TNF and chronic obstructive pulmonary disease: Previous studies have used quantitative enzyme-linked sandwich immunoassays (ELISA) to measure a limited number of biomarker proteins and have shown that serum C-reactive protein levels (CRP), and sputum neutrophil chemo-attractants such as interleukin-8 (IL-8), and tumor necrosis factor-α (TNFα), are significantly higher in patients with COPD compared to controls [3,4].