Comparative studies on the immunogenicity of theronts, tomonts and trophonts of Cryptocaryon irritans in grouper

Transcriptomic analysis of large yellow croaker (Larimichthys crocea) reveals the suppression of the inflammatory response from Cryptocaryon irritans infection

Large yellow croaker (Larimichthys crocea) is the most productive marine fish in China. Cryptocaryon irritans is an extremely destructive parasite that causes great economic losses in large yellow croaker aquaculture industry. Therefore, it is very necessary to study the immune response of large yellow croaker in response to C. irritans infection. In this study, the transcriptomic profiles of large yellow croaker were sequenced and analyzed in the brain and head kidney at 72 h after C. irritans infection. Cytokines and chemokines related terms were significantly enriched based on the GO enrichment of down-regulated differentially expressed genes (DEGs) from the head kidney. Meanwhile, cytokine-cytokine receptor interaction was significantly enriched based on the KEGG enrichment of up-regulated DEGs from the brain and down-regulated DEGs from the head kidney, respectively. Moreover, the majority of inflammation-related DEGs were significantly up-regulated in the brain, but distinctly down-regulated in the head kidney. These results showed that the brain and head kidney might play different roles against C. irritans infection, and the inflammatory response of large yellow croaker may be restrained during C. irritans infection. Taken together, the transcriptomic analyses will be helpful to more comprehensively understand the immune mechanism of teleost against C. irritans infection, and provide a theoretical basis for the prevention and treatment of Cryptosporidiosis.

Immune response of large yellow croaker Larimichthys crocea towards a recombinant vaccine candidate targeting the parasitic ciliate Cryptocaryon irritans

Cryptocaryon irritans, a parasitic ciliate, pose a major threat to marine teleost fish aquaculture. So far, no effective and safe control method is available. In this study, the protective efficacy of a recombinant truncated surface antigen of C. irritans (rCiSA32.6t) for large yellow croaker (Larimichthys crocea) against the parasite challenge with a sub-lethal dose of the infective theronts was evaluated by comparing the relative percent survivals (RPS), the specific antibody titers in sera, and the expression levels of the immune-related genes among the negative or adjuvant control fish, fish intraperitoneally immunized with rCiSA32.6t. The results showed that a RPS of 50.1% in rCiSA32.6t-immunized fish was achieved in comparison to negative control fish against C. irritans. A significant increase was noted in the antigen-specific immunoglobulin M (IgM) and immunoglobulin T (IgT) antibody levels in the sera of the rCiSA32.6t-vaccinated fish. Compared to the negative control fish, quantitative real-time PCR analysis indicated that the interleukin-1beta, IgT, and IgM heavy chain mRNA level in the fish head kidney, spleen, gill, and skin tissue were upregulated post-rCiSA32.6t immunization. This study indicates that the rCiSA32.6t can provide a high level of immune protection against C. irritans infection in grouper and is therefore pursued as a candidate C. irritans vaccine.

Host responses against the fish parasitizing ciliate Cryptocaryon irritans

The parasitic ciliate Cryptocaryon irritans, which infects almost all marine fish species occurring in both tropical and subtropical regions throughout the world. The disease, cryptocaryonosis, accounts for significant economic losses to the aquaculture industry. This review attempts to provide a comprehensive overview of the biology of the parasite, host-parasite interactions and both specific and non-specific host defense mechanisms are responsible for the protection of fish against challenge infections with this ciliate. Also, this article reflects the current interest in this subject area and the quest to develop an available vaccine against the disease. Due to the high frequency of clinical fish cryptocaryonosis, the study of fish immune responses to C. irritans provides an optimal experimental model for understanding immunity against extracellular protozoa.

Protection of Grouper Against Cryptocaryon irritans by Immunization With Tetrahymena thermophila and Protective Cross-Reactive Antigen Identification

Vaccination is an effective method to prevent Cryptocaryon irritans infection. Although some vaccines have been developed, large-scale production of these vaccines is costly. Development of a heterogenous vaccine generated by low-cost antigens is an alternative method. In the present study, grouper immunized with Tetrahymena thermophila, a free-living ciliate that easily grows in inexpensive culture media at high density, showed protective immunity against C. irritans infection. Higher immobilization against C. irritans theronts was detected in T. thermophila–immunized grouper serum, which suggested the existence of a cross-reactive antibody in the serum. By immunoprecipitation and mass spectrometry analyses, tubulin was identified as a potential cross-reactive antigen between C. irritans and T. thermophila. Recombinant T. thermophila tubulin protein (rTt-tubulin) and its antibody were prepared, and immunofluorescence showed that both C. irritans and T. thermophila cilia were stained by the anti–rTt-tubulin antibody. Grouper immunized with rTt-tubulin showed a reduced infective rate after the C. irritans challenge. An enhanced level of C. irritans–binding immunoglobulin M (IgM) antibody was detected in serum from rTt-tubulin–immunized grouper. Moreover, specific antibodies were also found in the mucus and tissue culture medium from rTt-tubulin–immunized grouper. Overall, these findings suggested that vaccination with T. thermophila elicits cross-reactive protective immunity in grouper against C. irritans, and T. thermophila may be a potential heterologous antigen for vaccine development.

