From the diet to the nucleus: vitamin A and TGF-beta join efforts at the mucosal interface of the intestine

The role of fat-soluble vitamins for graft-versus host disease after myeloablative conditioning in allogeneic stem cell transplanted patients

Whether the fat-soluble vitamins A, D, E, and K are associated with development of graft-versus-host disease (GvHD) after allogeneic stem cell transplantation, is unclear. We assessed if the levels of these vitamins were associated with development of GvHD during the first year after transplantation using data from a two-armed randomized nutritional intervention trial. Changes in plasma levels during 1-year follow-up were analyzed using a linear mixed model for repeated measurements. Vitamin A, D, E, and K levels changed significantly the first year in both study arms (p < 0.001). Higher levels of vitamin E over time were associated with less acute GvHD grades 3-4 (OR = 0.997, 95% CI: (0.994, 0.999), p = 0.017). No associations were found with vitamin A, D, E and K levels and chronic GvHD. Multivariable analysis adjusted for treatment group, age, pre-transplant vitamin level and risk factors for GvHD did not change the results. Six weeks post-transplantation, higher levels of vitamin E were associated with less acute GvHD grades 3-4, (p = 0.012). In conclusion, we found an association between higher levels of vitamin E over time and less severe acute GvHD. Whether this reflects a causal relationship warrants further study. ClinicalTrials.gov (NCT01181076).

Insulin resistance in nonobese type 2 diabetic Goto Kakizaki rats is associated with a proinflammatory T lymphocyte profile

Goto-Kakizaki (GK) rats develop a well-defined insulin resistance (IR) and type 2 diabetes mellitus (T2DM) without presenting obesity. The lymphocyte profile in nonobese diabetic conditions is not yet characterized. Therefore, GK rats were chosen to explore T lymphocyte (TL) dynamics at various stages (21, 60, and 120 days) compared to Wistar rats. GK rats exhibit progressive disruption of glucose regulation, with early glucose intolerance at 21 days and reduced insulin sensitivity at 60 days, confirming IR. Glucose transporter 1 (GLUT1) expression was consistently elevated in GK rats, suggesting heightened TL activation. T-regulatory lymphocyte markers diminished at 21 days. However, GK rats showed increased Th1 markers and reduced Gata-3 expression (crucial for Th2 cell differentiation) at 120 days. These findings underscore an early breakdown of anti-inflammatory mechanisms in GK rats, indicating a proinflammatory TL profile that may worsen chronic inflammation in T2DM.

Interactions of Nutrition and Infection: The Role of Micronutrient Deficiencies in the Immune Response to Pathogens and Implications for Child Health

Approximately five million children die each year from preventable causes, including respiratory infections, diarrhea, and malaria. Roughly half of those deaths are attributable to undernutrition, including micronutrient deficiencies (MNDs). The influence of infection on micronutrient status is well established: The inflammatory response to pathogens triggers anorexia, while pathogens and the immune response can both alter nutrient absorption and cause nutrient losses. We review the roles of vitamin A, vitamin D, iron, zinc, and selenium in the immune system, which act in the regulation of molecular- or cellular-level host defenses, directly affecting pathogens or protecting against oxidative stress or inflammation. We further summarize high-quality evidence regarding the synergistic or antagonistic interactions between MNDs, pathogens, and morbidity or mortality relevant to child health in low- and middle-income countries. We conclude with a discussion of gaps in the literature and future directions for multidisciplinary research on the interactions of MNDs, infection, and inflammation.

Dietary vitamin A modifies the gut microbiota and intestinal tissue transcriptome, impacting intestinal permeability and the release of inflammatory factors, thereby influencing Aβ pathology

Background

Alzheimer's disease (AD) is an age-related neurodegenerative disorder with no effective interventions for curing or modifying its progression. However, emerging research suggests that vitamin A in the diet may play a role in both the prevention and treatment of AD, although the exact mechanisms are not fully understood.

Objectives

This study aims to investigate the dietary vitamin A modifies the gut microbiota and intestinal tissue transcriptome, impacting intestinal permeability and the release of inflammatory factors, thereby influencing Aβ pathology shedding light on its potential as a dietary intervention for AD prevention and treatment.

Methods

The APP/PS1-AD mouse model was employed and divided into three dietary groups: vitamin A-deficient (VAD), normal vitamin A (VAN), and vitamin A-supplemented (VAS) for a 12-week study. Neurobehavioral functions were assessed using the Morris Water Maze Test (MWM). Enzyme-linked immunosorbent assay (ELISA) was used to quantify levels of Diamine Oxidase (DAO), D-lactate, IL-6, IL-1β, and TNF-a cytokines. Serum vitamin A levels were analyzed via LC-MS/MS analysis. Immunohistochemical analysis and morphometry were performed to evaluate the deposition of Aβ in brain tissue. The gut microbiota of APP/PS1 mice was analyzed using 16S rRNA sequencing analysis. Additionally, transcriptomic analysis was conducted on intestinal tissue from APP/PS1 mice.

Results

No significant changes in food intake and body weight were observed among the groups. However, the VAD and VAS groups showed reduced food intake compared to the VAN group at various time points. In terms of cognitive function, the VAN group performed better in the Morris Water Maze Test, indicating superior learning and memory abilities. The VAD and VAS groups exhibited impaired performance, with the VAS group performing relatively better than the VAD group. Serum vitamin A concentrations differed significantly among the groups, with the VAS group having the highest concentration. Aβ levels were significantly higher in the VAD group compared to both the VAN and VAS groups. Microbial analysis revealed that the VAS and VAN groups had higher microbial diversity than the VAD group, with specific taxa characterizing each group. The VAN group was characterized by taxa such as Actinohacteriota and Desulfovibrionaceae, while the VAD group was characterized by Parabacteroides and Tannerellaceae. The VAS group showed similarities with both VAN and VAD groups, with taxa like Desulfobacterota and Desulfovibrionaceae being present. The VAD vs. VAS, VAD vs. VAN, and VAS vs. VAN comparisons identified 571, 313, and 243 differentially expressed genes, respectively, which associated with cellular and metabolic processes, and pathway analysis revealed enrichment in pathways related to chemical carcinogenesis, drug metabolism, glutathione metabolism, and immune-related processes. The VAD group exhibited higher levels of D-lactate, diamine oxidase, and inflammatory cytokines (TNF-a, IL-1β, IL-6) compared to the VAN and VAS groups.

Conclusion

Dietary vitamin A supplementation modulates the gut microbiota, intestinal permeability, inflammatory factors, and Aβ protein formation, offering insights into the pathogenesis of AD and potential therapeutic avenues for further exploration. This research highlights the intricate interplay between diet, gut microbiota, and neurodegenerative processes, emphasizing the importance of dietary interventions in managing AD-related pathologies.

