily, is constitutively expressed by intestinal epithelial cells and is important for protection from pathogenic bacteria. Here, we showed that at steady-state LIGHT, an HVEM ligand, binding to epithelial HVEM promoted the survival of small intestine IETs. RNA-seq and addition of HVEM ligands to epithelial organoids indicated that HVEM increased epithelial synthesis of basement membrane proteins, including collagen IV, which bound to β₁ integrins expressed by IETs. Therefore, we proposed that IET survival depended on β₁ integrin binding to collagen IV and showed that β₁ integrin-collagen IV interactions supported IET survival in vitro. Moreover, the absence of β₁ integrin expression by T lymphocytes decreased TCR αβ⁺ IETs in vivo. Intravital microscopy showed that the patrolling movement of IETs was reduced without epithelial HVEM. As likely consequences of decreased number and movement, protective responses to Salmonella enterica were reduced in mice lacking either epithelial HVEM, HVEM ligands, or β₁ integrins. Therefore, IETs, at steady state and after infection, depended on HVEM expressed by epithelial cells for the synthesis of collagen IV by epithelial cells. Collagen IV engaged β₁ integrins on IETs that were important for their maintenance and for their protective function in mucosal immunity.

TCR-Vγδ usage distinguishes protumor from antitumor intestinal γδ T cell subsets

γδ T cells represent a substantial fraction of intestinal lymphocytes at homeostasis, but they also constitute a major lymphocyte population infiltrating colorectal cancers (CRCs); however, their temporal contribution to CRC development or progression remains unclear. Using human CRC samples and murine CRC models, we found that most γδ T cells in premalignant or nontumor colons exhibit cytotoxic markers, whereas tumor-infiltrating γδ T cells express a protumorigenic profile. These contrasting T cell profiles were associated with distinct T cell receptor (TCR)-Vγδ gene usage in both humans and mice. Longitudinal intersectional genetics and antibody-dependent strategies targeting murine γδ T cells enriched in the epithelium at steady state led to heightened tumor development, whereas targeting γδ subsets that accumulate during CRC resulted in reduced tumor growth. Our results uncover temporal pro- and antitumor roles for γδ T cell subsets.

A single-cell analysis of thymopoiesis and thymic iNKT cell development in pigs

Many aspects of the porcine immune system remain poorly characterized, which poses a barrier to improving swine health and utilizing pigs as preclinical models. Here, we employ single-cell RNA sequencing (scRNA-seq) to create a cell atlas of the early-adolescent pig thymus. Our data show conserved features as well as species-specific differences in cell states and cell types compared with human thymocytes. We also describe several unconventional T cell types with gene expression profiles associated with innate effector functions. This includes a cell census of more than 11,000 differentiating invariant natural killer T (iNKT) cells, which reveals that the functional diversity of pig iNKT cells differs substantially from the iNKT0/1/2/17 subset differentiation paradigm established in mice. Our data characterize key differentiation events in porcine thymopoiesis and iNKT cell maturation and provide important insights into pig T cell development.

Histological and neuronal changes in the duodenum of hamsters infected with Leishmania (Leishmania) infantum

Visceral leishmaniasis is a neglected tropical disease caused by parasites belonging to the Leishmania genus that infect macrophages in different tissues such as the spleen, liver, lymph nodes, bone marrow, and intestine. Therefore, this study aimed to investigate the integrity of the intestinal tract and the nitrergic (NADPH-dp) and metabolically active (NADH-dp) myenteric neurons of the duodenum of golden hamsters infected with L. (L.) infantum. Therefore, thirty golden hamsters were divided into six groups (n = 5); three of them were infected with 2 × 10⁷ promastigote forms of L. (L.) infantum by intraperitoneal route (Infected Group - IG) and three were inoculated with saline solution (control group - CG). After 30, 60 and 90 days post-infection (DPI) infected animals were euthanized and the liver, spleen and duodenum were collected to analyze tissue parasitism. The duodenum was processed using usual histological techniques to analyze the main changes that occurred during infection and histochemical techniques to phenotype myenteric neurons. Amastigote forms were observed in the spleen, liver, and duodenum during all experimental periods, and tissue parasitism in these organs increased significantly over time. At 30 DPI, reduction in muscle tunic, increase in the total intestinal wall and the number of goblet cells PAS+ was observed. At 60 DPI, an increase in intestinal crypts and intraepithelial lymphocytes was observed, and a reduction in intestinal villi was observed at 90 DPI, along with an increase in crypt size. Regarding neurons, an increase in the density of the NADPH-dp population was observed at 30 DPI, but at 60 and 90 DPI a significant reduction of this population was observed. In general, infection progression was observed to cause significant morphofunctional changes in the duodenum of infected hamsters.