Differential immune and metabolic responses underlie differences in the resistance of Siganus oramin and Trachinotus blochii to Cryptocaryon irritans infection

Numerous studies have demonstrated that Cryptocaryon irritans can efficiently propagate in golden pompano (Trachinotus blochii), especially under intensive high-density culture, which can lead to large-scale infection, bacterial invasion, and major economic losses. By contrast, Siganus oramin is less susceptible to C. irritans infection. Here, we artificially infected S. oramin and T. blochii with C. irritans. We then used RNA-seq to characterize the expression of genes in the gills of S. oramin and T. blochii at different times after infection, conducted bioinformatics analysis of relevant pathways, and compared the differentially expressed genes in the two species. The aim of this study was to enhance our understanding of host-parasite interactions to aid the development of effective prevention and treatment strategies for C. irritans. Infection with C. irritans induced the differential expression of a large number of genes in the gills of S. oramin, indicating that S. oramin may respond to C. irritans infection by modifying the expression of genes at the transcriptional level. Our research showed that the Toll-like receptor signaling pathway, Antigen processing and presentation, Complement and coagulation cascades, and Cytosolic DNA-sensing pathway are involved in the immune response of S. oramin and T. blochii to C. irritans infection. However, T. blochii has a weak ability to mobilize neutrophils to participate in defense against C. irritans infection and differs from S. oramin in its ability to induce specific immune responses. Because of gill tissue damage during infection, dissolved oxygen intake is reduced, which increases physiological and metabolic stress. The metabolic pathways of S. oramin and T. blochii significantly differed; specifically, the main pathways in S. oramin were related to glucose and lipid metabolism, and the main pathways in T. blochii were related to amino acid metabolism. This may reduce the efficiency of ATP biosynthesis in T. blochii and result in dysfunctional energy metabolism. Therefore, differential immune and metabolic responses underlie differences in the resistance of S. oramin and T. blochii to C. irritans.

Characteristics delineation of piscidin 5 like from Larimichthys crocea with evidence for the potent antiparasitic activity

Several researches reported that piscidin members of teleosts owned strong antiparasitic activity. Cryptocaryon irritans, a type of ectoparasite, could infect most of the marine teleosts. Larimichthys crocea could severely suffer from marine white spot disease caused by C. irritans, and their mortality rate was significantly high. Concentrating on this problem, we have done many related works. Piscidin 5 like (termed Lc-P5L) was another piscidin member isolated from a comparative transcriptome of C. irritans-immuned L. crocea. In the paper, quantitative Real-time PCR (qRT-PCR) showed Lc-P5L was upregulated in examined tissues, including gill, head kidney, muscle, liver, spleen and intestine after challenged by C. irritans, the significant upregulation time was in accordance to key developmental stages of C. irritans, which implied different infection stages could result in host immune response. Furthermore, using microscope techniques, we observed theronts or trophonts became weakly motile, cilia became detached, cells were out of shape, membranes eventually lysed in different cell positions and cytoplasmic contents leaked. Laser confocal scanning microscope (LCSM) observed theronts macronucleus grew swell and depolymerized after treated by recombinant Lc-P5L (rLc-P5L). Data suggested rLc-P5L was significantly lethal to C. irritans, and the death state of the parasite incubated with rLc-P5L was remarkably similar to other piscidin members or other antiparasitic peptides (APPs). Thus, these data provided new insights into L. crocea immunity against C. irritans and potential of rLc-P5L as a therapeutic agent against pathogen invasion.

Infectivity and genes differentially expressed between young and aging theront cells of the marine fish parasite Cryptocaryon irritans

The ciliated protozoan Cryptocaryon irritans infects a wide range of marine fish and causes the highly lethal white spot disease. This parasite possesses three morphologically and physiologically distinct life stages: an infectious theront, a parasitic trophont, and an asexually reproductive tomont. In the past few years, several attempts have been made to help elucidate how C. irritans transforms from one stage to another using transcriptomic or proteomic approaches. However, there has been no research studying changes in transcription profiles between different time points of a single C. irritans life stage—the development of this parasite. Here we use RNA-seq and compare gene expression profiles of theront cells collected by 1 and 10 hrs after they emerged from tomonts. It has been shown that infectivity of theront cells declines 6–8 hours post-emergence, and we used this characteristic as a physiological marker to confirm the aging of theront cells. We identified a total of 41 upregulated and 90 downregulated genes that were differentially expressed between young and aging theront cells. Using Blast2Go to further analyze functions of these genes, we show that genes related to energy production are downregulated, but quite surprisingly many genes involved in transcription/translation processes are upregulated. We also show that expression of all nine detectable agglutination/immobilization antigen genes, with great sequence divergence, is invariably downregulated. Functions of other differentially expressed genes and indications are also discussed in our study.

Barcode sequence could be a good target for developing a species-specific anti-parasite agent based on CRISPR-Cas9

Parasitic infections are a severe issue in many regions of the world. We assume that if a chemical can destroy a DNA barcode sequence, then this chemical could be developed as a species-specific parasiticidal agent. To test this hypothesis, we designed sgRNAs that target the sequences of both a DNA barcode (ITS-2) and a control (5.8S rDNA) in Cryptocaryon irritans. In in vivo tests, we found that exposure to Cas9 mRNA mixed with sgRNAs was able to significantly reduce the hatching rate of tomont and the survival rate of theront. Quantitative Real-time PCR demonstrated that the DNAs of tomont and theront exposed to sgRNAs and Cas9 mRNA were significantly disrupted, no matter whether they were exposed to a single sgRNA or a mixture of two sgRNAs. DNA sequencing also suggested the test group that was exposed to a single sgRNA mixed with Cas9-induced mutation at sgRNA targeted fragments and the test group exposed to two sgRNAs combined with Cas9-induced deletion of large pieces. The findings and principles provided by this study contribute to the development of novel nucleic acid therapeutic drugs for cryptocaryoniasis and other parasitic diseases and provide insight into the development of species-specific parasiticidal agents.

