Occurrence of amyloid-related serum proteins in patients with benign monoclonal gammopathy.

The serum protein SAA, which is related to the amyloid fibril protein AA, was detected by double immunodiffusion using anti-protein AA antiserum. The SAA level was elevated in 16 to 32 patients with benign monoclonal gammopathy (BMG). In addition, two BMG sera reacted with an antiserum to amyloid fibril protein of immunoglobulin light-chain type, V lambdaI (EF), and one reacted with antiamyloid protein VlambdaV (AR). The reactivity of the BMG sera with antisera to the various amyloid fibril proteins was strikingly similar to that of 35 sera from patients with myelomatosis. In the age group of 50--70 years the proportion of SAA-positive sera in BMG (53%) and myelomatosis (56%) was strikingly higher than that of the normal controls (5%). In older subjects (70--90 years), however, the frequency of SAA in BMG or myelomatosis, although increased (53%--54%), was not significantly greater than that of a control group of apparently healthy individuals (44%).