title: Leukocyte-derived complement inhibitor. IV. The functional properties of C1 bound to erythrocytes pretreated with leukocyte culture supernatant.
abstract: E, pretreated with leukocyte cultures supernatant (ES), binds C1 through C1q; ES and EIgM that bind the same amount of C1 as measured in a hemolytic assay have the same uptake of 125I-C1q; ESC1q and EIgMC1q, carrying the same number of molecules of CUq per cell, have the same uptake of CUr and CUs; soluble immune compleses prevent the binding of C1 and C1q to ES. The activity of C1 bound to ES is impaired; ESC1 can react with C4 but not with C2. The C4 turnover and the C1 ING turnover by ESC1 are reduced so that ES-bound C1 is protected from destruction by C1 ING. These modifications are fully reversed when C1 is transferred from ES to EA:C1 recovers its ability to react with C2, and C1 INH. Thus the C1s activity can be modulated inside the C1 molecular complex upon binding of C1q to a lymphocyte product. In addition, the 125I-C1q uptake is proportional to the amount of IgM hemolysin used to sensitize E; it has, however, an exponential relationship to the amount of IgG or S used to sensitize E. The ratio of 125I-C1q uptake towhole C1 uptake measured in a hemolytic assay is lowerthan 2. This indicates that one molecule of IgM is sufficient to bind one molecule of C1q on E, that several molecules of IgG or S are required to bind one molecule of C1q, and that one molecule of C1q is sufficient to create a lytic site on E.
mesh_terms: D000818:Animals; D000936:Antigen-Antibody Complex; D001666:Binding Sites, Antibody; D002474:Cell-Free System; D003172:Complement C1 / Q000378:metabolism; D003174:Complement C1 Inactivator Proteins; D003175:Complement C2 / Q000378:metabolism; D003181:Complement C4 / Q000378:metabolism; D003169:Complement Inactivator Proteins; D004912:Erythrocytes / Q000276:immunology*; D007075:Immunoglobulin M / Q000378:metabolism; D007700:Kinetics; D007962:Leukocytes / Q000276:immunology*; D051379:Mice; D012995:Solubility
chemical_list: D000936:Antigen-Antibody Complex; D003172:Complement C1; D003174:Complement C1 Inactivator Proteins; D003175:Complement C2; D003181:Complement C4; D003169:Complement Inactivator Proteins; D007075:Immunoglobulin M