Identification and function analysis of a novel vascular endothelial growth factor, LvVEGF3, in the Pacific whiteleg shrimp Litopenaeus vannamei

The involvement of VEGF and VEGFR in bacterial recognition and regulation of antimicrobial peptides in Eriocheir sinensis

Vascular endothelial growth factor (VEGF) and VEGF reporter (VEGFR) are essential molecules in VEGF signalling pathway. Although the functions of VEGF and VEGFR have been well reported in vertebrates, their functions are still poorly understood in invertebrates. In this study, the open reading frame sequences of EsVEGF1 and EsVEGFR4 were cloned from Eriocheir sinensis, and their corresponding proteins shared typical structure characteristics with their counterparts in other species. EsVEGF1 were predominantly expressed in hepatopancreas and muscle while EsVEGFR4 mainly expressed in hemocytes and intestine. The expression levels of EsVEGF1 in hemocytes were rapidly induced by Staphylococcus aureus and Vibrio parahaemolyticus, and it also increased rapidly in hepatopancreas after being challenged with V. parahaemolyticus. The expression levels of EsVEGFR4 only increased in hepatopancreas of crabs injected with S. aureus. The extracellular immunoglobulin domain of EsVEGFR4 could bind with Gram-negative and Gram-positive bacteria as well as lipopolysaccharide and peptidoglycan. EsVEGF1 could act as the ligand for EsVEGFR4 and Toll-like receptor and regulate the expression of crustins and lysozyme with a tissue-specific manner, while have no regulatory function on that of anti-lipopolysaccharide factors. This study will provide new insights into the immune defense mechanisms mediated by VEGF and VEGFR in crustaceans.

Phylogenetic and transcriptomic characterization of insulin and growth factor receptor tyrosine kinases in crustaceans

Receptor tyrosine kinases (RTKs) mediate the actions of growth factors in metazoans. In decapod crustaceans, RTKs are implicated in various physiological processes, such molting and growth, limb regeneration, reproduction and sexual differentiation, and innate immunity. RTKs are organized into two main types: insulin receptors (InsRs) and growth factor receptors, which include epidermal growth factor receptor (EGFR), fibroblast growth factor receptor (FGFR), vascular endothelial growth factor receptor (VEGFR), and platelet-derived growth factor receptor (PDGFR). The identities of crustacean RTK genes are incomplete. A phylogenetic analysis of the CrusTome transcriptome database, which included all major crustacean taxa, showed that RTK sequences segregated into receptor clades representing InsR (72 sequences), EGFR (228 sequences), FGFR (129 sequences), and PDGFR/VEGFR (PVR; 235 sequences). These four receptor families were distinguished by the domain organization of the extracellular N-terminal region and motif sequences in the protein kinase catalytic domain in the C-terminus or the ligand-binding domain in the N-terminus. EGFR1 formed a single monophyletic group, while the other RTK sequences were divided into subclades, designated InsR1-3, FGFR1-3, and PVR1-2. In decapods, isoforms within the RTK subclades were common. InsRs were characterized by leucine-rich repeat, furin-like cysteine-rich, and fibronectin type 3 domains in the N-terminus. EGFRs had leucine-rich repeat, furin-like cysteine-rich, and growth factor IV domains. N-terminal regions of FGFR1 had one to three immunoglobulin-like domains, whereas FGFR2 had a cadherin tandem repeat domain. PVRs had between two and five immunoglobulin-like domains. A classification nomenclature of the four RTK classes, based on phylogenetic analysis and multiple sequence alignments, is proposed.

Biochemical, histological and transcriptional response of intestines in Litopenaeus vannamei under chronic zinc exposure

