Complement-mediated killing ofPhilasterides dicentrarchi(Ciliophora) by turbot serum: relative importance of alternative and classical pathways

Scuticociliatosis caused by Philasterides dicentrarchi

The ciliate Philasterides dicentrarchi has been previously identified as a new agent of scuticociliatosis in marine fish. The parasite can cause high mortalities in fish reared on farms or kept in aquariums. P. dicentrarchi is usually a free-living protozoan but can become an opportunistic histophagous parasite causing rapid lethal systemic infections in cultured fish. This review provides information about the morphology and biology of the scuticociliate P. dicentrarchi, as well as information about the pathological and immunological reactions of the host in response to the infection with the parasite. The epidemiology and the control strategies of the disease are also reviewed.

Potential Efficacy of Chitosan-Poly (Lactide-Co-Glycolide)-Encapsulated Trivalent Immersion Vaccine in Olive Flounder (Paralichthys olivaceus) Against Viral Hemorrhagic Septicemia Virus, Streptococcus parauberis Serotype I, and Miamiensis avidus (Scuticociliate)

Olive flounder (Paralichthys olivaceus) is the most valuable aquaculture species in Korea, corresponding to ~60% of its total production. However, infectious diseases often break out among farmed flounders, causing high mortality and substantial economic losses. Although some deleterious pathogens, such as Vibrio spp. and Streptococcus iniae, have been eradicated or contained over the years through vaccination and proper health management, the current disease status of Korean flounder shows that the viral hemorrhagic septicemia virus (VHSV), Streptococcus parauberis, and Miamiensis avidus are causing serious disease problem in recent years. Furthermore, these three pathogens have differing optimal temperature and can attack young fingerlings and mature fish throughout the year-round culture cycle. In this context, we developed a chitosan-poly(lactide-co-glycolide) (PLGA)-encapsulated trivalent vaccine containing formalin-killed VHSV, S. parauberis serotype-I, and M. avidus and administered it to olive flounder fingerlings by immersion route using a prime-boost strategy. At 35 days post-initial vaccination, three separate challenge experiments were conducted via intraperitoneal injection with the three targeted pathogens at their respective optimal temperature. The relative percentages of survival were 66.63%, 53.3%, and 66.75% in the group immunized against VHSV, S. parauberis serotype-I, and M. avidus, respectively, compared to the non-vaccinated challenge (NVC) control group. The immunized fish also demonstrated significantly (p < 0.05) higher specific antibody titers in serum and higher transcript levels of Ig genes in the mucosal and systemic tissues than those of NVC control fish. Furthermore, the study showed significant (p < 0.05) upregulation of various immune genes in the vaccinated fish, suggesting induction of strong protective immune response, ultimately leading to improved survival against the three pathogens. Thus, the formulated mucosal vaccine can be an effective prophylactic measure against VHS, streptococcosis, and scuticociliatosis diseases in olive flounder.

Transcriptomic analysis reveals innate immune mechanisms of an underlying parasite-resistant grouper hybrid (Epinephelus fuscogutatus × Epinephelus lanceolatus)

Hybridization is an artificial breeding strategy for generating potentially desirable offspring. Recently, a novel Hulong grouper hybrid (Epinephelus fuscogutatus × Epinephelus lanceolatus) yielded significant growth superiority over its parent. Improved innate immunity is considered as another desirable feature during hybridization. However, whether this Hulong grouper achieved disease resistance has not yet been revealed. In this study, we first examine the infection intensity of C. irritans in the Hulong grouper, and found that the Hulong grouper is less susceptible to C. irritans primary infection. A higher immobilization titer was found in the infected Hulong grouper at Day 2 when compared with the control grouper. Furthermore, severe hyperplasia was observed in the orange-spotted grouper, but not in the Hulong grouper's skin epidermis. To further understand the innate immune mechanism against C. irritans, we conducted a comparative transcriptome analysis of the Hulong grouper during the infection. There are 6464 differentially expressed genes (DEGs) identified in the skin between the control and infected Hulong grouper. This indicates that the innate immune components, such as the complement system, nicotinamide adenine dinucleotide phosphate (NADPH) oxidase, Interleukin 17 (IL-17) signaling pathway, and Toll-like receptor (TLR) signaling pathway were up-regulated during the infection. These results show that the C. irritans infection can induce a remarkable inflammatory response in the Hulong grouper. Moreover, a total of 75 pairs of orthologs with the ratio of nonsynonymous (Ka) to synonymous (Ks) substitutions ＞1, considered rapidly evolving genes (REGs), was identified between the Hulong and orange-spotted grouper. More critically, most REGs were enriched in the immune system, suggesting that rapid evolution of the immune system might occur in the Hulong grouper. These results provide a more comprehensive understanding of the innate immunity mechanism of the hybrid Hulong grouper.

