CD103+ GALT DCs promote Foxp3+ regulatory T cells

Cross-talk between adipose tissue and microbiota-gut-brain-axis in brain development and neurological disorder

The gut microbiota is an important factor responsible for the physiological processes as well as pathogenesis of host. The communication between central nervous system (CNS) and microbiota occurs by different pathways i.e., chemical, neural, immune, and endocrine. Alteration in gut microbiota i.e., gut dysbiosis causes alteration in the bidirectional communication between CNS and gut microbiota and linked to the pathogenesis of neurological and neurodevelopmental disorder. Therefore, now-a-days microbiota-gut-brain-axis (MGBA) has emerged as therapeutic target for the treatment of metabolic disorder. But, experimental data available on MGBA from basic research has limited application in clinical study. In present study we first summarized molecular mechanism of microbiota interaction with brain physiology and pathogenesis via collecting data from different sources i.e., PubMed, Scopus, Web of Science. Furthermore, evidence shows that adipose tissue (AT) is active during metabolic activities and may also interact with MGBA. Hence, in present study we have focused on the relationship among MGBA, brown adipose tissue, and white adipose tissue. Along with this, we have also studied functional specificity of AT, and understanding heterogeneity among MGBA and different types of AT. Therefore, molecular interaction among them may provide therapeutic target for the treatment of neurological disorder.

Dietary nucleic acids promote oral tolerance through innate sensing pathways in mice

Oral tolerance is essential for intestinal homeostasis and systemic immune function. However, our understanding of how oral tolerance is maintained is inadequate. Here we report that food-derived nucleic acids promote oral tolerance through innate sensing pathways. We find that dietary nucleic acids, but not microbiota, expand the natural intraepithelial lymphocyte (IEL) pool, specifically in the small intestine. TGF-β1, produced by natural IELs, then promotes activation of gut CD103+ dendritic cells to support the induction of antigen-specific Treg cells in a mouse model of OVA-induced oral tolerance. Mechanistically, MAVS and STING are redundantly required for sensing dietary RNAs and DNAs to activate downstream TBK1 signalling to induce IL-15 production, which results in the accumulation of natural IELs. Thus, our study demonstrates a key role of food-triggered innate sensing pathways in the maintenance of natural IELs and oral tolerance.

Engineering nanoparticle therapeutics for food allergy

Food allergy is a growing public health issue among children and adults that can lead to life-threatening anaphylaxis following allergen exposure. The criterion standard for disease management includes food avoidance and emergency epinephrine administration because current allergen-specific immunotherapy treatments are limited by adverse events and unsustained desensitization. A promising approach to remedy these shortcomings is the use of nanoparticle-based therapies that disrupt disease-driving immune mechanisms and induce more sustained tolerogenic immune pathways. The pathophysiology of food allergy includes multifaceted interactions between effector immune cells, including lymphocytes, antigen-presenting cells, mast cells, and basophils, mainly characterized by a TH2 cell response. Regulatory T cells, TH1 cell responses, and suppression of other major allergic effector cells have been found to be major drivers of beneficial outcomes in these nanoparticle therapies. Engineered nanoparticle formulations that have shown efficacy at reducing allergic responses and revealed new mechanisms of tolerance include polymeric-, lipid-, and emulsion-based nanotherapeutics. This review highlights the recent engineering design of these nanoparticles, the mechanisms induced by them, and their future potential therapeutic targets.

Immunological characteristics of CD103+CD8+ Tc cells in the liver of C57BL/6 mouse infected with plasmodium NSM

CD103 is an important marker of tissue-resident memory T cells (TRM) which play important roles in fighting against infection. However, the immunological characteristics of CD103+ T cells are not thoroughly elucidated in the liver of mouse infected with Plasmodium. Six- to eight-week-old C57BL/6 mice were infected with Plasmodium yoelii nigeriensis NSM. Mice were sacrificed on 12-16 days after infection and the livers were picked out. Sections of the livers were stained, and serum aspartate aminotransferase (AST) and alanine transaminase (ALT) levels were measured. Moreover, lymphocytes in the liver were isolated, and the expression of CD103 was determined by using qPCR. The percentage of CD103 on different immune cell populations was dynamically observed by using flow cytometry (FCM). In addition, the phenotype and cytokine production characteristics of CD103+CD8+ Tc cell were analyzed by using flow cytometry, respectively. Erythrocyte stage plasmodium infection could result in severe hepatic damage, a widespread inflammatory response and the decrease of CD103 expression on hepatic immune cells. Only CD8+ Tc and γδT cells expressed higher levels of CD103 in the uninfected state.CD103 expression in CD8+ Tc cells significantly decreased after infection. Compared to that of CD103- CD8+ Tc cells, CD103+ CD8+ Tc cells from the infected mice expressed lower level of CD69, higher level of CD62L, and secreted more IL-4, IL-10, IL-17, and secreted less IFN-γ. CD103+CD8+ Tc cells might mediate the hepatic immune response by secreting IL-4, IL-10, and IL-17 except IFN-γ in the mice infected with the erythrocytic phase plasmodium, which could be involved in the pathogenesis of severe liver damage resulted from the erythrocytic phase plasmodium yoelii nigeriensis NSM infection.

Tolerogenic dendritic cells generated in vitro using a novel protocol mimicking mucosal tolerance mechanisms represent a potential therapeutic cell platform for induction of immune tolerance

Dendritic cells (DCs) are mediators between innate and adaptive immunity and vital in initiating and modulating antigen-specific immune responses. The most important site for induction of tolerance is the gut mucosa, where TGF-β, retinoic acid, and aryl hydrocarbon receptors collaborate in DCs to induce a tolerogenic phenotype. To mimic this, a novel combination of compounds - the synthetic aryl hydrocarbon receptor (AhR) agonist IGN-512 together with TGF-β and retinoic acid - was developed to create a platform technology for induction of tolerogenic DCs intended for treatment of several conditions caused by unwanted immune activation. These in vitro-generated cells, designated ItolDCs, are phenotypically characterized by their low expression of co-stimulatory and activating molecules along with high expression of tolerance-associated markers such as ILT3, CD103, and LAP, and a weak pro-inflammatory cytokine profile. When co-cultured with T cells and/or B cells, ItolDC-cultures contain higher frequencies of CD25+Foxp3+ regulatory T cells (Tregs), CD49b+LAG3+ 'type 1 regulatory (Tr1) T cells, and IL-10-producing B cells and are less T cell stimulatory compared to cultures with matured DCs. Factor VIII (FVIII) and tetanus toxoid (TT) were used as model antigens to study ItolDC antigen-loading. ItolDCs can take up FVIII, process, and present FVIII peptides on HLA-DR. By loading both ItolDCs and mDCs with TT, antigen-specific T cell proliferation was observed. Cryo-preserved ItolDCs showed a stable tolerogenic phenotype that was maintained after stimulation with LPS, CD40L, or a pro-inflammatory cocktail. Moreover, exposure to other immune cells did not negatively impact ItolDCs' expression of tolerogenic markers. In summary, a novel protocol was developed supporting the generation of a stable population of human DCs in vitro that exhibited a tolerogenic phenotype with an ability to increase proportions of induced regulatory T and B cells in mixed cultures. This protocol has the potential to constitute the base of a tolDC platform for inducing antigen-specific tolerance in disorders caused by undesired antigen-specific immune cell activation.

