SP-A enhances phagocytosis of Klebsiella by interaction with capsular polysaccharides and alveolar macrophages

Am J Physiol. 1997 Feb;272(2 Pt 1):L344-52. doi: 10.1152/ajplung.1997.272.2.L344.


We found that surfactant protein A (SP-A) enhances phagocytosis of Klebsiella pneumoniae K21a but not of K2 serotypes by alveolar macrophages. SP-A interacted with the capsule of K21a (containing Man alpha1 Man sequences) as shown by SP-A-induced agglutination of the bacteria, by binding of SP-A-coated particles onto the bacterial surface, and by binding of SP-A to immobilized parent K21a strain and recombinant strains that switched their capsule from K2 to K21a. In contrast, only marginal binding of SP-A to K2 parent strain (lacking this sequence) could be detected. Furthermore, binding of capsular polysaccharide of K21a to immobilized SP-A was inhibited by mannan but not by lipopolysaccharide and K2 capsular polysaccharide. SP-A-treated macrophages bound increased numbers of parent K21a strain and recombinant strains of K21a capsule type but considerably less parent K2 strain. SP-A also enhanced killing of K21a strains by macrophages. The enhanced binding of K21a by macrophages pretreated with SP-A was inhibited by mannan, suggesting that binding is mediated by the mannose receptor on macrophages. We conclude that SP-A increases phagocytosis of the Klebsiella by two mechanisms, one of which is by serving as an opsonin, which binds to the capsular polysaccharides of the bacteria and potentially to SP-A receptors on the macrophages, and the other by activating the macrophages, resulting in increased activity of the mannose receptor.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Bacterial Capsules / metabolism*
  • Guinea Pigs
  • Klebsiella pneumoniae* / metabolism
  • Lectins, C-Type*
  • Macrophages, Alveolar / metabolism
  • Macrophages, Alveolar / physiology*
  • Mannose-Binding Lectins*
  • Phagocytosis / drug effects*
  • Polysaccharides / metabolism
  • Polysaccharides / physiology*
  • Proteolipids / metabolism
  • Proteolipids / pharmacology*
  • Pulmonary Surfactant-Associated Protein A
  • Pulmonary Surfactant-Associated Proteins
  • Pulmonary Surfactants / metabolism
  • Pulmonary Surfactants / pharmacology*
  • Rats
  • Receptors, Cell Surface / metabolism


  • Lectins, C-Type
  • Mannose-Binding Lectins
  • Polysaccharides
  • Proteolipids
  • Pulmonary Surfactant-Associated Protein A
  • Pulmonary Surfactant-Associated Proteins
  • Pulmonary Surfactants
  • Receptors, Cell Surface
  • mannose receptor