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

Expression profiles of NOD1 and NOD2 and pathological changes in gills during Flavobacterium columnare infection in yellow catfish, Tachysurus fulvidraco

NOD-like receptors are significant contributors to the immune response of fish against different types of pathogen invasion. NOD1 and NOD2 genes of yellow catfish (Tachysurus fulvidraco) were identified and characterized in this study. Yellow catfish NOD1 and NOD2 have open reading frames (ORFs) of 2841 and 2949 bp, encoding 946 and 982 amino acids, respectively. Both NOD1 and NOD2 are intracellular proteins lacking transmembrane regions and signal peptides. Sequence homology analysis revealed that the protein sequences of NOD1 and NOD2 of yellow catfish are highly similar to those of channel catfish. Both NOD1 and NOD2 showed high expression in the head kidney, and spleen. Following challenge with Flavobacterium columnare, NOD1 expression obviously increased in the liver, spleen, midgut, and hindgut, whereas NOD2 clearly increased in head kidney, and gut. Microscopic observation of gill tissues revealed evident epithelial hyperplasia in the secondary gill filaments at 3 and 6 hpi, with a notable decrease in the aspect ratio in comparison with the control group, followed by a return to baseline levels. These findings indicate a potential involvement of NOD1 and NOD2 genes in defense against F. columnare invasion. The findings of this study contribute valuable insights into NOD1 and NOD2's functions in the innate immune response of yellow catfish and other fish species to bacterial infection.

Experimental evidence of effective disinfectant to control the transmission of Micropterus salmoides rhabdovirus

Micropterus salmoides rhabdovirus (MSRV) is a significant pathogen that causes high morbidity and mortality in largemouth bass, leading to enormous economic losses for largemouth bass aquaculture in China. The aim of this study was to investigate the efficacy of four disinfectants (potassium permanganate, glutaraldehyde, trichloroisocyanuric acid and povidone iodine) on MSRV, to control the infection and transmission of MSRV in largemouth bass aquaculture. The disinfectants were tested at different concentrations (5, 25, 50, 100 and 500 mg/L) prepared with distilled water for 30 min contact time, and the viral nucleic acid was quantified using qPCR and the infectivity was tested by challenge experiment. Potassium permanganate at 5-500 mg/L, glutaraldehyde at 500 mg/L, trichloroisocyanuric acid at 50-500 mg/L and povidone iodine at 500 mg/L concentration could effectively decrease the virus nucleic acid, and the survival rate of largemouth bass juveniles after challenge experiment increased significantly from 3.7% ± 6.41% to 33.33 ± 11.11% - 100%. Moreover, the minimum effective time of 5 mg/L potassium permanganate was further studied at 2, 5, 10 and 20 min contact time. The viral nucleic acid decreased significantly at 5-20 min exposure time, and the survival rate increased significantly from 7.41% ± 6.41% to 77.78 ± 11.11% - 100%. The median lethal concentration (LC50 ) values of potassium permanganate were 10.64, 6.92 and 3.7 mg/L at 24, 48 and 96 h, respectively. Potassium permanganate could be used for the control of MSRV in the cultivation process; the recommended concentration is 5 mg/L and application time should be less than 24 h. The results could be applied to provide a method to control the infection and transmission of MSRV in water, and improve the health status of largemouth bass.

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.

Comparative Study on Immune Function of the Head and Trunk Kidney in Rainbow Trout Responding to IHNV Infection

A teleost's kidney was divided into head kidney and trunk kidney. The head kidney is an important lymphatic organ, while the trunk kidney mainly performs osmotic pressure regulation and excretion functions. Previous studies have shown that the teleost's head kidney exerts a strong immune response against pathogen invasion, while the mechanism of immune response in the trunk kidney is still rarely reported. Therefore, in this study, we established an Infectious hematopoietic necrosis virus (IHNV) immersion infection model to compare the similarities and differences of immune response mechanisms between the head kidney and trunk kidney against viral infection. The results showed that IHNV infection causes severe tissue damage and inflammatory reaction in the head and trunk kidney, triggers a series of interferon cascade reactions, and produces strong immune response. In addition, the transcriptome data showed that the head kidney and trunk kidney had similar immune response mechanisms, which showed that the NOD-like receptor signaling pathway and Toll-like receptor signaling pathway were activated. In conclusion, despite functional differentiation, the teleost's trunk kidney still has a strong immune response, especially the interferon-stimulated genes, which have stronger immune response in the trunk kidney than in the head kidney when responding to IHNV infection. This study contributes to a more comprehensive understanding of the teleost immune system and enriches the theory of kidney immunity in teleosts.