To identify monoclonal bone marrow-derived (B) lymphocytes in human myelomatosis specific rabbit antisera were produced against idiotypic specificities on IgG-κ myeloma proteins from three patients. The antisera neither cross-reacted nor reacted with normal immunoglobulins. By indirect immunofluorescence surface immunoglobulins were demonstrated on 20–47% of peripheral blood lymphocytes from untreated patients after staining with idiotypic antiserum against the patient's own myeloma protein, but not after staining with other idiotypic antisera. The antisera also stained autologous plasma cells. The monoclonal surface Ig on myeloma lymphocytes was removed by trypsin and regenerated after incubation in serum-free medium. Myeloma protein was not adsorbed onto lymphocytes. It is concluded that monoclonal B lymphocytes belonging to the plasma cell myeloma clone are present in myeloma patients. There were few normal B lymphocytes in untreated patients.
During treatment the monoclonal lymphocyte population and the plasma cells content in bone marrow, as well as the concentration of monoclonal immunoglobulin in serum, decreased simultaneously. These findings were associated with other signs of clinical improvement.