title: Activation of human complement by immunoglobulin G antigranulocyte antibody.
abstract: The ability of antigranulocyte antibody to fix the third component of complement (C3) to the granulocyte surface was investigated by an assay that quantitates the binding of monoclonal anti-C3 antibody to paraformaldehyde-fixed cells preincubated with Felty's syndrome serum in the presence of human complement. The sera from 7 of 13 patients with Felty's syndrome bound two to three times as much C3 to granulocytes as sera from patients with uncomplicated rheumatoid arthritis. The complement-activating ability of Felty's syndrome serum seemed to reside in the monomeric IgG-containing serum fraction. For those sera capable of activating complement, the amount of C3 fixed to granulocytes was proportional to the amount of granulocyte-binding IgG present in the serum. Thus, complement fixation appeared to be a consequence of the binding of antigranulocyte antibody to the cell surface. These studies suggest a role for complement-mediated injury in the pathophysiology of immune granulocytopenia, as has been demonstrated for immune hemolytic anemia and immune thrombocytopenia.
mesh_terms: D001172:Arthritis, Rheumatoid / Q000276:immunology; D001323:Autoantibodies; D003167:Complement Activation; D003176:Complement C3 / Q000276:immunology*; D005258:Felty Syndrome / Q000276:immunology*; D006098:Granulocytes / Q000276:immunology*; D006801:Humans; D007074:Immunoglobulin G / Q000276:immunology
chemical_list: D001323:Autoantibodies; D003176:Complement C3; D007074:Immunoglobulin G