Induction of acute pleural inflammation by Staphylococcus aureus. I. CD4+ T cells play a critical role in experimental empyema.

Bacterial empyema is a frequent complication of pneumonia in patients with acquired immunodeficiency syndrome (AIDS). A model of Staphylococcus aureus empyema was developed that closely resembles bacterial empyema in patients infected with human immunodeficiency virus (HIV). Results show a compartmentalized chemokine response in bacterial empyema. The chemokine levels were higher in the pleural compartment than in the peripheral circulation. Polymorphonuclear leukocyte counts, murine GRO-alpha (KC), and macrophage inflammatory protein-2 levels were significantly (P<.001) lower in CD4+ knockout (CD4 KO) mice pleural fluid than in CD4+ wild-type (CD4 WT) mice. The CD4 KO mice had poorer bacterial clearance than CD4 WT mice. During S. aureus infection, interleukin-10 levels increased in the CD4 KO mice, whereas interferon-gamma levels were increased in CD4 WT mice. CD4+ T cell depletion results in a decreased pleural chemokine response, decreased neutrophil influx into pleural space, and impaired bacterial clearance in empyema.