International Journal of Molecular Sciences

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4 pages, 204 KiB

Open AccessEditorial

Updating Our Knowledge on Fish Immunology

by Elena Chaves-Pozo and Alberto Cuesta

Int. J. Mol. Sci. 2023, 24(13), 10856; https://doi.org/10.3390/ijms241310856 - 29 Jun 2023

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Abstract

Fish is the first group of vertebrates to appear during animal evolution [...] Full article

(This article belongs to the Special Issue Fish Immunology 3.0)

Research

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21 pages, 6731 KiB

Open AccessArticle

Vitamin D Promotes Mucosal Barrier System of Fish Skin Infected with Aeromonas hydrophila through Multiple Modulation of Physical and Immune Protective Capacity

by Yao Zhang, Xiao-Qiu Zhou, Wei-Dan Jiang, Pei Wu, Yang Liu, Hong-Mei Ren, Xiao-Wan Jin and Lin Feng

Int. J. Mol. Sci. 2023, 24(14), 11243; https://doi.org/10.3390/ijms241411243 - 8 Jul 2023

Cited by 5 | Viewed by 1918

Abstract

The vertebrate mucosal barrier comprises physical and immune elements, as well as bioactive molecules, that protect organisms from pathogens. Vitamin D is a vital nutrient for animals and is involved in immune responses against invading pathogens. However, the effect of vitamin D on [...] Read more.

The vertebrate mucosal barrier comprises physical and immune elements, as well as bioactive molecules, that protect organisms from pathogens. Vitamin D is a vital nutrient for animals and is involved in immune responses against invading pathogens. However, the effect of vitamin D on the mucosal barrier system of fish, particularly in the skin, remains unclear. Here, we elucidated the effect of vitamin D supplementation (15.2, 364.3, 782.5, 1167.9, 1573.8, and 1980.1 IU/kg) on the mucosal barrier system in the skin of grass carp (Ctenopharyngodon idella) challenged with Aeromonas hydrophila. Dietary vitamin D supplementation (1) alleviated A. hydrophila-induced skin lesions and inhibited oxidative damage by reducing levels of reactive oxygen species, malondialdehyde, and protein carbonyl; (2) improved the activities and transcription levels of antioxidant-related parameters and nuclear factor erythroid 2-related factor 2 signaling; (3) attenuated cell apoptosis by decreasing the mRNA and protein levels of apoptosis factors involved death receptor and mitochondrial pathway processes related to p38 mitogen-activated protein kinase and c-Jun N-terminal kinase signaling; (4) improved tight junction protein expression by inhibiting myosin light-chain kinase signaling; and (5) enhanced immune barrier function by promoting antibacterial compound and immunoglobulin production, downregulating pro-inflammatory cytokine expression, and upregulating anti-inflammatory cytokines expression, which was correlated with nuclear factor kappa B and the target of rapamycin signaling pathways. Vitamin D intervention for mucosal barrier via multiple signaling correlated with vitamin D receptor a. Overall, these results indicate that vitamin D supplementation enhanced the skin mucosal barrier system against pathogen infection, improving the physical and immune barriers in fish. This finding highlights the viability of vitamin D in supporting sustainable aquaculture. Full article

(This article belongs to the Special Issue Fish Immunology 3.0)

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11 pages, 3460 KiB

Open AccessArticle

Deletion of the foxO4 Gene Increases Hypoxia Tolerance in Zebrafish

by Linlin Shi, Axin Zhang, Hong Liu and Huanling Wang

Int. J. Mol. Sci. 2023, 24(10), 8942; https://doi.org/10.3390/ijms24108942 - 18 May 2023

Cited by 3 | Viewed by 1606

Abstract

Oxygen homeostasis is an important organizing principle for understanding development, physiology, disease, and evolution. Under various physiological and pathological states, organisms experience oxygen deficiency or hypoxia. FoxO4 has been recognized as an important transcriptional regulator involved in a variety of cellular functions, including [...] Read more.

Oxygen homeostasis is an important organizing principle for understanding development, physiology, disease, and evolution. Under various physiological and pathological states, organisms experience oxygen deficiency or hypoxia. FoxO4 has been recognized as an important transcriptional regulator involved in a variety of cellular functions, including proliferation, apoptosis, differentiation, and stress resistance, but its role in hypoxia adaptation mechanisms in animals is not so clear. To explore the role of foxO4 in the hypoxia response, we detected the expression of foxO4 and the regulatory relationship between Hif1α and foxO4 under hypoxic conditions. It was found that the expression of foxO4 was up-regulated in ZF4 cells and zebrafish tissues after hypoxia treatment, and Hif1α could directly target the HRE of the foxO4 promoter to regulate foxO4 transcription, indicating that foxO4 was involved in the hypoxia response by the Hif1α-mediated pathway. Furthermore, we obtained foxO4 knockout zebrafish and found that the disruption of foxO4 increased the tolerance to hypoxia. Further research found that the oxygen consumption and locomotor activity of foxO4^−/− zebrafish were lower than those of WT zebrafish, as was true for NADH content, NADH/NAD⁺ rate, and expression of mitochondrial respiratory chain complex-related genes. This suggests that disruption of foxO4 reduced the oxygen demand threshold of the organism, which explained why the foxO4^−/− zebrafish were more tolerant to hypoxia than WT zebrafish. These results will provide a theoretical basis for further study of the role of foxO4 in the hypoxia response. Full article

(This article belongs to the Special Issue Fish Immunology 3.0)

