Retinoic acid-dependent regulation of immune responses by dendritic cells and macrophages

Investigating the In Vivo Biodistribution of Extracellular Vesicles Isolated from Various Human Cell Sources Using Positron Emission Tomography

Positron emission tomography (PET) is a powerful tool for investigating the in vivo behavior of drug delivery systems. We aimed to assess the biodistribution of extracellular vesicles (EVs), nanosized vesicles secreted by cells isolated from various human cell sources using PET. EVs were isolated from mesenchymal stromal cells (MSCs) (MSC EVs), human macrophages (Mϕ EVs), and a melanoma cell line (A375 EVs) by centrifugation and were conjugated with deferoxamine for radiolabeling with Zr-89. PET using conjugated and radiolabeled EVs evaluated their in vivo biodistribution and tissue tropisms. Our study also investigated differences in mouse models, utilizing immunocompetent and immunocompromised mice and an A375 xenograft tumor model. Lastly, we investigated the impact of different labeling techniques on the observed EV biodistribution, including covalent surface modification and membrane incorporation. PET showed that all tested EVs exhibited extended in vivo circulation and generally low uptake in the liver, spleen, and lungs. However, Mϕ EVs showed high liver uptake, potentially attributable to the intrinsic tissue tropism of these EVs from the surface protein composition. MSC EV biodistribution differed between immunocompetent and immunodeficient mice, with increased spleen uptake observed in the latter. PET using A375 xenografts demonstrated efficient tumor uptake of EVs, but no preferential tissue-specific tropism of A375 EVs was found. Biodistribution differences between labeling techniques showed that surface-conjugated EVs had preferential blood circulation and low liver, spleen, and lung uptake compared to membrane integration. This study demonstrates the potential of EVs as effective drug carriers for various diseases, highlights the importance of selecting appropriate cell sources for EV-based drug delivery, and suggests that EV tropism can be harnessed to optimize therapeutic efficacy. Our findings indicate that the cellular source of EVs, labeling technique, and animal model can influence the observed biodistribution.

ALDH1 immunoexpression in epithelial and stromal cells of oral lichen planus and lesions with lichenoid inflammatory infiltrate

BACKGROUND

Oral Lichen Planus is a potential malignant disorder and shares clinical and histopathological features with other similar lesions. ALDH1 is a specific biomarker for stem cells identification, however its role in stromal cells of immune inflammatory infiltrate has not been explored. The aim of this study was to investigate the ALDH1 immunoexpression in epithelial and stromal cells of Oral Lichen Planus and other lesions with lichenoid inflammatory infiltrate.

MATERIAL AND METHODS

64 samples of Oral Lichen Planus, Oral Lichenoid Lesions, Oral Leukoplakia and Unspecific Chronic Inflammation were included. ALDH1 was evaluated in both epithelium and stromal cells. ALDH1+ cells ≥ 5% were considered positive in epithelium. Stromal cells were evaluated semi quantitatively. Fields were ranked in scores, according to criteria: 1 (0 to 10%); 2 (11 to 50%) and 3 (>50%). The mean value of the sum of the fields was the final score. Statistical differences among groups were investigated, considering p < 0.05.

RESULTS

ALDH1 expression in epithelium was low in all groups without difference among them. ALDH1+ cells in the lamina propria were higher for Lichen Planus [2.0], followed by Leukoplakia [1.3], Lichenoid lesions [1.2] and control [1.1] (p<0.05).

CONCLUSIONS

ALDH1 immunoexpression in epithelium of lichenoid potential malignant disorders did not show a contributory tool, however ALDH1 in stromal cells of lichen planus might be involved in the complex process of immune regulation associated with the pathogenesis of this disease.

Combined Treatment With TGF-β1, Retinoic Acid, and Lactoferrin Robustly Generate Inducible Tregs (iTregs) Against High Affinity Ligand

Forkhead box P3-positive (Foxp3+)-inducible Tregs (iTregs) are readily generated by TGF-β1 at low TCR signaling intensity. TGF-β1-mediated Foxp3 expression is further enhanced by retinoic acid (RA) and lactoferrin (LF). However, the intensity of TCR signaling required for induction of Foxp3 expression by TGF-β1 in combination with RA and LF is unknown. Here, we found that either RA or LF alone decreased TGF-β1-mediated Foxp3 expression at low TCR signaling intensity. In contrast, at high TCR signaling intensity, the addition of either RA or LF strongly increased TGF-β1-mediated Foxp3 expression. Moreover, decreased CD28 stimulation was more favorable for TGF-β1/LF-mediated Foxp3 expression. Lastly, we found that at high signaling intensities of both TCR and CD28, combined treatment with TGF-β1, RA, and LF induced robust expression of Foxp3, in parallel with powerful suppressive activity against responder T cell proliferation. Our findings that TGFβ/RA/LF strongly generate high affinity Ag-specific iTreg population would be useful for the control of unwanted hypersensitive immune reactions such as various autoimmune diseases.

The Impact of Vitamin A Deficiency on Tuberculosis Progression

BACKGROUND

Although previous studies have shown that vitamin A deficiency is associated with incident tuberculosis (TB) disease, the direction of the association has not been established. We investigated the impact of vitamin A deficiency on TB disease progression.

METHODS

We conducted a longitudinal cohort study nested within a randomized clinical trial among HIV-infected patients in Haiti. We compared serial vitamin A levels in individuals who developed TB disease to controls matched on age, gender, follow-up time, and time to antiretroviral therapy initiation. We also evaluated histopathology, bacterial load, and immune outcomes in TB infection in a guinea pig model of dietary vitamin A deficiency.

RESULTS

Among 773 participants, 96 developed incident TB during follow-up, 62.5% (60) of whom had stored serum samples obtained 90-365 days before TB diagnosis. In age- and sex- adjusted and multivariate analyses, respectively, incident TB cases were 3.99 times (95% confidence interval [CI], 2.41 to 6.60) and 3.59 times (95% CI, 2.05 to 6.29) more likely to have been vitamin A deficient than matched controls. Vitamin A-deficient guinea pigs manifested more extensive pulmonary pathology, atypical granuloma morphology, and increased bacterial growth after experimental TB infection. Reintroduction of dietary vitamin A to deficient guinea pigs after established TB disease successfully abrogated severe disease manifestations and altered cellular immune profiles.

CONCLUSIONS

Human and animal studies support the role of baseline vitamin A deficiency as a determinant of future TB disease progression.

Alkannin reverses lipopolysaccharides-induced inflammatory responses by suppressing mitogen-activated protein kinase and nuclear factor kappa-B signalling

Rheumatoid arthritis (RA) is an inflammatory disease that seriously affects human health worldwide. Meanwhile, inflammation in RAW264.7 cells could lead to the progression of RA. Alkannin (ALK) is derived from Alkanna tinctoria and is known to exert anti-tumor effects. However, the function of ALK in inflammation of RAW264.7 cells remains unclear. Thus, this research sought to investigate the detailed function of ALK in inflammatory responses of RAW264.7 cells. To induce an inflammatory response, RAW264.7 cells were exposed to lipopolysaccharide (LPS). MTT assay was applied to examine cell viability. Enzyme-linked immunosorbent assay (ELISA) was used to assess the levels of inflammatory cytokines. Furthermore, the mechanism underlying ALK function in inflammatory responses was investigated using RT-qPCR and western blotting. The data revealed that LPS significantly increased the expression of cyclooxygenase 2 (COX-2), Interleukin (IL)-1β, inducible nitric oxide synthase (iNOS), tumor necrosis factor-α (TNF-α), and IL-6, whereas ALK reversed this effect. ALK also restored LPS-induced nuclear factor kappa-B (NF-κB) activation by inhibiting the downregulation of p-inhibitor kappa B alpha (IκBα). LPS elevated p-extracellular regulated protein kinases 1/2 (ERK1/2), phosphorylated p38 (p-p38), and phosphorylated -c-Jun N-terminal kinase (p-JNK) levels, which were markedly decreased in the presence of ALK. In summary, Alkannin attenuated LPS-induced inflammation by inhibiting NF-κB and MAPK signaling. Thus, our research might provide a new theoretical basis for exploring new strategies against RA.

