title: The role of C1s, C1r and properdin in the initiation of the C3b-dependent feedback mechanism of the complement system.
abstract: The influence of activated C1s, C1r and properdin in the fluid phase initiation of the C3b-dependent feedback mechanism of the human complement was studied. It was found that C1s caused conversion of C3 and factor B in a normal serum, but not in a serum genetically deficient in C4 or in a serum to which Na2EDTA had been added. When a normal serum was incubated with C1r before incubation with C1s, only C3 was converted, whereas factor B remained in the unaltered native state. Properdin did not influence the C1s mediated conversion of C3 and factor B. When activated properdin was added to a properdin-depleted serum, both C3 and factor B were converted. Activated properdin was also incubated with purified C3 and purified C3b. It was shown that C3 was converted to C3b, but C3b was not degraded despite prolonged incubation.
mesh_terms: D002846:Chromatography, Affinity; D003167:Complement Activation; D003172:Complement C1 / Q000276:immunology; D003176:Complement C3 / Q000378:metabolism*; D011415:Complement Factor B / Q000378:metabolism; D003170:Complement Pathway, Alternative; D006801:Humans; D007106:Immune Sera; D007123:Immunoelectrophoresis, Two-Dimensional; D011414:Properdin / Q000276:immunology
chemical_list: D003172:Complement C1; D003176:Complement C3; D007106:Immune Sera; D011414:Properdin; D011415:Complement Factor B