Dinophyceae use exudates as weapons against the parasite Amoebophrya sp. (Syndiniales)

SummaryParasites of the genus Amoebophrya sp. are important contributors to marine ecosystems and can be determining factors in the demise of blooms of Dinophyceae, including microalgae commonly responsible for toxic red tides. Yet they rarely lead to the total collapse of Dinophyceae blooms. The addition of resistant Dinophyceae (Alexandrium minutum or Scrippsiella donghaienis) or their exudate into a well-established host-parasite culture (Scrippsiella acuminata-Amoebophrya sp.) mitigated the success of the parasite and increased the survival of the sensitive host. Effect were mediated via water-borne molecules without the need of a physical contact. Severity of the anti-parasitic defenses fluctuated depending on the species, the strain and its concentration, but never totally prevented the parasite transmission. The survival time of Amoebophrya sp. free-living stages (dinospores) decreased in presence of A. minutum but not of S. donghaienis. The progeny drastically decreased with both species. Integrity of the membrane of dinospores was altered by A. minutum which provided a first indication on the mode of action of these anti-parasitic molecules. These results demonstrate that extracellular defenses are an effective strategy against parasites that does not only protect the resistant cells but also have the potential to affect the whole surrounding community.

Antimalarial Activity of Human Group IIA Secreted Phospholipase A2 in Relation to Enzymatic Hydrolysis of Oxidized Lipoproteins

ABSTRACT The level of human group IIA secreted phospholipase A2 (hGIIA sPLA2) is increased in the plasma of malaria patients, but its role is unknown. In parasite culture with normal plasma, hGIIA is inactive against Plasmodium falciparum, contrasting with hGIIF, hGV, and hGX sPLA2s, which readily hydrolyze plasma lipoproteins, release nonesterified fatty acids (NEFAs), and inhibit parasite growth. Here, we revisited the anti-Plasmodium activity of hGIIA under conditions closer to those of malaria physiopathology where lipoproteins are oxidized. In parasite culture containing oxidized lipoproteins, hGIIA sPLA2 was inhibitory, with a 50% inhibitory concentration value of 150.0 ± 40.8 nM, in accordance with its capacity to release NEFAs from oxidized particles. With oxidized lipoproteins, hGIIF, hGV, and hGX sPLA2s were also more potent, by 4.6-, 2.1-, and 1.9-fold, respectively. Using specific immunoassays, we found that hGIIA sPLA2 is increased in plasma from 41 patients with malaria over levels for healthy donors (median [interquartile range], 1.6 [0.7 to 3.4] nM versus 0.0 [0.0 to 0.1] nM, respectively; P < 0.0001). Other sPLA2s were not detected. Malaria plasma, but not normal plasma, contains oxidized lipoproteins and was inhibitory to P. falciparum when spiked with hGIIA sPLA2. Injection of recombinant hGIIA into mice infected with P. chabaudi reduced the peak of parasitemia, and this was effective only when the level of plasma peroxidation was increased during infection. In conclusion, we propose that malaria-induced oxidation of lipoproteins converts these into a preferential substrate for hGIIA sPLA2, promoting its parasite-killing effect. This mechanism may contribute to host defense against P. falciparum in malaria where high levels of hGIIA are observed.

PlasmoTron: an open-source platform for automated culture of malaria parasites

We have created a system which allows an inexpensive opensource liquid-handling robot to automate most aspects of bloodstage malaria parasite culture. Parasites are cultured in multiwell microplates, with their details recorded in a database. Information in the database is used to generate commands for the robot to feed, monitor and passage parasite cultures. We show that the system is capable of raising cultures after transfection and then maintaining them at desired parasitaemias, facilitiating significant scale up of both routine culture and experimental genetic modification. The PlasmoTron software is available at plasmotron.org.

Insights Gained fromP. falciparumCultivation in Modified Media

In vitrocultivation ofPlasmodium falciparum, the agent of severe human malaria, has enabled advances in basic research and accelerated the development of new therapies. Since the introduction ofin vitroparasite culture nearly 40 years ago, most workers have used a medium consisting of RPMI 1640 medium supplemented with lipids and hypoxanthine. While these standardized conditions yield robust parasite growth and facilitate comparison of results from different studies, they may also lead to implicit assumptions that limit future advances. Here, I review recent studies that used modified culture conditions to challenge these assumptions and explore parasite physiology. The findings are relevant to understandingin vivoparasite phenotypes and the prioritization of antimalarial targets.

Study of Some Parameters to Evaluate Immunization against Leishmaniasis in Golden hamsters

Incubation period, smears, impression and parasite culture for each liver, spleen, foot and blood were observed along five times follow up (15,30, 45, 60, 75, 90) days after challenge infection with virulent Leishmania tropica isolate in four groups of golden hamsters, inoculated with (one, two, three) doses of different antigens as following: Group (1) inoculated with autoclaved killed Leishmania tropica, Group (2) inoculated with BCG vaccine alone while Group (3) Inoculated with mixed vaccines (autoclaved killed Leishmania + BCG) and (4) control animals inoculated with phosphate buffer saline. Group 3, was considered as the best vaccine in this study because animal inoculated with this vaccine showed the following results compared with other antigens: - No lesion appeared along 90 days of following up.- Negative foot impression and culture up to 15 and 30 days of infection respectively, - Negative spleen and liver impression up to 30 days of infection when comparing with other groups.

Malaria Parasites Giving Rise to Recrudescence In Vitro

ABSTRACT Recrudescences were simulated in vitro with drug treatment to examine how drug-sensitive parasites survive the treatment. Various numbers of cultured parasites were treated with lethal doses of pyrimethamine or mefloquine for various lengths of time. Recrudescences were observed in parasite populations with larger initial numbers of parasites when the treatment duration was prolonged. Equal numbers of parasitized erythrocytes were treated with various concentrations of pyrimethamine or mefloquine. There was no clear linear relationship between the incidence of recrudescence and the drug concentration. Parasites that had recrudesced were continuously allowed to recrudesce in the succeeding recrudescence experiments. Both the duration from the cessation of treatment to the time at which the recrudescent parasitemia level reached 1% and the growth rate of recrudescent parasites were equal among these recrudescences. The recrudescent parasites in these experiments were as sensitive to the drugs as the parasites tested before treatment were. These results suggest that a parasite culture may contain parasites in some phases that are not killed by drug for up to 10 days, which explains the recrudescences that occur even after treatment.