title: Leptin-deficient mice exhibit impaired host defense in Gram-negative pneumonia.
abstract: Leptin is an adipocyte-derived hormone that is secreted in correlation with total body lipid stores. Serum leptin levels are lowered by the loss of body fat mass that would accompany starvation and malnutrition. Recently, leptin has been shown to modulate innate immune responses such as macrophage phagocytosis and cytokine synthesis in vitro. To determine whether leptin plays a role in the innate host response against Gram-negative pneumonia in vivo, we compared the responses of leptin-deficient and wild-type mice following an intratracheal challenge of Klebsiella pneumoniae. Following K. pneumoniae administration, we observed increased leptin levels in serum, bronchoalveolar lavage fluid, and whole lung homogenates. In a survival study, leptin-deficient mice, as compared with wild-type mice, exhibited increased mortality following K. pneumoniae administration. The increased susceptibility to K. pneumoniae in the leptin-deficient mice was associated with reduced bacterial clearance and defective alveolar macrophage phagocytosis in vitro. The exogenous addition of very high levels of leptin (500 ng/ml) restored the defect in alveolar macrophage phagocytosis of K. pneumoniae in vitro. While there were no differences between wild-type and leptin-deficient mice in lung homogenate cytokines TNF-alpha, IL-12, or macrophage-inflammatory protein-2 after K. pneumoniae administration, leukotriene synthesis in lung macrophages from leptin-deficient mice was reduced. Leukotriene production was restored by the addition of exogenous leptin (500 ng/ml) to macrophages in vitro. This study demonstrates for the first time that leptin-deficient mice display impaired host defense in bacterial pneumonia that may be due to a defect in alveolar macrophage phagocytosis and leukotriene synthesis.
authors.affiliation: Department of Environmental Health Sciences, University of Michigan, Ann Arbor, MI 48109, USA. pmancuso@umich.edu
authors.forename: Peter
authors.initials: P
authors.lastname: Mancuso
authors.forename: Andrew
authors.initials: A
authors.lastname: Gottschalk
authors.forename: Susan M
authors.initials: SM
authors.lastname: Phare
authors.forename: Marc
authors.initials: M
authors.lastname: Peters-Golden
authors.forename: Nicholas W
authors.initials: NW
authors.lastname: Lukacs
authors.forename: Gary B
authors.initials: GB
authors.lastname: Huffnagle
mesh_terms: D000818:Animals; D000942:Antigens, Bacterial / Q000008:administration & dosage / Q000276:immunology; D001992:Bronchoalveolar Lavage Fluid / Q000737:chemistry; D002478:Cells, Cultured; D054426:Chemokine CXCL2; D018925:Chemokines / Q000096:biosynthesis; D015169:Colony Count, Microbial; D003545:Cysteine / Q000037:antagonists & inhibitors / Q000096:biosynthesis; D005260:Female; D007113:Immunity, Innate / Q000235:genetics; D018664:Interleukin-12 / Q000096:biosynthesis; D007442:Intubation, Intratracheal; D007710:Klebsiella Infections / Q000235:genetics* / Q000276:immunology* / Q000382:microbiology / Q000401:mortality; D007711:Klebsiella pneumoniae / Q000254:growth & development / Q000276:immunology*; D020738:Leptin / Q000097:blood / Q000172:deficiency* / Q000235:genetics* / Q000494:pharmacology; D007958:Leukocyte Count; D020024:Leukotriene Antagonists; D015289:Leukotrienes / Q000096:biosynthesis; D008168:Lung / Q000378:metabolism; D016676:Macrophages, Alveolar / Q000276:immunology; D051379:Mice; D008810:Mice, Inbred C57BL; D008820:Mice, Obese; D010587:Phagocytosis / Q000235:genetics; D018410:Pneumonia, Bacterial / Q000235:genetics* / Q000276:immunology* / Q000382:microbiology / Q000401:mortality; D014409:Tumor Necrosis Factor-alpha / Q000096:biosynthesis
chemical_list: D000942:Antigens, Bacterial; D054426:Chemokine CXCL2; D018925:Chemokines; C404915:Cxcl2 protein, mouse; D020738:Leptin; D020024:Leukotriene Antagonists; D015289:Leukotrienes; D014409:Tumor Necrosis Factor-alpha; C112381:cysteinyl-leukotriene; D018664:Interleukin-12; D003545:Cysteine