Abstract

The ultrastructure of neoplastic plasma cells from a patient with prolonged multiple myeloma was studied in relation to its function, that is, the secretion of immunoglobulin light chain. Peroxidase-labelled antibodies, each monospecific to its immunoglobulin component chain, were used to localize intracellular immunoglobulin within myeloma cells under the electron microscope. By this method, only the κ type light chain was detected within myeloma cells in bone marrow tissue of this patient, indicating that the occurrence of free κ type light chains in serum and urine was due to the cessation of heavy chain synthesis within the myeloma cells. The κ chain was demonstrated as conspicuous electron-dense precipitates in ergastoplasm, its cisternal space, external layer of nuclear membrane, and ribosomes associated with ergastoplasm and nuclear membrane. No immunoglobulin was demonstrated in an atypical Golgi complex, an organelle which is ordinarily engaged in protein synthesis. Numerous crystalline structures and similar inclusion bodies found in myeloma cells appeared to have arisen from the Golgi area, but they did not ever react with the peroxidase label. Discharge of the κ chain from the cell seems to be carried out through cell fragmentation, possibly caused by progressive distension of the ergastoplasmic cavity.