title: Complement-subcomponent-C1-inhibitor synthesis by human monocytes.
abstract: By using a radioimmunoassay, C1-inhibitor was found to accumulate in the supernatants of human monocyte cultures. The production of this protein was inhibited reversibly by cycloheximide. When C1-inhibitor synthesis was compared with C2 synthesis, it was found that C1-inhibitor synthesis continued, whereas synthesis of C2 appeared to cease after about 7 days in culture. Immunoprecipitation of supernatants of monocyte cultures that had been pulsed with [35S]methionine showed a specific band with an Mr of 105 000. Immunoprecipitates of the lysates revealed a band of Mr 83 000; this was thought to represent a partially or non-glycosylated precursor of C1-inhibitor. C1-inhibitor produced by the monocytes was shown, by using a haemolytic assay, to be functionally active. However, the functional activity of C1-inhibitor was reduced by only 44% in the presence of cycloheximide, whereas the concentration of this protein in cycloheximide-treated culture supernatants fell by more than 93%. This finding suggests that monocytes secrete a second molecule, which inhibits C1 activity but is distinct from classical C1-inhibitor.
mesh_terms: D002478:Cells, Cultured; D003174:Complement C1 Inactivator Proteins / Q000037:antagonists & inhibitors / Q000096:biosynthesis*; D003175:Complement C2 / Q000037:antagonists & inhibitors / Q000096:biosynthesis; D003513:Cycloheximide / Q000494:pharmacology; D004591:Electrophoresis, Polyacrylamide Gel; D006461:Hemolysis; D006801:Humans; D007700:Kinetics; D009000:Monocytes / Q000187:drug effects / Q000276:immunology*
chemical_list: D003174:Complement C1 Inactivator Proteins; D003175:Complement C2; D003513:Cycloheximide