Serum amyloid A protein in mink during endotoxin induced inflammation and amyloidogenesis

Two-dimensional electrophoresis was used to study SAA and AA proteins in mink during lipopolysaccharide-induced inflammation and amyloidogenesis. Three isotypes, SAA pI 6.8 and SAA pI 6.5 (both SAA1-like), and SAA pI 6.0 (SAA1- and SAA2-like), were identified in serum after both single and multiple LPS injections. Total SAA serum levels were highest in the early phase of induction, followed by a decrease ranging from 1 to 50% of the peak value during the rest of the experiment. The variation in the total SAA levels correlated with the total SAA mRNA levels. Low total SAA levels were seen both in non-amyloidotic and amyloidotic animals, and a general decrease of all isotypes was demonstrated. In hepatic amyloid fibrils, several AA isotypes, with amino acid sequence homologous exclusively to that of SAA2, were found. In the corresponding splenic material, fragments of histones H2A and H2B constituted most of the low molecular mass proteins, and no protein AA was detected. In spite of low serum levels and a non-specific isotype removal, the results confirm that SAA2 is amyloidogenic in mink.