title: A novel CD8 molecule expressed by alveolar and peritoneal macrophages stimulates nitric oxide production.
abstract: Macrophages play an essential role in host defense, and we have identified a novel CD8 molecule, on alveolar and peritoneal macrophages, that may be involved in regulating this function. Flow cytometric analysis of bronchoalveolar lavage from normal rats identified a large number of CD8-positive cells that could not be accounted for by T lymphocytes. Within the scatter profile region in which the majority of cells were alveolar macrophages (OX41; 89 +/- 1%), 63 +/- 5% of the cells stained positively for CD8alpha (OX8) and 52 +/- 3% for CD8beta (341). Double-staining of lavage cells confirmed the presence of CD8 on alveolar macrophages. Interestingly, flow cytometry showed differences between CD8 on alveolar macrophages and on T lymphocytes within the ligand binding domain for MHC class I. Reverse transcription-PCR analysis on FACS-enriched alveolar macrophages showed the presence of CD8alpha mRNA, determining that macrophages synthesize CD8. Further studies identified both the alpha (49 +/- 8%)- and beta (37 +/- 4%)-chains of CD8 on peritoneal lavage cells (86 +/- 3% macrophages (OX42, CD11b)). As with alveolar macrophages, there were differences within the ligand-binding domain of CD8 on peritoneal macrophages compared with T lymphocytes. Functional studies determined that anti-CD8alpha (OX8) stimulated a dose-dependent release of nitric oxide, indicating that CD8 can directly regulate macrophage function. Thus, macrophages express an unusual CD8 molecule that differs within its ligand-binding domain, compared with T lymphocytes, and these findings suggest hitherto unknown ligand(s) for CD8. These findings will lead to a greater understanding of macrophage function and regulation.
authors.affiliation: Pulmonary Research Group, Department of Medicine, University of Alberta, Edmonton, Canada.
authors.forename: N
authors.initials: N
authors.lastname: Hirji
authors.forename: T J
authors.initials: TJ
authors.lastname: Lin
authors.forename: A D
authors.initials: AD
authors.lastname: Befus
mesh_terms: D000818:Animals; D001992:Bronchoalveolar Lavage Fluid / Q000166:cytology / Q000276:immunology; D016827:CD8 Antigens / Q000235:genetics / Q000502:physiology*; D016676:Macrophages, Alveolar / Q000276:immunology / Q000378:metabolism*; D017737:Macrophages, Peritoneal / Q000276:immunology / Q000378:metabolism*; D008297:Male; D009569:Nitric Oxide / Q000096:biosynthesis*; D016133:Polymerase Chain Reaction; D012333:RNA, Messenger / Q000032:analysis; D051381:Rats; D017207:Rats, Sprague-Dawley
chemical_list: D016827:CD8 Antigens; D012333:RNA, Messenger; D009569:Nitric Oxide