Characterization and immune regulation role of an immobilization antigen from Cryptocaryon irritans on groupers

Immobilization antigens (i-antigens) are surface membrane proteins that are widely recognized to be the ideal candidates as vaccines antigens for immunization against Cryptocaryon irritans. In this study, we cloned a putative i-antigen gene from C. irritans, which was expressed in all three stages of the C. irritans life-cycle, and localized primarily to the cell surface. The recombinant GDCI3 i-antigen was expressed and purified using the free-living ciliate, Tetrahymena thermophila as an expression system. The purified recombinant protein was recognized by rabbit anti-C. irritans antiserum and was capable of eliciting immobilizing antibodies in rabbits and fish suggesting that the antigen itself was correctly folded. Following immunization and parasite challenge, groupers vaccinated with, recombinant GDCI3 i-antigen had a 25% cumulative percent survival rate compared to 8.3% for controls. Both non-specific and parasite-specific IgMs were generated in fish following immunization, with the levels of both increasing following challenge. Parasite-specific IgM in mucus could only be elicited after challenge of the GDCI3 i-antigen vaccinated groupers. To our knowledge, this is the first report using the Tetrahymena expression system to generate C. irritans i-antigens and investigate their use for fish vaccination.

Three new piscidins from orange-spotted grouper (Epinephelus coioides): Phylogeny, expression and functional characterization

The present study reports the identification, and characterization of three new putative piscidin paralogues, ecPis-2, ecPis-3 and ecPis-4, from orange-spotted grouper (Epinephelus coioides). The cDNA of the three piscidins with the 207, 216, and 231 nt open reading frame encoded respectively a 68-, 71-, and 76-amino acid preprotein consisting of the predicted signal peptide, and putative mature peptide and prodomain. The phylogenetic analysis indicated that multiple piscidin paralogues in one fish species are highly diversified, the analysis suggested that the piscidins should be a family belonging to the superfamily of ancient cationic, linear, and amphipathic host defence peptides widespread across invertebrate and vertebrate taxa comprising insect cecropins and ceratotoxins, and the amphibian dermaseptins. The synthetic putative mature peptides, ecPis-2S, ecPis-3S and ecPis-4S, had strong activities against bacterial and fungal species. EcPis-3S exhibited powerful activity against the infective stage of Cryptocaryon irritans, theronts. The full length ecPis-2 and ecPis-4 by removal of signal peptide, ecPis-2L and ecPis-4L respectively, had potency against bacterial, fungal and parasitic species. The peptide ecPis-2S was proved to exist in spleen of orange-spotted grouper by HPLC followed by ESI-LCMS analysis. Basal transcriptions of ecPis-2, ecPis-3 and ecPis-4 were detected not only in the potential sites of pathogen entry such as gills, skin and intestine, but also in tissues such as head kidney, trunk kidney, blood cells, and spleen with highly abundant immune cells, however different paralogues expressed constitutively with different levels in the tissues. In addition, the expression of ecPis-2, ecPis-3 and ecPis-4 was upregulated in orange-spotted grouper challenged by Vibrio Parahaemolyticus, in different tissues at different time point after bacteria injection. These results support ecPis-2, ecPis-3 and ecPis-4 being the important immune-related genes in orange-spotted grouper innate immune system and playing multifunctional and complementary roles following their structural and functional diversification, and expression pattern difference. Finally, this study facilitates the evaluation of ecPis-2S, 2L, ecPis-3S, and ecPis-4S, -4L as potential templates of therapeutic agents against pathogens.

Ultrastructural features of the tomont of Cryptocaryon irritans (Ciliophora: Prostomatea), a parasitic ciliate of marine fishes

Numerous studies have been conducted on the cellular morphology of Cryptocaryon irritans. However, details regarding the tomont stage of its life cycle remain lacking. In this study, we investigated the morphology of the tomont stage throughout encystment and cell division using light and electron microscopy. Results showed that there was no secretion of encystation-specific secretory vesicles or extrusomes during formation of the cyst wall. Instead, the synthesis and construction of the C. irritans cyst wall materials may involve molecular events at the pellicle. The somatic cilia and the cytostome were present during encystment and covered by the newly formed cyst wall. New somatic cilia were continuously created between old cilia and showed various lengths during cell division, a process that was similar to morphogenesis in many free-living ciliates. During cell division inside the tomont, dividing daughter cells formed temporary cell chains with no oral primordia before separating from each other into dissociative tomite precursors. The process of cell division may not be accompanied by stomatogenesis, and new oral primordia in offspring cells likely formed before the dividing cell chains split into dissociative spherical tomites. Mitochondrial autophagy was observed in encysting C. irritans cells. Numerous endosymbionts and Golgi structures were observed in the tomont cytoplasm. Cellular metabolic activity in the C. irritans tomont was quite high, with large amounts of materials or cellular organelles potentially being synthesized and prepared for the following infective theront stage.