Elucidating the Role of Innate and Adaptive Immune Responses in the Pathogenesis of Canine Chronic Inflammatory Enteropathy-A Search for Potential Biomarkers

Simple Summary

Canine chronic inflammatory enteropathy (CIE) is a chronic disease affecting the small or large intestine and, in some cases, the stomach of dogs. This gastrointestinal disorder is common and is characterized by recurrent vomiting, diarrhea, and weight loss in affected dogs. The pathogenesis of IBD is not completely understood. Similar to human IBD, potential disease factors include genetics, environmental exposures, and dysregulation of the microbiota and the immune response. Some important components of the innate and adaptive immune response involved in CIE pathogenesis have been described. However, the immunopathogenesis of the disease has not been fully elucidated. In this review, we summarized the literature associated with the different cell types and molecules involved in the immunopathogenesis of CIE, with the aim of advancing the search for biomarkers with possible diagnostic, prognostic, or therapeutic utility.

Abstract

Canine chronic inflammatory enteropathy (CIE) is one of the most common chronic gastrointestinal diseases affecting dogs worldwide. Genetic and environmental factors, as well as intestinal microbiota and dysregulated host immune responses, participate in this multifactorial disease. Despite advances explaining the immunological and molecular mechanisms involved in CIE development, the exact pathogenesis is still unknown. This review compiles the latest reports and advances that describe the main molecular and cellular mechanisms of both the innate and adaptive immune responses involved in canine CIE pathogenesis. Future studies should focus research on the characterization of the immunopathogenesis of canine CIE in order to advance the establishment of biomarkers and molecular targets of diagnostic, prognostic, or therapeutic utility.

Epithelial-immune crosstalk in health and disease

Far from inert structures, our body's epithelial boundaries engage in a dynamic crosstalk with immune cells that is vital for immune surveillance and barrier function. Using the skin and gut epithelium, two structurally distinct but critical environmental interfaces, here we review the context-dependent interactions between myriad immune cells and epithelial subsets. We discuss immune communique reserved for epithelial progenitors and the enduring consequences for tissue fitness. Then, we delve into the cellular and molecular exchanges between differentiated epithelial subsets and adjacent immune cells. Therapeutically targeting stage-specific immune-epithelial interaction could boost regeneration and mitigate inflammatory pathologies.

Carnosol Maintains Intestinal Barrier Function and Mucosal Immune Homeostasis in DSS-Induced Colitis

Ulcerative colitis (UC) is a chronic inflammatory disease, characterized by recurrent flares of mucosal inflammation, which is limited in the colon and rectum. Compromised epithelial barrier functions have been indicated in the initiation of UC. Carnosol (CA), a natural active ortho-diphenol diterpene compound, is one of the active ingredients in plants such as rosemary and sage. The anti-inflammatory and anti-oxidative effects of CA have been reported in several animal models, but its effect on mucosal inflammation remains elusive. We established a mouse experimental colitis model characterized by epithelial barrier destruction using dextran sulfate sodium (DSS). CA was intraperitoneally administrated. Flow cytometry was performed to determine phenotypes of intraepithelial lymphocytes and lamina propria cells. qRT-PCR was used for gene expression. ER stress in the colon was determined by immunofluorescence staining and qRT-PCR. Thapsigargin was used to induce ER stress in HCT-116 cells in vitro. We found CA significantly alleviated DSS-induced colitis in mice marked by relieved clinical symptoms and colonic pathological damage. Inflammatory cell infiltration and cytokine expression in the colon were suppressed by CA during colitis. Furthermore, CA restored epithelial barrier functions and intestinal intraepithelial lymphocyte (IEL) homeostasis in mice with DSS insults. Mechanistically, we induced endoplasmic reticulum (ER) stress in HCT-116 cells (an intestinal epithelial cell line) with thapsigargin, and CA reversed this effect. In addition, we collected inflamed mucosal biopsies from 23 patients with UC, and cultured overnight with or without CA, showing CA significantly reduced expression of ER stress signaling molecule and pro-inflammatory agents. Our data demonstrate that CA acts as an effective drug for experimental colitis and maintains proper epithelial barrier functions via suppressing epithelial ER stress, providing new evidence that CA might be a promising therapeutic candidate for UC.

