Retinoic acid enhances the T helper 2 cell development that is essential for robust antibody responses through its action on antigen-presenting cells

Vitamin A and vitamin D induced nuclear hormone receptor activation and its impact on B cell differentiation and immunoglobulin production

Vitamin A and vitamin D metabolites are ligands to nuclear receptors - namely RAR, RXR and VDR. The activation of these receptors in human B cells impacts B cell maturation and function. In this review, we discuss how 9-cis retinoic acid (9cRA) and 1,25-dihydroxyvitamin D3 (calcitriol) individually or in conjunction, signal through their nuclear receptors and thereby impact B cell differentiation, immunoglobulin class switching to IgA at the expense of IgE, and also B cell migration and homing. Impact of the vitamin metabolites individually on B cell survival factors are well elucidated, be it the regulation of BAFF and APRIL, the induction of TGF-β or suppression of NF-κB. Very little is known about the impact of 9cRA and calcitriol together on B cells. Recently our group revealed that 9cRA and calcitriol together in the context of the B cell differentiation, induces naïve B cell differentiation into IgA+ plasmablasts, the functional and underlying molecular regulations however require further investigation. In conclusion, the conjunctional impact of these nuclear receptor ligands on B cell functionality is important to better understand B cell dependent clinical outcomes in allergy and autoimmunity. Within this review, we hypothesize that a balance between both vitamins is of utmost importance to provide a robust humoral immune response and a better treatment of disorders characterised by dysregulated immune responses such as IgE-dependent allergy or autoimmunity such as lupus erythematosus.

Hypovitaminosis A Drives the Progression of Tubulointerstitial Lupus Nephritis through Potentiating Predisease Cellular Autoreactivity

Vitamin A (VA) deficiency (VAD) is observed in both humans and mice with lupus nephritis. However, whether VAD is a driving factor for accelerated progression of lupus nephritis is unclear. In this study, we investigated the effect of VAD on the progression of lupus nephritis in a lupus-prone mouse model, MRL/lpr. We initiated VAD either during gestation or after weaning to reveal a potential time-dependent effect. We found exacerbated lupus nephritis at ∼15 wk of age with both types of VAD that provoked tubulointerstitial nephritis leading to renal failure. This was concomitant with significantly higher mortality in all VAD mice. Importantly, restoration of VA levels after weaning reversed VAD-induced mortality. These results suggest VAD-driven acceleration of tubulointerstitial lupus nephritis. Mechanistically, at the earlier time point of 7 wk of age and before the onset of clinical lupus nephritis, continued VAD (from gestation until postweaning) enhanced plasma cell activation and augmented their autoantibody production, while also increasing the expansion of T lymphocytes that could promote plasma cell autoreactivity. Moreover, continued VAD increased the renal infiltration of plasmacytoid dendritic cells. VAD initiated after weaning, in contrast, showed modest effects on autoantibodies and renal plasmacytoid dendritic cells that were not statistically significant. Remarkably, analysis of gene expression in human kidney revealed that the retinoic acid pathway was decreased in the tubulointerstitial region of lupus nephritis, supporting our findings in MRL/lpr mice. Future studies will elucidate the underlying mechanisms of how VAD modulates cellular functions to exacerbate tubulointerstitial lupus nephritis.

Multiple Micronutrient Supplementation: As a Supportive Therapy in the Treatment of COVID-19

During the infection and treatment of the SARS-CoV-2 viral infection, age and comorbidities play a major role in the successful management of COVID-19. The nutritional status changes which occur in the body vary with the age and underlying conditions and has a vital role in the functioning of the immune system and cellular membrane integrity, thus minimizing the vulnerability to the infection. Considering the data already published by eminent researchers, a few micronutrients have shown outstanding results as supportive therapies in the treatment of viral infections. Micronutrient like zinc improves the membrane barrier integrity, has anti-inflammatory activity, and is involved in antibody production. Vitamin A supports the phagocytic activity of macrophages, while vitamin C reduces the worsening of respiratory tract infections by restoring the dysfunctional epithelial barrier of the lungs. Vitamin D, vitamin E, selenium, and omega-3 fatty acid metabolites play a major role in immunomodulation and in the inhibition of proinflammatory cytokine production. Magnesium is involved in the synthesis of antibodies, while copper, vitamin B12, and folate have significant effects on immune cells. A few researchers suggest that iron supplementation has reduced the risk of acquiring respiratory tract infections in children. As the age of the patient increases, the need for micronutrients increases, thus leading to an imbalanced nutritional status which in turn increases the risk and fatality of the infections. The use of micronutrients in modulating the inflammatory, immune responses, and the epithelial barrier integrity is explored during the treatment of viral infections for faster recovery.

Calcitriol and Retinoic acid antagonize each other to suppress the production of IL-9 by Th9 cells

Distinct T helper cells, including Th9 cells help maintain homeostasis in the immune system. Vitamins play pivotal role in the immune system through many mechanisms, including regulating the differentiation of T helper cells. Calcitriol (1,25-dihydroxyvitamin D3) and retinoic acid possess hormone-like properties and are the bioactive metabolites of vitamin D and A, respectively, that signal through heterodimers containing the common retinoid X receptor. In contrast to individual treatment with the vitamins that significantly attenuates IL-9 production from Th9 cells, Th9 cells treated with both vitamins demonstrated IL-9 production similar to untreated Th9 cells. This is associated with reciprocal expression of PU.1 and Foxp3. While the recruitment of PU.1 was significantly impaired to the Il9 gene in the presence of calcitriol or retinoic acid in Th9 cells, addition of both vitamins together increased the recruitment of PU.1 to the Il9 gene. Calcitriol and retinoic acid together impaired the recruitment of HDAC1 to the Il9 gene without impacting Gcn5 recruitment. Importantly, retinoic acid negated the effect of calcitriol and impaired the binding of VDR on the Il9 gene by dampened VDR-RXR formation. Collectively, our data show that calcitriol and retinoic acid antagonize each other to regulate the differentiation of Th9 cells.

Vitamin A controls the allergic response through T follicular helper cell as well as plasmablast differentiation

BACKGROUND

Vitamin A regulates the adaptive immune response and a modulatory impact on type I allergy is discussed. The cellular mechanisms are largely unknown.

OBJECTIVE

To determine the vitamin A-responding specific lymphocyte reaction in vivo.

METHODS

Antigen-specific B and T lymphocytes were analyzed in an adoptive transfer airway inflammation mouse model in response to 9-cis retinoic acid (9cRA) and after lymphocyte-specific genetic targeting of the receptor RARα. Flow cytometry, quantitative PCR, next-generation sequencing, and specific Ig-ELISA were used to characterize the cells functionally.

RESULTS

Systemic 9cRA profoundly enhanced the specific IgA-secreting B-cell frequencies in the lung tissue and serum IgA while reducing serum IgE concentrations. RARα overexpression in antigen-specific B cells promoted differentiation into plasmablasts at the expense of germinal center B cells. In antigen-specific T cells, RARα strongly promoted the differentiation of T follicular helper cells followed by an enhanced germinal center response.

