Characterization Of An Acquired IgG Autoantibody To Bβ and γ Chains Of Fibrinogen Resulting In Delayed Fibrin Polymerization and Severe Bleeding

A 88 year-old woman was referred to our center for 3 weeks of gastrointestinal bleeding and a spontaneous right rectus femoris hematoma. The prothrombin time (PT), activated partial thromboplastin time (aPTT), thrombin time (TT) and reptilase time (RT) were markedly prolonged (Table 1). Assays for coagulation factors V, VIII, IX and X were normal. A fibrinogen concentration of < 50 mg/dl was measured by Clauss method while fibrinogen concentration measured by radial immunodiffusion was 180 mg/dl. Following infusions of cryoprecipitate there was accelerated clearance of fibrinogen as measured by the Clauss method. An inhibitor of fibrinogen function was suspected.

When the patient’s plasma was tested towards immobilized fibrinogen in ELISA plates, a concentration dependent specific binding of IgG was seen while under similar conditions control IgG had no significant binding (Figure 1). The IgG antibody was polyclonal comprising of both kappa and lambda subtypes.

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The IgG fraction was purified on a Protein A column and the isolated IgG fraction prolonged the thrombin time of normal plasma in a concentration dependent manner. The effect of the isolated IgG fraction on fibrin polymerization was measured by monitoring the absorbance at λ390 in a spectrophotometer. The IgG inhibited fibrin polymerization in a concentration dependent manner. Control IgGs had no significant effect on polymerization under these conditions (Figure 2).

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The immunologic specificity of antibody was tested in immunoblots of fibrinogen subjected to SDS-PAGE. The patients IgG reacted with fibrinogen in unreduced buffers. Under reducing conditions, the IgG reacted with Bβ and γ chains of fibrinogen while the control IgG did not (Figure 3).

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The patient was treated with rituximab and steroids. After four, weekly doses of rituximab, fibrinogen levels by Clauss method normalized (450 mg/dl). There was no detectable antibody to fibrinogen and no further bleeding was noted.