Expression of pro-inflammatory cytokines by TCR alpha beta+ and TCR gamma delta+ T cells in an experimental model of colitis

The recent progress of γδ T cells and its targeted therapies in rheumatoid arthritis

Rheumatoid arthritis (RA) is an autoimmune condition that mostly impacts the joints. During the advanced phases of the disorder, it may be accompanied by other problems. While the precise cause of RA is uncertain, various research has been conducted to gain a better understanding of the immunological processes involved in the development of RA. T cells are acknowledged as significant contributors to the progression of RA because of their roles in cytokine secretion, antigen presentation, and facilitating B cells in the manufacture of antibodies. γδ T cells are a small subset of T cells that have significant functions in the context of infection and diseases linked with tumors. γδ T cells have been the subject of investigation in autoimmune disorders in recent years. This review focused on the involvement of γδ T lymphocytes in the development of RA. In this article, we provide an analysis of the immunological capabilities of γδ T cells, intending to comprehend their significance in RA, which could be pivotal in the creation of innovative clinical treatments.

Intraepithelial lymphocytes promote intestinal regeneration through CD160/HVEM signaling

Chemotherapy and radiotherapy frequently lead to intestinal damage. The mechanisms governing the repair or regeneration of intestinal damage are still not fully elucidated. Intraepithelial lymphocytes (IELs) are the primary immune cells residing in the intestinal epithelial layer. However, whether IELs are involved in intestinal epithelial injury repair remains unclear. Here, we found that IELs rapidly infiltrated the intestinal crypt region and are crucial for the recovery of the intestinal epithelium post-chemotherapy. Interestingly, IELs predominantly promoted intestinal regeneration by modulating the proliferation of transit-amplifying (TA) cells. Mechanistically, the expression of CD160 on IELs allows for interaction with herpes virus entry mediator (HVEM) on the intestinal epithelium, thereby activating downstream nuclear factor kappa (NF-κB) signaling and further promoting intestinal regeneration. Deficiency in either CD160 or HVEM resulted in reduced proliferation of intestinal progenitor cells, impaired intestinal damage repair, and increased mortality following chemotherapy. Remarkably, the adoptive transfer of CD160-sufficient IELs rescued the Rag1 deficient mice from chemotherapy-induced intestinal inflammation. Overall, our study underscores the critical role of IELs in intestinal regeneration and highlights the potential applications of targeting the CD160-HVEM axis for managing intestinal adverse events post-chemotherapy and radiotherapy.

IL-15 in T-Cell Responses and Immunopathogenesis

IL-15 belongs to the common gamma chain cytokine family and has pleiotropic immunological functions. IL-15 is a homeostatic cytokine essential for the development and maintenance of NK cells and memory CD8+ T cells. In addition, IL-15 plays a critical role in the activation, effector functions, tissue residency, and senescence of CD8+ T cells. IL-15 also activates virtual memory T cells, mucosal-associated invariant T cells and γδ T cells. Recently, IL-15 has been highlighted as a major trigger of TCR-independent activation of T cells. This mechanism is involved in T cell-mediated immunopathogenesis in diverse diseases, including viral infections and chronic inflammatory diseases. Deeper understanding of IL-15-mediated T-cell responses and their underlying mechanisms could optimize therapeutic strategies to ameliorate host injury by T cell-mediated immunopathogenesis. This review highlights recent advancements in comprehending the role of IL-15 in relation to T cell responses and immunopathogenesis under various host conditions.

Microbiota as key factors in inflammatory bowel disease

Inflammatory Bowel Disease (IBD) is characterized by prolonged inflammation of the gastrointestinal tract, which is thought to occur due to dysregulation of the immune system allowing the host's cells to attack the GI tract and cause chronic inflammation. IBD can be caused by numerous factors such as genetics, gut microbiota, and environmental influences. In recent years, emphasis on commensal bacteria as a critical player in IBD has been at the forefront of new research. Each individual harbors a unique bacterial community that is influenced by diet, environment, and sanitary conditions. Importantly, it has been shown that there is a complex relationship among the microbiome, activation of the immune system, and autoimmune disorders. Studies have shown that not only does the microbiome possess pathogenic roles in the progression of IBD, but it can also play a protective role in mediating tissue damage. Therefore, to improve current IBD treatments, understanding not only the role of harmful bacteria but also the beneficial bacteria could lead to attractive new drug targets. Due to the considerable diversity of the microbiome, it has been challenging to characterize how particular microorganisms interact with the host and other microbiota. Fortunately, with the emergence of next-generation sequencing and the increased prevalence of germ-free animal models there has been significant advancement in microbiome studies. By utilizing human IBD studies and IBD mouse models focused on intraepithelial lymphocytes and innate lymphoid cells, this review will explore the multifaceted roles the microbiota plays in influencing the immune system in IBD.

Double-edged sword: γδ T cells in mucosal homeostasis and disease

The mucosa is a tissue that covers numerous body surfaces, including the respiratory tract, digestive tract, eye, and urogenital tract. Mucosa is in direct contact with pathogens, and γδ T cells perform various roles in the tissue. γδ T cells efficiently defend the mucosa from various pathogens, such as viruses, bacteria, and fungi. In addition, γδ T cells are necessary for the maintenance of homeostasis because they select specific organisms in the microbiota and perform immunoregulatory functions. Furthermore, γδ T cells directly facilitate pregnancy by producing growth factors. However, γδ T cells can also play detrimental roles in mucosal health by amplifying inflammation, thereby worsening allergic responses. Moreover, these cells can act as major players in autoimmune diseases. Despite their robust roles in the mucosa, the application of γδ T cells in clinical practice is lacking because of factors such as gaps between mice and human cells, insufficient knowledge of the target of γδ T cells, and the small population of γδ T cells. However, γδ T cells may be attractive targets for clinical use due to their effector functions and low risk of inducing graft-versus-host disease. Therefore, robust research on γδ T cells is required to understand the crucial features of these cells and apply these knowledges to clinical practices.

Ex vivo assays show human gamma-delta T cells specific for common allergens are Th1-polarized in allergic donors

Gamma-delta (γδ) T cells contribute to the pathology of many immune-related diseases; however, no ex vivo assays to study their activities are currently available. Here, we established a methodology to characterize human allergen-reactive γδ T cells in peripheral blood using an activation-induced marker assay targeting upregulated 4-1BB and CD69 expression. Broad and reproducible ex vivo allergen-reactive γδ T cell responses were detected in donors sensitized to mouse, cockroach, house dust mite, and timothy grass, but the response did not differ from that in non-allergic participants. The reactivity to 4 different allergen extracts was readily detected in 54.2%-100% of allergic subjects in a donor- and allergen-specific pattern and was abrogated by T cell receptor (TCR) blocking. Analysis of CD40L upregulation and intracellular cytokine staining revealed a T helper type 1 (Th1)-polarized response against mouse and cockroach extract stimulation. These results support the existence of allergen-reactive γδ T cells and their potential use in rebalancing dysregulated Th2 responses in allergic diseases.

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.