Comparative transcriptional profile of the fish parasite Cryptocaryon irritans

BACKGROUND

Cryptocaryon irritans is an obligate ectoparasitic ciliate pathogen of marine fishes. It can infect most marine teleosts and cause heavy economic losses in aquaculture. There is currently no effective method of controlling this disease, and little information is available regarding the genes involved in its development and virulence. We aimed to investigate the distinct features of the three major life-cycle stages of C. irritans in terms of gene transcription level, and identify candidate vaccines/drug targets. We established a reference transcriptome of C. irritans by RNA-seq.

METHODS

Three cDNA libraries using total poly(A)⁺ mRNA isolated from trophonts, tomonts, and theronts was constructed and sequenced, respectively. Clean reads from the three stages were de novo assembled to generated unigene. Annotation of unigenes and transcriptomic comparison of three stages was performed.

RESULTS

Totals of 73.15, 62.23, and 109.57 million clean reads were generated from trophont, tomont, and theront libraries, respectively. After de novo assembly, 49,104 unigenes were obtained, including 9,253 unigenes with significant similarities to proteins from other ciliates. Transcriptomic comparisons revealed that 2,470 genes were differentially expressed among the three stages, including 2,011, 1,404, and 1,797 genes that were significantly differentially expressed in tomont/theront, tomont/trophont, and theront/trophont pairwise comparisons, respectively. Based on the results of hierarchical clustering, all differentially expressed genes (DEGs) were located in five major clusters. DEGs in clusters 1 and 2 were more highly expressed in tomonts than in other stages, DEGs in cluster 3 were dominant in the tomont and trophont stages, whereas clusters 4 and 5 included genes upregulated in the theront stage. In addition, Immobilization antigens (I-antigens) and proteases have long been considered major targets for vaccine development and potential drug targets in parasites, respectively. In the present study, nine putative I-antigens transcripts and 161 protease transcripts were found in the transcriptome of C. irritans.

CONCLUSION

It was concluded that DEGs enriched in tomonts were involved in cell division, to increase the number of theronts and ensure parasite continuity. DEGs enriched in theronts were associated with response to stimuli, whereas genes enriched in trophonts were related to nutrient accumulation and cell growth. In addition, the I-antigen and protease transcripts in our transcriptome could contribute to the development of vaccines or targeted drugs. Together, the results of the present study provide novel insights into the physiological processes of a marine parasitic ciliate.

Cryptocaryon irritans recombinant proteins as potential antigens for sero-surveillance of cryptocaryonosis

Cryptocaryonosis is a major problem for mariculture, and the absence of suitable sero-surveillance tools for the detection of cryptocaryonosis makes it difficult to screen Cryptocaryon irritans-infected fish, particularly asymptomatic fish. In this study, we proposed a serum-based assay using selected C. irritans proteins to screen infected and asymptomatic fish. Eight highly expressed genes were chosen from an earlier study on C. irritans expressed sequence tags and ciliate glutamine codons were converted to universal glutamine codons. The chemically synthesized C. irritans genes were then expressed in an Escherichia coli expression host under optimized conditions. Five C. irritans proteins were successfully expressed in E. coli and purified by affinity chromatography. These proteins were used as antigens in an enzyme-linked immunosorbent assay (ELISA) to screen sera from experimentally immunized fish and naturally infected fish. Sera from both categories of fish reacted equally well with the expressed C. irritans recombinant proteins as well as with sonicated theronts. This study demonstrated the utility of producing ciliate recombinant proteins in a heterologous expression host. An ELISA was successfully developed to diagnose infected and asymptomatic fish using the recombinant proteins as antigens.

Ultrastructure observation on the cells at different life history stages of Cryptocaryon irritans (Ciliophora: Prostomatea), a parasitic ciliate of marine fishes

Cells of Cryptocaryon irritans at different life history stages were studied using both light and electron microscopy. The characteristics of several organelles were revealed for the first time at the ultrastructural level. It was confirmed that the cytostome of trophonts, protomonts and theronts was surrounded by cilium–palp triplets rather than ciliary triplets. The nematodesmata underlying the circumoral dikinetids were single bundles, whereas these were always paired in Prorodontids. Toxicysts were present in late-stage tomonts and theronts, but were absent in trophonts and protomonts. We posited that toxicysts might play a role in infection and invasion of host-fish tissue by theronts. The adoral brosse was unlike that of any other family of the class Prostomatea based on its location and morphology. Membranous folds were present in trophonts, protomonts and theronts. These folds were longer and more highly developed in C. irritans than in exclusively free-living prostome ciliates suggesting that they might be linked to parasitism in C. irritans. Trophonts, protomonts and theronts had multiple contractile vacuoles. The basic ultrastructure of the contractile vacuole of C. irritans was similar to that of other kinetofragminophoran ciliates. They might play different roles in different stages of the life cycle since their ultrastructure varied among trophonts, protomonts and theronts.

