TNF and chronic obstructive pulmonary disease: TB, tuberculosis; TNF-α, tumor necrosis factor-alpha; IFN-γ, interferon-gamma; IL-6, interleukin-6; MIP, macrophage inflammatory protein; MTB, Mycobacterium tuberculosis; ETB, extrapulmonary tuberculosis; ELISA, enzyme-linked immunosorbent assay; VEGF-A, vascular endothelial growth factor-A; COPD, chronic obstructive pulmonary disease