Suppressed expression of hypoxanthine-guanine phosphoribosyltransferase (HGPRT) in an irradiation-attenuated Plasmodium berghei XAT strain

Plasmodium berghei XAT (XAT) is a non-reversible, non-lethal type malaria parasite strain derived from the highly virulent lethal P. berghei NK65 (NK65) by X-irradiation. The difference in polypeptide expression between NK65 and XAT was examined in this study. Western blot patterns of the parasite polypeptides showed that a 30-kDa polypeptide was not detected in XAT. In the present paper, we focused the study on the difference in the expression of the 30-kDa polypeptide between XAT and NK65. Although several other significant differences were noted in the spots shown by two-dimensional gel electrophoresis, the 30-kDa polypeptide was isolated by means of preparative 2D-gel electrophoresis followed by HPLC, and N-terminal amino acid sequence of the polypeptide was eventually determined. Complementary DNA clones encoding the 30-kDa polypeptide were isolated and characterized. Full-length cDNA clones from XAT encoded a protein of 231 amino acid residues with a 693-bp open reading frame. The deduced amino acid sequence exhibited 67% identity with that for P. falciparum hypoxanthine-guanine phosphoribosyltransferase (HGPRT; EC 2.4.2.8), suggesting that this protein is P. berghei HGPRT. Northern blot analysis revealed that expression of HGPRT in XAT was only one-eighth of that in NK65. This finding indicates that HGPRT gene expression is markedly suppressed in XAT. The amino acid sequence of HGPRT from NK65 was identical to that from XAT. This finding showed that the amino acid sequence of XAT-HGPRT was not mutated and had not undergone deletion.     

Plasmodium berghei berghei: ectopic development of the ANKA strain in Anopheles stephensi

Sporogonic development of Plasmodium berghei berghei is frequently ectopic, occurring deep within the tissue of the midgut with oocysts expelling sporozoites into its lumen. Inocula containing oocysts and sporozoites defecated with blood during the mosquito blood meal produced infections when introduced into mice. The fine structures and pellicle of luminal parasites appeared normal in all respects.     

Plasmodium berghei berghei: Irradiated sporozoites of the ANKA strain as Immunizing Antigens in mice

Mice were protected against challenge with infective Sporozoites following immunization with X-ray irradiated Sporozoites. The immunity lasted at least 8 weeks. Mice immune against sporozoite challenge remained fully susceptible to challenge with erythrocytic stages. Immunization of mice with extracts of mosquito thorax failed to protect them, indicating that mosquito antigens were not directly responsible for the immunity observed in the basic experiments.     

Effects of Malaria (Plasmodium berghei) on the Maternal-Fetal Relationship in Mice

Plasmodium berghei infection was more severe in pregnant than in nonpregnant mice. Infection initiated on gestation day 7 resulted in rapidly increasing parasitemia and deaths of all pregnant mice within 12 days, while some nonpregnant mice survived until day 21 postinfection. When mice were infected on gestation day 12 or 14, a proportion of mice died before parturition; but some animals survived to deliver living pups. Reduced birthweights and increased spleen weight to body weight ratios were seen in pups from infected mice as compared with pups from uninfected animals. Histopathological abnormalities of placentae from infected animals included degeneration of the normal labyrinthine architecture and thickening of the trophobast separating maternal and fetal blood vessels.     

Reaktionen von Milzzellen in vitro bei der experimentellen Malaria-Infektion (Plasmodium berghei)

Zusammenfassung Es wurden Milzkulturen (vorwiegend weiße Pulpa) von normalen, von malaria-infizierten (Pl. berghei, 7. Inf. Tag) und von sicher immunen Swiss-Mäusen angelegt und den Explantaten am 7. Züchtungstag teils normales, teils stark parasitiertes Blut (mit flüssigem Medium 110 verdünnt) zugegeben.Ohne Behandlung besitzen Milzkulturen von frisch infizierten Tieren die größte Wachstumstendenz. Sie wird durch eine kürzere Latenzzeit und eine stärker ausgedehnte Zuwachszone gekennzeichnet. Die geringste Wachstumstendenz ist bei Explantaten von immunen Tieren zu beobachten.Im Gegensatz zu Milzkulturen von normalen Mäusen weist die vom explantierten Milzgewebe frisch infizierter und immuner Mäuse auswachsende Epitheloidmembran deutliche Zell- und Kerngrößendifferenzen auf.Durch die Zugabe von Blut wird bei allen Milzkulturen von normalen und von infizierten Tieren die Vermehrung und das Auswandern von Makrophagen gefördert. Es lassen sich sowohl morphologisch als auch funktionell 4 verschiedene Makrophagentypen abgrenzen. Bei Explantaten vom Milzgewebe immuner Mäuse bewirkt die Blutzugabe erst wesentlich später und dann auch nicht im gleichen Ausmaß die Proliferation und das Auswandern von Makrophagen.Die den Explantaten zugegebenen normalen und parasitierten Erythrozyten werden durch Makrophagen der Milzkulturen von normalen und infizierten Mäusen in sehr großer Anzahl phagozytiert. Normales oder parasitiertes Blut unterscheiden sich in ihrer Wirkung nur quantitativ, nicht qualitativ. Vermutlich befinden sich die Erythrozyten in der Gewebekultur in einem Milieu, das dem der physiologischen Zwangsarretierung im Retikulum der Milzpulpa gleicht. In Milzkulturen von immunen Mäusen sind dagegen nur ausnahmsweise Zellen vorhanden, die rote Blutkörperchen inkorporiert haben, auch parasitierte Erythrozyten werden nicht häufiger phagozytiert.Diese Beobachtungen lassen den Schluß zu, daß die Phagozytose von ganzen Erythrozyten und somit die mechanische Beseitigung der in ihnen eingeschlossenen Parasiten nur als unspezifische Abwehrleistung gegen den Malariaerreger zu bewerten ist. Auf eine gesteigerte Erythrozytenphagozytose läßt sich jedoch die Pathogenese der Anämie zurückführen, die sowohl für die menschliche Malaria als auch für die der Nagetiere charakteristisch ist.

