IgD myeloma protein with "unreactive" light chain determinants.

Serum from a patient with multiple myeloma showed a monoclonal protein, classified by immunoelectrophoresis as IgD. Immunofixation electrophoresis and immunoelectrophoresis failed to demonstrate a precipitation reaction between the paraprotein and antisera to immunoglobulin light chains. The light chains of the monoclonal protein, immunologically inaccessible in the intact molecule, reacted with anti-lambda chain antisera only after reduction and alkylation of the paraprotein. Moreover, interpretation of the immunoelectrophoretic patterns was hampered by the presence in patient's serum of free lambda chains having about the same mobility as that of the paraprotein.