Development of Fish Parasite Vaccines in the OMICs Era: Progress and Opportunities

Globally, parasites are increasingly being recognized as catastrophic agents in both aquaculture sector and in the wild aquatic habitats leading to an estimated annual loss between 1.05 billion and 9.58 billion USD. The currently available therapeutic and control measures are accompanied by many limitations. Hence, vaccines are recommended as the "only green and effective solution" to address these concerns and protect fish from pathogens. However, vaccine development warrants a better understanding of host-parasite interaction and parasite biology. Currently, only one commercial parasite vaccine is available against the ectoparasite sea lice. Additionally, only a few trials have reported potential vaccine candidates against endoparasites. Transcriptome, genome, and proteomic data at present are available only for a limited number of aquatic parasites. Omics-based interventions can be significant in the identification of suitable vaccine candidates, finally leading to the development of multivalent vaccines for significant protection against parasitic infections in fish. The present review highlights the progress in the immunobiology of pathogenic parasites and the prospects of vaccine development. Finally, an approach for developing a multivalent vaccine for parasitic diseases is presented. Data sources to prepare this review included Pubmed, google scholar, official reports, and websites.

Interactions between the Parasite Philasterides dicentrarchi and the Immune System of the Turbot Scophthalmus maximus. A Transcriptomic Analysis

The present study analyses the interactions between Philasterides dicentrarchi (a ciliate parasite that causes high mortalities in cultured flatfish) and the peritoneal cells of the turbot Scophthalmus maximus during an experimental infection. The transcriptomic response was evaluated in the parasites and in the fish peritoneal cells, at 1, 2 and 4 h post-infection (hpi) in turbot injected intraperitoneally (ip) with 10⁷ ciliates and at 12 and 48 hpi in turbot injected ip with 10⁵ ciliates. Numerous genes were differentially expressed (DE) in P. dicentrarchi, relative to their expression in control ciliates (0 hpi): 407 (369 were up-regulated) at 1 hpi, 769 (415 were up-regulated) at 2 hpi and 507 (119 were up-regulated) at 4 hpi. Gene ontology (GO) analysis of the DE genes showed that the most representative categories of biological processes affected at 1, 2 and 4 hpi were biosynthetic processes, catabolic processes, biogenesis, proteolysis and transmembrane transport. Twelve genes of the ABC transporter family and eight genes of the leishmanolysin family were DE at 1, 2 and 4 hpi. Most of these genes were strongly up-regulated (UR), suggesting that they are involved in P. dicentrarchi infection. A third group of UR genes included several genes related to ribosome biogenesis, DNA transcription and RNA translation. However, expression of tubulins and tubulin associated proteins, such as kinesins or dyneins, which play key roles in ciliate division and movement, was down-regulated (DR). Similarly, genes that coded for lysosomal proteins or that participate in the cell cycle mitotic control, glycolysis, the Krebs cycle and/or in the electron transport chain were also DR. The transcriptomic analysis also revealed that in contrast to many parasites, which passively evade the host immune system, P. dicentrarchi strongly stimulated turbot peritoneal cells. Many genes related to inflammation were DE in peritoneal cells at 1, 2 and 4 hpi. However, the response was much lower at 12 hpi and almost disappeared completely at 48 hpi in fish that were able to kill P. dicentrarchi during the first few hpi. The genes that were DE at 1, 2 and 4 hpi were mainly related to the apoptotic process, the immune response, the Fc-epsilon receptor signalling pathway, the innate immune response, cell adhesion, cell surface receptors, the NF-kappaB signalling pathway and the MAPK cascade. Expression of toll-like receptors 2, 5 and 13 and of several components of NF-κB, MAPK and JAK/STAT signalling pathways was UR in the turbot peritoneal cells. Genes expressing chemokines and chemokine receptors, genes involved in prostaglandin and leukotriene synthesis, prostaglandins, leukotriene receptors, proinflammatory cytokines and genes involved in apoptosis were strongly UR during the first four hours of infection. However, expression of anti-inflammatory cytokines such as Il-10 and lipoxygenases with anti-inflammatory activity (i.e., arachidonate 15-lipoxygenase) were only UR at 12 and/or 48 hpi, indicating an anti-inflammatory state in these groups of fish. In conclusion, the present study shows the regulation of several genes in P. dicentrarchi during the early stages of infection, some of which probably play important roles in this process. The infection induced a potent acute inflammatory response, and many inflammatory genes were regulated in peritoneal cells, showing that the turbot uses all the protective mechanisms it has available to prevent the entry of the parasite.

