EXPRESSION OF SERUM AMYLOID-A GENES IN MINK DURING INDUCTION OF INFLAMMATION AND AMYLOIDOSIS

Serum amyloid A (SAA) is an acute phase protein and the precursor of a myloid protein A (AA) in deposits of secondary amyloidosis. Several is otypes exist in mink, but previous studies suggest that mink AA is der ived from only one. To assess the effect of repeated episodes of infla mmation and induction of amyloidosis, qualitative and quantitative cha nges in hepatic and extrahepatic SAA mRNA were studied. Young female m ink received subcutaneous lipopolysaccharide injections for amyloid in duction. Studies were performed using RNA probes and oligonucleotide p robes specific for each of two SAA mRNA species. Northern blot hybridi zation showed that hepatic SAA1 and SAA2 mRNA levels increased dramati cally after inflammatory stimulation, and were subsequently maintained at elevated levels, showing considerable interindividual variation, b ut only a slight decrease during repeated inflammatory stimuli and the early stages of amyloid deposition. No preferential accumulation of m RNA specifying a particular isotype was found during the experiment. D ifferential expression of mink SAA mRNA during repeated inflammatory s timulation does not seem to explain why only SAA2-derived AA is found in amyloid deposits. Extrahepatic SAA mRNA seemed to be independently regulated and may thus represent another, yet not characterized, SAA i sotype.