Maturation-associated changes in the non-specific immune response against Flavobacterium psychrophilum in Ayu Plecoglossus altivelis

In this study, we investigated maturation-associated changes in non-specific immune responses of ayu against Flavobacterium psychrophilum. The gonadosomatic index was minimum on 16 June, began to increase on 17 July, and reached the maximum value during August. The highest phagocytic rate (16.3%) was observed on 16 June, which decreased significantly to 5.6% on 26 August. The number of viable bacteria after the serum treatment was highest during August, suggesting that bactericidal activity of the serum decreased along with the sexual maturation. Gene expression levels of interleukin-8, and tumor necrosis factor-α in the spleen did not change significantly during this period, whereas the level of suppressor of cytokine signaling (SOCS)3 was significantly higher on 26 August than that on 16 July (p < 0.05). These results suggest that phagocytic activity of trunk kidney leukocytes and serum bactericidal activity against F. psychrophilum decreased with sexual maturation, and that SOCS3 may be related to the decrease in non-specific immune activity in ayu

Passive immunisation of goldfish with the serum of those surviving a Cyprinid herpesvirus 2 infection after high temperature water treatment

Herpesviral haematopoietic necrosis of goldfish caused by cyprinid herpesvirus 2 (CyHV-2) can be controlled by raising water temperature to a virus non-permissive temperature of 34℃. Consequently, the goldfish can survive and acquire resistance to the disease; the underlying mechanism of acquired resistance, however, remains unclear. In this study, we investigated serological changes in the surviving goldfish, with a focus on their humoral immunity, and examined whether sera of the surviving goldfish conferred passive immunity to naive goldfish. Levels of the anti-CyHV-2 antibodies in 8 of the 9 survivors measured via ELISA were higher than those in control fish. Neutralising antibodies were detected in the sera of 2 survivors, but no direct correlation was observed between ELISA optical density value and neutralising antibody titer. Passive immunisation tests showed that recipients injected with the serum containing neutralising antibodies showed higher survival rates than the control group. The sera from 6 other survivors showed no effect on the recipient\u27s mortality regardless of anti-CyHV-2 antibody levels. These results suggest that neutralising antibodies can contribute to acquired immunity in survivors, and other protective factors, including cell-mediated immunity, may work in the survivors that show no detectable neutralising antibodies

Characterization of Aquimarina hainanensis isolated from diseased mud crab Scylla serrata larvae in a hatchery

Mass mortality due to necrosis signs occurred in hatchery‐reared zoea stage larvae of the mud crab Scylla serrata in Okinawa, Japan, and a causative bacterium was isolated. In this study, we identified and characterized the bacterium by genome analysis, biochemical properties and pathogenicity. The bacterium was a Gram‐negative, non‐motile, long rod, forming yellow colonies on a marine agar plate. It grew at 20–33°C (not at 37°C) and degraded chitin and gelatin. Phylogenetic analysis of the 16S rRNA gene sequence identified the bacterium as Aquimarina hainanensis. Genome sequence data obtained from Illumina MiSeq generated 29 contigs with 3.56 Mbp in total length and a G + C content of 32.5%. The predicted 16 chitinase genes, as putative virulence factors, had certain homologies with those of genus Aquimarina. Experimental infection with the bacterium conducted on larvae of four crustacean species, brine shrimp Artemia franciscana, freshwater shrimp Caridina multidentata, swimming crab Portunus trituberculatus and mud crab S. serrata, revealed that this bacterium was highly virulent to these species. The present study suggests that the bacterium caused mass mortality in mud crab seed production was A. hainanensis and can be widely pathogenic to crustaceans

A Novel Antigen-Sampling Cell in the Teleost Gill Epithelium With the Potential for Direct Antigen Presentation in Mucosal Tissue

In mammals, M cells can take up antigens through mucosal surfaces of the gut and the respiratory tract. Since M cells are deficient of lysosomes and phagosomes, the antigens are directly delivered to the mucosa-associated lymphoid tissue (MALT) without degradation. In teleost fish, the entire body surface (gills, skin, and intestinal system) is covered by mucus; however, specific antigen-sampling cells have not yet been identified in their mucosal tissues. Here, we show that two phenotypes of antigen-sampling cells take up antigens through epithelial surfaces of the rainbow trout gill. One phenotype of antigen-sampling cells has features of monocyte/macrophage/dendritic cell-type cells; they have large vacuoles in the cytoplasm and express PTPRC (CD45), CD83, IL-1β, and IL-12p40b. The second phenotype exhibits similar characteristics to mammalian M cells; the corresponding cells bind the lectin UEA-1 but not WGA and show expression of M cell marker gene Anxa5. In contrast to mammalian M cells, teleost M-type cells were found to exhibit small vacuoles in their cytoplasm and to express almost all genes related to the “phagosome”, “lysosome,” and “antigen processing and presentation” pathways. Furthermore, MHC class II was constitutively expressed on a fraction of M-type cells, and this expression was significantly increased after antigen uptake, suggesting that the MHC class II is inducible by antigen stimulation. Here, we suggest that teleost M-type cells play a role in the phylogenetically primitive teleost immune system, similar to bona-fide M cells. In addition, the presence of MHC class II expression suggests an additional role in antigen presentation in the gills, which are an organ with high T cell abundance, especially in interbranchial lymphoid tissue. The present results suggest an unconventional antigen presentation mechanism in the primitive mucosal immune system of teleosts, which generally lack highly organized lymphoid tissues. Moreover, the results of this work may be valuable for the development of mucosal vaccines that specifically target M-type cells; mucosal vaccines significantly reduce working costs and the stress that is usually induced by vaccination via injection of individual fish

Cell-mediated immune response against mycolic acids of Mycobacteroides salmoniphilum in rainbow trout Oncorhynchus mykiss

Mycobacteriosis caused by Mycobacterium spp. causes economic damages to the world aquaculture industry.In mammals, mycolic acids contained in the cell wall of Mycobacterium spp. are presented by CD1b molecule as lipid antigens and induce cell-mediated immunity (CMI).Here, we investigated CMI responses against the mycolic acids of Mycobacterioides salmoniphilum in a CD1-lacking teleost fish, rainbow trout.After stimulation of trout leukocytes with mycolic acids, the number and percentage of CD8α+ T cells increased.Fish immunized with mycolic acids showed an up-regulation of IFN-γ. Further, in vitro re-stimulation of leukocytes derived from immunized fish resulted in proliferation of CD8α+ cells.These data suggest that mycolic acids are recognized as lipid antigens resulting in an activation of rainbow trout CD8α+ cells and up-regulation of the Th1 cytokine IFN-γ.The mycolic acids are promising candidates for vaccines to activate CD8α+ T cells against fish mycobacteriosis.公開日: 2022-07-0