Brian Dixon

Brian Dixon
University of Waterloo | UWaterloo · Department of Biology

PhD
Co-Editor-in-Chief Developmental and Comparative Immunology Co-Editor-in-Chief Comparative Immunology Reports

About

270
Publications
31,563
Reads
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4,926
Citations
Introduction
Brian Dixon currently works at the Department of Biology, University of Waterloo. Brian does research in Fish and Environmental Immunology. One current outreach project is the 'Elsevier Reference Collection.'
Additional affiliations
September 2001 - present
Memorial University of Newfoundland
Position
  • Professor (Associate)
November 2011 - present
University of Waterloo
Position
  • Canada Research Chair
July 2009 - present
University of Waterloo
Position
  • Professor (Full)

Publications

Publications (270)
Article
Full-text available
Innate immunity is the first line of defense against infections and the only known available strategy for invertebrates. Crustaceans, being mostly aquatic invertebrates, are constantly exposed to potential pathogens in the surrounding water. Their immune system abolishes most microbes that enter and are recognized as a threat. However, the stress p...
Article
Full-text available
Pituitary adenylate cyclase-activating polypeptide (PACAP) is a highly conserved multifunctional neuropeptide belonging to the secretin/glucagon/vasoactive intestinal peptide superfamily. In recent years, the role of PACAP in immunoregulation has been partially elucidated in mammals and teleost fishes, demonstrating that PACAP modulates both innate...
Preprint
Full-text available
Ecologically and socio-economically important salmonid fishes in Canada are threatened by diverse environmental stressors. However, predicting species responses to environmental change requires understanding the underlying molecular mechanisms governing environmental stress tolerance. Developing advanced molecular genetic tools will provide opportu...
Article
Full-text available
Exposure to temperatures outside of a fish's optimal range results in suppression of the immune system, ultimately leaving aquaculture stocks susceptible to disease outbreaks. This effect is exacerbated in triploid fishes, which demonstrate greater susceptibility to stress than their diploid counterparts. This study investigates the impacts of acut...
Article
Full-text available
Rainbow trout is an important fish species for Peruvian artisanal aquaculture, comprising over 60% of the total aquaculture production. However, their industry has been highly affected by several bacterial agents such as Yersinia ruckeri. This pathogen is the causative agent of Enteric Redmouth Disease, and causes high mortality in fingerlings and...
Article
Full-text available
Antimicrobial peptides (AMPs) are an alternative to antibiotics for treatment and prevention of infections with a lower risk of bacterial resistance. Pituitary adenylate cyclase activating polypeptide (PACAP) is an outstanding AMP with versatile effects including antimicrobial activity and modulation of immune responses. The objective of this resea...
Article
Full-text available
For decades, the Th1/2 paradigm has been used to classify immune responses as either Th1 or Th2-biased. However, in recent years, a staggering amount of evidence has emerged to support rejection of the classical Th1/Th2 paradigm, such as the discoveries of new helper T cell subsets, helper T cell plasticity and protective mixed-Th1/Th2 responses. T...
Article
Full-text available
Microbial management is central to aquaculture’s efficiency. Pediococcus acidilactici MA18/5M has shown promising results promoting growth, modulation of the immune response, and disease resistance in many fishes. However, the mechanisms through which this strain confers health benefits in fish are poorly understood, particularly in Pacific salmoni...
Article
Full-text available
Chinook salmon is a native species of the Canadian Pacific coast with potential economic and environmental benefits for aquaculture. However, its production is jeopardized by low tolerance to high densities and disease susceptibility. Due to this, Chinook salmon represents a great candidate for evaluating the effect of non-polluting alternatives to...
Article
Full-text available
Pituitary Adenylate Cyclase-Activating Polypeptide (PACAP) is a multifunctional neuropeptide that is widely distributed and conserved across species. We have previously shown that in teleost fish, PACAP not only possesses direct antimicrobial properties but also immunomodulatory effects against the bacterial pathogens Flavobacterium psychrophilum a...
Article
Recently, we showed that Atlantic salmon vaccinated against Piscirickettsia salmonis lose their protection upon coinfection with Caligus rogercresseyi (sea lice). However, the causes of the overriding effect of C. rogercresseyi infection have not been elucidated, and the molecular basis of the cellular and humoral immune responses upon C. rogercres...
Article
Full-text available
Recent work has identified pituitary adenylate cyclase activating polypeptide (PACAP) as a potential antimicrobial and immune stimulating agent which may be suitable for use in aquaculture. However, its effects on teleost immunity are not well studied and may be significantly different than what has been observed in mammals. In this study we examin...