CONCLUSIONS

9cRA signaling via RARα impacts the allergen-specific immunoglobulin response directly by the differentiation of B cells and indirectly by promoting T follicular helper cells.

Nutraceuticals in the Prevention of Viral Infections, including COVID-19, among the Pediatric Population: A Review of the Literature

In recent years, there has been a growth in scientific interest in nutraceuticals, which are those nutrients in foods that have beneficial effects on health. Nutraceuticals can be extracted, used for food supplements, or added to foods. There has long been interest in the antiviral properties of nutraceuticals, which are especially topical in the context of the ongoing COVID-19 pandemic. Therefore, the purpose of this review is to evaluate the main nutraceuticals to which antiviral roles have been attributed (either by direct action on viruses or by modulating the immune system), with a focus on the pediatric population. Furthermore, the possible applications of these substances against SARS-CoV-2 will be considered.

The Role of Micronutrients in Support of the Immune Response against Viral Infections

Viral infections are a leading cause of morbidity and mortality worldwide, and the importance of public health practices including handwashing and vaccinations in reducing their spread is well established. Furthermore, it is well known that proper nutrition can help support optimal immune function, reducing the impact of infections. Several vitamins and trace elements play an important role in supporting the cells of the immune system, thus increasing the resistance to infections. Other nutrients, such as omega-3 fatty acids, help sustain optimal function of the immune system. The main aim of this manuscript is to discuss of the potential role of micronutrients supplementation in supporting immunity, particularly against respiratory virus infections. Literature analysis showed that in vitro and observational studies, and clinical trials, highlight the important role of vitamins A, C, and D, omega-3 fatty acids, and zinc in modulating the immune response. Supplementation with vitamins, omega 3 fatty acids and zinc appears to be a safe and low-cost way to support optimal function of the immune system, with the potential to reduce the risk and consequences of infection, including viral respiratory infections. Supplementation should be in addition to a healthy diet and fall within recommended upper safety limits set by scientific expert bodies. Therefore, implementing an optimal nutrition, with micronutrients and omega-3 fatty acids supplementation, might be a cost-effective, underestimated strategy to help reduce the burden of infectious diseases worldwide, including coronavirus disease 2019 (COVID-19).

The effect of calcitriol and all-trans retinoic acid on T-bet, IFN-γ, GATA3 and IL-4 genes expression in experimental autoimmune encephalomyelitis

Multiple sclerosis (MS) is an immune-mediated inflammatory disease which affects the central nervous system (CNS). In the present study, the in vivo effects of ATRA, calcitriol, and their combinations on the expression of murine CD4+ T cell cytokines and their specific transcription factors in experimental autoimmune encephalomyelitis (EAE)-induced mice were explored. Thirty-two EAE induced inbred C57BL/6 female mice with an age ranged from 8 to 10 weeks were divided into four categories in a random manner. The first, second, and third groups received ATRA, calcitriol, ATRA+ calcitriol, respectively, and the fourth group received vehicle. The treatment started on the day prior to immunization and through the IP injections every other days for 21 days. The dosages of administration for calcitriol, ATRA, and calcitriol+ ATRA were 100 ng, 250 μg, and 50ng + 125 μg, respectively per mouse. An equal volume of excipient was administered for the vehicle group. T-bet, IFN-γ, GATA-3, and IL-4 genes expression were assessed in the splenocytes of EAE -induced mice. The expression of T-bet and IFN-γ genes in the splenocytes of ATRA, calcitriol and combination- treated mice were significantly reduced compared to vehicle group (p < 0.05). A significant decrease in T-bet expression was observed in the combination-treated group compared to the ATRA-treated group (p < 0.05). The expression of GATA3 and IL-4 genes was significantly increased in the ATRA-, calcitriol-, and combination-treated mice when compared with the control group (p < 0.05). Furthermore, the effect of calcitriol alone and in combination with ATRA was more considerable than that of ATRA alone. The nutraceutical approaches may be promising in the prevention and/or treatment of MS.

Effects of supplementation with β-carotene on the growth performance and intestinal mucosal barriers in layer-type cockerels

β-carotene is a robust modulator of mucosal barriers, and it can amplify the immunoglobulin A (IgA) response via the retinoic acid (RA)-mediated pathway. We investigated the influence of β-carotene on intestinal barriers in layer-type cockerels. In this study, β-carotene has a positive influence on growth performance and intestinal morphology. β-carotene remarkably enhanced serum secretory immunoglobulin A (sIgA) levels, jejunal mucosal sIgA, and IgA concentrations. β-Carotene significantly enhanced mRNA expression levels of IgA, CC chemokine receptor-9 (CCR9), polymeric immunoglobulin receptor (pIgR), and retinoic acid receptor α (RARα) in the ileal tissues and pIgR in the jejunal tissues. β-Carotene improves mRNA expression of intestinal barrier-related proteins including: mucin-2 (MUC-2), zonula occludens-2 (ZO-2), occludins (OCLN), and zonula occludens-1 (ZO-1) in the ileal tissues. Moreover, β-carotene decreased the levels of Escherichia coli and elevates the levels of Lactobacillus. The results indicate that β-carotene can promote growth performance and contribute to the gradual development of intestinal barriers in Hyline Brown chicks. This study enriches our knowledge about the effects of β-carotene on intestinal barrier and highlights a theoretical basis of β-carotene application in the poultry industry.

Allergy Modulation by N-3 Long Chain Polyunsaturated Fatty Acids and Fat Soluble Nutrients of the Mediterranean Diet

The Mediterranean diet, containing valuable nutrients such as n-3 long chain poly-unsaturated fatty acids (LCPUFAs) and other fat-soluble micronutrients, is known for its health promoting and anti-inflammatory effects. Its valuable elements might help in the battle against the rising prevalence of non-communicable diseases (NCD), including the development of allergic diseases and other (chronic) inflammatory diseases. The fat fraction of the Mediterranean diet contains bioactive fatty acids but can also serve as a matrix to dissolve and increase the uptake of fat-soluble vitamins and phytochemicals, such as luteolin, quercetin, resveratrol and lycopene with known immunomodulatory and anti-inflammatory capacities. Especially n-3 LCPUFAs such as eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) derived from marine oils can target specific receptors or signaling cascades, act as eicosanoid precursors and/or alter membrane fluidity and lipid raft formation, hereby exhibiting anti-inflammatory properties. Beyond n-3 LCPUFAs, fat-soluble vitamins A, D, E, and K1/2 have the potential to affect pro-inflammatory signaling cascades by interacting with receptors or activating/inhibiting signaling proteins or phosphorylation in immune cells (DCs, T-cells, mast cells) involved in allergic sensitization or the elicitation/effector phase of allergic reactions. Moreover, fat-soluble plant-derived phytochemicals can manipulate signaling cascades, mostly by interacting with other receptors or signaling proteins compared to those modified by fat-soluble vitamins, suggesting potential additive or synergistic actions by applying a combination of these nutrients which are all part of the regular Mediterranean diet. Research concerning the effects of phytochemicals such as polyphenols has been hampered due to their poor bio-availability. However, their solubility and uptake are improved by applying them within the dietary fat matrix. Alternatively, they can be prepared for targeted delivery by means of pharmaceutical approaches such as encapsulation within liposomes or even unique nanoparticles. This review illuminates the molecular mechanisms of action and possible immunomodulatory effects of n-3 LCPUFAs and fat-soluble micronutrients from the Mediterranean diet in allergic disease development and allergic inflammation. This will enable us to further appreciate how to make use of the beneficial effects of n-3 LCPUFAs, fat-soluble vitamins and a selection of phytochemicals as active biological components in allergy prevention and/or symptom reduction.

