Characterization of T Lymphocytes in Chronic Obstructive Pulmonary Disease

Perspectives Open access, freely available online C hronic obstructive pulmonary disease (COPD) is a global epidemic of major proportions that is predicted to become the third most common cause of death and fi fth most frequent cause of chronic disability by 2020. In developed countries it is mainly caused by cigarette smoking, but the reasons why only a proportion (10%–20%) of smokers develop progressive airfl ow limitation is currently unknown. The disease is characterized by a chronic infl ammatory process predominantly in the small airways and lung parenchyma, with increased numbers of macrophages, neutrophils, and T lymphocytes [1]. The difference between smokers without COPD and smokers with COPD appears to be the intensity rather than the nature of the infl ammatory process. This infl ammation in the small airways is associated with fi brosis and increases with the severity of airfl ow limitation [2], which has led to the view that COPD represents an amplifi cation of the normal infl ammatory response to inhaled irritants such as cigarette smoke. T Lymphocytes in COPD T lymphocytes were fi rst reported to be increased in patients with COPD by Finkelstein and colleagues, who showed a correlation between the number of T lymphocytes/mm 3 of lung and the extent of emphysema [3]. It was later shown that both CD4 + (T helper) and CD8 + (suppressor/cytotoxic) T cells were increased in the airways and lung parenchyma of patients with COPD, with a predominance of CD8 + cells [4,5]. This is in contrast to the fi ndings in asthma, in which there is a predominance of CD4 + cells, which are predominantly of the T helper 2 (Th2) pattern, with increased expression of interleukin (IL)-4, IL-5, and IL-13 (see Glossary), and which are associated with an increased number of eosinophils. In smokers who develop COPD there appears to be activation of adaptive immunity, with the infi ltration of CD8 + and CD4 + cells in the alveolar walls and small airways and—in patients with the most severe disease—the presence of lymphoid follicles that contain a core of B lymphocytes surrounded by T cells [2]. This activation presumably follows on from the initial and then sustained innate immune response characterized by increased numbers of macrophages and neutrophils; it may involve the migration of dendritic cells from the epithelium to the local lymph nodes and presentation of antigenic substances to T cells, resulting in clonal expansion …