The gene for an abundant parasite coat protein predicts tandemly repetitive metal binding domains

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.

Scuticociliatosis and its recent prophylactic measures in aquaculture with special reference to South Korea Taxonomy, diversity and diagnosis of scuticociliatosis: Part I Control strategies of scuticociliatosis: Part II

Scuticociliatosis caused by about 20 species belonging to the Phylum Ciliophora has been recognized as an emerging problem inflicting significant economic loss in aquaculture industry in the world. Among these Philasterides dicentrarchi, Miamiensis avidus, and Uronema marinum are the three species responsible for scuticociliatosis in olive flounder farms of South Korea. Some of the parasites living or scavenger ciliates also have become parasites of aquaculture fish. The major clinico-pathological manifestations of scuticociliatosis infected fishes are anemia, weight loss, dark coloration, enteritis, excessive body mucus, yellowish intestinal mucus, loss of scales, hemorrhagic and/or bleached spots on the skin, and dermal necrotic lesions that finally destroy tissues lead to high mortalities. Affected fish exhibit organ-specific pathological changes in the brain, eyes, muscle, gills, liver, kidney, intestine, and stomach that lead to severe mortality. At present, farmers in South Korea manage scuticociliatosis by using therapeutic measures, such as application of antibiotics like oxytetracycline, gentamycine, tetracycline, amoxycililin, and cefazolin and chemicals, such as formalin, hydrogen peroxide, malachite green, and jenoclean at a concentration of 350 +/- 150 ppm. However till date, no systematic scientific study has been conducted under field condition on the efficacy of these management measures. Under laboratory condition the ciliate can be effectively controlled with the antibiotics and chemicals while on the host, but on entering the host no systemic chemotherapeutic treatment has been yet proven effective. Furthermore the indiscriminate uses of harmful chemicals in aquaculture are increasingly becoming a cause of concern. Recently formalin and malachite green, the most widely used chemicals have been banned in food fish production by FDA as not consumer friendly and being carcinogenic respectively. Vaccines and immunostimulants can induce good immune response and protect against scuticociliatosis as it has been proved in the case of freshwater Ich. Now a days a number of probiotics and herbal formulations are in use against freshwater bacterial and fungal diseases, while, little information is available regarding the different prophylactic measures against marine scuticociliatosis. This review attempts to provide information on the various prophylaxic measures practiced against scuticociliatosis with special reference to olive flounder farms in South Korea.

Endosymbiotic bacteria in the parasitic ciliate Ichthyophthirius multifiliis

Endosymbiotic bacteria were identified in the parasitic ciliate Ichthyophthirius multifiliis, a common pathogen of freshwater fish. PCR amplification of DNA prepared from two isolates of I. multifiliis, using primers that bind conserved sequences in bacterial 16S rRNA genes, generated an approximately 1,460-bp DNA product, which was cloned and sequenced. Sequence analysis demonstrated that 16S rRNA gene sequences from three classes of bacteria were present in the PCR product. These included Alphaproteobacteria (Rickettsiales), Sphingobacteria, and Flavobacterium columnare. DAPI (4',6-diamidino-2-phenylindole) staining showed endosymbionts dispersed throughout the cytoplasm of trophonts and, in most, but not all theronts. Endosymbionts were observed by transmission electron microscopy in the cytoplasm, surrounded by a prominent, electron-translucent halo characteristic of Rickettsia. Fluorescence in situ hybridization demonstrated that bacteria from the Rickettsiales and Sphingobacteriales classes are endosymbionts of I. multifiliis, found in the cytoplasm, but not in the macronucleus or micronucleus. In contrast, F. columnare was not detected by fluorescence in situ hybridization. It likely adheres to I. multifiliis through association with cilia. The role that endosymbiotic bacteria play in the life history of I. multifiliis is not known.