The Pleiotropic Role of Retinoic Acid/Retinoic Acid Receptors Signaling: From Vitamin A Metabolism to Gene Rearrangements in Acute Promyelocytic Leukemia

The family of retinoic acid receptors (RARs: RARα, -β, and -γ) has remarkable pleiotropy characteristics, since the retinoic acid/RARs pathway is involved in numerous biological processes not only during embryonic development, but also in the postnatal phase and during adulthood. In this review, we trace the roles of RA/RARs signaling in the immune system (where this pathway has both an immunosuppressive role or is involved in the inflammatory response), in hematopoiesis (enhancing hematopoietic stem cell self-renewal, progenitor cells differentiation or maintaining the bone marrow microenvironment homeostasis), and in bone remodeling (where this pathway seems to have controversial effects on bone formation or osteoclast activation). Moreover, in this review is shown the involvement of RAR genes in multiple chromosomal rearrangements generating different fusion genes in hematological neoplasms, with a particular focus on acute promyelocytic leukemia and its variant subtypes. The effect of different RARs fusion proteins on leukemic transformation, on patients’ outcome, and on therapy response is also discussed.

Comorbidity of Vitamin A and Vitamin D Deficiency Exacerbates the Severity of Atopic Dermatitis in Children

<b><i>Background:</i></b> Several studies have suggested that vitamin D (VD) deficiency (VDD) is associated with atopic dermatitis (AD). However, little is known about the relationship between AD and vitamin A (VA). The interaction between VA and VD on AD requires further study. <b><i>Objective:</i></b> We detected serum levels of VA and VD in children with AD to explore how VA deficiency (VAD) and VDD affect AD severity. <b><i>Methods:</i></b> We assessed the SCORing Atopic Dermatitis (SCORAD) index, total immunoglobin E levels and peripheral blood eosinophil counts. VA and VD levels were determined with high-performance liquid chromatography. Correlations among variables were investigated with Pearson’s correlation analysis. <b><i>Results:</i></b> The VD and VA levels were significantly lower in children with AD than in normal children (p &#x3c; 0.001, p = 0.0423). Both VD and VA levels were negatively correlated with SCORAD scores. The SCORAD scores were significantly higher in AD patients with both VDD and VAD (co-deficiency) than in other AD patients. Significant inverse correlations were observed between peripheral blood eosinophil counts and serum VA and VD levels. <b><i>Conclusions:</i></b> VA and VD co-deficiency may exacerbate AD symptoms in children, but the specific mechanism underlying this relationship requires further study. These findings may indicate the need for studies evaluating the use of VD and VA as potential treatments for AD patients.

The Role of the Status of Selected Micronutrients in Shaping the Immune Function

OBJECTIVE

This narrative review gives an overview on the essential role of adequate nutrition to an optimally functioning immune defence. Micronutrients act as regulators of the immune response, with the focus of this review on the immunomodulatory effects of the trace elements iron, zinc and selenium, and the vitamins A, D, E, C, B6 and B12 and folic acid.

RESULTS

Iron deficiency especially impairs the Th1 cell-borne cellular immunity. T lymphocytes are also most affected by a deficiency of zinc, needed for their maturation and the balance between the different T cell subpopulations and acting as a redox signal in the regulation of many enzymes. Selenium is also involved in redox reactions as the glutathione peroxidases and other redox enzymes are selenoproteins. Selenium status has shown special effects on cellular immunity and resistance to viral infections. Vitamin A in the form of retinoic acid induces a humoral Th2 cell response via antigen-presenting cells and is involved in maintaining intestinal immune defence and tolerance through its nuclear receptor RAR and via kinase signalling cascades. Immune tolerance is particularly promoted by vitamin D acting through dendritic cells to stimulate the differentiation of regulatory T cells. Vitamin E has antiinflammatory effects and stimulates naïve T cells especially in the elderly. Besides its antioxidative properties, vitamin C has effects on cell signalling and epigenetic regulation. The B vitamins are required for cytotoxic cellular immunity and modulate T cell responses.

CONCLUSION

A diverse diet and regular exposure to sunlight are the best sources for a balanced nutrient supply to maintain an optimal immune defence.

Effect of vitamin A supplementation on iron status in humans: A systematic review and meta-analysis

Anemia is a worldwide public health problem that can be related to many causes, including vitamin A deficiency. The aim of this study was to assess and estimate the effect of vitamin A supplementation (VAS) on iron status biomarkers and anemia in humans. Six databases, including Cochrane, EMBASE, LILACS, Pubmed, Scopus and Web of Science, were searched for clinical trials and cohort studies that investigated the effect of vitamin A supplementation alone on iron status and anemia, without time-restriction. The search yielded 23 eligible studies, 21 clinical trials and 2 cohort studies, with children, teenagers, pregnant or lactating women. The meta-analysis of the clinical trials showed that VAS reduces the risk of anemia by 26% and raises hemoglobin levels, compared to non-treated group, independent of the life stage. VAS did not alter the prevalence of iron deficiency among the clinical trials conducted with children and teenagers (RR 0.82, 95% CI 0.60 to 1.12, p = 0.204), whereas a significant increase in serum ferritin levels was observed in trials conducted with pregnant and lactating women (WMD 6.61 μg/L; 95% CI 6.00 to 7.21 μg/L; p < 0.001). Therefore, vitamin A supplementation alone may reduce the risk of anemia, by improving hemoglobin and ferritin levels in individuals with low serum retinol levels.

Control of Innate and Adaptive Lymphocytes by the RAR-Retinoic Acid Axis

Lymphocytes, such as T cells, B cells, and innate lymphoid cells (ILCs), play central roles in regulating immune responses. Retinoic acids (RAs) are vitamin A metabolites, produced and metabolized by certain tissue cells and myeloid cells in a tissue-specific manner. It has been established that RAs induce gut-homing receptors on T cells, B cells, and ILCs. A mounting body of evidence indicates that RAs exert far-reaching effects on functional differentiation and fate of these lymphocytes. For example, RAs promote effector T cell maintenance, generation of induced gut-homing regulatory and effector T cell subsets, antibody production by B cells, and functional maturation of ILCs. Key functions of RAs in regulating major groups of innate and adaptive lymphocytes are highlighted in this article.