Zinc (Zn) is an essential trace element for the normal physiological function of aquatic organisms, but it could become toxic to organisms when the concentration increased in water. As the first line of defense, the shrimp intestines are the most susceptible organ to environmental stress. In this study, the chronic toxicity of 0 (control, IC), 0.01(IL), 0.1(IM) and 1 mg/L (IH) Zn in intestines of Litopenaeus vannamei was investigated from the perspectives of biochemical, histological and transcriptional changes after exposure for 30 days. The results showed that the intestinal tissue basement membrane is swollen in the IM and IH groups and detached in the IH group. The total antioxidant capacities (T-AOC) were reduced while the content of malondialdehyde (MDA) were increased significantly in IM and IH groups. The production of reactive oxygen species (ROS) was increased significantly in IH group. Many differentially expressed genes (DEGs) were identified in IL, IM and IH groups, respectively. GO and KEGG enrichment analyses were conducted on the DEGs to obtain the underlying biological processes and pathways. The gene modules related to the sample were identified by weighted gene co-expression network analysis (WGCNA), and genes in modules highly corelated with IH group were mainly enriched in immune related pathways. Nine DEGs were selected for validation by quantitative real time PCR (qRT-PCR) and the expression profiles of these DEGs kept a well consistent with the high-throughput data, which confirmed reliability of transcriptome results. Additionally, 10 DEGs were screened to detect the changes of expression level in different groups. All these results indicated that Zn exposure could damage the intestinal barrier, provoke oxidative stress, reduce the immune function, increase the susceptibility to bacterial infections of L. vannamei and cause inflammation, ultimately result in cell apoptosis. Our study provides more perspective on the stress response of crustacean under Zn exposure.

The combination of hypoxia and high temperature affects heat shock, anaerobic metabolism, and pentose phosphate pathway key components responses in the white shrimp (Litopenaeus vannamei)

Due to global warming, world water bodies have higher temperatures and lower oxygen concentrations that affect aquatic species including the white shrimp Litopenaeus vannamei. This species withstands these conditions, but the information of the physiological responses that allow them to survive are scarce. We analyzed the effects of high temperature, hypoxia, reoxygenation, and the combination of these factors on the relative expression of selected genes: HSF1, Hsp70, p53, TIGAR, HIF-1α, and VEGF1-3 in gills of L. vannamei. Additionally, glucose, lactate, NADP, and NADPH were determined. HSF1 was up-regulated in the high temperature and oxygen stress conditions, but Hsp70 was up-regulated only in reoxygenation at both temperatures. HIF-1α was also up-regulated by reoxygenation in both temperatures. Meanwhile, the VEGF genes were not altered by the stress conditions, since none of them changed expression drastically. p53 relative expression remained stable at the tested stress conditions, which prompts to the maintenance of antioxidant defenses. TIGAR expression was induced in normoxia and hypoxia at high temperature, which induced NADPH content helping to scavenge reactive oxygen species (ROS). Additionally, high temperature caused higher glucose and lactate content in normoxia and hypoxia, indicating carbohydrate mobilization and a switch to anaerobic metabolism. The results showed that HSF1, the anaerobic metabolism and the pentose phosphate pathway (PPP) are crucial for the shrimp response to these abiotic stress conditions and contribute to their survival.

MicroRNA Regulation in Infectious Diseases and Its Potential as a Biosensor in Future Aquaculture Industry: A Review

An infectious disease is the most apprehensive problem in aquaculture as it can lead to high mortality in aquatic organisms and massive economic loss. Even though significant progress has been accomplished in therapeutic, prevention, and diagnostic using several potential technologies, more robust inventions and breakthroughs should be achieved to control the spread of infectious diseases. MicroRNA (miRNA) is an endogenous small non-coding RNA that post-transcriptionally regulates the protein-coding genes. It involves various biological regulatory mechanisms in organisms such as cell differentiation, proliferation, immune responses, development, apoptosis, and others. Furthermore, an miRNA also acts as a mediator to either regulate host responses or enhance the replication of diseases during infection. Therefore, the emergence of miRNAs could be potential candidates for the establishment of diagnostic tools for numerous infectious diseases. Interestingly, studies have revealed that miRNAs can be used as biomarkers and biosensors to detect diseases, and can also be used to design vaccines to attenuate pathogens. This review provides an overview of miRNA biogenesis and specifically focuses on its regulation during infection in aquatic organisms, especially on the host immune responses and how miRNAs enhance the replication of pathogens in the organism. In addition to that, we explored the potential applications, including diagnostic methods and treatments, that can be employed in the aquaculture industry.

