Two IgM paraproteins bearing cryoglobulin and anti-smooth muscle activities in a patient with Waldenström's macroglobulinaemia.

A 52-year-old white male subject with typical clinical and laboratory findings of Waldenström's macroglobulinaemia is described. Two paraprotein peaks of IgM lambda class, with different physical and chemical properties and different amino acid compositions, in both heavy and light chains, were found in the patient's serum. One of the IgM components (M1) was a cryoglobulin, and the other (M2) showed strong antismooth muscle activity. As far as we know, this is the first report of double paraproteins each of which has different properties.