A randomized phase 2 trial of oral vitamin A for graft-versus-host disease in children and young adults

ABSTRACT

Vitamin A plays a key role in the maintenance of gastrointestinal homeostasis and promotes a tolerogenic phenotype in tissue resident macrophages. We conducted a prospective randomized double-blinded placebo-controlled clinical trial in which 80 recipients of hematopoietic stem cell transplantation (HSCT) were randomized 1:1 to receive pretransplant high-dose vitamin A or placebo. A single oral dose of vitamin A of 4000 IU/kg, maximum 250 000 IU was given before conditioning. The primary end point was incidence of acute graft-versus-host disease (GVHD) at day +100. In an intent-to-treat analysis, incidence of acute GVHD was 12.5% in the vitamin A arm and 20% in the placebo arm (P = .5). Incidence of acute gastrointestinal (GI) GVHD was 2.5% in the vitamin A arm (P = .09) and 12.5% in the placebo arm at day +180. Incidence of chronic GVHD was 5% in the vitamin A arm and 15% in the placebo arm (P = .02) at 1 year. In an "as treated" analysis, cumulative incidence of acute GI GVHD at day +180 was 0% and 12.5% in recipients of vitamin A and placebo, respectively (P = .02), and cumulative incidence of chronic GVHD was 2.7% and 15% in recipients of vitamin A and placebo, respectively (P = .01). The only possibly attributable toxicity was asymptomatic grade 3 hyperbilirubinemia in 1 recipient of vitamin A at day +30, which self-resolved. Absolute CCR9+ CD8+ effector memory T cells, reflecting gut T-cell trafficking, were lower in the vitamin A arm at day +30 after HSCT (P = .01). Levels of serum amyloid A-1, a vitamin A transport protein with proinflammatory effects, were lower in the vitamin A arm. The vitamin A arm had lower interleukin-6 (IL-6), IL-8, and suppressor of tumorigenicity 2 levels and likely a more favorable gut microbiome and short chain fatty acids. Pre-HSCT oral vitamin A is inexpensive, has low toxicity, and reduces GVHD. This trial was registered at www.ClinicalTrials.gov as NCT03202849.

A novel in vitro model of the small intestinal epithelium in co-culture with 'gut-like' dendritic cells

Cross-talk between dendritic cells (DCs) and the intestinal epithelium is important in the decision to mount a protective immune response to a pathogen or to regulate potentially damaging responses to food antigens and the microbiota. Failures in this decision-making process contribute to the development of intestinal inflammation, making the molecular signals that pass between DCs and intestinal epithelial cells potential therapeutic targets. Until now, in vitro models with sufficient complexity to understand these interactions have been lacking. Here, we outline the development of a co-culture model of in vitro differentiated 'gut-like' DCs with small intestinal organoids (enteroids). Sequential exposure of murine bone marrow progenitors to Flt3L, granulocyte macrophage colony-stimulating factor (GM-CSF) and all-trans-retinoic acid (RA) resulted in the generation of a distinct population of conventional DCs expressing CD11b+SIRPα+CD103+/- (cDC2) exhibiting retinaldehyde dehydrogenase (RALDH) activity. These 'gut-like' DCs extended transepithelial dendrites across the intact epithelium of enteroids. 'Gut-like' DC in co-culture with enteroids can be utilized to define how epithelial cells and cDCs communicate in the intestine under a variety of different physiological conditions, including exposure to different nutrients, natural products, components of the microbiota, or pathogens. Surprisingly, we found that co-culture with enteroids resulted in a loss of RALDH activity in 'gut-like' DCs. Continued provision of GM-CSF and RA during co-culture was required to oppose putative negative signals from the enteroid epithelium. Our data contribute to a growing understanding of how intestinal cDCs assess environmental conditions to ensure appropriate activation of the immune response.

MAdCAM-1 costimulation in the presence of retinoic acid and TGF-β promotes HIV infection and differentiation of CD4+ T cells into CCR5+ TRM-like cells

CD4+ tissue resident memory T cells (TRMs) are implicated in the formation of persistent HIV reservoirs that are established during the very early stages of infection. The tissue-specific factors that direct T cells to establish tissue residency are not well defined, nor are the factors that establish viral latency. We report that costimulation via MAdCAM-1 and retinoic acid (RA), two constituents of gut tissues, together with TGF-β, promote the differentiation of CD4+ T cells into a distinct subset α4β7+CD69+CD103+ TRM-like cells. Among the costimulatory ligands we evaluated, MAdCAM-1 was unique in its capacity to upregulate both CCR5 and CCR9. MAdCAM-1 costimulation rendered cells susceptible to HIV infection. Differentiation of TRM-like cells was reduced by MAdCAM-1 antagonists developed to treat inflammatory bowel diseases. These finding provide a framework to better understand the contribution of CD4+ TRMs to persistent viral reservoirs and HIV pathogenesis.

Animal unit hygienic conditions influence mouse intestinal microbiota and contribute to T-cell-mediated colitis

Inflammatory bowel disease (IBD) is a group of chronic inflammatory disorders of the gastrointestinal tract with worldwide increasing incidence. Recent studies indicate that certain species of intestinal bacteria are strongly associated with IBD. Helper T lymphocytes are not only the key players in mediating host defense against a wide variety of pathogens but also contribute to pathogenesis of many immune-related diseases. Here, using the T cell transfer model of colitis, we observed that the mice maintained in a specific-pathogen free (SPF) unit after receiving naïve CD4⁺ T cells developed mild disease. The same mice developed different degrees of disease when they were maintained in a conventional animal facility (non-SPF), where some pathogens were detected during routine health monitoring. Consistently, increased circulating inflammatory cytokines as well as Th1 and Th17 cells were detected in mice housed in non-SPF units. 16S rRNA sequencing of feces samples enabled us to identify changes in the microbiota composition of mice kept in different facilities. Our data indicate that environmental factors influence gut microbiota composition of mice, leading to development of colitis in a T-cell-dependent manner. In conclusion, changes in environmental conditions and microbial status of experimental animals appear to contribute to progression of colitis.

Vitamin A, systemic T-cells, and the eye: Focus on degenerative retinal disease

The first discovered vitamin, vitamin A, exists in a range of forms, primarily retinoids and provitamin carotenoids. The bioactive forms of vitamin A, retinol and retinoic acid, have many critical functions in body systems including the eye and immune system. Vitamin A deficiency is associated with dysfunctional immunity, and presents clinically as a characteristic ocular syndrome, xerophthalmia. The immune functions of vitamin A extend to the gut, where microbiome interactions and nutritional retinoids and carotenoids contribute to the balance of T cell differentiation, thereby determining immune status and contributing to inflammatory disease around the whole body. In the eye, degenerative conditions affecting the retina and uvea are influenced by vitamin A. Stargardt's disease (STGD1; MIM 248200) is characterised by bisretinoid deposits such as lipofuscin, produced by retinal photoreceptors as they use and recycle a vitamin A-derived chromophore. Age-related macular degeneration features comparable retinal deposits, such as drusen featuring lipofuscin accumulation; and is characterised by parainflammatory processes. We hypothesise that local parainflammatory processes secondary to lipofuscin deposition in the retina are mediated by T cells interacting with dietary vitamin A derivatives and the gut microbiome, and outline the current evidence for this. No cures exist for Stargardt's or age-related macular degeneration, but many vitamin A-based therapeutic approaches have been or are being trialled. The relationship between vitamin A's functions in systemic immunology and the eye could be further exploited, and further research may seek to leverage the interactions of the gut-eye immunological axis.

