Surfactant proteins A and D enhance pulmonary clearance of Pseudomonas aeruginosa

Am J Respir Cell Mol Biol. 2006 Jun;34(6):704-10. doi: 10.1165/rcmb.2005-0461OC. Epub 2006 Feb 2.


Surfactant protein (SP)-A and SP-D, members of the collectin family, are involved in innate host defenses against various bacterial and viral pathogens. In this study, we asked whether SP-A and SP-D enhance clearance of a nonmucoid strain of Pseudomonas aeruginosa from the lungs. We infected mice deficient in SP-A (SP-A-/-), SP-D (SP-D-/-) and both pulmonary collectins (SP-AD-/-) by intratracheal administration of P. aeruginosa. Six hours after infection, bacterial counts were significantly higher in SP-A-/-, SP-D-/-, and SP-AD-/- compared with wild-type (WT) mice. Forty-eight hours after infection, bacterial counts were significantly higher in SP-A-/- mice compared with WT mice and in SP-AD-/- mice compared with WT, SP-A-/-, and SP-D-/- mice. Phagocytosis of the bacteria by alveolar macrophages was decreased in SP-A-/- and SP-D-/- mice. Levels of macrophage inflammatory peptide-2 and IL-6 were more elevated in the lungs of SP-D and SP-AD-/- mice compared with WT mice. There was more infiltration by neutrophils in the lungs of SP-D-/- compared with WT and SP-A-/- mice 48 h after infection. This study shows that SP-A and SP-D enhance pulmonary clearance of P. aeruginosa by stimulating phagocytosis by alveolar macrophages and by modulating the inflammatory response in the lungs. These findings also show that the functions of SP-A and SP-D are not completely redundant in vivo.

Publication types

  • Comparative Study
  • Research Support, N.I.H., Extramural

MeSH terms

  • Animals
  • Cells, Cultured
  • Chemokine CXCL2
  • Colony Count, Microbial
  • Interleukin-6 / biosynthesis
  • Lung / immunology*
  • Lung / microbiology
  • Macrophages, Alveolar / drug effects
  • Macrophages, Alveolar / immunology*
  • Macrophages, Alveolar / microbiology
  • Mice
  • Mice, Inbred C57BL
  • Mice, Knockout
  • Monokines / biosynthesis
  • Neutrophil Infiltration
  • Phagocytosis*
  • Pneumonia, Bacterial / immunology*
  • Pneumonia, Bacterial / microbiology
  • Pseudomonas Infections / immunology*
  • Pseudomonas Infections / microbiology
  • Pseudomonas aeruginosa / isolation & purification*
  • Pulmonary Surfactant-Associated Protein A / genetics
  • Pulmonary Surfactant-Associated Protein A / immunology
  • Pulmonary Surfactant-Associated Protein A / physiology*
  • Pulmonary Surfactant-Associated Protein D / genetics
  • Pulmonary Surfactant-Associated Protein D / immunology
  • Pulmonary Surfactant-Associated Protein D / physiology*
  • Recombinant Proteins / pharmacology


  • Chemokine CXCL2
  • Interleukin-6
  • Monokines
  • Pulmonary Surfactant-Associated Protein A
  • Pulmonary Surfactant-Associated Protein D
  • Recombinant Proteins