Neutralizing autoantibody against factor XIII A subunit resulted in severe bleeding diathesis with a fatal outcome - characterization of the antibody

Auto- and alloantibodies against factor XIII: laboratory diagnosis and clinical consequences

Acquired FXIII deficiencies caused by autoantibodies against FXIII subunits represent rare but very severe bleeding diatheses. Alloantibodies in FXIII-deficient patients also cause life-threatening bleeding complications, but they develop extremely rarely. In this review we provide an overview of the diagnosis and classification of anti-FXIII antibodies and analyze 48 patients with autoimmune FXIII deficiency and four additional FXIII-deficient patients who developed anti-FXIII alloantibody. The patients were collected from peer-reviewed publications from which relevant data could be extracted. With the exception of two cases the antibodies were directed against FXIII-A. The difficulties in the diagnosis of FXIII deficiency in the presence of anti-FXIII antibodies are discussed and a scheme for the functional classification of the anti-FXIII antibodies is recommended. The three main categories are neutralizing and non-neutralizing antibodies and antibodies with combined effect. The methods being used for detecting and quantifying the inhibitory effect on FXIII activation and on the transglutaminase activity of activated FXIII are summarized and techniques for the classification of neutralizing anti-FXIII antibodies are outlined. The importance of clearance studies in these cases is emphasized. Binding assays, useful for the identification of non-neutralizing and combined type antibodies, were collected from the literature and their informative power is demonstrated by examples. The most frequently occurring bleeding symptoms in patients with anti-FXIII antibodies were soft tissue bleeding; intracranial bleedings also occurred, but less frequently than in inherited FXIII deficiency. Treatment of such patients is extremely challenging; the main aim should be eradication of the antibody.

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

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.