Retinoic Acid and Retinoic Acid Receptors as Pleiotropic Modulators of the Immune System

Vitamin A is a multifunctional vitamin implicated in a wide range of biological processes. Its control over the immune system and functions are perhaps the most pleiotropic not only for development but also for the functional fate of almost every cell involved in protective or regulatory adaptive or innate immunity. This is especially key at the intestinal border, where dietary vitamin A is first absorbed. Most effects of vitamin A are exerted by its metabolite, retinoic acid (RA), which through ligation of nuclear receptors controls transcriptional expression of RA target genes. In addition to this canonical function, RA and RA receptors (RARs), either as ligand-receptor or separately, play extranuclear, nongenomic roles that greatly expand the multiple mechanisms employed for their numerous and paradoxical functions that ultimately link environmental sensing with immune cell fate. This review discusses RA and RARs and their complex roles in innate and adaptive immunity.

Retinoic Acid and Immune Homeostasis: A Balancing Act

In the immune system, the vitamin A metabolite retinoic acid (RA) is known for its role in inducing gut-homing molecules in T and B cells, inducing regulatory T cells (Tregs), and promoting tolerance. However, it was suggested that RA can have a broad spectrum of effector functions depending on the local microenvironment. Under specific conditions, RA can also promote an inflammatory environment. We discuss the dual role of RA in immune responses and how this might be regulated. Furthermore, we focus on the role of RA in autoimmune diseases and whether RA might be used as a therapeutic agent.

The dual nature of retinoic acid in pemphigus and its therapeutic potential: Special focus on all-trans Retinoic Acid

The efficient treatment of pemphigus with no certain side effect remained a controversial issue. Although there are various options for controlling disease severity, the majority of them may cause serious side effects. Retinoic acid (RA), an active metabolite converted from vitamin A, plays an active role in immune functions. Effects of RA, especially all-trans-Retinoic Acid (ATRA) on different types of cells involved in immune responses were analyzed in vitro and in vivo. RAs could affect the differentiation of T helper (Th) cells, B cells responses, stabilization of both natural regulatory T cells (nTregs) and regulatory B cells (Bregs) populations, and regulating the expression of critical genes in immune responses. The role of RA, based on major immune cells involved in pemphigus has not been addressed so far. In this study, we sought to determine the possible effects of RA, with a special focus on ATRA in pemphigus. All the evidences of ATRA effects on the immune system were collected and their association with the pemphigus was analyzed. According to the previous results, ATRA causes a decline in Th17 populations; increase in CD4+ induced regulatory T cells (iTregs), stabilization of nTregs, and promotion of suppressive B cells, which are critical in the improvement of pemphigus. Nevertheless, it also causes shifting of the Th1:Th2 balance toward Th2 cells, which is not favorable for pemphigus patients. In conclusion, ATRA acts via different ways in pemphigus. Due to increase in the suppressive function via iTregs, nTregs, and Bregs, it is suggested that patients with pemphigus may benefit from systemic ATRA therapy. To clarify this issue, further studies, such as clinical trials are needed.

Vitamin A Deficiency Impairs Induction of Oral Tolerance in Mice

Oral tolerance is a phenomenon of induction of systemic unresponsiveness to antigens ingested by the oral route and loss of immune response. Studies have shown the importance of vitamin A in oral tolerance in vitro but not in an in vivo experimental model. Therefore, we carried out experiments to determine how vitamin A deficiency affects tolerance induction and the ability of mesenteric lymph node (MLN) CD11c(+) cells to induce regulatory T cells (Tregs). Immunological tolerance was induced by oral ovalbumin (OVA) administration in vitamin A-sufficient mice. OVA-specific antibody and cytokine production were significantly reduced. On the other hand, in vitamin A-deficient mice, both OVA-specific antibody and cytokine production were not suppressed by oral OVA administration. Regarding induction of Tregs, the conversion rate of Foxp3(+) cells from naïve CD4(+) cell by CD11c(+) cells was decreased in vitamin A-deficient mice. Our study indicates that vitamin A deficiency causes the breakdown of oral tolerance in vivo.

Modulation of dendritic cell alternative activation and function by the vitamin A metabolite retinoic acid

Retinoic acid modulates the functions of IL-4 in alternatively activated DCs

The archetypal T_h2 cytokine IL-4 has previously been shown to alternatively activate murine macrophages and, more recently, dendritic cells (DCs) both in vitro and in vivo. IL-4 has also been shown to induce Aldh1a2 (aldehyde dehydrogenase 1a2) expression in murine macrophages recruited to the peritoneal cavity. However, the influence of IL-4 on DC Aldh1a2 induction in vivo has not yet been addressed. In this work, we found that DCs show enhanced aldehyde dehydrogenase enzyme activity in vivo, which led us to investigate the impact of the vitamin A metabolite all-trans retinoic acid (RA) on DC alternative activation and function. Antagonism of RA receptors reduced production of resistin-like molecule alpha by DCs responding to IL-4, while addition of exogenous RA enhanced production of this marker of alternative activation. Functionally, RA increased DC induction of CD4⁺ T-cell IL-10, while reducing CD4⁺ T-cell IL-4 and IL-13, revealing a previously unidentified role for RA in regulating the ability of alternatively activated DCs to influence T_h2 polarization.

Race differences in the association between multivitamin exposure and wheezing in preterm infants

OBJECTIVE

We aimed to determine whether vitamin D exposure, as estimated by use of multivitamins, is positively or negatively associated with recurrent wheezing in infants born preterm.

STUDY DESIGN

This prospective cohort study enrolled 300 infants, born at 28(0/7) to 34(6/7) weeks gestational age, and conducted follow-up at 3-, 6-, 9- and 12-month adjusted age.

RESULT

Black (55.9%) and non-black (36.6%) infants experienced recurrent wheezing. Adjusted odds ratios (ORs) for the association between multivitamin exposure at 3 months and recurrent wheezing were 2.15 (95% confidence interval (CI): 0.97, 4.75) for black and 0.43 (95% CI: 0.19, 0.96) for non-black infants with an interaction by race (P=0.003). In lag-effect models, ORs were 2.69 (95% CI: 1.41, 5.14) for black and 0.50 (95% CI: 0.27, 0.92) for non-black infants.

CONCLUSION

Differences by race were seen in association between multivitamins and wheezing; population heterogeneity should be considered when evaluating vitamin supplementation.

Does vitamin A supplementation protect schoolchildren from acquiring soil-transmitted helminthiasis? A randomized controlled trial

Background

Despite the intensive global efforts to control intestinal parasitic infections, the prevalence of soil-transmitted helminth (STH) infections is still very high in many developing countries particularly among children in rural areas.