Article
Production of sterile fishes through artificial retention of a third set of chromosomes (triploidy) is a sustainable alternative for aquaculture since it reduces escapee pressure on wild populations. However, these fishes have reduced survival in stressful conditions and in response to infection. In this study, the impact of Vibrio anguillarum infe...
Article
Interleukin-1β (IL-1β) is one of the first cytokines expressed during immune responses, and its levels are affected by many factors, including stress. To date, it has only been possible to measure IL-1β transcript (mRNA) expression quantitatively in fish using qPCR. This is because previous studies that measured IL-1β protein concentrations in thes...
Article
Antigen presentation is a key process of the immune system and is responsible for the activation of T cells. The main characters are the major histocompatibility complex class I (MHC-I) and class II (MHC-II) molecules, and accessory proteins that act as chaperones for these glycoproteins. Current knowledge of this process and also the elucidation o...
Article
Cytokines are small proteins that regulate innate and adaptive immune responses and are released by both immune and non-immune cell types. In the current study, the constitutive and induced gene expression profiles of a suite of proinflammatory and regulatory cytokines was examined comparatively in eight rainbow trout (Oncorhynchus mykiss) cell lin...
Article
Full-text available
Citation: Machimbirike, V.I.; Vasquez, I.; Cao, T.; Chukwu-Osazuwa, J.; Onireti, O.; Segovia, C.; Khunrae, P.; Rattanarojpong, T.; Booman, M.; Jones, S.; et al. Comparative Genomic Analysis of Virulent Vibrio (Listonella) anguillarum Serotypes Revealed Genetic Diversity and Genomic Signatures in the O-Antigen Abstract: Vibrio anguillarum is the mos...
Article
Higher water temperatures and pathogens are both significant factors that negatively affect the welfare of teleost fish. In aquaculture, compared to natural populations, these problems are especially exacerbated, as the animals have relatively limited mobility, and the higher density promotes faster spread of infectious diseases. Because of the pot...
Data
Why vaccines fail against Piscirickettsiosis in farmed salmon and trout and how to avoid it: A review
Conference Paper
Las vacunas han sido la principal estrategia para prevenir y controlar los brotes de Piscirickettsiosis en la salmonicultura chilena. Sin embargo, se desconocen los mecanismos inmunológicos involucrados en la respuesta contra Piscirickettsia salmonis en salmón del Atlántico inmunizados en coinfección con el piojo de mar. Este estudio analizó el per...
Data
Why vaccines fail against Piscirickettsiosis in farmed salmon and trout and how to avoid it: A review
Data
Host genetic variation explains reduced protection of commercial vaccines against Piscirickettsia salmonis in Atlantic salmon
Article
Prolactin and 11‐ketotestosterone (11‐KT) are important reproductive hormones in fishes, which may also influence immunocompetence. The immunocompetence handicap hypothesis states that higher androgen concentrations that support secondary sex traits are traded off against a decrease in immune system function. To test the relationships between these...
Article
Full-text available
Piscirickettsiosis is the most severe, persistent, and damaging disease that has affected the Chilean salmon industry since its origins in the 1980s. As a preventive strategy for this disease, different vaccines have been developed and used over the last 30 years. However, vaccinated salmon and trout frequently die in the sea cages and the use of a...
Article
Full-text available
Cyanobacterial harmful algal blooms (cHABs) pose a risk to exposed aquatic and terrestrial species. Numerous studies have addressed effects of single toxins while much less attention has been devoted to mixtures of cHAB metabolites that are continually released by living cyanobacteria. Neuro-impairment associated with cHABs has been reported in fis...
Article
The overuse and misuse of antibiotics has led to the emergence of antibiotic-resistant bacterial species which remain a challenge to treat therapeutically. Novel and efficacious drugs are desperately needed to combat pathogens. One method to facilitate these discoveries is the use of in silico methods. Computational biology has the power to scan la...
Article
Full-text available
In Atlantic salmon, vaccines have failed to control and prevent Piscirickettsiosis, for reasons that remain elusive. In this study, we report the efficacy of two commercial vaccines developed with the Piscirickettsia salmonis isolates AL100005 and AL 20542 against another two genogroups which are considered highly and ubiquitously prevalent in Chil...
