CD4 and chronic obstructive pulmonary disease: Along with innate cells, there is an increase in adaptive immune cells, predominatory CD4+ and CD8+ T lymphocytes and B lymphocytes in both the large and peripheral airways in patients with COPD.13, 14, 15, 16 In mice exposed to CS, CD8‐deficient (−/−), but not CD4−/− mice, are protected from CS‐induced hallmark features of COPD, specifically macrophage accumulation, MMP2 and MMP9 activity, and emphysema,17, 18 indicating a key role of CD8+ lymphocytes in disease pathogenesis.