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Infection and Immunity, January 2001, p. 24-33, Vol. 69, No. 1
Department of Human Microbiology, Tel Aviv
University, Tel Aviv, Israel1;
Department of Medical Microbiology and Virology, University of
Kiel, Kiel Germany2; and Department of
Pathology and Immunology, Washington University, St. Louis,
Missouri3
Received 25 May 2000/Returned for modification 14 August
2000/Accepted 4 October 2000
Pulmonary surfactant protein D (SP-D) is a collagenous C-type
lectin (collectin) that is secreted into the alveoli and distal airways
of the lung. We have studied the interactions of SP-D and alveolar
macrophages with Klebsiella pneumoniae, a common cause of
nosocomial pneumonia. SP-D does not agglutinate encapsulated K. pneumoniae but selectively agglutinates spontaneous,
unencapsulated phase variants, such as Klebsiella strain
K50-3OF, through interactions with their lipopolysaccharides (LPS).
These effects are calcium dependent and inhibited with maltose but not
lactose, consistent with involvement of the SP-D carbohydrate
recognition domain. Precoating of K50-3OF with SP-D enhances the
phagocytosis and killing of these organisms by rat alveolar macrophages
in cell culture and stimulates the production of nitric oxide by the
NR-8383 rat alveolar macrophage cell line. SP-D similarly enhances the NO response to K50-3OF LPS adsorbed to Latex beads under conditions where soluble LPS or SP-D, or soluble complexes of SP-D and LPS, do not
stimulate NO production. Our studies demonstrate that interactions of
SP-D with exposed arrays of Klebsiella LPS on a particulate surface can enhance the host defense activities of alveolar macrophages and suggest that activation of macrophages by SP-D requires binding to
microorganisms or other particulate ligands. Because unencapsulated phase variants are likely to be responsible for the initial stages of
tissue invasion and infection, we speculate that SP-D-mediated agglutination and/or opsonization of K. pneumoniae is an
important defense mechanism for this respiratory pathogen in otherwise
healthy individuals.
0019-9567/01/$04.00+0 DOI: 10.1128/IAI.69.1.24-33.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.
Surfactant Protein D Enhances Phagocytosis and
Killing of Unencapsulated Phase Variants of Klebsiella
pneumoniae
*
Corresponding author. Mailing address: Barnes-Jewish
Hospital, North Campus, 216 S. Kingshighway, St. Louis, MO 63110. Phone: (314) 454-8462. Fax: (314) 454-5505. E-mail:
crouch{at}path.wustl.edu.
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