SARF004: Vaccine performance/efficacy in gadoids measured by cell mediated immune responses.

Start Date: 01/05/2005
End Date: 30/04/2006
Main Contractor(s): Scottish Fish Immunology Centre, University of Aberdeen 
Other Sponsor(s): Seafish Industry Authority and Schering-Plough Aquaculture

Objectives

1. Clone the cod/haddock IFNg and IL2 genes (6 months).

2. Produce the molecules as recombinant proteins (6 months).

3. Raise antisera to the IFNg and IL2 proteins (4 months).

4. Establish the ELISPOT assay to detect cells secreting either cytokine, using the produced antisera (4 months).

5. Determine the size of the cytokine response following vaccination, by stimulating leucocytes from vaccinated fish in vitro (4 months).

6. Determine the size of the cytokine response following vaccination, by exposing fish to pathogens in vivo (6 months).

7. Determine the size of the cytokine response using vaccines of variable efficacy, and correlate with protection seen in parallel groups of fish (6 months).

Summary

Vaccine production as a means of improving the health of farmed fish has been well established in salmonid fish farming. With new marine species beginning to be farmed, particularly gadoids, there is a need to evaluate whether existing salmonid vaccines are effective, and whether new vaccines require development for gadoid specific diseases. Gadoid immune responses are beginning to be studied, with emphasis to date on antibody responses post-vaccination. These studies reveal that unlike most animals that possess a specific immune system, cod and haddock do not appear to generate substantial antibody responses despite having relatively high levels of antibodies in the blood. Nevertheless, examples of effective vaccination in cod are known, suggesting that other mechanisms of protection are operating in these species. To date studies of cell-mediated immune responses elicited by vaccination have been impossible to perform, mainly due to the lack of knowledge of fish immune systems. This situation is rapidly changing with the sequencing of the Fugu genome and shortly the zebrafish genome, leading to the current tremendous phase of gene discovery in fish. My laboratory specialises in cytokine genes, for which we are considered the world leaders. We have recently discovered in the Fugu genome the genes for interferon gamma (IFNG)(Zou et al., 2004), known to be released during cell-mediated immune responses to activate phagocytes for enhanced killing of microbes, in addition to a direct antiviral action (Schreiber & Schreiber, 2003), and interleukin-2 (IL2) (Bird et al., in press) a cytokine that augments the proliferation of T lymphocytes following contact with foreign molecules, thereby increasing the number of cells able to respond to infection (Lin & Leonard, 2003). These two molecules are considered to be key markers of specific cell-mediated immunity in mammals, and by determining the number of cells able to secrete them a means of assessing the relative efficacy of immunisation is possible. To date we have focused on the IFNg molecule and have now sequenced the gene in both zebrafish and rainbow trout (Zou et al., 2003; Yoshiura et al., 2004). We do not foresee a problem of extending this to cod/haddock. The IL2 gene has not yet been isolated form other fish species, but by a combination of approaches we are confident it can be found also. Thus, the way is set to find these molecules and use them to detect and quantify cell-mediated immune responses in fish, and to establish whether their production correlates with disease resistance post-vaccination. As stated above, this is particularly important where antibody responses do not appear to be elicited post-vaccination, as occurs in gadoid species. Since vibriosis is a clear problem for gadoid culture, we propose to use vibriosis vaccines supplied by Schering-Plough Aquaculture (see in-kind contribution) in addition to vaccines being developed in the current TCS/KTP programme between the University of Aberdeen and SEAFISH.