Fish and shellfish immunology reports: A new open access journal

Introduction

Fish and Shellfish Immunology Reports was founded with the intention of providing another high-quality journal for the aquatic comparative immunology community as there are still relatively few outlets in this area, especially providing open access publishing. Our scope is designed to capture manuscripts from around the world covering basic discoveries in the evolution and function of immune systems of fish and shellfish, as well as the latest state of the art diagnostics and treatments for disease in aquaculture. As the Co-editors-In-Chief, we wanted to introduce ourselves and provide some perspective on what we see as the future directions and challenges of our research areas.

Shellfish immunology: Dr. Linsheng Song

My research over the past 20 years is mainly focused on the immunity of aquatic invertebrates, such as sea cucumber, shrimp, crab, oyster, and scallop. With the help of modern biological technology, my lab has characterized invertebrate immune systems and investigated their responses upon pathogen challenge, including immune recognition of invading pathogens, transduction of immune signals, synthesis of effector molecules, and clearance of pathogens. Currently, my interests are expanding to unravel the complex adaptation mechanisms that cope with environmental stresses, in order to provide support for disease control of aquaculture invertebrates.

Challenges for invertebrate immunology researchers

Immune memory

Evidence for innate immune memory (or ‘priming’) in invertebrates has been accumulated over the last few years. It is noteworthy that the phenomenon of immune memory differs largely for the diverse invertebrate taxa [1]. A few promising candidate mechanisms have been proposed in some taxa where there is currently no direct proof of immune memory, while there are still no reasonable mechanisms described for many other taxa even if there is evidence for the phenomenon of immune memory. Evidence for immune memory in many invertebrates is fragmentary or even lacking and needs much more rigourous investigation [2].

Nutritional immunology

Nutrition is critical to immune defense and resistance to pathogens. The immune system must be properly nourished to function optimally, and malnutrition will cause immunodeficiency. Knowledge of the regulatory network between nutrition and the immune system is essential to comprehensively understand the key determinants of the outcome of host–pathogen interactions [3].

Neuroendocrine immunology

Invertebrate species, such as mollusks and crustaceans, have evolved sophisticated stress response mechanisms to cope with harsh and changing environments, for which neuroendocrine regulation plays an important role. The nervous system and the haemocyte mediated immune system are the pillars of the neuroendocrine system in invertebrates [4]. Various neurotransmitters, hormones, neuropeptides and cytokines have also been characterized as signal messengers or effectors that regulate humoral and cellular immunity in response to a vast array of environmental stressors [5].

Eco-immunology

More recently, an appreciation of the environmental influences on immune system has occurred within the fields of ecology and evolutionary biology, leading to the development of ecological immunology which broadly defined as eco-immunology. A lot of eco-immunology research is focused on the interactions and trade-offs between immunity and other life-history traits, both within and across individuals, populations, and species [6].

Comparative immunology

Invertebrates are excellent species for deciphering the basic mechanisms of immune reactions due to their distinctive cellular immunity and the lack of circulating immunoglobulin. Their complicated and efficient immune responses provide evidence for the nature and evolution of immune system [7,8].

The outbreak and control of aquatic invertebrate diseases

Aquaculture is the fastest growing agro-industry globally, but the frequent occurrence of diseases, which will be exacerbated by climate change (such as increased temperature, ocean acidification and hypoxia) is threatening healthy and sustainable industrial development. Therefore, the establishment of disease prevention and control systems is very important for the development of aquaculture, which may include the monitoring of pathogen community, assessment of host physical health, and the simulation and prediction of environmental stress [9].

