a) Activation of CD4+cells: Studies have reported an increased concentration of CD4+ T lymphocytes in the airways and lung tissue of COPD patients as well as an increased proportion of activated CD4+ cells relative to non-COPD patients.132,149 A study reported the presence of fully activated forms of both CD4+ and CD8+ T lymphocytes manifesting a predominant Th1/cytotoxic phenotype resulting in an exaggerated expression of proinflammatory and tissue injury cytokines.150. Here, CD8A is linked to chronic obstructive pulmonary disease.