Plasminogen activator inhibitor type 1 is protective during severe Gram-negative pneumonia

Abstract

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 replicationdefective 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. (Blood. 2007;109:1593-1601)

PAI-1 inhibits neutrophil efferocytosis

“…Because apoptotic cell clearance is critical to the resolution of inflammation, our data suggest that PAI-1 may exacerbate inflammatory responses by blocking the clearance of apoptotic neutrophils, thereby allowing such neutrophils to become necrotic and to release their intracellular contents into the extracellular milieu. Our findings, together with previous studies demonstrating that PAI-1 enhances LPS induced neutrophil activation (22) and promotes the migration and infiltration of lymphocytes and neutrophils into inflammatory sites (19)(20)(21)27), demonstrate that PAI-1 has multiple proinflammatory roles that are independent of its participation in coagulation and microvascular thrombosis. We found that the enhanced neutrophil phagocytosis associated with PAI-1 deficiency can be abrogated by blocking LRP on macrophages with anti-LRP antibodies or the LRP-specific blocking peptide RAP, indicating that LRP participates in PAI-1 mediated modulation of efferocytosis.…”

Interleukin-1 Receptor-Associated Kinase M-Deficient Mice Demonstrate an Improved Host Defense during Gram-negative Pneumonia

“…Thus far, the involvement of IRAK-M in the innate immune response to primary bacterial pneumonia in the previously healthy host remained unexplored. Here, we used an established model of primary pneumonia caused by a common respiratory pathogen in which the bacterial load grows over time at the primary site of infection, followed by dissemination to distant body sites and sepsis, thereby allowing investigation of normal innate defense mechanisms in the respiratory tract in a clinically relevant setting (13,14). Previous studies have documented that the complete absence of MyD88 results in an impaired immune response to K. pneumoniae pneumonia (30).…”

“…Therefore, we infected WT mice with K. pneumoniae via the airways using an established model of severe pneumonia (13,14) and determined pulmonary IRAK-M expression at mRNA and protein level. IRAK-M mRNA was present at low levels in lungs of uninfected mice and displayed strong increases after infection with K. pneumoniae ( Figure 1).…”

“…Pneumonia was induced as described (13,14). Briefly, K. pneumoniae serotype 2 (ATCC 43816; American Type Culture Collection, Manassas, VA, USA) was grown for 3 h to mid-logarithmic phase at 37°C using Tryptic Soy broth (Difco, Detroit, MI, USA).…”

“…Mice were lightly anesthetized by inhalation of isoflurane (Upjohn, Ede, the Netherlands) and bacteria were inoculated intranasally. In most experiments, mice were euthanized at predefined time points (n = 7-9 per group at each time point); sample harvesting and processing, and determinations of bacterial loads and cell counts were done as described (13,14). Briefly, mice were anesthetized with Domitor (Pfizer Animal Health Care, Capelle aan der IJssel, the Netherlands; active ingredient: medetomidine) and Nimatek (Eurovet Animal Health, Bladel, the Netherlands; active ingredient: ketamine) and euthanized by heart puncture.…”