CD4 and chronic obstructive pulmonary disease: Chronic obstructive pulmonary disease (COPD) is the third leading cause of death globally and is characterized by progressive airway inflammation, emphysema, and reduced lung function.1, 2, 3, 4 Chronic pulmonary inflammation in COPD is underpinned by innate immune responses and primarily involves macrophages (alveolar and interstital), neutrophils, dendritic cells, natural killer cells, and innate lymphoid cells (ILCs).5–7 This is associated with concomitant increases in the number of adaptive immune cells, primarily infiltrating CD4+ and CD8+ T and B lymphocytes.5, 6