Stress, antioxidant defence and mucosal immune responses of the large yellow croaker Pseudosciaena crocea challenged with Cryptocaryon irritans

To clarify the effects of a Cryptocaryon irritans infection on the stress, antioxidant and mucosal immune response of the large yellow croaker Pseudosciaena crocea, this study utilized C. irritans at dose of 12,000 (group I); 24,000 (group II); and 36,000 (group III) theronts/fish to infect large yellow croaker weighing 100 ± 10 g. The food intake, survival and relative infection intensity (RII); levels of reactive oxygen species (ROS), malondialdehyde (MDA) and vitamin C (VC), activities of super oxide dismutase (SOD) and catalase (CAT) in liver; variation patterns of lysozyme (LZM), alkaline phosphatase (AKP), complement component 3 (C3) and immunoglobulin M (IgM) levels in the body surface mucus at different time points after infection were compared. These results showed that with the increase of the infection dose and the passage of time, the food intake and survival of the fish gradually decreased. The final survival of the control group (0 theronts/fish), group I, group II, and group III was 100, 100, 96.67 ± 5.77, and 48.33 ± 7.64. Group I, II, and III stopped feeding respectively on the third, third and second days after infection. RII increased significantly with increased infection dose. The RII of the control group, group I, group II, and group III was 0, 0.73 ± 0.06, 1.30 ± 0.26, and 1.84 ± 0.02. With the infection dose increased, ROS contents showed an overall upward trend; MDA contents of the group I, group II and group III did not show significant changes at any timepoint compared with the control group; Activities of SOD and CAT and the overall VC levels in the liver of P. crocea dropped; LZM activity showed an overall upward trend; AKP activity increased first then dropped at each timepoint with its highest level appearing at group II; Complement C3 and IgM levels in body surface mucus were significantly increased. In conclusion, P. crocea has a strong ability to resist oxidative stress caused by the infection of C. irritans. The body surface mucus of P. crocea contains high levels of immune factors, which presented a rapid and significant response to the infection of C. irritans.

Immobilization antigen vaccine adjuvanted by parasitic heat shock protein 70C confers high protection in fish against cryptocaryonosis

The immobilization antigen (iAg) has been demonstrated as a protective immunogen against Cryptocaryon irritans infection. In this study, C-terminal domain of heat shock protein 70 cloned from C. irritans (Hsp70C) was tested for its immuno-stimulatory effects. The iAg and Hsp70C cDNAs were constructed independently in secretory forms and were encapsulated in chitosan nanoparticles. In the first immunization trial, grouper fingerlings orally intubated with iAg and iAg:Hsp70C presented 96% and 100% relative percent survival (RPS), respectively, after a lethal challenge. In the second trial, both iAg and iAg:Hsp70C groups showed 100% RPS and the skin trophont burden was significantly lowered. The iAg:Hsp70C still provides a significantly high protection of 51% RPS at 49 days post immunization, when an even more serious lethal infection occurs. RT-qPCR results showed that Hsp70C could up-regulate the expression of i) T cell markers: Cluster of Differentiation 8 alpha (CD8α) and CD4, ii) cytokine genes: Interferon gamma (IFNγ), Tumor Necrosis Factor alpha (TNFα) and Interleukin 12 p40 (IL-12/P40), iii) antibody genes: Immunoglobulin M heavy chain (IgMH) and IgTH, and iv) major histocompatibility complex (MHC-I & MHC-II), in the spleen of iAg:Hsp70C group. Furthermore, significantly high levels of iAg-specific IgM was detected in skin mucus which efficiently immobilized live theronts in iAg- and iAg:Hsp70C-immunized fish at 5 weeks post immunization. Hsp70C significantly increased the number of nonspecific CD8(+) skin leucocytes which exerted cytotoxicity against theronts, although cytotoxic activity showed no difference among the various groups. Because of this complementary cooperation of cellular and humoral immune responses, Hsp70C enhances the efficacy of iAg vaccine and constrains C. irritans infection. In view of the severe loss caused by cryptocaryonosis, application of this parasitic vaccine in farmed and ornamental fish, is worthy to be considered.

Proteomic analysis of differentially expressed proteins in the marine fish parasitic ciliate Cryptocaryon irritans

Cryptocaryoniasis is a severe disease of farmed marine fish caused by the parasitic ciliate Cryptocaryon irritans. This disease can lead to considerable economic loss, but studies on proteins linked to disease development and antigenic proteins for vaccine development have been relatively scarce to date. In this study, 53 protein spots with differential abundance, representing 12 proteins, were identified based on a pair-wise comparison among theronts, trophonts, and tomonts. Meanwhile, 33 protein spots that elicited serological responses in rabbits were identified, representing 9 proteins. In addition, 27 common antigenic protein spots reacted with grouper anti-sera, representing 10 proteins. Most of the identified proteins were involved in cytoskeletal and metabolic pathways. Among these proteins, actin and α-tubulin appeared in all three developmental stages with differences in molecular weights and isoelectric points; 4 proteins (vacuolar ATP synthase catalytic subunit α, mcm2-3-5 family protein, 26S proteasome subunit P45 family protein and dnaK protein) were highly expressed only in theronts; while protein kinase domain containing protein and heat shock protein 70 showed high levels of expression only in trophonts and tomonts, respectively. Moreover, actin was co-detected with 3 rabbit anti-sera while β-tubulin, V-type ATPase α subunit family protein, heat shock protein 70, mitochondrial-type hsp70, and dnaK proteins showed immunoreactivity with corresponding rabbit anti-sera in theronts, trophonts, and tomonts. Furthermore, β-tubulin, the metabolic-related protein enolase, NADH-ubiquinone oxidoreductase 75 kDa subunit, malate dehydrogenase, as well as polypyrimidine tract-binding protein, glutamine synthetase, protein kinase domain containing protein, TNFR/NGFR cysteine-rich region family protein, and vacuolar ATP synthase catalytic subunit α, were commonly detected by grouper anti-sera. Therefore, these findings could contribute to an understanding of the differences in gene expression and phenotypes among the different stages of parasitic infection, and might be considered as a source of candidate proteins for disease diagnosis and vaccine development.

