Research plan: Patients with chronic obstructive pulmonary disease (COPD) suffer from reduced lung function, in particular a decrease in maximum expiratory flow. The airflow limitation is in general not reversible, and progresses steadily over time, especially with continued exposure to cigarette smoke. Further symptoms include cough, dyspnoea, an increase of airway secretions and sputum production. The airflow limitation is the result of airway inflammation and/or emphysema in most patients. The signs of inflammation are not restricted to the airways: abnormal levels of inflammatory proteins are present in the blood, and several cells in the blood show signs of inflammatory activation. The exact pathogenetic mechanisms in COPD are unknown, but cigarette smoking is a prominent risk factor. Recently, the presence of subepithelial CD8 T lymphocytes in the central and peripheral airways has been shown to be associated with the impairment of lung function. The demonstration of increased numbers of subepithelial CD8 T lymphocytes and their relation with decreased lung function warrants further investigation of their role in the pathophysiology of COPD. We propose that CD8 T cells contribute to the immunopathological reactions in COPD either by direct cytotoxic reactions to cells in the airways and/or by release of proteolytic enzymes. The activation of the CD8 T cells may be autoimmune in nature and/or directed to virus-infected cells and/or antigenic structures of cells induced by toxic environmental agents. Irrespective of their exact antigenic specificity, the CD8 effector responses may cause damage and activation of airway epithelial cells, resulting in increased secretory activities. As a consequence there may be increased secretion of interleukin (IL)-8 and chemo-attraction of neutrophilic granulocytes into the airway lumen. This may result in a continuous cycle of inflammation sustained by proteolytic enzymes from neutrophils. In this hypothesis antigen-specific immune activation of CD8 T cells is important. Recent developments in the insight into the characteristics of CD8 T cells make it possible to test the hypothesis of a functional role of CD8 T cells in the pathology of COPD. CD8 T cells in the blood can be subdivided into naive, memory and memory effector cells, characterized by unique combinations of membrane surface markers. The memory effector cells have a high capacity for the production of IFN-gamma and TNF-alpha, they produce perforin and granzyme B and have potential cytotoxic capacity. Interestingly, the subpopulation of memory effector cells occurs in increased numbers in the blood after antigen-specific stimulation of the immune system, e.g. in acute and chronic viral infections. In our own studies in patients with obstructive lung diseases, we have found abnormal numbers of such cells in both asthma and COPD patients. Further advancements in the characterization of T cells involve the level of markers for cells that home to defined organs and markers for the restriction in the heterogeneity of T cell diversity, thereby allowing us to focus on cells that are supposed to be chronically stimulated antigen-specific T cells. In this project we want to test our hypothesis that antigen-specific immune activation of CD8 T cells is important in the pathophysiology of COPD. We plan to do this in the following stepwise approach: first we shall investigate whether there are abnormal numbers of CD8 memory effector cells in the blood of patients with COPD, and whether these cells are oligoclonal on the basis of restricted heterogeneity of the T cell receptor CDR3 length. Establishing this will form a firm basis for further investigation into the role of such cells: How are the numbers of such cells in the blood affected by exacerbations? Is their occurrence related to a decrease of lung function? Is it possible to demonstrate enrichment of such cells in the BAL fluid and biopsy sections of lung tissue from patients? Is it possible to demonstrate specific activation of these cells by material from BAL fluid and brushes from the airways? These studies will be done in a cross-sectional as well as in an longitudinal approach. In the cross-sectional study we plan to study 30 patients with COPD (15 not regularly using inhaled corticosteroids and 15 using inhaled steroids), 30 age- and sex-matched subjects with smoking habits matched to the COPD group but without airway obstruction, and 30 age- and sex-matched non-smoking healthy subjects. In the longitudinal study we plan to do a follow-up of 40 patients with COPD, and collect blood samples at regular time intervals and during exacerbations of the disease. In a subgroup af patients, bronchoscopy will be performed to obtain BAL fluid cells, bronchial brushes and biopsies. Cells thus obtained will be analysed for their correspondence with the defined memory effector cells. Furthermore, material thus obtained will be tested for the capacity to specifically stimulate the memory effector cells. The results of this study will provide more insight into the characteristics of the CD8 T cell population in COPD and will answer the question of to what extent this cell population may play a role in the pathophysiological reactions in COPD.