Intracellular formation of amyloid fibrils in myeloma. Cytochemical, immunochemical, and electron microscopic observations.

Needle-like, rod-shaped, and rhomboid intracytoplasmic crystalline inclusions were found in myeloma cells from the bone marrow of a patient with IgA-kappa and Bence Jones-kappa type multiple myeloma. Cytochemical, immunochemical, and electron microscopic studies revealed that these inclusions consisted of at least three kinds of components: kappa light chain crystals, lysosomal enzymes, and amyloid fibrils. The coexistence of these three kinds of inclusions in one myeloma cell suggests an intracellular site for the formation of amyloid fibrils. From these observations, the authors postulated that the excessively produced light chains were transported to the Golgi apparatus where they were transformed into crystalline inclusions, and thereafter, digested by lysosomal enzymes to form amyloid fibrils. The demonstration of crystalline inclusions which reacted exclusively with antisera against free light chains indicates that the Bence Jones protein is a precursor of amyloid light chain.