Characterization of the Monoclonal Blood and Bone Marrow B Lymphocytes in Waldenström's Macroglobulinaemia

Abstract

Blood lymphocytes were studied in 16 patients with Waldenstrom''s macroglobulinemia. In 4 of them bone marrow lymphocytes were studied simultaneously. In all 4, a monoclonal lymphocyte plasma cell fraction carrying the L chain isotype of the serum M-component was identified by direct immunofluorescence. The cell-bound immunoglobulins [Ig] had idiotypic structures in common with the serum M-component. The monoclonal cell component was pleomorphic, varying from small lymphocytes carrying surface IgM/IgD or IgM only, to plasma-cytoid cells with both surface and cytoplasmic IgM, to mature plasma cells with only cytoplasmic IgM. A differentiating B [bone marrow-derived] cell clone was further suggested by the sequential loss of complement and Fc receptors during maturation to plasma cells. In 9 patients monoclonal lymphocytes were increased also in blood. The monoclonal fraction was small in all except 2 patients with advanced disease. The assumption that a clone of B lymphocytes differentiates into Ig-secreting cells in Waldenstrom''s macroglobulinemia was supported. The pattern of cell differentiation in bone marrow was the same in patients with and without a monoclonal blood cell fraction. Progression of the disease is probably the main factor determining the appearance of large numbers of tumor cells in blood.