title: Local opsonization by secreted macrophage complement components. Role of receptors for complement in uptake of zymosan.
abstract: We have examined the role of macrophage (M phi plasma membrane receptors for the cleaved third complement component (iC3b; CR3) and mannosyl, fucosyl terminated glycoproteins (MFR) in uptake of unopsonized zymosan. Monoclonal antibodies against CR3, M1/70 (Mac-1) and MO1, each inhibited approximately 50% of uptake of 125I-zymosan by murine and human M phi, respectively. Yeast mannan inhibited 0-50% of zymosan uptake in various M phi, in parallel with their expression of MFR. We demonstrated that M phi were the source of C3 in our assay and that the activity of other components of the complement system, namely a C3 convertase, factor I, and a factor I cofactor were also present in serum-free cultures of human monocytes. Macrophage C3 was deposited rapidly, within 10 min, on the zymosan particles and mediated binding, ingestion, and stimulation of superoxide release in BCG-activated and thioglycollate-elicited peritoneal M phi via CR3. Local secretion of complement proteins by M phi themselves can therefore opsonize pathogens and cells able to activate the alternative pathway and effect their destruction.
mesh_terms: D000818:Animals; D000911:Antibodies, Monoclonal / Q000502:physiology; D000954:Antigens, Surface / Q000276:immunology; D001667:Binding, Competitive; D003176:Complement C3 / Q000096:biosynthesis; D050577:Complement C3-C5 Convertases / Q000378:metabolism; D003170:Complement Pathway, Alternative; D003165:Complement System Proteins / Q000378:metabolism* / Q000502:physiology; D005260:Female; D006801:Humans; D037181:Lectins, C-Type; D016177:Macrophage-1 Antigen; D008264:Macrophages / Q000276:immunology / Q000378:metabolism*; D008297:Male; D008351:Mannans / Q000494:pharmacology; D000090323:Mannose Receptor; D037241:Mannose-Binding Lectins; D051379:Mice; D009000:Monocytes / Q000378:metabolism; D009895:Opsonin Proteins / Q000276:immunology*; D051381:Rats; D011956:Receptors, Cell Surface / Q000502:physiology; D011951:Receptors, Complement / Q000276:immunology / Q000502:physiology*; D015054:Zymosan / Q000378:metabolism
chemical_list: D000911:Antibodies, Monoclonal; D000954:Antigens, Surface; D003176:Complement C3; D037181:Lectins, C-Type; D016177:Macrophage-1 Antigen; D008351:Mannans; D000090323:Mannose Receptor; D037241:Mannose-Binding Lectins; D009895:Opsonin Proteins; D011956:Receptors, Cell Surface; D011951:Receptors, Complement; D003165:Complement System Proteins; D015054:Zymosan; D050577:Complement C3-C5 Convertases