Serum amyloid A in the mouse. Sites of uptake and mRNA expression.

Murine serum amyloid A1 (SAA1) and serum amyloid A2 (SAA2) are circulating, acute phase, high density apolipoproteins of unknown function. To pursue issues relating to their possible function their uptake and formation were studied. Kinetics of SAA protein distribution and gene expression after acute phase stimulation by casein or lipopolysaccharide were examined using immunocytochemistry for protein and RNA blot and in situ hybridization with probes for SAA1 and SAA2 mRNA. After casein injection, interstitial cells of testes, cells of adrenal cortex, kidney proximal convoluted tubule epithelia, and some parafollicular cells of spleen took up SAA in a time pattern related to plasma SAA levels. Extrahepatic SAA1 and SAA2 mRNA were induced by lipopolysaccharide in kidney proximal and distal convoluted tubule epithelia, and SAA1 mRNA was induced in epithelial lining the mucosa of the ileum and large intestine, indicating that there may be more than one function for the apoSAA gene family related to site of and stimulus for expression.