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.

Retinoic acid restores the levels of cellular cholesterol in Leishmania donovani infected macrophages by increasing npc1 and npc2 expressions

Visceral leishmaniasis (VL) is a fatal form among all forms of leishmaniasis and is caused by visceralization of the Leishmania donovani (Ld) parasite to the critical organs. Mild to severe malnutrition is common in VL patients and the deficiency of retinoic acid (RA), an important micronutrient, results in a compromised state of immune response in macrophages (mφ) leading to the increased parasite load. In the continuation of our earlier work, we observed loss of cellular cholesterol in infected mφ in the absence of RA i.e., upon inhibition of RALDH pathway. Moreover, the Leishmania utilizes host cholesterol for the establishment of infection and causes a decrease in the expressions of Niemann-Pick C2 (npc2) and Niemann-Pick C1 (npc1) genes involved in the uptake of extracellular cholesterol. This results in reduced levels of cellular cholesterol in infected mφ. Intrigued by this, as the first sign of our hypothesis, we investigated the presence of RA Response Element (RARE) sequences in the upstream of npc1 and npc2 genes. To functionally confirm this, we measured their expressions and the levels of cellular cholesterol in Ld infected mφ in the absence (i.e., using an inhibitor of RALDH pathway) and presence of RA. We found restoration of the levels of cellular cholesterol in infected mφ under the supplementation of RA resulting in the decreased parasite load. Hence, the supplementation of RA with the standard therapy and/or preventive use of RA could be potentially an advancement in the treatment and cure of VL patients.

Persistent hypercobalaminemia three months after successful gradual attenuation of extrahepatic shunts in dogs: a prospective cohort study

Background

Deficiencies in vitamin A and D and disorders in the vitamin B complex are often present in people with chronic liver diseases. So far, the serum concentrations of these vitamins have not yet been studied in dogs with congenital extrahepatic portosystemic shunts (EHPSS), who also have some degree of liver dysfunction. The objective was to assess serum vitamin concentrations in dogs with EHPSS from diagnosis to complete closure. A prospective cohort study was performed using ten client-owned dogs with EHPSS, closed after gradual surgical attenuation. Serum concentrations of vitamin A, 25-hydroxyvitamin D, folic acid, cobalamin and methylmalonic acid (MMA) were measured at diagnosis prior to institution of medical therapy, prior to surgery, and three months after gradual attenuation and complete closure of the EHPSS.

Results

At diagnosis, median serum concentrations of vitamin A, 25-hydroxyvitamin D and folic acid were 18.2 μg/dL (8.8 - 79.5 μg/dL), 51.8 ng/mL (19.4 - 109.0 ng/mL), and 8.1 μg/L (5.2 - 14.5 μg/L), respectively, which increased significantly postoperatively (88.3 μg/dL (51.6 - 182.2 μg/dL, P=0.005), 89.6 ng/mL (49.3 - >150.0 ng/mL, P =0.005), and 14.8 μg/L (11.5 - 17.7 μg/L, P <0.001), respectively). Median serum cobalamin concentrations were 735.5 ng/L (470 - 1388 ng/L) at diagnosis and did not significantly decrease postoperatively (P =0.122). Both at diagnosis and three months postoperatively 7/10 dogs had hypercobalaminemia.

Conclusions

Serum concentrations of vitamin A, 25-hydroxyvitamin D and folic acid significantly increase after surgical attenuation. Nevertheless, persistent hypercobalaminemia is suggestive of ongoing liver dysfunction, despite successful surgery.

Diet and Hygiene in Modulating Autoimmunity During the Pandemic Era

The immune system is an efficiently toned machinery that discriminates between friends and foes for achieving both host defense and homeostasis. Deviation of immune recognition from foreign to self and/or long-lasting inflammatory responses results in the breakdown of tolerance. Meanwhile, educating the immune system and developing immunological memory are crucial for mounting defensive immune responses while protecting against autoimmunity. Still to elucidate is how diverse environmental factors could shape autoimmunity. The emergence of a world pandemic such as SARS-CoV-2 (COVID-19) not only threatens the more vulnerable individuals including those with autoimmune conditions but also promotes an unprecedented shift in people's dietary approaches while urging for extraordinary hygiene measures that likely contribute to the development or exacerbation of autoimmunity. Thus, there is an urgent need to understand how environmental factors modulate systemic autoimmunity to better mitigate the incidence and or severity of COVID-19 among the more vulnerable populations. Here, we discuss the effects of diet (macronutrients and micronutrients) and hygiene (the use of disinfectants) on autoimmunity with a focus on systemic lupus erythematosus.

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

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

Immunity boosting nutraceuticals: Current trends and challenges

The immune function of the human body is highly influenced by the dietary intake of certain nutrients and bioactive compounds present in foods. The preventive effects of these bioactive ingredients against various diseases have been well investigated. Functional foods are consumed across various diverse cultures, in some form or the other, which provide benefits greater than the basic nutritional needs. Novel functional foods are being developed using novel bioactive ingredients such as probiotics, polyunsaturated fatty acids, and various phytoconstituents, which have a range of immunomodulatory properties. Apart from immunomodulation, these ingredients also affect immunity by their antioxidant, antibacterial, and antiviral properties. The global pandemic of Severe Acute Respiratory Syndrome Coronavirus-2 has forced the scientific community to race against time to find a proper and effective drug or a vaccine. In this review, various non-pharmacological interventions using nutraceuticals and functional foods have been discussed. PRACTICAL APPLICATIONS: Despite a plethora of research being undertaken to understand the immunity boosting properties of the various bioactive present in food, the findings are not translating to nutraceutical products in the market. Immunity has proved to be one of the most important factors for the health and well-being of an individual, especially when the world has been under the grip of the novel coronavirus Severe Acute Respiratory Syndrome Coronavirus-2. The anti-inflammatory properties of various nutraceuticals can come out as potential inhibitors of the various inflammatory processes such as cytokine storms, usually being observed in COVID 19. This review gives an insight into how various nutraceuticals can help in the prevention of various diseases through different mechanisms. The lack of awareness and proper clinical trials pose a challenge to the nutraceutical industry. This review will help and encourage researchers to further design and develop various functional foods, which might help in building immunity.