Donor Batf3 inhibits murine lung allograft rejection and airway fibrosis

Chronic lung allograft dysfunction (CLAD) limits survival after lung transplantation. Noxious stimuli entering the airways foster CLAD development. Classical dendritic cells (cDCs) link innate and adaptive immunity and exhibit regional and functional specialization in the lung. The transcription factor basic leucine zipper ATF-like 3 (BATF3) is absolutely required for the development of type 1 cDCs (cDC1s), which reside in the airway epithelium and have variable responses depending on the context. We studied the role of BATF3 in a mouse minor alloantigen-mismatched orthotopic lung transplant model of CLAD with and without airway inflammation triggered by repeated administration of intratracheal lipopolysaccharide (LPS). We found that cDC1s accumulated in allografts compared with isografts and that donor cDC1s were gradually replaced by recipient cDC1s. LPS administration increased the number of cDC1s and enhanced their state of activation. We found that Batf3^-/- recipient mice experienced reduced acute rejection in response to LPS; in contrast, Batf3^-/- donor grafts underwent enhanced lung and skin allograft rejection and drove augmented recipient cluster of differentiation 8⁺ T-cell expansion in the absence of LPS. Our findings suggest that donor and recipient cDC1s have differing and context-dependent roles and may represent a therapeutic target in lung transplantation.

Communication of gut microbiota and brain via immune and neuroendocrine signaling

The gastrointestinal tract of the human is inhabited by about 5 × 10¹³ bacteria (of about 1,000 species) as well as archaea, fungi, and viruses. Gut microbiota is known to influence the host organism, but the host may also affect the functioning of the microbiota. This bidirectional cooperation occurs in three main inter-organ signaling: immune, neural, and endocrine. Immune communication relies mostly on the cytokines released by the immune cells into circulation. Also, pathogen-associated or damage-associated molecular patterns (PAMPs or DAMPs) may enter circulation and affect the functioning of the internal organs and gut microbiota. Neural communication relies mostly on the direct anatomical connections made by the vagus nerve, or indirect connections via the enteric nervous system. The third pathway, endocrine communication, is the broadest one and includes the hypothalamic-pituitary-adrenal axis. This review focuses on presenting the latest data on the role of the gut microbiota in inter-organ communication with particular emphasis on the role of neurotransmitters (catecholamines, serotonin, gamma-aminobutyric acid), intestinal peptides (cholecystokinin, peptide YY, and glucagon-like peptide 1), and bacterial metabolites (short-chain fatty acids).

Regulatory T Cells, a Viable Target Against Airway Allergic Inflammatory Responses in Asthma

Asthma is a multifactorial disorder characterized by the airway chronic inflammation, hyper-responsiveness (AHR), remodeling, and reversible obstruction. Although asthma is known as a heterogeneous group of diseases with various clinical manifestations, recent studies suggest that more than half of the clinical cases are ‘‘T helper type 2 (Th2)-high’’ type, whose pathogenesis is driven by Th2 responses to an inhaled allergen from the environmental exposures. The intensity and duration of inflammatory responses to inhaled allergens largely depend on the balance between effector and regulatory cells, but many questions regarding the mechanisms by which the relative magnitudes of these opposing forces are remained unanswered. Regulatory T cells (Tregs), which comprise diverse subtypes with suppressive function, have long been attracted extensive attention owing to their capability to limit the development and progression of allergic diseases. In this review we seek to update the recent advances that support an essential role for Tregs in the induction of allergen tolerance and attenuation of asthma progression once allergic airway inflammation established. We also discuss the current concepts about Treg induction and Treg-expressed mediators relevant to controlling asthma, and the therapies designed based on these novel insights against asthma in clinical settings.

Mega doses of retinol: A possible immunomodulation in Covid-19 illness in resource-limited settings

Of all the nutrients, vitamin A has been the most extensively evaluated for its impact on immunity. There are three main forms of vitamin A, retinol, retinal and retinoic acid (RA) with the latter being most biologically active and all-trans-RA (ATRA) its main derivative. Vitamin A is a key regulator of the functions of various innate and adaptive immune cells and promotes immune-homeostasis. Importantly, it augments the interferon-based innate immune response to RNA viruses decreasing RNA virus replication. Several clinical trials report decreased mortality in measles and Ebola with vitamin A supplementation.During the Covid-19 pandemic interventions such as convalescent plasma, antivirals, monoclonal antibodies and immunomodulator drugs have been tried but most of them are difficult to implement in resource-limited settings. The current review explores the possibility of mega dose vitamin A as an affordable adjunct therapy for Covid-19 illness with minimal reversible side effects. Insight is provided into the effect of vitamin A on ACE-2 expression in the respiratory tract and its association with the prognosis of Covid-19 patients. Vitamin A supplementation may aid the generation of protective immune response to Covid-19 vaccines. An overview of the dosage and safety profile of vitamin A is presented along with recommended doses for prophylactic/therapeutic use in randomised controlled trials in Covid-19 patients.

Cellular scars and local crosstalk in relapsing psoriasis: an example of a skin sticking disease

Psoriasis is an inflammatory disease that arises in genetically predisposed individuals. Chronic skin lesions that contain activated immune cells can persist for years. Systemic inhibition of TNF, IL‐17 and IL‐23 cytokines has revolutionized psoriasis care during the recent decades. Unfortunately, local relapse of disease is common at previously inflamed sites after cessation of treatment. This highlights that fundamental pathologic alterations of the affected tissues are not completely resolved during clinical remission. Here, we present arguments for a local disease memory located in both dermis and epidermis in psoriasis skin. We decipher different cellular components and intercellular crosstalk that sustain local disease memory and amplify disease relapse in human psoriasis. Decrypting the mechanisms underlying the establishment and persistence of pathogenic memory cells in resolved psoriasis may provide new therapeutic perspectives aimed at long‐term remission of psoriasis.

