Anti-human immunoglobulin G activity of membrane-bound monoclonal immunoglobulin M in lymphoproliferative disorders.

Lymphocytes from a patient with Waldenström's macroglobulinemia and known anti-immunoglobulin IgG activity of serum monoclonal IgM and lymphocytes from selected patients with chronic lymphocytic leukemia were studied by the membrane immunofluorescence procedure. Freshly drawn lymphocytes were shown to bear simultaneously mu, gamma, [unk], and lambda chain determinants. Experiments combining redistribution induced by antibody and double labeling proved that IgG was bound to surface IgM. After removal of surface immunoglobulins by treatment with trypsin followed by incubation in culture medium, or after redistribution induced by antibody, the exclusive presence of a newly synthetized monoclonal IgM was demonstrated. Several experiments showed that this surface IgM does specifically bind normal human IgG molecules devoid of aggregated material. The IgG molecules could be removed from the cell surface by lowering the pH. In addition to its high incidence among serum monoclonal macroglobulins, anti-IgG activity of membrane-bound monoclonal IgM is not uncommon in patients with chronic lymphocytic leukemia, a disease that provides homogeneous populations of lymphocytes derived from bone marrow, with receptor sites of defined antibody activity.