Respiratory tract epithelial cells express retinaldehyde dehydrogenase ALDH1A and enhance IgA production by stimulated B cells in the presence of vitamin A

How Estrogen, Testosterone, and Sex Differences Influence Serum Immunoglobulin Isotype Patterns in Mice and Humans

Females often exhibit superior immune responses compared to males toward vaccines and pathogens such as influenza viruses and SARS-CoV-2. To help explain these differences, we first studied serum immunoglobulin isotype patterns in C57BL/6 male and female mice. We focused on IgG2b, an isotype that lends to virus control and that has been previously shown to be elevated in murine females compared to males. Improvements in IgG2b serum levels, and/or IgG2b ratios with other non-IgM isotypes, were observed when: (i) wildtype (WT) female mice were compared to estrogen receptor knockout mice (IgG2b, IgG2b/IgG3, IgG2b/IgG1, and IgG2b/IgA were all higher in WT mice), (ii) unmanipulated female mice were compared to ovariectomized mice (IgG2b/IgA was higher in unmanipulated animals), (iii) female mice were supplemented with estrogen in the context of an inflammatory insult (IgG2b and IgG2b/IgG3 were improved by estrogen supplementation), and (iv) male mice were supplemented with testosterone, a hormone that can convert to estrogen in vivo (IgG2b, IgG2b/IgG3, IgG2b/IgG1, and IgG2b/IgA were all improved by supplementation). We next examined data from three sets of previously described male and female human blood samples. In each case, there were higher IgG2 levels, and/or ratios of IgG2 with non-IgM isotypes, in human females compared to males. The effects of sex and sex hormones in the mouse and human studies were subtle, but frequent, suggesting that sex hormones represent only a fraction of the factors that influence isotype patterns. Examination of the gene loci suggested that upregulation of murine IgG2b or human IgG2 could be mediated by estrogen receptor binding to estrogen response elements and cytosine-adenine (CA) repeats upstream of respective Cγ genes. Given that murine IgG2b and human IgG2 lend to virus control, the isotype biases in females may be sufficient to improve outcomes following vaccination or infection. Future attention to sex hormone levels, and consequent immunoglobulin isotype patterns, in clinical trials are encouraged to support the optimization of vaccine and drug products for male and female hosts.

Porcine bile acids promote the utilization of fat and vitamin A under low-fat diets

Fat-soluble vitamin malabsorption may occur due to low dietary fat content, even in the presence of an adequate supply of fat-soluble vitamins. Bile acids (BAs) have been confirmed as emulsifiers to promote fat absorption in high-fat diets. However, there are no direct evidence of exogenous BAs promoting the utilization of fat-soluble vitamins associated with fat absorption in vitro and in vivo. Therefore, we chose laying hens as model animals, as their diet usually does not contain much fat, to expand the study of BAs. BAs were investigated in vitro for emulsification, simulated intestinal digestion, and release rate of fat-soluble vitamins. Subsequently, a total of 450 healthy 45-week-old Hy-Line Gray laying hens were chosen for an 84-day feeding trial. They were divided into five treatments, feeding diets supplemented with 0, 30, 60, 90, and 120 mg/kg BAs, respectively. No extra fat was added to the basic diet (crude fat was 3.23%). In vitro, BAs effectively emulsified the water-oil interface. Moreover, BAs promoted the hydrolysis of fat by lipase to release more fatty acids. Although BAs increased the release rates of vitamins A, D, and E from vegetable oils, BAs improved for the digestion of vitamin A more effectively. Dietary supplementation of 60 mg/kg BAs in laying hens markedly improved the laying performance. The total number of follicles in ovaries increased in 30 and 60 mg/kg BAs groups. Both the crude fat and total energy utilization rates of BAs groups were improved. Lipase and lipoprotein lipase activities were enhanced in the small intestine in 60, 90, and 120 mg/kg BAs groups. Furthermore, we observed an increase in vitamin A content in the liver and serum of laying hens in the 60, 90, and 120 mg/kg BAs groups. The serum IgA content in the 90 and 120 mg/kg BAs groups was significantly improved. A decrease in serum malondialdehyde levels and an increase in glutathione peroxidase activity were also observed in BAs groups. The present study concluded that BAs promoted the absorption of vitamin A by promoting the absorption of fat even under low-fat diets, thereupon improving the reproduction and health of model animals.

