title: Role of the scavenger receptor MARCO in alveolar macrophage binding of unopsonized environmental particles.
abstract: Alveolar macrophages (AMs) avidly bind and ingest unopsonized environmental particles and bacteria through scavenger-type receptors (SRs). AMs from mice with a genetic deletion of the major macrophage SR (types AI and AII; SR-/-) showed no decrease in particle binding compared with SR+/+ mice, suggesting that other SRs are involved. To identify these receptors, we generated a monoclonal antibody (mAb), PAL-1, that inhibits hamster AM binding of unopsonized particles (TiO2, Fe2O3, and latex beads; 66 +/- 5, 77 +/- 2, and 85 +/- 2% inhibition, respectively, measured by flow cytometry). This antibody identifies a protein of approximately 70 kD on the AM surface (immunoprecipitation) that is expressed by AMs and other macrophages in situ. A cDNA clone encoding the mAb PAL-1-reactive protein isolated by means of COS cell expression was found to be 84 and 77% homologous to mouse and human scavenger receptor MARCO mRNA, respectively. Transfection of COS cells with MARCO cDNA conferred mAb-inhibitable TiO2 binding. Hamster MARCO also mediates AM binding of unopsonized bacteria (67 +/- 5 and 47 +/- 4% inhibition of Escherichia coli and Staphylococcus aureus binding by mAb PAL-1). A polyclonal antibody to human MARCO identified the expected approximately 70-kD band on Western blots of lysates of normal bronchoalveolar lavage (BAL) cells (>90% AMs) and showed strong immunolabeling of human AMs in BAL cytocentrifuge preparations and within lung tissue specimens. In normal mouse AMs, the anti-MARCO mAb ED31 also showed immunoreactivity and inhibited binding of unopsonized particles (e.g., TiO2 approximately 40%) and bacteria. The novel function of binding unopsonized environmental dusts and pathogens suggests an important role for MARCO in the lungs' response to inhaled particles.
authors.affiliation: Physiology Program, Harvard School of Public Health, Boston, Massachusetts 02115, USA.
authors.forename: A
authors.initials: A
authors.lastname: Palecanda
authors.forename: J
authors.initials: J
authors.lastname: Paulauskis
authors.forename: E
authors.initials: E
authors.lastname: Al-Mutairi
authors.forename: A
authors.initials: A
authors.lastname: Imrich
authors.forename: G
authors.initials: G
authors.lastname: Qin
authors.forename: H
authors.initials: H
authors.lastname: Suzuki
authors.forename: T
authors.initials: T
authors.lastname: Kodama
authors.forename: K
authors.initials: K
authors.lastname: Tryggvason
authors.forename: H
authors.initials: H
authors.lastname: Koziel
authors.forename: L
authors.initials: L
authors.lastname: Kobzik
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D000911:Antibodies, Monoclonal / Q000276:immunology; D001483:Base Sequence; D019556:COS Cells; D003001:Cloning, Molecular; D006224:Cricetinae; D018076:DNA, Complementary; D004926:Escherichia coli / Q000378:metabolism; D006801:Humans; D016676:Macrophages, Alveolar / Q000378:metabolism*; D008565:Membrane Proteins; D051379:Mice; D008969:Molecular Sequence Data; D011233:Precipitin Tests; D011791:Quartz / Q000378:metabolism; D011971:Receptors, Immunologic / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D018110:Receptors, Lipoprotein; D051116:Receptors, Scavenger; D051122:Scavenger Receptors, Class B; D013211:Staphylococcus aureus / Q000378:metabolism; D014025:Titanium / Q000378:metabolism
chemical_list: D000911:Antibodies, Monoclonal; D018076:DNA, Complementary; C490460:MARCO protein, human; C092228:Marco protein, mouse; D008565:Membrane Proteins; D011971:Receptors, Immunologic; D018110:Receptors, Lipoprotein; D051116:Receptors, Scavenger; C454739:Scarb1 protein, mouse; D051122:Scavenger Receptors, Class B; D011791:Quartz; C009495:titanium dioxide; D014025:Titanium