Tissue-resident memory CD8+ T cells possess unique transcriptional, epigenetic and functional adaptations to different tissue environments

Tissue-resident memory T cells (T_RM cells) provide protective immunity, but the contributions of specific tissue environments to T_RM cell differentiation and homeostasis are not well understood. In the present study, the diversity of gene expression and genome accessibility by mouse CD8⁺ T_RM cells from distinct organs that responded to viral infection revealed both shared and tissue-specific transcriptional and epigenetic signatures. T_RM cells in the intestine and salivary glands expressed transforming growth factor (TGF)-β-induced genes and were maintained by ongoing TGF-β signaling, whereas those in the fat, kidney and liver were not. Constructing transcriptional-regulatory networks identified the transcriptional repressor Hic1 as a critical regulator of T_RM cell differentiation in the small intestine and showed that Hic1 overexpression enhanced T_RM cell differentiation and protection from infection. Provision of a framework for understanding how CD8⁺ T_RM cells adapt to distinct tissue environments, and identification of tissue-specific transcriptional regulators mediating these adaptations, inform strategies to boost protective memory responses at sites most vulnerable to infection.

A novel hypothesis for COVID-19 pathogenesis: Retinol depletion and retinoid signaling disorder

The SARS-CoV-2 virus has caused a worldwide COVID-19 pandemic. In less than a year and a half, more than 200 million people have been infected and more than four million have died. Despite some improvement in the treatment strategies, no definitive treatment protocol has been developed. The pathogenesis of the disease has not been clearly elucidated yet. A clear understanding of its pathogenesis will help develop effective vaccines and drugs. The immunopathogenesis of COVID-19 is characteristic with acute respiratory distress syndrome and multiorgan involvement with impaired Type I interferon response and hyperinflammation. The destructive systemic effects of COVID-19 cannot be explained simply by the viral tropism through the ACE2 and TMPRSS2 receptors. In addition, the recently identified mutations cannot fully explain the defect in all cases of Type I interferon synthesis. We hypothesize that retinol depletion and resulting impaired retinoid signaling play a central role in the COVID-19 pathogenesis that is characteristic for dysregulated immune system, defect in Type I interferon synthesis, severe inflammatory process, and destructive systemic multiorgan involvement. Viral RNA recognition mechanism through RIG-I receptors can quickly consume a large amount of the body's retinoid reserve, which causes the retinol levels to fall below the normal serum levels. This causes retinoid insufficiency and impaired retinoid signaling, which leads to interruption in Type I interferon synthesis and an excessive inflammation. Therefore, reconstitution of the retinoid signaling may prove to be a valid strategy for management of COVID-19 as well for some other chronic, degenerative, inflammatory, and autoimmune diseases.

IL-35 promotes CD4+Foxp3+ Tregs and inhibits atherosclerosis via maintaining CCR5-amplified Treg-suppressive mechanisms

Tregs play vital roles in suppressing atherogenesis. Pathological conditions reshape Tregs and increase Treg-weakening plasticity. It remains unclear how Tregs preserve their function and how Tregs switch into alternative phenotypes in the environment of atherosclerosis. In this study, we observed a great induction of CD4⁺Foxp3⁺ Tregs in the spleen and aorta of ApoE^–/– mice, accompanied by a significant increase of plasma IL-35 levels. To determine if IL-35 devotes its role in the rise of Tregs, we generated IL-35 subunit P35–deficient (IL-35P35–deficient) mice on an ApoE^–/– background and found Treg reduction in the spleen and aorta compared with ApoE^–/– controls. In addition, our RNA sequencing data show the elevation of a set of chemokine receptor transcripts in the ApoE^–/– Tregs, and we have validated higher CCR5 expression in ApoE^–/– Tregs in the presence of IL-35 than in the absence of IL-35. Furthermore, we observed that CCR5⁺ Tregs in ApoE^–/– have lower Treg-weakening AKT-mTOR signaling, higher expression of inhibitory checkpoint receptors TIGIT and PD-1, and higher expression of IL-10 compared with WT CCR5⁺ Tregs. In conclusion, IL-35 counteracts hyperlipidemia in maintaining Treg-suppressive function by increasing 3 CCR5-amplified mechanisms, including Treg migration, inhibition of Treg weakening AKT-mTOR signaling, and promotion of TIGIT and PD-1 signaling.

Identification of Key Functional Modules and Immunomodulatory Regulators of Hepatocellular Carcinoma

Despite the advances in the treatment of hepatocellular carcinoma (HCC), the prognosis of HCC patients remains unsatisfactory due to postsurgical recurrence and treatment resistance. Therefore, it is important to reveal the mechanisms underlying HCC and identify potential therapeutic targets against HCC, which could facilitate the development of novel therapies. Based on 12 HCC samples and 12 paired paracancerous normal tissues, we identified differentially expressed mRNAs and lncRNAs using the "limma" package in R software. Moreover, we used the weighted gene coexpression network analysis (WGCNA) to analyze the expression data and screened hub genes. Furthermore, we performed pathway enrichment analysis based on the Kyoto Encyclopedia of Genes and Genomes (KEGG) database. In addition, the relative abundance of a given gene set was estimated by single-sample Gene Set Enrichment Analysis. We identified 687 differentially expressed mRNAs and 260 differentially expressed lncRNAs. A total of 6 modules were revealed by WGCNA, and MT1M and MT1E genes from the red module were identified as hub genes. Moreover, pathway analysis revealed the top 10 enriched KEGG pathways of upregulated or downregulated genes. Additionally, we also found that CD58 might act as an immune checkpoint gene in HCC via PD1/CTLA4 pathways and regulate the levels of tumor-infiltrating immune cells in HCC tissues, which might be an immunotherapeutic target in HCC. Our research identified key functional modules and immunomodulatory regulators for HCC, which might offer novel diagnostic biomarkers and/or therapeutic targets for cancer immunotherapy.

Redox Regulation of Tolerogenic Dendritic Cells and Regulatory T Cells in the Pathogenesis and Therapy of Autoimmunity

Significance: Autoimmune diseases are progressively affecting westernized societies, as the proportion of individuals suffering from autoimmunity is steadily increasing over the past decades. Understanding the role of reactive oxygen species (ROS) in modulation of the immune response in the pathogenesis of autoimmune disorders is of utmost importance. The focus of this review is the regulation of ROS production within tolerogenic dendritic cells (tolDCs) and regulatory T (Treg) cells that have the essential role in the prevention of autoimmune diseases and significant potency in their therapy. Recent Advances: It is now clear that ROS are extremely important for the proper function of both DC and T cells. Antigen processing/presentation and the ability of DC to activate T cells depend upon the ROS availability. Treg differentiation, suppressive function, and stability are profoundly influenced by ROS presence. Critical Issues: Although a plethora of results on the relation between ROS and immune cells exist, it remains unclear whether ROS modulation is a productive way for skewing T cells and DCs toward a tolerogenic phenotype. Also, the possibility of ROS modulation for enhancement of regulatory properties of DC and Treg during their preparation for use in cellular therapy has to be clarified. Future Directions: Studies of DC and T cell redox regulation should allow for the improvement of the therapy of autoimmune diseases. This could be achieved through the direct therapeutic application of ROS modulators in autoimmunity, or indirectly through ROS-dependent enhancement of tolDC and Treg preparation for cell-based immunotherapy. Antioxid. Redox Signal. 34, 364-382.

COVID-19: Is there a role for immunonutrition in obese patient?

