Induction of Acute Pleural In¯ammation 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 immunode®ciency syndrome (AIDS). A model of Staphylococcus aureus empyema was de-veloped that closely resembles bacterial empyema in patients infected with human immuno-de®ciency 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-a (KC), and macrophage in¯ammatory protein±2 levels were signi®cantly ( ) lower in CD4+ knockout (CD4P!.001 KO) mice pleural ¯uid 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-g levels were increased in CD4 WT mice. CD4+ T cell depletion results in a decreased pleural chemokine response, decreased neutrophil in¯ux into pleural space, and impaired bacterial clearance in empyema. The presence of bacterial organisms in the pleural space is de®ned as empyema, a well-described complication of pneu-monia [1]. Bacterial pneumonia is more frequent in patient