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Title: The immunomodulatory properties of vitamin D in vitro and in vivo
Author: Chambers, Emma Sarah
Awarding Body: King's College London (University of London)
Current Institution: King's College London (University of London)
Date of Award: 2013
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Asthma is a chronic inflammatory disease of the airways. The current cornerstone for asthma treatment is glucocorticoids (steroids), and the majority of patients respond to steroids with an improvement in lung function (Steroid Sensitive; SS). However a proportion of asthmatics do not respond to steroids with improvement in lung function (Steroid Resistant; SR), who represent those patients most at risk. Epidemiological studies demonstrate that asthma severity and poor responsiveness to treatment, is associated with vitamin D insufficiency and deficiency. Vitamin D is an immunomodulatory molecule which induces the synthesis of antimicrobial peptides and anti-inflammatory molecules, and inhibits pro-inflammatory cytokine synthesis. The overall goal of this work was to investigate immunological differences between SS and SR asthma patients, and effects of vitamin D that may explain the epidemiological observations. Peripheral blood from a clinically well-characterized cohort of SS (n=14; mean improvement in lung function or FEV1 post 2-weeks oral prednisolone 16.1%) and SR (n=23; no improvement in FEV1) asthmatics was studied by ex vivo flow cytometry. Major findings included evidence for significantly higher frequency of myeloid dendritic cells, and lower frequency of Foxp3+ CD4+ T cells in the peripheral blood of SR as compared to SS asthmatics. The accepted measure of vitamin D status is serum 25-hydroxyvitamin D3, 25(OH)D, and the severe asthmatics had significantly lower levels of serum 25(OH)D as compared to healthy controls. A significant positive correlation between the number of Foxp3+ T cells in the peripheral blood and serum 25(OH)D was observed. Following culture of PBMCs with anti-CD3 activation it was found that severe asthmatics synthesised significantly higher IL-17A levels than healthy controls, which was most striking in the SR patients. The steroid Dexamethasone (Dex) enhanced IL-3 17A production in culture, whereas the active form of vitamin D 1,25-hydroxyvitamin D3 (1,25(OH)2D3) significantly reduced IL-17A production in a Dex-independent manner. This work proposed that IL-17A inhibition by 1,25(OH)2D3 may be partially due to a CD39-dependent mechanism. In vivo evidence for a positive association between serum 25(OH)D and Foxp3+Treg numbers was further investigated in vitro. High concentrations of 1,25(OH)2D3 (10-6M) increased the frequency of Foxp3+ T cells in culture through two main mechanisms: the induction of IL-2, on which Foxp3+Treg are dependent, as well as less inhibition of Foxp3+ over Foxp3- T cell proliferation. Lower, and likely more physiological concentrations of 1,25(OH)2D3 (10-7M), which are known to enhance IL-10 synthesis, failed to significantly increase the frequency of Foxp3+ CD4+ T cells. However upon modulation of the cytokine environment to one of low IL-10 and high TGFβ, this concentration of 1,25(OH)2D3 significantly increased Foxp3+ Treg frequency. Collectively this data highlights additional immunoregulatory properties of 1,25(OH)2D3 including induction of anti-inflammatory cytokines such as IL-10 and TGFβ, inhibition of pro-inflammatory cytokines such as IL-17A and IL-22 as well as the direct induction of Foxp3+ Tregs. In conclusion evidence for a number of immunomodulatory effects of 1,25(OH)2D3 exists that may help to reduce uncontrolled inflammatory responses associated with severe asthma.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available