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W Trager

Publications and source records attributed to W Trager.

At least 19 recordsLinked to original sources
PubMed1992

Extracellular (axenic) development in vitro of the erythrocytic cycle of Plasmodium falciparum.

Merozoites of the erythrocytic stage of Plasmodium falciparum were suspended in erythrocyte sonicate medium with ATP and pyruvate and mixed with Matrigel to form a soft gel. The gel was overlaid with complete medium; this was replaced with fresh medium at 12, 24, and 36 hr. At these times and also at 45 hr rhodamine 123 was added to some cultures and gels were sampled. Viable extracellular forms showing rhodamine fluorescence were seen: rings at 12 hr, trophozoites and early schizonts with pigment at 36 hr, and late schizonts with developing merozoites at 45 hr. These merozoites were shown to be infective to erythrocytes added to the cultures at 45 hr. Electron micrographs of 36-hr trophozoites show the organisms to have only their single plasma membrane; no parasitophorous membrane is evident. We conclude that the complex process of entry, the intactness of the host erythrocyte, and the parasitophorous membrane are not essential to the development of a merozoite through its complete asexual cycle.

Adenosine Triphosphate↗
PubMed1992

Transfer of a dense granule protein of Plasmodium falciparum to the membrane of ring stages and isolation of dense granules.

A 14-kDa protein was localized to the dense granules of Plasmodium falciparum by immunoelectron microscopy with monoclonal antibody 1H1. The protein was present in dense granules in late-stage schizonts and free merozoites. After invasion, the protein was localized exclusively on the membrane of the newly invaded ring. The protein is referred to as RIMA, for ring membrane antigen. The 14-kDa protein was synthesized late in schizogony as determined by immunofluorescence microscopy and immunoblotting. At the late schizont stage it was distributed diffusely throughout the intracellular schizont. Only at the segmenter stage was the protein localized in defined spots that correspond to dense granules. Dense granules were isolated from schizont-infected erythrocytes by subcellular fractionation on a sucrose gradient. Fractions containing the 14-kDa protein were detected by immunoblotting with monoclonal antibody 1H1. The 14-kDa protein was first detected in vesicles at the late (8-nucleus) schizont stage. Mature dense granules sedimented with a peak density of 1.17 g/ml, which is similar to the density of rhoptries isolated by the same procedure.

Animals↗
PubMed1991

Initial extracellular forms of Plasmodium falciparum: their ultrastructure and their definition with monoclonal antibodies.

Merozoites of the erythrocytic stage of the human malaria parasite Plasmodium falciparum, when placed under appropriate conditions in a culture medium with erythrocyte extract, differentiate into early trophic forms. These forms have much the same ultrastructure as rings of the same age that have developed intracellularly and have then been freed from their host cells by immune lysis. However, these forms differ in two respects: the extracellular forms have only their single plasma membrane, whereas the forms freed from host cells have, in addition, a surrounding parasitophorous vacuole membrane; the forms that develop extracellularly have fewer ribosomes. Five monoclonal antibodies against the ring stage have been prepared and characterized. Their pattern of immunofluorescence localization differs in merozoites as compared with rings, but their pattern is identical in rings developed extracellularly and those developed intracellularly. These results and the observations on fine structure demonstrate biochemical and morphological differentiation in the extracellular forms.

Animals↗
PubMed1990

Initial extracellular development in vitro of erythrocytic stages of malaria parasites (Plasmodium falciparum).

Merozoites of Plasmodium falciparum placed in culture medium with a 50% erythrocyte extract and supplemented with ATP and pyruvate differentiated extracellularly into early trophic forms. Erythrocyte extract prepared by sonication was found superior to extract prepared by freezing and thawing. Under the best conditions, up to 30% of the merozoites showed some development after 16 hr of incubation and approximately 5% developed into larger forms, often ring-shaped and occasionally showing pigment. The small as well as the larger forms took up the fluorescent dye rhodamine 123. Under similar conditions, partial further development was also obtained of young rings freed from their host cells. Again, the sonicated erythrocyte extract gave better development than the frozen-thawed extract, and ATP with pyruvate had a marked favorable effect. These parasites had both a plasma membrane and a surrounding closely apposed parasitophorous membrane, whereas the forms derived by extracellular development of merozoites had only their plasma membrane. We conclude that initial development requires neither an intact erythrocyte nor a parasitophorous membrane.

Adenosine Diphosphate↗
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

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

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↗