Anti‐platelet and Anti‐DNA IgM in waldenström macroglobulinemia and ITP

We describe a monoclonal IgM that was purified from the serum of a patient with Waldenstrom macroglobulinemia and thrombocytopenia. The binding and idiotypic characteristics of the patient's macroglobulin were similar to those of a human monoclonal IgM secreted by a hybridoma established from peripheal blood lymphocytes of a patient with systemic lupus erythematosus and immune thrombocytepenia. In the absence of other causes for thrombocytopenia in this patient, our results suggest an autoimmune mechanism for destruction of platelets by the monoclonal IgM. This is the first report of a Waldenstrom macroglobulinemia with anti‐platelet activity of monoclonal IgM. Although the study involves a single patient, the results suggest that there may be a common origin for autoantibodies in autoimmune diseases and monoclonal immunoglobulins having autoantibody activity in monoclonal gammopathies.