Identity of a peritoneal fluid immunoglobulin light chain and the amyloid fibril in primary amyloidosis.

A monoclonal immunoglobulin has been isolated from the peritoneal fluid of a patient with primary amyloidosis. The immunoglobulin was reduced and alkylated and the light and heavy chains were compared to the major protein constituent of that patient's hepatic amyloid fibrils. N-terminal amino acid sequences of the light chain and amyloid fibril were identical when carried to 20 residues and were typical of a kappa I light chain. Molecular weight studies suggested that the fibril protein was composed of an intact light chain with a molecular weight of 23,000. The hypothesis that amyloid fibril protein in primary amyloid is derived from circulating monoclonal immunoglobulin is discussed.