The histiocytic origin of the multinucleated giant cells in myeloma kidney.

A recent case of myeloma kidney disease was studied to determine the cellular origin of the syncytial multinucleated giant cell. Light, immunofluorescence, and electron microscopy of the giant cells revealed features characteristic of histiocytes. This finding contradicts the generally accepted conclusion that the giant cell represents a syncytial mass of degenerating or reactive tubular epithelial cells. We conclude that the giant cells arise in the interstitial tissues, migrate through breaks in the tubular basement membrane, and engulf and surround intratubular protein casts.