Immunoglobulins on the surface of lymphoid cells in Waldenström's macroglobulinemia

Immunofluorescence study of viable and fixed cells was performed on marrow and blood samples from 25 patients with Waldenström's macroglobulinemia. Whereas intracytoplasmic staining for IgM was restricted to the plasma cells and to a limited number of lymphocytic cells, the vast majority of the pleomorphic "lymphoid" proliferating cells in the marrow were shown to bear the monoclonal IgM on their surface. All IgM-secreting plasma cells displayed membrane positivity. Most lymphocytic proliferating cells carried the monoclonal IgM on their surface in the absence of detectable amounts of intracytoplasmic IgM. Despite the usual absence of increase in blood lymphocyte counts, a large number of circulating lymphocytes were shown to bear membrane-bound monoclonal IgM in patients with active disease. The number of fluorescent spots, their size and brightness varied greatly from cell to cell in marrow and blood samples of a given patient, and this finding is in contrast to the homogeneous fluorescent pattern observed in chronic lymphocytic leukemia. The data suggest that macroglobulinemia represents the proliferation of a clone of B cells which continues to mature and differentiate.