Intestinal intraepithelial lymphocytes: Maintainers of intestinal immune tolerance and regulators of intestinal immunity

Intestinal immune tolerance is essential for the immune system, as it prevents abnormal immune responses to large quantities of antigens from the intestinal lumen, such as antigens from commensal microorganisms, and avoids self‐injury. Intestinal intraepithelial lymphocytes (IELs), a special group of mucosal T lymphocytes, play a significant role in intestinal immune tolerance. To accomplish this, IELs exhibit a high threshold of activation and low reactivity to most antigens from the intestinal lumen. In particular, CD8αα⁺TCRαβ⁺ IELs, TCRγδ⁺ IELs, and CD4⁺CD8αα⁺ IELs show great potential for maintaining intestinal immune tolerance and regulating intestinal immunity. However, if the intestinal microenvironment becomes abnormal or intestinal tolerance is broken, IELs may be activated abnormally and become pathogenic.

Development, Homeostasis, and Functions of Intestinal Intraepithelial Lymphocytes

The intestine is continuously exposed to commensal microorganisms, food, and environmental agents and also serves as a major portal of entry for many pathogens. A critical defense mechanism against microbial invasion in the intestine is the single layer of epithelial cells that separates the gut lumen from the underlying tissues. The barrier function of the intestinal epithelium is supported by cells and soluble factors of the intestinal immune system. Chief among them are intestinal intraepithelial lymphocytes (iIELs), which are embedded in the intestinal epithelium and represent one of the single largest populations of lymphocytes in the body. Compared with lymphocytes in other parts of the body, iIELs exhibit unique phenotypic, developmental, and functional properties that reflect their key roles in maintaining the intestinal epithelial barrier. In this article, we review the biology of iIELs in supporting normal health and how their dysregulation can contribute to disease.

An Insight Into the Intestinal Web of Mucosal Immunity, Microbiota, and Diet in Inflammation

The rising global incidence of autoimmune and inflammatory conditions can be attributed to changes in the large portion of the immune system that belongs to our gastrointestinal tract (GI). The intestinal immune system serves as a gatekeeper to prevent pathogenic invasions and to preserve a healthier gut microbiota. The gut microbiota has been increasingly studied as a fundamental contributor to the state of health and disease. From food fermentation, the gut microbiota releases metabolites or short chain fatty acids (SCFAs), which have anti-inflammatory properties and preserve gut homeostasis. Immune responses against food and microbial antigens can cause inflammatory disorders such as inflammatory bowel disease (IBD) and celiac disease. As such, many autoimmune and inflammatory diseases also have a “gut origin”. A large body of evidence in recent years by ourselves and others has uncovered the link between the immune system and the SCFAs in specific diseases such as autoimmune type 1 diabetes (T1D), obesity and type 2 diabetes (T2D), cardiovascular disease, infections, allergies, asthma, and IBD. Thus, the power of these three gut dynamic components—the mucosal immunity, the microbiota, and diet—can be harnessed in tandem for the prevention and treatment of many inflammatory and infectious diseases.

The portal vein as a distinct immunological compartment - A comprehensive immune phenotyping study

Advanced liver diseases are associated with impaired intestinal barrier function, which results in bacterial influx via the portal vein to the liver, causing hepatic and systemic inflammation. Little is known about possible concomitant trafficking of immune cells from the intestines to the liver. We therefore performed a comprehensive immunophenotyping study of the portal venous versus peripheral blood compartment in patients with liver cirrhosis who received a transjugular intrahepatic portosystemic stent shunt (TIPS). Our analysis suggests that the portal vein constitutes a distinct immunological compartment resembling that of the intestines, at least in patients with advanced liver cirrhosis. In detail, significantly lower frequencies of naïve CD4⁺ T cells, monocytes, dendritic cells and Vδ2 T cells were observed in the portal vein, whereas frequencies of activated CD4⁺ and CD8⁺ T cells, as well as of mucosa-associated Vδ1 T cells were significantly higher in portal venous compared to peripheral blood. In conclusion, our data raises interesting questions, e.g. whether liver cirrhosis-associated chronic inflammation of the intestines and portal hypertension promote an influx of activated intestinal immune cells like γδ T cells into the liver.

The Innate Immune System in the Gastrointestinal Tract: Role of Intraepithelial Lymphocytes and Lamina Propria Innate Lymphoid Cells in Intestinal Inflammation

BACKGROUND

The gastrointestinal tract harbors the largest microbiota load in the human body, hence maintaining a delicate balance between immunity against invading pathogens and tolerance toward commensal. Such immune equilibrium, or intestinal homeostasis, is conducted by a tight regulation and cooperation of the different branches of the immune system, including the innate and the adaptive immune system. However, several factors affect this delicate equilibrium, ultimately leading to gastrointestinal disorders including inflammatory bowel disease. Therefore, here we decided to review the currently available information about innate immunity lymphocyte subsets playing a role in intestinal inflammation.

RESULTS

Intestinal innate lymphocytes are composed of intraepithelial lymphocytes (IELs) and lamina propria innate lymphoid cells (ILCs). While IELs can be divided into natural or induced, ILCs can be classified into type 1, 2, or 3, resembling, respectively, the properties of TH1, TH2, or TH17 adaptive lymphocytes. Noteworthy, the phenotype and function of both IELs and ILCs are disrupted under inflammatory conditions, where they help to exacerbate intestinal immune responses.

CONCLUSIONS

The modulation of both IELs and ILCs to control intestinal inflammatory responses represents a major challenge, as they provide tight regulation among the epithelium, the microbiota, and the adaptive immune system. An improved understanding of the innate immunity mechanisms involved in gastrointestinal inflammation would therefore aid in the diagnosis and further treatment of gastrointestinal inflammatory disorders.

Intestinal Intraepithelial Lymphocytes: Sentinels of the Mucosal Barrier

Intestinal intraepithelial lymphocytes (IELs) are a large and diverse population of lymphoid cells that reside between the intestinal epithelial cells (IECs) that form the intestinal mucosal barrier. Although IEL biology has traditionally focused on T cells, recent studies have identified several subsets of T cell receptor (TCR)-negative IELs with intriguing properties. New insight into the development, homeostasis, and functions of distinct IEL subsets has recently been provided. Additional studies have revealed intricate interactions between different IEL subsets, reciprocal interactions between IELs and IECs, and communication of IELs with immune cells that reside outside the intestinal epithelium. We review here sentinel functions of IELs in the maintenance of the mucosal barrier integrity, as well as how dysregulated IEL responses can contribute to pathology.

Gammadelta T Cells in Crohn's Disease: A New Player in the Disease Pathogenesis?

Crohn's disease [CD] is a chronic relapsing systemic disease affecting the gastrointestinal tract. An altered immune response to commensal intestinal bacteria takes place in genetically predisposed individuals, resulting in chronic inflammation in the gut. Several alterations in the innate immunity mechanisms have been described in recent years. Thus, the study of the immunological aspects of CD, specifically the role of lymphocytes, is a key element for understanding the pathogenesis of the disease.Gammadelta T cells [γδ T cells] constitute only a small proportion of the lymphocytes that circulate in the blood and peripheral organs and they are present mainly in the epithelia, where they can constitute up to 40% of intraepithelial lymphocytes [IEL] in the intestinal mucosa. Due to their lack of major histocompatibility complex [MHC] restriction and their unique plasticity and immune-regulating properties, they are considered key cells in the first line of defence against infections and in wound healing in the gut. Although there is growing experimental and clinical evidence of their implication in inflammatory bowel disease [IBD], including CD, their clinical relevance is still unclear.In this review, we address the possible involvement of γδ T cells in the pathogenesis of CD, reviewing their role against infections and in inflammation and the current evidence suggesting their implication in CD, offering a novel potential target for immunotherapy in IBD.

