SP-A enhances phagocytosis of Klebsiella by interaction with capsular polysaccharides and alveolar macrophages.
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.
Kabha
K
K
Department of Human Microbiology, Sackler Faculty of Medicine, Tel-Aviv University, Israel.
Schmegner
J
J
Keisari
Y
Y
Parolis
H
H
Schlepper-Schaeffer
J
J
Ofek
I
I
D000818:Animals; D016667:Bacterial Capsules / Q000378:metabolism*; D006168:Guinea Pigs; D007711:Klebsiella pneumoniae / Q000378:metabolism; D037181:Lectins, C-Type; D016676:Macrophages, Alveolar / Q000378:metabolism / Q000502:physiology*; D000090323:Mannose Receptor; D037241:Mannose-Binding Lectins; D010587:Phagocytosis / Q000187:drug effects*; D011134:Polysaccharides / Q000378:metabolism / Q000502:physiology*; D011510:Proteolipids / Q000378:metabolism / Q000494:pharmacology*; D037662:Pulmonary Surfactant-Associated Protein A; D037661:Pulmonary Surfactant-Associated Proteins; D011663:Pulmonary Surfactants / Q000378:metabolism / Q000494:pharmacology*; D051381:Rats; D011956:Receptors, Cell Surface / Q000378:metabolism
D037181:Lectins, C-Type; D000090323:Mannose Receptor; D037241:Mannose-Binding Lectins; D011134:Polysaccharides; D011510:Proteolipids; D037662:Pulmonary Surfactant-Associated Protein A; D037661:Pulmonary Surfactant-Associated Proteins; D011663:Pulmonary Surfactants; D011956:Receptors, Cell Surface