CD4 and chronic obstructive pulmonary disease: Increased levels of EVs derived from T cell could be caused by the activation of CD4+/CD8+ T lymphocytes that already exist in the airways, or by the accumulation of up-regulated CD4+/CD8+ cells, recruited during the development of COPD, suggesting that also these subtypes of EVs could be considered putative biomarkers to distinguish different types of inflammation.