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18 pages, 2567 KiB

Open AccessArticle

Evaluation of Flathead Grey Mullets (Mugil cephalus) Immunization and Long-Term Protection against Vibrio harveyi Infection Using Three Different Vaccine Preparations

by Rosa Strem, Iris Meiri-Ashkenazi, Na’ama Segal, Roberto Ehrlich, Nadav Shashar and Galit Sharon

Int. J. Mol. Sci. 2023, 24(9), 8277; https://doi.org/10.3390/ijms24098277 - 5 May 2023

Cited by 3 | Viewed by 1659

Abstract

In recent years, flathead grey mullets (Mugil cephalus) cultured in Eilat (Israel) have been highly affected by Vibrio harveyi, showing neurological signs such as uncoordinated circular swimming followed by high mortality rates. Despite the advances in and different approaches to [...] Read more.

In recent years, flathead grey mullets (Mugil cephalus) cultured in Eilat (Israel) have been highly affected by Vibrio harveyi, showing neurological signs such as uncoordinated circular swimming followed by high mortality rates. Despite the advances in and different approaches to control vibriosis associated with Vibrio harveyi, including commercial vaccines, most of them have not succeeded in long-term protection. In this study, we evaluated the effectiveness, long-term protection, and antibody production of three vaccine preparations: heat-killed bacteria (HKB), membrane proteins denaturation (BME PROT), and internal proteins (INT PROT) developed specifically against Vibrio harveyi for grey mullets. Our results show that fish immunized with heat-killed bacteria emulsified with adjuvant presented the most effective and long-lasting protection against the bacterium, and a cross-protection against other bacteria from the harveyi clade. The effectiveness of each immunization treatment correlated with the levels of specific antibody production against Vibrio harveyi in the serum of the immunized fish. Full article

(This article belongs to the Special Issue Fish Immunology 3.0)

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20 pages, 2934 KiB

Open AccessArticle

Identification and Functional Analysis of Tartrate-Resistant Acid Phosphatase Type 5b (TRAP5b) in Oreochromis niloticus

by Yang Lei, Shengli Fu, Yanjian Yang, Jianlin Chen, Bingxi Li, Zheng Guo and Jianmin Ye

Int. J. Mol. Sci. 2023, 24(8), 7179; https://doi.org/10.3390/ijms24087179 - 13 Apr 2023

Cited by 7 | Viewed by 3087

Abstract

Tartrate-resistant acid phosphatase type 5 (TRAP5) is an enzyme that is highly expressed in activated macrophages and osteoclasts and plays important biological functions in mammalian immune defense systems. In the study, we investigated the functions of tartrate-resistant acid phosphatase type 5b from Oreochromis [...] Read more.

Tartrate-resistant acid phosphatase type 5 (TRAP5) is an enzyme that is highly expressed in activated macrophages and osteoclasts and plays important biological functions in mammalian immune defense systems. In the study, we investigated the functions of tartrate-resistant acid phosphatase type 5b from Oreochromis niloticus (OnTRAP5b). The OnTRAP5b gene has an open reading frame of 975 bp, which encodes a mature peptide consisting of 302 amino acids with a molecular weight of 33.448 kDa. The OnTRAP5b protein contains a metallophosphatase domain with metal binding and active sites. Phylogenetic analysis revealed that OnTRAP5b is clustered with TRAP5b of teleost fish and shares a high amino acid sequence similarity with other TRAP5b in teleost fish (61.73–98.15%). Tissues expression analysis showed that OnTRAP5b was most abundant in the liver and was also widely expressed in other tissues. Upon challenge with Streptococcus agalactiae and Aeromonas hydrophila in vivo and in vitro, the expression of OnTRAP5b was significantly up-regulated. Additionally, the purified recombinant OnTRAP5b ((r)OnTRAP5) protein exhibited optimal phosphatase activity at pH 5.0 and an ideal temperature of 50 °C. The V_max, K_m, and k_cat of purified (r)OnTRAP5b were found to be 0.484 μmol × min⁻¹ × mg⁻¹, 2.112 mM, and 0.27 s⁻¹ with respect to pNPP as a substrate, respectively. Its phosphatase activity was differentially affected by metal ions (K⁺, Na⁺, Mg²⁺, Ca²⁺, Mn²⁺, Cu²⁺, Zn²⁺, and Fe³⁺) and inhibitors (sodium tartrate, sodium fluoride, and EDTA). Furthermore, (r)OnTRAP5b was found to promote the expression of inflammatory-related genes in head kidney macrophages and induce reactive oxygen expression and phagocytosis. Moreover, OnTRAP5b overexpression and knockdown had a significant effect on bacterial proliferation in vivo. When taken together, our findings suggest that OnTRAP5b plays a significant role in the immune response against bacterial infection in Nile tilapia. Full article

(This article belongs to the Special Issue Fish Immunology 3.0)

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14 pages, 3320 KiB

Open AccessArticle

Differential Expression Genes of the Head Kidney and Spleen in Streptococcus iniae-Infected East Asian Fourfinger Threadfin Fish (Eleutheronema tetradactylum)

by Shun Maekawa, Pei-Chi Wang and Shih-Chu Chen

Int. J. Mol. Sci. 2023, 24(4), 3832; https://doi.org/10.3390/ijms24043832 - 14 Feb 2023

Cited by 8 | Viewed by 2198

Abstract

Streptococcus iniae is a Gram-positive bacterium and is considered a harmful aquaculture pathogen worldwide. In this study, S. iniae strains were isolated from East Asian fourfinger threadfin fish (Eleutheronema tetradactylum) reared on a farm in Taiwan. A transcriptome analysis of the [...] Read more.