BCG Vaccination in Humans Elicits Trained Immunity via the Hematopoietic Progenitor Compartment

Induction of trained immunity by Bacille-Calmette-Guérin (BCG) vaccination mediates beneficial heterologous effects, but the mechanisms underlying its persistence and magnitude remain elusive. In this study, we show that BCG vaccination in healthy human volunteers induces a persistent transcriptional program connected to myeloid cell development and function within the hematopoietic stem and progenitor cell (HSPC) compartment in the bone marrow. We identify hepatic nuclear factor (HNF) family members 1a and b as crucial regulators of this transcriptional shift. These findings are corroborated by higher granulocyte numbers in BCG-vaccinated infants, HNF1 SNP variants that correlate with trained immunity, and elevated serum concentrations of the HNF1 target alpha-1 antitrypsin. Additionally, transcriptomic HSPC remodeling was epigenetically conveyed to peripheral CD14+ monocytes, displaying an activated transcriptional signature three months after BCG vaccination. Taken together, transcriptomic, epigenomic, and functional reprogramming of HSPCs and peripheral monocytes is a hallmark of BCG-induced trained immunity in humans.

The Role of Dendritic Cells During Infections Caused by Highly Prevalent Viruses

Dendritic cells (DCs) are a type of innate immune cells with major relevance in the establishment of an adaptive response, as they are responsible for the activation of lymphocytes. Since their discovery, several reports of their role during infectious diseases have been performed, highlighting their functions and their mechanisms of action. DCs can be categorized into different subsets, and each of these subsets expresses a wide arrange of receptors and molecules that aid them in the clearance of invading pathogens. Interferon (IFN) is a cytokine -a molecule of protein origin- strongly associated with antiviral immune responses. This cytokine is secreted by different cell types and is fundamental in the modulation of both innate and adaptive immune responses against viral infections. Particularly, DCs are one of the most important immune cells that produce IFN, with type I IFNs (α and β) highlighting as the most important, as they are associated with viral clearance. Type I IFN secretion can be induced via different pathways, activated by various components of the virus, such as surface proteins or genetic material. These molecules can trigger the activation of the IFN pathway trough surface receptors, including IFNAR, TLR4, or some intracellular receptors, such as TLR7, TLR9, and TLR3. Here, we discuss various types of dendritic cells found in humans and mice; their contribution to the activation of the antiviral response triggered by the secretion of IFN, through different routes of the induction for this important antiviral cytokine; and as to how DCs are involved in human infections that are considered highly frequent nowadays.

Tracking of an Oral Salmonella-Based Vaccine for Type 1 Diabetes in Non-obese Diabetic Mice

Type 1 diabetes (T1D) arises secondary to immune-driven destruction of pancreatic β-cells and manifests as insulin-deficient hyperglycemia. We showed that oral vaccination with live attenuated Salmonella, which simultaneously delivers autoantigens and a TGFβ expression vector to immune cells in the gut mucosa, provides protection against the progression of T1D in non-obese diabetic (NOD) mice. In this study we employed the Sleeping Beauty (SB) transposon system that is composed of a transposase and transposon encoding the td-Tomato to express red fluorescent protein (RFP) to permanently mark the cells that take up the Salmonella vaccine. After animal vaccination, the transposon labeled-dendritic cells (DCs) with red fluorescence appeared throughout the secondary lymphoid tissues. Furthermore, Sleeping Beauty containing tgfβ1 gene (SB-tgfβ1) co-expressed TGFβ and RFP. The labeled DCs were detected predominantly in Peyer's patches (PP) and mesenteric lymph nodes (MLN) and expressed CD103 surface marker. CD103+ DCs induced tolerogenic effects and gut homing. TGFβ significantly increased programmed death-ligand-1 (PDL-1 or CD274) expression in the DCs in the MLN and PP of treated mice. Also, TGFβ increased cytotoxic T-lymphocyte-associated protein-4 (CTLA-4) levels in CD4+ cells in MLN and PP. Interestingly, DCs increased in all lymphatic organs of mice vaccinated with oral live Salmonella-based vaccine expressing preproinsulin (PPI), in combination with TGFβ, IL10, and subtherapeutic-doses of anti-CD3 mAb compared with vehicle-treated mice. These DCs are mostly tolerogenic in MLN and PP. Furthermore the DCs obtained from vaccine-treated but not vehicle-treated mice suppressed in vitro T cell proliferation. These data suggest that the MLN and the PP are a central hub for the beneficial anti-diabetic effects of an oral Salmonella-based vaccine prevention of diabetes in rodents.

Crosstalk Between Gut Microbiota and Innate Immunity and Its Implication in Autoimmune Diseases

The emerging concept of microbiota contributing to local mucosal homeostasis has fueled investigation into its specific role in immunology. Gut microbiota is mostly responsible for maintaining the balance between host defense and immune tolerance. Dysbiosis of gut microbiota has been shown to be related to various alterations of the immune system. This review focuses on the reciprocal relationship between gut microbiota and innate immunity compartment, with emphasis on gut-associated lymphoid tissue, innate lymphoid cells, and phagocytes. From a clinical perspective, the review gives a possible explanation of how the “gut microbiota—innate immunity” axis might contribute to the pathogenesis of autoimmune diseases like rheumatoid arthritis, spondyloarthritis, and systemic lupus erythematosus.

Rapid Downregulation of DAB2 by Toll-Like Receptor Activation Contributes to a Pro-Inflammatory Switch in Activated Dendritic Cells

Dendritic cells (DCs) are pivotal in regulating tolerogenic as well as immunogenic responses against microorganisms by directing both the innate and adaptive immune response. In health, phenotypically different DC subsets found in the gut mucosa are maintained in their tolerogenic state but switch to a pro-inflammatory phenotype during infection or chronic autoinflammatory conditions such as inflammatory bowel disease (IBD). The mechanisms that promote the switch among the mucosal DCs from a tolerogenic to an immunogenic, pro-inflammatory phenotype are incompletely understood. We hypothesized that disabled homolog 2 (DAB2), recently described as a negative regulator of DC immunogenicity during their development, is regulated during intestinal inflammation and modulates mucosal DC function. We show that DAB2 is highly expressed in colonic CD11b⁺CD103⁻ DCs, a subset known for its capacity to induce inflammatory Th1/Th17 responses in the colon, and is downregulated predominantly in this DC subset during adoptive T cell transfer colitis. Administration of Dab2-deficient DCs (DC2.4^Dab2−/− cells) modulated the course of DSS colitis in wild-type mice, enhanced mucosal expression of Tnfa, Il6, and Il17a, and promoted neutrophil recruitment. In bone-marrow derived dendritic cells (BMDC), DAB2 expression correlated with CD11b levels and DAB2 was rapidly and profoundly inhibited by TLR ligands in a TRIF- and MyD88-dependent manner. The negative modulation of DAB2 was biphasic, initiated with a quick drop in DAB2 protein, followed by a sustained reduction in Dab2 mRNA. DAB2 downregulation promoted a more functional and activated DC phenotype, reduced phagocytosis, and increased CD40 expression after TLR activation. Furthermore, Dab2 knockout in DCs inhibited autophagy and promoted apoptotic cell death. Collectively, our results highlight the immunoregulatory role for DAB2 in the intestinal dendritic cells and suggest that DAB2 downregulation after microbial exposure promotes their switch to an inflammatory phenotype.

