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W Trager

Publications and source records attributed to W Trager.

At least 37 records · Page 2Linked to original sources
PubMed1985

Variations in the organization of repetitive DNA sequences in the genomes of Plasmodium falciparum clones.

Repetitive DNA in cultured Plasmodium falciparum was examined by restriction digestion and transfer hybridization, using cloned repetitive DNA probes. The arrangement of repetitive DNA was unstable: after 6 months culture of a cloned population, variations could be detected. Significant differences can be seen between clones derived from a single isolate, and are even more marked between isolates of diverse geographical origin. No cross-species conservation was seen for the sequences examined, and no relationship was observed between their representation in the P. falciparum genome and the potential for sexual differentiation.

Animals↗
PubMed1984

Comparative infectivity of knobless and knobby clones of Plasmodium falciparum in splenectomized and intact Aotus trivirgatus monkeys.

In two experiments, two knobless (K-) and two knob-producing (K+) clone-cultures of Plasmodium falciparum, FCR-3/Gambia strain, were injected into four Aotus trivirgatus monkeys. The parasitemia in the K(-)-infected splenectomized (S-) monkey rose to a peak of 2.1% on the 16th day, while it reached only 0.7% at the same time in the K+ infected S- animal. Passage from these animals (karyotype VI) into two intact (S+), naive monkeys of karyotype III resulted in very light infections somewhat higher with K+ than with K-. This experiment was repeated with two different clones in two other S- monkeys of karyotype III. Again, the parasitemia of the K+ infected monkey was appreciably below that of the K- monkey. Transfer of parasites into S+ animals of karyotype II resulted in very light infection and, as before, the K+ did somewhat better. About 2 months after its initial infection, the K(+)-infected S- animal from the second experiment came down with a recurrent malaria infection. Electron-microscopic observations on blood from this monkey revealed that the previously K+ parasites had become knobless (K-). Transfer of this material into an S+, naive monkey, again, gave a barely detectable infection. After splenectomy a recrudescence occurred. The results strongly indicate that K- clones of P. falciparum are more infectious to S- Aotus monkeys than K+ clones, whereas in S+ monkeys the situation is reversed.

Animals↗
PubMed1984

Histidine-rich protein genes and their transcripts in Plasmodium falciparum and P. lophurae.

The presence of histidine-rich protein (HRP) related genes and gene products in Plasmodium falciparum was demonstrated using a synthetic pentahistidine-encoding oligonucleotide and a cloned HRP cDNA probe prepared from the avian parasite P. lophurae. In Northern blotting experiments, two knobby clones of P. falciparum were found to contain a 3500 nucleotide RNA species that hybridized with the oligonucleotide and HRP cDNA probes. As this component had the expected size for an mRNA encoding an 80-90 kDa protein and was absent from two knobless clones of P. falciparum, we concluded that it represented a 'knob protein' mRNA. Using the restriction enzyme EcoRI, three identical cross-hydribizing HRP gene fragments were found in the DNA of both knobby and knobless clones of P. falciparum. These fragments differed in size from those present in P. lophurae. These results suggest that the absence of knob protein mRNA in knobless clones is not due to loss of the corresponding gene(s).

Animals↗
PubMed1984

Intranuclear structures in pyrimethamine-resistant isolates of the malaria parasite Plasmodium falciparum.

The ultrastructure of the malaria parasite Plasmodium falciparum is well known, both from natural infections and from culture material ( Aikawa , 1977, Langreth et al., 1978). It is noteworthy that all of these studies were done with pyrimethamine-sensitive strains, e.g. FCR-3/Gambia. Except for spindle microtubules during schizogony, no intranuclear structures have been described in any of the asexual erythrocytic stages. In the course of isolating clones from the pyrimethamine-resistant strain Honduras I/CDC (V.K. Bhasin and W. Trager , in print) and checking by electron microscopy for the presence or absence of knobs, we noticed intranuclear structures that might be correlated with pyrimethamine resistance. For comparison, we then examined the multi-drug-resistant strain Indochina 1. We present here a first report on these structures as a basis for further studies.

Animals↗
PubMed1984

Initial extracellular development in vitro of merozoites of Plasmodium falciparum.

