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PubMed2000

Zoosporulation of a new Perkinsus species isolated from the gills of the softshell clam Mya arenaria.

A gill-associated Perkinsus sp. isolated from the softshell clam (Mya arenaria) is described as a new species, P. chesapeaki sp. nov. Examination of the parasite in seawater cultures revealed life cycle stages and zoosporulation processes similar to those described for other species of the genus Perkinsus. Prezoosporangia developed thickened cell walls upon contraction of the cytoplasm and development of a distinctive clear area between the cell wall and the protoplast. Successive bipartition of the protoplast led to the formation of hundred's of zoospores within mature sporangia. Zoospores were released into seawater through one or more discharge tubes. Ultrastructural studies revealed an oblong zoospore possessing two flagella that arose from a concave side located in the upper third of the zoospore body. The anterior flagellum possessed a unilateral array of hair-like structures. A large anterior vacuole and basolateral nucleus dominated the cytoplasm of the zoospore body. The presence of a rudimentary apical complex including an open-sided conoid, rhoptries, micronemes, and subpellicular microtubules were also discerned. Differences in zoospore morphology, and sequence analyses of two genes previously reported, support the designation of the gill-associated Perkinsus from the softshell clam as a new species.

Animals↗
PubMed2004

Hepatozoon cf. terzii (Sambon & Seligman, 1907) infection in the snake boa constrictor constrictor from north Brazil: transmission to the mosquito Culex quinquefasciatus and the lizard Tropidurus torquatus.

Specimens of Hepatozoon-infected Boa constrictor constrictor were obtained from localities in Pará State, north Brazil. Gametocytes in erythrocytes of the peripheral blood measured 10 x 2.5-16.2 x 3.7 microns. They were similar to those described as Haemogregarina terzii by Sambon & Seligmann (1907) in B. c. constrictor, in that they did not distort the infected erythrocyte, and their dimensions approximated those given by Carini (1947). Lungs and liver of infected snakes contained actively dividing meronts of a single type, and cysts containing two to six cystozoites were also present in the liver. Our initial feeding of Culex quinquefasciatus on infected snakes consistently resulted in a heavy death-rate of the engorged mosquitoes, with only a few surviving till the 9th day post feeding. These contained numerous oocysts which were undivided or in early stages of division. A fifth and final experiment, however, provided a few mosquitoes surviving up to 21 days post infection (dpi), and these contained fully sporulated oocysts measuring 190-200 microns in diameter and containing over 60 sporocysts of 19-30 microns in diameter. The number of sporozoites in each sporocyst was estimated as approximately 50. The nature of the parasite's sporogonic cycle in the mosquito thus justifies inclusion of this haemogregarine in the genus Hepatozoon. Two wild-caught specimens of the lizard Tropidurus torquatus were fed with mosquitoes containing fully developed oocysts (21 dpi). When sacrificed, three months later, large numbers of dizoic, tetrazoic and hexazoic cysts were demonstrated in their livers. Cystozoites released from these cysts were shown to possess a conspicuous refractile body.

Animals↗
PubMed2004

Parasites in the thoracic ganglion of Pachygrapsus marmoratus (Brachyura: Grapsidae) from the coast of Portugal.

We examined 149 marbled shore crabs, Pachygrapsus marmoratus, from the coast of Portugal for parasites. In particular, we focused our effort on the crab thoracic ganglion. The thoracic ganglion is the largest concentration of nervous tissue in a crab and thus, parasites associated with this organ are well situated to influence host behavior. We found metacercariae of two microphallid trematode species in the thoracic ganglion. We also found a microsporan and an apicomplexan associated with the thoracic ganglion. Other parasites not associated with the thoracic ganglion included gregarine trophozoites which were present in the digestive diverticulae in some of the crabs and the entoniscid isopod, Grapsion cavolini. Metacercariae of one of the trematodes (probably Microphallus pachygrapsi (Deblock and Prevot)), may influence the mortality of its host.

Animals↗
PubMed2006

New insights into myosin evolution and classification.

Myosins are eukaryotic actin-dependent molecular motors important for a broad range of functions like muscle contraction, vision, hearing, cell motility, and host cell invasion of apicomplexan parasites. Myosin heavy chains consist of distinct head, neck, and tail domains and have previously been categorized into 18 different classes based on phylogenetic analysis of their conserved heads. Here we describe a comprehensive phylogenetic examination of many previously unclassified myosins, with particular emphasis on sequences from apicomplexan and other chromalveolate protists including the model organism Toxoplasma, the malaria parasite Plasmodium, and the ciliate Tetrahymena. Using different phylogenetic inference methods and taking protein domain architectures, specific amino acid polymorphisms, and organismal distribution into account, we demonstrate a hitherto unrecognized common origin for ciliate and apicomplexan class XIV myosins. Our data also suggest common origins for some apicomplexan myosins and class VI, for classes II and XVIII, for classes XII and XV, and for some microsporidian myosins and class V, thereby reconciling evolutionary history and myosin structure in several cases and corroborating the common coevolution of myosin head, neck, and tail domains. Six novel myosin classes are established to accommodate sequences from chordate metazoans (class XIX), insects (class XX), kinetoplastids (class XXI), and apicomplexans and diatom algae (classes XXII, XXIII, and XXIV). These myosin (sub)classes include sequences with protein domains (FYVE, WW, UBA, ATS1-like, and WD40) previously unknown to be associated with myosin motors. Regarding the apicomplexan "myosome," we significantly update class XIV classification, propose a systematic naming convention, and discuss possible functions in these parasites.

