[Anti-smooth-muscle antibody activity of monoclonal IgM in Waldenström's disease].

: The authors report a case of Waldenstrom disease in which the IgM kappa immunoglobulin had an anti-smooth-muscle activity at a very high titre (1/100 000). This activity was found in the purified IgM but not in the Fab fragment; nevertheless, the immunofluorescence inhibition by this fragment is evidence in support of the anti-smooth-muscle activity of the IgM. The IgM specificity in this patient is different from the anti-smooth-muscle antibodies already described.