Surface modulation of classical pathway activation: C2 and C3 convertase formation and regulation on sheep, guinea pig, and human erythrocytes.

摘要: We examined the formation of early classical complement (C) pathway enzymes on sheep (Es), guinea pig (Egp), and human (Eh) erythrocytes (E). Each species' E were sensitized with sufficient IgM or IgG anti-E Ab to establish equal numbers C1-fixing sites all E. After sensitization 100 excess C1, uptake C4 was equivalent three cell types, judged by anti-C4 binding (for C4) direct radiolabeled protein C4). With cell-bound C1 C4, however, there marked differences in C2 convertase activity Es, Egp, Eh. Sheep EAC14 utilized at least 20 times faster than Egp Eh bearing same number molecules. C3 cleavage even further depressed Eh, not changed substitution oxyC2 for normal C2. In whole serum (GPS), 300 more required Es achieve similar amounts lysis; associated extents lysis, demonstrating that GPS lysis these cells regulated steps (CP) activation. Incubation C4b Factor I demonstrated highly resistant compared bound Studies partially purified decay-accelerating factors from stroma membrane proteins could account observed surface regulation CP because do affect rate EAC14. conclude molecules have an important role modulation This surface-associated occurs level C4b.