Vitamin D/CD46 Crosstalk in Human T Cells in Multiple Sclerosis

Full spectrum of vitamin D immunomodulation in multiple sclerosis: mechanisms and therapeutic implications

Vitamin D deficiency has been associated with the risk of multiple sclerosis, disease activity and progression. Results from in vitro experiments, animal models and analysis of human samples from randomized controlled trials provide comprehensive data illustrating the pleiotropic actions of Vitamin D on the immune system. They globally result in immunomodulation by decreasing differentiation of effector T and B cells while promoting regulatory subsets. Vitamin D also modulates innate immune cells such as macrophages, monocytes and dendritic cells, and acts at the level of the blood–brain barrier reducing immune cell trafficking. Vitamin D exerts additional activity within the central nervous system reducing microglial and astrocytic activation. The immunomodulatory role of Vitamin D detected in animal models of multiple sclerosis has suggested its potential therapeutic use for treating multiple sclerosis. In this review, we focus on recent published data describing the biological effects of Vitamin D in animal models of multiple sclerosis on immune cells, blood–brain barrier function, activation of glial cells and its potential neuroprotective effects. Based on the current knowledge, we also discuss optimization of therapeutic interventions with Vitamin D in patients with multiple sclerosis, as well as new technologies allowing in-depth analysis of immune cell regulations by vitamin D.

Risk Factors from Pregnancy to Adulthood in Multiple Sclerosis Outcome

Multiple sclerosis (MS) is an autoimmune disease characterized by a robust inflammatory response against myelin sheath antigens, which causes astrocyte and microglial activation and demyelination of the central nervous system (CNS). Multiple genetic predispositions and environmental factors are known to influence the immune response in autoimmune diseases, such as MS, and in the experimental autoimmune encephalomyelitis (EAE) model. Although the predisposition to suffer from MS seems to be a multifactorial process, a highly sensitive period is pregnancy due to factors that alter the development and differentiation of the CNS and the immune system, which increases the offspring’s susceptibility to develop MS. In this regard, there is evidence that thyroid hormone deficiency during gestation, such as hypothyroidism or hypothyroxinemia, may increase susceptibility to autoimmune diseases such as MS. In this review, we discuss the relevance of the gestational period for the development of MS in adulthood.

Vitamin D as a Risk Factor for Multiple Sclerosis: Immunoregulatory or Neuroprotective?

Vitamin D insufficiency during childhood has been linked to the development of multiple sclerosis (MS), typically an adult-onset inflammatory demyelinating disease of the central nervous system (CNS). Since vitamin D was known to have immunoregulatory properties on both innate and adaptive immunity, it was hypothesized that low vitamin D resulted in aberrant immune responses and the development of MS. However, vitamin D receptors are present on many cell types, including neurons, oligodendrocytes, astrocytes and microglia, and vitamin D has profound effects on development and function of the CNS. This leads to the possibility that low vitamin D may alter the CNS in a manner that makes it vulnerable to inflammation and the development of MS. This review analysis the role of vitamin D in the immune and nervous system, and how vitamin D insufficiency in children may contribute to the development of MS.

Improving Glucocorticoid Sensitivity of Brain-Homing CD4+ T Helper Cells by Steroid Hormone Crosstalk

In early multiple sclerosis (MS), an IFN-γ^highGM-CSF^highIL-17^low CD4⁺ T-cell subset termed T helper 17.1 (Th17.1) reveals enhanced capacity to infiltrate the central nervous system. Th17.1 cells express high levels of multidrug resistance protein 1 (MDR1), which contributes to their poor glucocorticoid responsiveness. In this study, we explored whether glucocorticoid sensitivity of Th17.1 cells can generically be improved through synergy between steroid hormones, including calcitriol (1,25(OH)₂D₃), estradiol (E2) and progesterone (P4). We showed that human blood Th17.1 cells were less sensitive to 1,25(OH)₂D₃ than Th17 cells, as reflected by lower vitamin D receptor (VDR) levels and reduced modulation of MDR1, IFN-γ and GM-CSF expression after 1,25(OH)₂D₃ exposure. Upon T-cell activation, VDR levels were increased, but still lower in Th17.1 versus Th17 cells, which was accompanied by a 1,25(OH)₂D₃-mediated decline in MDR1 surface expression as well as secretion of IFN-γ and GM-CSF. In activated Th17.1 cells, 1,25(OH)₂D₃ amplified the suppressive effects of methylprednisolone (MP) on proliferation, MDR1 surface levels, secretion of IFN-γ and granzyme B, as well as expression of brain-homing markers CCR6 and VLA-4. The addition of P4 to 1,25(OH)₂D₃ further enhanced MP-mediated reduction in proliferation, CD25, CCR6 and CXCR3. Overall, this study indicates that glucocorticoid sensitivity of Th17.1 cells can be enhanced by treatment with 1,25(OH)₂D₃ and further improved with P4. Our observations implicate steroid hormone crosstalk as a therapeutic avenue in Th17.1-associated inflammatory diseases including MS.