Molecular cloning of NCCRP-1 gene from orange-spotted grouper (Epinephelus coioides) and characterization of NCCRP-1(+) cells post Cryptocaryon irritans infection

Nonspecific cytotoxic cells (NCCs) are an important cytotoxic cell population in the innate teleost immune system. The receptor designated "NCC receptor protein 1" (NCCRP-1) has been reported to be involved in the recognition and activation of NCCs. In this study, the full-length cDNA of Epinephelus coioides NCCRP-1 (ecnccrp-1) was cloned. The open reading frame (ORF) of ecnccrp-1 is 699 bp, encoding a 232 amino acid protein that includes proline-rich motifs at the N-terminus and is related to the F-box associated family. Although a bioinformatics analysis showed that EcNCCRP-1 had no signal peptide or transmembrane helices, a polyclonal antibody directed against recombinant EcNCCRP-1 efficiently labeled a membrane protein in the head kidney, detected with Western blot analysis, which indicated that the protein localized to the cell surface. RT-PCR showed that the constitutive expression of ecnccrp-1 was higher in the lymphoid organs, such as the trunk kidney, spleen, head kidney, and thymus, and lower in brain, heart, fat, liver, muscle, and skin. After infection with Cryptocaryon irritans, the transcription of ecnccrp-1 was analyzed at the infected sites (skin and gills) and in the systemic immune organs (head kidney and spleen). At the infected sites, especially the skin, ecnccrp-1 expression was upregulated at 6h post infection, reaching peak expression on day 3 post the primary infection. However, the expression patterns differed in the systemic immune organs. In the spleen, ecnccrp-1 was gradually increased in the early infection period and decreased sharply on day 3 post the primary infection, whereas in the head kidney, the transcription of ecnccrp-1 was depressed during almost the whole course of infection. An immunohistochemical analysis showed that EcNCCRP-1(+) cells accumulated at the sites of infection with C. irritans. These results suggested that NCCs were involved in the process of C. irritans infection in E. coioides.

Molecular characterization and functional analysis of TRAF6 in orange-spotted grouper (Epinephelus coioides)

Tumor necrosis factor receptor (TNFR)-associated factor 6 (TRAF6) is a crucial signal transducer in both the TNFR superfamily and Toll-like receptor/interleukin 1R family. Although significant progress has been made in clarifying the role of TRAF6 in mammals, the function of TRAF6 in fish is still poorly understood. In this study, we cloned the orange-spotted grouper (Epinephelus coioides) TRAF6 (EcTRAF6) cDNA, with an open reading frame of 1713bp encoding 570 amino acids. Sequence analysis indicated that EcTRAF6 contains the four characteristic domains conserved in the TRAF family, including an N-terminal RING finger, two zinc fingers, a coiled-coil domain, and a C-terminal MATH domain. Homology alignment and phylogenetic analysis demonstrated that EcTRAF6 shares high sequence identity with TRAF6 of other fish species. The EcTRAF6 gene contains seven exons and six introns, which is similar to the organization in ayu, but not in the common carp, human, or mouse (six exons and five introns). EcTRAF6 transcripts were broadly expressed in all tissues tested, and increased after infection with Cryptocaryon irritans. Intracellular localization showed EcTRAF6 was distributed mainly in the cytoplasm. Over-expression of wild type (WT) EcTRAF6, truncated forms of EcTRAF6, including ΔZinc finger 2 and ΔMATH, and a mutant of C78A activated NF-κB strongly in HEK293T cells; whereas truncations, including ΔRING, ΔZinc finger 1 and Δcoiled-coiled, and a mutant of K132R induced the activity of NF-κB slightly compared to WT EcTRAF6, implying the latter has a more crucial role in downstream signal transduction. Together, these results suggested EcTRAF6 functions like that of mammals to activate NF-κB, and it might have an important role in host defense against parasitic infections.

Growth, feed intake and immune responses of orange-spotted grouper (Epinephelus coioides) exposed to low infectious doses of ectoparasite (Cryptocaryon irritans)

