Acute phase response to inflammation in salmonid fishes

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Simko, Elemir

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University of Guelph

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The studies in this thesis were focused on investigating and comparing quantitative changes in rainbow trout and brook trout plasma proteins induced by several inflammatory and non-inflammatory stimuli. The objectives were to determine if fish have an acute phase protein synthesis response similar to mammals and to determine if genetic variation in susceptibility to furunculosis in salmonids correlates with differences in acute phase responses. In addition, the inducibility and hepatic origin of previously reported Aeromonas salmonicida lipopolysaccharide binding proteins, namely C-reactive protein (CRP), serum amyloid P (SAP), ladderlectin and RT-L37 lectin (Hoover et al. 1998) were investigated. Two dimensional electrophoresis (2D-SDS-PAGE) of plasma samples and autoradiography of \sp35S labeled proteins synthesized by control and acute phase hepatocytes revealed that rainbow trout CRP, SAP and RT-L37 lectins were constitutively expressed plasma proteins produced by the liver. Ladderlectin was not detectable as an hepatic product and its plasma concentration was below detectable limits of 2D-SDS-PAGE. Rainbow trout and brook trout developed similar local acute inflammatory reactions after intraperitoneal Lipogen Triple vaccination or intramuscular A. salmonicida LPS injection. Inflammation was accompanied by a systemic acute phase response, manifested by an acute transient hypoferremia in rainbow trout and brook trout, and an acute transient hypozincemia in rainbow trout. Inflammatory reactions induced an up to 4-fold increase in concentration of plasma proteins p48, p19 and p16 in rainbow trout, but not in brook trout. Rainbow trout p16 and p19 were not produced by hepatocytes; accordingly, they did not qualify as acute phase proteins. Only p48 was produced by rainbow trout hepatocytes, but it was similarly expressed in control and LPS-exposed hepatocytes. The p48 had N-terminal amino acid sequence homology with an internal region of serum albumin of Atlantic salmon but was smaller than trout plasma albumin. This implied that p48 was most likely a proteolytic cleavage product of albumin and not an acute phase reacting protein. Collectively, these studies demonstrate that salmonids do not exhibit the same degree of inducibility of acute phase plasma proteins as is seen in mammals exposed to sterile acute inflammation.

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Salmonid fishes, inflammation, acute phase protein, synthesis response, plasma protein

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