The Impact of Therapeutic Antibodies on the Management of Digestive Diseases: History, Current Practice, and Future Directions

The development of therapeutic antibodies represents a revolutionary change in medical therapy for digestive diseases. Beginning with the initial studies that confirmed the pathogenicity of cytokines in inflammatory bowel disease, the development and application of therapeutic antibodies brought challenges and insights into their potential and optimal use. Infliximab was the first biological drug approved for use in Crohn's disease and ulcerative colitis. The lessons learned from infliximab include the importance of immunogenicity and the influence of pharmacokinetics on disease response and outcomes. Building on this foundation, other therapeutic antibodies achieved approval for inflammatory bowel disease and many more are in development for several digestive diseases. In this review, we reflect on the history of therapeutic antibodies and discuss current practice and future directions for the field.

Interaction between the gut microbiome and mucosal immune system

The gut microbiota, the largest symbiotic ecosystem with the host, has been shown to play important roles in maintaining intestinal homeostasis. Dysbiosis of the gut microbiome is caused by the imbalance between the commensal and pathogenic microbiomes. The commensal microbiome regulates the maturation of the mucosal immune system, while the pathogenic microbiome causes immunity dysfunction, resulting in disease development. The gut mucosal immune system, which consists of lymph nodes, lamina propria and epithelial cells, constitutes a protective barrier for the integrity of the intestinal tract. The composition of the gut microbiota is under the surveillance of the normal mucosal immune system. Inflammation, which is caused by abnormal immune responses, influences the balance of the gut microbiome, resulting in intestinal diseases. In this review, we briefly outlined the interaction between the gut microbiota and the immune system and provided a reference for future studies.

Branched Fatty Acid Esters of Hydroxy Fatty Acids (FAHFAs) Protect against Colitis by Regulating Gut Innate and Adaptive Immune Responses

We recently discovered a structurally novel class of endogenous lipids, branched palmitic acid esters of hydroxy stearic acids (PAHSAs), with beneficial metabolic and anti-inflammatory effects. We tested whether PAHSAs protect against colitis, which is a chronic inflammatory disease driven predominantly by defects in the innate mucosal barrier and adaptive immune system. There is an unmet clinical need for safe and well tolerated oral therapeutics with direct anti-inflammatory effects. Wild-type mice were pretreated orally with vehicle or 5-PAHSA (10 mg/kg) and 9-PAHSA (5 mg/kg) once daily for 3 days, followed by 10 days of either 0% or 2% dextran sulfate sodium water with continued vehicle or PAHSA treatment. The colon was collected for histopathology, gene expression, and flow cytometry. Intestinal crypt fractions were prepared for ex vivo bactericidal assays. Bone marrow-derived dendritic cells pretreated with vehicle or PAHSA and splenic CD4⁺ T cells from syngeneic mice were co-cultured to assess antigen presentation and T cell activation in response to LPS. PAHSA treatment prevented weight loss, improved colitis scores (stool consistency, hematochezia, and mouse appearance), and augmented intestinal crypt Paneth cell bactericidal potency via a mechanism that may involve GPR120. In vitro, PAHSAs attenuated dendritic cell activation and subsequent T cell proliferation and Th1 polarization. The anti-inflammatory effects of PAHSAs in vivo resulted in reduced colonic T cell activation and pro-inflammatory cytokine and chemokine expression. These anti-inflammatory effects appear to be partially GPR120-dependent. We conclude that PAHSA treatment regulates innate and adaptive immune responses to prevent mucosal damage and protect against colitis. Thus, PAHSAs may be a novel treatment for colitis and related inflammation-driven diseases.

Regulatory immune cells in regulation of intestinal inflammatory response to microbiota

The intestinal lumen harbors nearly 100 trillion commensal bacteria that exert crucial function for health. An elaborate balance between immune responses and tolerance to intestinal microbiota is required to maintain intestinal homeostasis. This process depends on diverse regulatory mechanisms, including both innate and adaptive immunity. Dysregulation of the homeostasis between intestinal immune systems and microbiota has been shown to be associated with the development of inflammatory bowel diseases (IBD) in genetically susceptible populations. In this review, we discuss the recent progress reported in studies of distinct types of regulatory immune cells in the gut, including intestinal intraepithelial lymphocytes, Foxp3(+) regulatory T cells, regulatory B cells, alternatively activated macrophages, dendritic cells, and innate lymphoid cells, and how dysfunction of this immune regulatory system contributes to intestinal diseases such as IBD. Moreover, we discuss the manipulation of these regulatory immune cells as a potential therapeutic method for management of intestinal inflammatory disorders.

Phenotypic characterization of canine intestinal intraepithelial lymphocytes in dogs with inflammatory bowel disease

Background

Many dogs suffering from inflammatory bowel disease (IBD) are presented to veterinary clinics. These patients are diagnosed based on a history of chronic gastrointestinal signs and biopsy‐confirmed histopathologic intestinal inflammation. Intestinal intraepithelial lymphocytes (IEL) are part of the first line of defense in the gastrointestinal immune system. Alterations in IEL subsets may play a role in the pathogenesis of IBD.

Hypothesis

The aim of this study was to characterize the phenotypes of IEL in dogs with IBD compared with healthy control dogs.

Animals

Intestinal intraepithelial lymphocytes subpopulations of control dogs (n = 5) obtained from endoscopic biopsies (EB) were compared to those obtained from full thickness biopsies (FTB) on the same day. In addition, the phenotypes of IEL from FTB of control dogs (n = 10) were compared with EB of IBD dogs (n = 10). Each participant was scored clinically using the canine inflammatory bowel disease activity index (CIBDAI), and all samples were graded histopathologically. Three‐color flow cytometry of isolated IEL was performed using monoclonal antibodies against T‐ and B‐lymphocyte subpopulations.

Results

No significant differences in the composition of IEL subpopulations were found in control dogs based on method of biopsy. The IBD dogs had significantly higher CIBDAI and histopathologic scores compared with control dogs and their IEL contained a significantly higher frequency TCRγδ T‐cells.

Conclusions and Clinical Importance

Endoscopic biopsies provide suitable samples for 3‐color flow cytometry when studying canine intestinal IEL and IBD patients show significant changes of major T‐cell subsets compared to healthy control dogs.

The mucosal immune system in the oral cavity-an orchestra of T cell diversity

The mucosal immune system defends against a vast array of pathogens, yet it exhibits limited responses to commensal microorganisms under healthy conditions. The oral-pharyngeal cavity, the gateway for both the gastrointestinal and respiratory tracts, is composed of complex anatomical structures and is constantly challenged by antigens from air and food. The mucosal immune system of the oral-pharyngeal cavity must prevent pathogen entry while maintaining immune homeostasis, which is achieved via a range of mechanisms that are similar or different to those utilized by the gastrointestinal immune system. In this review, we summarize the features of the mucosal immune system, focusing on T cell subsets and their functions. We also discuss our current understanding of the oral-pharyngeal mucosal immune system.

