title: Solubilization of an activity regulating C3b function from Raji cell membranes.
abstract: A fraction of isolated Raji cell membranes solubilized with 2m KBr which was capable of inhibiting C3-dependent rosettes was examined for its ability to inhibit the alternative pathway of complement. It was shown to decrease alternative pathway-dependent haemolysis of sheep erythrocytes and to accelerate decay of factor B from these cells. It had no effect on C2 decay, the classical pathway analog of factor B. Inhibitory activity solubilized from Raji cells was not removed by immunoadsorption with anti-factor H or anti-factor I, two well-characterized serum C3b-control proteins. It also differed in two functional respects from these proteins. Firstly, it failed to result in cleavage of a peptide bone in C3 which is characteristic of factor I; secondly, its inhibitory activity did not synergize with factor I in inhibiting the alternative pathway, unlike factor H. These results suggest that Raji cells contain a regulatory factor in their membranes for the alternative pathway of complement which is distinct from factors H and I.
mesh_terms: D002051:Burkitt Lymphoma / Q000276:immunology*; D002457:Cell Extracts / Q000494:pharmacology; D002460:Cell Line; D002462:Cell Membrane / Q000276:immunology; D003176:Complement C3 / Q000378:metabolism; D003179:Complement C3b / Q000302:isolation & purification*; D011415:Complement Factor B / Q000378:metabolism; D003429:Cross Reactions; D004591:Electrophoresis, Polyacrylamide Gel; D006801:Humans; D007163:Immunosorbent Techniques; D012397:Rosette Formation; D012995:Solubility
chemical_list: D002457:Cell Extracts; D003176:Complement C3; D003179:Complement C3b; D011415:Complement Factor B