On December 12, 2019 a new coronavirus (SARS-CoV-2) emerged in Wuhan, China, triggering a pandemic of severe acute respiratory syndrome in humans (COVID-19). Today, the scientific community is investing all the resources available to find any therapy and prevention strategies to defeat COVID-19. In this context, immunonutrition can play a pivotal role in improving immune responses against viral infections. Immunonutrition has been based on the concept that malnutrition impairs immune function. Therefore, immunonutrition involves feeding enriched with various pharmaconutrients (Omega 3 Fatty Acids, Vitamin C, Arginine, Glutamine, Selenium, Zinc, Vitamin, E and Vitamin D) to modulate inflammatory responses, acquired immune response and to improve patient outcomes. In literature, significant evidences indicate that obesity, a malnutrition state, negatively impacts on immune system functionality and on host defense, impairing protection from infections. Immunonutrients can promote patient recovery by inhibiting inflammatory responses and regulating immune function. Immune system dysfunction is considered to increase the risk of viral infections, such as SARS-CoV-2, and was observed in different pathological situations. Obese patients develop severe COVID-19 sequelae, due to the high concentrations of TNF-α, MCP-1 and IL-6 produced in the meantime by visceral and subcutaneous adipose tissue and by innate immunity. Moreover, leptin, released by adipose tissue, helps to increase inflammatory milieu with a dysregulation of the immune response. Additionally, gut microbiota plays a crucial role in the maturation, development and functions of both innate and adaptive immune system, as well as contributing to develop obese phenotype. The gut microbiota has been shown to affect lung health through a vital crosstalk between gut microbiota and lungs, called the "gut-lung axis". This axis communicates through a bi-directional pathway in which endotoxins, or microbial metabolites, may affect the lung through the blood and when inflammation occurs in the lung, this in turn can affect the gut microbiota. Therefore, the modulation of gut microbiota in obese COVID-19 patients can play a key role in immunonutrition therapeutic strategy. This umbrella review seeks to answer the question of whether a nutritional approach can be used to enhance the immune system's response to obesity in obese patients affected by COVID-19.

KLRG1 and CD103 Expressions Define Distinct Intestinal Tissue-Resident Memory CD8 T Cell Subsets Modulated in Crohn's Disease

Intestinal tissue-resident memory CD8 T cells (Trm) are non-recirculating effector cells ideally positioned to detect and react to microbial infections in the gut mucosa. There is an emerging understanding of Trm cell differentiation and functions, but their implication in inflammatory bowel diseases, such as Crohn's disease (CD), is still unknown. Here, we describe CD8 cells in the human intestine expressing KLRG1 or CD103, two receptors of E-cadherin. While CD103 CD8 T cells are present in high numbers in the mucosa of CD patients and controls, KLRG1 CD8 T cells are increased in inflammatory conditions. Mucosal CD103 CD8 T cells are more responsive to TCR restimulation, but KLRG1 CD8 T cells show increased cytotoxic and proliferative potential. CD103 CD8 T cells originate mostly from KLRG1 negative cells after TCR triggering and TGFβ stimulation. Interestingly, mucosal CD103 CD8 T cells from CD patients display major changes in their transcriptomic landscape compared to controls. They express Th17 related genes including CCL20, IL22, and IL26, which could contribute to the pathogenesis of CD. Overall, these findings suggest that CD103 CD8 T cells in CD induce a tissue-wide alert increasing innate immune responses and recruitment of effector cells such as KLRG1 CD8 T cells.

Immune cells in the tumour: new routes of retinoids for chemoprevention and chemotherapeutics

Retinoids, vitamin A and its natural and synthetic analogues have various functions, including being involved in cell proliferation and differentiation and participating in the formation of vertebrate morphology. In addition, they may activate certain tumour suppressor genes that then act as tumour inhibitors. In the past decades, retinoids have been regarded as promising chemotherapeutic and chemopreventive agents; however, their mechanisms are still not fully understood. Immune cells that participate in or are associated with the immune response play vital roles in the initiation and development of many cancers. Interestingly, recent studies have demonstrated that retinoids can also exert various effects on immune cells including macrophages, T cells and dendritic cells in tumour tissues to execute anti-tumour actions, providing new insights into chemoprevention and chemotherapeutics. In this review, we focus on the effects of retinoids on immune cells in the tumour, which may provide new approaches for antineoplastic strategies.

The Aryl Hydrocarbon Receptor Preferentially Marks and Promotes Gut Regulatory T Cells

The local environment may affect the development and function of tissue-resident T regulatory cells (Tregs), which are crucial for controlling inflammation. Although the aryl hydrocarbon receptor (Ahr), an environmental sensor, is expressed by Tregs, its role in Treg cell development and/or function remains elusive. Here, we generated mouse genetic models to ablate or activate Ahr expression specifically in Tregs. We showed that Ahr was expressed more abundantly by peripherally induced Tregs (pTregs) in the gut and that its expression was independent of microbiota. Ahr was important for Treg gut homing and function. Ahr inhibited pro-inflammatory cytokines produced by Tregs but was dispensable for Treg stability. Furthermore, Ahr-expressing Tregs had enhanced in vivo suppressive activity compared with Tregs lacking Ahr expression in a T cell transfer model of colitis. Our data suggest that Ahr signaling in Tregs may be important for gut immune homeostasis.

Commensal Propionibacterium strain UF1 mitigates intestinal inflammation via Th17 cell regulation

Consumption of human breast milk (HBM) attenuates the incidence of necrotizing enterocolitis (NEC), which remains a leading and intractable cause of mortality in preterm infants. Here, we report that this diminution correlates with alterations in the gut microbiota, particularly enrichment of Propionibacterium species. Transfaunation of microbiota from HBM-fed preterm infants or a newly identified and cultured Propionibacterium strain, P. UF1, to germfree mice conferred protection against pathogen infection and correlated with profound increases in intestinal Th17 cells. The induction of Th17 cells was dependent on bacterial dihydrolipoamide acetyltransferase (DlaT), a major protein expressed on the P. UF1 surface layer (S-layer). Binding of P. UF1 to its cognate receptor, SIGNR1, on dendritic cells resulted in the regulation of intestinal phagocytes. Importantly, transfer of P. UF1 profoundly mitigated induced NEC-like injury in neonatal mice. Together, these results mechanistically elucidate the protective effects of HBM and P. UF1-induced immunoregulation, which safeguard against proinflammatory diseases, including NEC.

Interleukin 17A in atherosclerosis - Regulation and pathophysiologic effector function

This review summarizes the current data on the interleukin (IL)-17A pathway in experimental atherosclerosis and clinical data. IL-17A is a prominent cytokine for early T cell response produced by both innate and adaptive leukocytes. In atherosclerosis, increased total IL-17A levels and expression in CD4⁺ T helper and γδ T cells have been demonstrated. Cytokines including IL-6 and TGFβ that increase IL-17A expression are elevated. Many other factors such as lipids, glucose and sodium chloride concentrations as well as vitamins and arylhydrocarbon receptor agonists that promote IL-17A expression are closely associated with cardiovascular risk in the human population. In acute inflammation models, IL-17A mediates innate leukocyte recruitment of both neutrophils and monocytes. In atherosclerosis, IL-17A increased aortic macrophage and T cell infiltration in most models. Secondary recruitment effects via the endothelium and according to recent data also pericytes have been demonstrated. IL-17 receptor A is highly expressed on monocytes and direct effects have been reported as well. Beyond leukocyte accumulation, IL-17A may affect other factors of plaque formation such as endothelial function, and according to some reports, fibrous cap formation and vascular relaxation with an increase in blood pressure. Anti-IL-17A agents are now available for clinical use. Cardiovascular side effect profiles are benign at this point. IL-17A appears to be a differential regulator of atherosclerosis and its effects in mouse models suggest that its modulation may have contradictory effects on plaque size and possibly stability in different patient populations.

