Innate immunity is induced when pathogen-associated molecular patterns (PAMPs) bind host pattern recognition receptors (PRRs). Polyinosinic:polycytidylic acid [poly(I:C)] is a synthetic analogue of viral dsRNA that acts as a PAMP, inducing type I interferons (IFNs) in vertebrates. In the present study, the immunostimulatory effects of high molecular weight (HMW) poly(I:C) in rainbow trout cells were measured when bound to a cationic phytoglycogen nanoparticle (Nano-HMW). The physical characteristics of the nanoparticle itself, when bound to different lengths of dsRNA and when cell associated was evaluated. Optimal concentration and timing for innate immune stimulation was measured using the RTG-P1 reporter cell line. The immunostimulatory effects of HMW poly (I:C) was compared to Nano-HMW in vitro using the RTgutGC cell line cultured in a conventional monolayer or a transwell culture system. The ability of an activated intestinal epithelium to transmit an antiviral signal to macrophages was evaluated using a co-culture of RTgutGC cells and RTSll (a monocyte/macrophage cell). In all culture conditions, Nano-HMW was a more effective inducer of IFN-related antiviral immune responses compared to HMW poly (I:C) alone. This study introduces the use of cationic phytoglycogen nanoparticles as a novel delivery system for immunomodulatory molecules to enhance immune responses in aquatic vertebrates.

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Rainbow Trout Oncorhynchus mykiss are a commonly farmed fish worldwide and, as such, are of economic importance in many countries. Inosine monophosphate (IMP) has been shown to have a positive effect on Rainbow Trout growth performance and overall health. The aim of the current study was to test whether a novel phytoglycogen nanoparticle (NP) was nontoxic and if it could enhance the positive effects of IMP on Rainbow Trout health at the cellular and whole-animal level. The NP used in this study is derived from sweet corn and can act as a carrier, delivering its payload to the cell. The NP was chemically modified to covalently bind IMP. The effects of four experimental groups were tested on Rainbow Trout at the in vitro and in vivo level: untreated control, NP alone, IMP alone, and IMP covalently conjugated to the NP (IMP-NP). The effects of the four experimental groups were measured at the cellular level using a Rainbow Trout intestinal epithelial cell line (RTgutGC). Cellular metabolism was significantly increased in RTgutGC when treated with IMP-NP for 24 and 48 h compared with NP or IMP alone. These treatments did not result in a compromised cell membrane, with the exception of minimal membrane integrity loss at 48 h with the higher doses of IMP-NP. During the 48-h time frame, enhanced metabolism did not result in enhanced cell proliferation. A pilot study was performed in Rainbow Trout to test the safety of the NP to fish. Over an 8-week feeding trial, no mortalities were observed. Additionally, intestinal villi density increased with IMP-NP and NP treatments, while villus height and width were unaffected. This study introduces the use of a phytoglycogen-based NP as a novel delivery system for IMP that is able to increase metabolism at the cellular level and is nontoxic in Rainbow Trout.