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 (EA IgG ). 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 th…