The coagulation system helps control infection caused by the ciliate parasite Philasterides dicentrarchi in the turbot Scophthalmus maximus (L.)

Many studies have shown that coagulation systems play an important role in the defence against pathogens in invertebrates and vertebrates. In vertebrates, particularly in mammals, it has been established that the coagulation system participates in the entrapment of pathogens and activation of the early immune response. However, functional studies investigating the importance of the fish coagulation system in host defence against pathogens are scarce. In the present study, injection of turbot (Scopthalamus maximus) with the pathogenic ciliate Philasterides dicentrarchi led to the formation of macroscopic intraperitoneal clots in the fish. The clots contained abundant, immobilized ciliates, many of which were lysed. We demonstrated that the plasma clots immobilize and kill the ciliates in vitro. To test the importance of plasma clotting in ciliate killing, we inhibited the process by adding a tetrapeptide known to inhibit fibrinogen/thrombin clotting in mammals. Plasma tended to kill P. dicentrarchi slightly faster when clotting was inhibited by the tetrapeptide, although the total mortality of ciliates was similar. We also found that kaolin, a particulate activator of the intrinsic pathway in mammals, accelerates plasma clotting in turbot. In addition, PMA-stimulated neutrophils, living ciliates and several ciliate components such as cilia, proteases and DNA also displayed procoagulant activity in vitro. Injection of fish with the ciliates generated the massive release of neutrophils to the peritoneal cavity, with formation of large aggregates in those fish with live ciliates in the peritoneum. We observed, by SEM, numerous fibrin-like fibres in the peritoneal exudate, many of which were associated with peritoneal leukocytes and ciliates. Expression of the CD18/CD11b gene, an integrin associated with cell adhesion and the induction of fibrin formation, was upregulated in the peritoneal leukocytes. In conclusion, the findings of the present study show that P. dicentrarchi induces the formation of plasma clots and that the fish coagulation system may play an important role in immobilizing and killing this parasite.

Polyclonal anti-Candida antibody improves phagocytosis and overall outcome in zebrafish model of disseminated candidiasis

Fungal infections are a major cause of animal and plant morbidity and mortality worldwide. Effective biological therapeutics could complement current antifungal drugs, but understanding of their in vivo mechanisms has been hampered by technical barriers to intravital imaging of host-pathogen interactions. Here we characterize the fungal infection of zebrafish as a model to understand the mechanism-of-action for biological antifungal therapeutics through intravital imaging of these transparent animals. We find that non-specific human IgG enhances phagocytosis by zebrafish phagocytes in vivo. Polyclonal anti-Candida antibodies enhance containment of fungi in vivo and promote survival. Analysis suggests that early phagocytic containment is a strong prognostic indicator for overall survival. Although polyclonal anti-Candida antibodies protect against disease, this is not necessarily the case for individual monoclonal anti-Candida antibodies. Thus, the zebrafish appears to provide a useful model host for testing if a biological therapeutic promotes phagocytosis in vivo and enhances protection against candidemia.

