[Truncated abstract] Atopic asthma pathogenesis is driven by the combined effects of airway inflammation generated during responses to viral infections and aeroallergens, and both of these pathways are regulated by dendritic cells (DC) that differentiate locally from monocytic precursors. These DC normally exhibit a sentinel phenotype characterised by active antigen sampling but attenuated presentation capability, which limits the intensity of local expression of adaptive immunity. How this tight control of airway DC functions is normally maintained and why it breaks down in some atopics leading to immunopathological changes in airway tissues, is unknown. In the airway mucosa, DC are intimately associated with airway epithelial cells (AEC), which are a source of a range of both pro- and anti-inflammatory mediators. A few studies have previously examined the effects of AEC-derived surface-expressed and soluble mediators upon the function of pre-differentiated DC, although there is a dearth of information as to the extent of AEC-conditioning of DC during their generation from incoming monocytic precursors within the airways. Therefore, this study was designed to test the hypothesis that signals from adjacent AEC contribute to regulation of local differentiation of airway mucosal DC, especially in the context of allergic airway disease. A direct co-culture model was developed containing the AEC line 16HBE 14o- as a surrogate for primary AEC, and purified peripheral blood monocytes derived from atopic patients in a GM-CSF/IL-4-enriched cytokine milieu. Cells were cultured for 5 days, at which time the phenotype and functional attributes of the monocyte-derived DC (MDDC) generated in the presence of AEC (AEC-MDDC) were compared to the control MDDC population generated without AEC contact (Ctrl- MDDC). ... In parallel, an attenuation of mRNA boosting for 7 out of 12 selected Th2-asscociated genes as well as IL-13 protein, was observed in AEC-MDDC supplemented cultures compared to ctrl-MDDC supplemented cultures. The data collected in the initial characterisation of the AEC-MDDC in Chapter 3 and further analysis of their gene expression profiles by microarray suggest a number of DC-associated factors could be involved in directing a potential bias against Th2 immunity within the T-cell recall response. These include increased expression of IL- 12 subunit mRNA and the enhanced levels of surface MHC Class II, CD80, ICAM-1 and SLAM. Further to Th1/Th2 modulation, a number of T-regulatory (Treg) genes were differentially expressed in the AEC-MDDC-re-activated CD4+ T-cells, and members of the chemokine and metallothionein families were elevated in the same population. Collectively the results of this study suggest that in the context of the atopic airway microenvironment where there is an abundance of Th2-related mediators, healthy AEC arm locally maturing DC with an arsenal of anti-microbial defences that can be rapidly employed in response to encounter with inhaled pathogens, in particular viruses. In this way, the DC are maintained in an ideal functional phenotype to efficiently mobilise both innate and Th1-polarised adaptive immune defences against infection, whilst achieving tight control of potentially-damaging Th2 immunity to aeroallergens, thus contributing to the maintenance of immunological homeostasis within the respiratory tract.
|Qualification||Doctor of Philosophy|
|Publication status||Unpublished - 2009|