To explore the effect of low-dose Cryptocaryon irritans infection on growth, feeding and antiparasitic immunity of orange-spotted grouper (Epinephelus coioides), this study utilized C. irritans at concentrations of 5500 theronts/fish (Group I, 1/10 of 96 h LC50) or 11,000 theronts/fish (Group II) to infect E. coioides weighing 38 g on average at week 0, 2 and 4, respectively. Food consumption was recorded daily; the fish were weighed weekly; serum immobilizing titer (SIT), and acid phosphatase (ACP), alkaline phosphatase (AKP), superoxide dismutase (SOD), lysozyme (LZM) activity were recorded every 2 weeks; the fish were treated with lethal dose (70,000 theronts/fish) of C. irritans in the 8th week and death number were recorded. The result shows that in the 1st week after the first infection, the fish's weight gain (WG), length gain (LG), and specific growth rate (SGR) dropped as parasite dose increased, and WG, SGR values were negative; while, after the 2nd and the 3rd infection, no significant differences were detected among the three groups. These results indicated that the 1st infection affected the fish most, while the following infections were protected by some immunity. In the 3rd, 7th, and 8th week, condition factor (CF) increased with the increased infectious dose, indicating that the parasite affected body length more than body weight. As the experiment went on, accumulated food consumption (AFC) of all three groups steadily grew (control > Group I > Group II). But on the 2nd day after the first infection, daily food consumption (DFC) of Group I and II significantly dropped, the decline of Group II was greater than that of Group I, DFC recovered in the following week, with Group I earlier than Group II. After the 2nd infection, DFC of Group I and II dropped again, Group II still dropped more than Group I, and both groups recovered on the 3rd day after infection. The 3rd infection caused no significant difference in week food consumption (WFC). These results indicated that a higher dose of infection causes a greater drop in FC and a slower recovery. Weekly feed conversion ratio (WFCR) values of Group I and II in the 1st week was negative; in the 2nd week, WFCR was lower in the group infected by a higher dose of parasite; while in the 3rd and following weeks, no significant pattern was observed. Accumulate feed conversion ratio (AFCR) dropped as the infectious dose increased (control > Group I > Group II), AFCR of Group I and II reached above 0 in the 2nd and 4th week, respectively. From the 4th week on, the inter-group AFCR of the 3 groups still took on a declining trend with the increased infectious dose but the gap became smaller. One week after the first infection, SIT of Group I and Group II were 0; one week after the 2nd infection, SIT reached up to 8 (Group I) and 16 (Group II) respectively; and after the 3rd infection, SIT further increased and peaked in the 7th week. When challenged by lethal dose of C. irritans, fish of all 3 groups began to die since the 3rd day after infection, and the final deaths were 14, 12 and 8 for the control group, Group I and Group II, respectively. ACP activity in the 1st, 5th, 7th but the 3rd week was higher in the experiment group than that in the control group, but no significant difference was detected between Group I and II throughout the experiment. AKP activity increased as the infectious dose increased, but the difference among the three groups gradually became less obvious in latter infections, and no significant difference can be detected in the end. SOD activity increased with infection dose at each time point, while both group I and group II had their SOD activities first increased and then decreased as times of infection increased. The LZM activity of the two infection groups increased as the infectious times increased. Combining the results on growth and feeding, we speculated that the fish's physiological condition stabilized after 3 rounds of infection. To sum up, low-dose infection by C. irritans can induce the fish's immunity, but at the cost of decreasing food intake, decreased food conversion, and lagged growth.

Effects of Cryptocaryon irritans infection on the survival, feeding, respiratory rate and ionic regulation of the marbled rockfish Sebastiscus marmoratus

To clarify the effects of a Cryptocaryon irritans infection on the physiological functions of the marbled rockfish Sebastiscus marmoratus, this study utilized C. irritans at concentrations of 2500; 5000; 7500; 10 000; 20 000; and 30 000 theronts/fish to infect marbled rockfish weighing 45±3 g. The survival rate, food intake, respiratory rate, serum ion concentrations and gill Na+/K+-ATPase activity were determined. With the increase of the infection concentration and the passage of time, the survival rate of the rockfish gradually decreased. The groups infected with more than 5000 theronts/fish had stopped feeding within 4 days. The respiratory rates of the fish in the groups infected with 2500 and 5000 theronts/fish initially increased and then decreased. In contrast, the respiratory rate of the fish in the groups infected with more than 7500 theronts/fish was elevated to levels significantly higher than the control group after 12 h. The Na+/K+-ATPase activity and serum Na+ and Cl− concentrations increased with increasing infection concentration. In conclusion, the physiological functions of the fish infected with low concentrations of C. irritans can be effectively restored, whereas a high concentration infection induced severe stress. The declined food intake and accelerated respiratory rate could be useful for an early warning system as important indicators.

Immune responses and immune-related gene expression profile in orange-spotted grouper after immunization with Cryptocaryon irritans vaccine

In order to elucidate the immune-protective mechanisms of inactivated Cryptocaryon irritans vaccine, different doses of C. irritans theronts were used to immunize orange-spotted grouper (Epinephelus coioides). We measured serum immobilization titer, blood leukocyte respiratory burst activity, serum alternative complement activity, and serum lysozyme activity weekly. In addition, the expression levels of immune-related genes such as interleukin-1β (IL-1β), tumor necrosis factor-α (TNF-α), major histocompatibility complexes I and II (MHC I and II), and transforming growth factor-β1 (TGF-β1) were determined in spleen and gills. The results showed that the immobilization titer, respiratory burst activity, and alternative complement activity of immunized fish were significantly increased, and the levels of the last two immune parameters in the high-dose vaccine group were significantly higher than in the low-dose vaccine group. Serum lysozyme activity in the high-dose vaccine group was significantly higher than in the PBS control group. Vaccination also regulated host immune-related gene expression. For example, at 2- and 3- weeks post immunization, IL-1β expression in the high-dose vaccine group spleen was significantly increased. At 4-weeks post immunization, the fish were challenged with a lethal dose of parasite, and the survival rates of high-dose vaccine group, low-dose vaccine group, PBS control group, and adjuvant control group were 80%, 40%, 0%, and 10% respectively. These results demonstrate that inactivated C. irritans vaccination improves specific and nonspecific immune responses in fish, enhancing their anti-parasite ability. These effects are vaccine antigen dose-dependent.