Streptococcus iniae is a Gram-positive bacterium and is considered a harmful aquaculture pathogen worldwide. In this study, S. iniae strains were isolated from East Asian fourfinger threadfin fish (Eleutheronema tetradactylum) reared on a farm in Taiwan. A transcriptome analysis of the head kidney and spleen was performed in the fourfinger threadfin fish 1 day after infection using the Illumina HiSeq™ 4000 platform for RNA-seq to demonstrate the host immune mechanism against S. iniae. A total of 7333 genes based on the KEGG database were obtained after the de novo assembly of transcripts and functional annotations. Differentially expressed genes (DEGs) (2-fold difference) were calculated by comparing the S. iniae infection and phosphate-buffered saline control group gene expression levels in each tissue sample. We identified 1584 and 1981 differentially expressed genes in the head kidney and spleen, respectively. Based on Venn diagrams, 769 DEGs were commonly identified in both the head kidney and spleen, and 815 and 1212 DEGs were specific to the head kidney and spleen, respectively. The head-kidney-specific DEGs were enriched in ribosome biogenesis. The spleen-specific and common DEGs were found to be significantly enriched in immune-related pathways such as phagosome, Th1, and Th2 cell differentiation; complement and coagulation cascades; hematopoietic cell lineage; antigen processing and presentation; and cytokine–cytokine receptor interactions, based on the KEGG database. These pathways contribute to immune responses against S. iniae infection. Inflammatory cytokines (IL-1β, IL-6, IL-11, IL-12, IL-35, and TNF) and chemokines (CXCL8 and CXCL13) were upregulated in the head kidney and spleen. Neutrophil-related genes, including phagosomes, were upregulated post-infection in the spleen. Our results could offer a strategy for the treatment and prevention of S. iniae infection in fourfinger threadfin fish. Full article

(This article belongs to the Special Issue Fish Immunology 3.0)

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12 pages, 6544 KiB

Open AccessArticle

Immunohistochemistry of the Gut-Associated Lymphoid Tissue (GALT) in African Bonytongue (Heterotis niloticus, Cuvier 1829)

by Eugenia Rita Lauriano, Alessio Alesci, Marialuisa Aragona, Simona Pergolizzi, Anthea Miller, Kristina Zuwala, Michal Kuciel, Giacomo Zaccone, Antonino Germanà and Maria Cristina Guerrera

Int. J. Mol. Sci. 2023, 24(3), 2316; https://doi.org/10.3390/ijms24032316 - 24 Jan 2023

Cited by 10 | Viewed by 3155

Abstract

Heterotis niloticus is a basal teleost, belonging to the Osteoglossidae family, which is widespread in many parts of Africa. The digestive tract of H. niloticus presents similar characteristics to those of higher vertebrates, exhibiting a gizzard-like stomach and lymphoid aggregates in the intestinal [...] Read more.

Heterotis niloticus is a basal teleost, belonging to the Osteoglossidae family, which is widespread in many parts of Africa. The digestive tract of H. niloticus presents similar characteristics to those of higher vertebrates, exhibiting a gizzard-like stomach and lymphoid aggregates in the intestinal lamina propria. The adaptive immune system of teleost fish is linked with each of their mucosal body surfaces. In fish, the gut-associated lymphoid tissue (GALT) is generally a diffuse immune system that represents an important line of defense against those pathogens inhabiting the external environment that can enter through food. The GALT comprises intraepithelial lymphocytes, which reside in the epithelial layer, and lamina propria leukocytes, which consist of lymphocytes, macrophages, granulocytes, and dendritic-like cells. This study aims to characterize, for the first time, the leukocytes present in the GALT of H. niloticus, by confocal immuno- fluorescence techniques, using specific antibodies: toll-like receptor 2, major histocompatibility complex class II, S100 protein, serotonin, CD4, langerin, and inducible nitric oxide synthetase. Our results show massive aggregates of immune cells in the thickness of the submucosa, arranged in circumscribed oval-shaped structures that are morphologically similar to the isolated lymphoid follicles present in birds and mammals, thus expanding our knowledge about the intestinal immunity shown by this fish. Full article

(This article belongs to the Special Issue Fish Immunology 3.0)

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22 pages, 4783 KiB

Open AccessArticle

Comparative Expression Profiling Reveals the Regulatory Effects of Dietary Mannan Oligosaccharides on the Intestinal Immune Response of Juvenile Megalobrama amblycephala against Aeromonas hydrophila Infection

by Xiaoheng Zhao, Xu Wang, Hong Li, Yunlong Liu, Yancui Zheng, Hongping Li, Minying Zhang, Hanliang Cheng, Jianhe Xu, Xiangning Chen and Zhujin Ding

Int. J. Mol. Sci. 2023, 24(3), 2207; https://doi.org/10.3390/ijms24032207 - 22 Jan 2023

Cited by 4 | Viewed by 1847

Abstract

Mannan oligosaccharides (MOS) are functional oligosaccharides with beneficial effects on the non-specific immunity of Megalobrama amblycephala, but systematic studies on the immunomodulatory mechanisms of MOS are still lacking. To investigate the protective mechanisms of three different levels of dietary MOS supplementation on [...] Read more.

