IgG subclasses of FVIII inhibitors in an argentine cohort of severe hemophilia A patients: Analysis by flow cytometry.

INTRODUCTION: FVIII inhibitors consist of a polyclonal population of antibodies. Previous studies have demonstrated different distribution of IgG subclasses. IgG4 was associated to high level of FVIII inhibitors and failure of immune tolerance induction (ITI) treatment. This study monitored the relative distribution of IgG subclasses of anti-FVIII in patients with severe hemophilia A (SHA). METHODS: Anti-FVIII antibodies were measured employing an immunomethod, developed in our laboratory, that combines flow cytometry (FC) with microspheres coupled (FVIII-m) or not (Control-m) to FVIII. Seventy-five patients with SHA were studied, 17 without inhibitors (Group I); 58 with inhibitor history, 13 low responders: (LR: Group II), and 45 high responders (HR: Group III). Eight patients undergoing ITI were also included. RESULTS: We found anti-FVIII antibodies in 11 of 27 patients (40%) without inhibitors and in 45 of 48 with inhibitors at the moment of the study. IgG4 was predominant only in the Group III: P=0.02 in patients with low level of inhibitors and P=0.0001 with high titer of inhibitors. Longitudinal analysis performed on patients undergoing ITI showed a gradual decrease of IgG4 values that was associated to improvement of clinical parameters during treatment. CONCLUSION: We suggest the use of the FC method to supplement functional traditional assays and to help to improve the management of patients with SHA.

Natural coagulation inhibitory proteins and activated protein C resistance in Turkish patients with inflammatory bowel disease.

BACKGROUND/AIMS: Thromboembolic events are a rare but significant complication of inflammatory bowel disease. The aim of this study was to investigate the level of natural coagulation inhibitors and activated protein C resistance in Turkish patients with inflammatory bowel disease. METHODS: Fifty patients (29 male, 21 female) without venous thrombosis history and 37 healthy controls were included in the study. Erythrocyte sedimentation rate, C-reactive protein, thrombocyte count, prothrombin time, activated partial thromboplastin time, fibrinogen concentration, von Willebrand factor antigen, factor VIII activity, activated protein C resistance, functional levels of antithrombin III, protein C and protein S were measured. Patients and controls with activated protein C resistance were further studied using a polymerase chain reaction assay for factor V Leiden mutation. RESULTS: There was no significant difference between patients and the controls in terms of antithrombin III, protein C, protein S, factor (F) VIII and Willebrand factor levels. The mean thrombocyte counts, fibrinogen levels, and Willebrand factor levels were found to be significantly higher in patients who were in the active period of the disease than in controls and patients in remission. No significant difference was observed in those showing activated protein C resistance and factor V Leiden mutation between patients and controls. CONCLUSIONS: The presence of inherited thrombophilic defects, in particular activated protein C resistance and natural coagulation inhibitor deficiency, is uncommon in Turkish patients with inflammatory bowel disease in both active and remission periods. As a result, a controlled study in inflammatory bowel disease patients with thrombosis history is recommended.

Classification of the kinetics of factor VIII inhibitors in haemophilia A: plasma dilution studies are more discriminatory than time-course studies.

Factor VIII inhibitors have previously been classified as type I or type II using complex experiments that study the time course of inactivation of factor VIII and the effect of varying the antibody concentration. Classification may be important to better understand inhibitor behaviour in vivo. To determine the most reliable method of classifying the kinetics of factor VIII inactivation, we studied 11 patients with haemophilia A, comprising five severe, three mild and three acquired cases, and compared the classification obtained from plasma dilution studies and time-course studies. The plasma dilution studies showed two distinctly different patterns: a steep slope with complete FVIII:C inactivation at high antibody concentrations for type I inhibitors and a FVIII:C plateau with incomplete inactivation for type II inhibitors. Six type I (four severe, one mild and one acquired) and two type II (one mild and one acquired) inhibitors were classified using either plasma samples or purified and concentrated IgG, while the remaining were undetermined owing to insufficient available plasma. In contrast, the time-course studies could not discriminate between these groups. We recommend that plasma dilution studies be used for the classification of in vitro kinetics of factor VIII inhibitors.