title: Evidence that C1q, a subcomponent of the first component of complement, is an Fc receptor of peritoneal and alveolar macrophages.
abstract: Guinea pig peritoneal macrophages were cultured for 24 h in the presence of two inhibitors of the biosynthesis of collagen-like molecules such as C1q : 10(-3) M 3,4-dehydroproline or 10(-4) M 2,2'-dipyridyl. Their Fc-receptor activity was measured by rosette formation, using sheep erythrocytes (E) coated with rabbit anti-sheep IgG (EAIgG). The Fc-receptor activity was decreased by 40 to 70% of control cultures depending on the amount of IgG on the E. The activity of a second receptor on the macrophages, mediating the binding of C3b coated E, was not altered by this treatment. Rat alveolar macrophages were depleted of their Fc-receptor activity by pronase treatment (1.5 mg/ml) in the presence of 2,2'-dipyridyl. After washing the cells, the EAIgG-binding activity was restored to about half of the initial level within 2 h. With 2,2'-dipyridyl also present during the second incubation, the re-expression of the Fc-receptor activity was suppressed further. Preincubation of guinea pig peritoneal macrophages with anti-C1q-F(ab')2 for 45 min at 37 degrees C caused a dose-dependent reduction of the Fc receptor activity, but not C3b receptor activity. These results support our hypothesis that C1q synthesized and secreted by macrophages serves as an Fc-receptor in the membrane during the secretion.
mesh_terms: D015082:2,2'-Dipyridyl / Q000494:pharmacology; D000818:Animals; D001202:Ascitic Fluid / Q000166:cytology; D003172:Complement C1 / Q000276:immunology*; D003176:Complement C3 / Q000276:immunology; D005260:Female; D006168:Guinea Pigs; D008264:Macrophages / Q000276:immunology*; D008297:Male; D011392:Proline / Q000031:analogs & derivatives; D011402:Pronase / Q000494:pharmacology; D011650:Pulmonary Alveoli / Q000166:cytology; D051381:Rats; D011951:Receptors, Complement / Q000276:immunology; D011961:Receptors, Fc / Q000276:immunology*; D012397:Rosette Formation
chemical_list: D003172:Complement C1; D003176:Complement C3; D011951:Receptors, Complement; D011961:Receptors, Fc; D015082:2,2'-Dipyridyl; D011392:Proline; D011402:Pronase