Mannan oligosaccharides (MOS) are functional oligosaccharides with beneficial effects on the non-specific immunity of Megalobrama amblycephala, but systematic studies on the immunomodulatory mechanisms of MOS are still lacking. To investigate the protective mechanisms of three different levels of dietary MOS supplementation on the intestinal immunity of juvenile M. amblycephala, comparative digital gene expression (DGE) profiling was performed. In this study, 622 differentially expressed genes (DEGs) were identified, while the similar expression tendency of 34 genes by qRT-PCR validated the accuracy of the DGE analyses. Gene Ontology (GO) enrichment revealed that the DEGs were mainly enriched in two functional categories of biological process and molecular function. Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis revealed that the DEGs were mainly related to complement and coagulation cascades, coagulation cascades, platelet activation, natural killer cell mediated cytotoxicity, Fc gamma R-mediated phagocytosis and antigen processing and presentation. In addition, the pro-inflammatory, apoptosis and tight junction-related genes were more significantly up-regulated upon infection in the dietary MOS groups to enhance host immune functions and maintain the stability of the intestinal barrier. These results will be helpful to clarify the regulatory mechanism of MOS on the intestinal immunity of M. amblycephala and lay the theoretical foundation for the prevention and protection of fish bacterial diseases. Full article

(This article belongs to the Special Issue Fish Immunology 3.0)

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16 pages, 3472 KiB

Open AccessArticle

Molecular Characterization, Expression, and Regulatory Signal Pathway Analysis of Inflammasome Component Apoptosis-Associated Speck-like Protein Containing a CARD Domain (ASC) in Large Yellow Croaker (Larimichthys crocea)

by Xin Tang, Xiande Liu, Zhiyong Wang, Meiling Chen and Dongling Zhang

Int. J. Mol. Sci. 2023, 24(3), 2175; https://doi.org/10.3390/ijms24032175 - 22 Jan 2023

Cited by 4 | Viewed by 2511

Abstract

ASC (apoptosis-associated speck-like protein containing a caspase recruitment domain (CARD)) is the only adaptor involved in the formation of multiple types of inflammasomes. Accumulating evidence demonstrates that ASC plays a critical role in the protection of the host against pathogen infection. In this [...] Read more.

ASC (apoptosis-associated speck-like protein containing a caspase recruitment domain (CARD)) is the only adaptor involved in the formation of multiple types of inflammasomes. Accumulating evidence demonstrates that ASC plays a critical role in the protection of the host against pathogen infection. In this study, we identified an ASC gene in the large yellow croaker (Larimichthys crocea), namely LcASC, and then investigated the expression characteristics and related signal pathways. On one hand, LcASC has several conserved protein modules, i.e., an N-terminal PYD region, a C-terminal CARD region, and twelve α-helix structures. On the other hand, it has a high variable linker between PYD and CARD domains. Moreover, LcASC has varying degrees of expression in different tissues, among which the highest expression is observed in the spleen followed by the gills and skin. It also shows induced expressions in the head kidney, liver, and spleen following immune stimulation, especially Vibrio Parahaemolyticus infection. Further subcellular localization analysis showed that LcASC formed a clear aggregated speck in the cytoplasm close to the nucleus. In addition, we found 46 DEGs in a comparative transcriptome analysis between the LcASC overexpression group and the control vector group. Notedly, the up-regulated gene Fos and down-regulated gene DOK3 in LcASC overexpressed cells play important roles in the immune system. How ASC contacts these two genes needs to be clarified in upcoming studies. These findings collectively provide new insights into finfish ASC and its potential regulatory signaling pathway as well. Full article

(This article belongs to the Special Issue Fish Immunology 3.0)

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19 pages, 20222 KiB

Open AccessArticle

Complement C3 Regulates Inflammatory Response and Monocyte/Macrophage Phagocytosis of Streptococcus agalactiae in a Teleost Fish

by Hao Bai, Liangliang Mu, Li Qiu, Nuo Chen, Jiadong Li, Qingliang Zeng, Xiaoxue Yin and Jianmin Ye

Int. J. Mol. Sci. 2022, 23(24), 15586; https://doi.org/10.3390/ijms232415586 - 9 Dec 2022

Cited by 17 | Viewed by 2735

Abstract

The complement system is composed of a complex protein network and is pivotal to innate immunity. Complement 3 (C3) is a critical protein in the complement cascade and participates in complement activation and immune defense. In this study, C3 from Nile tilapia ( [...] Read more.

The complement system is composed of a complex protein network and is pivotal to innate immunity. Complement 3 (C3) is a critical protein in the complement cascade and participates in complement activation and immune defense. In this study, C3 from Nile tilapia (Oreochromis niloticus) was cloned and its function in resisting pathogen infection was characterized. The full length of OnC3 open reading frame is 4974 bp, encoding 1657 aa, and the predicted protein mass weight is 185.93 kDa. The OnC3 amino acid sequence contains macroglobulin domains. The expression pattern of OnC3 mRNA in the tissues of healthy fish was detected, with the highest in the liver and the lowest in the muscle. After challenged with Streptococcus agalactiae and Aeromonas hydrophila, the expression of OnC3 mRNA was significantly up-regulated in the liver, spleen, and head kidney. Further, the recombinant OnC3 protein alleviated the inflammatory response and pathological damage of tissues after infected with S. agalactiae. Moreover, the OnC3 promoted the phagocytosis of monocytes/macrophages to S. agalactiae. The data obtained in this study provide a theoretical reference for in-depth understanding of C3 in host defense against bacterial infection and the immunomodulatory roles in teleost fish. Full article

