Asthma is an inflammatory airways disease affecting over 339 million people of all ages worldwide. More than 10% of asthmatics have uncontrolled severe disease which is insensitive to high doses of oral corticosteroid treatment. Type 2 innate lymphoid cells (ILC2) are pro-inflammatory lymphomononuclear cells proposed as critical drivers of eosinophilic inflammatory disease of the upper and lower airways. Controlling this activity may provide novel therapies for asthma. This thesis aimed to investigate factors that affect the local activation and expansion of ILC2 in the airways including anti-inflammatory medications such as (i) corticosteroids, (ii) neuro-immune regulation of ILC2, and (iii) effect of locally generated cytokines on ILC phenotypes and the relationship to the ongoing airway inflammatory profile. We firstly investigated the effect of intranasal corticosteroids on activation levels of ILC2 in the upper airway of allergic rhinitics with mild asthma following controlled nasal allergen challenge (Chapter 2). Following pre-treatment with intranasal corticosteroid there was an attenuation in the allergen-induced increase in total ILC2 and IL-5/13+ ILC2 in the nasal mucosa. In addition, HLA-DR expression on ILC2 in the nasal mucosa was down-regulated. Overnight culture with IL-2, TSLP or IFN-γ up-regulated HLA-DR expression on ILC2, in vitro; an effect that is inhibited in the presence of corticosteroids. Attenuation of HLA-DR expression by ILC2 may be an additional mechanism by which corticosteroids modulate adaptive immune responses in the airways. We have previously reported that lung ILC2 are activated within 7h following allergen-inhalation challenge. Since airway mucosal tissue is highly innervated, we investigated whether neuroimmune interactions may trigger early and rapid host immune responses (Chapter 3). In a diluent-controlled allergen-inhalation challenge cross-over study, where mild asthmatics developed early and late bronchoconstrictor responses with sputum eosinophilia (>3%), NMUR1, a receptor for the neuropeptide, neuromedin-U, was up-regulated on sputum ILC2 in 7h post allergen challenge. This was associated with increased expression of IL-5/IL-13 by sputum ILC2 post-allergen and following in vitro culture. ILC2 activation was mediated through a MAPK/PI3 kinase dependent-signaling pathway that was attenuated in the presence of dexamethasone. Co-culture with IL-33 and TSLP, in vitro up-regulated NMUR1 expression on ILC2 at the protein and transcriptomic level which was attenuated by dexamethasone. The close interplay between neuropeptide signalling and tissue-derived alarmin cytokines may be important interactions for rapid ILC2 activation in airway inflammatory responses in asthma. We have reported increased ILC2 with the highest level of IL-5/13+ ILC2 in the airways of severe asthma with uncontrolled eosinophilia (>3%). The prevalence and phenotypic analyses of innate lymphoid cells subsets in severe asthma with neutrophilic or mixed granulocytic airway inflammatory endotypes remains unclear and was investigated in Chapter 4. Sputum ILC3 were most abundant in severe asthma with neutrophilic airway inflammation where IL-17A+ ILC3 correlated with airway neutrophilia. ILC2 were predominant in severe asthma with airway eosinophilia. Importantly, we identified an intermediate ILC2 phenotype displaying ILC3-like markers (c-kit and IL-17A) in severe asthma with neutrophilic and mixed granulocytic airway inflammation. Inflammasome related cytokines, IL-1β and IL-18 were significantly increased in the airways of these patients. At both proteomic and transcriptomic levels, flow sort-purified ILC2 trans-differentiated to the intermediate phenotype when co-cultured with IL-1β+IL-18. Blocking inflammasome-related cytokines may control T2-low severe asthma exacerbations. Collectively, the findings of this thesis highlight the role of corticosteroids, neuropeptides and airway inflammasome related cytokines as modulators of ILC fate and activity in asthma. / Thesis / Doctor of Philosophy (PhD) / Asthma is a disease of the airways that makes breathing difficult. About 10% of asthma patients have uncontrolled severe symptoms despite treatment with high doses of corticosteroids which imposes many unwanted side effects. Investigating processes that worsen the disease will help to discover new treatments for asthma. Type 2 innate lymphoid cells (ILC2) are novel cells that produce large quantities of factors which attract and activate effector cells to the lungs which in turn make breathing difficult. This thesis investigated whether controlling ILC2 activity reduces asthma symptoms by studying i) responsiveness of ILC2 to corticosteroids using a controlled allergen exposure through the nose in people with allergic rhinitis and mild asthma, ii) the role of airway nerves and mediators on ILC2 activation, and iii) the ability of signals produced by the lungs to impact factors released by ILC2 and the relationship to effector cells found in the airways of severe asthma. Overall, ILC2 activation can be modulated by corticosteroids, nerve derived factors and lung tissue derived cytokines, and this is associated with changes in the number and type of effector cells in the lungs.