Disentangling the determinants of symbiotic species richness in native and invasive gammarids (Crustacea, Amphipoda) of the Baltic region.

Dispersal of alien species is a global problem threatening native biodiversity. Co-introduction of non-native parasites and pathogens adds to the severity of this threat, but this indirect impact has received less attention. To shed light on the key factors determining the richness of microorganisms in native and invasive host species, we compared symbiotic (parasitic and epibiotic) communities of gammarids across different habitats and localities along the Baltic coast of Poland. Seven gammarid species, two native and five invasive, were sampled from 16 freshwater and brackish localities. Sixty symbiotic species of microorganisms of nine phyla were identified. This taxonomically diverse species assemblage of symbionts allowed us to assess the effect of host translocation and regional ecological determinants driving assembly richness in the gammarid hosts. Our results revealed that (i) the current assemblages of symbionts of gammarid hosts in the Baltic region are formed by native and co-introduced species; (ii) species richness of the symbiotic community was higher in the native Gammarus pulex than in the invasive hosts, probably reflecting a process of species loss by invasive gammarids in the new area and the distinct habitat conditions occupied by G. pulex and invasive hosts; (iii) both host species and locality were key drivers shaping assembly composition of symbionts, whereas habitat condition (freshwater versus brackish) was a stronger determinant of communities than geographic distance; (iv) the dispersion patterns of the individual species richness of symbiotic communities were best described by Poisson distributions; in the case of an invasive host, the dispersion of the rich species diversity may switch to a right-skewed negative binomial distribution, suggesting a host-mediated regulation process. We believe this is the first analysis of the symbiotic species richness in native and invasive gammarid hosts in European waters based on original field data and a broad range of taxonomic groups including Microsporidia, Choanozoa, Ciliophora, Apicomplexa, Platyhelminthes, Nematoda, Nematomorha, Acanthocephala and Rotifera, to document the patterns of species composition and distribution.

Molecular characterization and transcriptional regulation of two types of H+-pyrophosphatases in the scuticociliate parasite Philasterides dicentrarchi.

Proton-translocating inorganic pyrophosphatases (H+-PPases) are an ancient family of membrane bound enzymes that couple pyrophosphate (PPi) hydrolysis to H+ translocation across membranes. In this study, we conducted a molecular characterization of two isoenzymes (PdVP1 and PdVP2) located in respectively the alveolar sacs and in the membranes of the intracellular vacuoles of a scuticociliate parasite (Philasterides dicentrarchi) of farmed turbot. We analyzed the genetic expression of the isoenzymes after administration of antiparasitic drugs and after infection in the host. PdVP1 and PdVP2 are encoded by two genes of 2485 and 3069 bp, which respectively contain 3 and 11 exons and express proteins of 746 and 810 aa of molecular mass 78.9 and 87.6 kDa. Topological predictions from isoenzyme sequences indicate the formation of thirteen transmembrane regions (TMRs) for PdVP1 and seventeen TMRs for PdVP2. Protein structure modelling indicated that both isoenzymes are homodimeric, with three Mg2+ binding sites and an additional K+ binding site in PdVP2. The levels of identity and similarity between the isoenzyme sequences are respectively 33.5 and 51.2%. The molecular weights of the native proteins are 158 kDa (PdVP1) and 178 kDa (PdVP2). The isoenzyme sequences are derived from paralogous genes that form a monophyletic grouping with other ciliate species. Genetic expression of the isoenzymes is closely related to the acidification of alveolar sacs (PdVP1) and intracellular vacuoles (PdVP2): antiparasitic drugs inhibit transcription, while infection increases transcription of both isoenzymes. The study findings show that P. dicentrarchi possesses two isoenzymes with H+-PPase activity which are located in acidophilic cell compartment membranes and which are activated during infection in the host and are sensitive to antiparasitic drugs. The findings open the way to using molecular modelling to design drugs for the treatment of scuticociliatosis.