Cutaneous antibody-secreting cells and B cells in a teleost fish

Antibodies in cutaneous mucus and skin of teleosts play a critical role in the protective immune response against infection. We demonstrate by ELISPOT that antibody-secreting cells (ASC), which include LPS-inducible B cells (plasmablasts) and non-replicating plasma cells, reside in low numbers in the skin of channel catfish. Following immunization against the protozoan parasite Ichthyophthirius multifiliis, which infects skin and gills, the number of ASC in skin increased 20-fold, indicating that the number of ASC in skin is dynamic and increases in response to parasite infection. The number of ASC in skin remained elevated for at least 17 weeks after the last parasite exposure. Cutaneous ASC included I. multifiliis-specific ASC, which undoubtedly serve as the primary source of cutaneous antibodies that confer long-term humoral immunity against reinfection. Our demonstration that skin contains B cells and plasma cells suggests that it is an integral component of the teleost immune system.

Whole-genome natural histories of apicomplexan surface proteins

The natural histories of free-living and pathogenic protozoans have been described in over a century of studies, spanning a range of disciplines such as microscopic, cellular, taxonomic, pathological, clinical and molecular. Only in the last decade has this landscape of work benefited from the availability of whole-genome nucleotide sequence data. For many pathogens, it is now possible to overlay analyses of protein repertoires onto the current spectrum of knowledge. This article illuminates protozoan natural histories, particularly the rapidly evolving and highly adaptive direct physical interface of apicomplexan parasites and their hosts, by providing a brief introduction to the origin and phylogenetic distribution of parasite-encoded surface proteins and their component domains.

Ichthyophthirius multifiliis Fouquet and Ichthyophthiriosis in Freshwater Teleosts

The ciliate Ichthyophthirius multifiliis is an important pathogen of freshwater teleosts occurring in both temperate and tropical regions throughout the world. The disease, ichthyophthiriosis, accounts for significant economic losses to the aquaculture industry, including the ornamental fish trade, and epizootics in wild fish populations can result in mass kills. This review attempts to provide a comprehensive overview of the biology of the parasite, covering the free-living and parasitic stages in the life cycle, host-parasite interactions, and the immune response of host and immune evasion strategies by the parasite. Emphasis on the immunological aspects of infection within the fish host, including molecular studies of i-antigens, reflects the current interest in this subject area and the quest to develop a recombinant vaccine against the disease. The current status of methods for the control of ichthyophthiriosis is discussed, together with new approaches in combating this important disease.

Immunisation of channel catfish, Ictalurus punctatus, with Ichthyophthirius multifiliis immobilisation antigens elicits serotype-specific protection

Surface immobilisation antigens (i-antigens) were purified from two strains of Ichthyophthirius multifiliis (NY1 and G5) that represent different i-antigen serotypes, namely A and D, respectively. The efficacy of the purified antigens as subunit vaccines was then tested in challenge studies using parasites of the homologous or heterologous serotype. Three groups of juvenile channel catfish (70 animals per group) were immunised with i-antigens from either the G5 or NY1 isolates, or with bovine serum albumin (BSA) as a control. Proteins were injected intraperitoneally (i.p.) at a dose of 10 microg/fish with complete Freund's adjuvant on day 1, followed by a second injection in incomplete Freund's adjuvant on day 15. Fish immunised with the purified i-antigens developed high titres of serum immobilising antibodies whereas sera from BSA-injected control fish did not. Fish antisera immobilised parasites of the homologous, but not the heterologous strain, and recognised the corresponding i-antigens on Western blots run under non-reducing conditions. On day 36, each group was divided into two subgroups (n=30). One subgroup was challenged with G5 parasites, and the other was challenged with NY1 parasites. When challenged with G5 parasites, 70% of fish immunised with the G5 i-antigens survived. When challenged with NY1 parasites, 33.3% of fish immunised with the NY1 i-antigens survived. All BSA-injected control fish died, as did all fish injected with the purified antigens and challenged with the non-homologous parasite strain. Statistical analyses indicated significant differences among test and control groups with regard to the mean days to death (MDD). While the results of these studies clearly support a role for i-antigens in protection, active immunity in response to natural infection is not serotype-specific. The utility of i-antigens, as well as the existence of other potential vaccine candidates for the prevention of 'white-spot' disease, are discussed.