Retinol Binding Protein, Sunlight Hours, and the Influenza Virus-Specific Immune Response

Healthy pediatric immune responses depend on adequate vitamin A and D levels. Relationships between solar ultraviolet B (UVB) radiation and vitamin D are well understood, while relationships between sunlight, vitamin A, and its serum escort, retinol binding protein (RBP), are not. A pediatric clinical study enrolled 2–8-year-old children at various times between September 2016 and March 2017, inclusive, in Memphis, Tennessee. A serum sample from each child was then assayed to examine the influence of season on vitamin levels. We found that RBP and RBP/retinol molar ratios decreased in winter months and RBP/retinol ratios correlated positively with the average daily sunlight hours per month. A food frequency questionnaire given to parents/guardians indicated a shift in dietary intake from plant-based foods to animal-based foods by children between winter and spring months. This translated to higher retinol and zinc (integral to RBP–transthyretin–retinol complexes) in the spring, perhaps explaining the seasonal influence on RBP/retinol. RBP and retinol were associated positively with IgG/IgM and IgA/IgM ratios. RBP and retinol, but not 25(OH)D, also correlated positively with influenza virus-specific antibodies. Retinol correlated negatively, while 25(OH)D correlated positively, with certain serum cytokine/chemokine levels. Significant differences in 25(OH)D, immunoglobulin ratios, and cytokines/chemokines were observed between black and white children. In sum, seasonal changes in dietary foods rich in retinol and zinc may have influenced RBP levels, which in turn influenced innate and adaptive immune responses. Results encourage routine monitoring and reporting of season, RBP, and vitamin levels in future clinical studies, as seasons may affect sunlight exposures, diet, vitamin levels, and immune protection against infectious disease.

Hypothesis: Low Vitamin A and D Levels Worsen Clinical Outcomes When Children with Sickle Cell Disease Encounter Parvovirus B19

Human parvovirus B19 causes life-threatening anemia due to transient red cell aplasia (TRCA) in individuals with sickle cell disease (SCD). Children with SCD experiencing profound anemia during TRCA often require red blood cell transfusions and hospitalization. The prevalence of vitamin deficiencies in SCD is high and deficiencies are associated with respiratory and pain symptoms, but the effects of vitamins on acute infection with parvovirus B19 remain unclear. We performed a clinical study in which 20 SCD patients hospitalized with parvovirus B19 infections (Day 0) were monitored over a 120-day time course to query relationships between vitamins A and D and clinical outcomes. There were significant negative correlations between Day 0 vitamin levels and disease consequences (e.g., red blood cell transfusion requirements, inflammatory cytokines). There were significant positive correlations (i) between Day 0 vitamins and peak virus-specific antibodies in nasal wash, and (ii) between Day 0 virus-specific serum plus nasal wash antibodies and absolute reticulocyte counts. There was a significant negative correlation between Day 0 virus-specific serum antibodies and virus loads. To explain the results, we propose circular and complex mechanisms. Low baseline vitamin levels may weaken virus-specific immune responses to permit virus amplification and reticulocyte loss; consequent damage may further reduce vitamin levels and virus-specific immunity. While the complex benefits of vitamins are not fully understood, we propose that maintenance of replete vitamin A and D levels in children with SCD will serve as prophylaxis against parvovirus B19-induced TRCA complications.

Exploring the Immune-Boosting Functions of Vitamins and Minerals as Nutritional Food Bioactive Compounds: A Comprehensive Review

Food components have long been recognized to play a fundamental role in the growth and development of the human body, conferring protective functionalities against foreign matter that can be severe public health problems. Micronutrients such as vitamins and minerals are essential to the human body, and individuals must meet their daily requirements through dietary sources. Micronutrients act as immunomodulators and protect the host immune response, thus preventing immune evasion by pathogenic organisms. Several experimental investigations have been undertaken to appraise the immunomodulatory functions of vitamins and minerals. Based on these experimental findings, this review describes the immune-boosting functionalities of micronutrients and the mechanisms of action through which these functions are mediated. Deficiencies of vitamins and minerals in plasma concentrations can lead to a reduction in the performance of the immune system functioning, representing a key contributor to unfavorable immunological states. This review provides a descriptive overview of the characteristics of the immune system and the utilization of micronutrients (vitamins and minerals) in preventative strategies designed to reduce morbidity and mortality among patients suffering from immune invasions or autoimmune disorders.

Might Routine Vitamin A Monitoring in Cystic Fibrosis Patients Reduce Virus-Mediated Lung Pathology?

Cystic fibrosis (CF) is an autosomal recessive gene disorder that affects tens of thousands of patients worldwide. Individuals with CF often succumb to progressive lung disease and respiratory failure following recurrent infections with bacteria. Viral infections can also damage the lungs and heighten the CF patient's susceptibility to bacterial infections and long-term sequelae. Vitamin A is a key nutrient important for immune health and epithelial cell integrity, but there is currently no consensus as to whether vitamin A should be monitored in CF patients. Here we evaluate previous literature and present results from a CF mouse model, showing that oral vitamin A supplements significantly reduce lung lesions that would otherwise persist for 5-6 weeks post-virus exposure. Based on these results, we encourage continued research and suggest that programs for the routine monitoring and regulation of vitamin A levels may help reduce virus-induced lung pathology in CF patients.

