MARCO is the major binding receptor for unopsonized particles and bacteria on human alveolar macrophages.
Alveolar macrophages (AMs) avidly bind and ingest inhaled environmental particles and bacteria. To identify the particle binding receptor(s) on human AMs, we used functional screening of anti-human AM hybridomas and isolated a mAb, PLK-1, which inhibits AM binding of unopsonized particles (e.g., TiO2, latex beads; 63 +/- 5 and 67 +/- 4% inhibition, respectively, measured by flow cytometry; n = 11) and unopsonized bacteria ( approximately 84 and 41% inhibition of Escherichia coli and Staphylococcus aureus binding by mAb PLK-1, respectively). The PLK-1 Ag was identified as the human class A scavenger receptor (SR) MARCO (macrophage receptor with collagenous structure) by observing specific immunolabeling of COS cells transfected with human MARCO (but not SR-AI/II) cDNA and by immunoprecipitation by PLK-1 of a protein of appropriate molecular mass (approximately 70 kDa) from both normal human bronchoalveolar lavage cells (>90% AMs) and human MARCO-transfected COS cells. PLK-1 also specifically inhibited particle binding by COS cells, only after transfection with human MARCO cDNA. Immunostaining showed specific labeling of AMs within human lung tissue, bronchoalveolar lavage samples, as well as macrophages in other sites (e.g., lymph node and liver). Using COS transfectants with different truncated forms of MARCO, allowed epitope mapping for the PLK-1 Ab to MARCO domain V between amino acid residues 420 and 431. A panel of Abs to various SRs identified expression on AMs, but failed to inhibit TiO2 or S. aureus binding. The data support a dominant role for MARCO in the human AM defense against inhaled particles and pathogens.
Arredouani
Mohamed S
MS
Physiology Program, Harvard School of Public Health, Boston, MA 02115, USA.
Palecanda
Aiyappa
A
Koziel
Henry
H
Huang
Yuh-Ching
YC
Imrich
Amy
A
Sulahian
Timothy H
TH
Ning
Yao Yu
YY
Yang
Zhiping
Z
Pikkarainen
Timo
T
Sankala
Marko
M
Vargas
Sara O
SO
Takeya
Motohiro
M
Tryggvason
Karl
K
Kobzik
Lester
L
D000328:Adult; D000911:Antibodies, Monoclonal / Q000276:immunology; D018797:Cell Cycle Proteins / Q000502:physiology; D006801:Humans; D016676:Macrophages, Alveolar / Q000276:immunology*; D010587:Phagocytosis; D011494:Protein Kinases / Q000502:physiology; D017346:Protein Serine-Threonine Kinases; D017434:Protein Structure, Tertiary; D011518:Proto-Oncogene Proteins / Q000502:physiology; D011971:Receptors, Immunologic / Q000032:analysis / Q000737:chemistry / Q000502:physiology*; D014025:Titanium / Q000378:metabolism; D000097869:Polo-Like Kinase 1
D000911:Antibodies, Monoclonal; D018797:Cell Cycle Proteins; D011494:Protein Kinases; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins; D011971:Receptors, Immunologic; D014025:Titanium; D000097869:Polo-Like Kinase 1; C490460:MARCO protein, human; C009495:titanium dioxide