Cellular Origins and Pathogenesis of Gastrointestinal NK- and T-Cell Lymphoproliferative Disorders

The intestinal immune system, which must ensure appropriate immune responses to both pathogens and commensal microflora, comprises innate lymphoid cells and various T-cell subsets, including intra-epithelial lymphocytes (IELs). An example of innate lymphoid cells is natural killer cells, which may be classified into tissue-resident, CD56bright NK-cells that serve a regulatory function and more mature, circulating CD56dim NK-cells with effector cytolytic properties. CD56bright NK-cells in the gastrointestinal tract give rise to indolent NK-cell enteropathy and lymphomatoid gastropathy, as well as the aggressive extranodal NK/T cell lymphoma, the latter following activation by EBV infection and neoplastic transformation. Conventional CD4+ TCRαβ+ and CD8αβ+ TCRαβ+ T-cells are located in the lamina propria and the intraepithelial compartment of intestinal mucosa as type 'a' IELs. They are the putative cells of origin for CD4+ and CD8+ indolent T-cell lymphoproliferative disorders of the gastrointestinal tract and intestinal T-cell lymphoma, NOS. In addition to such conventional T-cells, there are non-conventional T-cells in the intra-epithelial compartment that express CD8αα and innate lymphoid cells that lack TCRs. The central feature of type 'b' IELs is the expression of CD8αα homodimers, seen in monomorphic epitheliotropic intestinal T-cell lymphoma (MEITL), which primarily arises from both CD8αα+ TCRαβ+ and CD8αα+ TCRγδ+ IELs. EATL is the other epitheliotropic T-cell lymphoma in the GI tract, a subset of which arises from the expansion and reprograming of intracytoplasmic CD3+ innate lymphoid cells, driven by IL15 and mutations of the JAK-STAT pathway.

Immunity to enteric viruses

Pathogenic enteric viruses are a major cause of morbidity and mortality, particularly among children in developing countries. The host response to enteric viruses occurs primarily within the mucosa, where the intestinal immune system must balance protection against pathogens with tissue protection and tolerance to harmless commensal bacteria and food. Here, we summarize current knowledge in natural immunity to enteric viruses, highlighting specialized features of the intestinal immune system. We further discuss how knowledge of intestinal anti-viral mechanisms can be translated into vaccine development with particular focus on immunization in the oral route. Research reveals that the intestine is a complex interface between enteric viruses and the host where environmental factors influence susceptibility and immunity to infection, while viral infections can have lasting implications for host health. A deeper mechanistic understanding of enteric anti-viral immunity with this broader context can ultimately lead to better vaccines for existing and emerging viruses.

Chemokine receptor CCR9 suppresses the differentiation of CD4+CD8αα+ intraepithelial T cells in the gut

The chemokine receptor CCR9 equips T cells with the ability to respond to CCL25, a chemokine that is highly expressed in the thymus and the small intestine (SI). Notably, CCR9 is mostly expressed on CD8 but not on CD4 lineage T cells, thus imposing distinct tissue tropism on CD4 and CD8 T cells. The molecular basis and the consequences for such a dichotomy, however, have not been fully examined and explained. Here, we demonstrate that the forced expression of CCR9 interferes with the tissue trafficking and differentiation of CD4 T cells in SI intraepithelial tissues. While CCR9 overexpression did not alter CD4 T cell generation in the thymus, the forced expression of CCR9 was detrimental for the proper tissue distribution of CD4 T cells in the periphery, and strikingly also for their terminal differentiation in the gut epithelium. Specifically, the differentiation of SI epithelial CD4 T cells into immunoregulatory CD4+CD8αα+ T cells was impaired by overexpression of CCR9 and conversely increased by the genetic deletion of CCR9. Collectively, our results reveal a previously unappreciated role for CCR9 in the tissue homeostasis and effector function of CD4 T cells in the gut.

Three Layers of Intestinal γδ T Cells Talk Different Languages With the Microbiota

The mucosal surfaces of our body are the main contact site where the immune system encounters non-self molecules from food-derived antigens, pathogens, and symbiotic bacteria. γδ T cells are one of the most abundant populations in the gut. Firstly, they include intestinal intraepithelial lymphocytes, which screen and maintain the intestinal barrier integrity in close contact with the epithelium. A second layer of intestinal γδ T cells is found among lamina propria lymphocytes (LPL)s. These γδ LPLs are able to produce IL-17 and likely have functional overlap with local Th17 cells and innate lymphoid cells. In addition, a third population of γδ T cells resides within the Peyer´s patches, where it is probably involved in antigen presentation and supports the mucosal humoral immunity. Current obstacles in understanding γδ T cells in the gut include the lack of information on cognate ligands of the γδ TCR and an incomplete understanding of their physiological role. In this review, we summarize and discuss what is known about different subpopulations of γδ T cells in the murine and human gut and we discuss their interactions with the gut microbiota in the context of homeostasis and pathogenic infections.