Effect of HIV status and retinol on immunogenicity to oral cholera vaccine in adult population living in an endemic area of Lukanga Swamps, Zambia

Background

We set out to assess the impact of human immunodeficiency virus (HIV) and micronutrient deficiency as indicated by serum retinol levels on the immune responses to Oral Cholera Vaccine (Shanchol™) in a cohort of participants in Lukanga Swamps, Zambia. Cholera remains endemic in Zambia with vaccines being the only effective preventive measures. However, the effect of these vaccines on populations living with HIV has not been widely documented.

Methods

HIV testing and confirmation was done using the Alere Determine™ HIV-1/2 and Uni-Gold™ kits while vibriocidal antibody assay was applied for vaccine immunogenicity. Serum retinol analysis was assessed by Shimadzu Prominence HCT-2010 High Performance Liquid Chromatography (HPLC). The primary outcome was log transformed geometric mean titre.

Results

From 47 participants screened for HIV, 51% (24) tested positive. There was a statistically significant reduction in Ogawa geometric mean ratio (GMR) by 67% (GMR = 0.33; 95% CI: -0.15, 0.76; p-value = 0.009) attributable to HIV positivity with a non-significant reduction in Inaba GMR by about 50% due to HIV positivity. When doubling of retinol levels modelled, GMR reduction against Ogawa were non-significant but that against Inaba resulted in a significant reduction in geometric mean titer (GMT) (GMT-0.33, C.I 0.16–0.66, p-value 0.002). At 1000copies/ml viral load cut off and 350 cells/μl CD4 counts, Ogawa GMT was two times higher 11.16 (95%CI: 8.20–15.19) versus 6.06 (95%CI: 4.04–9.10) in low viremia participants, and three times higher in above threshold CD4 count participants; 24.81 (95%CI: 18.94–32.50) versus 7.07 (95%CI: 5.22–9.58).

Conclusion

Our results show that while Shanchol™ is immunogenic in both HIV+/- individuals, HIV + participants responded poorly. Viral load and CD4 count affected vaccine immunogenicity. More research is required for detailed understanding of this in order to appropriately inform policy and practice.

Nutraceuticals in Viral Infections: An Overview of the Immunomodulating Properties

Nutraceuticals, including vitamin D, vitamin A, zinc, lactoferrin, polyphenols coenzyme Q, magnesium, and selenium, are implicated in the modulation of the complex molecular pathways involved in the immune response against viral pathogens. A common element of the activity of nutraceuticals is their ability to enhance the innate immune response against pathogens by acting on the major cellular subsets and inducing the release of pro-inflammatory cytokines and antimicrobial peptides. In some cases, this action is accompanied by a direct antimicrobial effect, as evidenced in the specific case of lactoferrin. Furthermore, nutraceuticals act through complex molecular mechanisms to minimize the damage caused by the activation of the immune system against pathogens, reducing the oxidative damage, influencing the antigen presentation, enhancing the differentiation and proliferation of regulatory T cells, driving the differentiation of lymphocyte subsets, and modulating the production of pro-inflammatory cytokines. In this paper, we review the main molecular mechanisms responsible for the immunomodulatory function of nutraceuticals, focusing on the most relevant aspects for the prevention and treatment of viral infections.

Association of Food Intake Quality with Vitamin D in SARS-CoV-2 Positive Patients from Mexico: A Cross-Sectional Study

One of the micronutrients that has attracted the most attention in relation to COVID-19 is vitamin D. Although several factors affect its sufficiency; it has been argued that an optimal diet can ensure the intake of micronutrients with effects on immune response. Therefore, in this work we aimed to evaluate the food intake quality of SARS-CoV-2 positive Mexican patients and some of the common factors related to vitamin D deficiency. We conducted a cross-sectional study in 40 SARS-CoV-2 positive patients. Serum samples and clinical parameters were collected. Micronutrient intake and food intake quality were assessed with a 24-h dietary recall and the Mini-ECCA v.2, respectively. Thirty-eight percent of the sample had a healthy food intake. The median 25(OH)D concentration was 22.7 ng/mL. A considerable insufficient intake of micronutrients with immunomodulatory effects such as vitamin D (p < 0.0001), vitamin E (p < 0.0001), and zinc (p < 0.0001) was shown. Patients with 25(OH)D sufficiency, defined as a concentration >30 ng/mL, had better food intake quality (p = 0.02) and an intense physical activity (p = 0.03). In conclusion, a better level of food intake quality and intense physical activity are associated with 25(OH)D sufficiency in SARS-CoV-2 positive Mexican patients.

