CD4 and chronic obstructive pulmonary disease: For many years, CD4+ Th1 lymphocytes have been considered key players in the COPD inflammation process due to the high expression of cytokines related to the Th1 response, such as TNF-α (tumour necrosis factor-α) during exacerbations and interferon-γ (IFN-γ), in emphysematous patients (12–14).