Mechanisms underlying enhanced IgA production in Peyer's patch cells by membrane vesicles derived from Lactobacillus sakei

We analyzed the mechanisms underlying enhanced IgA production in the cells of Peyer's patch cells via membrane vesicles derived from Lactobacillus sakei subsp. sakei NBRC 15893. Depletion of CD11c+ cells from Peyer's patch cells suppressed the enhanced IgA production mediated by membrane vesicles. Meanwhile, the stimulation of bone-marrow-derived dendritic cells with membrane vesicles increased gene expression of inducible nitric oxide synthase, retinaldehyde dehydrogenase 2, and several inflammatory cytokines. The production of nitric oxide and interleukin (IL)-6 by membrane vesicle stimulation was induced via Toll-like receptor 2 on bone marrow-derived dendritic cells. Inhibition of inducible nitric oxide synthase and retinaldehyde dehydrogenase 2, as well as the neutralization of IL-6 in Peyer's patch cells, suppressed the enhanced IgA production by membrane vesicle stimulation. Hence, nitric oxide, retinoic acid, and IL-6 induced by membrane vesicles play crucial roles in the enhanced IgA production elicited by membrane vesicles in Peyer's patch cells.

Intestinal Regulatory T Cells as Specialized Tissue-Restricted Immune Cells in Intestinal Immune Homeostasis and Disease

FOXP3+ regulatory T cells (Treg cells) are a specialized population of CD4+ T cells that restrict immune activation and are essential to prevent systemic autoimmunity. In the intestine, the major function of Treg cells is to regulate inflammation as shown by a wide array of mechanistic studies in mice. While Treg cells originating from the thymus can home to the intestine, the majority of Treg cells residing in the intestine are induced from FOXP3neg conventional CD4+ T cells to elicit tolerogenic responses to microbiota and food antigens. This process largely takes place in the gut draining lymph nodes via interaction with antigen-presenting cells that convert circulating naïve T cells into Treg cells. Notably, dysregulation of Treg cells leads to a number of chronic inflammatory disorders, including inflammatory bowel disease. Thus, understanding intestinal Treg cell biology in settings of inflammation and homeostasis has the potential to improve therapeutic options for patients with inflammatory bowel disease. Here, the induction, maintenance, trafficking, and function of intestinal Treg cells is reviewed in the context of intestinal inflammation and inflammatory bowel disease. In this review we propose intestinal Treg cells do not compose fixed Treg cell subsets, but rather (like T helper cells), are plastic and can adopt different programs depending on microenvironmental cues.

Lactate-Dependent Regulation of Immune Responses by Dendritic Cells and Macrophages

For decades, lactate has been considered an innocuous bystander metabolite of cellular metabolism. However, emerging studies show that lactate acts as a complex immunomodulatory molecule that controls innate and adaptive immune cells’ effector functions. Thus, recent advances point to lactate as an essential and novel signaling molecule that shapes innate and adaptive immune responses in the intestine and systemic sites. Here, we review these recent advances in the context of the pleiotropic effects of lactate in regulating diverse functions of immune cells in the tissue microenvironment and under pathological conditions.

CD137 Signaling Regulates Acute Colitis via RALDH2-Expressing CD11b-CD103+ DCs

CD137, a potent costimulatory receptor for CD8⁺ T cells, is expressed in various non-T cells, but little is known about its regulatory functions in these cells. In this study, we show that CD137 signaling, specifically in intestinal CD11b^-CD103⁺ dendritic cells (DCs), restricts acute colitis progression. Mechanistically, CD137 engagement activates TAK1 and subsequently stimulates the AMPK-PGC-1α axis to enhance expression of the Aldh1a2 gene encoding the retinoic acid (RA) metabolizing enzyme RALDH2. RA can act on CD11b⁺CD103^- DCs and induce SOCS3 expression, which, in turn, suppresses p38MAPK activation and interleukin-23 (IL-23) production. Administration of RA in DC-specific CD137^-/- mice represses IL-23-producing CD11b⁺CD103^- DCs and T_H17 cells, indicating that RA is a major inhibitory effector molecule against intestinal CD11b⁺CD103^- DCs. Additionally, the therapeutic effect of the anti-CD137 antibody is abrogated in DC-specific CD137^-/- mice. Taken together, our results define a mechanism of paracrine immunoregulation operating between adjacent DC subsets in the intestine.

The coronavirus disease (COVID-19) - A supportive approach with selected micronutrients

Worldwide the pandemic of COVID-19 spreads rapidly and has had an enormous public health impact with substantial morbidity and mortality especially in high-risk groups, such as older people and patients with comorbidities like diabetes, dementia or cancer. In the absence of a vaccine against COVID-19 there is an urgent need to find supportive therapies that can stabilize the immune system and can help to deal with the infection, especially for vulnerable groups such as the elderly. This is especially relevant for our geriatric institutions and nursing homes. A major potential contributing factor for elderly is due to their high incidence of malnutrition: up to 80% among the hospitalized elderly. Malnutrition results when adequate macronutrients and micronutrients are lacking in the diet. Often missing in public health discussions around preventing and treating COVID-19 patients are nutritional strategies to support optimal function of their immune system. This is surprising, given the importance that nutrients play a significant role for immune function. Several micronutrients, such as vitamin D, retinol, vitamin C, selenium and zinc are of special importance supporting both the adaptive and innate immune systems. As suboptimal status or deficiencies in these immune-relevant micronutrients impair immune function and reduces the resistance to infections, micronutrient deficiencies should therefore be corrected as soon as possible, especially in the elderly and other vulnerable groups. According to epidemiological, experimental and observational studies, some case reports and a few intervention studies the supplementation of vitamin D and/or zinc are promising. The multiple anti-inflammatory and immunomodulatory effects of Vitamin D could explain its protective role against immune hyper reaction and cytokine storm in patients with severe COVID-19. A randomized, placebo-controlled intervention study even shows that high dose vitamin D supplementation promotes viral clearance in asymptomatic and mildly symptomatic SARS-CoV-2 positive individuals. Besides, the data of a recent prospective study with COVID-19 patients reveal that a significant number of them were zinc deficient. The zinc deficient patients had more complications and the deficiency was associated with a prolonged hospital stay and increased mortality. Thus, immune-relevant micronutrients may help to increase the physiological resilience against COVID-19.

p38 MAPK signaling mediates retinoic acid-induced CD103 expression in human dendritic cells

Retinoic acid (RA) is an active derivative of vitamin A and a key regulator of immune cell function. In dendritic cells (DCs), RA drives the expression of CD103 (integrin α_E ), a functionally relevant DC subset marker. In this study, we analyzed the cell type specificity and the molecular mechanisms involved in RA-induced CD103 expression. We show that RA treatment caused a significant up-regulation of CD103 in differentiated monocyte-derived DCs and blood DCs, but not in differentiated monocyte-derived macrophages or T cells. DC treatment with an RA receptor α (RARα) agonist led to an increase in CD103 expression similar to that in RA treatment, whereas RARA gene silencing with small interfering RNA blocked RA-induced up-regulation of CD103, pointing to a major role of RARα in the regulation of CD103 expression. To elucidate RA-induced signaling downstream of RARα, we used Western blot analysis of RA-treated DCs and showed a significant increase of p38 mitogen-activated protein kinase (MAPK) phosphorylation. In addition, DCs cultured with RA and a p38 MAPK inhibitor had a significantly reduced expression of CD103 compared with DCs cultured with RA only, indicating that p38 MAPK is involved in CD103 regulation. In summary, these findings suggest that the RA-induced expression of CD103 is specific to DCs, is mediated primarily through RARα and involves p38 MAPK signaling.

