Dendritic cells and lipidomics in asthma

Lead Research Organisation: Imperial College London
Department Name: UNLISTED

Abstract

Health problems resulting from asthma are increasing despite advances in its treatment. There is some evidence that a diet that includes fish oils in early life may confer protection against disease, although evidence that increased intake of the omega-3 fats found in fish oils are beneficial once disease has developed is not convincing. However, some chemicals derived from fats are changed in the airways in asthma suggesting that the way in which fats are used is important in the disease. Another feature of asthma is that ?dendritic cells? - the cells that introduce foreign substances to stimulate the immune system - are involved in stimulating the unwanted inflammation in the airways. One problem in studying the immune activity in the airways has been that the cells involved are difficult to obtain and so invasive techniques are required for this. However, we have recently found that we can obtain airway dendritic cells from sputum, if we induce its production by getting people to inhale a harmless salt spray. This means that we can now more easily study airway dendritic cells in asthma.
In background studies, we have shown that exposure of dendritic cells to some types of fats and stimulation with foreign antigen or other factors results in the appearance of fatty material of a distinct structure inside the cells that can be seen with a high powered microscope. These fatty structures are called ?lipid bodies?. Lipid bodies are known to be the sites in cells where fats are metabolised to produce factors that modulate immune activity.
We propose to study the factors that influence the production and breakdown of lipid bodies in dendritic cells and how they relate to the function of the dendritic cells. Furthermore we plan to identify differences in these processes in patients with asthma compared with healthy people. An understanding of these processes and factors in relation to the functioning of the immune system will help us to develop better ways to prevent and to treat asthma.

Technical Summary

Allergic asthma, which shows increasing prevalence, is characterised by chronic inflammation and smooth muscle hyper-reactivity of airways, symptoms probably induced by excessive T-helper cell type 2 responses to normally benign inhaled antigens. There is a changed eicosenoid production and involvement of dendritic antigen presenting cells (DC) in production of inflammatory lesions. Using in vitro studies, we showed that lipid bodies - known to be sites of eicosanoid metabolism - appear in DC influenced by certain fatty acids, cytokines or antigenic exposure. We have also shown that, in vivo, the balance of fatty acids and hence availability of lipid mediator precursors differs between leukocytes, serum and adipose tissue. A major challenge in studying lipid-DC interactions in human inflammatory diseases such as asthma is the difficulty in sampling relevant tissues. By inducing sputum, a comparatively non-invasive technique, we were able to harvest human airways DC. In asthma, these DC showed a mature phenotype, increased capacity to endocytose antigen and increased expression of CD1 molecules.
We will investigate the hypothesis that changes in uptake and metabolism of fatty acids within DC alter signalling pathways, modulating DC functions instrumental in the development of asthma. In order to test this hypothesis we shall study DC from both sputum and peripheral blood and ask whether distribution of fatty acids and their metabolites in lymphocytes and DC are altered in asthma. The induction of lipid bodies and their molecular components will be studied using electron and confocal microscopy, flow cytometry and fatty acid/eicosenoid analysis to test whether they are sites of changed lipid mediator production in asthma. We shall then ask whether mechanisms of activation of DC via receptors involved in both immune activation and lipid metabolism, particularly PPARgamma, are changed in asthma and whether ex vivo airway DC from asthma patients show evidence of activation via these pathways using our sensitive quantitative gene expression technique in purified DC. Finally, in parallel we will investigate the role of upregulated CD1 on DC in asthma, by characterising the CD1-restricted responses of T- and NKT-cells, stimulated by DC, using 5- (and 6-) carboxyfluorescein diacetate succinimidyl ester (CFSE) labelling and multi-colour flow cytometry.
In conclusion, study of uptake and metabolism of fatty acids by DC will provide novel information about links between the roles of fatty acids and eicosanoids and the immune system in asthma and provide a sounder evidence-base for development of rational dietary and immunomodulatory therapies for asthma.

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