TNF and pericardial effusion: Inflammatory cell infiltration and fibrosis confirm that, despite minimal virulence, P. acnes has an immune-stimulatory effect on the mononuclear phagocyte system [4]. P. acnes stimulates production of inflammatory mediators such as metalloproteinases and tumor necrosis factor alpha by macrophages [4], which could lead to exuberant inflammation of the pericardium, pericardial effusions, and constrictive physiology.