The Need to Consider Context in the Evaluation of Anti-infectious and Immunomodulatory Effects of Vitamin A and its Derivatives

Vitamin A and its derivatives (retinoids) act as potent regulators in many aspects of mammalian reproduction, development, repair, and maintenance of differentiated tissue functioning. Unlike other vitamins, Vitamin A and retinoids, which have hormonal actions, present significant toxicity, which plays roles in clinically relevant situations, such as hypervitaminosis A and retinoic acid ("differentiation") syndrome. Although clinical presentation is conspicuous in states of insufficient or excessive Vitamin A and retinoid concentration, equally relevant effects on host resistance to specific infectious agents, and in the general maintenance of immune homeostasis, may go unnoticed, because their expression requires either pathogen exposure or the presence of inflammatory co-morbidities. There is a vast literature on the roles played by retinoids in the maintenance of a tolerogenic, noninflammatory environment in the gut mucosa, which is considered by many investigators representative of a general role played by retinoids as anti-inflammatory hormones elsewhere. However, in the gut mucosa itself, as well as in the bone marrow and inflammatory sites, context determines whether one observes an anti-inflammatory or proinflammatory action of retinoids. Both interactions between specialized cell populations, and interactions between retinoids and other classes of mediators/regulators, such as cytokines and glucocorticoid hormones, must be considered as important factors contributing to this overall context. We review evidence from recent studies on mucosal immunity, granulocyte biology and respiratory allergy models, highlighting the relevance of these variables as well as their possible contributions to the observed outcomes.

Intestinal Macrophages at the Crossroad between Diet, Inflammation, and Cancer

Intestinal macrophages are key players in the regulation of the oral tolerance, controlling gut homeostasis by discriminating innocuous antigens from harmful pathogens. Diet exerts a significant impact on human health, influencing the composition of gut microbiota and the developing of several non-communicable diseases, including cancer. Nutrients and microbiota are able to modify the profile of intestinal macrophages, shaping their key function in the maintenance of the gut homeostasis. Intestinal disease often occurs as a breakdown of this balance: defects in monocyte-macrophage differentiation, wrong dietary habits, alteration of microbiota composition, and impairment in the resolution of inflammation may contribute to the development of intestinal chronic inflammation and colorectal cancer. Accordingly, dietary interventions and macrophage-targeted therapies are emerging as innovative tools for the treatment of several intestinal pathologies. In this review, we will describe the delicate balance between diet, microbiota and intestinal macrophages in homeostasis and how the perturbation of this equilibrium may lead to the occurrence of inflammatory conditions in the gut. The understanding of the molecular pathways and dietary factors regulating the activity of intestinal macrophages might result in the identification of innovative targets for the treatments of intestinal pathologies.

Inconsistently impairment of immune function and structural integrity of head kidney and spleen by vitamin A deficiency in grass carp (Ctenopharyngodon idella)

To investigate effects of vitamin A (VA) on fish immune function and structural integrity in the head kidney and spleen of fish, total of 540 on-growing grass carp (Ctenopharyngodon idella) were divided into six groups, feeding graded levels of VA (0, 600, 1200, 1800, 2800 and 3800 IU/kg diet) for 70 days. Results showed that dietary VA deficiency depressed antibacterial ability and aggravated inflammatory response partially linked to nuclear factor κB p65 (NF-κB p65) and target of rapamycin (TOR) signaling pathways in the head kidney and spleen of fish. Meanwhile, VA deficiency caused oxidative damage, apoptosis and disruption of tight junctions (TJs), which were partially attributed to the down-regulation of NF-E2-related factor 2 (Nrf2) signaling mediated antioxidant ability, the up-regulation of p38 mitogen-activated protein kinase (p38MAPK) signaling mediated apoptosis and myosin light chain kinase (MLCK) signaling mediated disruption of tight junctions (TJs). Taken together, current study firstly demonstrated that VA deficiency decreased the immune function and damaged the structural integrity of the head kidney and spleen in fish.

Retinoic Acid Exerts Disease Stage-Dependent Effects on Pristane-Induced Lupus

We previously showed that all-trans-retinoic acid (tRA), an active metabolite of vitamin A, exacerbated pre-existing autoimmunity in lupus; however, its effects before the development of autoimmunity are unknown. Here, using a pristane-induced model, we show that tRA exerts differential effects when given at the initiation vs. continuation phase of lupus. Unlike tRA treatment during active disease, pre-pristane treatment with tRA aggravated glomerulonephritis through increasing renal expression of pro-fibrotic protein laminin β1, activating bone marrow conventional dendritic cells (cDCs), and upregulating the interaction of ICAM-1 and LFA-1 in the spleen, indicating an active process of leukocyte activation and trafficking. Transcriptomic analysis revealed that prior to lupus induction, tRA significantly upregulated the expression of genes associated with cDC activation and migration. Post-pristane tRA treatment, on the other hand, did not significantly alter the severity of glomerulonephritis; rather, it exerted immunosuppressive functions of decreasing circulatory and renal deposition of autoantibodies as well as suppressing the renal expression of proinflammatory cytokines and chemokines. Together, these findings suggest that tRA differentially modulate lupus-associated kidney inflammation depending on the time of administration. Interestingly, both pre- and post-pristane treatments with tRA reversed pristane-induced leaky gut and modulated the gut microbiota in a similar fashion, suggesting a gut microbiota-independent mechanism by which tRA affects the initiation vs. continuation phase of lupus.

Human Intestinal Mononuclear Phagocytes in Health and Inflammatory Bowel Disease

Inflammatory bowel disease (IBD), including Crohn's disease and ulcerative colitis, is a complex immune-mediated disease of the gastrointestinal tract that increases morbidity and negatively influences the quality of life. Intestinal mononuclear phagocytes (MNPs) have a crucial role in maintaining epithelial barrier integrity while controlling pathogen invasion by activating an appropriate immune response. However, in genetically predisposed individuals, uncontrolled immune activation to intestinal flora is thought to underlie the chronic mucosal inflammation that can ultimately result in IBD. Thus, MNPs are involved in fine-tuning mucosal immune system responsiveness and have a critical role in maintaining homeostasis or, potentially, the emergence of IBD. MNPs include monocytes, macrophages and dendritic cells, which are functionally diverse but highly complementary. Despite their crucial role in maintaining intestinal homeostasis, specific functions of human MNP subsets are poorly understood, especially during diseases such as IBD. Here we review the current understanding of MNP ontogeny, as well as the recently identified human intestinal MNP subsets, and discuss their role in health and IBD.

Wnt Signaling Cascade in Dendritic Cells and Regulation of Anti-tumor Immunity

Dendritic cells (DCs) control the strength and quality of antigen-specific adaptive immune responses. This is critical for launching a robust immunity against invading pathogens while maintaining a state of tolerance to self-antigens. However, this also represents a fundamental barrier to anti-tumor immune responses and cancer immunotherapy. DCs in the tumor microenvironment (TME) play a key role in this process. The factors in the TME and signaling networks that program DCs to a regulatory state are not fully understood. Recent advances point to novel mechanisms by which the canonical Wnt signaling cascade in DCs regulates immune suppression, and the same pathway in tumors is associated with the evasion of anti-tumor immunity. Here, we review these recent advances in the context of the pleiotropic effects of the Wnts in shaping anti-tumor immune responses by modulating DC functions. In addition, we will discuss how Wnt/β-catenin pathway in DCs can be targeted for successful cancer immunotherapy.