Impact of Retinoic Acid on Immune Cells and Inflammatory Diseases

Vitamin A metabolite retinoic acid (RA) plays important roles in cell growth, differentiation, organogenesis, and reproduction and a key role in mucosal immune responses. RA promotes dendritic cells to express CD103 and to produce RA, enhances the differentiation of Foxp3⁺ inducible regulatory T cells, and induces gut-homing specificity in T cells. Although vitamin A is crucial for maintaining homeostasis at the intestinal barrier and equilibrating immunity and tolerance, including gut dysbiosis, retinoids perform a wide variety of functions in many settings, such as the central nervous system, skin aging, allergic airway diseases, cancer prevention and therapy, and metabolic diseases. The mechanism of RA is interesting to explore as both a mucosal adjuvant and a combination therapy with other effective agents. Here, we review the effect of RA on innate and adaptive immunity with a special emphasis on inflammatory status.

Acute small intestinal inflammation results in persistent lymphatic alterations

Inflammatory bowel disease (IBD) has a complex pathophysiology with limited treatments. Structural and functional changes in the intestinal lymphatic system have been associated with the disease, with increased risk of IBD occurrence linked to a history of acute intestinal injury. To examine the potential role of the lymphatic system in inflammation recurrence, we evaluated morphological and functional changes in mouse mucosal and mesenteric lymphatic vessels, and within the mesenteric lymph nodes during acute ileitis caused by a 7-day treatment with dextran sodium sulfate (DSS). We monitored whether the changes persisted during a 14-day recovery period and determined their potential consequences on dendritic cell (DC) trafficking between the mucosa and lymphoid tissues. DSS administration was associated with marked lymphatic abnormalities and dysfunctions exemplified by lymphangiectasia and lymphangiogenesis in the ileal mucosa and mesentery, increased mesenteric lymphatic vessel leakage, and lymphadenopathy. Lymphangiogenesis and lymphadenopathy were still evident after recovery from intestinal inflammation and correlated with higher numbers of DCs in mucosal and lymphatic tissues. Specifically, a deficit in CD103⁺ DCs observed during acute DSS in the lamina propria was reversed and further enhanced during recovery. We concluded that an acute intestinal insult caused alterations of the mesenteric lymphatic system, including lymphangiogenesis, which persisted after resolution of inflammation. These morphological and functional changes could compromise DC function and movement, increasing susceptibility to further gastrointestinal disease. Elucidation of the changes in mesenteric and intestinal lymphatic function should offer key insights for new therapeutic strategies in gastrointestinal disorders such as IBD. NEW & NOTEWORTHY Lymphatic integrity plays a critical role in small intestinal homeostasis. Acute intestinal insult in a mouse model of acute ileitis causes morphological and functional changes in mesenteric and intestinal lymphatic vessels. While some of the changes significantly regressed during inflammation resolution, others persisted, including lymphangiogenesis and altered dendritic cell function and movement, potentially increasing susceptibility to the recurrence of gastrointestinal inflammation.

Regulatory T cells in allergic diseases

The pathogenesis of allergic diseases entails an ineffective tolerogenic immune response to allergens. Regulatory T (Treg) cells play a key role in sustaining immune tolerance to allergens, yet mechanisms by which Treg cells fail to maintain tolerance in patients with allergic diseases are not well understood. We review current concepts and established mechanisms regarding how Treg cells regulate different components of allergen-triggered immune responses to promote and maintain tolerance. We will also discuss more recent advances that emphasize the "dual" functionality of Treg cells in patients with allergic diseases: how Treg cells are essential in promoting tolerance to allergens but also how a proallergic inflammatory environment can skew Treg cells toward a pathogenic phenotype that aggravates and perpetuates disease. These advances highlight opportunities for novel therapeutic strategies that aim to re-establish tolerance in patients with chronic allergic diseases by promoting Treg cell stability and function.

The transcription factor musculin promotes the unidirectional development of peripheral Treg cells by suppressing the TH2 transcriptional program

Although master transcription factors (TFs) are key to the development of specific T cell subsets, whether additional transcriptional regulators are induced by the same stimuli that dominantly repress the development of other, non-specific T cell lineages has not been fully elucidated. Through the use of regulatory T cells (T_reg cells) induced by transforming growth factor-β (TGF-β), we identified the TF musculin (MSC) as being critical for the development of induced T_reg cells (iT_reg cells) by repression of the T helper type 2 (T_H2) transcriptional program. Loss of MSC reduced expression of the T_reg cell master TF Foxp3 and induced T_H2 differentiation even under iT_reg-cell-differentiation conditions. MSC interrupted binding of the TF GATA-3 to the locus encoding T_H2-cell-related cytokines and diminished intrachromosomal interactions within that locus. MSC-deficient (Msc^-/-) iT_reg cells were unable to suppress T_H2 responses, and Msc^-/- mice spontaneously developed gut and lung inflammation with age. MSC therefore enforced Foxp3 expression and promoted the unidirectional induction of iT_reg cells by repressing the T_H2 developmental program.

Compartmentalization of immunosenescence: a deeper look at the mucosa

Developments in medical care and living conditions led to an astonishing increase in life-span perspective and subsequently a rise in the old population. This can be seen as a success for public health policies but it also challenges society to adapt, in order to cope with the potentially overwhelming cost for the healthcare system. A fast-growing number of older people lose their ability to live independently because of diseases and disabilities, frailty or cognitive impairment. Many require long-term care, including home-based nursing, communities and hospital-based care. Immunosenescence, an age-related deterioration in immune functions, is considered a major contributory factor for the higher prevalence and severity of infectious diseases and the poor efficacy of vaccination in the elderly. When compared with systemic immunosenescence, alterations in the mucosal immune system with age are less well understood. For this reason, this area deserves more extensive and intensive research and support. In this article, we provide an overview of age-associated changes occurring in systemic immunity and discuss the distinct features of mucosal immunosenescence.

Etrolizumab as induction therapy for ulcerative colitis: a randomised, controlled, phase 2 trial

BACKGROUND

Etrolizumab is a humanised monoclonal antibody that selectively binds the β7 subunit of the heterodimeric integrins α4β7 and αEβ7. We aimed to assess etrolizumab in patients with moderately-to-severely active ulcerative colitis.

