The presence of B cell-activating factor belonging to the tumour necrosis factor (TNF) family (BAFF) is increased within follicles in severe and very severe COPD patients [58, 59], around CD4+ cells, dendritic cells, follicular dendritic cells and fibroblastic reticular cells [60] as well as in patients with emphysema [61]. Here, CD4 is linked to chronic obstructive pulmonary disease.