Comentario sobre: «Aportes de la tomografía de coherencia óptica Visante(R) y la ecografía ocular en el diagnóstico y seguimiento del síndrome de efusión ciliocoroidea bilateral secundario a topiramato» / Comment on: «Contribution of the Visante(R) OCT and B-scan ultrasound in the diagnosis and follow up of a topiramate-induced bilateral ciliochoroidal effusion syndrome»

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Antibody responses to chimeric peptides derived from parasite antigens in mice and other animal species.

Peptide vaccines constitute an interesting alternative to classical vaccines due to the possibility of selecting specific epitopes, easy of production and safety. However, an inadequate design may render these peptides poorly immunogenic or lead to undesirable outcomes (e.g., formation of B neoepitopes). As an approach to vaccine development, we evaluated the antibody response to chimeras composed of two or three known B epitopes from Trichinella and Fasciola, and several linkers (GSGSG, GPGPG and KK) in species as different as mice, sheep and turbot. All these species could mount an effective immune response to the short chimeric peptides. Nevertheless, this response depended on several factors including a favorable orientation of B-cell epitopes, adequateness of linkers and/or probability of formation of T neoepitopes. We also observed that, at least in mice, the inclusion of a decoy epitope may have favorable consequences on the antibody response to other epitopes in the chimera.

Turbot (Scophthalmus maximus) Nk-lysin induces protection against the pathogenic parasite Philasterides dicentrarchi via membrane disruption.

P. dicentrarchi is one of the most threatening pathogens for turbot aquaculture. This protozoan ciliate is a causative agent of scuticociliatosis, which is a disease with important economic consequences for the sector. Neither vaccines nor therapeutic treatments are commercially available to combat this infection. Numerous antimicrobial peptides (AMPs) have demonstrated broad-spectrum activity against bacteria, viruses, fungi, parasites and even tumor cells; an example is Nk-lysin (Nkl), which is an AMP belonging to the saposin-like protein (SAPLIP) family with an ability to interact with biological membranes. Following the recent characterization of turbot Nkl, an expression plasmid encoding Nkl was constructed and an anti-Nkl polyclonal antibody was successfully tested. Using these tools, we demonstrated that although infection did not clearly affect nkl mRNA expression, it induced changes at the protein level. Turbot Nkl had the ability to inhibit proliferation of the P. dicentrarchi parasite both in vivo and in vitro. Moreover, a shortened peptide containing the active core of turbot Nkl (Nkl71-100) was synthesized and showed high antiparasitic activity with a direct effect on parasite viability that probably occurred via membrane disruption. Therefore, the nkl gene may be a good candidate for genetic breeding selection of fish, and either the encoded peptide or its shortened analog is a promising antiparasitic treatment in aquaculture.

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.

Protocol for cryopreservation of the turbot parasite Philasterides dicentrarchi (Ciliophora, Scuticociliatia).

Philasterides dicentrarchi is a free-living marine ciliate that can become an endoparasite that causes a severe disease called scuticociliatosis in cultured fish. Long-term maintenance of this scuticociliate in the laboratory is currently only possible by subculture, with periodic passage in fish to maintain the virulence of the isolates. In this study, we developed and optimized a cryopreservation protocol similar to that used for the long-term storage of scuticociliates of the genus Miamiensis. The cryogenic medium comprised ATCC medium 1651 and a combination of 11% dimethylsulfoxide and 5% glycerol. We have verified that the most important factor ensuring the efficiency of the cryopreservation procedure is the growth phase of the culture, and that ciliates should be cryopreserved at the stationary phase (around the sixth day of culture). The cryopreservation protocol described here can be used for all strains of P. dicentrarchi as well as commercial strains of Miamiensis and enables the virulence of the strains to be maintained. Finally, this cryopreservation protocol has been shown to be more effective than others routinely applied to scuticociliates, yielding a higher survival rate with a lower initial concentration of ciliates. The results obtained indicate that the cropreservation protocol enables the long-term storage of scuticociliate parasites while maintaining the virulence of the isolates. The protocol is therefore suitable for use in vaccine production and related studies.