METHODS

In this double-blind, placebo-controlled, randomised, phase 2 study, patients with moderately-to-severely active ulcerative colitis who had not responded to conventional therapy were recruited from 40 referral centres in 11 countries. Eligible patients (aged 18-75 years; Mayo Clinic Score [MCS] of 5 of higher [or ≥6 in USA]; and disease extending 25 cm or more from anal verge) were randomised (1:1:1) to one of two dose levels of subcutaneous etrolizumab (100 mg at weeks 0, 4, and 8, with placebo at week 2; or 420 mg loading dose [LD] at week 0 followed by 300 mg at weeks 2, 4, and 8), or matching placebo. The primary endpoint was clinical remission at week 10, defined as MCS of 2 or less (with no individual subscore of >1), analysed in the modified intention-to-treat population (mITT; all randomly assigned patients who had received at least one dose of study drug, had at least one post-baseline disease-activity assessment, and had a centrally read screening endoscopic subscore of ≥2). This study is registered with ClinicalTrials.gov, number NCT01336465.

FINDINGS

Between Sept 2, 2011, and July 11, 2012, 124 patients were randomly assigned, of whom five had a endoscopic subscore of 0 or 1 and were excluded from the mITT population, leaving 39 patients in the etrolizumab 100 mg group, 39 in the etrolizumab 300 mg plus LD group, and 41 in the placebo group for the primary analyses. No patients in the placebo group had clinical remission at week 10, compared with eight (21% [95% CI 7-36]) patients in the etrolizumab 100 mg group (p=0·0040) and four (10% [0·2-24]) patients in the 300 mg plus LD group (p=0·048). Adverse events occurred in 25 (61%) of 41 patients in the etrolizumab 100 mg group (five [12%] of which were regarded as serious), 19 (48%) of 40 patients in the etrolizumab 300 mg plus LD group (two [5%] serious), and 31 (72%) of 43 patients in the placebo group (five [12%] serious).

INTERPRETATION

Etrolizumab was more likely to lead to clinical remission at week 10 than was placebo. Therefore, blockade of both α4β7 and αEβ7 might provide a unique therapeutic approach for the treatment of ulcerative colitis, and phase 3 studies have been planned.

FUNDING

Genentech.

Galectin-9-CD44 interaction enhances stability and function of adaptive regulatory T cells

The β-galactoside-binding protein galectin-9 is critical in regulating the immune response, but the mechanism by which it functions remains unclear. We have demonstrated that galectin-9 is highly expressed by induced regulatory T cells (iTreg) and was crucial for the generation and function of iTreg cells, but not natural regulatory T (nTreg) cells. Galectin-9 expression within iTreg cells was driven by the transcription factor Smad3, forming a feed-forward loop, which further promoted Foxp3 expression. Galectin-9 increased iTreg cell stability and function by directly binding to its receptor CD44, which formed a complex with transforming growth factor-β (TGF-β) receptor I (TGF-βRI), and activated Smad3. Galectin-9 signaling was further found to regulate iTreg cell induction by dominantly acting through the CNS1 region of the Foxp3 locus. Our data suggest that exogenous galectin-9, in addition to being an effector molecule for Treg cells, acts synergistically with TGF-β to enforce iTreg cell differentiation and maintenance.

Dendritic cell-based approaches for therapeutic immune regulation in solid-organ transplantation

To avoid immune rejection, allograft recipients require drug-based immunosuppression, which has significant toxicity. An emerging approach is adoptive transfer of immunoregulatory cells. While mature dendritic cells (DCs) present donor antigen to the immune system, triggering rejection, regulatory DCs interact with regulatory T cells to promote immune tolerance. Intravenous injection of immature DCs of either donor or host origin at the time of transplantation have prolonged allograft survival in solid-organ transplant models. DCs can be treated with pharmacological agents before injection, which may attenuate their maturation in vivo. Recent data suggest that injected immunosuppressive DCs may inhibit allograft rejection, not by themselves, but through conventional DCs of the host. Genetically engineered DCs have also been tested. Two clinical trials in type-1 diabetes and rheumatoid arthritis have been carried out, and other trials, including one trial in kidney transplantation, are in progress or are imminent.

Dendritic cell subsets in the intestinal lamina propria: ontogeny and function

The intestinal mucosa is exposed to large amounts of foreign antigen (Ag) derived from commensal bacteria, dietary Ags, and intestinal pathogens. Dendritic cells (DCs) are believed to be involved in the induction of tolerance to harmless Ags and in mounting protective immune responses to pathogens and, as such, to play key roles in regulating intestinal immune homeostasis. The characterization of classical DCs (cDCs) in the intestinal lamina propria has been under intense investigation in recent years but the use of markers (including CD11c, CD11b, MHC class II), which are also expressed by intestinal MΦs, has led to some controversy regarding their definition. Here we review recent studies that help to distinguish cDCs subsets from monocyte-derived cells in the intestinal mucosa. We address the phenotype and ontogeny of these cDC subsets and highlight recent findings indicating that these subsets play distinct roles in the regulation of mucosal immune responses in vivo.

Tailoring gut immune responses with lipoteichoic acid-deficient Lactobacillus acidophilus

As highlighted by the development of intestinal autoinflammatory disorders when tolerance is lost, homeostatic interactions between gut microbiota, resident immune cells, and the gut epithelium are key in the maintenance of gastrointestinal health. Gut immune responses, whether stimulatory or regulatory, are dictated by the activated dendritic cells (DCs) that first interact with microorganisms and their gene products to then elicit T and B cell responses. Previously, we have demonstrated that treatment with genetically modified Lactobacillus acidophilus is sufficient to tilt the immune balance from proinflammatory to regulatory in experimental models of colitis and colon cancer. Given the significant role of DCs in efficiently orchestrating intestinal immune responses, characterization of the signals induced within these cells by the surface layer molecules, such as lipoteichoic acid (LTA), and proteins of L. acidophilus is critical for future treatment and prevention of gastrointestinal diseases. Here, we discuss the potential regulatory pathways involved in the downregulation of pathogenic inflammation in the gut, and explore questions regarding the immune responses to LTA-deficient L. acidophilus that require future studies.

Intestinal dendritic cells: their role in intestinal inflammation, manipulation by the gut microbiota and differences between mice and men

The intestinal immune system maintains a delicate balance between immunogenicity against invading pathogens and tolerance of the commensal microbiota and food antigens. Dendritic cells (DC) generate primary T-cell responses, and determine whether these responses are immunogenic or tolerogenic. The regulatory role of DC is of particular importance in the gut due to the high antigenic load. Intestinal DC act as sentinels, sampling potentially pathogenic antigens but also harmless antigens including the commensal microbiota. Following antigen acquisition, intestinal DC migrate to secondary lymphoid organs to activate naive T-cells. DC also imprint specific homing properties on T-cells that they stimulate; gut DC specifically induce gut-homing properties on T-cells upon activation, enabling T-cell migration back to intestinal sites. Data regarding properties on gut DC in humans is scarce, although evidence now supports the role of DC as important players in intestinal immunity in humans. Here, we review the role of intestinal DC in shaping mucosal immune responses and directing tissue-specific T-cell responses, with a special focus on the importance of distinguishing DC subsets from macrophages at intestinal sites. We compare and contrast human DC with their murine counterparts, and discuss the ability of the gut microbiota to shape intestinal DC function, and how this may be dysregulated in inflammatory bowel disease (IBD). Lastly, we describe recent advances in the study of probiotics on intestinal DC function, including the use of soluble secreted bacterial products.