Late schizonts from continuous cultures of P. falciparum were concentrated over Percoll, inoculated to various experimental media at the rate of about 20 X 10(6) per 0.5 ml of medium, and incubated in a candle jar at 37 degrees for 1 day. Controls in standard culture medium showed a heavy invasion with young rings in the previously uninfected red cells introduced with the inoculum of schizonts. In a medium of high potassium content containing a 33% extract of human erythrocytes, this invasion was inhibited and many free merozoites were present. If, however, this same medium was supplemented with both ATP, as the dipotassium salt at 1.6 mM, and sodium pyruvate at 3.6 mM, there appeared large numbers of extracellular forms resembling young rings. Examination of these by electron microscopy shows that they are indeed merozoites that have begun to differentiate extracellularly. This suggests that the trigger for differentiation of merozoites may not depend on the process of entry into a red cell but rather on specific factors within the red cell.

Adenosine Triphosphate↗
PubMed1984

Gametocyte-forming and non-gametocyte-forming clones of Plasmodium falciparum.

Three clones have been prepared from the Honduras I/CDC strain of Plasmodium falciparum by a method of microscopic selection. One of these (HB-2) does not form gametocytes whereas the others (HB-1 and HB-3) do. All three are as resistant to pyrimethamine as the original line, and all three form knobs on the erythrocyte surface.

Animals↗
PubMed1983

Sexuality in piroplasms as revealed by electron microscopy in Babesia microti.

Protozoa of the closely related genera Babesia and Theileria are intraerythrocytic parasites of vertebrates. They have a complex life cycle that includes development in an intermediate vector host, a tick. Whether sexual stages occur in the tick has been a subject of great controversy. The small size of the organism and the complexity of developmental stages in the gut of the tick have prevented a definitive solution of this problem. By means of a simple and straightforward although time-consuming method, it became possible to demonstrate gametes and their sexual fusion in Babesia microti developing in the gut of larvae of the tick Ixodes dammini. Tick larvae fed on hamsters infected with a human strain of B. microti were fixed and processed for electron microscopy. It was found that some of the parasites formed a unique structure shaped like an arrowhead. Because it was suspected that these forms might represent gametes, a search was made for pairs of parasites that were fusing and with each member of the pair emerging from a different erythrocyte. Such a fusing pair could not possibly represent a parasite undergoing division. By study of serial sections such pairs were indeed found. In every case one member of the pair of gametes had an arrowhead structure. This proves sexuality of B. microti and makes highly likely its existence in all members of the genera Babesia and Theileria.

Animals↗
PubMed1983

Immunization of owl monkeys to Plasmodium falciparum with merozoites from cultures of a knobless clone.

Summary Aotus trivirgatus monkeys of karyotype 2 were treated as follows. Three received two injections of purified merozoites of a knobless (K-) clone of Plasmodium falciparum with muramyl dipeptide as adjuvant; three received similar injections but with merozoites of a wild-type knobby (K+) strain; three controls received MDP with human erythrocytes in the amounts estimated to be present as contaminants in the merozoite preparations. A month after the second injection all nine monkeys were inoculated with parasites of the wild-type knobby strain from another infected Aotus. The monkeys that had received the K- material developed only extremely low infections markedly different from the infections in the controls. Of those that received K+ material, one died early with low parasitaemia, one was protected and one had the same level of infection as the controls. In the combined group of immunized animals, four out of six were protected.

Animals↗
PubMed1982

Peptidases from Plasmodium falciparum cultured in vitro.

An acid peptidase that degrades hemoglobin optimally at pH 3.5, a neutral aminopeptidase and an alkaline endopeptidase that acts on an alpha-N-blocked synthetic substrate have been demonstrated in Plasmodium falciparum in culture. The enzymes were shown to be distinct by anion exchange chromatography, gel filtration on Sephadex G-200 and isoelectric focusing. The activities of the acid peptidase and the aminopeptidase were inhibited by antimalarial compounds.

Animals↗
PubMed1982

Comparative analyses of the ribosomal RNA from four isolates of Plasmodium falciparum.

The T1-resistant oligonucleotides of the ribosomal RNAs from four isolates of Plasmodium falciparum, the Southeast Asian strain FCR-1/Vietnam, the West African strains FCR-3/Gambia and FCR-8/West Africa, and an isolate from Honduras, were analyzed by two-dimensional polyacrylamide gel electrophoresis. Comparison of the largest 33--35 oligonucleotides indicated that 30 were common to all four of the isolates examined, with each isolate giving a characteristic pattern. Similar analyses were undertaken with cloned preparations of the FCR-3/Gambia isolate to determine if variation within a population of parasites could be detected. The patterns obtained for the five clones examined were identical.

