Experimental infection by Yersinia ruckeri O1 biotype 2 induces brain lesions and neurological signs in rainbow trout (Oncorhynchus mykiss)

Single-cell transcriptome, phagocytic activity and immunohistochemical analysis of crucian carp (Carassius auratus) in response to Rahnella aquatilis infection

In teleost fish, kidney is an important immune and hematopoietic organ with multiple physiological functions. However, the immune cells and cellular markers of kidney require further elucidation in crucian carp (C. auratus). Here we report on the single-cell transcriptional landscape in posterior kidney, immunohistochemical and phagocytic features of C. auratus with R. aquatilis infection. The results showed that a total of 18 cell populations were identified for the main immune cells such as monocytes/macrophages (Mo/Mφ), dendritic cells (DCs), B cells, T cells, granulocytes and hematopoietic progenitor cells (HPCs). Pseudo-time trajectory analysis was reconstructed for the immune cells using Monocle2 to obtain additional insights into their developmental lineage relationships. In the detected tissues (liver, spleen, kidney, intestine, skin, and gills) of infected fish exhibited positive immunohistochemical staining with prepared for antibody to R. aquatilis. Apoptotic cells were fluorescently demonstrated by TUNEL assay, and bacterial phagocytic activity were observed for neutrophils and Mo/Mφ cells, respectively. Moreover, a similar up-ward/down-ward expression trend of the selected immune and inflammatory genes was found in the kidney against R. aquatilis infection, which were significantly involved in TLR/NLR, ECM adhesion, phago-lysosome, apoptosis, complement and coagulation pathways. To our knowledge, this is the first report on the detailed characterization of immune cells and host-R. aquatilis interaction, which will contribute to understanding on the biology of renal immune cells and repertoire of potential markers in cyprinid fish species.

The knowns and many unknowns of CNS immunity in teleost fish

Many disease agents infect the central nervous system (CNS) of teleost fish causing severe losses for the fish farming sector. Yet, neurotropic fish pathogens remain poorly documented and immune responses in the teleost CNS essentially unknown. Previously thought to be devoid of an immune system, the mammalian CNS is now recognized to be protected from infection by diverse immune cells that mostly reside in the meningeal lymphatic system. Here we review the current body of work pertaining immune responses in the teleost CNS to infection. We identify important knowledge gaps with regards to CNS immunity in fish and make recommendations for rigorous experimentation and reporting in manuscripts so that fish immunologists can advance this burgeoning field.

Blood brain barrier permeability and immune function of brain in rainbow trout responding to IHNV infection

Viral infection of the central nervous system (CNS) is often associated with blood-brain barrier (BBB) disruption. Mammals have developed complicated and efficient immune strategies to protect the BBB. However, the immune defense of brain and BBB permeability changes are not well-understood in teleost during virus invading. In this study, we constructed an infectious hematopoietic necrosis virus (IHNV) immersion infected rainbow trout model. After IHNV infection, pathological changes occurred in the brain, and MPO and ROS activities were significantly increased. In addition, the expression levels of BBB permeability-related genes were also changed. Transcriptome analysis showed that immune-related genes and signaling pathways in the brain were activated after IHNV infection. These results showed that the permeability of BBB increased significantly after IHNV infection, thus activating immune related factors and cells to enter the CNS through blood circulation to resist pathogenic infection.

Evaluation of the efficacy of enrofloxacin in rainbow trout (Oncorhynchus mykiss) following experimental challenge with Yersinia ruckeri

BACKGROUND

Use of enrofloxacin in trout farms is reported, especially for the treatment of yersiniosis, albeit various dosing regimens have been used. Therefore, optimal doses should be investigated.

METHODS

Five groups of 15 fish were challenged with Y. ruckeri. Two days later, three groups received feed containing enrofloxacin (ENR) at 1, 2.5 and 5 mg/kg fish respectively, during 7 days; one group received a single intraperitoneal injection of ENR at 10 mg/kg; and one group was left untreated. On day 15, surviving fish were euthanized.

RESULTS

All fish survived in the group treated by injection, compared to 53%, 60% and 40% of the fish treated with 1, 2.5 and 5 mg/kg oral ENR, respectively, and 53% in the infected untreated group.

CONCLUSION

A single intraperitoneal injection of ENR at 10 mg/kg seems more relevant than repeated oral administrations. The ENR oral doses used in trout farms should be revised.

Fish nasal immunity: From mucosal vaccines to neuroimmunology

Like terrestrial vertebrates, bony fishes have a nasopharynx-associated lymphoid tissue (NALT) that protects the host against invading pathogens. Despite nasal immunity being a relatively new field in fish immunology, the investigation of nasal immune systems has already illuminated fundamental aspects of teleost mucosal immune systems as well as neuroimmunology. In this review, we highlight the importance of nasal infections in bony fish and the progress that has been made towards understanding how fish respond locally and systemically to nasal infection or vaccination. We also want to highlight the complex interactions between neurons and immune cells that occur in the olfactory organ during the course of an immune response. We predict that similar neuroimmune interactions govern immune responses at all mucosal tissues in bony fish. Understanding the principles of mucosal immune responses in teleost NALT has therefore revealed important aspects of fish mucosal immunity that are critical for mucosal vaccination in aquaculture.