Identification Of α1-antitrypsin As A Positive Acute Phase Protein In Ayu

αl-Antitrypsin (AAT), a secretory glycoprotein produced mainly in the liver. AAT isimplicated in the regulation of a variety of mammalian immune responses and was recentlyidentified as a major serpin in blood plasma of some fish. However, AAT expression followingbacterial infection in fish has not been well described. In this study, we cloned the full-length ayu(Plecoglossus altivelis) AAT gene cDNA. It contained1507-bp excluding3’-polyA tail, whichencodes a19-amino acids (aa) signal peptide and a437-aa mature AAT with a molecular weight of48.3kDa. Phylogenetic analysis indicated that ayu AAT shared54%amino acid sequence identitywith spotted green pufferfish AAT. he real-time quantitative PCR data showed that the AATtranscript was determined to be significantly abundant in the liver, and low in the intestine, heart,muscle, head kidney, brain and spleen of healthy fish. After challenge with L. anguillarum, theAAT transcripts in the liver immediately increased up to1.85-fold at4hpi, reached the top level(4.83-fold) at8hpi, and went back to the control level at24hpi. The change of AAT transcript inthe head kidney，brain and muscle had a similar tendency like that in the liver. In the intestine andspleen, the AAT transcript significantly increased at4hpi, went back to the control level at8hpi,and reached the top level at24hpi. In the heart, the AAT transcript reached the top level at4hpi,and then decreased gradually. Western blot analysis revealed that the serum AAT protein levelsignificantly increased in response to inflammation, but displayed no significant changes aftercadmium exposure or salinity challenge. PNGase F digestion confirmed that the ayu AAT was aglycoprotein. This work represents the first report that identifies AAT as a positive acute-phaseprotein in ayu fish associated with bacterial infection, suggesting that it might play a role in fishinnate immunity.