Treatment of chronic airway diseases using nutraceuticals: Mechanistic insight

Respiratory diseases, both acute and chronic, are reported to be the leading cause of morbidity and mortality, affecting millions of people globally, leading to high socio-economic burden for the society in the recent decades. Chronic inflammation and decline in lung function are the common symptoms of respiratory diseases. The current treatment strategies revolve around using appropriate anti-inflammatory agents and bronchodilators. A range of anti-inflammatory agents and bronchodilators are currently available in the market; however, the usage of such medications is limited due to the potential for various adverse effects. To cope with this issue, researchers have been exploring various novel, alternative therapeutic strategies that are safe and effective to treat respiratory diseases. Several studies have been reported on the possible links between food and food-derived products in combating various chronic inflammatory diseases. Nutraceuticals are examples of such food-derived products which are gaining much interest in terms of its usage for the well-being and better human health. As a consequence, intensive research is currently aimed at identifying novel nutraceuticals, and there is an emerging notion that nutraceuticals can have a positive impact in various respiratory diseases. In this review, we discuss the efficacy of nutraceuticals in altering the various cellular and molecular mechanisms involved in mitigating the symptoms of respiratory diseases.

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

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

Effect of Vitamin A Deficiency in Dysregulating Immune Responses to Influenza Virus and Increasing Mortality Rates After Bacterial Coinfections

BACKGROUND

Secondary bacterial coinfections are ranked as a leading cause of hospitalization and morbid conditions associated with influenza. Because vitamin A deficiency (VAD) and insufficiency are frequent in both developed and developing countries, we asked how VAD influences coinfection severity.

METHODS

VAD and control mice were infected with influenza virus for evaluation of inflammatory cytokines, cellular immune responses, and viral clearance. Influenza-infected mice were coinfected with Streptococcus pneumoniae to study weight loss and survival.

RESULTS

Naive VAD mouse lungs exhibited dysregulated immune function. Neutrophils were enhanced in frequency and there was a significant reduction in RANTES (regulated on activation of normal T cells expressed and secreted), a chemokine instrumental in T-cell homing and recruitment. After influenza virus infection, VAD mice experienced failures in CD4+ T-cell recruitment and B-cell organization into lymphoid structures in the lung. VAD mice exhibited higher viral titers than controls and slow viral clearance. There were elevated levels of inflammatory cytokines and innate cell subsets in the lungs. However, arginase, a marker of alternatively activated M2 macrophages, was rare. When influenza-infected VAD animals were exposed to bacteria, they experienced a 100% mortality rate.

CONCLUSION

Data showed that VAD dysregulated the immune response. Consequently, secondary bacterial infections were 100% lethal in influenza-infected VAD mice.

Consequences of Vitamin A Deficiency: Immunoglobulin Dysregulation, Squamous Cell Metaplasia, Infectious Disease, and Death

Vitamin A is an important regulator of immune protection, but it is often overlooked in studies of infectious disease. Vitamin A binds an array of nuclear receptors (e.g., retinoic acid receptor, peroxisome proliferator-activated receptor, retinoid X receptor) and influences the barrier and immune cells responsible for pathogen control. Children and adults in developed and developing countries are often vitamin A-deficient or insufficient, characteristics associated with poor health outcomes. To gain a better understanding of the protective mechanisms influenced by vitamin A, we examined immune factors and epithelial barriers in vitamin A deficient (VAD) mice, vitamin D deficient (VDD) mice, double deficient (VAD+VDD) mice, and mice on a vitamin-replete diet (controls). Some mice received insults, including intraperitoneal injections with complete and incomplete Freund’s adjuvant (emulsified with PBS alone or with DNA + Fus-1 peptide) or intranasal inoculations with Sendai virus (SeV). Both before and after insults, the VAD and VAD+VDD mice exhibited abnormal serum immunoglobulin isotypes (e.g., elevated IgG2b levels, particularly in males) and cytokine/chemokine patterns (e.g., elevated eotaxin). Even without insult, when the VAD and VAD+VDD mice reached 3–6 months of age, they frequently exhibited opportunistic ascending bacterial urinary tract infections. There were high frequencies of nephropathy (squamous cell hyperplasia of the renal urothelium, renal scarring, and ascending pyelonephritis) and death in the VAD and VAD+VDD mice. When younger VAD mice were infected with SeV, the predominant lesion was squamous cell metaplasia of respiratory epithelium in lungs and bronchioles. Results highlight a critical role for vitamin A in the maintenance of healthy immune responses, epithelial cell integrity, and pathogen control.

Nuclear Receptors, Ligands and the Mammalian B Cell

Questions concerning the influences of nuclear receptors and their ligands on mammalian B cells are vast in number. Here, we briefly review the effects of nuclear receptor ligands, including estrogen and vitamins, on immunoglobulin production and protection from infectious diseases. We describe nuclear receptor interactions with the B cell genome and the potential mechanisms of gene regulation. Attention to the nuclear receptor/ligand regulation of B cell function may help optimize B cell responses, improve pathogen clearance, and prevent damaging responses toward inert- and self-antigens.

