TNF and infection: The cytokine response to parapneumonic empyema has been referenced by Dal Nogare et al.[11, 12] Infection stimulates the simultaneous expression of multiple pro-inflammatory cytokines, such as TNF-α (tumor necrosis factor, alpha), interleukin IL-1, IL-2, IL-6 and TGF-β (transforming growth factor beta); this last cytokine in turn stimulates over-expression of PAI-1 (plasminogen activator inhibitor, type 1) in the pleura.