Monoclonal IgM with anti-muscle tissue activity in a patient with Waldenström's macroglobulinaemia: secretion of identical immunoglobulin by the established lymphoid cell line.

The monoclonal IgM kappa protein from a patient with Waldenström's macroglobulinaemia displayed antibody like activity against muscle and alpha-actinin. An Epstein-Barr virus associated lymphoid cell line, spontaneously established from blood lymphocytes, has been continuously secreting an immunoglobulin of the same isotype, isoelectric focusing spectrotype and reactivity; the cell line is probably leukaemic in origin since all cells display the translocation t (1; 19) and are aneuploid. We suggest these two monoclonal immunoglobulins have a common malignant origin.