Molecular Size,pH, Temperature Stability,and Ontogeny of Inhibitor(s) of Infectious Pancreatic Necrosis Virus (IPNV) in Normal Rainbow Trout Serum

Abstract

In this study, we investigated the characteristics of inhibitor(s) of infectious pancreatic necrosis virus (IPNV) found in the serum of normal rainbow trout Oncorhynchus mykiss (RTS). The molecular size, stability to pH and temperature, and ontogeny of the inhibitor in trout were studied, and the effect of cations (Ca²⁺ and Mg²⁺) on the activity of the inhibitor was tested. The strongest inhibition of virus was obtained at approximately 150 kDa as measured by ultracentrifugation, sieve gel chromatography, and ultrafiltration. The inhibition decreased significantly when RTS was dialyzed or filtered in the absence of divalent cations, but replacement of at least one cation restored activity. Activity was stable at temperatures ranging from 30°C to 50°C, but 55°C completely destroyed the inhibitory capacity of RTS. The inhibitory activity of RTS was not reduced between pH 4 and 10 but was diminished below pH 4 and above pH 10; such activity was not abrogated by proteases. Additionally, pretreatment of RTS with the polysaccharide mannan significantly reduced inhibition. Thus, the serum inhibitor(s) had many characteristics of a lectin. To determine the ontogeny of inhibition, serum samples were taken from normal rainbow trout, beginning at 2 weeks posthatch; consistent inhibition was not obtained until the rainbow trout had reached the age of 23 weeks posthatch.