A Novel Hemocyte-Specific Small Protein Participates in White Spot Syndrome Virus Infection via Binding to Viral Envelope Protein

Hemocytes are essential components of the immune system against invading pathogens in shrimp. Many uncharacterized transcripts exist in hemocytes but the knowledge of them is very limited. In the present study, we identified a novel small protein from the uncharacterized transcripts in hemocytes of Litopenaeus vannamei. This transcript was specifically expressed in hemocytes and encoded a novel secretory protein, which was designated as hemocyte-specific small protein (LvHSSP). The expression level of LvHSSP was significantly up-regulated in the hemocytes of shrimp infected with white spot syndrome virus (WSSV). After knockdown of LvHSSP by RNA interference, the WSSV copy number in shrimp decreased significantly. Conversely, WSSV copy number increased in shrimp when they were infected by WSSV after incubation with recombinant LvHSSP protein. These results suggested that LvHSSP might promote viral infection in shrimp. Immunocytochemical assay showed that the recombinant LvHSSP protein was located on the membrane of hemocytes. Co-IP results showed that LvHSSP could interact with VP26, the main envelope protein of WSSV, suggesting that LvHSSP might mediate WSSV adhesion and entry into host cells by binding to viral envelope protein. Meanwhile, the total hemocyte counts were significantly decreased after LvHSSP knockdown while increased after supplementing with recombinant LvHSSP protein, supporting the idea of hemocytes as the carrier for systemic dissemination of WSSV. This study reported a novel small protein in hemocytes, which modulated the viral infection in shrimp. Our results will enrich the knowledge of invertebrate innate immunity and provide a new field in the study of hemocyte function.

First Discovery of Beta-Sitosterol as a Novel Antiviral Agent against White Spot Syndrome Virus

The outbreak of white spot syndrome (WSS) is a looming challenge, due to dramatic losses to the crustacean aquaculture industry. However, at present, there are no prophylactic or therapeutic means to control this infectious viral disease. Here, we screened fifteen medicinal plants for their inhibitory activity on the white spot syndrome virus (WSSV), using red swamp crayfish (Procambarus clarkii) as a model species. The results showed that the crude extracts of Pinellia ternata (Thunb.) Breit. had the highest inhibitory effect (91.59%, 100 mg/kg) on WSSV proliferation, and its main component, beta-sitosterol, showed a much higher activity (95.79%, 50 mg/kg). Further, beta-sitosterol potently reduced (p < 0.01) viral loads and viral gene transcription levels in a concentration-dependent fashion, and significantly promoted the survival rate of WSSV-challenged crayfish (57.14%, 50 mg/kg). The co-incubation assay indicated that beta-sitosterol did not influence the infectivity of WSSV particles. Both pre- and post-treatment of beta-sitosterol exerted a significant inhibitory effect (p < 0.01) on the viral load in vivo. Mechanistically, beta-sitosterol not only interfered with the expression of viral genes (immediate early gene 1, ie1; DNA polymerase, DNApol) that are important in initiating WSSV transcription, but it also attenuated the hijacking of innate immune signaling pathways (Toll, IMD, and JAK/STAT pathways) by viral genes to block WSSV replication. Moreover, the expression of several antiviral immune, antioxidant, pro-inflammatory, and apoptosis-related genes changed significantly in beta-sitosterol-treated crayfish. Beta-sitosterol is a potent WSSV inhibitor and has the potential to be developed as an effective anti-WSSV agent against a WSS outbreak in crustacean aquaculture.

A Novel TRIM9 Protein Promotes NF-κB Activation Through Interacting With LvIMD in Shrimp During WSSV Infection

The TRIpartite Motif (TRIM) proteins play key roles in cell differentiation, apoptosis, development, autophagy, and innate immunity in vertebrates. In the present study, a novel TRIM9 homolog (designated as LvTRIM9-1) specifically expressed in the lymphoid organ of shrimp was identified from the Pacific whiteleg shrimp Litopenaeus vannamei. Its deduced amino acid sequence possesses the typical features of TRIM proteins, including a RING domain, two B-boxes, a coiled-coil domain, a FN3 domain, and a SPRY domain. The transcripts of LvTRIM9-1 were mainly located in the lymphoid tubules of the lymphoid organ. Knockdown of LvTRIM9-1 could apparently inhibit the transcriptions of some genes from white spot syndrome virus (WSSV) and reduce the viral propagation in the lymphoid organ. Overexpression of LvTRIM9-1 in mammalian cells could activate the promoter activity of NF-κB, and an in vivo experiment in shrimp showed that knockdown of LvTRIM9-1 reduced the expression of LvRelish in the lymphoid organ. Yeast two-hybridization and co-immunoprecipitation (Co-IP) assays confirmed that LvTRIM9-1 could directly interact with LvIMD, a key component of the IMD pathway, through its SPRY domain. These data suggest that LvTRIM9-1 could activate the IMD pathway in shrimp via interaction with LvIMD. This is the first evidence to show the regulation of a TRIM9 protein on the IMD pathway through its direct interaction with IMD, which will enrich our knowledge on the role of TRIM proteins in innate immunity of invertebrates.