Heligmosomoides polygyrus bakeri induces tolerogenic dendritic cells that block colitis and prevent antigen-specific gut T cell responses

Immunological diseases such as inflammatory bowel disease (IBD) are infrequent in less developed countries, possibly because helminths provide protection by modulating host immunity. In IBD murine models, the helminth Heligmosomoides polygyrus bakeri prevents colitis. It was determined whether H. polygyrus bakeri mediated IBD protection by altering dendritic cell (DC) function. We used a Rag IBD model where animals were reconstituted with IL10⁻/⁻ T cells, making them susceptible to IBD and with OVA Ag-responsive OT2 T cells, allowing study of a gut antigenic response. Intestinal DC from H. polygyrus bakeri-infected Rag mice added to lamina propria mononuclear cells (LPMC) isolated from colitic animals blocked OVA IFN-γ/IL-17 responses in vitro through direct contact with the inflammatory LPMC. DC from uninfected Rag mice displayed no regulatory activity. Transfer of DC from H. polygyrus bakeri-infected mice into Rag mice reconstituted with IL10⁻/⁻ T cells protected animals from IBD, and LPMC from these mice lost OVA responsiveness. After DC transfer, OT2 T cells populated the intestines normally. However, the OT2 T cells were rendered Ag nonresponsive through regulatory action of LPMC non-T cells. The process of regulation appeared to be regulatory T cell independent. Thus, H. polygyrus bakeri modulates intestinal DC function, rendering them tolerogenic. This appears to be an important mechanism through which H. polygyrus bakeri suppresses colitis. IFN-γ and IL-17 are colitogenic. The capacity of these DC to block a gut Ag-specific IFN-γ/IL-17 T cell response also is significant.

NK cells promote Th-17 mediated corneal barrier disruption in dry eye

BACKGROUND

The conjunctiva contains a specialized population of lymphocytes that reside in the epithelium, named intraepithelial lymphocytes (IEL).

METHODOLOGY/PRINCIPAL FINDINGS

Here we characterized the IEL population prior to and after experimental desiccating stress (DS) for 5 or 10 days (DS5, DS10) and evaluated the effect of NK depletion on DS. The frequency of IELs in normal murine conjunctiva was CD3(+)CD103(+) (~22%), CD3(+)γδ(+) (~9.6%), CD3(+)NK(+) (2%), CD3(-)NK(+) (~4.4%), CD3(+)CD8α (~0.9%), and CD4 (~0.6%). Systemic depletion of NK cells prior and during DS led to a decrease in the frequency of total and activated DCs, a decrease in T helper-17(+) cells in the cervical lymph nodes and generation of less pathogenic CD4(+)T cells. B6.nude recipient mice of adoptively transferred CD4(+)T cells isolated from NK-depleted DS5 donor mice showed significantly less corneal barrier disruption, lower levels of IL-17A, CCL20 and MMP-3 in the cornea epithelia compared to recipients of control CD4(+)T cells.

CONCLUSIONS/SIGNIFICANCE

Taken together, these results show that the NK IELs are involved in the acute immune response to desiccation-induced dry eye by activating DC, which in turn coordinate generation of the pathogenic Th-17 response.

Directed antigen targeting in vivo identifies a role for CD103+ dendritic cells in both tolerogenic and immunogenic T-cell responses

The αE integrin chain CD103 identifies a subset of migratory dendritic cells (DCs) in the gut, lung, and skin. To gain further understanding of the function of CD103(+) DCs in regulating adaptive immunity in vivo, we coupled ovalbumin (OVA) to the CD103 antibody M290 (M290.OVA). Intraperitoneal injection of M290.OVA induced OVA-specific CD8(+) and CD4(+) T-cell proliferation in lymph nodes (LNs) of wild-type but not CD103(-/-) mice, or in mice depleted of CD11c(+) cells. In the absence of maturation stimuli, systemic antigen targeting to CD103(+) DCs led to tolerance of CD8(+) T cells, whereas coadministration of adjuvant induced cytotoxic T-lymphocyte (CTL) immunity and antibody production. Mucosal intratracheal application of M290.OVA also induced T-cell proliferation in mediastinal LNs, yet the functional outcome was tolerance that inhibited subsequent development of allergic airway inflammation and immunoglobulin E (IgE) responses to inhaled OVA. These findings identify antigen targeting to CD103(+) DCs as a potential strategy to regulate immune responses in nonlymphoid mucosal tissues.

Influence of dietary components on regulatory T cells

Common dietary components including vitamins A and D, omega-3 and probiotics are now widely accepted to be essential to protect against many diseases with an inflammatory nature. On the other hand, high-fat diets are documented to exert multiple deleterious effects, including fatty liver diseases. Here we discuss the effect of dietary components on regulatory T cell (Treg) homeostasis, a central element of the immune system to prevent chronic tissue inflammation. Accordingly, evidence on the impact of dietary components on diseases in which Tregs play an influential role will be discussed. We will review chronic tissue-specific autoimmune and inflammatory conditions such as inflammatory bowel disease, type 1 diabetes mellitus, multiple sclerosis, rheumatoid arthritis and allergies among chronic diseases where dietary factors could have a direct influence via modulation of Tregs homeostasis and functions.

Phenotypical and functional analysis of intraepithelial lymphocytes from small intestine of mice in oral tolerance

In this work, we evaluated the effects of administration of OVA on phenotype and function of intraepithelial lymphocytes (IELs) from small intestine of transgenic (TGN) DO11.10 and wild-type BALB/c mice. While the small intestines from BALB/c presented a well preserved structure, those from TGN showed an inflamed aspect. The ingestion of OVA induced a reduction in the number of IELs in small intestines of TGN, but it did not change the frequencies of CD8⁺ and CD4⁺ T-cell subsets. Administration of OVA via oral + ip increased the frequency of CD103⁺ cells in CD4⁺ T-cell subset in IELs of both BALB/c and TGN mice and elevated its expression in CD8β⁺ T-cell subset in IELs of TGN. The frequency of Foxp3⁺ cells increased in all subsets in IELs of BALB/c treated with OVA; in IELs of TGN, it increased only in CD25⁺ subset. IELs from BALB/c tolerant mice had lower expression of all cytokines studied, whereas those from TGN showed high expression of inflammatory cytokines, especially of IFN-γ, TGF-β, and TNF-α. Overall, our results suggest that the inability of TGN to become tolerant may be related to disorganization and altered proportions of inflammatory/regulatory T cells in its intestinal mucosa.