Article
Full-text available
A large number of polymorphonuclear neutrophils (PMNs) invade the ocular surface during prolonged eye closure (sleep); these leukocytes are commonly referred as tear PMNs. PMNs contribute to homeostasis and possess an arsenal of inflammatory mediators to protect against pathogens and foreign materials. This study examined the ability of tear PMNs t...
Article
Full-text available
Aquaculture in North America is currently dominated by Atlantic salmon, but there has been an increasing interest in the production of species native to the Pacific coast. Chinook salmon is relatively new to production; therefore, the selection of appropriate stocks is critical. Often genes from wild populations are incorporated into farmed stocks...
Article
Pituitary adenylate cyclase-activating polypeptide (PACAP) is a multifunctional neuropeptide belonging to the glucagon/secretin superfamily. Its role in fish growth and immunity has been previously demonstrated using different administration routes such as injection or immersion bath. The present study evaluated the physiological effects of a new f...
Article
Pituitary adenylate cyclase-activating polypeptide (PACAP) is a multifunctional neuropeptide that belongs to the secretin/glucagon/GHRH/VIP superfamily. Some of these molecules have antimicrobial activity and they are capable of stimulating the immune system. The present work studied the antibacterial and immunostimulatory activity of PACAP-38 from...
Article
Full-text available
Effective aquaculture management strategies are paramount to global food security. Growing demands stimulate the intensification of production and create the need for practices that are both economically viable and environmentally sustainable. Importantly, pathogenic microbes continue to be detrimental to fish growth and survival. In terms of host...
Article
Full-text available
The abilities and ways in which organisms respond to stress have long been demonstrated to affect the immune response of the organism. In mammalian studies, researchers have observed that chronic/long-term stress has a pronounced immunosuppressive effect, while studies in acute stress have demonstrated some immunoenhansive properties. These dynamic...
Article
Full-text available
In the spring of 2020, we and others hypothesized that T cells in COVID-19 patients may recognize identical protein fragments shared between the coronaviruses of the common cold and COVID-19 and thereby confer cross-virus immune memory. Here, we look at this issue by screening studies that, since that time, have experimentally addressed COVID-19 as...
Article
Full-text available
While sexual dimorphism in immune responses has been documented in other vertebrates, evidence for a similar phenomenon in fish is lacking. Here, we review the relationship between immunity, stress, spawning, and sex hormones in fish to gain a better understanding of sex-based differences in fish immune responses and its consequences for aquacultur...
Preprint
Full-text available
In Atlantic salmon, vaccines have failed to control and prevent Piscirickettsiosis, for reasons that remain elusive. In this study, we report the efficacy of a commercial vaccine developed with the Piscirickettsia salmonis isolate AL100005 against other two isolates which are considered highly and ubiquitously prevalent in Chile: LF-89-like and EM-...
Article
The Atlantic cod immune system deviates from antigen presentation processes seen in other vertebrates in that it lacks the necessary genes for exogenous antigen presentation (i.e., MHC-II and li) and a key MHC-II interacting molecule necessary for T-helper cell function (i.e., CD4), while possessing an expanded repertoire of MHC-I genes that facili...
Article
Full-text available
Vaccination is a widely used control strategy to prevent Piscirickettsia salmonis causing disease in salmon farming. However, it is not known why all the currently available commercial vaccines generally fail to protect against this pathogenic bacteria. Here, we report, from two different populations, that between-family variation is a strong intri...
Article
Full-text available
The aquaculture industry is continuously threatened by infectious diseases, including those of bacterial origin. Regardless of the disease burden, aquaculture is already the main method for producing fish protein, having displaced capture fisheries. One attractive sector within this industry is the culture of salmonids, which are (a) uniquely under...
Article
Full-text available
Antimicrobial peptides (AMPs) are small, usually cationic, and amphiphilic molecules that play a crucial role in molecular and cellular host defense against pathogens, tissue damage, and infection. AMPs are present in all metazoans and several have been discovered in teleosts. Some teleosts, such as salmonids, have undergone whole genome duplicatio...
Article
Pituitary adenylate cyclase-activating polypeptide (PACAP) is a multifunctional neuropeptide belonging to the glucagon/secretin superfamily. In teleost fish, PACAP has been demonstrated to have an immunomodulatory role. Although previous studies have shown that viral/bacterial infections can influence the transcription of PACAP splicing variants an...
Chapter
Most aquaculture systems operate in a way that makes it impossible to avoid exposing fishes to pathogens and parasites. Even with the best technology to mitigate exposure to pathogens/parasites, there is always risk and thus it is critical that cultured fishes be able to mount an effective immune response. This chapter summarizes current knowledge...
