Differential regulation of the mannose and SP-A receptors on macrophages.
Two carbohydrate-dependent mechanisms exist on alveolar macrophages to clear mannose-containing pathogens: receptor-mediated entry of non-opsonized microorganisms via the mannose receptor and receptor recognition of pathogens opsonized with surfactant-associated protein A (SP-A). A number of studies have demonstrated that mannose receptor expression is tightly linked to the functional state of the macrophage. In the present study, we investigated regulation of binding of SP-A to its receptor on macrophages by the same agents that regulate mannose-receptor expression. Phorbol 12-myristate 13-acetate, lipopolysaccharide (LPS), and interferon-gamma treatment of rat marrow-derived macrophages increased SP-A binding by 163, 296, and 337%, respectively, over untreated controls. Mannose-receptor activity was reduced to 75, 60, and 25% of control levels by these agents. Dexamethasone increased mannose receptor activity to 225%, while decreasing SP-A binding to 44% of controls. Addition of granulocyte macrophage-colony stimulating factor (GM-CSF) to human monocytes on day 0 dramatically increased mannose-receptor activity on day 5 over the non-serum control. SP-A binding was highest to freshly isolated monocytes and decreased to < 10% after differentiation in the presence of GM-CSF. After intraperitoneal injection of dexamethasone, rat alveolar macrophages isolated at 24 h expressed increased mannose-receptor activity and decreased SP-A binding. LPS injection resulted in increased SP-A binding and decreased mannose-receptor activity. In every instance, SP-A binding was inversely regulated with respect to mannose-receptor expression. We therefore speculate that the mannose receptor is a first-line host-defense receptor that is turned off during inflammation. SP-A in the alveolar space can then act as a lung-specific opsonin and mediate clearance of pathogens via the upregulated SP-A receptor.
Chroneos
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Department of Medicine, Vanderbilt University School of Medicine, Nashville, Tennessee, USA.
Shepherd
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D000818:Animals; D002454:Cell Differentiation; D002478:Cells, Cultured; D003907:Dexamethasone / Q000494:pharmacology; D005260:Female; D016178:Granulocyte-Macrophage Colony-Stimulating Factor / Q000037:antagonists & inhibitors / Q000494:pharmacology; D006735:Horseradish Peroxidase / Q000493:pharmacokinetics; D006801:Humans; D007274:Injections, Intraperitoneal; D007371:Interferon-gamma / Q000494:pharmacology; D037181:Lectins, C-Type; D008070:Lipopolysaccharides / Q000494:pharmacology; D008264:Macrophages / Q000166:cytology / Q000378:metabolism*; D016676:Macrophages, Alveolar / Q000378:metabolism; D000090323:Mannose Receptor; D037241:Mannose-Binding Lectins; D009000:Monocytes / Q000166:cytology; D051381:Rats; D017207:Rats, Sprague-Dawley; D011956:Receptors, Cell Surface / Q000378:metabolism*; D013997:Time Factors
D037181:Lectins, C-Type; D008070:Lipopolysaccharides; D000090323:Mannose Receptor; D037241:Mannose-Binding Lectins; D011956:Receptors, Cell Surface; C067774:surfactant protein A receptor; D003907:Dexamethasone; D007371:Interferon-gamma; D016178:Granulocyte-Macrophage Colony-Stimulating Factor; D006735:Horseradish Peroxidase