A Review of Micronutrients and the Immune System-Working in Harmony to Reduce the Risk of Infection

Immune support by micronutrients is historically based on vitamin C deficiency and supplementation in scurvy in early times. It has since been established that the complex, integrated immune system needs multiple specific micronutrients, including vitamins A, D, C, E, B6, and B12, folate, zinc, iron, copper, and selenium, which play vital, often synergistic roles at every stage of the immune response. Adequate amounts are essential to ensure the proper function of physical barriers and immune cells; however, daily micronutrient intakes necessary to support immune function may be higher than current recommended dietary allowances. Certain populations have inadequate dietary micronutrient intakes, and situations with increased requirements (e.g., infection, stress, and pollution) further decrease stores within the body. Several micronutrients may be deficient, and even marginal deficiency may impair immunity. Although contradictory data exist, available evidence indicates that supplementation with multiple micronutrients with immune-supporting roles may modulate immune function and reduce the risk of infection. Micronutrients with the strongest evidence for immune support are vitamins C and D and zinc. Better design of human clinical studies addressing dosage and combinations of micronutrients in different populations are required to substantiate the benefits of micronutrient supplementation against infection.

A Comprehensive Review and Update on the Pathogenesis of Inflammatory Bowel Disease

Inflammatory bowel disease (IBD) is a chronic and life-threating inflammatory disease of gastroenteric tissue characterized by episodes of intestinal inflammation. The pathogenesis of IBD is complex. Recent studies have greatly improved our knowledge of the pathophysiology of IBD, leading to great advances in the treatment as well as diagnosis of IBD. In this review, we have systemically reviewed the pathogenesis of IBD and highlighted recent advances in host genetic factors, gut microbiota, and environmental factors and, especially, in abnormal innate and adaptive immune responses and their interactions, which may hold the keys to identify novel predictive or prognostic biomarkers and develop new therapies.

Goblet cell-produced retinoic acid suppresses CD86 expression and IL-12 production in bone marrow-derived cells

Conjunctival goblet cell loss in ocular surface diseases is accompanied by increased number of interleukin-12 (IL-12)-producing antigen-presenting cells (APCs) and increased interferon-γ (IFN-γ) expression. This study tested the hypothesis that mouse conjunctival goblet cells produce biologically active retinoic acid (RA) that suppresses CD86 expression and IL-12 production by myeloid cells. We found that conditioned media from cultured conjunctival goblet cells (CjCM) suppressed stimulated CD86 expression, NF-κB p65 activation and IL-12 and IFN-γ production in unstimulated and lipopolysaccharide-stimulated cultured bone marrow-derived cells (BMDCs) containing a mixed population of APCs. Goblet cell-conditioned, ovalbumin-loaded APCs suppressed IFN-γ production and increased IL-13 production in co-cultured OTII cells. The goblet cell suppressive activity is due in part to their ability to synthesize RA from retinol. Conjunctival goblet cells had greater expression of aldehyde dehydrogenases Aldh1a1 and a3 and ALDEFLUOR activity than cornea epithelium lacking goblet cells. The conditioning activity was lost in goblet cells treated with an ALDH inhibitor, and a retinoid receptor alpha antagonist blocked the suppressive effects of CjCM on IL-12 production. Similar to RA, CjCM increased expression of suppressor of cytokine signaling 3 (SOCS3) in BMDCs. SOCS3 silencing reversed the IL-12-suppressive effects of CjCM. Our findings indicate that conjunctival goblet cells are capable of synthesizing RA from retinol secreted by the lacrimal gland into tears that can condition APCs. Evidence suggests goblet cell RA may function in maintaining conjunctival immune tolerance and loss of conjunctival goblet cells may contribute to increased Th1 priming in dry eye.

Functions of Macrophages in the Maintenance of Intestinal Homeostasis

Intestinal macrophages constitute the largest pool of macrophages in the body and have emerged as crucial sentinels for pathogen recognition and elimination. The source and development of intestinal macrophages, as well as their distinct properties have been well documented. Intestinal macrophages exert their functions in the maintenance of intestinal homeostasis by shaping host-microbiota symbiosis, managing gut inflammation, crosstalking with T cells, and facilitating wound repair. Recently, nutritional regulation of intestinal macrophages has attracted substantial attention and is becoming a promising approach to disease prevention and control. Understanding the mechanisms employed by intestinal macrophages in mediating intestinal immune homeostasis and inflammation, as well as the mode of action of dietary nutrients in the modulating functions of intestinal macrophages, represents an opportunity to prevent and control inflammatory bowel diseases.

The Use of Probiotic Therapy to Modulate the Gut Microbiota and Dendritic Cell Responses in Inflammatory Bowel Diseases

Recent investigations have shown that different conditions such as diet, the overuse of antibiotics or the colonization of pathogenic microorganisms can alter the population status of the intestinal microbiota. This modification can produce a change from homeostasis to a condition known as imbalance or dysbiosis; however, the role-played by dysbiosis and the development of inflammatory bowel diseases (IBD) has been poorly understood. It was actually not until a few years ago that studies started to develop regarding the role that dendritic cells (DC) of intestinal mucosa play in the sensing of the gut microbiota population. The latest studies have focused on describing the DC modulation, specifically on tolerance response involving T regulatory cells or on the inflammatory response involving reactive oxygen species and tissue damage. Furthermore, the latest studies have also focused on the protective and restorative effect of the population of the gut microbiota given by probiotic therapy, targeting IBD and other intestinal pathologies. In the present work, the authors propose and summarize a recently studied complex axis of interaction between the population of the gut microbiota, the sensing of the DC and its modulation towards tolerance and inflammation, the development of IBD and the protective and restorative effect of probiotics on other intestinal pathologies.

Early-onset inflammatory bowel disease as a model disease to identify key regulators of immune homeostasis mechanisms

Rare, monogenetic diseases present unique models to dissect gene functions and biological pathways, concomitantly enhancing our understanding of the etiology of complex (and often more common) traits. Although inflammatory bowel disease (IBD) is a generally prototypic complex disease, it can also manifest in an early-onset, monogenic fashion, often following Mendelian modes of inheritance. Recent advances in genomic technologies have spurred the identification of genetic defects underlying rare, very early-onset IBD (VEO-IBD) as a disease subgroup driven by strong genetic influence, pinpointing key players in the delicate homeostasis of the immune system in the gut and illustrating the intimate relationships between bowel inflammation, systemic immune dysregulation, and primary immunodeficiency with increased susceptibility to infections. As for other human diseases, it is likely that adult-onset diseases may represent complex diseases integrating the effects of host genetic susceptibility and environmental triggers. Comparison of adult-onset IBD and VEO-IBD thus provides beautiful models to investigate the relationship between monogenic and multifactorial/polygenic diseases. This review discusses the present and novel findings regarding monogenic IBD as well as key questions and future directions of IBD research.

Serum concentrations of lipid-soluble vitamins in dogs with exocrine pancreatic insufficiency treated with pancreatic enzymes

Background

In humans, exocrine pancreatic insufficiency (EPI) is associated with deficiencies in lipid‐soluble vitamins. Little is reported regarding lipid‐soluble vitamin status in dogs with EPI.

Hypothesis/Objectives

Compare serum concentrations of retinol, 25‐hydrocholecalciferol (25OHD), and α‐tocopherol among dogs with EPI, those with subclinical EPI (sEPI), and healthy dogs. Detect associations between serum concentrations of lipid‐soluble vitamins and residual clinical signs in treated dogs with EPI and sEPI.