The microbiome and regulation of mucosal immunity

The gastrointestinal tract is a mucosal surface constantly exposed to foreign antigens and microbes, and is protected by a vast array of immunologically active structures and cells. Epithelial cells directly participate in immunological surveillance and direction of host responses in the gut and can express numerous pattern recognition receptors, including Toll-like receptor 5 (TLR5), TLR1, TLR2, TLR3, TLR9, and nucleotide oligomerization domain 2, as well as produce chemotactic factors for both myeloid and lymphoid cells following inflammatory stimulation. Within the epithelium and in the underlying lamina propria resides a population of innate lymphoid cells that, following stimulation, can become activated and produce effector cytokines and exert both protective and pathogenic roles during inflammation. Lamina propria dendritic cells play a large role in determining whether the response to a particular antigen will be inflammatory or anti-inflammatory. It is becoming clear that the composition and metabolic activity of the intestinal microbiome, as a whole community, exerts a profound influence on mucosal immune regulation. The microbiome produces short-chain fatty acids, polysaccharide A, α-galactosylceramide and tryptophan metabolites, which can induce interleukin-22, Reg3γ, IgA and interleukin-17 responses. However, much of what is known about microbiome-host immune interactions has come from the study of single bacterial members of the gastrointestinal microbiome and their impact on intestinal mucosal immunity. Additionally, evidence continues to accumulate that alterations of the intestinal microbiome can impact not only gastrointestinal immunity but also immune regulation at distal mucosal sites.

Oral delivery of oligomeric procyanidins in Apple Poly® enhances type I IFN responses in vivo

Type I IFN signaling is a central pathway that provides critical innate protection from viral and bacterial infection and can have regulatory outcomes in inflammatory settings. We determined previously that OPCs contained in the dietary supplement APP enhanced responses to type I IFN in vitro. Here, we confirm that OPCs from two different sources significantly increased pSTAT1, whereas a monomeric form of procyanidin did not. We hypothesized that similar responses could be induced in vivo following ingestion of APP. Ingestion of APP before injection of polyI:C enhanced in vivo responses to type I IFNs in mice. When human subjects ingested APP, enhanced responses to type I IFN and enhanced pSTAT1 ex vivo were detected, whereas ingestion of RES, a monomeric polyphenol, induced minimal such changes. Polyphenols are best known for induction of anti-inflammatory and antioxidant responses; however, our findings suggest a unique, nonantioxidant aspect of OPCs that is broadly applicable to many disease settings. The capacity of oral OPCs to enhance type I IFN signaling in vivo can augment innate protection and may, in part, contribute to the noted anti-inflammatory outcome of ingestion of OPCs from many sources.

Phenotypic and functional plasticity of gamma-delta (γδ) T cells in inflammation and tolerance

Gamma-delta T cells (γδ T cells) are an unique group of lymphocytes and play an important role in bridging the gap between innate and adaptive immune systems under homeostatic condition as well as during infection and inflammation. They are predominantly localized into the mucosal and epithelial sites, but also exist in other peripheral tissues and secondary lymphoid organs. γδ T cells can produce cytokines and chemokines to regulate the migration of other immune cells, can bring about lysis of infected or stressed cells by secreting granzymes, provide help to B cells and induce IgE production, can present antigen to conventional T cells, activate antigen presenting cells (APC) maturation, and are also known to produce growth factors that regulate the stromal cell function. γδ T cells spontaneously produce IFN-γ and IL-17 cytokines compared to delayed differentiation of Th1 and Th17 cells. In this review, we discussed the current knowledge about the mechanism of γδ T cell function including its mode of antigen recognition, and differentiation into various subsets of γδ T cells. We also explored how γδ T cells interact with different types of innate and adaptive immune cells, and how these interactions shape the immune response highlighting the plasticity and role of these cells-protective or pathogenic under inflammatory and tolerogenic conditions.

Disturbance of intraepithelial lymphocytes in a murine model of acute intestinal ischemia/reperfusion

Strategically located at the epithelial basolateral surface, intraepithelial lymphocytes (IELs) are intimately associated with epithelial cells and maintain the epithelial barrier integrity. Intestinal ischemia-reperfusion (I/R)-induced acute injury not only damages the epithelium but also affects the mucosal barrier function. Therefore, we hypothesized that I/R-induced mucosal damage would affect IEL phenotype and function. Adult C57BL/6J mice were treated with intestinal I/R or sham. Mice were euthanized at 6 h after I/R, and the small bowel was harvested for histological examination and to calculate the transmembrane resistance. Occludin expression and IEL location were detected through immunohistochemistry. The IEL phenotype, activation, and apoptosis were examined using flow cytometry. Cytokine and anti-apoptosis-associated gene expressions were measured through RT-PCR. Intestinal I/R induced the destruction of epithelial cells and intercellular molecules (occludin), resulting in IEL detachment from the epithelium. I/R also significantly increased the CD8αβ, CD4, and TCRαβ IEL subpopulations and significantly changed IEL-derived cytokine expression. Furthermore, I/R enhanced activation and promoted apoptosis in IELs. I/R-induced acute intestinal mucosal damage significantly affected IEL phenotype and function. These findings provide profound insight into potential IEL-mediated epithelial barrier dysfunction after intestinal I/R.

Glucocorticoid-induced TNF receptor family-related protein ligand regulates the migration of monocytes to the inflamed intestine

Glucocorticoid-induced TNF receptor family-related protein (GITR) regulates the function of both T cells and antigen-presenting cells (APCs), while the function of GITR ligand (GITR-L) is largely unknown. Here we evaluate the role of GITR-L, whose expression is restricted to APCs, in the development of enterocolitis. On injecting naive CD4(+) T cells, GITR-L(-/-)Rag(-/-) mice develop a markedly milder colitis than Rag(-/-) mice, which correlates with a 50% reduction of Ly6C(+)CD11b(+)MHCII(+) macrophages in the lamina propria and mesenteric lymph nodes. The same result was observed in αCD40-induced acute colitis and during peritonitis, suggesting an altered monocyte migration. In line with these observations, the number of nondifferentiated monocytes was approximately 3-fold higher in the spleen of GITR-L(-/-)Rag(-/-) mice than in Rag(-/-) mice after αCD40 induction. Consistent with the dynamic change in the formation of an active angiotensin II type 1 receptor (AT1) dimer in GITR-L(-/-) splenic monocytes during intestinal inflammation, the migratory capability of splenic monocytes from GITR-L-deficient mice was impaired in an in vitro transwell migration assay. Conversely, αGITR-L reduces the number of splenic Ly6C(hi) monocytes, concomitantly with an increase in AT1 dimers. We conclude that GITR-L regulates the number of proinflammatory macrophages in sites of inflammation by controlling the egress of monocytes from the splenic reservoir.

Differentiation and activation of γδ T Lymphocytes: Focus on CD27 and CD28 costimulatory receptors

γδ T lymphocytes are major providers of the pro-inflammatory cytokines interferon-γ (IFN-γ) and interleukin-17 (IL-17) at early stages of (auto)immune responses. We and others have recently described the phenotype and differentiation requirements of two distinct murine γδ T cell subsets producing either IFN-γ or IL-17. Here we summarize our current understanding of the molecular mechanisms that control γδ T cell differentiation, which is programmed in the thymus, and peripheral activation upon infection. We focus on the costimulatory receptors CD27 and CD28, which play independent and non-redundant roles in the physiology of γδ T cells in mice and in humans.

Glucocorticoid-induced tumor necrosis factor receptor family-related protein regulates CD4(+)T cell-mediated colitis in mice

BACKGROUND & AIMS

The glucocorticoid-induced tumor necrosis factor receptor family-related protein (GITR; also called TNFRSF18 or CD357) regulates the T cell-mediated immune response and is present on surfaces of regulatory T (Treg) cells and activated CD4(+) T cells. We investigated the roles of GITR in the development of colitis in mice.

