title: A new activity of complement component C3: cell-bound C3b potentiates lysis of erythrocytes by C5b,6 and terminal components.
abstract: EAC4b,3b (sheep erythrocytes carrying rabbit antibody and guinea pig complement component fragments C4b and C3) adsorb human C5b,6 reversibly; the avidity of binding varies inversely with ionic strength. We believe that the receptor of C5b,6 is contributed by the cell-bound C3b because the binding capacity of EAC4b,3b varies with C3b multiplicity and can be blocked with rabbit antibody to guinea pig C3. The fixation of C5b,6 to the erythrocyte-bound C3b serves to concentrate C5b,6 on the cell surface; as a consequence, the hemolytic efficiency of C5b,6 is almost 100 times greater when assayed with EAC4b,3b than with plain erythrocytes. This potentiation represents a hitherto unrecognized function of cell-bound C3b.
mesh_terms: D000818:Animals; D001665:Binding Sites; D003176:Complement C3 / Q000378:metabolism*; D003182:Complement C5 / Q000378:metabolism; D003183:Complement C6 / Q000378:metabolism; D003165:Complement System Proteins / Q000378:metabolism*; D004912:Erythrocytes / Q000276:immunology*; D006168:Guinea Pigs; D006461:Hemolysis; D006801:Humans; D007700:Kinetics
chemical_list: D003176:Complement C3; D003182:Complement C5; D003183:Complement C6; D003165:Complement System Proteins