From Influenza Virus Infections to Lupus: Synchronous Estrogen Receptor α and RNA Polymerase II Binding Within the Immunoglobulin Heavy Chain Locus

Males and females respond to pathogens differently and exhibit significantly different frequencies of autoimmune disease. For example, vaccinated adult females control influenza virus better than males, but females suffer systemic lupus erythematosus at a 9:1 frequency compared to males. Numerous explanations have been offered for these sex differences, but most have involved indirect mechanisms by which estrogen, a nuclear hormone, modifies cell barriers or immunity. In search of a direct mechanism, we examined the binding of estrogen receptor α (ERα), a class I nuclear hormone receptor, to the immunoglobulin heavy chain locus. Here, we show that in purified murine B cells, ERα and RNA polymerase II (RNA Pol II) exhibit extraordinarily similar DNA binding patterns. We further demonstrate that ERα preferentially binds adenosine-cytidine (AC)-repeats in the immunoglobulin heavy chain locus when supplemental estrogen is added to purified, lipopolysaccharide-activated B cells. Based on these and previous data, we hypothesize that (i) estrogen guides the binding of ERα and its RNA Pol II partner within the locus, which in turn instructs sterile transcription and class switch recombination (CSR), (ii) ERα binding to AC-repeats modifies the DNA architecture and loops associated with CSR, and (iii) by these mechanisms, estrogen instructs antibody expression. By targeting ERα-DNA interactions in the immunoglobulin heavy chain locus, clinicians may ultimately enhance antibody responses in the context of infectious diseases and reduce antibody responses in the context of allergic or autoimmune reactions.

Influences of Vitamin A on Vaccine Immunogenicity and Efficacy

Vitamin A deficiencies and insufficiencies are widespread in developing countries, and may be gaining prevalence in industrialized nations. To combat vitamin A deficiency (VAD), the World Health Organization (WHO) recommends high-dose vitamin A supplementation (VAS) in children 6–59 months of age in locations where VAD is endemic. This practice has significantly reduced all-cause death and diarrhea-related mortalities in children, and may have in some cases improved immune responses toward pediatric vaccines. However, VAS studies have yielded conflicting results, perhaps due to influences of baseline vitamin A levels on VAS efficacy, and due to cross-regulation between vitamin A and related nuclear hormones. Here we provide a brief review of previous pre-clinical and clinical data, showing how VAD and VAS affect immune responses, vaccines, and infectious diseases. We additionally present new results from a VAD mouse model. We found that when VAS was administered to VAD mice at the time of vaccination with a pneumococcal vaccine (Prevnar-13), pneumococcus (T4)-specific antibodies were significantly improved. Preliminary data further showed that after challenge with Streptococcus pneumoniae, all mice that had received VAS at the time of vaccination survived. This was a significant improvement compared to vaccination without VAS. Data encourage renewed attention to vitamin A levels, both in developed and developing countries, to assist interpretation of data from vaccine research and to improve the success of vaccine programs.

Nanoencapsulated retinoic acid as a safe tolerogenic adjuvant for intranasal vaccination against cutaneous leishmaniasis

Mucosal, but not peripheral, vaccination with whole Leishmania amazonensis antigen (LaAg) effectively protects mice against leishmaniasis, likely through a tolerogenic mechanism. Given the crucial role of retinoic acid (RA) in CD4⁺ Foxp3⁺ regulatory T cell (T_reg) differentiation and mucosal tolerance, here we evaluated the capacity of RA to improve intranasal (i.n.) vaccination with LaAg. To prevent degradation and possible mucosa irritation, RA was encapsulated in solid lipid nanoparticles (RA-SLN). Thus, BALB/c mice were given two i.n. doses of LaAg alone or in association with RA-SLN (LaAg/RA-SLN) prior to challenge with L. amazonensis. No histological sign of irritation or inflammation was produced in the nasal mucosa after RA-SLN administration. LaAg/RA-SLN vaccine was more effective in delaying lesion growth and reducing parasite burdens than LaAg alone (96% and 61% reduction, respectively). At two months after challenge, both vaccinated groups displayed similar T helper (Th) 1-skewed in situ cytokine responses, different from early infection where both Th1 and Th2 responses were suppressed, except for transforming growth factor (TGF)-β mRNA, that was higher in mice given RA-SLN. At the mucosa, RA-SLN promoted enhanced expression of interleukin (IL)-10 and CD4⁺ Foxp3⁺ T_reg population. In sum, these data show that RA-SLN is an effective and safe tolerogenic adjuvant for i.n. vaccination against leishmaniasis.

Vitamin A and D in allergy: from experimental animal models and cellular studies to human disease

Introduction

Vitamins A and D are able to modulate innate and adaptive immune responses and may therefore influence the development and the course of allergic diseases.

Materials and methods

This article reviews the current evidence for the experimental effects of vitamins A and D in vivo in animal models and on immune cells in vitro, and discusses their translational implication. A systematic literature search over the last 10 years was performed using MEDLINE and PubMed databases.

