Severe bleeding diatheses in an elderly patient with combined type autoantibody against factor XIII A subunit; novel approach to the diagnosis and classification of anti-factor XIII antibodies.
Haemophilia 2017;
23:590-597. [PMID:
28345289 DOI:
10.1111/hae.13205]
[Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 01/19/2017] [Indexed: 11/30/2022]
Abstract
INTRODUCTION
Acquired factor XIII (FXIII) deficiency due to autoantibody is a rare, severe bleeding diathesis. Its laboratory diagnosis and classification represents a difficult task.
AIM
Introduction of novel approaches into the diagnosis and characterization of anti-FXIII autoantibody and demonstration of their use in the diagnosis of a patient with autoimmune FXIII deficiency.
METHODS
Factor XIII activity, FXIII antigen levels and the titre of anti-FXIII-A antibody were monitored throughout the course of the disease. FXIII activity was measured by ammonia release assay; FXIII-A2 B2 complex, total and free FXIII-B concentrations were determined by ELISAs. The binding constant for the interaction of the autoantibody with recombinant FXIII-A2 (rFXIII-A2 ) and FXIII-A2 B2 was determined by surface plasmon resonance (SPR). The inhibitory capacity of IgG was expressed as the concentration exerting 50% inhibition of FXIII activation/activity (IC50). The truncation of FXIII-A by thrombin was monitored by western blotting. The inhibition of Ca2+ -induced FXIII activation and active FXIII (FXIIIa) were assessed by FXIII activity assay.
RESULTS
The antibody bound to rFXIII-A2 and FXIII-A2 B2 with high affinity and accelerated the decay of supplemented FXIII concentrate. An IC50 value of 170.1 μg IgG·mL-1 indicated effective FXIII neutralization. The main neutralizing effect of the autoantibody was the inhibition of FXIIIa. After 2 months, due to combined therapeutic modalities, the autoantibody disappeared and FXIII activity significantly elevated.
CONCLUSION
The anti-FXIII-A autoantibody exerted a combined effect including inhibition of FXIIIa and acceleration of FXIII decay in the plasma. IC50 and binding constant determinations added important information to the characterization of the autoantibody.
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