title: Characterization of an occult inhibitor to factor IX in a haemophilia B patient.
abstract: Six haemophilia B patients were studied while undergoing infusion with factor IX concentrate. All were negative for factor IX antigen (IX:AG) and inhibitor to factor IX coagulant activity (IX:C). One patient showed an atypical response pattern, with prolonged survival of IX:C and IX:Ag. This patient remained under prophylactic treatment and more than 1 year later developed an inhibitor to IX:C of clinical significance. Retrospective study revealed that this patient had significantly higher levels of circulating immune complexes than other haemophilia B patients and in vivo formation of immune complexes containing IX:Ag prior to detection of his inhibitor in conventional clotting assays, suggesting long-term persistence of an occult inhibitor. The inhibitor was shown to be an IgG antibody with both kappa and lambda light chains.
mesh_terms: D000328:Adult; D000906:Antibodies / Q000302:isolation & purification*; D000936:Antigen-Antibody Complex / Q000032:analysis; D000941:Antigens / Q000032:analysis; D005164:Factor IX / Q000037:antagonists & inhibitors* / Q000276:immunology / Q000627:therapeutic use; D002836:Hemophilia B / Q000097:blood* / Q000276:immunology / Q000628:therapy; D006801:Humans; D007123:Immunoelectrophoresis, Two-Dimensional; D007074:Immunoglobulin G; D008297:Male
chemical_list: D000906:Antibodies; D000936:Antigen-Antibody Complex; D000941:Antigens; D007074:Immunoglobulin G; D005164:Factor IX