(This article belongs to the Special Issue Fish Immunology 3.0)

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22 pages, 6159 KiB

Open AccessArticle

Vasoactive Intestinal Peptide (VIP) Protects Nile Tilapia (Oreochromis niloticus) against Streptococcus agalatiae Infection

by Zhiqiang Zhang, Qi Li, Yongxiong Huang, Zhou Xu, Xinjin Chen, Baijian Jiang, Yu Huang and Jichang Jian

Int. J. Mol. Sci. 2022, 23(23), 14895; https://doi.org/10.3390/ijms232314895 - 28 Nov 2022

Cited by 6 | Viewed by 2227

Abstract

Vasoactive intestinal peptide (VIP), a member of secretin/glucagon family, is involved in a variety of biological activities such as gut motility, immune responses, and carcinogenesis. In this study, the VIP precursor gene (On-VIP) and its receptor gene VIPR1 (On-VIPR1) [...] Read more.

Vasoactive intestinal peptide (VIP), a member of secretin/glucagon family, is involved in a variety of biological activities such as gut motility, immune responses, and carcinogenesis. In this study, the VIP precursor gene (On-VIP) and its receptor gene VIPR1 (On-VIPR1) were identified from Nile tilapia (Oreochromis niloticus), and the functions of On-VIP in the immunomodulation of Nile tilapia against bacterial infection were investigated and characterized. On-VIP and On-VIPR1 contain a 450 bp and a 1326 bp open reading frame encoding deduced protein of 149 and 441 amino acids, respectively. Simultaneously, the transcript of both On-VIP and On-VIPR1 were highly expressed in the intestine and sharply induced by Streptococcus agalatiae. Moreover, the positive signals of On-VIP and On-VIPR1 were detected in the longitudinal muscle layer and mucosal epithelium of intestine, respectively. Furthermore, both in vitro and in vivo experiments indicated several immune functions of On-VIP, including reduction of P65, P38, MyD88, STAT3, and AP1, upregulation of CREB and CBP, and suppression of inflammation. Additionally, in vivo experiments proved that On-VIP could protect Nile tilapia from bacterial infection and promote apoptosis and pyroptosis. These data lay a theoretical basis for further understanding of the mechanism of VIP guarding bony fish against bacterial infection. Full article

(This article belongs to the Special Issue Fish Immunology 3.0)

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14 pages, 2369 KiB

Open AccessCommunication

Molecular Characterization of a B Cell Adaptor for Phosphoinositide 3-Kinase Homolog in Lamprey (Lampetra japonica) and Its Function in the Immune Response

by Mengqi Chai, Xiujia Liu, Lin Wei, Jun Li, Meng Gou, Ting Zhu, Yinglun Han and Xin Liu

Int. J. Mol. Sci. 2022, 23(22), 14449; https://doi.org/10.3390/ijms232214449 - 21 Nov 2022

Cited by 1 | Viewed by 1391

Abstract

Human B cell adaptor for phosphoinositide 3-kinase (BCAP) is identified as an adaptor protein expressed in B cells and plays a critical immunomodulatory role in B cell receptor signaling and humoral immune response. In the current study, a homolog of BCAP (Lja-BCAP) was [...] Read more.

Human B cell adaptor for phosphoinositide 3-kinase (BCAP) is identified as an adaptor protein expressed in B cells and plays a critical immunomodulatory role in B cell receptor signaling and humoral immune response. In the current study, a homolog of BCAP (Lja-BCAP) was identified in Lampetra japonica. The open reading frame of Lja-BCAP contains 2181bp nucleotides and encodes a protein of 726 amino acids. After being stimulated by mixed bacteria, the mRNA and protein expression levels of Lja-BCAP and the activation levels of tyrosine kinases increased significantly in peripheral blood lymphocytes, gills and supraneural myeloid bodies, respectively. However, after the knockdown of Lja-BCAP by RNAi in vivo, the activation of tyrosine kinases was inhibited in the above tissues, which indicated that Lja-BCAP participated in the anti-bacterial immune response of lampreys. After lipopolysaccharide (LPS) stimulation, the expression of Lja-BCAP in peripheral blood lymphocytes, gills and supraneural myeloid bodies were significantly up-regulated 2.5, 2.2, and 11.1 times (p < 0.05) compared to the control group, respectively; while after phytohemagglutinin (PHA) stimulation, the up-regulation of Lja-BCAP was only detected in peripheral blood lymphocytes. The above results show that Lja-BCAP mainly participates in the LPS-mediated immune response of lampreys. Full article

(This article belongs to the Special Issue Fish Immunology 3.0)

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18 pages, 5906 KiB

Open AccessArticle

Molecular Characterization, Expression, Evolutionary Selection, and Biological Activity Analysis of CD68 Gene from Megalobrama amblycephala

by Hujun Cui, Hong Li, Minying Zhang, Hongping Li, Xu Wang, Zirui Wang, Wei Zhai, Xiangning Chen, Hanliang Cheng, Jianhe Xu, Xiaoheng Zhao and Zhujin Ding

Int. J. Mol. Sci. 2022, 23(21), 13133; https://doi.org/10.3390/ijms232113133 - 28 Oct 2022

Cited by 4 | Viewed by 1885

Abstract

CD68 is a highly glycosylated transmembrane glycoprotein that belongs to the lysosome-associated membrane glycoprotein family and is involved in various immune processes. In this study, Megalobrama amblycephala CD68 (MaCD68) was cloned and characterized, and its expression patterns and evolutionary characteristics were analyzed. [...] Read more.