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-1ß) 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.

Particle size and traffic of phagocytes between the turbot peritoneal cavity and lymphoid organs.

New adjuvants based on microparticles are being developed for use in fish vaccines. The size of the microparticles may affect the immune response generated, as the adjuvant can either be retained at the site of injection or transported to lymphoid organs. The objectives of this study were to evaluate the maximum size of particles that can be exported out of the cavity, to determine the phagocytosis kinetics and to establish the routes whereby particle-containing cells move from the peritoneal cavity after injection. Fish were injected intraperitoneally with fluorescent cyclodextrins or with fluorescent particles of different size (0.1-10 µm). Phagocytes containing beads of size 4 µm or larger did not reach lymphoid organs, although some were able to cross the peritoneal mesothelium. The number of free peritoneal neutrophils and macrophage-like cells containing beads peaked at 6 and 24 h respectively, and the numbers then decreased quickly, indicating migration of cells to the peritoneum or other body areas. Migration of cells containing beads mainly occurs through the visceral peritoneum. These cells were found on the latero-ventral surfaces of the peritoneal folds that connect the visceral organs. Except for some vascularised areas, the surfaces of liver, stomach and intestine were devoid of particle-containing cells. Some cells containing beads were also found attached to the parietal peritoneum, although in lower numbers than in the visceral peritoneum. Such cells were also found in high numbers in the spleen and kidney 6 h post injection. Because cells containing phagocytosed material quickly become attached to the peritoneum or migrate to lymphoid organs, the immune response generated by a vaccine or by an inflammatory stimulus should probably be evaluated in attached cells as well as in free peritoneal cells.

La ultrabiomicroscopía en la acomodación

El objetivo de este estudio es conocer el comportamiento biométrico de las estructuras oculares que participan en la acomodación. Para estudiar los cambios biométricos de las estructuras del segmento anterior del globo ocular, in vivo y durante la acomodación, hemos elegido el ultrasonido de alta frecuencia. Se estudiaron 75 pacientes divididos en 3 grupos, según su rango etario: grupo 1, de 30 a 45 años; grupo 2, de 46 a 60 años, y grupo 3, de 61 a 70 años. Los resultados obtenidos nos muestran cómo varían la forma y la dimensión de las estructuras del segmento anterior y las relaciones entre sí, permitiendo conocer sus comportamientos en la pérdida de la acomodación de los distintos grupos etarios estudiados. Esta técnica permite una evaluación biométrica, morfológica y funcional del segmento anterior, incluyendo la cápsula posterior del cristalino y los cambios del cuerpo ciliar (que no hemos logrado estudiar con otras técnicas). La ultrabiomicroscopía posibilita la visualización durante la acomodación de las cápsulas anterior y posterior del cristalino, la zónula con sus inserciones en la cápsula ecuatorial y el cuerpo ciliar, y la úvea anterior en relación con el cristalino. Las imágenes ultrasónicas obtenidas representan las estructuras del segmento anterior y sus modificaciones in vivo y en tiempo real durante la acomodación. El ultrasonido ha mostrado ser el método diagnóstico más adecuado para esta investigación.(AU)

The aim of this study is to understand the biometric behaviour of the ocular structures involved during accommodation. We chose high-frequency ultrasound to study ocular globe anterior segment structures biometric changes in vivo and during accommodation. This technique allows biometric screening, morphological and functional anterior segment, including the posterior lens capsule and changes of the ciliary body that we have failed to study with other techniques. The ultrabiomicroscopy allows visualization during accommodation of the anterior and posterior capsules of the lens, the zonules with insertions in the equatorial capsule and the ciliary body and anterior uvea relative to the lens. The ultrasound images obtained represent the anterior segment structures and their modifi cations in vivo and in real time during accommodation. We studied 75 patients divided into three groups according to age range: Group 1 from 30 to 45 years, Group 2 of 46-60 years, and Group 3 of 61-70 years. The results obtained show how they vary the shape and size of anterior segment structures and relationships with each other, allowing to know their behavior in the loss of accommodation of different age groups studied Ultrasound has proven to be the most appropriate diagnostic method for this research.(AU)