Characterization and Function Analysis of the Beta-Carotene Oxygenase-like Genes in Carotenoids Metabolism of the Ridgetail White Prawn Exopalaemon carinicauda

Carotenoids are almost universally distributed in living organisms. The oxidative metabolism by carotene oxygenase contributes to the metabolic processes of carotenoids. 15,15'-beta-carotene oxygenase (BCO1) and 9',10'-beta-carotene oxygenase (BCO2) are two important carotenoid oxygenases. In order to understand the function of carotenoid oxygenases in crustaceans, seven genes encoding carotenoid oxygenases (named EcBCO-like) were isolated from the transcriptome database of Exopalaemon carinicauda. After phylogenetic analysis with carotenoid oxygenases reported in other species, EcBCO-like1, EcBCO-like3, and EcBCO-like6 were chosen for further functional study. The prawns after EcBCO-like1 knockdown suffered continuous death, which suggested its important role for the survival of the animals. For the prawns after EcBCO-like3 knockdown, no phenotype change was observed. The prawns after EcBCO-like6 knockdown showed color changes in their hepatopancreas when they were fed with carotenoids-containing diet, and the content of carotenoid in their hepatopancreas was much higher than that in the control prawns. The present study will pave the way for further understanding the carotenoids metabolism in the prawns.

Identification of Single Nucleotide Polymorphisms Related to the Resistance Against Acute Hepatopancreatic Necrosis Disease in the Pacific White Shrimp Litopenaeus vannamei by Target Sequencing Approach

Acute hepatopancreatic necrosis disease (AHPND) is a major bacterial disease in Pacific white shrimp Litopenaeus vannamei farming, which is caused by Vibrio parahaemolyticus. AHPND has led to a significant reduction of shrimp output since its outbreak. Selective breeding of disease-resistant broodstock is regarded as a key strategy in solving the disease problem. Understanding the relationship between genetic variance and AHPND resistance is the basis for marker-assisted selection in shrimp. The purpose of this study was to identify single nucleotide polymorphisms (SNPs) associated with the resistance against AHPND in L. vannamei. In this work, two independent populations were used for V. parahaemolyticus challenge and the resistant or susceptible shrimp were evaluated according to the survival time after Vibrio infection. The above two populations were genotyped separately by a SNP panel designed based on the target sequencing platform using a pooling strategy. The SNP panel contained 508 amplicons from DNA fragments distributed evenly along the genome and some immune-related genes of L. vannamei. By analyzing the allele frequency in the resistant and susceptible groups, 30 SNPs were found to be significantly associated with the resistance of the shrimp against V. parahaemolyticus infection (false discovery rate corrected at P < 0.05). Three SNPs were further validated by individual genotyping in all samples of population 1. Our study illustrated that target sequencing and pooling sequencing were effective in identifying the markers associated with economic traits, and the SNPs identified in this study could be used as molecular markers for breeding disease-resistant shrimp.

An E3 ubiquitin ligase TRIM9 is involved in WSSV infection via interaction with β-TrCP

The TRIpartite Motif (TRIM) proteins are known to play key roles in cell differentiation, apoptosis, development, autophagy and innate immunity. In the present study, a TRIM9 homolog (named LvTRIM9) was identified from the transcriptome of the Pacific whiteleg shrimp Litopenaeus vannamei. The deduced amino acid sequence of LvTRIM9 possessed typical features of TRIMs, consisting of a RING domain, two B-boxes, a coiled-coil domain, a FN3 domain, and a SPRY domain. The transcript of LvTRIM9 was detected in most tissues of the shrimp. Its expression level was obviously up-regulated at 3, 12 and 24 h post white spot syndrome virus (WSSV) infection. Knockdown of LvTRIM9 gene expression by double-strand RNA mediated interference could lead to a decrease of virus copy number in WSSV-infected shrimp. Yeast two-hybrid analysis showed that LvTRIM9 could directly interact with beta-transducin repeat-containing protein of shrimp (Lvβ-TrCP), an inhibitor of NF-κB pathway. Meanwhile, knockdown of LvTRIM9 could also up-regulate the expression levels of LvRelish and downstream production of antimicrobial peptides in the intestine of shrimp. These data indicated that WSSV might hijack the LvTRIM9 for its propagation through inhibition of NF-κB pathway and downstream antimicrobial peptides production via interaction of LvTRIM9 with Lvβ-TrCP in shrimp. The study improved our understanding about the impact of E3 ubiquitin ligases on the innate immune signaling pathway of shrimp and its role during WSSV infection.