Animals

Twenty dogs with EPI and five dogs with sEPI receiving pancreatic enzyme replacement therapy. Ten healthy dogs sampled before and after 10 days of pancreatic enzyme supplementation.

Methods

Case‐control study. Serum retinol and α‐tocopherol concentrations were measured by high‐performance liquid chromatography. Serum 25OHD concentrations were measured by radioimmunoassay.

Results

Serum retinol concentration was significantly lower in dogs with EPI (median, 490 ng/mL; range, 322‐990 ng/mL) and serum α‐tocopherol concentration was significantly lower in dogs with EPI (median, 11.51 μg/L; range, 4.8‐27.1 μg/L) and sEPI (median, 12.66 μg/L; range, 10.21‐21.03 μg/L) compared with healthy dogs (median, 1203 ng/mL; range, 637‐1768 ng/mL and median, 43.54 μg/L; range, 34.26‐53.97 μg/L, respectively). Dogs with weight loss had significantly lower 25OHD (mean, 243.50 nmol/L; standard deviation [SD], 3.54 nmol/L) than dogs with stable weight (314.0 nmol/L; SD, 138.38 nmol/L).

Conclusions and Clinical Importance

Altered homeostasis of lipid‐soluble vitamins is present in dogs with EPI and sEPI, despite enzyme replacement therapy. Additional studies are needed to determine the clinical relevance of these findings and the therapeutic potential of lipid‐soluble vitamin supplementation in dogs with EPI and sEPI.

Retinoic Acid, Leaky Gut, and Autoimmune Diseases

A leaky gut has been observed in a number of autoimmune diseases including type 1 diabetes, multiple sclerosis, inflammatory bowel disease, and systemic lupus erythematosus. Previous studies from our laboratory have shown that lupus mice also bear a leaky gut and that the intestinal barrier function can be enhanced by gut colonization of probiotics such as Lactobacillus spp. Retinoic acid (RA) can increase the relative abundance of Lactobacillus spp. in the gut. Interestingly, RA has also been shown to strengthen the barrier function of epithelial cells in vitro and in the absence of probiotic bacteria. These reports bring up an interesting question of whether RA exerts protective effects on the intestinal barrier directly or through regulating the microbiota colonization. In this review, we will discuss the roles of RA in immunomodulation, recent literature on the involvement of a leaky gut in different autoimmune diseases, and how RA shapes the outcomes of these diseases.

Retinoic acid treated human dendritic cells induce T regulatory cells via the expression of CD141 and GARP which is impaired with age

Aged subjects display increased susceptibility to mucosal diseases. Retinoic Acid (RA) plays a major role in inducing tolerance in the mucosa. RA acts on Dendritic cells (DCs) to induce mucosal tolerance. Here we compared the response of DCs from aged and young individuals to RA with a view to understand the role of DCs in age-associated increased susceptibility to mucosal diseases. Our investigations revealed that compared to young DCs, RA stimulated DCs from aged subjects are defective in inducing IL-10 and T regulatory cells. Examinations of the underlying mechanisms indicated that RA exposure led to the upregulation of CD141 and GARP on DCs which rendered the DCs tolerogenic. CD141^hi, GARP⁺ DCs displayed enhanced capacity to induce T regulatory cells compared to CD141^lo and GARP⁻ DCs. Unlike RA stimulated DCs from young, DCs from aged subjects exhibited diminished upregulation of both CD141 and GARP. The percentage of DCs expressing CD141 and GARP on RA treatment was significantly reduced in DCs from aged individuals. Furthermore, the remaining CD141^hi, GARP⁺ DCs from aged individuals were also deficient in inducing T regs. In summary, reduced response of aged DCs to RA enhances mucosal inflammation in the elderly, increasing their susceptibility to mucosal diseases.

Dendritic Cell-Airway Epithelial Cell Cross-Talk Changes with Age and Contributes to Chronic Lung Inflammatory Diseases in the Elderly

Age-associated dysregulated immune and inflammatory responses are one of the major factors responsible for the prevalence of chronic respiratory diseases in the older population. Pulmonary dendritic cells (DCs) are present below the airway epithelial cells (AECs) and are critical in initiating effective immune responses to harmful pathogens while maintaining tolerance against harmless antigens. The interaction between DCs and AECs plays a crucial role in lung immunity at homeostasis and during infections. The functions of both DCs and AECs are impacted with age. The present report reviews how the potential crosstalk between pulmonary DCs and AECs is dysregulated in the elderly impairing the capacity to maintain tolerance at the respiratory surfaces, which results in severe and chronic respiratory inflammatory diseases. We also discuss how such DC-AECs crosstalk will provide insight into the mechanisms underlying the increased susceptibility of the elderly to pulmonary inflammatory diseases.

Vitamin A deficiency suppresses fish immune function with differences in different intestinal segments: the role of transcriptional factorNF-κBandp38 mitogen-activated protein kinasesignalling pathways

The present study investigated the effects of dietary vitamin A on immune function in the proximal intestine (PI), mid intestine (MI) and distal intestine (DI) of young grass carp (Ctenopharyngodon idella). Fish were fed graded levels of dietary vitamin A for 10 weeks, and then a challenge test using an injection ofAeromonas hydrophilawas conducted for 14 d. The results showed that, compared with the optimum vitamin A level, vitamin A deficiency significantly decreased fish growth performance, increased enteritis morbidity, decreased intestinal innate humoral immune response and aggravated intestinal inflammation. However, liver-expressed antimicrobial peptide 2A/B mRNA in the DI andIL-6,IL-17D,IL-10, transforming growth factor (TGF)-β1andTGF-β2mRNA in the PI were not affected by vitamin A levels. Meanwhile, vitamin A deficiency disturbed inflammatory cytokines in the PI, MI and DI, which might be partly linked to p38 mitogen-activated protein kinase (p38MAPK) signalling andNF-κBcanonical signalling pathway (IκB kinaseβ(IKKβ),IKKγ, inhibitor ofκBα,NF-κB p65andc-Rel) rather thanNF-κBnon-canonical signalling pathway (NF-κB p52andIKKα). However, the signalling moleculesNF-κB p65andp38MAPKdid not participate in regulating cytokines in the PI. These results suggested that vitamin A deficiency decreased fish growth and impaired intestinal immune function, and that different immune responses in the PI, MI and DI were mediated partly byNF-κBcanonical signalling andp38MAPKsignalling pathways. On the basis of percentage of weight gain, to protect fish against enteritis morbidity and acid phosphatase activity, the optimum dietary vitamin A levels were estimated to be 0·664, 0·707 and 0·722 mg /kg, respectively.

Effects of retinoic acid receptor-γ on the Aspergillus fumigatus induced innate immunity response in human corneal epithelial cells

AIM

To explore the effects of retinoic acid receptor-γ (RARγ) on innate immune responses against Aspergillus fumigatus (A. fumigatus) in cultured human corneal epithelial cells (HCECs).

METHODS

The HCECs were stimulated with A. fumigatus hyphae for 0, 2, 4, 8, 12 and 16h. RARγ mRNA and protein levels were tested by quantitative real-time polymerase chain reaction (qRT-PCR) and Western blot. Then HCECs were pretreated with or without BMS961 (RARγ agonist, 1 µg/mL). The mRNA and protein expression of Dectin-1 and the downstream cytokines (TNF-α and IL-6) were determined by qRT-PCR, Western blot and enzyme-linked immunosorbent assay (ELISA).