Myeloid dendritic cells isolated from tissues of SIV-infected Rhesus macaques promote the induction of regulatory T cells

OBJECTIVE

To determine whether the ability of primary myeloid dendritic cells (mDCs) to induce regulatory T cells (Treg) is affected by chronic simian immunodeficiency virus (SIV) infection.

DESIGN

Modulation of dendritic cell activity with the aim of influencing Treg frequency may lead to new treatment options for HIV and strategies for vaccine development.

METHODS

Eleven chronically infected SIV(+) Rhesus macaques were compared with four uninfected animals. Immature and mature mDCs were isolated from mesenteric lymph nodes and spleen by cell sorting and cultured with purified autologous non-Treg (CD4(+)CD25(-) T cells). CD25 and FOXP3 up-regulation was used to assess Treg induction.

RESULTS

The frequency of splenic mDC and plasmacytoid dendritic cell was lower in infected animals than in uninfected animals; their frequency in the mesenteric lymph nodes was not significantly altered, but the percentage of mature mDCs was increased in the mesenteric lymph nodes of infected animals. Mature splenic or mesenteric mDCs from infected animals were significantly more efficient at inducing Treg than mDCs from uninfected animals. Mature mDCs from infected macaques induced more conversion than immature mDCs. Splenic mDCs were as efficient as mesenteric mDCs in this context and CD103 expression by mDCs did not appear to influence the level of conversion.

CONCLUSIONS

Tissue mDCs from SIV-infected animals exhibit an enhanced capability to induce Treg and may contribute to the accumulation of Treg in lymphoid tissues during progressive infection. The activation status of dendritic cell impacts this process but the capacity to induce Treg was not restricted to mucosal dendritic cells in infected animals.

TGF-β induces the expression of the adaptor Ndfip1 to silence IL-4 production during iTreg cell differentiation

Mice deficient in the adaptor Ndfip1 develop inflammation at sites of environmental antigen exposure. We show here that such mice had fewer inducible regulatory T cells (iT(reg) cells). In vitro, Ndfip1-deficient T cells expressed normal amounts of the transcription factor Foxp3 during the first 48 h of iT(reg) cell differentiation; however, this expression was not sustained. Abortive Foxp3 expression was caused by production of interleukin 4 (IL-4) by Ndfip1(-/-) cells. We found that Ndfip1 expression was transiently upregulated during iT(reg) cell differentiation in a manner dependent on transforming growth factor-β (TGF-β). Once expressed, Ndfip1 promoted degradation of the transcription factor JunB mediated by the E3 ubiquitin ligase Itch, thus preventing IL-4 production. On the basis of our data, we propose that TGF-β signaling induces Ndfip1 expression to silence IL-4 production, thus permitting iT(reg) cell differentiation.

How vitamin A metabolizing dendritic cells are generated in the gut mucosa

CD103(+) dendritic cells (DCs) represent the major migratory DC population in the intestinal lamina propria and are believed to play an essential role in the initiation and regulation of mucosal adaptive immune responses. Small intestine (SI) CD103(+) DCs have an enhanced capacity to generate the vitamin A metabolite, retinoic acid, a property that underlies their ability to induce the gut homing receptors CC chemokine receptor 9 and α4β7 on responding T and B cells, and enhance forkhead box P3(+) T regulatory and IgA plasma cell differentiation in vitro. In this review, we discuss the environmental signals that appear to promote vitamin A metabolising activity in SI CD103(+) DCs in the steady state and thus which may contribute to driving the unique nature of SI immune responses.

Intestinal CD103+ dendritic cells: master regulators of tolerance?

CD103(+) dendritic cells (DCs) in the intestinal mucosa play a crucial role in tolerance to commensal bacteria and food antigens. These cells originate in the lamina propria (LP) and migrate to the mesenteric lymph nodes (MLNs), where they drive the differentiation of gut-homing FoxP3(+) regulatory T cells by producing retinoic acid from dietary vitamin A. Local 'conditioning' factors in the LP might also contribute to this tolerogenic profile of CD103(+) DCs. Considerably less is understood about the generation of active immunity or inflammation in the intestinal mucosa. This might require alterations in pre-existing CD103(+) DCs, arrival of new DCs, or the action of a distinct DC population. Here, we discuss our current knowledge of this as yet incompletely understood population.

Dendritic cell control of tolerogenic responses

One of the most fundamental problems in immunology is the seemingly schizophrenic ability of the immune system to launch robust immunity against pathogens, while acquiring and maintaining a state of tolerance to the body's own tissues and the trillions of commensal microorganisms and food antigens that confront it every day. A fundamental role for the innate immune system, particularly dendritic cells (DCs), in orchestrating immunological tolerance has been appreciated, but emerging studies have highlighted the nature of the innate receptors and the signaling pathways that program DCs to a tolerogenic state. Furthermore, several studies have emphasized the major role played by cellular interactions and the microenvironment in programming tolerogenic DCs. Here, we review these studies and suggest that the innate control of tolerogenic responses can be viewed as different hierarchies of organization, in which DCs, their innate receptors and signaling networks, and their interactions with other cells and local microenvironments represent different levels of the hierarchy.

Human nutrition, the gut microbiome and the immune system

Marked changes in socio-economic status, cultural traditions, population growth and agriculture are affecting diets worldwide. Understanding how our diet and nutritional status influence the composition and dynamic operations of our gut microbial communities, and the innate and adaptive arms of our immune system, represents an area of scientific need, opportunity and challenge. The insights gleaned should help to address several pressing global health problems.

Human colonic myofibroblasts promote expansion of CD4+ CD25high Foxp3+ regulatory T cells

BACKGROUND & AIMS

Regulatory T (Treg) cells (CD4+ CD25high FoxP3+) regulate mucosal tolerance; their adoptive transfer prevents or reduces symptoms of colitis in mouse models of inflammatory bowel disease. Colonic CD90+ mesenchymal myofibroblasts and fibroblasts (CMFs) are abundant, nonprofessional antigen-presenting cells in the normal human colonic mucosa that suppress proliferation of activated CD4+ effector T cells. We studied CMF suppressive capacity and evaluated the ability of CMF to induce Treg cells.

METHODS

Allogeneic cocultures of CD4+ T cells and CMFs, derived from normal mucosa of patients undergoing colectomy for colon cancer or inflamed colonic tissues from patients with ulcerative colitis or Crohn's disease, were used to assess activation of the Treg cells.

RESULTS

Coculture of normal CMF with resting or naïve CD4+ T cells led to development of cells with a Treg phenotype; it also induced proliferation of a CD25+ CD127- FoxP3+ T cells, which expressed CTLA-4, interleukin-10, and transforming growth factor-β and had suppressive activities. In contrast to dendritic cells, normal CMFs required exogenous interleukin-2 to induce proliferation of naturally occurring Treg cells. Induction of Treg cells by normal CMFs required major histocompatibility complex class II and prostaglandin E2. CMFs from patients with inflammatory bowel diseases had reduced capacity to induce active Treg cells and increased capacity to transiently generate CD4+CD25+/- CD127+ T cells that express low levels of FoxP3.