Animals↗
PubMed1985

Identification of a surface antigen on Theileria parva sporozoites by monoclonal antibody.

A mouse monoclonal antibody (mAbD1) that neutralizes sporozoites of different stocks of the protozoan parasite Theileria parva has been used to localize and identify a sporozoite antigen. Protein A-colloidal gold was used to localize bound mAbD1 in immunoelectron microscopic studies. mAbD1 bound to sporozoite antigen, which was evenly spread over the surface of all sporozoites. Immune complexes were obtained by incubation of sporozoite suspensions with mAbD1 followed by Zwittergent 3-14 extraction and precipitation with protein A-Sepharose. One- and two-dimensional NaDodSO4/polyacrylamide gel electrophoretic analyses were performed on these complexes, and a major protein with a molecular size of 68 kDa was identified. Other related components of 52 kDa, 47 kDa, and 28 kDa were also detected. Since antibody to this antigen(s) neutralizes T. parva sporozoites from different stocks, the results could be of relevance to the development of a broad spectrum vaccine against the cattle disease East Coast fever, which is caused by T. parva.

Animals↗
PubMed1986

Bovine cytotoxic T-cell clones specific for cells infected with the protozoan parasite Theileria parva: parasite strain specificity and class I major histocompatibility complex restriction.

We present information on the specificity of three bovine cytotoxic T-cell clones reactive with lymphoblasts infected with the protozoan parasite Theileria parva. The clones were derived from peripheral blood mononuclear cells of an animal immunized with T. parva (Muguga stock), after five stimulations in vitro with an autologous parasitized cell line. The three clones belonged to the BoT8+ subset of T cells, which is similar to the human CD8+ T-cell subset. On the basis of analysis on a panel of infected target cells originating from cattle of different major histocompatibility complex (MHC) phenotypes, killing by all three clones was found to be restricted to targets bearing the class I MHC specificity KN104, which is defined by alloantiserum KNA104 and monoclonal antibody IL-A4. This class I MHC restriction was confirmed by blocking of target cell lysis with these antibodies and monoclonal antibody w6/32, which reacts with a nonpolymorphic determinant on bovine class I MHC molecules. The three clones were parasite strain specific, in that they did not kill cells of the appropriate MHC type infected with T. parva (Marikebuni stock). These findings, taken together with previous observations that immunization of cattle with T. parva (Muguga) does not provide protection against challenge with T. parva (Marikebuni), suggest that the cytotoxic T cells recognize a cell surface antigen that may be important in induction of immunity to the parasite.

Animals↗
PubMed1988

Theileria parva infection induces autocrine growth of bovine lymphocytes.

Bovine lymphocytes infected with the parasite Theileria parva continuously secrete a growth factor that is essential for their proliferation in vitro and also constitutively express interleukin 2 receptors on their surface. Dilution of the secreted growth factor, caused by culturing cells at low density, results in retardation of culture growth. Human recombinant interleukin 2, however, effectively substitutes for the diluted growth factor by restoring normal growth rates and also allows Theileria-infected cells to be grown at low density without the use of feeder layers. Secretion of the growth factor and expression of the interleukin 2 receptor depend on the presence of the parasite in the cytoplasm of the host cell. Elimination of the parasite from the cell cytoplasm by the specific antitheilerial drug BW 720c results in the arrest of growth factor secretion and the disappearance of interleukin 2 receptors from the cell surface. This is accompanied by growth arrest and reversion of the infected cells to the morphology of resting lymphocytes. We propose that the continuous proliferation of infected cells in vitro is mediated by autocrine receptor activation.

Animals↗
PubMed1989

Theileria annulata sporozoite surface antigen expressed in Escherichia coli elicits neutralizing antibody.

Theileria annulata is an economically important protozoan parasite that threatens an estimated 250 million cattle with the disease tropical theileriosis. Development of a defined subunit vaccine is one means of trying to develop control measures against the disease. To this end we have characterized a surface antigen complex of the infective stage (sporozoite), by using a monoclonal antibody that neutralizes sporozoite infectivity in vitro. We have cloned the gene coding for this complex and have demonstrated that a fusion protein expressed from a fragment of this gene elicits strong neutralizing antibodies. Furthermore we provide data on the structure and expression of this gene. In particular we show that the region of the gene, expressed in one clone, codes for a protein segment relatively rich in proline residues. Also we demonstrate that expression of this gene appears to be stage specific, transcripts being present only in the sporoblast and sporozoite stages. The relevance of these findings to the production of a defined subunit vaccine is discussed.

