title: Pulmonary collectins protect macrophages against pore-forming activity of Legionella pneumophila and suppress its intracellular growth.
abstract: Pulmonary collectins, surfactant proteins A (SP-A) and D (SP-D), play important roles in innate immunity of the lung. Legionella pneumophila is a bacterial respiratory pathogen that can replicate within macrophages and causes opportunistic infections. L. pneumophila possesses cytolytic activity, resulting from insertion of pores in the macrophage membrane upon contact. We examined whether pulmonary collectins play protective roles against L. pneumophila infection. SP-A and SP-D bound to L. pneumophila and its lipopolysaccharide (LPS) and inhibited the bacterial growth in a Ca(2+)-dependent manner. The addition of LPS in the culture blocked the inhibitory effects on L. pneumophila growth by the collectins, indicating the importance of LPS-collectin interaction. When differentiated THP-1 cells were infected with L. pneumophila in the presence of SP-A and SP-D, the number of permeable cells was significantly decreased, indicating that pulmonary collectins inhibit pore-forming activity of L. pneumophila. The number of live bacteria within the macrophages on days 1-4 after infection was significantly decreased when infection was performed in the presence of pulmonary collectins. The phagocytosis experiments with the pH-sensitive dye-labeled bacteria revealed that pulmonary collectins promoted bacterial localization to an acidic compartment. In addition, SP-A and SP-D significantly increased the number of L. pneumophila co-localized with LAMP-1. These results indicate that pulmonary collectins protect macrophages against contact-dependent cytolytic activity of L. pneumophila and suppress intracellular growth of the phagocytosed bacteria. The promotion of lysosomal fusion with Legionella-containing phagosomes constitutes a likely mechanism of L. pneumophila growth suppression by the collectins.
authors.affiliation: Departments of Biochemistry, Sapporo Medical University School of Medicine, Sapporo 060-8556, Japan.
authors.forename: Kaku
authors.initials: K
authors.lastname: Sawada
authors.forename: Shigeru
authors.initials: S
authors.lastname: Ariki
authors.forename: Takashi
authors.initials: T
authors.lastname: Kojima
authors.forename: Atsushi
authors.initials: A
authors.lastname: Saito
authors.forename: Masami
authors.initials: M
authors.lastname: Yamazoe
authors.forename: Chiaki
authors.initials: C
authors.lastname: Nishitani
authors.forename: Takeyuki
authors.initials: T
authors.lastname: Shimizu
authors.forename: Motoko
authors.initials: M
authors.lastname: Takahashi
authors.forename: Hiroaki
authors.initials: H
authors.lastname: Mitsuzawa
authors.forename: Shin-Ichi
authors.initials: S
authors.lastname: Yokota
authors.forename: Norimasa
authors.initials: N
authors.lastname: Sawada
authors.forename: Nobuhiro
authors.initials: N
authors.lastname: Fujii
authors.forename: Hiroki
authors.initials: H
authors.lastname: Takahashi
authors.forename: Yoshio
authors.initials: Y
authors.lastname: Kuroki
mesh_terms: D002118:Calcium / Q000378:metabolism; D002241:Carbohydrates / Q000276:immunology; D002460:Cell Line; D002462:Cell Membrane / Q000276:immunology; D006801:Humans; D016952:Legionella pneumophila / Q000254:growth & development / Q000276:immunology*; D007877:Legionnaires' Disease / Q000276:immunology*; D008070:Lipopolysaccharides / Q000494:pharmacology; D008247:Lysosomes / Q000276:immunology; D016676:Macrophages, Alveolar / Q000382:microbiology*; D009000:Monocytes / Q000166:cytology; D010587:Phagocytosis / Q000276:immunology; D037662:Pulmonary Surfactant-Associated Protein A / Q000276:immunology*; D037663:Pulmonary Surfactant-Associated Protein D / Q000276:immunology*
chemical_list: D002241:Carbohydrates; D008070:Lipopolysaccharides; D037662:Pulmonary Surfactant-Associated Protein A; D037663:Pulmonary Surfactant-Associated Protein D; C445842:SFTPA1 protein, human; D002118:Calcium