CD4 and chronic obstructive pulmonary disease: Hallmarks of early stages of COPD include remodeling of small airways induced by persistently activated innate immune cells (alveolar macrophages, neutrophils, natural killer (NK), and DCs), while severe stages of COPD are characterized by the development of lung lymphoid follicles due to the enhanced activation of CD8+ cytotoxic T lymphocytes (CTLs) and CD4+ T helper cells and their crosstalk with B cells [4–8].