Results

Deficiencies of vitamin A or vitamin D in mouse models of allergic asthma seem to exacerbate allergic symptoms along with enhanced lung inflammation and Th2 cytokine production. In contrast, supplementation regimes especially with vitamin D were able to attenuate symptoms in therapeutic mouse models. The active metabolites retinoic acid (RA) and 1,25-dihydroxyvitamin D3 (VD3) induced tolerogenic dendritic cells (DCs) and up-regulated T‑regulatory cells in the allergic sensitization phase, which likely contributes to tolerance induction. Additionally, RA and VD3 maintained the stability of eosinophils and mast cells in the effector phase, thereby reducing allergic mediator release. Thus, both active vitamin metabolites RA and VD3 are able to influence allergic immune responses at several immunological sites.

Conclusion

Animal studies predict that vitamin A and D may also be attractive players in the control of allergy in humans. Whether these experimental observations can be translated to the human situation remains open, as results from clinical trials are controversial.

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.

Impact of Childhood Malnutrition on Host Defense and Infection

The global impact of childhood malnutrition is staggering. The synergism between malnutrition and infection contributes substantially to childhood morbidity and mortality. Anthropometric indicators of malnutrition are associated with the increased risk and severity of infections caused by many pathogens, including viruses, bacteria, protozoa, and helminths. Since childhood malnutrition commonly involves the inadequate intake of protein and calories, with superimposed micronutrient deficiencies, the causal factors involved in impaired host defense are usually not defined. This review focuses on literature related to impaired host defense and the risk of infection in primary childhood malnutrition. Particular attention is given to longitudinal and prospective cohort human studies and studies of experimental animal models that address causal, mechanistic relationships between malnutrition and host defense. Protein and micronutrient deficiencies impact the hematopoietic and lymphoid organs and compromise both innate and adaptive immune functions. Malnutrition-related changes in intestinal microbiota contribute to growth faltering and dysregulated inflammation and immune function. Although substantial progress has been made in understanding the malnutrition-infection synergism, critical gaps in our understanding remain. We highlight the need for mechanistic studies that can lead to targeted interventions to improve host defense and reduce the morbidity and mortality of infectious diseases in this vulnerable population.

Frontline Science: Nasal epithelial GM-CSF contributes to TLR5-mediated modulation of airway dendritic cells and subsequent IgA response

Flagellin, as a TLR5 agonist, is an established mucosal adjuvant for enhancing mucosal IgA responses by i.n. immunization. Nasal epithelial cells (NECs) are the first sentinel cells to be exposed to antigen and adjuvant in i.n. immunization, and it is suggested that they play an important role in the mucosal adjuvant activity of flagellin. However, the molecular mechanism leading to modulation and the response by flagellin-activated NECs remain unknown. We aimed to identify the soluble mediator(s) from flagellin-activated NECs that modulate the functions of airway dendritic cells (DCs) and enhance subsequent IgA response. In vitro studies showed that compared with the TLR4 agonist LPS, flagellin directly triggered slight up-regulation of CD80 on airway DCs but was insufficient to affect CD86 expression and DC-mediated IgA response. With the use of an in vitro system for culturing mouse primary NECs (mNECs), we demonstrated that flagellin-activated mNECs could functionally modulate airway DCs, which manifested as significant up-regulation of CD80/CD86 and enhancement of IgA production. The functional modulation of airway DCs was dependent on TLR5 activation of mNECs rather than direct TLR5 activation of airway DCs. With the use of cytokine array and antibody-blocking assays, we further identified that GM-CSF, a cytokine secreted from TLR5-activated mNECs, contributes to the activation of mNECs to airway DCs and subsequent IgA enhancement. In vivo blocking experiments confirmed that GM-CSF is an important factor in recombinant flagellin derived from Salmonella typhi (FliC)-induced airway DC activation and antigen-specific IgA enhancement. Our data directly demonstrate that nasal epithelial GM-CSF contributes to TLR5-mediated modulation of airway DCs and a subsequent IgA response.

Vitamin A differentially regulates cytokine expression in respiratory epithelial and macrophage cell lines

Vitamin A is an essential nutrient for the protection of children from respiratory tract disease. Supplementation with vitamin A is frequently prescribed in the clinical setting, in part to combat deficiencies among children in developing countries, and in part to treat respiratory infections in clinical trials. This vitamin influences immune responses via multiple, and sometimes seemingly contradictory mechanisms. For example, in separate reports, vitamin A was shown to decrease Th17 T-cell activity by downregulating IL-6, and to promote B cell production of IgA by upregulating IL-6. To explain these apparent contradictions, we evaluated the effects of retinoic acid (RA), a key metabolite of vitamin A, on cell lines of respiratory tract epithelial cells (LETs) and macrophages (MACs). When triggered with LPS or Sendai virus, a mouse respiratory pathogen, these two cell lines experienced opposing influences of RA on IL-6. Both IL-6 protein production and transcript levels were downregulated by RA in LETs, but upregulated in MACs. RA also increased transcript levels of MCP-1, GMCSF, and IL-10 in MACs, but not in LETs. Conversely, when LETs, but not MACs, were exposed to RA, there was an increase in transcripts for RARβ, an RA receptor with known inhibitory effects on cell metabolism. Results help explain past discrepancies in the literature by demonstrating that the effects of RA are cell target dependent, and suggest close attention be paid to cell-specific effects in clinical trials involving vitamin A supplements.