CD68 is a highly glycosylated transmembrane glycoprotein that belongs to the lysosome-associated membrane glycoprotein family and is involved in various immune processes. In this study, Megalobrama amblycephala CD68 (MaCD68) was cloned and characterized, and its expression patterns and evolutionary characteristics were analyzed. The coding region of MaCD68 was 987 bp, encoding 328 amino acids, and the predicted protein molecular weight was 34.9 kDa. MaCD68 contained two transmembrane helical structures and 18 predicted N-glycosylation sites. Multiple sequence alignments showed that the MaCD68 protein had high homology with other fish, and their functional sites were also highly conserved. Phylogenetic analysis revealed that MaCD68 and other cypriniformes fish clustered into one branch. Adaptive evolution analysis identified several positively selected sites of teleost CD68 using site and branch-site models, indicating that it was under positive selection pressure during evolution. Quantitative real-time reverse transcription polymerase chain reaction analysis showed that MaCD68 was highly expressed in the head kidney, spleen, and heart. After Aeromonas hydrophila infection, MaCD68 was significantly upregulated in all tested tissues, peaking at 12 h post-infection (hpi) in the kidney and head kidney and at 120 hpi in the liver and spleen, suggesting that MaCD68 participated in the innate immune response of the host against bacterial infection. Immunohistochemical and immunofluorescence analyses also showed that positive signals derived from the MaCD68 protein were further enhanced after bacterial and lipopolysaccharide treatment, which suggested that MaCD68 is involved in the immune response and could be used as a macrophage marker. Biological activity analysis indicated that recombinant MaCD68 (rMaCD68) protein had no agglutination or bactericidal effects on A. hydrophila but did have these effects on Escherichia coli. In conclusion, these results suggest that MaCD68 plays a vital role in the immune response against pathogens, which is helpful in understanding the immune responses and mechanisms of M. amblycephala. Full article

(This article belongs to the Special Issue Fish Immunology 3.0)

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22 pages, 9891 KiB

Open AccessArticle

Functional and Expressional Analyses Reveal the Distinct Role of Complement Factor I in Regulating Complement System Activation during GCRV Infection in Ctenopharyngodon idella

by Yi Liu, Zhao Lv, Tiaoyi Xiao, Xuewen Zhang, Chunhua Ding, Beibei Qin, Baohong Xu and Qiaolin Liu

Int. J. Mol. Sci. 2022, 23(19), 11369; https://doi.org/10.3390/ijms231911369 - 26 Sep 2022

Cited by 4 | Viewed by 1820

Abstract

Complement factor I (CFI), a complement inhibitor, is well known for regulating the complement system activation by degrading complement component 3b (C3b) in animal serum, thus becoming involved in innate defense. Nevertheless, the functional mechanisms of CFI in the complement system and in [...] Read more.

Complement factor I (CFI), a complement inhibitor, is well known for regulating the complement system activation by degrading complement component 3b (C3b) in animal serum, thus becoming involved in innate defense. Nevertheless, the functional mechanisms of CFI in the complement system and in host-pathogen interactions are far from being clarified in teleost fish. In the present study, we cloned and characterized the CFI gene, CiCFI, from grass carp (Ctenopharyngodon idella) and analyzed its function in degrading serum C3b and expression changes after grass carp reovirus (GCRV) infection. The open reading frame of CiCFI was found to be 2121 bp, encoding 706 amino acids with a molecular mass of 79.06 kDa. The pairwise alignments showed that CiCFI shared the highest identity (66.9%) with CFI from Carassius gibelio and the highest similarity (78.7%) with CFI from Danio rerio. The CiCFI protein was characterized by a conserved functional core Tryp_SPc domain with the catalytic triad and substrate binding sites. Phylogenetic analysis indicated that CiCFI and the homologs CFIs from other teleost fish formed a distinct evolutionary branch. Similar with the CFIs reported in mammals, the recombinant CiCFI protein could significantly reduce the C3b content in the serum, demonstrating the conserved function of CiCFI in the complement system in the grass carp. CiCFI mRNA and protein showed the highest expression level in the liver. After GCRV infection, the mRNA expressions of CiCFI were first down-regulated, then up-regulated, and then down-regulated to the initial level, while the protein expression levels maintained an overall downward trend to the late stage of infection in the liver of grass carps. Unexpectedly, the protein levels of CiCFI were also continuously down-regulated in the serum of grass carps during GCRV infection, while the content of serum C3b proteins first increases and then returns to the initial level, suggesting a distinct role of CiCFI in regulating complement activation and fish-virus interaction. Combining our previous results that complement factor D, a complement enhancer, shows continuously up-regulated expression levels in grass carps during GCRV infection, and this study may provide the further essential data for the full picture of complex complement regulation mechanism mediated by Df and CFI of the grass carp during pathogen infection. Full article

(This article belongs to the Special Issue Fish Immunology 3.0)

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20 pages, 3480 KiB

Open AccessArticle

Temperature-Biased miRNA Expression Patterns during European Sea Bass (Dicentrarchus labrax) Development

by Maria Papadaki, Elisavet Kaitetzidou, Ioannis E. Papadakis, Dimitris G. Sfakianakis, Nikos Papandroulakis, Constantinos C. Mylonas and Elena Sarropoulou

Int. J. Mol. Sci. 2022, 23(19), 11164; https://doi.org/10.3390/ijms231911164 - 22 Sep 2022

Cited by 4 | Viewed by 1982

Abstract

Environmental effects and, particularly, temperature changes have been demonstrated to influence the activity, function, and well-being of teleosts. Temperature may change seasonally in the wild, and in captivity under aquaculture operations. Moreover, climate change is expected to shift temperature profiles worldwide. MicroRNAs (miRNA) [...] Read more.

