Acquired dysfibrinogenemia: monoclonal λ-type IgA binding to fibrinogen caused lower functional plasma fibrinogen level and abnormal clot formation.

We report a case of acquired dysfibrinogenemia with monoclonal gammopathy of undetermined significance presenting λ-type IgA M protein. The patient showed lower functional (0.4 g/dL) and normal immunological fibrinogen (2.9 g/dL). To examine the cause of the false lower value of fibrinogen, we performed experiments using the patient's purified fibrinogen and IgA. Fibrinogen was purified from the patient's plasma; IgA was purified from plasma or serum by immunoaffinity chromatography. We performed thrombin-catalyzed fibrin polymerization, scanning electron microscopy (SEM), immunoblotting analysis, and enzyme-linked immunosorbent assays (ELISAs). Fibrin polymerization in the patient's plasma was markedly reduced and SEM showed no fiber bundles or sponge-like structures. Purified IgA did not influence polymerization, whereas immunoprecipitated plasma with an anti-IgA (α-chain) antibody indicated normalization of polymerization and clot structure. Western blotting analysis revealed the presence of monoclonal λ-type IgA-bound fibrinogen, the proportion of which was significantly higher than normal control plasma using ELISA. Our results suggest that IgA M protein-bound fibrinogen is not normally converted into fibrin, but rather leads to formation of an aberrantly structured fragile clot. The patient's reduced plasma fibrinogen level was caused by the presence of IgA M protein-bound fibrinogen, not by IgA M protein alone.