Antibody-secreting cells in respiratory tract tissues in the absence of eosinophils as supportive partners

Antibody-secreting cells (ASCs) in respiratory tract tissues provide a first line of defense against invading pathogens. These cells often secrete IgA that is efficiently transcytosed across epithelial barriers into the airway lumen where pathogens can be blocked at their point of entry. Previous literature has reported that in the bone marrow, eosinophils are required for the maintenance of ASCs, and that eosinophils co-localize with ASCs as nearest neighbors. To determine if these rules similarly apply to the maintenance of ASCs in respiratory tract tissues, we evaluated virus-specific responses 1 month and 4 months following an intranasal virus infection of eosinophil-null (∆dblGATA-1) mice. Results showed that ASCs were fractionally reduced, but were nonetheless observed in respiratory tract tissues in the absence of eosinophils. Virus-specific antibodies were similarly observed in the airways of eosinophil-deficient mice. Respiratory tract ASCs were also present in mice lacking neutrophils (Mcl1^∆M). The staining of tissue sections from the upper respiratory tract of wild-type mice following viral infections demonstrated that virus-specific ASCs were most frequently situated adjacent to epithelial cells rather than eosinophils or neutrophils. Taken together, these data emphasize that rules for cell maintenance are not absolute and that ASCs can survive in the respiratory tract without eosinophils or neutrophils as their nearest neighbors.

Hotspots for Vitamin-Steroid-Thyroid Hormone Response Elements Within Switch Regions of Immunoglobulin Heavy Chain Loci Predict a Direct Influence of Vitamins and Hormones on B Cell Class Switch Recombination

Vitamin A deficiencies are common throughout the world and have a significant negative influence on immune protection against viral infections. Mouse models demonstrate that the production of IgA, a first line of defense against viruses at mucosal sites, is inhibited in the context of vitamin A deficiency. In vitro, the addition of vitamin A to activated B cells can enhance IgA expression, but downregulate IgE. Previous reports have demonstrated that vitamin A modifies cytokine patterns, and in so doing may influence antibody isotype expression by an indirect mechanism. However, we have now discovered hundreds of potential response elements among Sμ, Sɛ, and Sα switch sites within immunoglobulin heavy chain loci. These hotspots appear in both mouse and human loci and include targets for vitamin receptors and related proteins (e.g., estrogen receptors) in the nuclear receptor superfamily. Full response elements with direct repeats are relatively infrequent or absent in Sγ regions although half-sites are present. Based on these results, we pose a hypothesis that nuclear receptors have a direct effect on the immunoglobulin heavy chain class switch recombination event. We propose that vitamin A may alter S site accessibility to activation-induced deaminase and nonhomologous end-joining machinery, thereby influencing the isotype switch, antibody production, and protection against viral infections at mucosal sites.

Vitamin Supplementation at the Time of Immunization with a Cold-Adapted Influenza Virus Vaccine Corrects Poor Mucosal Antibody Responses in Mice Deficient for Vitamins A and D

Vitamin A and D deficiencies and insufficiencies are prevalent worldwide in developed and developing countries. Vitamin metabolites are functionally intertwined in that they are high-affinity ligands for related receptors of the nuclear receptor superfamily. The effects of vitamin A deficiencies (VAD) on antibody responses to respiratory virus vaccines have already been demonstrated. Of particular concern was the reduction in IgA, a first line of defense against pathogens in the respiratory tract. Here, we describe the individual and combined effects of vitamin A and D deficiencies in mice immunized with an attenuated influenza virus vaccine. Relative to VAD, vitamin D deficiency (VDD) had a limited effect, but double deficiencies for vitamins A and D (VAD+VDD) further reduced antibody responses in the respiratory tract. The administration of supplemental vitamins A and D to VAD+VDD mice at the time of vaccination restored responses in a dose-dependent manner. Results suggest that vitamin supplementation programs may be beneficial in a clinical setting to promote healthy immune responses to respiratory virus vaccines in vitamin-deficient individuals.