METHODS

Chronic enterocolitis was induced by the transfer of wild-type or GITR(-/-) CD4(+) T cells to GITR(-/-) × Rag(-/-) or Rag(-/-) mice. We determined the severity of colitis by using the disease activity index; measured levels of inflammatory cytokines, T cells, and dendritic cells; and performed histologic analysis of colon samples.

RESULTS

Transfer of nonfractionated CD4(+) cells from wild-type or GITR(-/-) donors induced colitis in GITR(-/-) × Rag(-/-) but not in Rag(-/-) mice. Among mice with transfer-induced colitis, the percentage of Treg and T-helper (Th) 17 cells was reduced but that of Th1 cells increased. Treg cells failed to prevent colitis in GITR(-/-) × Rag(-/-) recipients; this was not the result of aberrant function of GITR(-/-) Treg or T effector cells but resulted from an imbalance between the numbers of tolerogenic CD103(+) and PDCA1(+) plasmacytoid dendritic cells in GITR(-/-) mice. This imbalance impaired Treg cell development and expanded the Th1 population in GITR(-/-) × Rag(-/-) mice following transfer of nonfractionated CD4(+) cells.

CONCLUSIONS

GITR is not required on the surface of Treg and T effector cells to induce colitis in mice; interactions between GITR and its ligand are not required for induction of colitis. GITR instead appears to control dendritic cell and monocyte development; in its absence, mice develop aggravated chronic enterocolitis via an imbalance of colitogenic Th1 cells and Treg cells.

Animal models of inflammatory bowel disease

Inflammatory bowel disease (IBD) is a chronic intestinal inflammatory condition that is medicated by genetic, immune, and environmental factors. At least 66 different kinds of animal models have been established to study IBD, which are classified primarily into chemically induced, cell-transfer, congenial mutant, and genetically engineered models. These IBD models have provided significant contributions to not only dissect the mechanism but also develop novel therapeutic strategies for IBD. In addition, recent advances on genetically engineered techniques such as cell-specific and inducible knockout as well as knockin mouse systems have brought novel concepts on IBD pathogenesis to the fore. Further, mouse models, which lack some IBD susceptibility genes, have suggested more complicated mechanism of IBD than previously predicted. This chapter summarizes the distinct feature of each murine IBD model and discusses the previous and current lessons from the IBD models.

The light and dark sides of intestinal intraepithelial lymphocytes

The intraepithelial lymphocytes (IELs) that reside within the epithelium of the intestine form one of the main branches of the immune system. As IELs are located at this critical interface between the core of the body and the outside environment, they must balance protective immunity with an ability to safeguard the integrity of the epithelial barrier: failure to do so would compromise homeostasis of the organism. In this Review, we address how the unique development and functions of intestinal IELs allow them to achieve this balance.

T regulatory cells maintain intestinal homeostasis by suppressing γδ T cells

Immune tolerance against enteric commensal bacteria is important for preventing intestinal inflammation. Deletion of phosphoinositide-dependent protein kinase 1 (Pdk1) in T cells via Cd4-Cre induced chronic inflammation of the intestine despite the importance of PDK1 in T cell activation. Analysis of colonic intraepithelial lymphocytes of PDK1-deficient mice revealed markedly increased CD8α(+) T cell receptor (TCR)γδ(+) T cells, including an interleukin-17 (IL-17)-expressing population. TCRγδ(+) T cells were responsible for the inflammatory colitis as shown by the fact that deletion of Tcrd abolished spontaneous colitis in the PDK1-deficient mice. This dysregulation of intestinal TCRγδ(+) T cells was attributable to a reduction in the number and functional capacity of PDK1-deficient T regulatory (Treg) cells. Adoptive transfer of wild-type Treg cells abrogated the spontaneous activation and proliferation of intestinal TCRγδ(+) T cells observed in PDK1-deficient mice and prevented the development of colitis. Therefore, suppression of intestinal TCRγδ(+) T cells by Treg cells maintains enteric immune tolerance.

Simvastatin Reduces OX40 and OX40 Ligand Expression in Human Peripheral Blood Mononuclear Cells and in Patients with Atherosclerotic Cerebral Infarction

This study investigated the effect of simvastatin on the expression of OX40 and OX40 ligand (OX40L) in vitro and in vivo. OX40 and OX40L mRNA and protein levels were measured in human peripheral blood mononuclear cells, using reverse transcription–polymerase chain reaction and Western blot, respectively, in response to simvastatin alone or given in combination with interferon-γ, mevalonate or GW9662, a peroxisome proliferator-activated receptor-γ (PPAR-γ) antagonist. Simvastatin induced down-regulation of OX40 and OX40L mRNA and protein in a concentration-dependent manner, and antagonized the interferon-γ-induced increase in OX40 and OX40L mRNA and protein levels. Mevalonate, but not GW9662, reversed the simvastatin-induced down-regulation of OX40 and OX40L expression, indicating that these effects were mediated through the mevalonate pathway. Serum levels of soluble OX40L and matrix metalloproteinase 9 levels were significantly reduced in patients with atherosclerotic cerebral infarction who were treated for 6 months with routine therapy plus simvastatin ( n = 46) compared with patients receiving routine therapy alone ( n = 30). These findings improve our understanding of the anti-inflammatory and immunomodulatory properties of simvastatin treatment for atherosclerotic disorders.

Immunoglobulin and cytokine production from mesenteric lymph node lymphocytes is regulated by extracts of Cordyceps sinensis in C57Bl/6N mice

Cordyceps sinensis, one of the well-known fungi used in traditional Chinese medicine, is recognized to play a role in the metabolic process of inflammation and immunity. The purpose of this study was to evaluate the effects of water extracts of C. sinensis on the immune function of mesenteric lymph node (MLN) lymphocytes in C57Bl/6N mice. C. sinensis-treated mice were administered the respective extract by oral gavage for 4 weeks. Immunoglobulin E concentrations in serum and MLN lymphocytes were significantly lower in C. sinensis-treated mice than in control mice. In contrast, the immunoglobulin A concentration from the C. sinensis group was higher than that in control mice. C. sinensis increased the proportion of CD4(+) and CD8(+) T cells in MLN lymphocytes. C. sinensis significantly decreased interleukin-4 and interleukin-10 cytokine concentrations. Therefore, water extracts of C. sinensis modulate immune parameters through regulation of immunoglobulin production resulting from decreased T-lymphocyte helper 2 cytokine secretion and reduce cytokine secretion in MLN lymphocytes.

Innate and adaptive interleukin-22 protects mice from inflammatory bowel disease

Inflammatory bowel disease (IBD) is a chronic inflammatory disease thought to be mediated by dysfunctional innate and/or adaptive immunity. This aberrant immune response leads to the secretion of harmful cytokines that destroy the epithelium of the gastrointestinal tract and thus cause further inflammation. Interleukin-22 (IL-22) is a T helper 17 (Th17) T cell-associated cytokine that is bifunctional in that it has both proinflammatory and protective effects on tissues depending on the inflammatory context. We show herein that IL-22 protected mice from IBD. Interestingly, not only was this protection mediated by CD4+ T cells, but IL-22-expressing natural killer (NK) cells also conferred protection. In addition, IL-22 expression was differentially regulated between NK cell subsets. Thus, both the innate and adaptive immune responses have developed protective mechanisms to counteract the damaging effects of inflammation on tissues.

