1alpha,25-Dihydroxyvitamin D3 downmodulates the functional differentiation of Th1 cytokine-conditioned bone marrow-derived dendritic cells beneficial for cytotoxic T lymphocyte generation

Interplay of calcium, vitamin D, and parathormone in the milieu of infections and immunity: Reassessed in the context of COVID-19

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is recognized for inducing severe respiratory symptoms like cough, and shortness of breathing. Although symptom severity varies, some individuals remain asymptomatic. This virus has sparked a global pandemic, imposing a substantial rate of mortality or morbidity, with extended periods of illness reported. People with underlying medical issues and the elderly are more likely to experience adverse results. The virus's frequent mutations pose challenges for medical professionals, necessitating adaptable therapeutic and preventive strategies. Vitamin D, a versatile regulatory molecule, not only influences physiological processes such as serum calcium regulation but also exhibits immunomodulatory functions. Calcium ions play a crucial role as secondary signal transduction molecules, impacting diverse cellular functions and maintaining homeostasis through ion channel regulation. Parathormone, another key regulator of serum calcium, often acts antagonistically to vitamin D. This review delves into the interplay of vitamin D, calcium, and parathormone, exploring their possible influence on the progression of COVID-19. The intricate signaling involving these elements contributes to adverse prognosis, emphasizing the need for comprehensive understanding. Monitoring and controlling these physiological factors and associated pathways have shown the potential to alter disease outcomes, underscoring the importance of a holistic approach.

GRAS-microparticle microarrays identify dendritic cell tolerogenic marker-inducing formulations

Microarrays, miniaturized platforms used for high-content studies, provide potential advantages over traditional in vitro investigation in terms of time, cost, and parallel analyses. Recently, microarrays have been leveraged to investigate immune cell biology by providing a platform with which to systematically investigate the effects of various agents on a wide variety of cellular processes, including those giving rise to immune regulation for application toward curtailing autoimmunity. A specific embodiment incorporates dendritic cells cultured on microarrays containing biodegradable microparticles. Such an approach allows immune cell and microparticle co-localization and release of compounds on small, isolated populations of cells, enabling a quick, convenient method to quantify a variety of cellular responses in parallel. In this study, the microparticle microarray platform was utilized to investigate a small library of sixteen generally regarded as safe (GRAS) compounds (ascorbic acid, aspirin, capsaicin, celastrol, curcumin, epigallocatechin-3-gallate, ergosterol, hemin, hydrocortisone, indomethacin, menadione, naproxen, resveratrol, retinoic acid, α-tocopherol, vitamin D3) for their ability to induce suppressive phenotypes in murine dendritic cells. Two complementary tolerogenic index ranking systems were proposed to summarize dendritic cell responses and suggested several lead compounds (celastrol, ergosterol, vitamin D3) and two secondary compounds (hemin, capsaicin), which warrant further investigation for applications toward suppression and tolerance.

Immunoinflammatory effects of dietary bioactive compounds

Inflammation is a key mechanism of the immune system that can be elicited by several factors, among them several chemical, physical and biological agents. Once stimulated, the inflammatory response activates a series of signaling pathways and a number of immune cells which promote, in a very coordinated manner, the neutralization of the infectious agent. However, if uncontrolled, the inflammatory status may become chronic leading, potentially, to tissue damage and disease onset. Several risk factors are associated with the development of chronic inflammation and, among these factors, diet plays an essential role. In this chapter the effects of some dietary bioactive compounds, including micronutrients, omega-3 fatty acids, nucleotides and polyphenols, on the immunoinflammatory responses in different cellular, animal and human studies have been summarized.

