As poikilothermic vertebrates, fish can experience changes in water temperature, and hence body temperature, as a result of seasonal changes, migration, or efflux of large quantities of effluent into a body of water. Temperature shifts outside of the optimal temperature range for an individual fish species can have negative impacts on the physiology of the animal, including the immune system. As a result, acute or chronic exposure to suboptimal temperatures can impair an organisms’ ability to defend against pathogens and thus compromise the overall health of the animal. This review focuses on the advances made towards understanding the impacts of suboptimal temperature on the soluble and cellular mediators of the innate and adaptive immune systems of fishes. Although cold stress can result in varying effects in different fish species, acute and chronic suboptimal temperature exposure generally yield suppressive effects, particularly on adaptive immunity. Knowledge of the effects of environmental temperature on fish species is critical for both the optimal management of wild species and the best management practices for aquaculture species.

A cell line, RTgutGC, was developed from the intestine of Oncorhynchus mykiss. RTgutGC has an epithelial-like shape, been passaged over 100 times, and cryopreserved successfully. A rainbow trout origin was confirmed by sequencing a 652 bp region of the mitochondrial cytochrome c oxidase I gene. RTgutGC is grown routinely in Leibovitz’s L15 without glutamine supplemented with 10% fetal bovine serum (FBS). Cell viability was evaluated with Alamar blue (AB) for metabolic activity and carboxyfluorescein diacetate acetoxymethyl ester (CFDA AM) for membrane integrity. Viability was unchanged by lipopolysaccharide (LPS) for cultures in FBS. For cultures at low cell densities in L15 without FBS or glutamine, cell viability declined in a LPS dose-dependent manner, allowing calculation of the concentration causing a 50% decline in viability (EC₅₀). When glutamine was present, the EC₅₀ was increased for both AB and CFDA AM. As the cell density increased, LPS became much less cytotoxic and no EC₅₀ could be calculated for very confluent cultures. Only high-density cultures had alkaline phosphatase (AP) activity. Thus, glutamine and possibly AP protect against LPS cytotoxicity. RTgutGC should be a useful in vitro tool for studying problems of nutrition and gastrointestinal health in fish.

Glutathione (GSH) and glutathione disulfide (GSSG) form the principal thiol redox couple in the endoplasmic reticulum (ER); however, few studies have attempted to quantify GSH redox status in this organelle. To address this gap, GSH and GSSG levels and the extent of protein glutathionylation were analyzed in rat liver microsomes. Because of the likelihood of artifactual GSH oxidation during the lengthy microsomal isolation procedure, iodoacetic acid (IAA) was used to preserve the physiological thiol redox state. Non-IAA-treated microsomes exhibited a GSH:GSSG ratio between 0.7:1 to 1.2:1 compared to IAA-treated microsomes that yielded a GSH:GSSG redox ratio between 4.7:1 and 5.5:1. The majority of artifactual oxidation occurred within the first 2 h of isolation. Thus, the ER GSH redox ratio is subject to extensive ex vivo oxidation and when controlled, the microsomal GSH redox state is significantly higher than previously believed. Moreover, in vitro studies showed that PDI reductase activity was markedly increased at this higher thiol redox ratio versus previously reported GSH:GSSG ratios for the ER. Lastly, we show by both HPLC and Western blot analysis that ER proteins are highly resistant to glutathionylation. Together, these results may necessitate a re-evaluation of GSH and its role in ER function.

It has become increasingly clear over the course of the past decade that the immune system genes of teleosts and tetrapods are plainly derived from common ancestral genes. The last 5 years, however, have also made it abundantly clear that in the teleost genome some of these genes are organized in a manner very different from that seen in mammals. These differences are probably the result of differences in life history traits, such as fecundancy, within each group of species when faced with an evolutionary fork in the road shortly after their divergence from each other. One group, the tetrapods, including mammals, chose a highly organized linked major histocompatibility complex, while in teleosts the major histocompatibility genes remained unlinked. In this review we will discuss the structural and functional implications of this different organization, particularly for major histocompatibility genes, but drawing on the current knowledge of some other genes for further support for the hypothesis that each group took a different road, one more traveled and one less taken.