Combined antiparasitic and anti-inflammatory effects of the natural polyphenol curcumin on turbot scuticociliatosis

The histiophagous scuticociliate Philasterides dicentrarchi is the aetiological agent of scuticociliatosis, a parasitic disease of farmed turbot. Curcumin, a polyphenol from Curcuma longa (turmeric), is known to have antioxidant and anti-inflammatory properties. We investigated the in vitro effects of curcumin on the growth of P. dicentrarchi and on the production of pro-inflammatory cytokines in turbot leucocytes activated by parasite cysteine proteases. At 100 μm, curcumin had a cytotoxic effect and completely inhibited the growth of the parasite. At 50 μm, curcumin inhibited the protease activity of the parasite and expression of genes encoding two virulence-associated proteases: leishmanolysin-like peptidase and cathepsin L-like. At concentrations between 25 and 50 μm, curcumin inhibited the expression of S-adenosyl-L-homocysteine hydrolase, an enzyme involved in the biosynthesis of the amino acids methionine and cysteine. At 100 μm, curcumin inhibited the expression of the cytokines tumour necrosis factor-alpha (TNF-α) and interleukin-1 beta (IL-1β) produced in turbot leucocytes activated by parasite proteases. Results show that curcumin has a dual effect on scuticociliatosis: an antiparasitic effect on the catabolism and anabolism of ciliate proteins, and an anti-inflammatory effect that inhibits the production of proinflammatory cytokines in the host. The present findings suggest the potential usefulness of this polyphenol in treating scuticociliatosis.

Role of H(+)-pyrophosphatase activity in the regulation of intracellular pH in a scuticociliate parasite of turbot: Physiological effects

The scuticociliatosis is a very serious disease that affects the cultured turbot, and whose causal agent is the anphizoic and marine euryhaline ciliate Philasterides dicentrarchi. Several protozoans possess acidic organelles that contain high concentrations of pyrophosphate (PPi), Ca(2+) and other elements with essential roles in vesicular trafficking, pH homeostasis and osmoregulation. P. dicentrarchi possesses a pyrophosphatase (H(+)-PPase) that pumps H(+) through the membranes of vacuolar and alveolar sacs. These compartments share common features with the acidocalcisomes described in other parasitic protozoa (e.g. acid content and Ca(2+) storage). We evaluated the effects of Ca(2+) and ATP on H (+)-PPase activity in this ciliate and analyzed their role in maintaining intracellular pH homeostasis and osmoregulation, by the addition of PPi and inorganic molecules that affect osmolarity. Addition of PPi led to acidification of the intracellular compartments, while the addition of ATP, CaCl2 and bisphosphonates analogous of PPi and Ca(2+) metabolism regulators led to alkalinization and a decrease in H(+)-PPase expression in trophozoites. Addition of NaCl led to proton release, intracellular Ca(2+) accumulation and downregulation of H(+)-PPase expression. We conclude that the regulation of the acidification of intracellular compartments may be essential for maintaining the intracellular pH homeostasis necessary for survival of ciliates and their adaptation to salt stress, which they will presumably face during the endoparasitic phase, in which the salinity levels are lower than in their natural environment.

Effects of the modified Huanglian Jiedu decoction on the disease resistance in grey mullet (Mugil cephalus) to Lactococcus garvieae

Lactococcosis is prevalent on grey mullet (Mugil cephalus) in Hong Kong aquaculture resulting in serious economic loss. A compound formulation of Traditional Chinese Medicines (TCM) (modified Huanglian Jiedu decoction (HLJDD)) comprising Rhizoma coptidis, Radix scutellaria, Cortex phellodendri, Fructus gardeniae, Fructus forsythiae and Flos lonicerae japonicae (in a ratio of 3:2:2:3:3:5) were applied as feed supplements to deal with the disease. The Nitroblue tetrazolium activity in blood, bactericidal activity and total immunoglobulin in plasma were significantly enhanced after feeding 1% of this TCM for 28 days. The disease resistances to Lactococcus garvieae in 1% and 2% TCM feeding groups were significantly enhanced. In the in vitro study, the modified HLJDD also activated the plasma bactericidal activities (p<0.01). Based on this study, 1% modified HLJDD feeding for 28 days may be an optimal dose to prevent L. garvieae infection and could be used in aquaculture industries.