Targeting the tumor immune microenvironment with "nutraceuticals": From bench to clinical trials

The occurrence of immune effector cells in the tissue microenvironment during neoplastic progression is critical in determining tumor growth outcomes. On the other hand, tumors may also avoid immune system-mediated elimination by recruiting immunosuppressive leukocytes and soluble factors, which coordinate a tumor microenvironment that counteracts the efficiency of the antitumor immune response. Checkpoint inhibitor therapy results have indicated a way forward via activation of the immune system against cancer. Widespread evidence has shown that different compounds in foods, when administered as purified substances, can act as immunomodulators in humans and animals. Although there is no universally accepted definition of nutraceuticals, the term identifies a wide category of natural compounds that may impact health and disease statuses and includes purified substances from natural sources, plant extracts, dietary supplements, vitamins, phytonutrients, and various products with combinations of functional ingredients. In this review, we summarize the current knowledge on the immunomodulatory effects of nutraceuticals with a special focus on the cancer microenvironment, highlighting the conceptual benefits or drawbacks and subtle cell-specific effects of nutraceuticals for envisioning future therapies employing nutraceuticals as chemoadjuvants.

1, 25-dihydroxyvitamin D3 downregulates cytotoxic effector response in pulmonary tuberculosis

1,25-dihydroxyvitaminD₃ [1,25(OH)₂D₃] modulates both the innate and adaptive immunity in tuberculosis. We explored the effect of 1,25(OH)₂D₃ on cytolytic molecules like perforin, granulysin, and granzyme-B in T-cells and natural killer cells during M. tuberculosis (Mtb) infection. Peripheral blood mononuclear cells (PBMCs) from 45 healthy controls (HCs) and 45 pulmonary tuberculosis (PTB) patients were cultured with Mtb in the absence or presence of 1,25(OH)₂D₃ for 72 h. The percentage of perforin, granulysin, and granzyme-B positive cells were estimated by flow cytometry. 1,25(OH)₂D₃ significantly decreased the percentage of cytolytic molecules in total, CD4+, CD8+ and CD56+ cells in HCs and PTB patients (p < 0.05). Moreover, 1,25(OH)₂D₃ downregulates IFN-γ levels while upregulate the anti-inflammatory cytokine IL-10. Correlation revealed that the total percentage of cytolytic molecules were positively correlated with IFN-γ level, whereas negatively correlated with IL-10 level in both the study subjects (p < 0.05). This results suggests that 1,25(OH)₂D₃ downregulate the expression of cytolytic molecues and act as anti-inflammatory in adaptive immune response, which might help to reduce inflammation and tissue damage during the active stage of the disease.

Spectrum of Darkness, Agent of Light: Myopia, Keratoconus, Ocular Surface Disease, and Evidence for a Profoundly Vitamin D-dependent Eye

Serial observations obtained over more than eight years and 10,000 patient encounters in a general ophthalmology practice serving a population highly prone to chronic vitamin D (D3) deficiency, facilitated by the Oculus Pentacam Scheimpflug imaging system (Oculus Optikgeräte GmbH, Wetzlar, Germany), resulted in the recognition of consistent, predictable, and highly reproducible patterns of mechanical, optical, and physiologic change in the cornea and other ocular structures correlated to adequate vs. inadequate vitamin D availability. These patterns were identified from an analysis of more than 20,000 topographical and digital imaging studies, manifest refraction results, and other clinical ophthalmic exam findings recorded during patient visits. The main outcome measures included improved corneal and global optical quality and function, decreased ametropia, improved stability, and decreased subjective symptoms of compromised acuity and comfort. Adequate D3 replacement consistently yielded some degree of objective structural improvement in all subjects observed. The rate of improvement varied and synergistic interaction with cofactors was also suggested in particular topical steroids. A plausible explanation for the cause and mechanism of most myopia emerged and keratoconus, in particular, appears to be the extreme presentation of otherwise common corneal disturbances associated with inadequate vitamin D availability. Emmetropization mechanisms appear to awaken and reactivate with adequate D3. Intraocular pressure control likewise shows evidence of being vitamin D regulated and may play a significant interactive role in emmetropization and relief from ametropia. Ocular surface disease and inflammatory activity can be markedly alleviated in addition. As the findings are most readily appreciated via topographical map changes, a series of case reports are presented, selected from the mass of similar data, to illustrate specific aspects of these findings in the hope of inspiring controlled trials to better delineate their significance. Taken as a whole, these observations suggest the human eye may be profoundly dependent upon adequate vitamin D availability for many critical optical, structural, and physiologic properties. Myopia may represent the end result of adverse emmetropization feedback generated by low vitamin D-related irregular corneal astigmatism.

