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Blood, 15 February 2007, Vol. 109, No. 4, pp. 1593-1601. Prepublished online as a Blood First Edition Paper on October 10, 2006; DOI 10.1182/blood-2006-05-025197.
IMMUNOBIOLOGY Plasminogen activator inhibitor type 1 is protective during severe Gram-negative pneumonia1 Center for Infection and Immunity Amsterdam, 2 Center for Experimental and Molecular Medicine, Departments of3 Pathology, 4 Biochemistry, and 5 Vascular Medicine, Academic Medical Center, University of Amsterdam, The Netherlands; 6 Center for Transgene Technology and Gene Therapy, University of Leuven, Belgium Plasminogen activator inhibitor type-1 (PAI-1) levels are consistently elevated in patients with severe pneumonia and sepsis and highly predictive for an unfavorable outcome. In addition, pneumonia is associated with strongly elevated PAI-1 levels in the pulmonary compartment. However, whether PAI-1 causally affects antibacterial host defense in vivo remains unknown. We report here that pneumonia caused by the common respiratory pathogen Klebsiella pneumoniae is associated with local production of PAI-1 in the lungs of wild-type mice. PAI-1 deficiency impaired host defense as reflected by enhanced lethality and increased bacterial growth and dissemination in mice with a targeted deletion of the PAI-1 gene. Conversely, transgenic overexpression of PAI-1 in the lung using a replication-defective adenoviral vector markedly improved host defense against Klebsiella pneumonia and sepsis. PAI-1 deficiency reduced accumulation of neutrophils in the lungs during pneumonia, whereas PAI-1 overexpression in healthy lungs resulted in neutrophil influx, suggesting that PAI-1 protects the host against Klebsiella pneumonia by promoting neutrophil recruitment to the pulmonary compartment. These data demonstrate for the first time that PAI-1 is essential for host defense against severe Gram-negative pneumonia.
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