Methods

A randomized, double-blind, placebo-controlled trial was conducted on 250 Aboriginal schoolchildren in Malaysia to investigate the effects of a single high-dose of vitamin A supplementation (200 000 IU) on STH reinfection. The effect of the supplement was assessed at 3 and 6 months after receiving interventions; after a complete 3-day deworming course of 400 mg/daily of albendazole tablets.

Results

Almost all children (98.6%) were infected with at least one STH species. The overall prevalence of ascariasis, trichuriasis and hookworm infection was 67.8%, 95.5% and 13.4%, respectively. Reinfection rates of Ascaris, Trichuris and hookworm were high; at 6 months, assessment reached 80% of the prevalence reported before treatment. There were no significant differences in the reinfection rates and intensities of STH between vitamin A supplemented-children and those who received placebo at 3 and 6 months (p > 0.05).

Conclusions

Vitamin A supplementation showed no protective effect against STH reinfection and this could be due to the high endemicity of STH in this community. Long-term interventions to reduce poverty will help significantly in reducing this continuing problem and there is no doubt that reducing intestinal parasitic infection would have a positive impact on the health, nutrition and education of these children.

Trial registration

This trial was registered at clinicaltrials.gov as NCT00936091.

Could retinoids be a potential treatment for rheumatic diseases?

Retinoid, a derivative of vitamin A, is a general term used to describe compounds that bind to and activate retinoic acid receptors [RARs (RARα, RARβ, and RARγ)] and/or retinoid X receptors [RXRs (RXRα, RXRβ, and RXRγ)]. They have been shown to surpress the differentiation of Th1/Th17 cells and induce the development of Th1/regulatory T cells. They also affect the proliferation of B cells as both an inducer and suppressor. Furthermore, retinoids may induce the maturation of dendritic cells and production of interleukin-10 from monocytes/macrophages. We recently demonstrated that retinoids suppressed the production of reactive oxygen species, the release of elastase from neutrophils by inhibiting mitogen-activated protein kinase signals, and both the migration speed and chemotaxis directionality of neutrophils. Retinoids, such as all-trans retinoic acid and tamibarotene, were previously shown to have positive effects on animal models of several rheumatic diseases, including arthritis, myositis, and vasculitis in vivo. Moreover, retinoids have been used in a pilot study to effectively treat patients with lupus nephritis and systemic sclerosis. We herein reviewed the effects of retinoids on immune cells, animal models of rheumatic diseases, and rheumatic patients.

Adaptation of innate lymphoid cells to a micronutrient deficiency promotes type 2 barrier immunity

How the immune system adapts to malnutrition to sustain immunity at barrier surfaces, such as the intestine, remains unclear. Vitamin A deficiency is one of the most common micronutrient deficiencies and is associated with profound defects in adaptive immunity. Here, we found that type 3 innate lymphoid cells (ILC3s) are severely diminished in vitamin A-deficient settings, which results in compromised immunity to acute bacterial infection. However, vitamin A deprivation paradoxically resulted in dramatic expansion of interleukin-13 (IL-13)-producing ILC2s and resistance to nematode infection in mice, which revealed that ILCs are primary sensors of dietary stress. Further, these data indicate that, during malnutrition, a switch to innate type 2 immunity may represent a powerful adaptation of the immune system to promote host survival in the face of ongoing barrier challenges.

The retinoic acid receptor agonist Am80 increases mucosal inflammation in an IL-6 dependent manner during Trichuris muris infection

Purpose

Vitamin A metabolites, such as all-trans-retinoic acid (RA) that act through the nuclear receptor; retinoic acid receptor (RAR), have been shown to polarise T cells towards Th2, and to be important in resistance to helminth infections. Co-incidentally, people harbouring intestinal parasites are often supplemented with vitamin A, as both vitamin A deficiency and parasite infections often occur in the same regions of the globe. However, the impact of vitamin A supplementation on gut inflammation caused by intestinal parasites is not yet completely understood.

Methods

Here, we use Trichuris muris, a helminth parasite that buries into the large intestine of mice causing mucosal inflammation, as a model of both human Trichuriasis and IBD, treat with an RARα/β agonist (Am80) and quantify the ensuing pathological changes in the gut.

Results

Critically, we show, for the first time, that rather than playing an anti-inflammatory role, Am80 actually exacerbates helminth-driven inflammation, demonstrated by an increased colonic crypt length and a significant CD4⁺ T cell infiltrate. Further, we established that the Am80-driven crypt hyperplasia and CD4⁺ T cell infiltrate were dependent on IL-6, as both were absent in Am80-treated IL-6 knock-out mice.

Conclusions

This study presents novel data showing a pro-inflammatory role of RAR ligands in T. muris infection, and implies an undesirable effect for the administration of vitamin A during chronic helminth infection.

Electronic supplementary material

The online version of this article (doi:10.1007/s10875-013-9936-8) contains supplementary material, which is available to authorized users.

The effect of vitamin A supplementation on retinoic acid-related orphan receptor γt (RORγt) and interleukin-17 (IL-17) gene expression in Avonex-treated multiple sclerotic patients

The aim of this study was to investigate the role of vitamin A on RORγt and IL-17 gene expression in multiple sclerotic patients. Patients in the vitamin A group received 25,000 IU retinyl palmitate per day, while patients in the placebo group took one capsule of placebo per day for 6 months. Gene expression was measured by real-time PCR at the first and end of the study. The results of this study show that vitamin A downregulates IL-17 and RORγt gene expression. No changes in gene expression occurred in the placebo group.

Host and microbial factors in regulation of T cells in the intestine

The intestine is divided into specialized tissue areas that provide distinct microenvironments for T cells. Regulation of T-cell responses in the gut has been a major focus of recent research activities in the field. T cells in the intestine are regulated by the interplay between host and microbial factors. In the small intestine, retinoic acid (RA) is a major tissue factor that plays important roles in regulation of immune responses. In the large intestine, the influence of RA diminishes, but that of commensal bacterial products increases. RA, gut microbiota, and inflammatory mediators co-regulate differentiation, distribution, and/or effector functions of T cells. Coordinated regulation of immune responses by these factors promotes well-balanced immunity and immune tolerance. Dysregulation of this process can increase infection and inflammatory diseases.

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.

The effect of vitamin a supplementation on biochemical parameters in multiple sclerosis patients

Background

Vitamin A has different functions in the body and after being converted to acid form; it can play many roles in immune system regulation. Therefore, this vitamin can be used as a supplement in the treatment of diseases, such as cancer and autoimmune diseases. Vitamin A is a fat-soluble compound and its long-term consumption in high doses can have some adverse effects.

Objective

The current study aimed to investigate the possible complications and find solutions to minimize the adverse effects.

