The role of lymphocytes in the pathogenesis of asthma and COPD

Asthma and chronic obstructive pulmonary disease (COPD) are two different inflammatory disorders of the lungs which share a common functional abnormality, i.e. airflow limitation [1,2]. In asthma, airflow limitation is largely reversible, either spontaneously or with treatment, and does not progress in most cases [1]. On the other hand, airflow limitation in COPD is usually progressive and poorly reversible [2]. In asthma, the chronic inflammation causes an associated increase in airway responsiveness to a variety of stimuli, leading to recurrent episodes of wheezing, breathlessness, chest tightness and cough, particularly at night and in the early morning. Many cells are involved in the inflammatory response in asthma and, among these, CD4+ Type-2 lymphocytes, mast cells and eosinophils are thought to play a crucial role. In COPD, the poorly reversible airflow limitation is associated with an abnormal inflammatory response of the lungs to noxious particles or gases [2]. This chronic inflammation is characterized by an increased number of CD8+ Type-1 T-lymphocytes and macrophages in the lung tissue and neutrophils in the airway lumen. Lymphocytes, which are markedly different in the two inflammatory conditions, play a crucial role in the pathogenesis of asthma and COPD. In this review, we will discuss the current concepts on the recruitment, homing and activity of lymphocytes in these two respiratory diseases.