Lower levels of vitamin A are associated with increased gastrointestinal graft-versus-host disease in children

Vitamin A promotes development of mucosal tolerance and enhances differentiation of regulatory T cells. Vitamin A deficiency impairs epithelial integrity, increasing intestinal permeability. We hypothesized that higher vitamin A levels would reduce the risk of graft-versus-host disease (GVHD) through reduced gastrointestinal (GI) permeability, reduced mucosal injury, and reduced lymphocyte homing to the gut. We tested this hypothesis in a cohort study of 114 consecutive patients undergoing allogeneic stem cell transplant. Free vitamin A levels were measured in plasma at day 30 posttransplant. GI GVHD was increased in patients with vitamin A levels below the median (38% vs 12.4% at 100 days, P = .0008), as was treatment-related mortality (17.7% vs 7.4% at 1 year, P = .03). Bloodstream infections were increased in patients with vitamin A levels below the median (24% vs 8% at 1 year, P = .03), supporting our hypothesis of increased intestinal permeability. The GI mucosal intestinal fatty acid-binding protein was decreased after transplant, confirming mucosal injury, but was not correlated with vitamin A levels, indicating that vitamin A did not protect against mucosal injury. Expression of the gut homing receptor CCR9 on T-effector memory cells 30 days after transplant was increased in children with vitamin A levels below the median (r = -0.34, P = .03). Taken together, these data support our hypothesis that low levels of vitamin A actively promote GI GVHD and are not simply a marker of poor nutritional status or a sicker patient. Vitamin A supplementation might improve transplant outcomes.

Deposition mode of transforming growth factor-β expressed in transgenic rice seed

Mouse TGF-β highly accumulated by expressing as a secretory homodimeric protein in transgenic rice endosperm. It was tightly deposited in ER-derived PBs by interaction with cysteine-rich prolamins. TGF-β is one of the key players involved in the induction and maintenance of mucosal immune tolerance to dietary proteins through the induction of regulatory T cells. In order to utilize rice-based TGF-β as a tool to promote oral immune tolerance induction, high production of TGF-β is essentially required. When the codon-optimized mTGF-β was expressed as a secretory protein by ligating an N-terminal signal peptide and C-terminal KDEL ER retention signal under the control of the endosperm-specific rice storage protein glutelin GluB-1 promoter, accumulation level was low in stable transgenic rice seeds. Then, to increase the accumulation level of mTGF-β, it was expressed as fusion proteins by inserting into the C terminus of acidic subunit of glutelin GluA and the variable region of 26 kDa globulin. When fused with the glutelin, it could accumulate well as visible bands by CBB staining gel, but not for the 26 kDa globulin. Unexpectedly, expression of homodimeric mTGF-β linked by a 6×Gly1×Ser linker as secretory protein resulted in higher level of accumulation. This expression level was further enhanced by reduction of some endogenous prolamins by RNA interference. The monomeric and dimeric mTGF-βs were deposited in ER-derived PBs containing prolamins. When highly produced in rice seed, it is notable that most of ER-derived PBs were distorted and granulated. Step-wise extraction of storage proteins from rice seeds suggested that the mTGF-β strongly interacted with cysteine-rich prolamins via disulfide bonds. This result was also supported by the finding that reducing agent was absolutely required for mTGF-β extraction.

Retinoic Acid as a Modulator of T Cell Immunity

Vitamin A, a generic designation for an array of organic molecules that includes retinal, retinol and retinoic acid, is an essential nutrient needed in a wide array of aspects including the proper functioning of the visual system, maintenance of cell function and differentiation, epithelial surface integrity, erythrocyte production, reproduction, and normal immune function. Vitamin A deficiency is one of the most common micronutrient deficiencies worldwide and is associated with defects in adaptive immunity. Reports from epidemiological studies, clinical trials and experimental studies have clearly demonstrated that vitamin A plays a central role in immunity and that its deficiency is the cause of broad immune alterations including decreased humoral and cellular responses, inadequate immune regulation, weak response to vaccines and poor lymphoid organ development. In this review, we will examine the role of vitamin A in immunity and focus on several aspects of T cell biology such as T helper cell differentiation, function and homing, as well as lymphoid organ development. Further, we will provide an overview of the effects of vitamin A deficiency in the adaptive immune responses and how retinoic acid, through its effect on T cells can fine-tune the balance between tolerance and immunity.

Thymic and Postthymic Regulation of Naïve CD4(+) T-Cell Lineage Fates in Humans and Mice Models

Our understanding of how thymocytes differentiate into many subtypes has been increased progressively in its complexity. At early life, the thymus provides a suitable microenvironment with specific combination of stromal cells, growth factors, cytokines, and chemokines to induce the bone marrow lymphoid progenitor T-cell precursors into single-positive CD4⁺ and CD8⁺ T effectors and CD4⁺CD25⁺ T-regulatory cells (Tregs). At postthymic compartments, the CD4⁺ T-cells acquire distinct phenotypes which include the classical T-helper 1 (Th1), T-helper 2 (Th2), T-helper 9 (Th9), T-helper 17 (Th17), follicular helper T-cell (Tfh), and induced T-regulatory cells (iTregs), such as the regulatory type 1 cells (Tr1) and transforming growth factor-β- (TGF-β-) producing CD4⁺ T-cells (Th3). Tregs represent only a small fraction, 5–10% in mice and 1-2% in humans, of the overall CD4⁺ T-cells in lymphoid tissues but are essential for immunoregulatory circuits mediating the inhibition and expansion of all lineages of T-cells. In this paper, we first provide an overview of the major cell-intrinsic developmental programs that regulate T-cell lineage fates in thymus and periphery. Next, we introduce the SV40 immortomouse as a relevant mice model for implementation of new approaches to investigate thymus organogenesis, CD4 and CD8 development, and thymus cells tumorogenesis.

Adoptively transferred Tregs accumulate in a site-specific manner and ameliorate signs of less advanced collagen-induced arthritis progress in rats

AIM

The aim of the study was to assess the therapeutic effect and migration of adoptively transferred Tregs in the course of collagen-induced arthritis (CIA) in rats.

METHODS

Sorted CD4(+)CD25(+) cells were cultured in the presence of 17-β-estradiol, stained with CellTracker and then administered into the articular capsule of ankle joint of animals in different stages of CIA progression.

RESULTS

Tregs diminished CIA signs only in animals with less advanced disease progress. Moreover, migration of transferred cells into the LN in the near proximity of the injection site and with distal location was almost completely stopped in animals with fully developed CIA.

CONCLUSION

Disease progression-related differences in migratory potential of in vitro induced Tregs may be responsible for the failure of cellular therapy during the advanced stages of CIA.

