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Atopic asthma is a chronic inflammatory disease of the airways. Even though T cell plasticity is becoming more important in the context of atopic asthma, TH2 cells still count as one of the main contributing factors in the pathophysiology of the disease. With their specific cytocine production, they orchestrate and maintain the chronic respiratory inflammation which can ultimately lead to a remodeling of the airways.
Why it is that atopic indiviuals react with a TH2 cell dominated immune response upon allergen contact is still not fully understood, but it is believed to be caused by a combination of genetic, epigenetic, and posttranscriptional regulation. An important part of posttranscriptional regulation is the large group of microRNAs (miRNAs) that was discovered only about twenty years ago. Changes in miRNA expression can have numerous effects on gene expression levels in both physiological and pathological conditions, including differentiation, activation, and key effector functions of immune cells. miRNA expression arrays of T helper cells isolated from lungs of mice with acute asthma phenotype showed higher miRNA-15b levels in TH2 cells compared to TH1 and naïve T helper cells. These results demanded further research and are the subject of this dissertation.
The research objective for this thesis was to contribute to a better understanding of the role of miRNA in the pathogenesis of atopic asthma. This was achieved by analyzing the expression of miRNA-15b during the differentiation of TH1 and TH2 cells from naïve T helper cells in vitro. Furthermore, the influence of the miRNA-15b on the expression of IFN-γ in T helper cells was investigated in vitro and in isolated CD4+ cells from mouse models of atopic asthma.
As a result, it could be shown that miRNA-15b is increasingly expressed during T helper cell differentiation compared to naïve T helper cells, but in contrast to the miRNA arrays mentioned above, no difference in expression levels between TH1 and TH2 cells was found in vitro. In addition to this finding, IFN-γ was shown to be a predicted target of miRNA-15b in silico and could be experimentally validated with luciferase reporter assays. Furthermore, it was demonstrated that transfection of anti miRNA-15b had no effect on IFN-γ expression in vitro but increased IFN-γ-mRNA in ex vivo isolated T helper cells from models of acute asthma. Methodically, lipofection with HiPerFect could be presented as an alternative method for transfecting primary T helper cells.
These findings show that miRNA-15b targets IFN γ and that it seems to have an effect on IFN-γ expression in T helper cells in atopic asthma. This makes it an interesting topic for further research.