Reprint of "fish immunity to scuticociliate parasites"

Some species of scuticociliates (Ciliophora) behave as facultative parasites and produce severe mortalities in cultured fish. Pathogenic scuticociliates can cause surface lesions and can also penetrate inside the body, where they feed on tissue and proliferate in the blood and most internal organs, killing the host in a few days. In this review, we describe the current knowledge on the protective role of fish cellular and humoral immune responses against these parasites. Immune humoral factors, especially complement, are of particular importance in defending fish against these ciliates. However, knowledge about how the fish immune system responds to scuticociliates is scant, and the cellular and molecular events that occur during the response are not known. We also describe the possible mechanisms used by scuticociliates to avoid or resist the defensive reaction of the host. For example, the release of proteases can help parasites enter fish tissues and impair the fish cellular and humoral responses. Several vaccine formulations containing scuticociliates have induced a good antibody response and protection in fish immunized and challenged with homologous strains of particular species. However, protection was not achieved in fish immunized and challenged with heterologous strains, and the antigens involved in protection and the antigenic differences between heterologous strains have not yet been determined.

Fish immunity to scuticociliate parasites

Some species of scuticociliates (Ciliophora) behave as facultative parasites and produce severe mortalities in cultured fish. Pathogenic scuticociliates can cause surface lesions and can also penetrate inside the body, where they feed on tissue and proliferate in the blood and most internal organs, killing the host in a few days. In this review, we describe the current knowledge on the protective role of fish cellular and humoral immune responses against these parasites. Immune humoral factors, especially complement, are of particular importance in defending fish against these ciliates. However, knowledge about how the fish immune system responds to scuticociliates is scant, and the cellular and molecular events that occur during the response are not known. We also describe the possible mechanisms used by scuticociliates to avoid or resist the defensive reaction of the host. For example, the release of proteases can help parasites enter fish tissues and impair the fish cellular and humoral responses. Several vaccine formulations containing scuticociliates have induced a good antibody response and protection in fish immunized and challenged with homologous strains of particular species. However, protection was not achieved in fish immunized and challenged with heterologous strains, and the antigens involved in protection and the antigenic differences between heterologous strains have not yet been determined.

Gene expression profiles of spleen, liver, and head kidney in turbot (Scophthalmus maximus) along the infection process with Philasterides dicentrarchi using an immune-enriched oligo-microarray

We evaluated the expression profiles of turbot in spleen, liver, and head kidney across five temporal points of the Philasterides dicentrarchi infection process using an 8x15K Agilent oligo-microarray. The microarray included 2,176 different fivefold replicated gene probes designed from a turbot 3' sequenced EST database. We were able to identify 221 differentially expressed (DE) genes (8.1% of the whole microarray), 113 in spleen, 83 in liver, and 90 in head kidney, in at least 1 of the 5 temporal points sampled for each organ. Most of these genes could be annotated (83.0%) and functionally categorized using GO terms (69.1%) after the additional sequencing of DE genes from the 5' end. Many DE genes were related to innate and acquired immune functions. A high proportion of DE genes were organ-specific (70.6%), although their associated GO functions showed notable similarities in the three organs. The most striking difference in functional distribution was observed between the up- and downregulated gene groups. Upregulated genes were mostly associated to immune functions, while downregulated ones mainly involved metabolism-related genes. Genetic response appeared clustered in a few groups of genes with similar expression profiles along the temporal series. The information obtained will aid to understand the turbot immune response and will specifically be valuable to develop strategies of defense to P. dicentrarchi to achieve more resistant broodstocks for turbot industry.