Patients and Methods

This study was a double blind randomized clinical trial. In the main study, vitamin A (as retinyl palmitate) was given to 35 multiple sclerosis (MS) patients in order to regulate their immune system with a dose of 25000 IU/day for a period of six months. To investigate the possible biochemical complications, lipid profiles, fasting blood sugar (FBS), liver enzymes, and C-reactive protein (CRP) were tested.

Results

Vitamin A did not have a significant difference in lipid profiles, FBS and liver enzymes between the two groups receiving vitamin A and the placebo, but CRP increased in patients who were taking vitamin A, 1.65±0.43 (mg/L) and 2.88±0.67, (Mean±SEM), before and after the intervention respectively (P=0.029), and statistical analysis showed significant differences with the group receiving placebo (P=0.011) and CRP level in vitamin A group was 1.3 mg/L more than those of the placebo group after intervention (P=0.011).

Conclusions

Considering that no significant difference was found in the proven vitamin A side effects, due to the increase in CRP, frequent clinical and biochemical controls are required along with vitamin A supplementation.

Endogenous retinoids in the pathogenesis of alopecia areata

Alopecia areata (AA) is an autoimmune disease that attacks anagen hair follicles. Gene array in graft-induced C3H/HeJ mice revealed that genes involved in retinoic acid (RA) synthesis were increased, whereas RA degradation genes were decreased in AA compared with sham controls. This was confirmed by immunohistochemistry in biopsies from patients with AA and both mouse and rat AA models. RA levels were also increased in C3H/HeJ mice with AA. C3H/HeJ mice were fed a purified diet containing one of the four levels of dietary vitamin A or an unpurified diet 2 weeks before grafting and disease progression followed. High vitamin A accelerated AA, whereas mice that were not fed vitamin A had more severe disease by the end of the study. More hair follicles were in anagen in mice fed high vitamin A. Both the number and localization of granzyme B-positive cells were altered by vitamin A. IFNγ was also the lowest and IL13 highest in mice fed high vitamin A. Other cytokines were reduced and chemokines increased as the disease progressed, but no additional effects of vitamin A were seen. Combined, these results suggest that vitamin A regulates both the hair cycle and immune response to alter the progression of AA.

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.

Retinoic acid signalling in gastrointestinal parasite infections: lessons from mouse models

Retinoic acid or vitamin A is important for an extensive range of biological processes, including immunomodulatory functions, however, its role in gastrointestinal parasite infections is not yet clear. Despite this, parasite infected individuals are often supplemented with vitamin A, given the co-localised prevalence of parasitic infections and vitamin deficiencies. Therefore, it is important to understand the impact of this vitamin on the immune responses to gastrointestinal parasites. Here, we review data regarding the role of retinoic acid signalling in mouse models of intestinal nematode infection, with a view to understanding better the practice of giving vitamin A supplements to worm-infected people.

Vitamin A and immune regulation: role of retinoic acid in gut-associated dendritic cell education, immune protection and tolerance

The vitamin A (VA) metabolite all-trans retinoic acid (RA) plays a key role in mucosal immune responses. RA is produced by gut-associated dendritic cells (DC) and is required for generating gut-tropic lymphocytes and IgA-antibody-secreting cells (IgA-ASC). Moreover, RA modulates Foxp3(+) regulatory T cell (T(REG)) and Th17 effector T cell differentiation. Thus, although RA could be used as an effective "mucosal adjuvant" in vaccines, it also appears to be required for establishing intestinal immune tolerance. Here we discuss the roles proposed for RA in shaping intestinal immune responses and tolerance at the gut mucosal interface. We also focus on recent data exploring the mechanisms by which gut-associated DC acquire RA-producing capacity.

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.

Vitamin A and retinoic acid in the regulation of B-cell development and antibody production

Signaling by vitamin A through its active metabolite retinoic acid (RA) is critical for the normal development and functions of the hematopoietic and immune systems. B cells, as both factories for antibody production and part of the immune regulatory system, are critical to a successful vaccination response. RA is a factor in the development and competence of mature B cells, in B cell proliferation, and in the regulation of transcription factors associated with B cell differentiation, class switch recombination, and the generation of antibody-secreting plasma cells. Emerging evidence suggests that RA can function alone and in combination with other immune system stimuli to augment the formation of germinal centers, leading to increased primary and secondary antibody responses. Taken together, RA could be a useful component in vaccine strategies and/or for immunotherapy.

Retinoic acid production by intestinal dendritic cells

Subpopulations of dendritic cells (DCs) in the small intestine and its related lymphoid organs can produce retinoic acid (RA) from vitamin A (retinol). Through the RA production, these DCs play a pivotal role in imprinting lymphocytes with gut-homing specificity, and contribute to the development of immune tolerance by enhancing the differentiation of Foxp3(+) regulatory T cells and inhibiting that of inflammatory Th17 cells. The RA-producing capacity in these DCs mostly depends on the expression of retinal dehydrogenase 2 (RALDH2, ALDH1A2). It is likely that the RALDH2 expression is induced in DCs by the microenvironmental factors in the small intestine and its related lymphoid organs. The major factor responsible for the RALDH2 expression appears to be GM-CSF. RA itself is essential for the GM-CSF-induced RALDH2 expression. IL-4 and IL-13 also enhance RALDH2 expression, but are dispensable. Toll-like receptor-mediated signals can also enhance the GM-CSF-induced RALDH2 expression in immature DCs.

Vitamin A deficiency alters splenic dendritic cell subsets and increases CD8(+)Gr-1(+) memory T lymphocytes in C57BL/6J mice

Vitamin A-deficient populations have impaired T cell-dependent antibody responses. Dendritic cells (DCs) are the most proficient antigen-presenting cells to naïve T cells. In the mouse, CD11b(+) myeloid DCs stimulate T helper (Th) 2 antibody immune responses, while CD8α(+) lymphoid DCs stimulate Th1 cell-mediated immune responses. Therefore, we hypothesized that vitamin A-deficient animals would have decreased numbers of myeloid DCs and unaffected numbers of lymphoid DCs. We performed dietary depletion of vitamin A in C57BL/6J male and female mice and used multicolor flow cytometry to quantify immune cell populations of the spleen, with particular focus on DC subpopulations. We show that vitamin A-depleted animals have increased polymorphonuclear neutrophils, lymphoid DCs, and memory CD8(+) T cells and decreased CD4(+) T lymphocytes. Therefore, vitamin A deficiency alters splenic DC subpopulations, which may contribute to skewed immune responses of vitamin A-deficient populations.

Neutrophils are immune cells preferentially targeted by retinoic acid in elderly subjects

Background

The immune system gradually deteriorates with age and nutritional status is a major factor in immunosenescence. Of the many nutritional factors implicated in age-related immune dysfunction, vitamin A may be a good candidate, since vitamin A concentrations classically decrease during aging whereas it may possess important immunomodulatory properties via its active metabolites, the retinoic acids. This prompted us to investigate the immune response induced by retinoids in adults and elderly healthy subjects. Before and after oral supplementation with 13cis retinoic acid (0.5 mg/kg/day during 28 days), whole blood cells were phenotyped, and functions of peripheral blood mononuclear cells (PBMC) and polymorphonuclear cells (PMN) were investigated by flow cytometry and ELISA tests.