The use of synthetic genes for the expression of ciliate proteins in heterologous systems

The common fish parasite, Ichthyophthirius multifiliis, expresses abundant glycosylated phosphatidylinositol (GPI)-anchored membrane proteins known as immobilization antigens, or i-antigens. These proteins are targets of the host immune response, and have been identified as potential candidates for recombinant subunit vaccine development. Nevertheless, because Ichthyophthirius utilizes a non-standard genetic code, expression of the corresponding gene products, either as subunit antigens in conventional protein expression systems, or as vector-encoded antigens in the case of DNA vaccines, is far from straightforward. To overcome this problem, we utilized 'assembly polymerase chain reaction' to manufacture synthetic versions of two genes (designated IAG52A[G5/CC] and IAG52B[G5/CC]) encoding approximately 52/55 kDa i-antigens from parasite strain G5. This approach made it possible to eliminate unwanted stop codons and substitute the preferred codon usage of channel catfish for the native sequences of the genes. To determine whether the synthetic alleles could be expressed in cells that use the standard genetic code, we introduced IAG52A[G5/CC] into a variety of heterologous cell types and tested for expression either by immunofluorescence light microscopy or Western blotting. When cloned downstream of appropriate promoters, IAG52A[G5/CC] was expressed in Escherichia coli, mammalian COS-7 cells, and channel catfish where it elicited antigen-specific immune responses. Interestingly, the localization pattern of the corresponding gene product in COS-7 cells indicated that while the protein was correctly folded, it was not present on the cell membrane, suggesting that the signal peptides required for GPI-anchor addition differ in ciliate and mammalian systems. Construction of synthetic alleles should have practical utility in the development of vaccines against Ichthyophthirius, and at the same time, provide a general method for the expression of ciliate genes in heterologous systems.

Surface immobilization antigen of the parasitic ciliate Ichthyophthirius multifiliis elicits protective immunity in channel catfish (Ictalurus punctatus)

Channel catfish (Ictalurus punctatus) that survive infection with the parasitic ciliate Ichthyophthirius multifiliis acquire immunity to subsequent challenge and produce specific antibodies in serum that immobilize the parasite in vitro. Cellular surface protein antigens targeted by these antibodies are referred to as immobilization antigens (i-antigens). By using an immobilizing mouse monoclonal antibody as a ligand, the i-antigen of I. multifiliis isolate G5 was purified to homogeneity by immunoaffinity chromatography, and its immunogenicity was confirmed by inoculating rabbit and channel catfish to produce immobilizing antisera. To test the purified i-antigen as a subunit vaccine, channel catfish fingerlings were injected intraperitoneally (i.p.) with purified i-antigen at a dose of 10 microg/fish in complete Freund's adjuvant on day 1, followed by a second i.p. injection of the same amount of i-antigen in incomplete Freund's adjuvant on day 15. Negative control fish were immunized similarly with either bovine serum albumin (BSA) or an immobilization-irrelevant I. multifiliis protein. On day 84, the fish were challenged with live I. multifiliis G5 theronts at a dose of 15,000 cells per fish. Seventy-two percent of the fish immunized with i-antigen survived the challenge. All negative control fish died within 16 days of exposure. There was a significant difference in the median days to death between the negative control fish injected with BSA and the fish that died following vaccination with i-antigen. Fish injected with i-antigen developed high immobilizing antibody titers in serum. This is the first demonstration of a direct role for i-antigens in the elicitation of protective immunity, suggesting that these proteins by themselves serve as effective subunit vaccines against I. multifiliis.

The I-antigens of Ichthyophthirius multifiliis are GPI-anchored proteins

The parasitic ciliate Ichthyophthirius multifiliis has abundant surface membrane proteins (i-antigens) that when clustered, trigger rapid, premature exit from the host. Similar antigens are present in free-living ciliates and are GPI-anchored in both Paramecium and Tetrahymena. Although transmembrane signalling through GPI-anchored proteins has been well-documented in metazoan cells, comparable phenomena have yet to be described in protists. Since premature exit of Ichthyophthirius is likely to involve a transmembrane signalling event, we sought to determine whether i-antigens are GPI-anchored in these cells as well. Based on their solubility properties in Triton X-114, the i-antigens of Ichthyophthirius are amphiphilic in nature and partition with the detergent phase. Nevertheless, following treatment of detergent lysates with phospholipase C, the same proteins become hydrophilic. Concomitantly, they are recognized by antibodies against a cross-reacting determinant exposed on virtually all GPI-anchored proteins following cleavage with phospholipase C. Finally, when expressed in recombinant form in Tetrahymena thermophila, full-length i-antigens are restricted to the membrane, while those lacking hydrophobic C-termini are secreted from the cell. Taken together, these observations argue strongly that the i-antigens of Ichthyophthirius multifiliis are, in fact, GPI-anchored proteins.