Article
The life cycle of Flavobacterium psychrophilum (Fp), the causative agent of bacterial coldwater disease (BCWD) and rainbow trout fry syndrome (RTFS), appears to involve interactions with spleen and head kidney macrophages. To develop an in vitro model for studying this, F. psychrophilum was incubated with a rainbow trout splenic monocyte/macrophage...
Article
A skin fibroblast cell line WE-skin11f from walleye (Sander vitreus) was used to study the impact of temperature (26 °C, 20 °C, 14 °C, or 4 °C) on the transcript levels of genes involved in the endogenous antigen processing and presentation pathway (EAPP), which is an important antiviral pathway of vertebrates. Partial coding sequences were found f...
Article
A walleye dermal fibroblastoid cell line, WE‐skin11f, was established and characterized. WE‐skin11f was immunocytochemically positive for two known dermal fibroblast protein markers: vimentin and collagen I. At passage 26, WE‐skin11f cultures contained both diploid and aneuploid populations. Ascorbic acid was required to produce extracellular colla...
Article
Full-text available
Pituitary adenylate cyclase-activating polypeptide (PACAP) is a multifunctional neuropeptide that is widely distributed in mammals and is capable of performing roles as a neurotransmitter, neuromodulator, and vasodilator. This polypeptide belongs to the glucagon/secretin superfamily, of which some members have been shown to act as antimicrobial pep...
Article
Rainbow trout (Oncorhynchus mykiss) face low environmental temperatures over winter months and during extreme low temperature events. Suboptimal temperatures are known to negatively impact the teleost immune system, although there is mixed evidence in rainbow trout as to the effect on the endogenous antigen processing and presentation pathway (EAPP...
Article
Salmon farming is one of Canada's fastest growing industries and contributes to Canada's economy as well as creating jobs in rural areas; however, the industry is challenged by the need to balance production economics against environmental impacts. While Atlantic salmon (Salmo salar) are the most commonly farmed species on the west coast of Canada,...
Article
A previous proteomic study examining the plasma acute‐phase response of rainbow trout to sterile inflammation highlighted an unidentified 9.5‐kDa spot using 2D‐PAGE, which was dramatically increased. The 15 amino acid sequence obtained from this protein spot allowed rapid amplification of cDNA ends PCR to generate a 443‐bp nucleotide sequence that...
Article
Full-text available
Major histocompatibility complex (MHC) class II-associated invariant chain is a chaperone responsible for targeting the MHC class II dimer to the endocytic pathway, thus enabling the loading of exogenous antigens onto the MHC class II receptor. In the current study, in vivo and in vitro methods were used to investigate the regulation of the rainbow...
Article
Full-text available
Pituitary adenylate cyclase-activating polypeptide (PACAP) is a multifunctional neuropeptide that is widely distributed in mammals and is capable of performing roles as a neurotransmitter, neuromodulator, and vasodilator. This polypeptide belongs to the glucagon/secretin superfamily, of which some members have been shown to act as antimicrobial pep...
Article
Phenotypic differences among populations within a species have been reported for a variety of traits, ranging from life history to physiology to gene transcription. Population‐level phenotypic variation has been attributed to genetic differences resulting from genetic drift and/or local adaptation as well as environmental differences resulting from...
Article
Full-text available
Understanding of immune function in humans and model organisms, such as mice, has advanced in the last few decades because of technological breakthroughs and availability of reagents. While novel genomic technologies have helped to increase knowledge of many aspects of immunology, most developments in immunology have occurred because of the availab...
Article
Telemetry transmitters are frequently used in studies of wild fish migration and behavior. Although the effects of surgically implanted transmitters on survival, tag retention, healing and growth have been studied, there has been little research regarding the potential immune response induced by these transmitters. In the current study, mature rain...
Article
Despite increased global interest in Chinook salmon aquaculture, little is known of their viral immune defenses. This study describes the establishment and characterization of a continuous cell line derived from Chinook salmon spleen, CHSS, and its use in innate immune studies. Optimal growth was seen at 14-18 °C when grown in Leibovitz's L-15 medi...
Article
Rainbow trout chemokine 2 (CK-2) is currently the only known CC chemokine to have a mucin stalk. Further analysis of the mucin stalk region revealed a second, related CC chemokine sequence, denoted here as CK-2.1. This second sequence was determined to be an allele of CK-2 following genomic PCR analysis on several outbred individuals. Furthermore,...