The IL-2 - IL-2 receptor pathway: Key to understanding multiple sclerosis

The development, progression, diagnosis and treatment of autoimmune diseases, such as multiple sclerosis (MS), are convoluted processes which remain incompletely understood. Multiple studies demonstrated that the interleukin (IL)-2 – IL-2 receptor (IL-2R) pathway plays a pivotal role within these processes. The most striking functions of the IL-2 – IL-2R pathway are the differential induction of autoimmune responses and tolerance. This paradoxical function of the IL-2 – IL-2R pathway may be an attractive therapeutic target for autoimmune diseases such as MS. However, the exact mechanisms that lead to autoimmunity or tolerance remain to be elucidated. Furthermore, another factor of this pathway, the soluble form of the IL-2R (sIL-2R), further complicates understanding the role of the IL-2 – IL-2R pathway in MS. The challenge is to unravel these mechanisms to prevent, diagnose and recover MS. In this review, first, the current knowledge of MS and the IL-2 – IL-2R pathway are summarized. Second, the key findings of the relation between the IL-2 – IL-2R pathway and MS have been highlighted. Eventually, this review may launch broad interest in the IL-2 – IL-2R pathway propelling further research in autoimmune diseases, including MS.

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The IL-2 – IL-2R pathway determines the balance between immunity and tolerance.

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The IL-2 – IL-2R pathway is involved in the pathogenesis of multiple sclerosis.

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The role of soluble IL-2R is controversial and requires further investigation.

Causal Links between Hypovitaminosis D and Dysregulation of the T Cell Connection of Immunity Associated with Obesity and Concomitant Pathologies

Subclinical inflammation in morbid obesity is associated with immune activation and the development of concomitant diseases. Impaired immune homeostasis and immune cell dysregulation in adipose tissue are associated with phenotypic and functional changes in the pool of T lymphocytes and the development of chronic hypovitaminosis D. Low vitamin D levels in obesity lead to the activation, proliferation and production of pro-inflammatory mediators by T cells. Hypovitaminosis D is the cause of a decrease in the functional potential of regulatory and anti-inflammatory lymphocytes and the maintenance of the inflammatory response. The exact molecular genetic mechanisms of the effect of vitamin D on T lymphocytes have not been fully elucidated. Therefore, uncovering the functional role of T cells and their relationship to vitamin D homeostasis in the context of obesity development may contribute to the development of new pathogenetic methods for clinical prediction of the risk of metabolic, oncologic, autoimmune and infectious complications. The review presents the molecular genetic mechanisms of the effect of vitamin D on adipose tissue resident T lymphocytes and the characteristics of vitamin D receptor expression, and analyzes the phenotypic and functional characteristics of potentially pathogenic T lymphocytes in relation to the development of obesity and its associated complications.

Oral and Topical Vitamin D, Sunshine, and UVB Phototherapy Safely Control Psoriasis in Patients with Normal Pretreatment Serum 25-Hydroxyvitamin D Concentrations: A Literature Review and Discussion of Health Implications

Vitamin D, sunshine and UVB phototherapy were first reported in the early 1900s to control psoriasis, cure rickets and cure tuberculosis (TB). Vitamin D also controlled asthma and rheumatoid arthritis with intakes ranging from 60,000 to 600,000 International Units (IU)/day. In the 1980s, interest in treating psoriasis with vitamin D rekindled. Since 1985 four different oral forms of vitamin D (D2, D3, 1-hydroxyvitaminD3 (1(OH)D3) and 1,25-dihydroxyvitaminD3 (calcitriol)) and several topical formulations have been reported safe and effective treatments for psoriasis-as has UVB phototherapy and sunshine. In this review we show that many pre-treatment serum 25(OH)D concentrations fall within the current range of normal, while many post-treatment concentrations fall outside the upper limit of this normal (100 ng/mL). Yet, psoriasis patients showed significant clinical improvement without complications using these treatments. Current estimates of vitamin D sufficiency appear to underestimate serum 25(OH)D concentrations required for optimal health in psoriasis patients, while concentrations associated with adverse events appear to be much higher than current estimates of safe serum 25(OH)D concentrations. Based on these observations, the therapeutic index for vitamin D needs to be reexamined in the treatment of psoriasis and other diseases strongly linked to vitamin D deficiency, including COVID-19 infections, which may also improve safely with sufficient vitamin D intake or UVB exposure.