CD8A and chronic obstructive pulmonary disease: Although some in vitro research has indicated that soluble components extracted from cigarette smoke can significantly reduce T cell activation and proliferation (Glader et al., 2006; Lambert et al., 2005), substantial evidence has shown that large numbers of CD8+ T cells are present in the airways and parenchyma of smokers with COPD (Saetta et al., 1999).