Surfactant Protein D Stimulates Phagocytosis of Pseudomonas aeruginosa by Alveolar Macrophages

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Abstract
Surfactant protein (SP)-D is an oligomeric glycoprotein belonging to the family of collagen-like lectins known as collectins, which have previously been shown to stimulate phagocytosis and other immune cell functions. The hypothesis investigated in this study was that SP-D would stimulate the phagocytosis of an important pulmonary pathogen, Pseudomonas aeruginosa . SP-D, isolated from the lavage fluid of silica- treated rats, significantly enhanced the uptake of three of six strains of P. aeruginosa by rat alveolar mac- rophages as analyzed by both fluorescence and electron microscopy. SP-D had only minimal effects on phagocytosis of Haemophilus influenzae . SP-D bound to live P. aeruginosa , and binding was inhibited by chelation of calcium and by a competing saccharide, inositol. In vitro killing assays demonstrated that macrophage-mediated killing of one of the mucoid strains of P. aeruginosa was modestly enhanced by SP-D. P. aeruginosa was not measurably aggregated by SP-D either macroscopically or microscopically. Further, SP-D does not appear to act as an activation ligand because adherence of macrophages to SP-D- coated slides did not stimulate the uptake of P. aeruginosa . These findings suggest that SP-D may be im- portant in controlling the pathogenesis of P. aeruginosa in the lung. Restrepo, C. I., Q. Dong, J. Savov, W. I. Mariencheck, and J. R. Wright. 1999. Surfactant protein D stimulates phagocytosis of Pseudo- monas aeruginosa by alveolar macrophages. Am. J. Respir. Cell Mol. Biol. 21:576-585.

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