Amino Acid Sequence↗
PubMed1997

Differential roles of T cell receptor alpha and beta chains in ligand binding among H-2Kd-restricted cytolytic T lymphocyte clones specific for a photoreactive Plasmodium berghei circumsporozoite peptide derivative.

To study the interaction of T cell receptor with its ligand, a complex of a major histocompatibility complex molecule and a peptide, we derived H-2Kd-restricted cytolytic T lymphocyte clones from mice immunized with a Plasmodium berghei circumsporozoite peptide (PbCS) 252-260 (SYIPSAEKI) derivative containing photoreactive Nepsilon-[4-azidobenzoyl] lysine in place of Pro-255. This residue and Lys-259 were essential parts of the epitope recognized by these clones. Most of the clones expressed BV1S1A1 encoded beta chains along with specific complementary determining region (CDR) 3beta regions but diverse alpha chain sequences. Surprisingly, all T cell receptors were preferentially photoaffinity labeled on the alpha chain. For a representative T cell receptor, the photoaffinity labeled site was located in the Valpha C-strand. Computer modeling suggested the presence of a hydrophobic pocket, which is formed by parts of the Valpha/Jalpha C-, F-, and G-strands and adjacent CDR3alpha residues and structured to be able to avidly bind the photoreactive ligand side chain. We previously found that a T cell receptor specific for a PbCS peptide derivative containing this photoreactive side chain in position 259 similarly used a hydrophobic pocket located between the junctional CDR3 loops. We propose that this nonpolar domain in these locations allow T cell receptors to avidly and specifically bind epitopes containing non-peptidic side chains.

Affinity Labels↗
PubMed2000

Apicomplexan parasites possess distinct nuclear-encoded, but apicoplast-localized, plant-type ferredoxin-NADP+ reductase and ferredoxin.

In searching for nuclear-encoded, apicoplast-localized proteins we have cloned ferredoxin-NADP(+) reductase from Toxoplasma gondii and a [2Fe-2S] ferredoxin from Plasmodium falciparum. This chloroplast-localized redox system has been extensively studied in photosynthetic organisms and is responsible for the electron transfer from photosystem I to NADP+. Besides this light-dependent reaction in nonphotosynthetic plastids (e.g. from roots), electrons can also flow in the reverse direction, from NADPH to ferredoxin, which then serves as an important reductant for various plastid-localized enzymes. These plastids possess related, but distinct, ferredoxin-NADP+ reductase and ferredoxin isoforms for this purpose. We provide phylogenetic evidence that the T. gondii reductase is similar to such nonphotosynthetic isoforms. Both the P. falciparum [2Fe-2S] ferredoxin and the T. gondii ferredoxin-NADP+ reductase possess an N-terminal bipartite transit peptide domain typical for apicoplast-localized proteins. The recombinant proteins were obtained in active form, and antibodies raised against the reductase recognized two bands on Western blots of T. gondii tachyzoite lysates, indicative of the unprocessed and native form, respectively. We propose that the role of this redox system is to provide reduced ferredoxin, which might then be used for fatty acid desaturation or other biosynthetic processes yet to be defined. Thus, the interaction of these two proteins offers an attractive target for drug intervention.

Amino Acid Sequence↗
PubMed2002

Purification and molecular characterization of cGMP-dependent protein kinase from Apicomplexan parasites. A novel chemotherapeutic target.

The trisubstituted pyrrole 4-[2-(4-fluorophenyl)-5-(1-methylpiperidine-4-yl)-1H-pyrrol-3-yl]pyridine (Compound 1) inhibits the growth of Eimeria spp. both in vitro and in vivo. The molecular target of Compound 1 was identified as cGMP-dependent protein kinase (PKG) using a tritiated analogue to purify a approximately 120-kDa protein from lysates of Eimeria tenella. This represents the first example of a protozoal PKG. Cloning of PKG from several Apicomplexan parasites has identified a parasite signature sequence of nearly 300 amino acids that is not found in mammalian or Drosophila PKG and which contains an additional, third cGMP-binding site. Nucleotide cofactor regulation of parasite PKG is remarkably different from mammalian enzymes. The activity of both native and recombinant E. tenella PKG is stimulated 1000-fold by cGMP, with significant cooperativity. Two isoforms of the parasite enzyme are expressed from a single copy gene. NH(2)-terminal sequence of the soluble isoform of PKG is consistent with alternative translation initiation within the open reading frame of the enzyme. A larger, membrane-associated isoform corresponds to the deduced full-length protein sequence. Compound 1 is a potent inhibitor of both soluble and membrane-associated isoforms of native PKG, as well as recombinant enzyme, with an IC(50) of <1 nm.

Amino Acid Sequence↗