More recently, using a mouse model of experimental empyema resulting from intranasal inoculation of S. pneumoniae, Wilkosz et al. found rapid bacterial invasion of the pleural space, with raised levels of interleukin 8 (IL-8), vascular endothelial growth factor (VEGF), monocyte chemoattractant protein 1 (MCP-1), and tumor necrosis factor alpha (TNF-α) (13). Here, TNF is linked to empyema.