TNF and chronic obstructive pulmonary disease: These include C-reactive protein (CRP), interleukin-1 beta (IL-1 beta), interleukin-6 (IL-6), interleukin-8 (IL-8) and tumor necrosis factor-alpha (TNF-alpha), which are among the most extensively evaluated inflammatory markers in COPD research and exhibit increased levels when compared with healthy subjects [17,18].