Environmental effects and, particularly, temperature changes have been demonstrated to influence the activity, function, and well-being of teleosts. Temperature may change seasonally in the wild, and in captivity under aquaculture operations. Moreover, climate change is expected to shift temperature profiles worldwide. MicroRNAs (miRNA) are important temperature-sensitive gene-expression regulators acting at the post-transcriptional level. They are known to be key regulators in development, reproduction, and immune responses. Therefore, early larval development of the European sea bass (Dicentrarchus labrax), one of the most extensively cultured species in Mediterranean aquaculture, was investigated at early rearing temperatures, i.e., 15, 17.5, and 20 °C, in regard to the impact of temperatures on miRNAs through sncRNA high-throughput sequencing but also at the phenotypic level in terms of growth, sex, vision, and skeletal deformities. Expression profiling revealed stage- and temperature-specific miRNA expression targeting genes with roles in reproduction and immune response mainly at the flexion and all-fins stages. Similar stage- and temperature-specific results were also observed concerning the number of rod cells and lower jaw elongation. The present work presents for the first time highly promising results on the influence of early rearing temperature at the post-transcriptional level during European sea bass development, with a putative impact on reproduction and immune response, as well as regarding teleost vision and larval development. Full article

(This article belongs to the Special Issue Fish Immunology 3.0)

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23 pages, 6018 KiB

Open AccessArticle

Integrated Analysis of Transcriptome and Metabolome Reveals Distinct Responses of Pelteobagrus fulvidraco against Aeromonas veronii Infection at Invaded and Recovering Stage

by Xianhui Ning, Ye Peng, Peng Tang, Yiran Zhang, Lingling Wang, Wenwen Zhang, Kai Zhang, Jie Ji and Shaowu Yin

Int. J. Mol. Sci. 2022, 23(17), 10121; https://doi.org/10.3390/ijms231710121 - 4 Sep 2022

Cited by 9 | Viewed by 2372

Abstract

Yellow catfish (Pelteobagrus fulvidraco) is an important aquaculture fish susceptible to Aeromonas veronii infection, which causes acute death resulting in huge economic losses. Understanding the molecular processes of host immune defense is indispensable to disease control. Here, we conducted the integrated [...] Read more.

Yellow catfish (Pelteobagrus fulvidraco) is an important aquaculture fish susceptible to Aeromonas veronii infection, which causes acute death resulting in huge economic losses. Understanding the molecular processes of host immune defense is indispensable to disease control. Here, we conducted the integrated and comparative analyses of the transcriptome and metabolome of yellow catfish in response to A. veronii infection at the invaded stage and recovering stage. The crosstalk between A. veronii-induced genes and metabolites uncovered the key biomarkers and pathways that strongest contribute to different response strategies used by yellow catfish at corresponding defense stages. We found that at the A. veronii invading stage, the immune defense was strengthened by synthesizing lipids with energy consumption to repair the skin defense line and accumulate lipid droplets promoting intracellular defense line; triggering an inflammatory response by elevating cytokine IL-6, IL-10 and IL-1β following PAMP-elicited mitochondrial signaling, which was enhanced by ROS produced by impaired mitochondria; and activating apoptosis by up-regulating caspase 3, 7 and 8 and Prostaglandin F1α, meanwhile down-regulating FoxO3 and BCL6. Apoptosis was further potentiated via oxidative stress caused by mitochondrial dysfunction and exceeding inflammatory response. Additionally, cell cycle arrest was observed. At the fish recovering stage, survival strategies including sugar catabolism with D-mannose decreasing; energy generation through the TCA cycle and Oxidative phosphorylation pathways; antioxidant protection by enhancing Glutathione (oxidized), Anserine, and α-ketoglutarate; cell proliferation by inducing Cyclin G2 and CDKN1B; and autophagy initiated by FoxO3, ATG8 and ATP6V1A were highlighted. This study provides a comprehensive picture of yellow catfish coping with A. veronii infection, which adds new insights for deciphering molecular mechanisms underlying fish immunity and developing stage-specific disease control techniques in aquaculture. Full article

(This article belongs to the Special Issue Fish Immunology 3.0)

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14 pages, 4457 KiB

Open AccessArticle

Functional Characterization of Serum Amyloid P Component (SAP) in Host Defense against Bacterial Infection in a Primary Vertebrate

by Jiadong Li, Hao Bai, Xiaoxue Yin, Zhelin Wu, Li Qiu, Xiayi Wei, Qingliang Zeng, Liangliang Mu and Jianmin Ye

Int. J. Mol. Sci. 2022, 23(16), 9468; https://doi.org/10.3390/ijms23169468 - 22 Aug 2022

Cited by 6 | Viewed by 1951

Abstract

Serum amyloid P component (SAP), an ancient short pentraxin of the pentraxin family, plays an essential role in resistance to bacterial infection. In this study, the expression and functional characterization of SAP (OnSAP) in Nile tilapia (Oreochromis niloticus), a primary vertebrate, [...] Read more.

