Interactions of surfactant protein D with bacterial lipopolysaccharides. Surfactant protein D is an Escherichia coli-binding protein in bronchoalveolar lavage

J Clin Invest. 1992 Jul;90(1):97-106. doi: 10.1172/JCI115861.

Abstract

Surfactant protein D (SP-D) is a collagenous glycoprotein that is secreted into the pulmonary airspaces by alveolar type II and nonciliated bronchiolar cells. SP-D exhibits Ca(++)-dependent carbohydrate binding in vitro and is structurally related to the collagenous C-type lectins, including serum conglutinin, serum mannose-binding proteins, and surfactant protein A. Preliminary studies showed calcium- and saccharide-dependent binding of fluorescein-conjugated or radioiodinated SP-D to a variety of microorganisms, including Gram-negative bacteria and fungi. A laboratory strain of Escherichia coli (Y1088) was chosen to further examine the mechanism(s) of binding. Binding of SP-D to Y1088 was time dependent, saturable, and inhibited by cold SP-D or competing saccharides; Scatchard analysis gave a Kd of 2 x 10(-11) M. At higher concentrations, SP-D also caused Ca(++)-dependent agglutination of Y1088 that was inhibited by alpha-glucosyl-containing saccharides, antisera to the carbohydrate-binding domain of SP-D, or Y1088 LPS. Lectin blots showed specific binding of 125I-SP-D to Y1088 LPS, as well as LPS from other several strains of enteric Gram-negative bacteria. Immunogold studies demonstrated strong and uniform surface labeling of the bacteria. Rat and human bronchoalveolar lavage (BAL) caused Ca(++)-dependent agglutination of E. coli that was dose dependent and inhibited by competing saccharides or anti-SP-D. SP-D was selectively and efficiently adsorbed from rat BAL by incubation with E. coli, and incubation of E. coli with radiolabeled rat type II cell medium revealed that SP-D is the major E. coli-binding protein secreted by freshly isolated cells in culture. We suggest that SP-D plays important roles in the lung's defense against Gram-negative bacteria.

Publication types

  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Agglutination
  • Bronchoalveolar Lavage Fluid / metabolism*
  • Escherichia coli / immunology
  • Glycoproteins / immunology
  • Glycoproteins / metabolism*
  • Gram-Negative Bacteria / immunology*
  • Humans
  • Lectins / metabolism
  • Lipopolysaccharides / metabolism*
  • Pulmonary Surfactant-Associated Protein D
  • Pulmonary Surfactants / immunology
  • Pulmonary Surfactants / metabolism*

Substances

  • Glycoproteins
  • Lectins
  • Lipopolysaccharides
  • Pulmonary Surfactant-Associated Protein D
  • Pulmonary Surfactants