RESULTS

The expression of RARγ was upregulated after stimulation with A. fumigatus. RARγ mRNA began to rise at 4h and peaked at 8h (P<0.001). The protein of RARγ reached to the peak at 16h (P<0.001). Pretreated with BMS961 before A. fumigatus hyphae stimulation, expression of Dectin-1, TNF-α and IL-6 decreased dramatically at mRNA and protein levels.

CONCLUSION

HCECs can express RARγ and A. fumigatus hyphae infection can increase RARγ expression. BMS961 can inhibit the expression of Dectin-1 and pro-inflammatory cytokines, and play an anti-inflammatory role in innate immune responses against A. fumigatus.

Modulation of Inflammatory Responses by Wnt/β-Catenin Signaling in Dendritic Cells: A Novel Immunotherapy Target for Autoimmunity and Cancer

The Wnt/β-catenin pathway is an evolutionarily conserved signaling pathway critical for several biological processes. An aberrant Wnt/β-catenin signaling is linked to several human diseases. Emerging studies have highlighted the regulatory role of the Wnt/β-catenin signaling pathway in normal physiological processes of parenchymal and hematopoietic cells. Recent studies have shown that the activation of Wnt/β-catenin pathway in dendritic cells (DCs) play a critical role in mucosal tolerance and suppression of chronic autoimmune pathologies. Alternatively, tumors activate Wnt/β-catenin pathway in DCs to induce immune tolerance and thereby evade antitumor immunity through suppression of effector T cell responses and promotion of regulatory T cell responses. Here, we review our work and current understanding of how Wnt/β-catenin signaling in DCs shapes the immune response in cancer and autoimmunity and discuss how Wnt/β-catenin pathway can be targeted for successful therapeutic interventions in various human diseases.

Aldehyde dehydrogenase inhibition blocks mucosal fibrosis in human and mouse ocular scarring

Mucous membrane pemphigoid (MMP) is a systemic mucosal scarring disease, commonly causing blindness, for which there is no antifibrotic therapy. Aldehyde dehydrogenase family 1 (ALDH1) is upregulated in both ocular MMP (OMMP) conjunctiva and cultured fibroblasts. Application of the ALDH metabolite, retinoic acid (RA), to normal human conjunctival fibroblasts in vitro induced a diseased phenotype. Conversely, application of ALDH inhibitors, including disulfiram, to OMMP fibroblasts in vitro restored their functionality to that of normal controls. ALDH1 is also upregulated in the mucosa of the mouse model of scarring allergic eye disease (AED), used here as a surrogate for OMMP, in which topical application of disulfiram decreased fibrosis in vivo. These data suggest that progressive scarring in OMMP results from ALDH/RA fibroblast autoregulation, that the ALDH1 subfamily has a central role in immune-mediated ocular mucosal scarring, and that ALDH inhibition with disulfiram is a potential and readily translatable antifibrotic therapy.

Decreased RARβ expression induces abundant inflammation and cervical precancerous lesions

It is well known that vitamin A and its receptors protect against cancer development and that Retinoid Acid Receptor β (RARβ) is epigenetically silenced during tumoral progression. Cervical Cancer (CC) has been causally linked to high risk human papillomavirus (HR-HPV) infection. However, host factors are important in determining the outcome of persistent HR-HPV infection as most cervical precancerous lesions containing HR-HPVs do not progress to invasive carcinomas. Increasing evidence suggests that low diet in vitamin A and their receptors participate in the development of CC. The aim of this study has been to investigate the effects of abated RARβ expression in the development of cervical premalignant lesions in 4 month-old conditional mice (RARβ(L-/L-)). Results demonstrated the development of spontaneous squamous metaplasia, inflammatory infiltrate, enhanced mitotic activity, loss of cell differentiation, as well as decreased apoptosis and p16(INK4a) protein levels in RARβ(L-/L-) mice cervix. All these changes are hallmarks of moderate dysplasia. Importantly, our results suggest that the low expression of RARβ, may induce the down regulation of p16(INK4a), chronic inflammation and decreased apoptosis and may be involved in vulnerability to HR-HPV and early stage cervical carcinogenesis.

Differential transcriptional response profiles in human myeloid cell populations

This study examines the transcriptional profiles of human adult brain-derived microglia in response to in vitro activating conditions previously used to polarize systemic myeloid cells into M1 and M2 phenotypes. A comparative study is done with monocyte-derived macrophages (MDMs), a myeloid cell type that also participates in disease relevant tissue injury and repair processes in the CNS. Current markers used to distinguish microglia and MDMs have been defined under homeostatic conditions. We observe that gene expression profiles of M1 microglia and MDMs overlap with an overrepresentation of immune-related pathways. M2 microglia and MDMs have distinct transcriptional signatures. Upregulated genes in M2 microglia favor neural-related pathways whereas upregulated genes in M2 MDMs are mostly involved in antigen presentation. Our microarray screen identifies candidate molecules that can potentially distinguish microglia and MDMs under all activation conditions. To be determined is how our observations made using conventional in vitro polarization translate into cellular responses to the complex combination of signals encountered in neurologic disease states.

Differentiation-Coupled Induction of Human Cytomegalovirus Replication by Union of the Major Enhancer Retinoic Acid, Cyclic AMP, and NF-κB Response Elements

Triggers and regulatory pathways that effectively link human cytomegalovirus (HCMV) major immediate early (MIE) latent-lytic switch activation with progeny production are incompletely understood. In the quiescently infected human NTera2 cell model of primitive neural stem cells, we found that costimulation with vasoactive intestinal peptide (V) and phorbol ester (P) synergistically activated viral infection, but this effect waned over time. Coupling retinoic acid (R), an inducer of neuronal differentiation, to VP pulse stimulation attenuated the decline in viral activity and promoted the spread of the active infection through concentric layers of neighboring cells as cellular differentiation progressed. R stimulation alone was unable to activate the infection. The MIE enhancer cis-regulatory mechanisms responsible for this result were characterized by a strategy of combinatorial mutagenesis of five cis-acting element types (retinoic acid receptor binding elements [RARE], cyclic AMP [cAMP] response elements [CRE], NF-κB binding sites [kB], serum response element, and ETS/ELK-1 binding site) and multiple methods of assessment. We found that the CRE and kB combination sets the preinduction enhancer tone, is the major initiator and amplifier of RVP-induced MIE gene expression, and cooperates with RARE during cellular differentiation to enhance viral spread. In predifferentiated NTera2, we also found that the CRE-kB combination functions as initiator and amplifier of unstimulated HCMV MIE gene expression and cooperatively interacts with RARE to enhance viral spread. We conclude that RVP-stimulated signaling cascades and cellular differentiation operate through the enhancer CRE-kB-RARE core in strengthening induction of HCMV MIE gene expression in linkage with viral propagation.

IMPORTANCE

Cytomegalovirus-seropositive persons commonly lack detectable levels of cytomegalovirus replication, even when profoundly immunocompromised. In a human NTera2 cell model of primitive neural stem cells carrying resting cytomegalovirus genomes, we show that costimulation of protein kinase A and C-delta signaling cascades in conjunction with retinoic acid-induced neuronal differentiation brings about progeny virus propagation. Iterated DNA binding sites for retinoic acid receptor, CREB, and NF-κB family members in the cytomegalovirus major enhancer are at the crux in the pathway to HCMV activation. The stimulated CREB and NF-κB binding site combination vigorously initiates and amplifies the active cytomegalovirus infection and cooperates with activated retinoic acid receptor binding sites to further promote viral proliferation and spread between differentiated cells. These results support a paradigm in which a specific combination of stimuli coupled with cellular differentiation satisfies a core cis-activating code that unlocks enhancer silence to repower the cycle of cytomegalovirus propagation.