Molecular characterization of the SerL paralogs of Tetrahymena thermophila

In the pond ciliate Tetrahymena thermophila, expression of genes encoding variant forms of the cell surface immobilization antigen (i-ag) is regulated by environmental conditions. Multiple isoforms of the L i-ags are found on the surface of cells grown at <20 degrees C as well as on the surface of rseC mutants which express SerL genes constitutively. Five cDNAs encoding variant L i-ags of rseC were sequenced and their expression studied. Two additional SerL genes from natural isolates were sequenced. Members of the SerL family encode polypeptides with 148, 316, or 371 amino acids, and the i-ags have two, five, or six imperfect repeats, respectively, flanked by putative ER translocation and GPI addition signals. Each repeat contains six periodic cysteines, in contrast to eight or ten in other i-ags of T. thermophila. At least three of the five genes constitutively expressed in rseC mutants are differentially expressed in cells expressing other i-ags. Northern analysis and RT-PCR indicate that expression of some members of the SerL family is regulated by both transcription and mRNA stability while another member is regulated primarily by mRNA stability.

Sequence and expression of the SerJ immobilization antigen gene of Tetrahymena thermophila regulated by dominant epistasis

In ciliates, variable surface protein genes encoding the immobilization antigen (-ag) are expressed under different environmental conditions, including temperature and salt stress. These i-ags are GPI-linked and coat the entire external surface of the cell, including the cilia. In Tetrahymena thermophila-ag in natural isolates is the result of dominant epistasis masking the expression of the H i-ag ordinarily expressed at 20-36 degrees C. This report describes the expression and sequence of the Ser-ag. J is present on the cell surface up to 38 degrees C; above 38 degrees C SerSeranked by an A-rich 5' UTR and a 3' UTR containing putative mRNA destabilization motifs. The encoded J polypeptide consists of 438 amino acids and is rich in alanine, cysteine, serine and threonine. The N- and resemble signal peptide and GPI-anchor addition sites, respectively. The majority of the molecule consists of four imperfect repeats with 10 periodic cysteines per repeat in the pattern CX(6)CX(2)CX(21)CX(4)CX(13-15)CX(2)CX(18)CX(3)CX(11)CX(9-10). Although H i-ags encoded by paralogous SerH genes have 3.5 imperfect repeats with eight periodic cysteines per repeat, J nevertheless resembles H with respect to amino acid composition, codon usage, N- and C-termini, the arrangement of the cysteine periods, and regulation by mRNA stability. However, despite these similarities and epistasis, the evolutionary relationship between SerH and SerJ is unclear.

Analysis of the conserved cysteine periodicity of Paramecium variable surface antigens

The major surface antigens expressed by free-living and parasitic protozoa commonly contain repeating cysteine motifs. Despite the common occurrence of these repeats their functional significance remains largely unexplored. In this paper we investigate the conserved cysteine repeats within the variable surface antigens of Paramecium tetraurelia. We show that deletion of 2 entire repeating units or portions of repeats near the N-terminus does not prevent expression of the A51 variable surface antigen. Alteration of a single cysteine to serine residue also has no effect on A51 expression. In contrast, deletions near the C-terminus of the protein have identified a small segment within the repeats that is required for expression on the surface. The required region contains a number of conserved amino acid residues, yet site-directed mutagenesis of two residues (serine and threonine to alanine) did not prevent expression. These studies demonstrate the feasibility of using deletion analysis to identify regions critical for the expression of cysteine-rich surface antigens. The relationship of these results to the structure and expression of cysteine-rich surface proteins in other protozoa is discussed.