Serum amyloid P component (SAP), an ancient short pentraxin of the pentraxin family, plays an essential role in resistance to bacterial infection. In this study, the expression and functional characterization of SAP (OnSAP) in Nile tilapia (Oreochromis niloticus), a primary vertebrate, are investigated. The open reading frame of OnSAP is 645 bp of a nucleotide sequence encoding a polypeptide of 214 amino acids. As a calcium-binding protein, the structure and relative motif of OnSAP is highly similar to those of humans, containing amino acid residues Asn, Glu, Gln and Asp. In healthy fish, OnSAP mRNA is extensively distributed in all eleven tissues examined, with the highest level in spleen. The mRNA expression of OnSAP was significantly up-regulated after being challenged with gram-positive bacterium Streptococcus agalactiae and gram-negative bacterium Aeromonas hydrophila in vivo. In addition, recombinant OnSAP ((r)OnSAP) protein had capacities of binding S. agalactiae or A. hydrophila in the presence of Ca²⁺. Further, (r)OnSAP helped monocytes/macrophages to efficiently phagocytize bacteria. Moreover, the (r)OnSAP was able to enhance the complement-mediated lysis of the chicken red blood cells. Collectively, the evidence of SAP in tilapia, based on the results including its evolutionary conserved protein structure, bacterial binding and agglutination, opsonophagocytosis of macrophage and hemolysis enhancement, enriches a better understanding of the biological functions of the pentraxin family. Full article

(This article belongs to the Special Issue Fish Immunology 3.0)

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15 pages, 6189 KiB

Open AccessArticle

Rag1 and Rag2 Gene Expressions Identify Lymphopoietic Tissues in Larvae of Rice-Field Eel (Monopterus albus)

by Yuchen Liu, Nan Jiang, Wenzhi Liu, Yong Zhou, Mingyang Xue, Qiwang Zhong, Zhong Li and Yuding Fan

Int. J. Mol. Sci. 2022, 23(14), 7546; https://doi.org/10.3390/ijms23147546 - 7 Jul 2022

Cited by 5 | Viewed by 2182

Abstract

In immature lymphocytes, recombination activating genes 1 and 2 are necessary for antigen receptor V (D) J recombination, representing immature lymphocyte biomarkers. Herein, we cloned and sequenced rice-field eel rag1 and rag2 genes. Their expressions in the thymus, liver, and kidney were significant [...] Read more.

In immature lymphocytes, recombination activating genes 1 and 2 are necessary for antigen receptor V (D) J recombination, representing immature lymphocyte biomarkers. Herein, we cloned and sequenced rice-field eel rag1 and rag2 genes. Their expressions in the thymus, liver, and kidney were significant from 0 days post hatching (dph) to 45 dph, peaking at 45 dph in these three tissues. In situ hybridization detected high rag1 and rag2 expressions in the liver, kidney, and thymus of rice-field eel from 2 to 45 dph, suggesting that multiple tissues of rice-field eel contain lymphocyte lineage cells and undergo lymphopoiesis. Tissue morphology was used to observe lymphopoiesis development in these three tissues. The thymus primordium began to develop at 2 dph, while the kidney and liver have generated. Our findings verified that the thymus is the primary lymphopoietic tissue and suggested that, in rice-field eel, lymphocyte differentiation also occurs in the liver and kidney. Full article

(This article belongs to the Special Issue Fish Immunology 3.0)

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16 pages, 2288 KiB

Open AccessArticle

Profile of Innate Immunity in Gilthead Seabream Larvae Reflects Mortality upon Betanodavirus Reassortant Infection and Replication

by Miguel Ángel García-Álvarez, Marta Arizcun, Elena Chaves-Pozo and Alberto Cuesta

Int. J. Mol. Sci. 2022, 23(9), 5092; https://doi.org/10.3390/ijms23095092 - 3 May 2022

Cited by 6 | Viewed by 1827

Abstract

Historically, gilthead seabream (Sparus aurata) has been considered a fish species resistant to nervous necrosis virus (NNV) disease. Nevertheless, mortality in seabream hatcheries, associated with typical clinical signs of the viral encephalopathy and retinopathy (VER) disease has been confirmed to be [...] Read more.

Historically, gilthead seabream (Sparus aurata) has been considered a fish species resistant to nervous necrosis virus (NNV) disease. Nevertheless, mortality in seabream hatcheries, associated with typical clinical signs of the viral encephalopathy and retinopathy (VER) disease has been confirmed to be caused by RGNNV/SJNNV reassortants. Because of this, seabream larvae at 37 and 86 days post-hatching (dph) were infected by immersion with RGNNV/SJNNV and SJNNV/RGNNV reassortants under laboratory conditions, and mortality, viral replication and immunity were evaluated. Our results show that gilthead seabream larvae, mainly those at 37 dph, are susceptible to infection with both NNV reassortant genotypes, with the highest impact from the RGNNV/SJNNV reassortant. In addition, viral replication occurs at both ages (37 and 86 dph) but the recovery of infective particles was only confirmed in 37 dph larvae,; this value was also highest with the RGNNV/SJNNV reassortant. Larvae immunity, including the expression of antiviral, inflammatory and cell-mediated cytotoxicity genes, was affected by NNV infection. Levels of the natural killer lysin (Nkl) peptide were increased in SJNNV/RGNNV-infected larvae of 37 dph, though hepcidin was not. Our results demonstrate that the seabream larvae are susceptible to both NNV reassortants, though mainly to RGNNV/SJNNV, in an age-dependent manner. Full article

(This article belongs to the Special Issue Fish Immunology 3.0)

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