Fish immunology: Dr. Brian Dixon

My career over the past approximately 30 years has spanned the years from which molecular biology started to have a large role in fish immunology research to the current “omics” era. Prior to the 1990’s there was a lot of very good work on fish immunology, especially immunoglobulins [10], but without the tools of PCR and cloning, progress was slow. True to the era, my first fish immunology publication was the cloning of β2 microglobulin from tilapia and carp [11], followed by many publications detailing the cloning and characterization of many immune genes, especially from fish antigen presentation pathways, but genes from other classes of molecules from cytokines to complement were also isolated. In the 2000’s molecular biology technology continued improve with the widespread application of qPCR, leading to bigger picture manuscripts examining immune pathways, and production of antibodies to immune proteins and cell lines to pursue more functional studies. My lab's focus was cloning genes and making antisera to their recombinant proteins, albeit one protein at a time and using these to investigate environmental effects on fish immunity [12]. In the 2010’s I forged closer alliances with the aquaculture industries in several countries, allowing me to perform larger scale experiments with pathogen challenges and gain industrial perspective [13]. I had also developed enough antibodies to study protein- protein interactions in the antigen presentation pathways [14]. I focused on producing even more antibodies and to develop assays allowing the quantification of cytokine proteins such as interferon 1 [15]. Now we are in the 2020’s where functional assays can truly be delivered and we are waiting to see how fish immunology knowledge and practice in aquaculture will advance, especially through new technologies that investigate cellular and protein function.

Challenges for fish immunology researchers

Function, function, function!

As one can tell from my biography, I see the main challenge for fish immunology academic research is to examine the function of immune cells and proteins directly. This will require more reagents, not only antibodies to cytokines, cell surface proteins and receptors, but validated reagents [16] that are standardized as much as possible within the main groups of fish, which of course, differ too much for one set of reagents to cross react with all of them for many immune proteins. The reagents need to be shared freely between lab groups (or commercially available) for further validation and maximum return on their use.

Cells and cell lines

Functional understand of fish immunity will also require detailed knowledge of the cells that immune proteins and receptors interact with and stimulate. This includes an understanding of the intercellular processes induced by receptor or ligand interactions. In addition to the reagents above, this goal will require improved techniques for the isolation a propagation of primary cells and cell lines from various tissues of multiple fish species. The knowledge gained, particularly regarding the processes conserved and altered among and between fishes will be critical to a full understanding of fish immunity, however.

Functional assays

A deeper understanding of function will require functional assays in which native cells and molecules can interact, such and an antigen presentation assay in which antigen presenting cells interact with allogeneic T cells or T cells activate B cells. This will require an enhancement of our knowledge of cell culture in fishes as well as much deeper knowledge of cell surface markers for the identification and sorting of cells. The ability to measure in vivo interactions and in vitro cell-cell communication and stimulation will provide tremendous advances that will fill current knowledge gaps.

Variation between and within fishes

It has been known for years that variation in fish responses – not just immune responses, but most genetic responses – are highly variable, even within single families. Recent studies have shown that individuals within a single family of Atlantic salmon can show highly variable responses to vaccination [17] even when the environment is constant, and the environment (such as temperature; [12]), stress and even the sex of a fish can modulate immune responses in major ways [18]. Thus, understanding and untangling all the influence of all of these factors and accounting for them when trying to develop a picture of fish immune responses will be a major challenge.

How does it work in the real world?

Finally, the largest challenge facing fish immunologists is how to apply the knowledge and reagents they have used to uncover immune mechanisms in various fish species in the real world. This could be in preserving wild fish, but more likely will require application to aquaculture. More than 50% of the world's fish for consumption comes from aquaculture and this proportion is only going to increase because of the exhaustion of wild fisheries. Breeding naturally resistant fish, developing vaccines and therapeutants to replace environmentally problematic drugs like antibiotics will be the challenge over the coming years and decades.

Conclusions

As can be seen above, comparative immunology of both fish and shellfish is an area with plenty of grand challenges for young and energetic scientists to take up in multiple areas. Applying modern technologies, using novel reagents, and innovating their own solutions, there will be plenty of high-quality research to be conducted and published. As the new Co-Editors-in-Chief of Fish and Shellfish Immunology Reports, we hope this new journal will attract papers addressing the issues above and more, pushing the boundaries of immunology to elucidate new evolutionary and immunological mechanisms while solving the real-world aquatic immune problems humanity faces.