La ultrabiomicroscopía en la acomodación / The ultrabiomicroscopy during the accommodation

El objetivo de este estudio es conocer el comportamiento biométrico de las estructuras oculares que participan en la acomodación. Para estudiar los cambios biométricos de las estructuras del segmento anterior del globo ocular, in vivo y durante la acomodación, hemos elegido el ultrasonido de alta frecuencia. Se estudiaron 75 pacientes divididos en 3 grupos, según su rango etario: grupo 1, de 30 a 45 años; grupo 2, de 46 a 60 años, y grupo 3, de 61 a 70 años. Los resultados obtenidos nos muestran cómo varían la forma y la dimensión de las estructuras del segmento anterior y las relaciones entre sí, permitiendo conocer sus comportamientos en la pérdida de la acomodación de los distintos grupos etarios estudiados. Esta técnica permite una evaluación biométrica, morfológica y funcional del segmento anterior, incluyendo la cápsula posterior del cristalino y los cambios del cuerpo ciliar (que no hemos logrado estudiar con otras técnicas). La ultrabiomicroscopía posibilita la visualización durante la acomodación de las cápsulas anterior y posterior del cristalino, la zónula con sus inserciones en la cápsula ecuatorial y el cuerpo ciliar, y la úvea anterior en relación con el cristalino. Las imágenes ultrasónicas obtenidas representan las estructuras del segmento anterior y sus modificaciones in vivo y en tiempo real durante la acomodación. El ultrasonido ha mostrado ser el método diagnóstico más adecuado para esta investigación.

The aim of this study is to understand the biometric behaviour of the ocular structures involved during accommodation. We chose high-frequency ultrasound to study ocular globe anterior segment structures biometric changes in vivo and during accommodation.This technique allows biometric screening, morphological and functional anterior segment, including the posterior lens capsule and changes of the ciliary body that we have failed to study with other techniques. The ultrabiomicroscopy allows visualization during accommodation of the anterior and posterior capsules of the lens, the zonules with insertions in the equatorial capsule and the ciliary body and anterior uvea relative to the lens. The ultrasound images obtained represent the anterior segment structures and their modifi cations in vivo and in real time during accommodation.We studied 75 patients divided into three groups according to age range: Group 1 from 30 to 45 years, Group 2 of 46-60 years, and Group 3 of 61-70 years.The results obtained show how they vary the shape and size of anterior segment structures and relationships with each other, allowing to know their behavior in the loss of accommodation of different age groups studiedUltrasound has proven to be the most appropriate diagnostic method for this research.

Inflammatory responses and side effects generated by several adjuvant-containing vaccines in turbot.

Several of the adjuvants used in fish vaccines cause adhesions in internal organs when they are injected intraperitoneally. We describe the damage caused by vaccines containing different adjuvants in the turbot Scophthalmus maximus and show that internal adhesions can be greatly reduced by injecting the fish in a specific way. Injection of fish with the needle directed towards the anterior part of the peritoneal cavity induced formation of a single cell-vaccine mass (CVM) that became attached to the parietal peritoneum. However, injection of the fish with the needle pointing in the opposite direction generated many small CVM that became attached to the visceral and parietal peritoneum and in some cases caused internal adhesions. We describe the structural and cellular changes in the adjuvant-induced CVMs. The CVMs mainly comprised neutrophils and macrophages, although most of the former underwent apoptosis, which was particularly evident from day 3 post-injection. The apoptotic cells were phagocytosed by macrophages, which were the dominant cell type from the first days onwards. All of the vaccines induced angiogenesis in the area of contact between the CVM and the mesothelium. Vaccines containing oil-based adjuvants or microspheres induced the formation of granulomas in the CVM; however, no granulomas were observed in the CVM induced by vaccines containing aluminium hydroxide or Matrix-Q(®) as adjuvants. All of the vaccines induced strong migration of cells to the peritoneal cavity. Although some of these cells remained unattached in the peritoneal cavity, most of them formed part of the CVM. We also observed migration of the cells from the peritoneal cavity to lymphoid organs, indicating bidirectional traffic of cells between the inflamed areas and these organs.

