Enzyme-linked immunosorbent assay of serum protein SAA in rhesus monkeys with secondary amyloidosis.

Tissue deposits of amyloid protein AA and a concomitant elevation of serum protein SAA have been demonstrated previously in mice and humans with secondary amyloidosis, but not in rhesus monkeys (Macaca mulatta). In this study, protein SAA was quantitated in normal and amyloidotic rhesus monkeys using an enzyme-linked immunosorbent assay. Protein AA was isolated from the liver of a rhesus monkey with secondary amyloidosis by a combination of water extraction and gel filtration chromatography. The purified material had rigid, nonbranching fibrillar structures typical of amyloid on electron microscopy and a molecular weight of 9000 by sodium dodecyl sulfate polyacrylamide gel electrophoresis. The amino acid content and partial sequence were comparable to those reported previously for protein AA of rhesus monkeys. As measured by enzyme-linked immunosorbent assay, normal rhesus monkeys had SAA levels of 40 to 64 ng. of AA equivalents per ml., whereas amyloidotic rhesus monkeys had SAA levels of 1700 to 95,000 ng. of AA equivalents per ml. An elevation of protein SAA was also detected in an amyloidotic pigtailed macaque (Macaca nemestrina) using rabbit antirhesus protein AA. Rabbit antisera against human and mouse protein AA reacted strongly with rhesus protein AA and with amyloidotic rhesus serum, but only slightly with normal rhesus serum, indicating that rhesus proteins AA and SAA have antigenic determinants cross-reactive with protein AA of xenotypic species.