Immune protection of Mozambique tilapia (Oreochromis mossambicus) exposed to different infectious doses of ectoparasite (Cryptocaryon irritans)

The objectives of the present study were to standardize a reproducible infection procedure with Cryptocaryon irritans and to examine the effects of infectious dose level on the immune protection in Mozambique tilapia (Oreochromis mossambicus). This study demonstrated that direct enumeration of trophonts on the pectoral fin was useful to quantitatively assess immune protection against C. irritans. The number of trophonts on a pectoral fin was positively correlated with infectious dose of live theronts. Fish immunized by direct exposure under controlled laboratory conditions allowed for in depth examination of the effects of the degree of infectious dose on immune response. There was no significant positive correlation between the initial infectious dose and degree of immune responses. Mozambique tilapia initiated a strong immune protection by direct exposure with even a small number of parasites (e.g. 300 theronts per fish). Moreover, as the result of the protein analysis, we identified 28 kD proteins that could be responsible for the immobilizing antigen.

Orange-spotted grouper (Epinephelus coioides) TLR2, MyD88 and IL-1β involved in anti-Cryptocaryon irritans response

Cryptocaryon irritans is one of the most important ectoparasites of marine fish, and can have a devastating effect on aquacultured fish populations. The role of TLR signaling pathways in anti-parasitic immune responses is poorly understood in fish. In this paper, we first cloned Epinephelus coioides MyD88 full-length cDNA (EcMyD88) and its respective gene. The open reading frame (ORF) of cDNA is 873bp encoding 291 amino acid residues. Similar to other species, the EcMyD88 gene contains of five conserved exons and four diverse introns. The constitutive expression of EcMyD88 was detected in the gill, trunk kidney, head kidney, spleen, and heart in high concentrations, while the skin, brain, liver, and muscles contained much lower titers, indicating that EcMyD88 may play a crucial role in host innate immunologic surveillance. To identify the potential role of TLR pathways in fish anti-C. irritans immune responses, we chose three important molecules involved in anti-parasite responses, TLR2, MyD88 and IL-1β to indicate TLR pathway's signal-in, signal transduction, and signal-out functions, respectively. The expression profile of these three genes was detected in grouper infected by C. irritans. Results showed these molecules each experience significant changes within the skin, gill (two infected mucosal sites), head kidney and spleen (two systematic immune organs) after C. irritans infection. These findings indicate the TLR signaling pathway may play an important role in host defense against C. irritans.

Elicited cross-protection and specific antibodies in Mozambique tilapia (Oreochromis mossambicus) against two different immobilization serotypes of Cryptocaryon irritans isolated in Hawaii

The objective of this study was to determine whether immunization of Mozambique tilapia with different Cryptocaryon irritans i-antigen serotypes elicited cross-protection against challenge infection by both serotypes. Fish were directly exposed to live theronts of isolate W1 or isolate K1, that express different surface i-antigens. There was no significant difference in the number of trophonts infecting the fish between the two isolates, W1 and K1, following primary exposure. Serum from immunized fish exposed to live theronts showed higher immobilization titres and ELISA values against homologous isolates than to heterologous isolates after the primary exposure. However, mucus antibody did not immobilize theronts although the ELISA results clearly indicated that mucus antibodies recognizing C. irritans were generated. In a study with Western blot analyses, serum antibodies recognized only an antigen of the corresponding serotype and no proteins common to both serotypes were identified. Sequence analyses of 754 bases of rDNA nucleotide sequence including complete nuclear ribosomal ITS-1-5.8S rDNA-ITS-2 region were conducted and found to be identical for W1- and K1-isolates. These findings confirmed that both isolates were members of the species, C. irritans, and that rDNA analysis would not distinguish the two isolates. In conclusion, despite the fact that the immobilization assays and ELISA detected two serotypes in vitro, challenge assays provided evidence for only one type of C. irritans.

A novel protein isolated from the serum of rabbitfish (Siganus oramin) is lethal to Cryptocaryon irritans

The susceptibility of eight marine fish species cultured in South China were tested for infection by the parasitic ciliate, Cryptocaryon irritans, via a challenge examination and an immobilization assay. All species of fish (representing six different families) that we investigated were infected by C. irritans except the rabbitfish (Siganus oramin), which displayed resistance to C. irritans infection. The infection intensity of rabbitfish (0.92+/-0.97, p<0.05) was significantly lower while the immobilization titres of rabbitfish serum were significantly higher (44.51+/-22.98, p<0.05) than the other seven species of fish. Additionally, the serum of the rabbitfish presented a strong killing effect to C. irritans in vitro. Light microscopy, scanning electron microscopy and fluorescence microscopy confirmed that rabbitfish serum could induce the theront cilia fall off, rupture of the cell membrane because of the swell and rupture of the macronucleus. Rabbitfish serum could also induce the rupture of the trophont membrane and content efflux. Herein a novel antiparasitic protein (APP) was isolated and purified from the serum of rabbitfish (S. oramin) by using a series of salting-out, cation exchange chromatography and two step of reversed phase high performance liquid chromatography (RP-HPLC). Analysis of sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) showed that APP was a homogenous polymeric protein with an N-terminal amino acid sequence of SSVEKNLAACLRDND. Its monomeric molecular mass, determined by matrix-assisted laser desorption ionization tandem time-of-flight mass spectrometer (MALDI-TOF-TOF-MS), was found to be 61,739.87 Da. Results of homology analyses indicated that this protein was a newly discovered functional protein in the rabbitfish serum. Laser confocal fluorescence microscopy conformed that the action site of the APP was mainly on the cell membrane and nucleus of theront, which agreed with the results of light microscopy, fluorescence microscopy and scanning electron microscopy. These findings suggest that this protein may contribute considerably to the innate host defence mechanism to combat microbes of the rabbitfish.