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Cathepsin Z (CTSZ) is a lysosomal cysteine protease that is known to be involved in the maintenance of homeostasis and the biological mechanisms of immune cells. In this study, we have confirmed the tissue specific expression of the cathepsin Z (PmCTSZ) gene in Pagrus major , and confirmed its biological function after producing recombinant protein using Escherichia coli (E. coli). Multiple sequence alignment analysis revealed that the active site of the cysteine proteases and three N -glycosylation sites of the deduced protein sequence were highly conserved among all of the organisms. Phylogenetic analysis revealed that PmCTSZ was included in the clusters of CTSZ and the cysteine proteases of other bony fish and is most closely related to Japanese flounder CTSZ. PmCTSZ was distributed in all of the tissues from healthy red sea bream that were used in the experiment and was most abundantly found in the spleen and gill. Analysis of mRNA expression after bacterial (Edwardsiella piscicida : E. piscicida and Streptococcus iniae : S. iniae) or viral (red seabream iridovirus: RSIV) challenge showed significant gene expression regulation in immune-related tissues, but they maintained relatively normal levels of expression. We produced recombinant PmCTSZ (rPmCTSZ) using an E. coli expression system and confirmed the biological function of extracellular rPmCTSZ in vitro. We found that bacterial proliferation was significantly inhibited by rPmCTSZ , and the leukocytes of red sea bream also induced apoptosis and viability reduction. • A cathepsin Z (CTSZ) was identified from red sea bream (Pagrus major). • PmCTSZ share high conserved cysteine proteases active site and three N-glycosylation sites with that of other species. • PmCTSZ mRNA was highly expressed in spleen and gill from healthy condition. • RPmCTSZ inhibited bacterial growth and induced leukocyte apoptosis. [ABSTRACT FROM AUTHOR]

Abstract Peptidoglycan recognition protein 2 (PGRP2) is a Zn2+-dependent peptidase that plays important roles in binding to microbial components of the cell membrane, inducing phagocytosis and antimicrobial activity. Rock bream (Oplegnathus fasciatus) PGRP2 (RbPGRP2) was identified in the intestine by next generation sequencing (NGS) analysis. The open reading frame (ORF) the RbPGRP2 cDNA (470 amino acid residues) contains a peptidoglycan recognition protein domain (residues 300 to 446). Alignment analysis revealed that RbPGRP2 shares 37.6–53.5% overall sequence identity with the PGRP2s of other species. Phylogenetic analysis revealed that RbPGRP2 clustered together with PGRP2s from teleosts. In healthy rock bream, RbPGRP2 was found to be ubiquitously expressed in all of the examined tissues, especially in the liver. RbPGRP2 expression was significantly upregulated in all of the examined tissues of rock bream after infection with Edwardsiella piscicida , Streptococcus iniae and red sea bream iridovirus (RSIV) compared with the control. Purified rRbPGRP2 interactions with bacteria and inhibited the growth of bacteria in the presence of Zn2+. These results indicate that RbPGRP2 plays an important role in the innate immune response against bacterial infection. Highlights • We cloned and identified peptidoglycan recognition protein 2 (PGRP2) gene from rock bream. • RbPGRP2 gene was highly expressed in liver from healthy rock bream. • RbPGRP2 was upregulated in the fish infected with several pathogens. • rRbPGRP2 was interacteds with bacteria and inhibited the growth of bacteria in the presence of Zn2+. [ABSTRACT FROM AUTHOR]

Red Sea bream iridovirus (RSIV) was initially isolated from marine fish, which belongs to Megalocytivirus , Iridoviridae . It can cause great economic losses in fish culture with high morbidity and mortality. In the present study, the pathogenicity and immune response associated with a RSIV genotype megalocytivirus infection were determined in mandarin fish ( Siniperca chuatsi ). Fish challenged showed typical clinical signs of iridovirus infection, including acute haemorrhages and enlarged visceral organs. Histopathological analysis revealed that extensive necrosis, vacuolization and inflammation were presented in the stomach, spleen, kidney and liver of the diseased fish. Blood cells counting and phagocytic assay indicated that the numbers of the red and white blood cells in the peripheral blood of infected fish increased significantly compared to the control group and the phagocytic percentage of leukocytes peaked at day 6 post infection. Quantitive real-time PCR (qRT-PCR) was also undertaken to analyse the host defensive response in mandarin fish challenged with RSIV. The expression level of ten genes including interferon-related factors (IRFs) IRF1 and IRF7 , Mx , Viperin , JAK1 , STAT1 , TCRα , TNFα , IL-1β and IL-8 during experimental infection were monitored at different point of time in liver, spleen and head kidney. Results revealed varying expression profiles and clear transcriptional activation of these immune related genes in different tissues, which will contribute to better understand the pathogenesis and host defensive system in iridovirus invasion. [ABSTRACT FROM AUTHOR]

A novel grouper immune gene, EcVig was identified in orange-spotted grouper ( Epinephelus coioides ). We recently determined that EcVig expression can be induced by infection with nervous necrosis virus (NNV, an RNA virus), whereas NNV replication may be suppressed when EcVig was overexpressed. Although EcVig appeared to be involved in grouper antiviral activity, its immune effects have not been well characterized. In the present study, two PAMPs (pathogen-associated molecular patterns; lipopolysaccharides [LPS] and synthetic double-stranded RNA polyriboinosinic-polyribocytidylic acid [poly(I:C)]), as well as fish DNA virus (red sea bream iridovirus, RSIV; grouper iridovirus, GIV), were used to study EcVig responses in orange-spotted grouper. In addition, groupers were given recombinant type I interferon to determine whether EcVig expression was induced. Poly(I:C) rapidly induced substantial expression of EcVig, whereas LPS stimulation did not appear to have any effect in grouper intestine. Expression levels of total EcVig and other IFN-stimulated genes (ISGs) were all significantly increased after RSIV and GIV infection. Furthermore, stimulation of recombinant type I IFN also increased EcVig expression. We conclude that EcVig may be a novel IFN-stimulated gene that demonstrates an antiviral immune response. [ABSTRACT FROM AUTHOR]