The effects of vitamin A supplementation with measles vaccine on leucocyte counts and in vitro cytokine production

As WHO recommends vitamin A supplementation (VAS) at vaccination contacts after age 6 months, many children receive VAS together with measles vaccine (MV). We aimed to investigate the immunological effect of VAS given with MV. Within a randomised placebo-controlled trial investigating the effect on overall mortality of providing VAS with vaccines in Guinea-Bissau, we conducted an immunological sub-study of VAS v. placebo with MV, analysing leucocyte counts, whole blood in vitro cytokine production, vitamin A status and concentration of C-reactive protein (CRP). VAS compared with placebo was associated with an increased frequency of CRP ≥ 5 mg/l (28 v. 12%; P=0·005). Six weeks after supplementation, VAS had significant sex-differential effects on leucocyte, lymphocyte, monocyte and basophil cell counts, decreasing them in males but increasing them in females. Mainly in females, the effect of VAS on cytokine responses differed by previous VAS: in previous VAS recipients, VAS increased the pro-inflammatory and T helper cell type 1 (Th1) cytokine responses, whereas VAS decreased these responses in previously unsupplemented children. In previous VAS recipients, VAS was associated with increased IFN-γ responses to phytohaemagglutinin in females (geometric mean ratio (GMR): 3·97; 95% CI 1·44, 10·90) but not in males (GMR 0·44; 95% CI 0·14, 1·42); the opposite was observed in previously unsupplemented children. Our results corroborate that VAS provided with MV has immunological effects, which may depend on sex and previous VAS. VAS may increase the number of leucocytes, but also repress both the innate and lymphocyte-derived cytokine responses in females, whereas this repression may be opposite if the females have previously received VAS.

Molecular Mechanisms of the Action of Vitamin A in Th17/Treg Axis in Multiple Sclerosis

Multiple sclerosis (MS) is an autoinflammatory disease of the central nervous system (CNS). The immunopathogenesis of this disease involves an impaired balance of T helper (Th) 17 cells and regulatory T (Tregs) cells. MS is an autoinflammatory disease characterized by the degeneration of the CNS. For many years, MS has been considered to be an autoreactive Th1 and Th17 cell-dominated disease. The activity and number of Th17 cells are increased in MS; however, the function and number of Treg cells are reduced. Therefore, in MS, the balance between Th17 cells and Treg cells is impaired. Th17 cells produce pro-inflammatory cytokines, which play a role in experimental autoimmune encephalomyelitis (EAE) and MS. However, Treg cell-mediated production of cytokines maintains immune homeostasis and can ameliorate the progression of MS. These observations, therefore, confirm the pathogenic and protective role of Th17 and Treg cells, respectively, and highlight the importance of maintaining the balance of both of these cell types. Evidence suggests that vitamin A and its active metabolites (all-trans-retinoic acid and 9-cis-retinoic acid) modulate the imbalance of Th17 and Treg cells through multiple molecular pathways and can be considered as a promising target in the prevention and treatment of MS.

Effect of Retinoic Acid in a Mouse Model of Allergic Rhinitis

PURPOSE

All-trans retinoic acid (ATRA) modulates immune responses by affecting T cells. Several studies have revealed that allergic inflammation of the lower airways is negatively associated with the vitamin A concentration. However, the role of ATRA in allergic inflammation of the upper airways is unclear. We investigated the effects of ATRA in an allergic rhinitis mouse model.

METHODS

BALB/c mice except control groups (CON group) were sensitized with and challenged intra-nasally with Dermatophagoides farina (AR group). The ATRA groups were administered ATRA intraperitoneally. The steroid groups were administered steroid intranasally (ST group). Allergic symptoms and the average eosinophil number were counted. Cytokines and transcription factors were measured by Real-Time PCR and Western blotting. Der f-specific immunoglobulin E (IgE) was measured. Flow cytometry results of CD4⁺CD25⁺Foxp3⁺ T cells were analyzed.

RESULTS

The symptom scores were lower in the ATRA group than in the AR group and higher than in the CON group. The levels of IgE were lower in the ATRA group than in the AR group and higher than in the CON and ST groups. The levels of Foxp3, TGF-β, and IL-10 mRNA, as well as the percentage of CD4⁺CD25⁺Foxp3⁺ T cells, were higher in the ATRA group than in theAR group. In the ATRA group the levels of IFN-γ mRNA were higher, and the levels of GATA-3 and IL-4 mRNA, and ROR-γt were lower. In Western blotting analyses, the expression patterns of all factors, except Foxp3, showed similar to those of mRNA expression.

CONCLUSIONS

ATRA has anti-allergic effects in an allergic rhinitis model, and its underlying mechanisms mainly include the induction of regulatory T cells and the inhibition of Th2 responses.

Alloreactive regulatory T cells generated with retinoic acid prevent skin allograft rejection

CD4(+) CD25(+) Foxp3(+) regulatory T (Treg) cells mediate immunological self-tolerance and suppress immune responses. Retinoic acid (RA), a natural metabolite of vitamin A, has been reported to enhance the differentiation of Treg cells in the presence of TGF-β. In this study, we show that the co-culture of naive T cells from C57BL/6 mice with allogeneic antigen-presenting cells (APCs) from BALB/c mice in the presence of TGF-β, RA, and IL-2 resulted in a striking enrichment of Foxp3(+) T cells. These RA in vitro-induced regulatory T (RA-iTreg) cells did not secrete Th1-, Th2-, or Th17-related cytokines, showed a nonbiased homing potential, and expressed several cell surface molecules related to Treg-cell suppressive potential. Accordingly, these RA-iTreg cells suppressed T-cell proliferation and inhibited cytokine production by T cells in in vitro assays. Moreover, following adoptive transfer, RA-iTreg cells maintained Foxp3 expression and their suppressive capacity. Finally, RA-iTreg cells showed alloantigen-specific immunosuppressive capacity in a skin allograft model in immunodeficient mice. Altogether, these data indicate that functional and stable allogeneic-specific Treg cells may be generated using TGF-β, RA, and IL-2. Thus, RA-iTreg cells may have a potential use in the development of more effective cellular therapies in clinical transplantation.

Retinoid levels influence enterohemorrhagic Escherichia coli infection and Shiga toxin 2 susceptibility in mice

Enterohemorrhagic Escherichia coli (EHEC) is a food-borne pathogen that produces Shiga toxin (Stx) and causes hemorrhagic colitis. Under some circumstances, Stx produced within the intestinal tract enters the bloodstream, leading to systemic complications that may cause the potentially fatal hemolytic-uremic syndrome. Although retinoids like vitamin A (VA) and retinoic acid (RA) are beneficial to gut integrity and the immune system, the effect of VA supplementation on gastrointestinal infections of different etiologies has been controversial. Thus, the aim of this work was to study the influence of different VA status on the outcome of an EHEC intestinal infection in mice. We report that VA deficiency worsened the intestinal damage during EHEC infection but simultaneously improved survival. Since death is associated mainly with Stx toxicity, Stx was intravenously inoculated to analyze whether retinoid levels affect Stx susceptibility. Interestingly, while VA-deficient (VA-D) mice were resistant to a lethal dose of Stx2, RA-supplemented mice were more susceptible to it. Given that peripheral blood polymorphonuclear cells (PMNs) are known to potentiate Stx2 toxicity, we studied the influence of retinoid levels on the absolute number and function of PMNs. We found that VA-D mice had decreased PMN numbers and a diminished capacity to produce reactive oxygen species, while RA supplementation had the opposite effect. These results are in line with the well-known function of retinoids in maintaining the homeostasis of the gut but support the idea that they have a proinflammatory effect by acting, in part, on the PMN population.

Isotretinoin and risk of inflammatory bowel disease: a French nationwide study

OBJECTIVES

Isotretinoin, a drug widely prescribed for severe acne, has been suspected to increase the risk of ulcerative colitis (UC), but data are conflicting. To further examine the association between isotretinoin use and risk for UC and Crohn's disease (CD), we conducted a large nationwide case-control study in France.