Vitamin A supplementation enhances Senegalese sole (Solea senegalensis) early juvenile's immunocompetence: New insights on potential underlying pathways

Senegalese sole (Solea senegalensis) has been considered since the 1990's to be a promising flatfish species for diversifying European marine aquaculture. However, pathogen outbreaks leading to high mortality rates can impair Senegalese sole commercial production at the weaning phase. Different approaches have been shown to improve fish immunocompetence; with this in mind the objective of the work described herein was to determine whether increased levels of dietary vitamin A (VA) improve the immune response in early juveniles of Senegalese sole. For this purpose, Senegalese sole were reared and fed with Artemia metanauplii containing increased levels of VA (37,000; 44,666; 82,666 and 203,000 total VA IU Kg(-1)) from 6 to 60 days post-hatch (early juvenile stage). After an induced bacterial infection with a 50% lethal dose of Photobacterium damselae subsp. damselae, survival rate, as well as underlying gene expression of specific immune markers (C1inh, C3, C9, Lgals1, Hamp, LysC, Prdx1, Steap4 and Transf) were evaluated. Results showed that fish fed higher doses of dietary VA were more resistant to the bacterial challenge. The lower mortality was found to be related with differential expression of genes involved in the complement system and iron availability. We suggest that feeding metamorphosed Senegalese sole with 203,000 total VA IU Kg(-1) might be an effective, inexpensive and environmentally friendly method to improve Senegalese sole immunocompetence, thereby improving survival of juveniles and reducing economic losses.

Impact of Toxoplasma gondii on Dendritic Cell Subset Function in the Intestinal Mucosa

The function of mucosal dendritic cell (DC) subsets in immunity and inflammation is not well understood. In this study, we define four DC subsets present within the lamina propria and mesenteric lymph node compartments based on expression of CD103 and CD11b. Using IL-12p40 YFP (Yet40) reporter mice, we show that CD103(+)CD11b(-) mucosal DCs are primary in vivo sources of IL-12p40; we also identified CD103(-)CD11b(-) mucosal DCs as a novel population producing this cytokine. Infection was preferentially found in CD11b(+) DCs that were negative for CD103. Lamina propria DCs containing parasites were negative for IL-12p40. Instead, production of the cytokine was strictly a property of noninfected cells. We also show that vitamin A metabolism, as measured by ALDH activity, was preferentially found in CD103(+)CD11b(+) DC and was strongly downregulated in all mucosal DC subsets during infection. Finally, overall apoptosis of lamina propria DC subsets was increased during infection. Combined, these results highlight the ability of intestinal Toxoplasma infection to alter mucosal DC activity at both the whole population level and at the level of individual subsets.

Retinoic acid potentiates inflammatory cytokines in human mast cells: identification of mast cells as prominent constituents of the skin retinoid network

Retinoic acid (RA), the active vitamin-A-metabolite, has well-established functions in skin homeostasis and in the immune system. Skin mast cells (MCs) combine traits of both structures, being of hematopoietic origin, but functional in the skin environment. It remains largely unknown whether mature MCs are targeted by the retinoid network. Here, we demonstrate that human skin MCs display substantial susceptibility to RA by which they are instructed to increase pro-inflammatory mediators (IL-1β, IL-8, TNF-α) but not histamine release. The effects are observed at physiological RA levels, in different microenvironments, and are largely donor-independent. RA susceptibility is owed to the cells' abundant expression of RARA, the receptor mediating MC cytokine responses. Unexpectedly, bioinformatics calculations on the FANTOM5 expression atlas revealed general enrichment of retinoid network components in MCs against other skin cells, and MCs rapidly upregulated RA responsive genes. In conclusion, MCs are important yet hitherto overlooked retinoid targets in the skin.

Seeing through the dark: New insights into the immune regulatory functions of vitamin A

The importance of vitamin A for host defense is undeniable and the study of its mechanisms is paramount. Of the estimated 250 million preschool children who are vitamin A-deficient (VAD), 10% will die from their increased susceptibility to infectious disease. Vitamin A supplementation was established in the 1980s as one of the most successful interventions in the developing world. Understanding how vitamin A controls immunity will help curb the mortality and morbidity associated with vitamin A deficiency and exploit the immune-enhancing capacity of vitamin A to heighten host resistance to infectious disease. The discoveries that retinoic acid (RA) imprints the homing of leukocytes to the gut and enhances the induction of regulatory T cells, highlighted a potential role for RA in mucosal tolerance. However, more recently emerging data tell of a more profound systemic impact of RA on leukocyte function and commitment. In animal models using genetic manipulation of RA signaling, we learned when and how RA controls T cell fate. Here, we review the role for RA as a critical checkpoint regulator in the differentiation of CD4(+) T cells within the immune system.

Wnt signaling in dendritic cells: its role in regulation of immunity and tolerance

A fundamental puzzle in immunology is how the immune system launches robust immunity against pathogens while maintaining a state of tolerance to the body's own tissues and the trillions of commensal microorganisms and food antigens that confront them every day. Innate immune cells, such as dendritic cells (DCs) and macrophages, play a fundamental role in this process. Emerging studies have highlighted that the Wnt signaling pathway, particularly in DCs, plays a major role in regulating tolerance versus immunity. Here, we review our current understanding of how Wnt-signaling shapes the immune response and, in addition, highlight unanswered questions, the solution of which will be imperative in the rational exploitation of this pathway in vaccine design and immune therapy.

Dendritic cell metabolism

The past 15 years have seen enormous advances in our understanding of the receptor and signalling systems that allow dendritic cells (DCs) to respond to pathogens or other danger signals and initiate innate and adaptive immune responses. We are now beginning to appreciate that many of these pathways not only stimulate changes in the expression of genes that control DC immune functions, but also affect metabolic pathways, thereby integrating the cellular requirements of the activation process. In this Review, we focus on this relatively new area of research and attempt to describe an integrated view of DC immunometabolism.

The varieties of immunological experience: of pathogens, stress, and dendritic cells

In the 40 years since their discovery, dendritic cells (DCs) have been recognized as central players in immune regulation. DCs sense microbial stimuli through pathogen-recognition receptors (PRRs) and decode, integrate, and present information derived from such stimuli to T cells, thus stimulating immune responses. DCs can also regulate the quality of immune responses. Several functionally specialized subsets of DCs exist, but DCs also display functional plasticity in response to diverse stimuli. In addition to sensing pathogens via PRRs, emerging evidence suggests that DCs can also sense stress signals, such as amino acid starvation, through ancient stress and nutrient sensing pathways, to stimulate adaptive immunity. Here, I discuss these exciting advances in the context of a historic perspective on the discovery of DCs and their role in immune regulation. I conclude with a discussion of emerging areas in DC biology in the systems immunology era and suggest that the impact of DCs on immunity can be usefully contextualized in a hierarchy-of-organization model in which DCs, their receptors and signaling networks, cell-cell interactions, tissue microenvironment, and the host macroenvironment represent different levels of the hierarchy. Immunity or tolerance can then be represented as a complex function of each of these hierarchies.