Abstract
Introduction
Currently, fish production through aquaculture and wild capture is growing as a result of the increased fish protein demand for human consumption. The adverse effects caused by pathogens both in hatchery and grow-out ponds, have decreased aquaculture production and causing high economic losses for the aquaculturalists . Therefore, it is becoming increasingly important to improve fish products in size and value through adequate disease management procedures . A systematic study using omics approaches can help us to understand the complex and sophisticated interactions in the host-pathogen network, leading to identifying new targets and biomarkers for diseases caused by bacteria, viruses, and parasites. The use of different omics approaches is a powerful that can provide new knowledge on host-pathogen interactions and can help us develop novel approaches for disease management and sustainable aquaculture production.
Materials and methods
We used the two prominent omics approaches proteomics and transcriptomics to study host immune responses and host-parasite interactions in a well-established co-infection disease model. W e have investigated how the myxozoans Myxobolus cerebralis , and Tetracapsuloides bryosalmonae modulate the host fish immune response after single and co-infections by quantitative proteomics and transcriptomics. For the infection experiment, o ne group of fish was infected with M. cerebralis (Mc group) and another group with T. bryosalmonae (Tb group) . After 30 day , half of the fish in each group were then co-infected with the other parasite (Mc+ group and Tb+ group). At day 31, t he proteomic changes and the transcriptomic modulation in the caudal fins, gills, head cartilage and kidney of rainbow trout were investigated at different time points . T he parasite load was determined post exposure in single and co-infection groups.
Results
In the caudal fins and the gills, multiple transcripts and proteins mostly involved in parasite recognition, tissue repair and the regulation of host immune responses were differentially modulated between the groups in the caudal fin. In the head cartilage and kidney, numerous transcripts and proteins were differentially regulated between the groups . The identified proteins in the head cartilage were primarily involved in host protection against oxidative stress, DNA and RNA synthesis and metabolism. T he differentially regulated proteins in the kidney were mainly involved in proteasomal degradation , metabolism and host immunity . S everal myxozoans transcripts and proteins involved in parasite development and virulence were identified. The biological processes, molecular pathways and molecular functions of the differentially regulated transcripts and proteins were also analysed . It appears that M. cerebralis modulates the rainbow trout immune response in a path that likely synergistically facilitates a subsequent co-infection with T. bryosalmonae . Conversely, T. bryosalmonae triggers the host immunity apparently by induction of the several B-cell markers including MHC II, B-cell receptor CD22 and Ig-like domain containing protein, which may antagonistically amend the outcome of a subsequent co-infection with M. cerebralis .
Conclusion
The results of the undertaken quantitative proteomic and transcriptomic analysis indicate the successful integration of multiple omics approaches for systemic investigation of biological systems in single and co-infection disease models. The investigations provide novel insights of how myxozoan parasites modulate host immune responses influencing the outcome of co-infections in rainbow trout. The analysis revealed key parasite virulence transcripts and proteins and highlighted p otential invasion/evasion strategies during myxozoan infections. The results reveal novel traits of host-parasite interactions and paves the way for the development of novel tools for myxozoan disease management in aquaculture.