Regulation of endogenous antigen presentation in response to suboptimal temperatures in a walleye skin fibroblast cell line

Diploid and triploid Chinook salmon (Oncorhynchus tshawytscha) have altered microRNA responses in immune tissues after infection with Vibrio anguillarum

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 infection on diploid and triploid Chinook salmon (Oncorhynchus tshawytscha) was investigated to identify if there was any significant immune regulation by microRNAs (miRNA). Small RNAs from hindgut, head kidney, and spleen were sequenced to determine if miRNA transcript abundance was altered due to ploidy and infection in nine-month old full-sibling diploids and triploids. All three tissues had differentially expressed miRNA prior to infection, indicating subtle changes in epigenetic regulation due to increased ploidy. Additionally, miRNA were altered by infection, but there was only a difference in spleen miRNA expression between diploids and triploids at three days of infection. Furthermore, one miRNA (ssa-miR-2188-3p) was confirmed as having an altered response to infection in triploids compared to diploids, implicating potential immune dysregulation due to increased ploidy. The miRNAs identified in this study are predicted to target immune pathways, providing evidence for their importance in regulating responses to pathogens. This study is the first to investigate how increased ploidy alters miRNA expression in response to infection. Additionally, it provides evidence for epigenetic dysregulation in triploid fishes, which may contribute to their poor performance in response to stress.

Hypersensitive response to interferon-stimulated gene (ISG)-inducing double-stranded RNA in American bullfrog tadpole fibroblasts

American bullfrogs are thought to be carriers of ranaviruses and contribute to their global spread via trade. Bullfrog tadpoles succumb to ranaviral infection's more severe and deadly effects than bullfrog adults. Presently, little is known about bullfrog tadpoles' innate antiviral immunity, possible due to the lack of available bullfrog tadpole cell lines. In this study, we describe a novel bullfrog tadpole fibroblast cell line named BullTad-leg. Its general cellular attributes, gene expression and function of class-A scavenger receptors (SR-As), and responses to poly IC (a synthetic dsRNA mimicking viral dsRNAs and a potent inducer of the interferon (IFN)-mediated antiviral responses) are investigated. Its abundant expression of vimentin corroborated with the cells' fibroblast morphology. BullTad-leg cells expressed transcripts of four SR-A members: SR-AI, SCARA3, SCARA4, and SCARA5, but transcripts of MARCO, the fifth SR-A member, were not detected. BullTad-leg cells expressed functional SR-As and could bind AcLDL. BullTad-leg cells exhibited cytotoxicity in response to poly IC treatment via SR-As. Additionally, very low doses of poly IC were able to induce dose-dependent expressions of ISGs including Mx, PKR, ISG20, and IFI35. This research sheds new light on the innate immune response, particularly SR-A biology and dsRNA responsiveness, in bullfrog tadpoles.

The acute inflammatory response of teleost fish

Acute inflammation is crucial to the immune responses of fish. The process protects the host from infection and is central to induction of subsequent tissue repair programs. Activation of proinflammatory signals reshapes the microenvironment within an injury/infection site, initiates leukocyte recruitment, promotes antimicrobial mechanisms and contributes to the resolution of inflammation. Inflammatory cytokines and lipid mediators are primary contributors to these processes. Uncontrolled or persistent induction results in delayed tissue healing. The kinetics by which inducers and regulators of acute inflammation exert their actions is essential for understanding the pathogenesis of fish diseases and identifying potential treatments. Although, a number of these are well-conserved across, others are not, reflecting the unique physiologies and life histories of members of this unique animal group.