VEGF-like protein from Apostichopus japonicus promotes cell proliferation and migration

Vascular endothelial growth factor (VEGF) is a key conservative regulator of inflammation response by promoting cell proliferation, migration, and vascular permeability. It also induces the release of inflammatory factors in vertebrates. We previously characterized NLR family pyrin domain containing 3 and HMGB3 homology in Apostichopus japonicus, providing the occurrence of inflammation in this species. However, to our knowledge, other inflammation-related molecules, such as VEGF, have rarely been investigated. In the present study, a novel VEGF homolog was identified from A. japonicus (designated as AjVEGF) by rapid amplification of cDNA ends. Full-length cDNA of AjVEGF was 3181 bp with a putative open reading frame of 1752 bp encoding 583 amino acid (aa) residue protein. Structural analysis revealed that AjVEGF processed characteristic VEGF domains of platelet-derived growth factor domain (132-232 aa) and CXC domain (223-270 aa). Multiple sequence alignment and phylogenetic analysis both supported that AjVEGF belongs to a new member of VEGF protein subfamily. Both Vibrio splendidus challenge in vivo and lipopolysaccharide stimulation in vitro could significantly upregulate mRNA expression of AjVEGF compared with the control group. Functional analysis indicated that recombinant AjVEGF promoted coelomocyte proliferation and migration not only in sea cucumber but also in human colorectal adenocarcinoma cells (HT29). This consistent function was also detected for human VEGFs. Taken together, these findings suggest that AjVEGF has a similar function of VEGF in higher animals and might serve as a candidate cytokine in sea cucumber inflammation.

Identification and characterization of two novel vascular endothelial growth factor genes in Litopenaeus vannamei

Vascular endothelial growth factor (VEGF) signaling pathway induces endothelial cell proliferation, promotes cell migration, and inhibits apoptosis. Although three VEGF and two VEGF receptor genes have been identified in Litopenaeus vannamei and demonstrated their roles in WSSV infection, another two novel VEGF genes (LvVEGF4, LvVEGF5) were isolated and their involvements in the WSSV infection of shrimp were studied in the present study. The deduced amino acid sequences of both LvVEGF4 and LvVEGF5 contained a signal peptide, a typical PDGF/VEGF domain and a cysteine knot motif (CXCXCX). Tissue distribution analysis showed that LvVEGF4 was predominantly expressed in gill and hemocytes, while LvVEGF5 was mainly detected in hemocytes and intestine. WSSV infection could cause up-regulation of the transcriptional levels of LvVEGF4 and LvVEGF5. Their functions were studied by double-strand RNA interference. The results showed that knock-down of LvVEGF4 and LvVEGF5 led to a decrease of the viral copy number in WSSV infected shrimp. Yeast two-hybrid analysis showed that both LvVEGF4 and LvVEGF5 could interact with LvVEGFR1 rather than LvVEGFR2. In addition, knock-down of LvVEGF4 and LvVEGF5 could reduce the expressional levels of downstream genes FAK and PI3K. The present study provides new clues in demonstrating that the VEGF signaling pathway is involved in the process of WSSV infection in shrimp.

Comparative transcriptome analysis of red swamp crayfish (Procambarus clarkia) hepatopancreas in response to WSSV and Aeromonas hydrophila infection

To better study the immune system of shrimp and understand the similarities and differences between the host's immune defense against viral and bacterial infections, this study used a comparative transcriptomics method to systematically analyze the hepatopancreas of the crayfish Procambarus clarkia in response to WSSV and A. hydrophila infection. After assembly, there was an average of 24,404,837 clean reads were obtained after filtering out low-quality reads. Unigenes were annotated by comparing against nr, Swiss-Prot\KEGG\COG\KOG\GO and Pfam databases, and 17,954 unigenes were annotated in at least one database. 2600 and 2073 differentially expressed genes (DEGs) in the hepatopancreas in response to WSSV and A. hydrophila infections were identified respectively. The GO and KEGG enrichment analyses of DEGs were conducted to further explore their functions. The pathways like PI3K-Akt signaling pathway, mTOR signaling pathway, Jak-STAT signaling pathway, NF-κB signaling pathway, VEGF signaling pathway, Ras signaling pathway, were the most prominent for immunity-related DEGs in C-/W-Groups, while Endocytosis, Lysozyme, Focal adhesion, Phagosome, Peroxisome, MAPK signaling pathway were observed in C-/A-Groups. Furthermore, the expression levels of nine selected immune-related DEGs were validated by qRT-PCR, substantiating the reliability of RNA-Seq results. This study not only provides effective data support to reveal the different immune defense strategies by P. clarkia to cope with bacterial and WSSV infections, but also to provide new information about the immune system and defense mechanisms of shrimp.