Results

In both young adults (n = 20, 25 ± 4 years) and older subjects (n = 20, 65 ± 4 years), retinoic acid supplementation had no effect on the distribution of leukocyte subpopulations or on the functions of PBMC (Il-2 and sIl-2R production, membrane expression of CD25). Concerning PMN, retinoic acid induced an increase in both spontaneous migration and cell surface expression of CD11b in the two different age populations, whereas bactericidal activity and phagocytosis remained unchanged.

Conclusions

We demonstrated that retinoic acid induces the same intensity of immune response between adult and older subjects, and more specifically affects PMN functions, i.e. adhesion and migration, than PBMC functions.

Vitamin A as a regulator of antigen presenting cells

Vitamin A has been long associated with immune system competence. Vitamin A deficiency is known to compromise many aspects of both innate and adaptive immune responses. Recent advances in retinol uptake and metabolism have identified the antigen presenting cell (APC) as a central immune cell capable of vitamin A metabolism. APC are now known to express retinaldehyde dehydrogenase and secrete retinoic acid. The retinoic acid produced has both autocrine and paracrine effects. Autocrine effects include upregulation of CD1d nonclassical major histocompatibility class I-like molecule and matrix metalloproteinase-9. Paracrine effects influence multiple lymphocyte lineage cell populations. Specifically, retinoic acid increases IgA isotype class switching by B lymphocytes, enhances regulatory T cell differentiation, and directs homing of lymphocytes to mucosa. CD1d lipid antigen presentation expands natural killer T cell populations. Previously, the focus of vitamin A action in adaptive immunity was on lymphocytes, but these recent advances suggest the APC may be the central player in carrying out the immune system functions of vitamin A.

Vitamin A upregulates matrix metalloproteinase-9 activity by murine myeloid dendritic cells through a nonclassical transcriptional mechanism

Myeloid dendritic cells (DC) are specialized antigen-presenting immune cells. Upon activation in peripheral tissues, DC migrate to lymph nodes to activate T lymphocytes. Matrix metalloproteinase (MMP)-9 is a gelatinase essential for DC migration. We have previously shown that all-trans retinoic acid (atRA), a bioactive metabolite of vitamin A, significantly augmented DC MMP-9 mRNA and protein production. We investigated the mechanisms by which atRA increased MMP-9 activity in vitro. Mouse myeloid DC cultured with atRA demonstrated increased gelatinase activity compared with cells cultured with retinoic acid receptor (RAR)-alpha antagonist. Adding MMP-9 inhibitor significantly blocked DC gelatinase activity and increased adherence of DC in a dose-dependent manner. AtRA-induced Mmp-9 gene expression in DC was blocked by transcriptional inhibition. Because the Mmp-9 promoter contains no canonical retinoic acid response element (RARE), we performed additional studies to determine how atRA regulated DC Mmp-9 transcription. Electrophoretic mobility shift assays for the consensus Sp1, activating protein-1, and nuclear factor-kappaB binding sites located in the Mmp-9 promoter did not indicate greater nuclear protein binding in response to atRA. Chromatin immunoprecipitation assays indicated RARalpha and histone acetyltransferase p300 recruitment to, and acetylation of, histone H3 at the Mmp-9 promoter was greater after atRA treatment. These data suggest that atRA regulated DC adhesion in vitro partly through MMP-9 gelatinase activity. Mmp-9 expression was enhanced through a transcriptional mechanism involving greater RARalpha promoter binding, recruitment of p300, and subsequent histone H3 acetylation, despite the absence of a consensus RARE.

The effect of synthetic retinoid, Am80, on T helper cell development and antibody production in murine collagen-induced arthritis

Retinoids are known to promote T helper (Th)2 and regulatory T cell (Treg) differentiation, and suppress Th1 and Th17 in vitro. Am80, a synthetic retinoid, is reported to ameliorate collagen-induced arthritis (CIA). The aims of this study are to determine the effects of Am80 on CIA in detail, and on Th development and antibody (Ab) production in vivo. Murine CIA was induced by immunization with bovine type II collagen (CII) at days 1 and 22. Treatment with Am80 from day 1 to 35 significantly lowered clinical arthritis score, suppressed cellular infiltration and bone destruction in the joint, decreased interleukin (IL)-17 and increased interferon (IFN)-gamma production by CII-stimulated splenocytes, and decreased proportion of Foxp3(+) splenic CD4 T cells and serum anti-CII Ab levels. Thus, Am80 inhibited Th17 and Treg and enhanced Th1 differentiation in vivo. In contrast, Am80 applied from day 15 to 35 did not alter arthritis score, IL-17 or IFN-gamma production by CII-stimulated splenocytes, but decreased the proportion of Foxp3(+) splenic CD4 T cells and serum anti-CII Ab levels. Am80 exhibits inhibitory effects on CIA and might regulate both Th development and Ab production in vivo. Decreased Th17 by treatment with Am80 might be responsible for the attenuation of arthritis.

Retinoid ameliorates experimental autoimmune myositis, with modulation of Th cell differentiation and antibody production in vivo

OBJECTIVE

Polymyositis and dermatomyositis are chronic inflammatory muscle diseases. Retinoids are compounds that bind to the retinoic acid binding site of retinoic acid receptors and have biologic activities similar to those of vitamin A. Recent studies indicate that retinoids promote Th2 differentiation and suppress Th1 and Th17 differentiation in vitro. The present study was undertaken to examine the effects of a synthetic retinoid, Am80, on experimental autoimmune myositis as well as on Th phenotype development and antibody production.

METHODS

Experimental autoimmune myositis was induced in SJL/J mice by immunization with rabbit myosin. Am80 was administered orally once daily. Its effects were evaluated by measurement of the numbers of infiltrating inflammatory cells, production of inflammatory cytokines in muscle, production of Th-specific cytokines by myosin-stimulated splenic T cells, and production of antimyosin antibodies in serum.

RESULTS

In mice with experimental autoimmune myositis, orally administered Am80 significantly reduced the number of infiltrating inflammatory cells and the expression of tumor necrosis factor alpha and interleukin-1beta (IL-1beta) in muscle. Moreover, Am80 increased production of interferon-gamma, IL-4, and IL-10, but not IL-17, by myosin-stimulated splenic T cells of mice with experimental autoimmune myositis, suggesting that it could enhance differentiation into Th1 and Th2, but not Th17, in vivo. Am80 also decreased serum levels of IgG2a and IgG2b antimyosin antibodies, but did not affect levels of IgG1 antimyosin antibodies. In addition, it suppressed chemokine expression and activator protein 1 activity in myoblasts in vitro.

CONCLUSION

The synthetic retinoid Am80 has an inhibitory effect on experimental autoimmune myositis. It might regulate the development of Th phenotype and antibody production in vivo, in addition to its effects on cytokine and chemokine production.