Base Sequence↗
PubMed1982

Plasmodium falciparum merozoites: isolation by density gradient centrifugation using Percoll and antigenic analysis.

Merozoites of Plasmodium falciparum were isolated and immunocytochemically analyzed. Mature parasites from knobby (K+) and knobless (K-) strains were incubated for 4 to 5 hr in RPMI 1640 with 10% serum and 10% RBC extract. About 12 to 14% of the merozoites released were recovered by density gradient centrifugation using Percoll. From 1 to 3 X 10(9) merozoites were obtained per collection. The merozoite preparations were contaminated with 10% residual bodies, about 0.1% infected and uninfected erythrocytes, about 0.1% RBC-free trophozoites and schizonts, and numerous small (less than 0.5 microns) membrane vesicles. Merozoites from the K+ and K- strains were morphologically and, by an indirect, ferritin-labeled antibody assay using serum from immune Aotus, antigenically indistinguishable. Although the residual body coats reacted with the immune Aotus serum, the membrane vesicles, some of which were seen to be blebbing from merozoites, did not react with this serum or a serum against erythrocytes. This paper describes a procedure that can be used to obtain large numbers of merozoites with little contamination by host erythrocytes.

Centrifugation, Density Gradient↗
PubMed1981

Preliminary characterization of the major RNA species from Plasmodium falciparum.

Polyacrylamide gel electrophoresis of the total RNA extracted from cultures of Plasmodium falciparum resolved two major RNA components with estimated molecular weights of 1.3 X 10(6) and 0.72 - 0.74 X 10(6). Oligo(dT)-cellulose column chromatography of the total cellular RNA indicates that more than 90% of the total radiolabeled RNA lacks substantial poly(A) sequences (poly(A)-). Resolution of the poly(A)- fraction on polyacrylamide or agarose gels indicates that the majority of the poly(A)- RNAs are the 1.3 X 10(6) and 0.72 - 0.74 X 10(6) species. This observation was confirmed by two-dimensional oligonucleotide fingerprint analysis of the total cellular RNA as well as the poly(A)- RNA components. Oligonucleotide fingerprint analysis confirmed that the small RNA species is not a breakdown or cleavage product of the larger RNA component. Base ratio analysis of the large and small RNA species indicate that they are typically protozoan type with a low guanine + cytosine (G + C) content. The findings that these two RNA species (i) are the major cellular RNA species, (ii) lack substantial poly(A) sequences, (iii) have estimated molecular weights similar to the ribosomal RNAs obtained from other protozoa, (iv) have a low G + C content (approximately equal to 35 - 37%), and (v) are distinct from one another, indicates that the 1.3 X 10(6) and 0.72 - 0.74 X 10(6) RNA components obtained from P. falciparum cultures are the major ribosomal RNAs.

Animals↗
PubMed1981

Clones of the malaria parasite Plasmodium falciparum obtained by microscopic selection: their characterization with regard to knobs, chloroquine sensitivity, and formation of gametocytes.

A culture line of Plasmodium falciparum (FCR-3/Gambia) was used to select and place in culture cells containing a single parasite. The method depends on examination of minute droplets of dilute cell suspensions with oil immersion phase-contrast microscopy. Droplets found to contain a single parasite were maintained under appropriate culture conditions until detectable numbers of parasites were present (generally by day 21). Of nine clones that grew up, seven were knobless and two were knobby. The clones differed somewhat in chloroquine sensitivity. Their 50% inhibition point under one set of conditions in vitro ranged from 0.02 to 0.06 micrograms of base per ml, compared with only 0.003 micrograms for the highly sensitive line FCR-8/West Africa. All three tested clones formed gametocytes under appropriate in vitro conditions.

Chloroquine↗
PubMed1981

Antimalarial activity of quassinoids against chloroquine-resistant Plasmodium falciparum in vitro.

The growth of Plasmodium falciparum in vitro was markedly inhibited by certain quassinoids (the bitter principles from plants of the family Simaroubaceae). The most active compound, simalikalactone D, gave complete inhibition at 0.005 microgram/ml. Glaucarubinone an soularubinone were equally effective at 0.006 microgram/ml, whereas chaparrinone and simarolide had little effect even at 0.01 microgram/ml. These relative activities are parallel to the antineoplastic activities of these materials.

Chloroquine↗