Sanhong Yu

Failure of T cell homing, reduced CD4/CD8αα intraepithelial lymphocytes, and inflammation in the gut of vitamin D receptor KO mice

Specific pathogen-free IL-10 KO mice failed to develop inflammatory bowel disease (IBD), whereas IL-10/vitamin D receptor (VDR) double KO mice developed fulminating IBD. WT CD4 T cells inhibited experimental IBD, while VDR KO CD4 T cells failed to suppress IBD. VDR KO mice had normal numbers and functions of regulatory T cells. The percentages of IL-17- and IFN-γ-secreting T cells in the gut of mice reconstituted with WT and VDR KO CD4 T cells were also not different. Instead, there were twice as many CD8αα intraepithelial lymphocytes (IEL) in mice that were reconstituted with WT CD4 T cells than in mice reconstituted with VDR KO CD4 T cells. Furthermore, VDR KO mice had reduced numbers of CD8αα IEL, absent CD4/CD8αα populations, and as a result low IL-10 production in the IEL. The lack of CD8αα IEL was due in part to decreased CCR9 expression on T cells that resulted in the failure of the VDR KO T cells to home to the small intestine. We conclude that the VDR mediates T cell homing to the gut and as a result the VDR KO mouse has reduced numbers of CD8αα IEL with low levels of IL-10 leading to increased inflammatory response to the normally harmless commensal flora.

The vitamin D receptor is required for iNKT cell development

CD1d-reactive natural killer T (NKT) cells with an invariant T cell receptor Vα14 rearrangement are a unique subset of lymphocytes, which play important roles in immune regulation, tumor surveillance, and host defense against pathogens. Vitamin D is a nutrient/hormone that has been shown to regulate conventional T cell responses but not T cell development. The data show that expression of the vitamin D receptor (VDR) is required for normal development and function of iNKT cells. The iNKT cells from VDR KO mice are intrinsically defective and lack T-bet expression. VDR KO iNKT cells fail to express NK1.1, although they express normal levels of CD122. Extrinsic factors that impact iNKT cell development and function in VDR KO mice include a failure of the liver to support homeostatic proliferation and reduced thymic expression of CD1d and other factors important for optimal antigen presentation in the thymus. In addition, VDR KO iNKT cells were intrinsically defective even when WT antigen-presenting cells were used to stimulate them.

Converging pathways lead to overproduction of IL-17 in the absence of vitamin D signaling

Multiple pathways converge to result in the overexpression of T(h)17 cells in the absence of either vitamin D or the vitamin D receptor (VDR). CD4(+) T cells from VDR knockout (KO) mice have a more activated phenotype than their wild-type (WT) counterparts and readily develop into T(h)17 cells under a variety of in vitro conditions. Vitamin D-deficient CD4(+) T cells also overproduced IL-17 in vitro and 1,25 dihydroxyvitamin D(3) inhibited the development of T(h)17 cells in CD4(+) T-cell cultures. Conversely, the induction of inducible (i) Tregs was lower in VDR KO CD4(+) T cells than WT and the VDR KO iTregs were refractory to IL-6 inhibition. Host-specific effects of the VDR were evident on in vivo development of naive T cells. Development of naive WT CD4(+) T cells in the VDR KO host resulted in the overexpression of IL-17 and more severe experimental inflammatory bowel disease (IBD). The increased expression of T(h)17 cells in the VDR KO mice was associated with a reduction in tolerogenic CD103(+) dendritic cells. The data collectively demonstrate that T(h)17 and iTreg cells are direct and indirect targets of vitamin D. The increased propensity for development of T(h)17 cells in the VDR KO host results in more severe IBD.

The paradoxical effects of vitamin D on Type 1 mediated immunity

Low vitamin D status is associated with an increased risk of Th1 mediated autoimmune diseases like inflammatory bowel disease. 1,25(OH)(2)D(3) treatments have been shown to suppress Th1 mediated immunity and protect animals from experimental autoimmunity. Th1 mediated immunity is important for clearance of a number of different infectious diseases. For tuberculosis 1,25(OH)(2)D(3) treatment is associated with decreased Th1 mediated immunity but increased bactericidal activity. Systemic candidiasis is unaffected by 1,25(OH)(2)D(3) treatment. The seemingly paradoxical effects of 1,25(OH)(2)D(3) and vitamin D on Th1 mediated autoimmunity versus infectious immunity point to a broad array of vitamin D targets in the immune system. The interplay of these vitamin D targets and their impact on the host-immune response then dictate the outcome.

Epigenetic Reduction in Invariant NKT Cells following In Utero Vitamin D Deficiency in Mice

Vitamin D status changes with season, but the effect of these changes on immune function is not clear. In this study, we show that in utero vitamin D deficiency in mice results in a significant reduction in invariant NKT (iNKT) cell numbers that could not be corrected by later intervention with vitamin D or 1,25-dihydroxy vitamin D3 (active form of the vitamin). Furthermore, this was intrinsic to hematopoietic cells, as vitamin D-deficient bone marrow is specifically defective in generating iNKT cells in wild-type recipients. This vitamin D deficiency-induced reduction in iNKT cells is due to increased apoptosis of early iNKT cell precursors in the thymus. Whereas both the vitamin D receptor and vitamin D regulate iNKT cells, the vitamin D receptor is required for both iNKT cell function and number, and vitamin D (the ligand) only controls the number of iNKT cells. Given the importance of proper iNKT cell function in health and disease, this prenatal requirement for vitamin D suggests that in humans, the amount of vitamin D available in the environment during prenatal development may dictate the number of iNKT cells and potential risk of autoimmunity.

Vitamin D and host resistance to infection? Putting the cart in front of the horse.

