Innate Immunity

Research on the innate immunity has accelerated over the last decades. The main reason for this has been the discovery of receptors recognizing danger molecules from pathogens. This has been facilitated through genome and transcriptome sequencing of different fish species. Also, endogenous host molecules from sterile physiological insults may also bind to certain receptors and induce immunological processes. The magnitude and quality of adaptive immunity are known to be dependent on the instructions the innate response gives. This chapter gives an overview of selected innate immune organs/tissues, factors, and processes that have been suggested to possess important roles during innate immune response in fish

Protection of teleost fish against infectious diseases through oral administration of vaccines: Update 2021

Immersion and intraperitoneal injection are the two most common methods used for the vaccination of fish. Because both methods require that fish are handled and thereby stressed, oral administration of vaccines as feed supplements is desirable. In addition, in terms of revaccination (boosting) of adult fish held in net pens, oral administration of vaccines is probably the only feasible method to obtain proper protection against diseases over long periods of time. Oral vaccination is considered a suitable method for mass immunization of large and stress-sensitive fish populations. Moreover, oral vaccines may preferably induce mucosal immunity, which is especially important to fish. Experimental oral vaccine formulations include both non-encapsulated and encapsulated antigens, viruses and bacteria. To develop an effective oral vaccine, the desired antigens must be protected against the harsh environments in the stomach and gut so they can remain intact when they reach the lower gut/intestine where they normally are absorbed and transported to immune cells. The most commonly used encapsulation method is the use of alginate microspheres that can effectively deliver vaccines to the intestine without degradation. Other encapsulation methods include chitosan encapsulation, poly D,L-lactide-co-glycolic acid and liposome encapsulation. Only a few commercial oral vaccines are available on the market, including those against infectious pancreatic necrosis virus (IPNV), Spring viremia carp virus (SVCV), infectious salmon anaemia virus (ISAV) and Piscirickettsia salmonis. This review highlights recent developments of oral vaccination in teleost fish

Scavenger endothelial cells of fish, a review

The definition of scavenger endothelial cells (SEC) is exclusively based on functional and structural characteristics. The following characteristics are common hallmarks for the vertebrate SEC: (a) All vertebrates examined are furnished with a population of special SEC that plays a role in the catabolism of physiologic and non-physiologic soluble waste macromolecules. (b) From the ligands that are endocytosed, SEC in all seven vertebrate classes appear to express the collagen α-chain receptor and the scavenger receptors. In addition, the hyaluronan and the mannose receptors are present on SEC of mammalia (several species) and osteichthyes (e.g., salmon and cod). It is likely that all four receptor types are present in all vertebrate classes. (c) Like liver endothelial cells (LEC) in mammals, SEC in all vertebrate classes are geared to endocytosis of soluble macromolecules, but phagocytic uptake of particles is taken care of mainly by macrophages. (d) The most primitive vertebrates (hagfish, lamprey and ray) carry their SEC in gill vessels, whereas phylogenetically younger fishes (salmon, carp, cod and plaice) carry their SEC in either kidney or heart and in all terrestrial vertebrates—SEC are found exclusively in the liver. (e) SEC of all vertebrates are localized in blood sinusoids or trabeculae that carry large amounts of slowly flowing and O2 poor blood. (f) SEC differs functionally and structurally from what is normally associated with “conventional vascular endothelium.

GATA-3 in Atlantic salmon (Salmo salar): Tissue distribution and its regulation of IL-4/13a promoter

GATA3 is a transcription factor that plays an important role in T cell lineage differentiation and T-helper 2 (Th2) type immune responses. In this study, we developed two rat antibodies against Atlantic salmon GATA-3 (anti-rSsGATA-3a and anti-rSsGATA-3b, respectively). The western blotting and immunofluorescence results showed that anti-rSsGATA-3b antibodies recognized endogenous SsGATA-3 proteins, while the anti-rSsGATA-3a antibodies did not bind SsGATA-3. Immunohistochemical analysis revealed that SsGATA-3 positive cells were detected in all tissues tested, with relatively high number of immune reactive cells in the gills and spleen. Furthermore, the immunohistochemical study revealed that SsGATA-3 was expressed in pillar cells, epithelial cells, chondrocytes, perichondrium cells, and some undifferentiated basal cells. In addition, we determined 577 bp of the upstream promoter sequence of SsIL-4/13a and found four motifs that matched SsGATA-3 binding sites. The promoter regions of SsIL-4/13a were assessed by transfecting four deletion reporter constructs and SsGATA-3 overexpression plasmids. The result showed that SsGATA-3 enhanced the activity of SsIL-4/13a promoters within the region ranging from -317 to -302 bp upstream of the transcriptional start site. Antibodies against Th2 markers such as GATA-3 are valuable in addressing the diversity of T cell responses in fish