Host-Directed Therapeutic Strategies for Tuberculosis

Tuberculosis (TB), caused by Mycobacterium tuberculosis (Mtb), remains a leading cause of morbidity and mortality in humans worldwide. Currently, the standard treatment for TB involves multiple antibiotics administered for at least 6 months. Although multiple antibiotics therapy is necessary to prevent the development of drug resistance, the prolonged duration of treatment, combined with toxicity of drugs, contributes to patient non-compliance that can leads to the development of drug-resistant Mtb (MDR and XDR) strains. The existence of comorbid conditions, including HIV infection, not only complicates TB treatment but also elevates the mortality rate of patients. These facts underscore the need for the development of new and/or improved TB treatment strategies. Host-directed therapy (HDT) is a new and emerging concept in the treatment of TB, where host response is modulated by treatment with small molecules, with or without adjunct antibiotics, to achieve better control of TB. Unlike antibiotics, HDT drugs act by directly modulating host cell functions; therefore, development of drug resistance by infecting Mtb is avoided. Thus, HDT is a promising treatment strategy for the management of MDR- and XDR-TB cases as well as for patients with existing chronic, comorbid conditions such as HIV infection or diabetes. Functionally, HDT drugs fine-tune the antimicrobial activities of host immune cells and limit inflammation and tissue damage associated with TB. However, current knowledge and clinical evidence is insufficient to implement HDT molecules as a stand-alone, without adjunct antibiotics, therapeutic modality to treat any form of TB in humans. In this review, we discuss the recent findings on small molecule HDT agents that target autophagy, vitamin D pathway, and anti-inflammatory response as adjunctive agents along with standard antibiotics for TB therapy. Data from recent publications show that this approach has the potential to improve clinical outcome and can help to reduce treatment duration. Thus, HDT can contribute to global TB control programs by potentially increasing the efficiency of anti-TB treatment.

Generation of Tolerogenic Dendritic Cells and Their Therapeutic Applications

Dendritic cells (DCs) are professional antigen-presenting cells (APCs) that bridge innate and adaptive immune responses, thereby leading to immune activation. DCs have been known to recognize pathogen-associated molecular patterns such as lipopolysaccharides (LPS) and nucleic acids via their pattern recognition receptors, which trigger signaling of their maturation and effector functions. Furthermore, DCs take up and process antigens as a form of peptide loaded on the major histocompatibility complex (MHC) and present them to T cells, which are responsible for the adaptive immune response. Conversely, DCs can also play a role in inducing immune suppression under specific circumstances. From this perspective, the role of DCs is related to tolerance rather than immunity. Immunologists refer to these special DCs as tolerogenic DCs (tolDCs). However, the definition of tolDCs is controversial, and there is limited information on their development and characteristics. In this review, we discuss the current concept of tolDCs, cutting-edge methods for generating tolDCs in vitro, and future applications of tolDCs, including clinical use.

Enhanced LL-37 expression following vitamin D supplementation in patients with cirrhosis and spontaneous bacterial peritonitis

BACKGROUND & AIMS

The morbidity and mortality of spontaneous bacterial peritonitis (SBP) are high among patients with cirrhosis; however, the mechanisms of SBP pathogenesis are poorly understood. This study aimed to determine the role of the vitamin D-LL-37 pathway in the pathogenesis and treatment in patients with cirrhosis and SBP.

METHODS

Serum 25-hydroxyvitamin D concentrations of 119 patients with chronic liver diseases were tested. Vitamin D receptor (VDR) and LL-37 in peritoneal leucocytes of cirrhotic and ascitic patients with SBP were detected and compared with those without SBP. Then the peritoneal macrophages of non-infected patients were cultured and activated by lipopolysaccharide (LPS) to analyse the changes of VDR and LL-37 expressions after incubation with vitamin D.

RESULTS

Vitamin D deficiency or insufficiency was found in all of patients with cirrhosis. LPS inhibited VDR and LL-37 expression in peritoneal macrophages [1.3-fold decrease (P = 0.003) and 20-fold decrease (P = 0.010) respectively]. However, vitamin D could reverse the inhibition of both VDR and LL-37 [1.5-fold increase (P = 0.001) and 2000-fold increase (P < 0.001) respectively]. The effect of the incubation time following vitamin D supplementation was significant for LL-37 expression, with a peak expression found at 36 h (P < 0.001).

