Investigation of the role of T cells in airway inflammation using novel murine models of disease

Asthma is a highly prevalent disease characterised by variable airflow obstruction, bronchial hyperresponsiveness and airways inflammation. Studies over the last 20 years have established that an immunological response centred on Th2 lymphocytes and their mediators is critical to the development of the disease, although other elements including structural cells are thought to contribute to the final outcome. In this thesis animal models have been developed to investigate the role of inflammation in the development and progression of allergic airways disease. As CD4+ T cells have been suggested as a possible therapeutic target in asthma, techniques were employed that allowed the identification and quantification of antigen-specific T cells in different anatomically relevant compartments including, draining and peripheral lymph nodes, lungs and bronchoalveolar lavage fluid, providing novel information on the role of T ceils in these models. This information produced has important implications for future development of therapeutic agents targeting T cells. To investigate the role of antigen-specific T cells in airways inflammation, an adoptive transfer model was established. The aim of the model was to allow tracking of antigen-specific T cells as well as inducing airway eosinophilia in conjunction with IgE production and associated Th2 cytokines. Our investigations revealed that a single immunisation with OVA followed by 1-3 intranasal antigen airway challenges did not induce BAL eosinophilia although identification of Ag-specific T cells was possible in the lymph nodes and the lung. However, it was found that a more aggressive regime of three immunisations and one airways challenge was required to induce lung eosinophilia and associated pathology (long model). Manipulation of the single immunisation, single airway challenge with the addition of LPS to antigen in the airways challenge resulted in lung eosinophilia and pathology (short model) as seen in the three prime, one challenge model, demonstrating that different models can be adapted to produce the same outcome. It was found that when antigen-specific T cells were compared between the two models where pathology or no pathology was see, resulted in different expression of certain cytokines, costimulatory molecules and chemokine receptors. When no pathology was present, it was found that IFNy was upregulated in both models. In the long model when pathology was present, IL-5 expression was upregulated, and in contrast IL-13 was upregulated in the short model when pathology was induced, with CCR3 upregulated in both models. This data demonstrates that although similar endpoints were observed the route by which the response was initiated differs. To determine the site of T cell division in airway inflammation, antigen-specific T cells were tracked in different compartments throughout the course of disease and their expression of proliferating cell nuclear antigen (PCNA) was measured as an indication of their recent division. When T cell division was quantified by LSC in the long model it was found that there was an early wave of T cell division seen in the lung, followed by similar in the draining lymph node. Subsequently, another wave of antigen-specific T cell division was seen in the lung tissue. The early T cell division may have been caused by uptake and presentation of antigen by resident dendritic cells, which have been shown to be present in the lung. The location of these dendritic cells allows them to have direct contact with incoming antigens. It is known that there is a dendritic cell network situated immediately above and beneath the basement membrane of the upper and lower airways enabling these cells to sample the epithelium for inhaled antigens. It has also been shown in experimental models of respiratory infection that a population of memory T cells are established in the lung parenchyma and the lung airways. Airway resident memory cells contribute significantly to recall responses by providing immediate effector activity at the site of antigen entry, showing that there is local antigen presentation in the lung. This data gives an insight into the location and timing of T cell division and activation and may enable more accurate therapeutic intervention in airways inflammation. (Abstract shortened by ProQuest.)