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

• Published in: The American journal of physiology Vol. 272; no. 2 Pt 1; pp. L344 - L352
• Main Authors: Kabha, K, Schmegner, J, Keisari, Y, Parolis, H, Schlepper-Schaeffer, J, Ofek, I
• Format: Journal Article
• Language: English
• Published: United States 01-02-1997
• Subjects: 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
• ISSN: 0002-9513
• 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.