CD4 and chronic obstructive pulmonary disease: As assessed by bronchoalveolar lavage, CD4+ T cells are reduced in the lungs of active smokers without airflow obstruction [25] and in active smokers regardless of airflow obstruction [26], whereas bronchial biopsies showed increased intraepithelial CD4+ T cells in COPD patients, relative to smokers and never-smokers [27].