Poly D,L-lactide-co-glycolic acid (PLGA)-encapsulated vaccine on immune system in Epinephelus bruneus against Uronema marinum

We investigate the efficacy of poly D,L-lactide-co-glycolic acid (PLGA)-encapsulated vaccine on innate and adaptive immune response in kelp grouper (Epinephelus bruneus) against Uronema marinum at weeks 1, 2, and 4. The respiratory burst (RB) activity, complement activity, and α2-macroglobulin were significantly enhanced in fish immunization with vaccine on week 4 whereas vaccine and PLGA-encapsulated vaccine from weeks 1 to 4. The serum lysozyme activity, antiprotease activity, and antibody level were significantly enhanced in fish immunized with vaccine and PLGA-encapsulated vaccine on weeks 2 and 4. The cumulative mortality was low in PLGA-encapsulated vaccine with 20% whereas high in PLGA and vaccine with 40% and 30%. The results from the present study suggest that PLGA-encapsulated vaccine is useful for further design of immunoprophylatic nano formulation against scuticociliatosis.

Poly D,L-lactide-co-glycolic acid-liposome encapsulated ODN on innate immunity in Epinephelus bruneus against Vibrio alginolyticus

The efficacy of poly D,L-lactide-co-glycolic acid (PLGA)-liposome (L) encapsulated oligodeoxynucleotides with unmethylated deoxycytidyl-deoxyguanosine motifs (CpG-ODNs) on innate and adaptive immune response and disease resistance in kelp grouper (Epinephelus bruneus) against Vibrio alginolyticus at weeks 1, 2, and 4 is reported. The superoxide dismutase (SOD), respiratory burst, and lysozyme activities significantly increased in E. bruneus when immunized with ODN, PLGA+ODN, L+ODN, and PLGA+L+ODN on weeks 2 and 4. The serum complement activity was significantly enhanced with L+ODN and PLGA+L+ODN on week 1 while it increased with PLGA+ODN, L+ODN, and PLGA+L+ODN on weeks 2 and 4. The antibody titre consistently was increased with PLGA or L encapsulated with ODN (PLGA+ODN, L+ODN, and PLGA+L+ODN) from weeks 1 to 4. The cumulative mortality was 20% each in PLGA+ODN administered groups and 15% each in ODN, L+ODN, and PLGA+L+ODN groups during a period of 30 days. The present study suggests that PLGA-liposome encapsulated ODN has the potential to modulate the immune system and can serve as a useful tool for further design of immunoprophylatic nano drug formulations against bacterial diseases.

Turbot resistance to Philasterides dicentrarchi is more dependent on humoral than on cellular immune responses

Philasterides dicentrarchi is a ciliate that causes high mortalities in cultured turbot, Psetta maxima (L.). This pathogen displays high phagocytic activity and after entering the body it multiplies and feeds on host cells and tissue components. In previous studies, we found that complement, activated through the classical pathway, is a potent killer of P. dicentrarchi. Here, we compared the killing activity of turbot leucocytes and humoral factors against two virulent isolates of P. dicentrarchi, in order to determine the importance of leucocytes in the defence against this pathogen. Components of P. dicentrarchi (ciliary and membrane) stimulated turbot leucocytes, and increased the respiratory burst, degranulation and the expression of pro-inflammatory cytokines. We tested the susceptibility of ciliates to reactive oxygen and nitrogen species, by incubating them with different oxidative systems (H(2)O(2), Fe/ascorbate, which induces lipid peroxidation, an O(2)(-) donor (XOD/HX), an NO donor (SNAP) and an ONOO(-) donor (SIN-1)), for 24h. Both isolates were susceptible to high concentrations of H(2)O(2,) Fe/ascorbate, XOD/HX, and SIN-1 but were resistant to incubation with SNAP. Leucocytes became strongly activated when they were in contact with or were phagocytosed by the ciliate. Incubation of P. dicentrarchi with a combination of fresh serum and specific antibodies killed most of the ciliates, but the addition of leucocytes to ciliate cultures did not increase the toxicity to the ciliates. On the contrary, the number of ciliates increased when leucocytes were added to the culture because the ciliates fed on them. Despite being activated, leucocytes did not produce sufficiently high concentrations of toxic substances to kill the parasite. The most virulent isolate was that which induced greatest activation of leucocytes but was least susceptible to complement. We concluded that humoral factors such as complement (activated through the classical pathway) are critical for fish defence against P. dicentrarchi and that cellular responses appear to play a minor role, if any, in defence against this ciliate.