CONCLUSIONS

When vitamin D levels were low, bacteria inhibited VDR and LL-37 responses in peritoneal macrophages as a mechanism to evade antibacterial defence. Vitamin D supplementation could up-regulate peritoneal macrophage VDR and LL-37 expressions, which resulted in an enhanced immunological defence against SBP in patients with cirrhosis and ascites.

Role of vitamin D in cytotoxic T lymphocyte immunity to pathogens and cancer

The discovery of vitamin D receptor (VDR) expression in immune cells has opened up a new area of research into immunoregulation by vitamin D, a niche that is distinct from its classical role in skeletal health. Today, about three decades since this discovery, numerous cellular and molecular targets of vitamin D in the immune system have been delineated. Moreover, strong clinical associations between vitamin D status and the incidence/severity of many immune-regulated disorders (e.g. infectious diseases, cancers and autoimmunity) have prompted the idea of using vitamin D supplementation to manipulate disease outcome. While much is known about the effects of vitamin D on innate immune responses and helper T (T(H)) cell immunity, there has been relatively limited progress on the frontier of cytotoxic T lymphocyte (CTL) immunity--an arm of host cellular adaptive immunity that is crucial for the control of such intracellular pathogens as human immunodeficiency virus (HIV), tuberculosis (TB), malaria, and hepatitis C virus (HCV). In this review, we discuss the strong historical and clinical link between vitamin D and infectious diseases that involves cytotoxic T lymphocyte (CTL) immunity, present our current understanding as well as critical knowledge gaps in the realm of vitamin D regulation of host CTL responses, and highlight potential regulatory connections between vitamin D and effector and memory CD8 T cell differentiation events during infections.

Mechanisms underlying effects of 1,25-Dihydroxyvitamin D3 on the Th17 cells

Th17 cells, a class of CD4(+) T cells, have been identified as novel effector cells, which play a pivotal role in several inflammatory and autoimmune diseases. 1,25-Dihydroxyvitamin D3 (1,25(OH)2D3), the active form of vitamin D, has emerged as a direct regulator of immune system function in humans. Accumulating reports demonstrated that 1,25(OH)2D3 possessed anti-inflammatory activity on Th17 cells to maintain immunologic homeostasis. This report will review the novel immune regulatory role of 1,25(OH)2D3 in its potential use for Th17 cell-related inflammatory and autoimmune conditions.

Efficacy and mechanisms of action of vitamin D in experimental polyarthritis

Vitamin D (vit D) status has been linked to the occurrence and severity of auto-immune and inflammatory diseases. This study evaluates the effects of vit D status on adoptive transfer of adjuvant-induced arthritis (ATA). Rats maintained on diets replete or deficient in vit D3 received arthritogenic thoracic duct cells and were monitored for severity of arthritis. CD45(+) cells obtained by collagenase digestion of hind-paw synovium-rich tissues (SRTs) were analysed to observe the effects of dietary vit D3 on the inflammatory process. Arthritis was more severe in vitamin D-deficient (vit-D(-)) rats compared with vitamin D-replete (vit-D(+)) rats. Resolution was delayed in vit-D(-) rats compared with vit-D(+) rats, or rats fed standard chow. During the acute phase of ATA, numbers of CD45(+) cells were significantly increased in the SRTs of vit-D(-) rats compared with vit-D(+) rats. This increase involved T-cells, polymorphonuclear leukocytes, macrophages, dendritic cells (DCs) and MHC II(hi) cells that resemble activated monocytes. A major difference between the dietary groups was that most DCs at the peak of inflammation in vit-D(-) rats were CD4(-), whereas in convalescent vit-D(+) rats most expressed CD4. Multiple categories of genes expressed by DCs differed between deficient and replete rats, with deficiency being associated with relative upregulation of certain pro-inflammatory genes and replete status being associated with upregulation of genes associated with resolution of inflammation. The findings indicate that ATA is more severe and prolonged in vit-D deficiency, that vit-D deficiency promotes accumulation of CD4(-) DCs in synovium during ATA and that a gene-expression profile is likely to contribute to the observed increased severity and duration of arthritis.