Innate and adaptive interleukin-22 protects mice from inflammatory bowel disease

Inflammatory bowel disease (IBD) is a chronic inflammatory disease thought to be mediated by dysfunctional innate and/or adaptive immunity. This aberrant immune response leads to the secretion of harmful cytokines that destroy the epithelium of the gastrointestinal tract and thus cause further inflammation. Interleukin-22 (IL-22) is a T helper 17 (Th17) T cell-associated cytokine that is bifunctional in that it has both proinflammatory and protective effects on tissues depending on the inflammatory context. We show herein that IL-22 protected mice from IBD. Interestingly, not only was this protection mediated by CD4+ T cells, but IL-22-expressing natural killer (NK) cells also conferred protection. In addition, IL-22 expression was differentially regulated between NK cell subsets. Thus, both the innate and adaptive immune responses have developed protective mechanisms to counteract the damaging effects of inflammation on tissues.

Gammadelta T lymphocytes: a new type of regulatory T cells suppressing murine 2,4,6-trinitrobenzene sulphonic acid (TNBS)-induced colitis

BACKGROUND

The intestinal immune system is continuously challenged by antigen without becoming dysregulated. However, injury of the mucosa by, i.e. dextran sulphate sodium causes severe inflammation in gammadelta T-cell-deficient mice. We therefore asked whether gammadelta T cells have regulatory functions.

MATERIALS AND METHODS

gammadelta T cells were isolated from spleens and mesenteric lymph nodes of C57BL/6 wild-type (wt) mice. Proliferation and cytokine secretion of gammadelta T cells were quantified by [(3)H] thymidine incorporation and ELISA. Additionally, proliferation of carboxyfluorescein diacetate succinimidylester-labelled CD4(+) T cells cocultured with gammadelta T cells was analysed by flow cytometry. Finally, gammadelta T cells from wt or interleukin-10 transgenic (IL-10tg) mice were transferred into congenic mice with 2,4,6-trinitrobenzene sulphonic acid (TNBS)-induced colitis.

RESULTS

gammadelta T cells were hyporesponsive to CD3/CD28 stimulation and suppressed CD4(+) T-cell proliferation (up to 66+/-7% suppression) in vitro. Further, the preventive transfer of wt or IL-10tg gammadelta T cells ameliorated TNBS-induced colitis resulting in prolonged survival and reduced histological damage (1.5+/-0.4 and 1.3+/-0.2, respectively vs. 3.8+/-0.3 in untransferred mice, p<0.05). This was accompanied by reduced TNF-alpha and increased IL-10 and TGF-beta secretion from intestinal and splenic lymphocytes.

CONCLUSIONS

Murine gammadelta T cells are a new type of regulatory T cells in vitro and act protective on mouse TNBS-induced colitis in vivo. Future studies have to define the underlying mechanism and to investigate whether gammadelta T cells can be used for immunotherapy of human inflammatory bowel disease.

Exacerbating role of gammadelta T cells in chronic colitis of T-cell receptor alpha mutant mice

BACKGROUND & AIMS

T-cell receptor (TCR) gammadelta T cells are an important component of the mucosal immune system and regulate intestinal epithelial homeostasis. Interestingly, there is a significant increase in gammadelta T cells in the inflamed mucosa of patients with ulcerative colitis (UC). However, the role of gammadelta T cells in chronic colitis has not been fully identified.

METHODS

TCRalpha-deficient mice, which spontaneously develop chronic colitis with many features of human UC including an increase in gammadelta T-cell population, represent an excellent model to investigate the role of gammadelta T cells in UC-like colitis. To identify the role of gammadelta T cells in this colitis, we herein have generated TCRgamma-deficient mice through deletion of all TCR Cgamma genes (Cgamma1, Cgamma2, Cgamma3, and Cgamma4) using the Cre/loxP site-specific recombination system and subsequently crossing these mice with TCRalpha-deficient mice.

RESULTS

An increase in colonic gammadelta T cells was associated with the development of human UC as well as UC-like disease seen in TCRalpha-deficient mice. Interestingly, the newly established TCRalpha(-/-) x TCRgamma(-/-) double mutant mice developed significantly less severe colitis as compared with TCRalpha-deficient mice. The suppression of colitis in TCRalpha(-/-) x TCRgamma(-/-) double mutant mice was associated with a significant reduction of proinflammatory cytokine and chemokine productions and a decrease in neutrophil infiltration.

CONCLUSIONS

gammadelta T cells are involved in the exacerbation of UC-like chronic disease. Therefore, gammadelta T cells may represent a promising therapeutic target for the treatment of human UC.

Regulatory CD4+ CD25+ T cells prevent thymic dysfunction in experimental chronic colitis

Chronic colitis in T-cell deficient Tg epsilon26 mice develops due to a dysfunction of the thymus which generates colitogenic T cells after bone marrow (BM) transplantation. Regulatory CD4+ CD25+ T cells have been shown to prevent colitis in this model by normalizing the peripheral T-cell pool. We tested the hypothesis that T-cell normalization takes place in the thymus. Tg epsilon26 mice were transplanted with BM (BM-->Tg epsilon26 mice) and consequently received either CD4+ CD25+ or CD4+ CD25- cells from syngenic wild type mice. Furthermore, untransplanted Tg epsilon26 mice received CD4+ CD25+ or CD4+ CD25- cells or complete mesenteric lymph node cells. Transfer of regulatory. CD4+ CD25+ cells normalized the total number of thymocytes and the percentage and number of double positive CD4+ CD8+ cells in transplanted mice while percentage of single positive CD4+ and CD8+ thymocytes in BM-->Tg epsilon26 mice was reduced upon CD4+ CD25+ transfer. Timing of CD4+ CD25+ cell injection was important as transfer later than 7 days after BM transplantation failed to prevent abnormal thymic T-cell distribution in BM-->Tg epsilon26 mice. Isolated CD4+ CD25+ cell transfer without preceding BM transplantation failed to reconstitute thymic architecture. Differences of thymic cell composition could not be exclusively explained by presence or absence of colitis, respectively, because 19 days after BM transplantation when both groups showed no histological signs of colitis, animals transferred with CD4+ CD25+ T cells had a significantly higher percentage and number of CD4+ CD25+ thymocytes and CD4+ Foxp3+ cells than BM-->Tg epsilon26 mice. In conclusion, early CD4+ CD25+ cotransfer prevents thymic dysfunction which underlies immune-mediated bowel inflammation in BM-->Tg epsilon26 mice.

Set a thief to catch a thief: self-reactive innate lymphocytes and self tolerance

Self-reactive lymphocytes form part of the peripheral repertoire in healthy individuals. Some of these cells are anergic classical lymphocytes, but a remarkable subset of self-reactive clones is related to innate immunity and many of them bear a partially activated phenotype. In the past few years growing evidence has pointed out the importance of this physiological autoimmunity in self tolerance, with special regard to the role of periportal innate lymphocytes. This population is involved in a wide range of immunoregulatory processes including immune privilege and oral tolerance, providing systemic tolerance to highly tissue-specific antigens as well as microbial epitopes cross-reactive to self. This kind of self-protection is dominantly mediated by self-reactive clones, which commonly play a dual role by acting as potent effectors and regulators at the same time. Here we provide an overview of the field.

