Interactions of surfactant protein D with bacterial lipopolysaccharides. Surfactant protein D is an Escherichia coli-binding protein in bronchoalveolar lavage.
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.
Kuan
S F
SF
Department of Pathology, Jewish Hospital, Washington University Medical Center, St. Louis, Missouri 63110.
Rust
K
K
Crouch
E
E
D000371:Agglutination; D001992:Bronchoalveolar Lavage Fluid / Q000378:metabolism*; D004926:Escherichia coli / Q000276:immunology; D006023:Glycoproteins / Q000276:immunology / Q000378:metabolism*; D006090:Gram-Negative Bacteria / Q000276:immunology*; D006801:Humans; D037102:Lectins / Q000378:metabolism; D008070:Lipopolysaccharides / Q000378:metabolism*; D037663:Pulmonary Surfactant-Associated Protein D; D011663:Pulmonary Surfactants / Q000276:immunology / Q000378:metabolism*
D006023:Glycoproteins; D037102:Lectins; D008070:Lipopolysaccharides; D037663:Pulmonary Surfactant-Associated Protein D; D011663:Pulmonary Surfactants