Differentiation between benign and malignant monoclonal gammopathy by the presence of the J chain.

Malignant monoclonal gammopathy (MMG) cannot easily be distinguished from the benign (BMG) form in a number of cases. Using two different anti-J chain reagents it could be shown in the present study that in MMG, J chain is present in most of the IgG-containing plasma cells in the bone marrow. In BMG, the frequency of J chain-containing IgG plasma cells is low and not different from that obtained in healthy individuals. Essentially similar findings regarding idiotype were obtained, using anti-idiotype conjugates, specific for the patients' monoclonal immunoglobulins. In one patient malignancy was indicated by the presence of a high percentage of J chain-containing IgG plasma cells in the bone marrow, prior to clinical expression of multiple myeloma.