Cleaner fish in aquaculture: review on diseases and vaccination

Combating and controlling sea lice causes large economic costs for the farmers, with estimated values of more than 305 million euros (€) per year. Increased resistance against traditional chemotherapeutants due to evolutionary drivers in the sea lice combined with the lack of an effective vaccine and few other chemical treatments available are expected to cause these costs to increase. Several possible methods for managing sea lice infestations have been investigated, but only cleaner fish has proven to have an effect on lice levels. Cleaning activity is well known in marine fish and has been observed in the wild as a form of symbiosis between two species: one species, the ‘client’ fish, seek out the other species, the ‘cleaner’ fish, to have ectoparasites and dead tissue cleared from its body. The Atlantic lumpfish is a relatively new aquaculture species, and wild‐caught mature fish are used as brood stock for farmed production. This poses a biosecurity risk, as wild fish can carry pathogens, and the use of quarantine and health screening is recommended. Vaccine development is unfortunately lagging far behind relatively to the wide spread and high utilisation of the fish. This review contains description of the main pathogens and diseases that affect cleaner fish

Anatomical distribution of scavenger endothelial cells in bony fishes (Osteichthyes)

The scavenger endothelial cells (SECs) of vertebrates are an important class of endocytic cells responsible for clearance of foreign and physiological waste macromolecules, partitioning in the immune system, functioning as a cellular powerplant by producing high energy metabolites like lactate and acetate. All animal phyla possess SECs, but the tissue localization of SECs has only been investigated in a limited number of species. By using a specific ligand for scavenger receptors (formalin treated bovine serum albumin), the study revealed that in all tetrapod species (amphibia, reptiles, birds and mammals) the SECs were found lining the sinusoids of the liver. No SECs were found in the liver of any of the bony fishes (Osteichthyes) investigated. Interestingly, we found the SECs not only to be located in the heart of marine species but also in some freshwater species such as Lota lota, Percichthys trucha and Perca fluviatilis. In some fish species, the SECs were found both in the heart and/or kidney in a number of marine and freshwater fishes, whereas in some marine, diadromous and freshwater fishes the SECs were confined only to the kidney tissue. However, from these results it can be suggested that there is neither a clear phylogenetic trend when it came to anatomical localization of SECs nor any pattern in terms of habitat (salinity preferences)

Genome editing on finfish: Current status and implications for sustainability

Novel genome editing techniques allow for efficient and targeted improvement of aquaculture stock and might be a solution to solve challenges related to disease and environmental impacts. This review has retrieved the latest research on genome editing on aquacultured finfish species, exploring the technological progress and the scope. Genome editing has most often been used on Nile tilapia (Oreochromis niloticus Linnaeus), followed by Atlantic salmon (Salmo salar Linnaeus). More than half of the studies have focused on developing solutions for aquaculture challenges, while the rest can be characterized as basic research on fish genetics/physiology or technology development. Main traits researched are reproduction and development, growth, pigmentation, disease resistance, use of trans-GFP and study of the omega-3 metabolism, respectively. There is a certain correlation between the species identified and their commercial relevance, indicating the relevance of most studies for present challenges of aquaculture. Reviewing geographical origin of the research, China has been in the forefront (29 publications), followed by the United States (9) and Norway (7). The research seems not to be dependent on regulative conditions in the respective countries, but merely on the purpose and objectives for the use of genome editing technologies. Some technical barriers identified in the studies are presented together with solutions to overcome these-off-target effects, ancestral genome duplication and mosaicism in F0. One of the objectives for use is the contribution to a more sustainable aquaculture, where the most prominent issues are solutions that contribute to minimizing impact on biodiversity

Antigen dose and humoral immune response correspond with protection for inactivated infectious pancreatic necrosis virus vaccines in Atlantic salmon (Salmo salar L)