Bacterial superantigens and T cell receptor beta-chain-bearing T cells in the immunopathogenesis of ulcerative colitis

Ulcerative colitis (UC) is a chronic relapsing-remitting inflammatory bowel disease (IBD) that affects the colon and the rectum producing debilitating symptoms, which impair ability to function and quality of life. The aetiology of IBD is incompletely understood, but within the lymphocyte population, specific T cell subsets are known to be major factors in the development of intestinal immune pathology while different subsets are essential regulators, controlling IBD. Hence, IBD is thought to reflect dysregulated T cell behaviour. This study was to investigate if the normal molecular configuration of the T cell receptor (TCR) repertoire is compromised in patients with UC. The percentage of T cell-bearing beta-chain 4 (TCRBV4) was high in patients with UC, and T cells showed polyclonal expansion in the presence of bacterial superantigens (SA) such as streptococcal mitogenic exotoxin Z-2 (SMEZ-2), indicating that bacterial SA promote specific TCRBV family expansion. Further, in patients with UC, the duration of UC was significantly longer in patients with skewed TCRBV4 compared with patients without TCRBV4 skewing, suggesting that long-term exposure to bacterial SA such as SMEZ-2 might promote systemic immune disorders like the remission-relapsing cycles seen in patients with UC. In conclusion, our observations in this study support the perception that the systemic activation of T cells by enteric bacterial SA might lead to a dysregulated, but exuberant immune activity causing the remission and flare-up cycle of mucosal inflammation in patients with UC. Future studies should strengthen our findings and increase understanding on the aetiology of IBD.

Influence of Mycobacterium avium subsp. paratuberculosis on colitis development and specific immune responses during disease

The granulomatous and intramural inflammation observed in cases of inflammatory bowel diseases (IBD) and veterinary Johne's disease suggests that Mycobacterium avium subsp. paratuberculosis is a causative agent. However, an incomplete understanding of the immunological steps responsible for the pathologies of IBD makes this conclusion uncertain. Sera from interleukin-10-deficient (IL-10(-/-)) mice with spontaneous colitis displayed significantly higher M. avium subsp. paratuberculosis-specific immunoglobulin G2a antibody responses than did sera from similar mice without disease. Pathogen-free IL-10(-/-) mice received control vehicle or the vehicle containing heat-killed or live M. avium subsp. paratuberculosis. Mucosal CD4(+) T cells from the mice that developed colitis proliferated and secreted higher levels of gamma interferon and tumor necrosis factor alpha after ex vivo stimulation with a Vbeta11(+) T-cell receptor-restricted peptide from the MPT59 antigen (Ag85B) than those secreted from cells from mice before the onset of colitis. The data from this study provide important information regarding the mechanisms of colitis in IL-10(-/-) mice, which are driven in part by Ag85B-specific T cells. The data suggest a plausible mechanism of Ag-specific T-cell responses in colitis driven by potent Ags conserved in Mycobacterium species.

gammadelta T cells: firefighters or fire boosters in the front lines of inflammatory responses

Intradermal inoculation of cloned self-reactive alphabeta T cells into the footpads of mice induced cutaneous graft-versus-host disease (GVHD), and after recovery from GVHD, the epidermis became resistant to subsequent attempts to induce GVHD. Resistance to GVHD was not induced in the epidermis of T-cell receptor delta-deficient (TCRdelta(-/-)) mice that lacked gammadelta T cells bearing canonical Vgamma5/Vdelta1(+)gammadeltaTCRs, known as dendritic epidermal T cells (DETCs), and resistance was restored by reconstitution of these mutant mice with precursors of Vgamma5(+) DETCs. Pulmonary infection by Cryptococcus neoformans induced an increase of gammadelta T cells in the lung, and in comparison with wildtype mice, TCRdelta(-/-) mice eliminated C. neoformans more rapidly and synthesized more interferon-gamma in the lung. In the mouse small intestine, the absence of gammadelta T cells is associated with a reduction in epithelial cell turnover and downregulation of the expression of major histocompatibility complex class II molecules. The protective role of gammadelta T cells was verified in a dextran sodium sulfate-induced inflammatory bowel disease (IBD) model, whereas in a spontaneous model of IBD, gammadelta T cells were involved in the exacerbation of colitis in TCRalpha(-/-) mice. Taken together, in addition to the homeostatic regulation of epithelial tissues, gammadelta T cells appear to play a pivotal role in the modification of inflammatory responses induced in many organs containing epithelia.

Mycobacterium paratuberculosisand the bovine immune system

Mycobacterium aviumsubspeciesparatuberculosis(M. paratuberculosis) is the causative agent of Johne’s disease, a deadly intestinal ailment of ruminants. Johne’s disease is of tremendous economic importance to the worldwide dairy industry, causing major losses due to reduced production and early culling of animals. A highly controversial but developing link between exposure toM. paratuberculosisand human Crohn’s disease in some individuals has led to the suggestion thatM. paratuberculosisis also a potential food safety concern. As with many other mycobacteria,M. paratuberculosisis exquisitely adapted to survival in the host, despite aggressive immune reactions to these organisms. One hallmark of mycobacteria, includingM. paratuberculosis, is their propensity to infect macrophages. Inside the macrophage,M. paratuberculosisinterferes with the maturation of the phagosome by an unknown mechanism, thereby evading the host’s normal first line of defense against bacterial pathogens. The host immune system begins a series of attacks againstM. paratuberculosis-infected macrophages, including the rapid deployment of activated γδ T cells, CD4+T cells and cytolytic CD8+T cells. These cells interact with the persistently infected macrophage and with each other through a complex network of cytokines and receptors. Despite these aggressive efforts to clear the infection,M. paratuberculosispersists and the constant struggle of the immune system leads to pronounced damage to the intestinal epithelial cells. Enhancing our ability to control this important and tenacious pathogen will require a deeper understanding of howM. paratuberculosisinterferes with macrophage action, the cell types involved in the immune response, the cytokines these cells use to communicate, and the host genetic factors that control the response to infection.

Type 1 and 2 T helper cell-mediated colitis

PURPOSE OF REVIEW

Abrogation of mucosal T cell homeostasis by exaggerated not only T helper 1, but also T helper 2 cells is a major problem that leads to intestinal inflammation. In this regard, it is important to understand these different aspects of mucosal inflammation.

RECENT FINDINGS

Both T helper 1 and 2 cells play central roles in the induction of mucosal immune responses including secretory IgA antibody production, which would be the most beneficial aspect for the host defense mechanism. T helper 1- and 2-type responses, however, exhibit other roles in the abrogation of intestinal homeostasis. Although it has been shown that T helper 1-type immune responses are key players in the induction of intestinal inflammation in mice colitis models and also in inflammatory bowel diseases in humans, studies in murine colitis models clearly show that T helper 2-type responses are also involved in the pathophysiology of the intestinal inflammation. Both regulatory type T cells and T helper 17 cells are involved to down- or upregulate aberrant T helper 1 and 2 cell responses.

SUMMARY

Understanding the cellular and molecular mechanisms of crosstalk among T helper 1, 2, 17 and T regulatory 1 cells is central for the prevention or treatment of inflammatory bowel diseases.