1α,25-Dihydroxyvitamin D3 and all-trans retinoic acid synergistically inhibit the differentiation and expansion of Th17 cells

1α,25-Dihydroxyvitamin D(3) (1,25D3), the active form of vitamin D(3), is an immunoregulatory hormone with beneficial effects on Th1 cell-mediated inflammatory diseases. Although IL-17-producing CD4(+) T helper (Th17) cells have been recently identified as novel effector cells, the immunomodulating effects of 1,25D3 on Th17 cells have not been well defined. We confirmed here that 1,25D3 inhibited the generation of Th17 cells in vitro. Interestingly, 1,25D3 synergistically suppressed the generation of Th17 cells by the combination with all-trans retinoic acid (ATRA). 1,25D3 and ATRA suppressed the development of allergen-induced contact hypersensitivity (CHS) in a mouse ear swelling model. In addition, we found that 1,25D3 and ATRA significantly inhibited the development of human Th17 cells from both naïve and memory human CD4(+) T cells. 1,25D3 and ATRA effectively suppressed mRNA expressions of IL-1R1, IL-21R, IL-23R, RORC, and AHR in human T cells. ATRA further suppressed IL-6R, whereas 1,25D3 did not. Finally, we found that 1,25D3 and ATRA remarkably blocked IL-22 as well as IL-17 mRNA expression in human memory CD4(+) T cells. Thus, we initially reveal that 1,25D3 and ATRA have synergistic effects on the generation of Th17 cells, suggesting that the combination with ATRA would provide a promising novel therapy for Th17 cell-related immune diseases including skin inflammation.

Advances in vitamin D and inflammatory bowel disease

In respect of the comprehensive effect in immunologic regulation (on innate immunity and adaptive immunity) and antibacterial activity, vitamin D is in a high profile position in recent years. Despite the uncertain mechanism, it is a common sense that commensal enteric microbiota initiate and perpetuate immune-mediated bowel inflammation. This suggests that there may be a link between vitamin D's function and pathogenesis of inflammatory bowel disease, and vitamin D-associated agents may be prospective for treatment of inflammatory bowel disease.

Elocalcitol inhibits inflammatory responses in human thyroid cells and T cells

T-helper 1 (Th1) cell-mediated inflammatory responses predominate in the early pathogenesis of Graves' disease (GD), whereas Th2 cell-mediated immunity may play a role in later stages. The chemokine CXCL10 and its receptor CXCR3 are expressed in most thyroid glands of early GD patients. Circulating CXCL10 levels inversely correlate with disease duration; CXCL10 maximal expression also correlates with interferon (IFN)gamma levels in recent GD onset. Methimazole (MMI) reduces CXCL10 secretion by isolated thyrocytes, decreases serum CXCL10 levels, and promotes a transition from Th1 to Th2 dominance in patients in GD active phase. Vitamin D receptor agonists exhibit antiinflammatory properties and promote tolerance induction. We investigated the effects and the mechanism of action of a nonhypercalcemic vitamin D receptor agonist, elocalcitol (BXL-628), compared with MMI on CXCL10 secretion induced by proinflammatory cytokines. Furthermore, we studied the effects of both drugs on Th1, Th17, and Th2 cytokine secretion in CD4+ T cells. ELISA, cytometry, immunocytochemistry, Western blot, and quantitative real-time PCR were used for protein and gene analysis. In human thyrocytes, elocalcitol inhibited IFNgamma and TNFalpha-induced CXCL10 protein secretion more potently than MMI. Elocalcitol impaired both cytokine intracellular pathways, whereas MMI was effective only on the IFNgamma pathway. In CD4+ T cells, elocalcitol decreased Th1- and Th17-type cytokines, and promoted Th2-type cytokine secretion. Elocalcitol and MMI inhibited Th1 cytokine-mediated responses in thyrocytes and CD4+ T cells. In addition, elocalcitol promoted a shift toward a Th2 response. In conclusion, elocalcitol could represent a novel pharmacological tool in the treatment of autoimmune thyroid diseases.