Study of three patients with monoclonal gammopathies and 'lupus-like' anticoagulants.

In three patients with monoclonal gammopathies: a case of multiple myeloma, a case of monoclonal gammopathy of uncertain significance (MGUS) and a case of monoclonal gammopathy associated with lymphocytic lymphoma, we found the presence of a circulating lupus-like anticoagulant. Coagulative studies showed that the paraproteins: an IgG3k, an IgG1k and an IgMlambda, were responsible for the anticoagulant activity by interacting with the thromboplastin phospholipids. Using isoelectrofocusing we demonstrated that the three monoclonal immunoglobulins had a strong basic charge which may have contributed to determining their interaction with the acidic thromboplastin phospholipids. The binding of various phospholipids to the monoclonal proteins was assessed by the fluorescence quenching method which showed heterogeneous specificity. In order to establish whether the electrical charge is also relevant in cases with polyclonal lupus anticoagulant, the polyclonal immunoglobulins were fractionated according to their charge. The strongest inhibitor activity was found in the most basic immunoglobulins. Monoclonal lupus-like anticoagulants represent useful tools for investigating the heterogeneous world of polyclonal lupus-like anticoagulants.