METHODS

We used information from the National Health Insurance system for all French people covered by the general scheme between 1 January 2008 and 31 December 2010, totaling over 50 million individuals (i.e., 76% of the whole French population). All incident claims for UC and CD and all medical drug reimbursements were automatically recorded in the database. For each case, four controls were matched on age, gender, year of enrollment, and follow-up duration. The association between isotretinoin use and UC or CD claim was estimated by conditional logistic regression.

RESULTS

We included 7,593 cases of inflammatory bowel disease (IBD; 3,187 UC, 4,397 CD, and 9 indeterminate colitis) and 30,372 controls; among them, 26 cases (0.3%) (15 UC (0.5%) and 11 CD (0.3%)) and 140 controls (0.4%) were exposed to isotretinoin. Isotretinoin exposure was not associated with an increased risk for UC (odds ratio (OR)=1.36 (95% confidence intervals (CI): 0.76, 2.45)) but was associated with a decreased risk for CD (OR=0.45 (95% CI: 0.24, 0.85)), P value for homogeneity between UC and CD=0.001. Results were similar in analyses restricted to individuals below the age of 40 years, to cases with colonoscopy or intestinal surgery, or when adjusting for other acne treatments.

CONCLUSIONS

In this population-based case-control study, isotretinoin use was not associated with increased UC risk but was associated with a decreased CD risk. This study provides reassuring data for people using isotretinoin.

The aryl hydrocarbon receptor and food allergy

The immune system is important for protection against pathogens and malignant cells. However, malfunction of the immune system can also result in detrimental auto-immune diseases, inflammatory diseases, cancers and allergies. The aryl hydrocarbon receptor (AhR), present in numerous tissues and cell subsets, including cells of the immune system, plays an important role in the functioning of the immune system. Activation of the AhR is for example associated with various effects on dendritic cells (DCs), regulatory T cells and the Th1/Th2 cell balance. These cells play a major role in the development of food allergy. Food allergy is an increasing health problem in both humans and animals. Despite the knowledge in risk factors and cellular mechanisms for food allergy, no approved treatments are available yet. Recently, it has been shown that activation of the AhR by dioxin-like compounds suppresses allergic sensitization by suppressing the absolute number of precursor and effector T cells, by preserving CD4(+)CD25(+)Foxp3(+) Treg cells and by affecting DCs and their interaction with effector T cells. Future research should elucidate whether and how AhR activation can be used to interfere in food allergic responses in humans and in animals. This may lead to new prevention strategies and therapeutic possibilities for food allergy.

Feeding the immune system

A well-functioning immune system is key to providing good defence against pathogenic organisms and to providing tolerance to non-threatening organisms, to food components and to self. The immune system works by providing an exclusion barrier, by identifying and eliminating pathogens and by identifying and tolerating non-threatening sources of antigens, and by maintaining a memory of immunological encounters. The immune system is complex involving many different cell types distributed throughout the body and many different chemical mediators some of which are involved directly in defence while others have a regulatory role. Babies are born with an immature immune system that fully develops in the first few years of life. Immune competence can decline with ageing. The sub-optimal immune competence that occurs early and late in life increases susceptibility to infection. Undernutrition decreases immune defences, making an individual more susceptible to infection. However, the immune response to an infection can itself impair nutritional status and alter body composition. Practically all forms of immunity are affected by protein-energy malnutrition, but non-specific defences and cell-mediated immunity are most severely affected. Micronutrient deficiencies impair immune function. Here, vitamins A, D and E, and Zn, Fe and Se are discussed. The gut-associated lymphoid tissue is especially important in health and well-being because of its close proximity to a large and diverse population of organisms in the gastrointestinal tract and its exposure to food constituents. Certain probiotic bacteria which modify the gut microbiota enhance immune function in laboratory animals and may do so in human subjects.

Update on the use of transgenic rice seeds in oral immunotherapy

Rice seed provides an ideal production platform for pharmaceuticals in terms of high productivity and stability, as well as the scalability, safety and economy that are expected in plant production systems. Furthermore, these therapeutic products are bioencapsulated in protein bodies, which are seed-specific storage organelles that provide protection from digestion by gastrointestinal enzymes during delivery to the gut-associated lymphoid tissue. Thus, rice seed provides an ideal delivery system for the mucosal immune system. Oral immunotherapy using unprocessed transgenic rice seed containing therapeutic products has been demonstrated to induce effective mucosal immune tolerance and immune reactions against allergies and pathogens.

The Th17 pathway and inflammatory diseases of the intestines, lungs, and skin

The recent discovery of a new CD4+ T cell subset, Th17, has transformed our understanding of the pathogenetic basis of an increasing number of chronic immune-mediated diseases. Particularly in tissues that interface with the microbial environment-such as the intestinal and respiratory tracts and the skin-where most of the Th17 cells in the body reside, dysregulated immunity to self (or the extended self, the diverse microbiota that normally colonize these tissues) can result in chronic inflammatory disease. In this review, we focus on recent advances in the biology of the Th17 pathway and on genome-wide association studies that implicate this immune pathway in human disease involving these tissues.

Mutual expression of the transcription factors Runx3 and ThPOK regulates intestinal CD4⁺ T cell immunity

The gut mucosa hosts large numbers of activated lymphocytes that are exposed to stimuli from the diet, microbiota and pathogens. Although CD4(+) T cells are crucial for defense, intestinal homeostasis precludes exaggerated responses to luminal contents, whether they are harmful or not. We investigated mechanisms used by CD4(+) T cells to avoid excessive activation in the intestine. Using genetic tools to label and interfere with T cell-development transcription factors, we found that CD4(+) T cells acquired the CD8-lineage transcription factor Runx3 and lost the CD4-lineage transcription factor ThPOK and their differentiation into the T(H)17 subset of helper T cells and colitogenic potential, in a manner dependent on transforming growth factor-β (TGF-β) and retinoic acid. Our results demonstrate considerable plasticity in the CD4(+) T cell lineage that allows chronic exposure to luminal antigens without pathological inflammation.

Retinoids: novel immunomodulators and tumour-suppressive agents?

Retinoids play important roles in the transcriptional activity of normal, degenerative and tumour cells. Retinoid analogues may be promising therapeutic agents for the treatment of immune disorders as different as type I diabetes and systemic lupus erythematosus. In addition, the use of retinoids in cancer treatment has progressed significantly in the last two decades; thus, numerous retinoid compounds have been synthesized and tested. In this paper, the actual or potential use of retinoids as immunomodulators or tumour-suppressive agents is discussed.

Retinoid and TGF-β families: crosstalk in development, neoplasia, immunity, and tissue repair

Transforming growth factor-β (TGF-β) isoforms are profibrotic cytokines, par excellence, and have complex multifunctional effects on many systems, depending on the biologic setting. Retinoids are vitamin A derivatives that also have diverse effects in development, physiology, and disease. The interactions between these classes of molecules are, not surprisingly, highly complex and are dependent on the tissue, cellular, and molecular settings.

Vitamin A and retinoic acid in T cell-related immunity

Interest in vitamin A as a regulator of immune function goes back to the early 1900s. Recently, several lines of evidence have converged to show that retinoic acid (RA), a major oxidative metabolite of vitamin A, plays a key role in the differentiation of T cell subsets, the migration of T cells into tissues, and the proper development of T cell-dependent antibody responses. This review discusses evidence from experimental studies that RA promotes the differentiation of regulatory T cells, which help to suppress inflammatory reactions, and plays a significant role in normal mucosal immunity by modulating T cell activation and regulating cell trafficking. RA also promotes antibody responses to T cell-dependent antigens. Conversely, in a state of vitamin A deficiency, inflammatory T cell reactions may be inadequately opposed and therefore become dominant. Although data from human studies are still needed, the framework now developed from studies in mice and rat models suggests that adequate vitamin A status, whether derived from ingestion of preformed retinol or β-carotene, is important for maintaining a proper balance of well-regulated T cell functions and for preventing excessive or prolonged inflammatory reactions.

