CD4 and chronic obstructive pulmonary disease: Several studies have suggested that COPD may have an autoimmune component that is related to Th17 cells, a subset of CD4+ T cells, present in COPD.21‐23 Peripheral-blood Th17 cell count was increased in patients with COPD, which was predictive of the severity of airflow limitation.24 Th17 cells release IL-17A, IL-17F, and IL-22, all of which have been implicated in the pathogenesis of several inflammatory and autoimmune diseases.