Expression of retinoic acid receptors in intestinal mucosa and the effect of vitamin A on mucosal immunity

OBJECTIVE

To explore the mechanism of vitamin A (VA) modulation of mucosal immunity, the expression of retinoic acid receptors in intestinal mucosa was measured, and the effect of VA on intestinal dendritic cells (DCs) and mucosal cytokine production was examined.

METHODS

The expression of retinoic acid receptor (RAR-alpha, RAR-beta, RAR-gamma, RXR-alpha, RXR-beta, RXR-gamma) mRNA, the distribution and number of DCs, and the protein secretion of interleukin (IL)-12, T-helper type 1/2 cells (interferon [IFN]-gamma/IL-4), and regulatory (IL-10) cytokines in the mucosa of terminal ileum in normal rats and rats with VA deficiency (VAD) were detected by reverse transcriptase polymerase chain reaction, immunohistochemistry, and enzyme-linked immunosorbent assay, respectively. The effect of all-trans retinoic acid on the number and maturation of DCs and the gene expression of RAR-alpha and cytokines listed earlier in cultured Peyer's patches were examined by flow cytometry and reverse transcriptase polymerase chain reaction, respectively.

RESULTS

In the intestinal mucosa of VAD rats, RAR-alpha mRNA was downregulated, DC number increased, the protein secretion of IL-12 was increased, but the secretion of IFN-gamma and IL-10 decreased. In in vitro cultured Peyer's patches, all-trans retinoic acid promoted DC maturation, upregulated RAR-alpha mRNA, reduced IL-12 and IFN-gamma, but increased IL-10 gene expression; these effects of all-trans retinoic acid were reversed when cultured with Ro 41-5253 (a specific antagonist of RAR-alpha).

CONCLUSION

Vitamin A may be potent in reducing intestinal inflammation and restoring impaired antibody responses in a VAD situation. The effect of VA on DCs could be an important mechanism contributing to altered mucosal immunity. RAR-alpha may mostly play a role in the action of VA.

Vitamin A status is associated with T-cell responses in Bangladeshi men

Recommendations for vitamin A intake are based on maintaining liver stores of > or = 0.070 micromol/g, which is sufficient to maintain normal vision. We propose that higher levels may be required to maintain normal immune function. To test this hypothesis, we conducted an 8-week residential study among thirty-six healthy Bangladeshi men with low vitamin A stores. Subjects were randomised to receive vitamin A (240 mg in four doses) or placebo during study weeks 2 and 3. Vitamin A stores were estimated by isotopic dilution at week 8. Total T-cells, the naive T-cells:memory T-cells ratio and mitogen-induced lymphocyte proliferation were positively and significantly correlated with vitamin A stores (P < 0.05). Mitogen-stimulated IL-2, IL-4 and TNFalpha increased significantly (P < 0.05) in the vitamin A but not placebo group after supplementation, while IL-10 production was significantly and negatively correlated with vitamin A stores (P < 0.05). Segmented linear regression analysis revealed that naive T-cell counts and T-cell blastogenesis were positively associated with vitamin A stores above but not below 0.070 mumol/g liver. These data show that increasing vitamin A stores above the level that maintains normal vision enhances some measures of T-cell-mediated immunity, suggesting a difference in requirements for maintaining vision and immune function.

Does vitamin A supplementation interact with routine vaccinations? An analysis of the Ghana Vitamin A Supplementation Trial

BACKGROUND

The World Health Organization recommends vitamin A supplementation (VAS) at vaccination contacts after 6 mo of age to reduce mortality. However, it is unknown whether the effect of VAS is independent of vaccinations. One of the original VAS trials from Ghana had collected vaccination information.

OBJECTIVE

We reanalyzed the data to explore the hypothesis that VAS reduces mortality in children who had bacille Calmette-Guérin or measles vaccine as their most recent vaccine but increased mortality when diphtheria-tetanus-pertussis vaccine (DTP) was the most recent vaccine. On the basis of previous studies, we expected the effects to be strongest in girls.

DESIGN

At enrollment, children aged 6-90 mo were randomly assigned to receive VAS or placebo every 4 mo for 2 y. Vaccination status was assessed at enrollment and after 1 and 2 y by reviewing the children's health cards. Lack of a health card was presumed to mean that the child had not been vaccinated.

RESULTS

VAS had a beneficial effect only in children with no record of vaccination at enrollment (n = 5066); the mortality rate ratio (MRR) was 0.64 (95% CI: 0.47, 0.88) compared with 0.95 (95% CI: 0.72, 1.26) in children with one or more vaccinations (n = 6656). Among vaccinated children, the effect of VAS differed between boys (MRR: 0.74; 95% CI: 0.51, 1.08) and girls (MRR: 1.18; 95% CI: 0.84, 1.67) (P = 0.046 for interaction). VAS had a negative effect in measles-vaccinated girls who were missing one or more doses of DTP at enrollment, a group who often received DTP during follow-up (MRR: 2.60; 95% CI: 1.41, 4.80).

CONCLUSIONS

The effect of VAS differed by vaccination status. This is potentially problematic because VAS is provided at vaccination contacts.

Toll-like receptor 3 ligand and retinoic acid enhance germinal center formation and increase the tetanus toxoid vaccine response

Immunizations with T-cell-dependent antigens induce the formation of germinal centers (GC), unique lymphoid microenvironments in which antigen-activated B cells undergo class switching, affinity maturation, and differentiation into memory B cells. Poly(I:C) (PIC), a double-stranded RNA, and retinoic acid (RA), a metabolite of vitamin A which induces cell differentiation, have been shown to augment both primary and memory anti-tetanus toxoid (anti-TT) IgG responses. However, their influence on the GC reaction is unknown. In the present study, 6-week-old C57BL/6 mice were immunized with TT and cotreated with PIC, RA, or both. The splenic GC reaction was evaluated using immunofluorescence staining 10 days after TT priming. Each treatment enhanced the TT-induced GC formation (number of GC/follicle and GC area) about two- to threefold, which correlated with the titers of plasma anti-TT immunoglobulin G (IgG). Isotype switching to IgG1 was dramatically stimulated, with the greatest increase in IgG1-positive GC B cells induced by RA-PIC (P < 0.001). Moreover, PIC alone and RA-PIC robustly promoted the formation of the follicular dendritic cell (FDC) network in the GC light zone. PIC and RA-PIC also increased IgG1-positive B cells in the periarterial lymphatic sheath regions, where most IgG1-positive cells were plasma cells (CD138/syndecan-1 positive), suggesting that plasma cell generation was also enhanced in non-GC regions. The stimulation of several processes, including antigen-induced GC formation, isotype switching, FDC network formation within GC, and plasma cell differentiation by RA and/or PIC, suggests that this nutritional-immunological combination could be an effective means of promoting a robust vaccine response.