CONCLUSIONS

CMFs suppress the immune response in normal colon tissue and might therefore help maintain colonic mucosal tolerance. Alterations in CMF-mediated induction of Treg cells might promote pathogenesis of inflammatory bowel diseases.

Small intestine CD11c+ CD8+ T cells suppress CD4+ T cell-induced immune colitis

The large (LI) and small intestine (SI) differ in patterns of susceptibility to chronic mucosal inflammation. In this study, we evaluated whether this might, in part, reflect differences in resident mucosal CD11c(+) T cells. These cells comprised 39-48% (SI) and 12-17% (LI) of the intraepithelial compartment, most of which were T-cell receptor-αβ(+). In the SI, the majority of these cells were CD103(+) CD8(+) NK1.1(-), whereas the opposite phenotype prevailed in the LI. In transfer models of CD4(+) T cell-induced colitis, small numbers (2.5 × 10(5)) of SI CD11c(+) CD8(+) T cells suppressed proinflammatory cytokine-producing CD4(+) T cells in mesenteric lymph nodes and mucosa-associated lymphoid compartments (SI and LI) and protected mice from chronic inflammation. On a per-cell basis, the regulatory function of SI CD11c(+) T cells in CD4(+) T cell colitis was potent compared with other reported regulatory CD4(+) or CD8(+) T cells. In contrast, neither LI CD11c(+) T cells nor SI CD11c(-) T cells were effective in such immunoregulation. SI CD11c(+) CD8(+) T cells were similarly effective in suppressing CD4(+)CD45RB(hi) T cell colitis, as evidenced by inhibition of intracellular proinflammatory cytokine expression and histological inflammation. These findings indicate that SI CD11c(+) CD8(+) T cells are a distinct intestinal T cell population that plays an immunoregulatory role in control of proinflammatory CD4(+) T cells and maintenance of intestinal mucosal homeostasis.

Localized delivery of interferon-β by Lactobacillus exacerbates experimental colitis

BACKGROUND

There have been conflicting reports of the role of Type I interferons (IFN) in inflammatory bowel disease (IBD). Clinical trials have shown potent efficacy of systemic interferon-beta (IFN-β) in inducing remission of ulcerative colitis. Likewise, IFNAR1(-/-) mice display an increased sensitivity to dextran sulfate sodium (DSS)-induced colitis, suggesting Type I IFN play a protective role during inflammation of the gut. Curiously, however, there have also been reports detailing the spontaneous development of IBD in patients receiving systemic IFN-β therapy for multiple sclerosis or hepatitis.

METHODOLOGY/PRINCIPAL FINDINGS

To investigate the effects of local administration of IFN-β on a murine model of colitis, we developed a transgenic Lactobacillus acidophilus strain that constitutively expresses IFN-β (La-IFN-β). While pretreatment of mice with control Lactobacillus (La-EV) provided slight protective benefits, La-IFN-β increased sensitivity to DSS. Analysis showed colitic mice pretreated with La-IFN-β had increased production of TNF-α, IFN-γ, IL-17A and IL-13 by intestinal tissues and decreased regulatory T cells (Tregs) in their small intestine. Examination of CD103(+) dendritic cells (DCs) in the Peyer's patches revealed that IFNAR1 expression was dramatically reduced by La-IFN-β. Similarly, bone marrow-derived DCs matured with La-IFN-β experienced a 3-fold reduction of IFNAR1 and were impaired in their ability to induce Tregs.

CONCLUSIONS/SIGNIFICANCE

Our IFNAR1 expression data identifies a correlation between the loss/downregulation of IFNAR1 on DCs and exacerbation of colitis. Our data show that Lactobacillus secreting IFN-β has an immunological effect that in our model results in the exacerbation of colitis. This study underscores that the selection of therapeutics delivered by a bacterial vehicle must take into consideration the simultaneous effects of the vehicle itself.

Retinoic acid, immunity, and inflammation

Vitamin A (also called retinol), absorbed in the intestine and stored mainly in the liver and fat, is normally maintained at significant concentrations in the human blood plasma. Vitamin A is constitutively metabolized at high levels in certain tissues such as the small intestine and eyes. Retinoic acid (RA) produced at high levels in the intestine plays important roles in mucosal immunity and immune tolerance. RA at basal levels is required for immune cell survival and activation. During immune responses, enzymes metabolizing vitamin A are induced in certain types of immune cells such as dendritic cells (DCs) and tissue cells for induced production of RA. As a result, induced gradients of RA are formed during immune responses in the body. RA regulates gene expression, differentiation, and function of diverse immune cells. The cells under the influence of RA in terms of differentiation include myeloid cells such as neutrophils, macrophages, and DCs. Also included are lymphoid cells such as effector T cells, regulatory T cells, and B cells. Our current understanding of the function of RA in regulation of these immune cells is reviewed in this chapter.

Gatekeepers of intestinal inflammation

The intestine is subjected to a barrage of insults from food, bacterial flora, and pathogens. Despite this constant antigenic challenge, the mucosal tissues lining the intestinal tract remain largely under control. The mechanisms regulating the homeostatic balance in the gut have been investigated for many years by many groups, but the precise nature of the regulatory control remains elusive. In this review, we provide an overview of pathways proposed to be involved in dampening the inflammatory response and maintaining the homeostatic balance in the intestine, and how these pathways may be disrupted in ulcerative colitis and Crohn's disease.

Regulatory T cells: roles of T cell receptor for their development and function

Naturally arising CD4(+)CD25(+) regulatory T cells (Treg cells), which specifically express the forkhead family transcription factor Foxp3, are essential for the maintenance of immunological self-tolerance and immune homeostasis. Stimulation of the T cell antigen receptor (TCR) via recognizing self-peptide/major histocompatibility complex (MHC) is required for their expression of Foxp3 in the course of their development in the thymus. The TCR repertoires displayed by Treg cells and naïve T cells are apparently distinct, suggesting that Treg cells with high reactivity to self-peptide/MHC ligands are somehow driven to Treg cell lineage in the thymus. Treg cells also require stimulation via TCR to exert suppression in the periphery. At the molecular level, assembly of Foxp3, Foxp3-interacting factors, and chromatin-remodeling factors is in part under the control of TCR signaling, and TCR stimulation alters Foxp3-dependent transcriptional regulation, protein-protein interaction, and Foxp3 recruitment to the specific genomic loci. These findings collectively indicate that the TCR signaling is essential for suppressive function of Treg cells and that TCR has a determinant role for driving developing T cells to the Foxp3(+)CD4(+)CD25(+) Treg cell lineage and differentiation.