Barriers of the Human Organism and Their Achilles’ Heels

The human body is covered by barriers separating it from the external and internal surroundings. The “milieu enterieur” has to be stabilised in spite of the variable external and internal conditions of toxic, osmotic, microbial and climatic environmental circumstances. This first line of barriers is composed of skin and mucous membranes of complicated structures.

A second line of barrier system is present in our organisms. Certain organs have to be separated from the immune system and other parts of the body because of evolutionary reasons (eye-bulb and testicles) because of unique proteins “unknown” for the acquired immune system. The blood-brain barrier (BBB) is providing enhanced safety circumstances for the central nervous system. The second line of barriers is represented by the special properties of the capillary endothelial system.

The maternal-fetal barrier is the most complex. At the maternal fetal interface two individuals of two different haplotypes has to be live 9 months separated by a very complicated dynamic barrier.

The placenta is the organ, which is separating the maternal and fetal tissues. Similar to others the bidirectional transport of gasses, metabolites, cells, proteins, regulatory substances, are transported by active or passive transcellular and intercellular mechanisms.

The fetal immune system develops immunotolerance to all maternal cells and antigens transferred transplacentally. The problem is to mitigate the maternal immune system to tolerate the paternal haplotype of the fetus. In the case of normal pregnancy a complex series of physiological modifications can solve the problem without harmful consequences to the mother and fetus.

The outermost contact cells of trophoblasts express instead of HLA-class Ia and class II antigens non-variable HLA-C, HLA-E, HLA-F and HLA-G antigens. The first consequence of this is reduction of the activity of maternal natural killer cells and maternal dendritic cells;

Progesteron, micro-RNA and mediators influence the development of T effector-cells. The production of soluble HLA-G(5 and 6) and IL-10 supports the differentiation of Th-2 CD4⁺ helper cells, reducing the ability of maternal cells to kill fetal cells.

Series of receptors and costimulators are expressed by the different lines of semi-allogenic trophoblast cells to bind HLA-G and mitigate maternal immune response;

The maternal immunotolerance is further facilitated by the activation of CD4⁺CD25^brightFoxp3⁺ regulatory T (T_REG) cells.

Infections have to be prevented during pregnancy. The cells of placenta express 10 Toll-like receptors a group of pattern recognition receptors responsible for innate immunity. The interferon level is also higher in the placental tissues than in the somatic fetal or maternal cells.

The complement system is also adapted to the requirements of the pregnancy and fetal damage is inhibited by the production of “assymmetric IgG antibodies” under hormonal and placental-regulation. These modifications prevent the activation of complement, cytotoxic activity, opsonising ability, antigen clearance and precipitating activity of the molecules.

The Achilles’ heels of the different barriers are regularly found by virus infections. Lamina cribrosa of the blood-brain barrier, optical nerve of the eyes, etc. the risk factors of the maternal-fetal barrier has been summarised in Table 1.1.

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.

Peaceful mutualism in the gut: revealing key commensal bacteria for the creation and maintenance of immunological homeostasis

Quantitative and qualitative aspects of commensal bacteria determine the active and quiescent status of host immunity. In a recent Science paper, Atarashi et al. (2011) identify Clostridium clusters IV and XIVa as indigenous commensal bacteria that induce regulatory T cells for the creation and maintenance of immunological homeostasis.

Immunological Links to Nonspecific Effects of DTwP and BCG Vaccines on Infant Mortality

A number of mainly observational studies suggest that many African females below the age of one year die each year from the nonspecific effects of vaccination with diphtheria-tetanus toxoids and killed (whole-cell) Bordetella pertussis (DTwP). In contrast, similar studies suggest that many African females and males may have their lives saved each year by the nonspecific immunological benefits of Bacillus Calmette-Guerin (BCG) vaccination. From an immunological point of view, we hypothesise that the adverse effects of DTwP vaccine may occur because of the Th2-polarising effect of the aluminium phosphate adjuvant in the vaccine and because intramuscular administration of the vaccine may cause chronic inflammation at the site of injection. However, the Th1-polarising effect of BCG is likely to be beneficial. Sexual dimorphism affecting immune functions and vitamin A supplementation may influence both the deleterious and beneficial nonspecific effects of immunisation.

The impact of vitamin D on regulatory T cells

Epidemiologic studies highlight the increasing prevalence of vitamin D deficiency and insufficiency and its association with an increased risk of autoimmune diseases and poor respiratory function, including asthma. These and additional studies have raised interest in the immunomodulatory properties of vitamin D beyond its well-established role in calcium homeostasis and bone health. Vitamin D has been shown to influence the function of cells intrinsic to innate and adaptive immunity. This review discusses recent evidence that vitamin D promotes--both directly and indirectly--regulatory or suppressor T-cell populations with the capacity to inhibit inappropriate immune responses that cause disease, suggesting that this property may in part underpin the epidemiologic findings.

Nutritional Status Driving Infection by Trypanosoma cruzi: Lessons from Experimental Animals

This paper reviews the scientific knowledge about protein-energy and micronutrient malnutrition in the context of Chagas disease, especially in experimental models. The search of articles was conducted using the electronic databases of SciELO (Scientific Electronic Library Online), PubMed and MEDLINE published between 1960 and March 2010. It was possible to verify that nutritional deficiencies (protein-energy malnutrition and micronutrient malnutrition) exert a direct effect on the infection by T. cruzi. However, little is known about the immunological mechanisms involved in the relationship "nutritional deficiencies and infection by T. cruzi". A hundred years after the discovery of Chagas disease many aspects of this illness still require clarification, including the effects of nutritional deficiencies on immune and pathological mechanisms of T. cruzi infection.

Pathophysiology of food allergy

In this article we review the pathophysiology of food allergy, which affects 4% of US children and 2% of adults, and is increasing in prevalence. Most food allergens share certain specific physicochemical characteristics that allow them to resist digestion, thus enhancing allergenicity. During allergic sensitization, these allergens are encountered by specialized dendritic cell populations in the gut, which leads to T-cell priming and the production of allergen-specific IgE production by B cells. Tissue-resident mast cells then bind IgE, and allergic reactions are elicited when mast cells are reexposed to allergen. Adjacent IgE molecules bound to the surface of the mast cell become cross-linked, causing mast cell degranulation and release of powerful vasoactive compounds that cause allergic symptoms.

Mechanisms of immune tolerance relevant to food allergy

The intestine has an unenviable task: to identify and respond to a constant barrage of environmental stimuli that can be both dangerous and beneficial. The proper execution of this task is central to the homeostasis of the host, and as a result, the gastrointestinal tract contains more lymphocytes than any other tissue compartment in the body, as well as unique antigen-presenting cells with specialized functions. When antigen is initially encountered through the gut, this system generates a robust T cell-mediated hyporesponsiveness called oral tolerance. Although seminal observations of oral tolerance were made a century ago, the relevant mechanisms are only beginning to be unraveled with the use of modern investigational techniques. Food allergy is among the clinical disorders that occur from a failure of this system, and therapies that seek to re-establish tolerance are currently under investigation.