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Summary Tissue cultures have been set up from the white pulp of spleens of normal mice, mice infected with P. berghei (seventh day of infection) and mice of a high degree of immunity to this parasite.On the seventh day of in vitro cultures of the splenic tissue, normal blood or highly parasitised blood was added in a concentration of 110 of the fluid medium. Spleen expiants from infected mice showed the highest growth activity, especially with regard to the shortening latency period and the size of the growth zone. Growth acticity in spleen explants from immune mice was found to be the least.The epitheloid membrane in spleen cultures from normal mice is composed of a uniform cell population, whereas the epitheloid membranes in cultures from mice during primary infection and from immune mice is composed of cells irregular in shape and size. Spleen cultures from normal or newly infected mice show an increased proliferation and migration of macrophages; on the other hand in spleen cultures from immune mice, proliferation of microphages was seen later and at a lesser degree.Phagocytosis of normal or parasitised erythrocytes by macrophages in cultures from normal or freshly infected mice is considerably higher than in those from immune mice.These findings lead to the conclusion that erythrophagocytosis (and thus the distribution of parasites within the red blood cells) is probably an early and unspecific defence mechanism of the host. On the other hand, anaemia observed in cases of malaria (rodent or human) may be caused by increased activity of macrophages against not only parasitised but also normal red cells.

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Als Gast von der Abteilung für experimentelle Cytologie der Slowakischen Akademie der Wissenschaften in Bratislava.     

Effect of inhibitors on glucose transport in malaria (Plasmodium berghei) infected erythrocytes

Effect of inhibitors on glucose transport in malaria (Plasmodium berghei) infected erythrocytes. International Journal for Parasitology16: 441–446. The effect of cytochalasin B and phloretin on transport of d-glucose and 2-deoxy-d-glucose into Plasmodium berghei-infected mouse erythrocytes was studied. Both the inhibitor-sensitive and insensitive fractions of transport in the infected erythrocytes were increased compared with normal erythrocytes. The i₅₀ values (concentrations of inhibitor producing 50% inhibition) were similar for both infected and normal erythrocytes, indicating that the binding affinities of the carrier were not substantially changed, but the turnover number, availability, or the number of the carrier may have increased in infection. There was a large increase in the transport of l-glucose into infected erythrocytes. Neither inhibitor showed any effect on transport of l-glucose into infected or normal erythrocytes. d-Galactose and d-fructose also showed a large transport increase mostly insensitive to cytochalasin B. The specificity of the transport increase raises the possibility of the presence of a new pathway other than simple diffusion, or the carrier-mediated pathway revealed by cytochalasin B or phloretin inhibition.     

Wolbachia strain wAlbB enhances infection by the rodent malaria parasite Plasmodium berghei in Anopheles gambiae mosquitoes

Wolbachia, a common bacterial endosymbiont of insects, has been shown to protect its hosts against a wide range of pathogens. However, not all strains exert a protective effect on their host. Here we assess the effects of two divergent Wolbachia strains, wAlbB from Aedes albopictus and wMelPop from Drosophila melanogaster, on the vector competence of Anopheles gambiae challenged with Plasmodium berghei. We show that the wAlbB strain significantly increases P. berghei oocyst levels in the mosquito midgut while wMelPop modestly suppresses oocyst levels. The wAlbB strain is avirulent to mosquitoes while wMelPop is moderately virulent to mosquitoes pre-blood meal and highly virulent after mosquitoes have fed on mice. These various effects on P. berghei levels suggest that Wolbachia strains differ in their interactions with the host and/or pathogen, and these differences could be used to dissect the molecular mechanisms that cause interference of pathogen development in mosquitoes.     

Fansidar prophylaxis, therapy, and immune responses in rodent malaria (Plasmodium berghei)

In order to determine the effect of Fansidar on plasmodial infection in mice, outbred, adult, Swiss-Webster mice were treated with Fansidar (20 mg sulfadoxine and 1 mg pyrimethamine/kg body weight) at various intervals before and/or after inoculation with blood stages of Plasmodium berghei. Drug therapy resulted in cure if it was given before the parasitemia rose to 53%. Oral administration of Fansidar was more effective in reducing or preventing parasitemia than intramuscular injection. Fatal infections were prevented if mice were treated orally with one dose of Fansidar 2 days before inoculation with P. berghei, whereas only partial protection occurred in animals treated 4 or more days before inoculation. Fansidar administered on two consecutive days provided protection if the drug was given at 3 and 2 days before inoculation. Administration of Fansidar for three consecutive days protected all animals if given on days 8 to 6 before inoculation. After oral administration of Fansidar, the parasitemia dropped dramatically and was undetectable at 60 hr. At 12 hr after oral treatment, schizonts and trophozoites were numerous, but there were few merozoites. Schizonts were the predominant stage at 24 hr, whereas merozoites predominated at 36 hr. Swiss-Webster and C57BL/6 mice became immune to a lethal dose of P. berghei after 4 cycles of inoculation and drug cure. Protective immunity was still present at 472 days after the fifth parasite inoculation.