Transcriptomic and morphological analyses of Litopenaeus vannamei intestinal barrier in response to Vibrio paraheamolyticus infection reveals immune response signatures and structural disruption

The white shrimp Litopenaeus vannamei has been greatly impacted by Vibrio infection. In this study, we investigated the intestinal barrier response of L vannamei following challenge with Vibrio parahaemolyticus E1, by examining morphological changes and transcriptome expression levels. A total of 16,4420 unigenes were obtained from RNAseq data after quality control and assembly, and 4646 differentially expressed genes (DEGs) were identified following Vibrio challenge, of which 2469 unigenes were significantly up-regulated and 2177 were significantly down-regulated. DEGs were determined to be involved in various physical, chemical and immunological intestinal barrier functions, including peritrophin, cytoskeleton and cell junction, pattern recognition receptors, antimicrobial peptide and immune signaling pathways, serine protease/protease inhibitor and prophenoloxidase system, apoptosis and phagocytosis, and antioxidant systems. Fifteen DEGs were randomly selected for validation by real-time quantitative PCR (RT-qPCR) and showed results consistent with the RNA-seq data. Intestinal epithelial cell morphology was also affected by Vibrio challenge, showing epithelial detachment, nuclear pyknosis, and destruction of cell junctions. These results improve our current understanding of the intestinal barrier function in the shrimp response to bacterial infection.

A Novel Vascular Endothelial Growth Factor Receptor Participates in White Spot Syndrome Virus Infection in Litopenaeus vannamei

Vascular endothelial growth factor (VEGF) signaling pathway is known to play key roles in endothelial cell proliferation, migration, angiogenesis, vascular permeability, inhibition of apoptosis, and virus infection. In the present study, a novel VEGFR gene (LvVEGFR2) was identified and characterized from Litopenaeus vannamei. The deduced amino acid sequence of LvVEGFR2 possessed typical features of VEGFRs reported in other species, including six IG-like domains, a transmembrane motif, a protein kinase (PK) domain, and one tyrosine-PK active site. The transcripts of LvVEGFR2 were mainly detected in hemocytes and lymphoid organ (Oka). Subcellular localization analysis showed that LvVEGFR2 was a membrane protein. Its expression level was obviously upregulated in hemocytes and Oka of the shrimp after white spot syndrome virus (WSSV) infection. Knockdown of LvVEGFR2 gene expression by double-strand RNA mediated interference could lead to a decrease of virus copy number in WSSV-infected shrimp. The interaction between LvVEGFR2 and different LvVEGFs (LvVEGF1, LvVEGF2, and LvVEGF3) in shrimp was analyzed at the transcription level and protein level, respectively. Knockdown of LvVEGF2 or LvVEGF3 could downregulate the expression level of LvVEGFR2, and injection of the recombinant LvVEGF2 or LvVEGF3 could upregulate the expression level of LvVEGFR2. Yeast two-hybrid analysis showed that LvVEGFR2 could interact with LvVEGF2 and LvVEGF3 directly. The study improved our understanding on the VEGF signaling pathway of shrimp and its role during WSSV infection.

The Role of Cytokine PF4 in the Antiviral Immune Response of Shrimp

During viral infection in vertebrates, cytokines play important roles in the host defense against the virus. However, the function of cytokines in invertebrates has not been well characterized. In this study, shrimp cytokines involved in viral infection were screened using a cytokine antibody microarray. The results showed that three cytokines, the Fas receptor (Fas), platelet factor 4 (PF4) and interleukin-22 (IL-22), were significantly upregulated in the white spot syndrome virus (WSSV)-challenged shrimp, suggesting that these cytokines played positive regulatory roles in the immune response of shrimp against the virus. Further experiments revealed that PF4 had positive effects on the antiviral immunity of shrimp by enhancing the shrimp phagocytic activity and inhibiting the apoptotic activity of virus-infected hemocytes. Therefore, our study presented a novel mechanism of cytokines in the innate immunity of invertebrates.