An enduring challenge in the vaccinology of infectious pancreatic necrosis virus (IPNV) is the lack of correlation between neutralizing antibodies and protection against mortality. To better understand the immunological basis of vaccine protection, an efficacy trial including Atlantic salmon (Salmo salar L.) vaccinated with a high antigen (HiAg) or low antigen (LoAg) dose vaccine was carried out in a cohabitation challenge model using the highly virulent Norwegian Sp strain NVI015. To pinpoint the immunological basis of vaccine protection, pathogenic mechanisms of IPNV were unraveled in control fish while obtaining feedback on mechanisms of protection in the vaccinated fish. During the incubation period, infection rates were highest in control fish, followed by the LoAg group with the lowest infections being in the HiAg group. Although both the liver and pancreas are target organs prone to tissue damage, infection in the liver was delayed until acute infection in most fish. A correlate of pathology determined as the cutoff threshold of viral copy numbers linked to tissue damage in target organs was estimated at ≥ 107.0, which corresponded with an increase in mortality. The kinetics of IFNα and Mx expression suggests that these genes can be used as biomarkers of IPNV infection progression. Mechanisms of vaccine protection involved reducing infection rates, preventing infection of the liver and reducing virus replication in target organs to levels below the correlate of pathology. Overall, the study shows that antigen dose corresponds with vaccine efficacy and that antibody levels can be used as a signature of protective immunity against pathological disease and mortality

Characterization of myeloperoxidase and its contribution to antimicrobial effect on extracellular traps in flounder (Paralichthys olivaceus)

Myeloperoxidase (MPO) is a cationic leukocyte haloperoxidase and together with other proteins, they possess activities against various microorganisms and are involved in extracellular trap (ET) formation. The present work describes the gene and deduced protein sequences, and functions of MPO in flounder (PoMPO). The PoMPO possesses a 2313 bp open reading frame (ORF) that encodes a protein of 770 amino acids. The highest PoMPO mRNA expression levels were found in the head kidney, followed by peritoneal cells, gill, spleen, skin, muscle, and liver. PoMPO was expressed in MHCII+ and GCSFR+ cells which indicated that PoMPO mainly is expressed in flounder macrophages and granulocytes. Bacterial lipopolysaccharide-stimulated peritoneal leukocytes showed an increased protein level of PoMPO while it seemed that LPS also promoted the migration of MPO+ cells from the head kidney into the peripheral blood and peritoneal cavity. After phorbol 12-myristate 13-acetate (PMA) or bacterial stimulation, flounder leukocytes produced typical ET structures containing DNA with decoration by MPO. The ETs containing DNA and PoMPO effectively inhibited the proliferation of ET-trapped bacteria. Blocking PoMPO with antibodies decreased the enzymatic activity, which attenuated the antibacterial activity of ETs. This study pinpoints the involvement of ETs in flounder innate responses to pathogens

A new IL6 isoform in Chinese soft-shelled turtle (Pelodiscus sinesis) discovered: Its regulation during cold stress and infection

The Chinese soft-shelled turtle (Pelodiscus sinesis) is a widely cultured commercial species in East and Southeast Asian countries. The turtles frequently suffer from acute cold stress during farming in China. Stress-induced factor such as Interleukin-6 (IL6) is a multifunctional molecule that plays important roles in innate and adaptive immune response. In the present study, we found that the turtle possessed two IL6 transcripts, where one IL6 transcript contained a signal peptide sequence (psIL6), while the other IL6 transcript (psIL6ns) possessed no such signal peptide gene. To test any differential expression of the two isoforms during temperature and microbial stress, turtles were adapted to optimal environmental water temperature (25 °C), stressed by acute cooling for 24 h, followed with the challenge of Aeromonas hydrophila (1.8 × 108 CFU) or Staphylococcus aureus (5.8 × 108 CFU). Gene characterization revealed that psIL6ns, a splicer without codons encoding a signal peptide and identical to the one predicted from genomic sequence, and psIL6, a splicer with codons encoding a signal peptide, were both present. Inducible expression was documented in primary spleen cells stimulated with ConA and poly I: C. The splenic and intestinal expression of psIL6ns and psIL6 was increased in response to temperature stress and bacterial infection