Vitamin D is being touted as an anti-infective agent and it has even been suggested that vitamin D supplementation could be effective against the H1N1 influenza virus. The claims are largely based on the ability of vitamin D to induce antibacterial peptides and evidence that the immune system produces active vitamin D (1,25(OH)2D3) in situ. While there are many examples of immune production of 1,25(OH)2D3 in vitro, there is little in vivo evidence. In addition, it is not clear what role immune production of 1,25(OH)2D3 has on the course of disease. Vitamin D and 1,25(OH)2D3 inhibit T helper type 1 (Th1)/Th17-mediated immune responses and autoimmune diseases by acting on the innate and acquired immune system to inhibit the function of Th1 and Th17 cells. Th1 and Th17 cells are important in host resistance to many infections including tuberculosis (TB) caused by Mycobacterium tuberculosis. Paradoxically the innate immune system is induced to produce antibacterial peptides that are effective against TB in vitro. Data from several models of infection have so far not supported a role for vitamin D in affecting the course of disease. There is also very little evidence that vitamin D affects the course of human TB infection. Experiments have not been done in cells, mice or humans to evaluate the effect of vitamin D on influenza virus. At this time it would be premature to claim that vitamin D has an effect on TB, influenza or any other infection.

The effects of whole mushrooms during inflammation.

BackgroundConsumption of edible mushrooms has been suggested to improve health. A number of isolated mushroom constituents have been shown to modulate immunity. Five commonly consumed edible mushrooms were tested to determine whether whole mushrooms stimulate the immune system in vitro and in vivo.ResultsThe white button (WB) extracts readily stimulated macrophage production of TNF-α. The crimini, maitake, oyster and shiitake extracts also stimulated TNF-α production in macrophage but the levels were lower than from WB stimulation. Primary cultures of murine macrophage and ovalbumin (OVA) specific T cells showed that whole mushroom extracts alone had no effect on cytokine production but co-stimulation with either lipopolysacharide or OVA (respectively) induced TNF-α, IFN-γ, and IL-1β while decreasing IL-10. Feeding mice diets that contained 2% WB mushrooms for 4 weeks had no effect on the ex vivo immune responsiveness or associated toxicity (changes in weight or pathology of liver, kidney and gastrointestinal tract). Dextran sodium sulfate (DSS) stimulation of mice that were fed 1% WB mushrooms were protected from DSS induced weight loss. In addition, 2% WB feeding protected the mice from transient DSS induced colonic injury. The TNF-α response in the colon and serum of the DSS challenged and 2% WB fed mice was higher than controls.ConclusionThe data support a model whereby edible mushrooms regulate immunity in vitro. The in vivo effects of edible mushrooms required a challenge with DSS to detect small changes in TNF-α and transient protection from colonic injury. There are modest effects of in vivo consumption of edible mushrooms on induced inflammatory responses. The result is not surprising since it would certainly be harmful to strongly induce or suppress immune function following ingestion of a commonly consumed food.

Invariant NKT Cell Defects in Vitamin D Receptor Knockout Mice Prevents Experimental Lung Inflammation

Vitamin D receptor (VDR) deficiency (knockout [KO]) results in a failure of mice to generate an airway hyperreactivity (AHR) response on both the BALB/c and C57BL/6 background. The cause of the failed AHR response is the defective population of invariant NKT (iNKT) cells in the VDR KO mice because wild-type (WT) iNKT cells rescued the AHR response. VDR KO mice had significantly fewer iNKT cells and normal numbers of T cells in the spleen compared with WT mice. In BALB/c VDR KO mice, the reduced frequencies of iNKT cells were not apparent in the liver or thymus. VDR KO and WT Th2 cells produced similar levels of IFN-γ and IL-5. On the BALB/c background, Th2 cells from VDR KO mice produced less IL-13, whereas on the C57BL/6 background, Th2 cells from VDR KO mice produced less IL-4. Conversely, VDR KO iNKT cells were defective for the production of multiple cytokines (BALB/c: IL-4, IL-5, and IL-13; C57BL/6: IL-4 and IL-17). Despite relatively normal Th2 responses, BALB/c and C57BL/6 VDR KO mice failed to develop AHR responses. The defect in iNKT cells as a result of the VDR KO was more important than the highly susceptible Th2 background of the BALB/c mice. Defective iNKT cell responses in the absence of the VDR result in the failure to generate AHR responses in the lung. The implication of these mechanistic findings for human asthma requires further investigation.

Interleukin-2-inducible T cell kinase (Itk) network edge dependence for the maturation of iNKT cell.

Invariant natural killer T (iNKT) cells are a unique subset of innate T lymphocytes that are selected by CD1d. They have diverse immune regulatory functions via the rapid production of interferon-γ (IFN-γ) and interleukin-4 (IL-4). In the absence of signaling nodes Itk and Txk, Tec family non-receptor tyrosine kinases, mice exhibit a significant block in iNKT cell development. We now show here that although the Itk node is required for iNKT cell maturation, the kinase domain edge of Itk is not required for continued maturation iNKT cells in the thymus compared with Itk-null mice. This rescue is dependent on the expression of the Txk node. Furthermore, this kinase domain independent edge rescue correlates with the increased expression of the transcription factors T-bet, the IL-2/IL-15 receptor β chain CD122, and suppression of eomesodermin expression. By contrast, α-galactosyl ceramide induced cytokine secretion is dependent on the kinase domain edge of Itk. These findings indicate that the Itk node uses a kinase domain independent edge, a scaffolding function, in the signaling pathway leading to the maturation of iNKT cells. Furthermore, the findings indicate that phosphorylation of substrates by the Itk node is only partially required for maturation of iNKT cells, while functional activation of iNKT cells is dependent on the kinase domain/activity edge of Itk.