Aggravation of intestinal inflammation by depletion/deficiency of gammadelta T cells in different types of IBD animal models

The role of gammadelta T cells in inflammatory bowel disease (IBD) is still controversial. Although gammadelta T cells induce IBD in immunodeficient animals, others suggest a protective role of gammadelta T cells. Therefore, this study was conducted in order to elucidate the effect of gammadelta T cell depletion/deficiency on different IBD animal models. Mice depleted of or deficient in gammadelta T cells were exposed to dextran sodium sulfate (DSS) in order to induce colitis. In addition, gammadelta T cells were depleted in mice with terminal ileitis (TNFDeltaARE) or colitis due to interleukin 2 deficiency (IL-2 ko). Finally, DSS-induced colitis was studied in mice deficient in interferon gamma (IFN-gamma ko) upon gammadelta T cell depletion. Depletion of gammadelta T cells aggravated DSS-induced colitis and terminal ileitis of TNFDeltaARE mice. Exacerbated DSS-induced colitis was also found in gammadelta T cell-deficient mice. IL-2 ko mice showed increased mortality upon early (starting at 4 wk of age) but not late depletion (starting at 8 wk of age). Early gammadelta T cell depletion or deficiency resulted in increased IFN-gamma production by both lamina propria lymphocytes and splenocytes in every model investigated herein. In IFN-gamma ko mice, gammadelta T cell depletion did not affect the development and course of DSS-induced colitis. The protective effect of gammadelta T cells in IBD was confirmed in various IBD animal models. Particularly, during the early phase of intestinal inflammation, gammadelta T cells appear to be important. The mechanism seems to involve the control of IFN-gamma production and epithelial regeneration.

CD48 controls T-cell and antigen-presenting cell functions in experimental colitis

BACKGROUND & AIMS

The cell-surface receptor CD48 is a lipid-anchored protein expressed on all antigen-presenting cells and T cells. CD2 and 2B4 are known ligands for CD48, which themselves are expressed on the surface of hematopoietic cells. Here we examine the effect of CD48 in the development of chronic experimental colitis and how CD48 affects adaptive and innate immune functions.

METHODS

The role of CD48 in experimental colitis was first assessed by transferring CD4(+)CD45RB(hi) cells isolated from either wild-type or CD48(-/-) mice into either Rag-2(-/-) or CD48(-/-) x Rag-2(-/-) mice. Development of chronic colitis in these adoptively transferred mice was assessed by disease activity index, histology, and production of interferon-gamma in mesenteric lymph nodes. Relevant functions of CD48(-/-)CD4(+) T cells and CD48(-/-) macrophages were examined using in vitro assays. In a second set of experiments, the efficacy of anti-CD48 in prevention or treatment of chronic colitis was determined.

RESULTS

CD48(-/-)CD4(+) cells induced colitis when transferred into Rag-2(-/-) mice, but not when introduced into CD48(-/-) x Rag-2(-/-) recipients. However, both recipient mouse strains developed colitis upon adoptive transfer of wild-type CD4(+) cells. Consistent with a CD4(+) T-cell defect was the observation that in vitro proliferation of CD48(-/-)CD4(+) T cells was impaired upon stimulation with CD48(-/-) macrophages. In vitro evidence for a modest macrophage functional defect was apparent because CD48(-/-) macrophages produced less tumor necrosis factor alpha and interleukin 12 than wild-type cells upon stimulation with lipopolysaccharide. Peritoneal macrophages also showed a defect in clearance of gram-negative bacteria in vitro. Treatment of the CD4(+)CD45RB(hi)-->Rag-2(-/-) mice or the wild-type BM-->tg26 mice with anti-CD48 (HM48-1) ameliorated development of colitis, even after its induction.

CONCLUSIONS

Both CD48-dependent activation of macrophages and CD48-controlled activation of T cells contribute to maintaining the inflammatory response. Consequently, T cell-induced experimental colitis is ameliorated only when CD48 is absent from both T cells and antigen-presenting cells. Because anti-CD48 interferes with these processes, anti-human CD48 antibody treatment may represent a novel therapy for inflammatory bowel disease patients.

Reversal of experimental colitis disease activity in mice following administration of an adenoviral IL-10 vector

Genetic deficiency in the expression of interleukin-10 (IL-10) is associated with the onset and progression of experimental inflammatory bowel disease (IBD). The clinical significance of IL-10 expression is supported by studies showing that immune-augmentation of IL-10 prevents inflammation and mucosal damage in animal models of colitis and in human colitis. Interleukin-10 (IL-10), an endogenous anti-inflammatory and immunomodulating cytokine, has been shown to prevent some inflammation and injury in animal and clinical studies, but the efficacy of IL-10 treatment remains unsatisfactory. We found that intra-peritoneal administration of adenoviral IL-10 to mice significantly reversed colitis induced by administration of 3% DSS (dextran sulfate), a common model of colitis. Adenoviral IL-10 (Ad-IL10) transfected mice developed high levels of IL-10 (394 +/- 136 pg/ml) within the peritoneal cavity where the adenovirus was expressed. Importantly, when given on day 4 (after the induction of colitis w/DSS), Ad-IL10 significantly reduced disease activity and weight loss and completely prevented histopathologic injury to the colon at day 10. Mechanistically, compared to Ad-null and DSS treated mice, Ad-IL10 and DSS-treated mice were able to suppress the expression of MAdCAM-1, an endothelial adhesion molecule associated with IBD. Our results suggest that Ad-IL10 (adenoviral IL-10) gene therapy of the intestine or peritoneum may be useful in the clinical treatment of IBD, since we demonstrated that this vector can reverse the course of an existing gut inflammation and markers of inflammation.

In vivo generation of oligoclonal colitic CD4+ T-cell lines expressing a distinct T-cell receptor Vbeta

BACKGROUND & AIMS

Transplantation of wild-type (H-2k) bone marrow into tg epsilon26 mice (BM-->tg epsilon26) induces colitis, characterized by T-helper cell type 1 activation in the lamina propria. Here we determined whether pathogenic T-cell clones could be derived by serial adoptive transfers into healthy tg epsilon26 recipients, starting with the population of CD4+ cells in the mesenteric lymph nodes of BM-->tg epsilon26 mice.

METHODS

CD4+ cells purified from the mesenteric lymph nodes of colitic BM-->tg epsilon26 mice were adoptively transferred into a second group of healthy tg epsilon26 recipients. Mesenteric lymph node CD4+ cells from the second group of mice were then used for consecutive transfers. Lamina propria CD4+ cells isolated from each mouse with colitis were analyzed for their cytokine profile and for their T-cell receptor Vbeta repertoire.

RESULTS

CD4+ T cells maintained a dominant T-helper 1 phenotype after multiple transfers (< or = 8) into recipient tg epsilon26 mice. A single T-cell receptor Vbeta was enriched (as much as 90%) in 8 CD4+ T-cell lines: Vbeta8S3, Vbeta8S1/2, Vbeta10S1, or Vbeta14. Sequence analyses of the T-cell receptor Vbetas showed clonality or the presence of a very restricted number of clones within each line. Adoptive transfers of the oligoclonal lines into either C3H x Rag-/- or severe combined immunodeficiency disease mice (H-2k) also induced colitis, whereas transfers into BALB/c x Rag-/- or severe combined immunodeficiency disease mice (H-2d) did not.

CONCLUSIONS

Colitis-inducing CD4+ T-helper 1 cell clones can be obtained by enrichment through sequential adoptive transfers of CD4+ cells from mesenteric lymph nodes. Distinct dominant T-cell receptor Vbetas in each cell line responded to antigens presented by class II major histocompatibility complex.