Effects of juvenile thermal preconditioning on the heat-shock, immune, and stress responses of rainbow trout upon a secondary thermal challenge

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 potential harm these stressors can inflict, methods that can limit the damage of these stressors are particularly valuable. As a method of interest, early-life thermal preconditioning of animals demonstrated some potential for effective improvements in thermotolerance. However, the potential effects of the method on the immune system via the heat-stress model have not been explored. In this experiment, juvenile-stage thermal preconditioned rainbow trout (Oncorhynchus mykiss) were subjected to a secondary thermal challenge, animals were collected and sampled at the time of lost equilibrium. The effects of preconditioning on the general stress response was assessed by measuring the plasma cortisol levels. In addition, we also examined hsp70 and hsc70 mRNA levels in the spleen and gill tissues, as well as IL-1β, IL-6, TNF-α, IFN-1, β2m, and MH class I transcripts via qRT-PCR. No changes in CTmax were observed between the preconditioned and control cohorts upon the second challenge. IL-1β and IL-6 transcripts were generally upregulated with increased temperature of the secondary thermal challenge, whereas IFN-1 transcripts were upregulated in the spleen, but downregulated in the gills, along with MH class I. The juvenile thermal preconditioning produced a series of changes in transcript levels for IL-1β, TNF-α, IFN-1, and hsp70 but the dynamics of these differences were inconsistent. Finally, analysis of plasma cortisol levels presented significantly lower cortisol levels in the pre-conditioned animals compared to the non-pre-conditioned control cohort.

Antigen Presentation and Autophagy in Teleost Adaptive Immunity

Infectious diseases are a burden for aquaculture. Antigen processing and presentation (APP) to the immune effector cells that fight pathogens is key in the adaptive immune response. At the core of the adaptive immunity that appeared in lower vertebrates during evolution are the variable genes encoding the major histocompatibility complex (MHC). MHC class I molecules mainly present peptides processed in the cytosol by the proteasome and transported to the cell surface of all cells through secretory compartments. Professional antigen-presenting cells (pAPC) also express MHC class II molecules, which normally present peptides processed from exogenous antigens through lysosomal pathways. Autophagy is an intracellular self-degradation process that is conserved in all eukaryotes and is induced by starvation to contribute to cellular homeostasis. Self-digestion during autophagy mainly occurs by the fusion of autophagosomes, which engulf portions of cytosol and fuse with lysosomes (macroautophagy) or assisted by chaperones (chaperone-mediated autophagy, CMA) that deliver proteins to lysosomes. Thus, during self-degradation, antigens can be processed to be presented by the MHC to immune effector cells, thus, linking autophagy to APP. This review is focused on the essential components of the APP that are conserved in teleost fish and the increasing evidence related to the modulation of APP and autophagy during pathogen infection.

Xela DS2 and Xela VS2: Two novel skin epithelial-like cell lines from adult African clawed frog (Xenopus laevis) and their response to an extracellular viral dsRNA analogue

The skin epithelial layer acts as an important immunological barrier against pathogens and is capable of recognizing and responding to pathogen-associated molecular patterns (PAMPs) in human and mouse models. Although presumed, it is unknown whether amphibian skin epithelial cells exhibit the ability to respond to PAMPs such as viral double-stranded RNA (dsRNA). To address this, two cell lines from the dorsal skin (Xela DS2) and ventral skin (Xela VS2) of the African clawed frog (Xenopus laevis) were established. Xela DS2 and Xela VS2 cells have an epithelial-like morphology, express genes associated with epithelial cells, and lack senescence-associated beta-galactosidase activity. Cells grow optimally in 70% Leibovitz's L-15 medium supplemented with 15% fetal bovine serum at 26 °C. Upon treatment with poly(I:C), a synthetic analogue of viral dsRNA and known type I interferon inducer, Xela DS2 and Xela VS2 exhibit marked upregulation of key antiviral and pro-inflammatory transcripts suggesting frog epithelial cells participate in the recognition of extracellular viral dsRNA and production of local inflammatory signals; similar to human and mouse models. Currently, these are the only known Xenopus laevis skin epithelial-like cell lines and will be important for future research in amphibian epithelial cell biology, initial host-pathogen interactions, and rapid screening of the effects of environmental stressors, including contaminants, on frog skin epithelial cells.