Biodegradable microparticles covalently linked to surface antigens of the scuticociliate parasite P. dicentrarchi promote innate immune responses in vitro.

The histiophagous scuticociliate endoparasite Philasterides dicentrarchi is an emerging pathogen that infects the turbot Scophthalmus maximus and thus causes important economic losses in turbot aquaculture. This in vitro study investigated the adjuvant capacity of biodegradable microspheres (MS) composed of two polymers (chitosan and Gantrez(®)) covalently coupled to surface antigens (Ag) of P. dicentrarchi. The coupled MS-Ag significantly stimulated the phagocytic response of both murine macrophages (RAW 264.7 cells) and leukocytes from the anterior kidney of turbot (HLK), at a level similar to that induced by zymosan A. The MS-Ag also significantly increased production of reactive oxygen and nitrogen species, as shown by the increased O(2) consumption and stimulation of the respiratory burst and nitric oxide production by murine and in particular by turbot HLK. The MS-Ag stimulated the production of the proinflammatory cytokine tumour necrosis factor alpha (TNFα) by murine and turbot HLK. The results confirm the high adjuvant capacity of biodegradable MS covalently bound to Ag as regards stimulating the innate immune response, and they justify the use of MS in the production of safe and effective vaccines against fish pathogens.

A vaccine based on biodegradable microspheres induces protective immunity against scuticociliatosis without producing side effects in turbot.

The histiophagous scuticociliate parasite Philasterides dicentrarchi is an emergent pathogen in aquaculture and causes significant economic losses on turbot (Scophthalmus maximus) farms. In this study, the surface antigens (Ag) of the parasite were encapsulated and covalently linked to a polymeric microparticle formulation composed of two biodegradable polymers (chitosan and Gantrez). The antigenicity of the formulation and the protection provided were compared in mice and turbot. This formulation induced a higher antibody (Ab) response in mice at doses of 5mg of microspheres (MS) conjugated with approximately 230 µg of Ag (MS-Ag(c)). However, Ab levels were significantly lower than in mice vaccinated with the same concentration of Ag in complete Freund's adjuvant (FCA). In turbot, the MS-Ag(c) formulation induced a higher level of Abs than that induced by the same vaccine emulsified in FCA. The challenge experiments performed with P. dicentrarchi and vaccinated turbot also showed a clear correlation between Ab levels and survival levels. Growth was significantly affected in fish vaccinated with FCA, but not in fish vaccinated with MS. The high adjuvant capacity of MS, together with its biodegradability and low toxicity to fish, makes this new vaccine an economical, effective and safe alternative to oil-based adjuvants for the immunoprophylaxis of scuticociliatosis in turbot.

Differences in the in vitro susceptibility to resveratrol and other chemical compounds among several Philasterides dicentrarchi isolates from turbot.

Philasterides dicentrarchi is a histophagous scuticociliate that causes important losses in aquaculture. Several strains that differ in morphological, genetic and serological characteristics and virulence have been isolated from outbreaks of turbot scuticociliatosis. In the present study, seven isolates of the ciliate were exposed in vitro to formalin, hydrogen peroxide and resveratrol (a phytoalexin produced by plants) in order to evaluate the susceptibility of the isolates to the different compounds. The LD50 values for the three compounds tested varied widely among the isolates. The LD100 values were similar among isolates for formalin (25-30 ppm) and resveratrol (60-70 ppm) but were very different for hydrogen peroxide (25->80 ppm). The results indicate that there are many physiological differences among isolates and even among specimens of the same isolates, which must be taken into account in designing control programmes. The naturally occurring resveratrol may be a good alternative to other compounds for reducing the amounts of viable ciliates in water.