Retinol binding protein and vitamin D associations with serum antibody isotypes, serum influenza virus-specific neutralizing activities and airway cytokine profiles

Vitamin A supports the induction of immunoglobulin (Ig)A responses at mucosal surfaces in mice, but much less is known about the influence of vitamins on antibody isotype expression in humans. To address this knowledge gap, we examined 46 residual blood samples from adults and children, some of whom were experiencing influenza virus infections of the respiratory tract. Assays were performed for retinol binding protein (RBP, a surrogate for vitamin A), vitamin D (a related vitamin) and antibody isotypes. Results showed that all but two tested samples exhibited RBP and/or vitamin D insufficiencies or deficiencies. Vitamin D correlated with blood IgM and IgG3, while RBP correlated with IgG4 and IgA. RBP also correlated positively with age and with influenza virus-specific antibody neutralization titres. Individuals with low blood RBP levels exhibited the highest frequencies of over-expressed cytokines and growth factors in nasal wash samples, an indication of inflamed mucosal tissues. While cause-effect relationships were not discerned, results support a hypothesis that vitamins directly influence B cell isotype expression in humans, and by so doing may help protect mucosal surfaces from respiratory viral disease.

Can procalcitonin levels indicate the need for adjunctive therapies in sepsis?

After decades of extensive experimental and clinical research, septic shock and the related multiple organ dysfunction still remain the leading cause of mortality in intensive care units (ICUs) worldwide. Defining sepsis is a difficult task, but what is even more challenging is differentiating infection-induced from non-infection-induced systemic inflammatory response-related multiple organ dysfunction. As conventional signs of infection are often unreliable in intensive care, biomarkers are used, of which one of the most frequently investigated is procalcitonin. Early stabilisation of vital functions via adequate supportive therapy and antibiotic treatment has resulted in substantial improvements in outcome over the last decades. However, there are certain patients who may need extra help, hence modulation of the immune system and the host's response may also be an important therapeutic approach in these situations. Polyclonal intravenous immunoglobulins have been used in critical care for decades. A relatively new potential approach could be attenuation of the overwhelming cytokine storm by specific cytokine adsorbents. Both interventions have been applied in daily practice on a large scale, with firm pathophysiological rationale but weak evidence supported by clinical trials. The purpose of this review is to give an overview on the pathophysiology of sepsis as well as the role and interpretation of biomarkers and their potential use in assisting adjunctive therapies in sepsis in the future.

Vitamin A deficient mice exhibit increased viral antigens and enhanced cytokine/chemokine production in nasal tissues following respiratory virus infection despite the presence of FoxP3+ T cells

The World Health Organization (WHO) estimates that 250 million children under the age of five suffer from vitamin A deficiencies (VAD). Individuals with VAD experience higher rates of mortality and increased morbidity during enteric and respiratory infections compared with those who are vitamin A sufficient. Previously, our laboratory has demonstrated that VAD mice have significantly impaired virus-specific IgA and CD8(+) T-cell responses in the airways. Here, we demonstrate that VAD mice experience enhanced cytokine/chemokine gene expression and release in the respiratory tract 10 days following virus infection compared with control vitamin A sufficient animals. Cytokines/chemokines that are reproducibly up-regulated at the gene expression and protein levels include IFNγ and IL-6. Despite previous indications that cytokine dysregulation in VAD animals might reflect low forkhead box P3 (FoxP3)-positive regulatory T-cell frequencies, we found no reduction in FoxP3(+) T cells in VAD respiratory tissues. As an alternative explanation for the high cytokine levels, we found that the extent of virus infection and the persistence of viral antigens were increased on day 10 post-infection in VAD animals compared with controls, and consequently that respiratory tract tissues had an increased potential to activate virus-specific T cells. Results encourage cautious management of viral infections in patients with VAD, as efforts to enhance FoxP3(+) T cell frequencies and quell immune effectors could potentially exacerbate disease if the virus has not been cleared.

Sepsis: From Pathophysiology to Individualized Patient Care

Sepsis has become a major health economic issue, with more patients dying in hospitals due to sepsis related complications compared to breast and colorectal cancer together. Despite extensive research in order to improve outcome in sepsis over the last few decades, results of large multicenter studies were by-and-large very disappointing. This fiasco can be explained by several factors, but one of the most important reasons is the uncertain definition of sepsis resulting in very heterogeneous patient populations, and the lack of understanding of pathophysiology, which is mainly based on the imbalance in the host-immune response. However, this heroic research work has not been in vain. Putting the results of positive and negative studies into context, we can now approach sepsis in a different concept, which may lead us to new perspectives in diagnostics and treatment. While decision making based on conventional sepsis definitions can inevitably lead to false judgment due to the heterogeneity of patients, new concepts based on currently gained knowledge in immunology may help to tailor assessment and treatment of these patients to their actual needs. Summarizing where we stand at present and what the future may hold are the purpose of this review.

Intranasal administration of retinyl palmitate with a respiratory virus vaccine corrects impaired mucosal IgA response in the vitamin A-deficient host

Our previous studies showed that intranasal vaccination of vitamin A-deficient (VAD) mice failed to induce normal levels of upper respiratory tract IgA, a first line of defense against respiratory virus infection. Here we demonstrate that the impaired responses in VAD animals are corrected by a single intranasal application of retinyl palmitate with the vaccine. Results encourage the clinical testing of intranasal vitamin A supplements to improve protection against respiratory viral disease in VAD populations.