Role of scuticociliate proteinases in infection success in turbot, Psetta maxima (L.).

Scuticociliatosis caused by Philasterides dicentrarchi is one of the most severe diseases of farmed turbot, Psetta maxima (L.). Immunized fish showed elevated levels of specific antibodies (Ab), which caused the destruction of parasites through the activation of complement by the alternative and classical pathways. By using affinity chromatography on bacitracin-sepharose columns, we demonstrated the existence of high levels of parasite proteinases in the serum and, to a lesser extent, in the ascitic fluid of experimentally infected fish, and the absence of such proteinases in the serum of uninfected fish. Serum from uninfected fish displayed haemolytic activity against sheep red blood cells. However, incubation of this serum with parasite proteinases led to a decrease in serum haemolytic activity, suggesting that proteinases are able to destroy fish complement. Proteinases isolated from serum or ascitic fluid of infected fish were also able to degrade turbot Ab. Preincubation of turbot serum containing specific Ab for P. dicentrarchi with the proteinases led to a significant decrease in the killing activity of the serum. The results confirm that P. dicentrarchi proteinases in serum from infected fish may provide a mechanism for circumventing normal host immunity by inactivating the Ab and complement factors required for complement activation.

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.

Resveratrol promotes an inhibitory effect on the turbot scuticociliate parasite Philasterides dicentrarchi by mechanisms related to cellular detoxification.

The mechanisms involved in antiparasitic activity of the natural nonflavonoid polyphenol resveratrol (RESV) on the turbot (Psetta maxima) scuticoliate parasite Philasterides dicentarchi were investigated. At concentrations higher than 50microM, RESV caused significant inhibition of the in vitro growth of the ciliates, which was apparent on the third day of culture and, at the same concentration, RESV caused significant inhibition of O(2) consumption. RESV, at a concentration of 100microM, produced a significant increase in the production of intracellular reactive oxygen species (ROS), which were inhibited by the addition of 1mM of L (+) ascorbic acid. RESV (100microM) also caused significant inhibition of peroxidase, catalase and superoxide dismutase activities, but stimulated the activity of the redox regulating enzyme glutathione S-transferase. Confocal microscopy with the mitochondria-sensitive dye MitoTracker Orange CMTMRos revealed that RESV at concentrations higher than 50microM significantly increased the levels of fluorescence inside mitochondria and, at the same concentration, also caused an increase in the vacuolization of the trophozoites. The results obtained in the present study suggest that the inhibitory activity of RESV on the ciliate P. dicentrarchi is related to the induction of oxidative stress and to the inability of the parasite to eliminate ROS as a result of modified activity of antioxidant enzymes.

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

The present study was carried out to elucidate the in vitro killing activity of turbot complement and specific antibodies against the ciliate parasite Philasterides dicentrarchi. Fresh serum from nonimmunized fish showed a moderate ability to kill the parasite, which indicates that P. dicentrarchi is able to activate the alternative complement pathway (ACP). Fresh serum from immunized fish, which contained high levels of specific antibodies, showed greater killing activity. Heat-inactivated serum, with or without antibodies, and antibodies alone did not have any effect on parasite viability, which indicates that serum mainly kills P. dicentrarchi through the antibody-mediated classical complement pathway (CCP). Ascitic fluid from infected fish, but containing low levels of specific antibodies, showed a low ability to kill the parasite, and fresh serum from nonimmunized infected fish did not kill the parasite. The latter serum contained some specific antibodies but lower levels of complement than serum from control and vaccinated fish, and the lack of ability of this serum to kill the parasite was probably related to low levels of complement. In addition, serum and ascitic fluid from infected turbot showed high proteolytic activity which degraded fish Igs. The proteolytic activity generated may favour survival of the parasite during infection.