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Vol. 92(1), Jan./Feb. 1997 RESEARCH NOTE
Inactivation of Plasmodium falciparum Parasites
Using Maria de Fatima Ferreira-da-Cruz, Antonio Teva, Erika da Cruz Espindola-Mendes, Luiz Gonzaga dos Santos*, Claudio Tadeu Daniel-Ribeiro/+
Laboratorio de Pesquisas em Malaria, Departamento de
Imunologia, Instituto Oswaldo Cruz, Av. Brasil 4365, 21045-900 Rio de
Janeiro, RJ, Brasil +Correponding author. Fax: +55-21-280.1589
Received 13 May 1996 Code Number:OC97029 Sizes of Files: Text: 6.9K Graphics: Line drawings (gif) - 7.1K Key words: Plasmodium falciparum - gamma-irradiation - blood Bank - erythrocytes - transfusional malaria RESEARCH NOTE The high and relatively stable number of malaria cases in endemic areas shows us continuously how difficult is to control malaria. In addition, besides the mosquito bites, the transmission can also occur through transfusion of infected blood, fact that concerns particularly, but not exclusively, blood Banks in malaria endemic areas. In these centers, to the worry of preventing transfusional malaria cases, is added the preoccupation of avoiding the lose of a high number of donors during the screening procedures. These facts denote the need of alternative methodologies - for the selection of blood to be used in transfusion - that could offer fast, cheap and safe results. Irradiation of blood stage Plasmodium falciparum parasite had mainly been performed in order to attenuate Plasmodia for preparing malaria vaccines but no attention has been given regarding its use with prophylactic purposes (S Waki et al. 1983 Exper Parasitol 56: 339-345; S Waki et al. 1985 Z Parasitenkd 71: 213-218). Therefore, to determine the dose of gamma-irradiation which would produce attenuated parasites without affecting the erythrocyte stability was the ultimate goal of this study. For this purpose red blood cells (RBC) parasitized with the Palo Alto P. falciparum strain were asynchronously cultivated in RPMI 1640 medium enriched with 10% of normal human serum at 37 C in relatively anaerobic conditions (W Trager & JB Jensen 1976 Science 193: 673-675). This strain of P. falciparum was chosen in view of its adaptability to Saimiri sp. monkeys in our breeding conditions. For each experiment four Petri plaques (100x15 mm) containing 1 ml of RBC and 11 ml of RPMI medium - in order to obtain a 8% hematocrit - were utilized. From these, two contained 3-5% of parasitized RBC, and two were filled with nonparasitized RBC as controls. The contents of each plate was divided in two tubes, being one of them submitted to gamma-ray irradiation while nonirradiated ones were maintained at exactly the same locale conditions. The gamma-irradiation was performed at the National Cancer Institute (INCA) of Rio de Janeiro, Brazil using a Cobalt-60 deep therapy apparatus at a source to mid-sample distance of 40 cm. The tubes were placed in the gamma-ray source and irradiated at room temperature with a constant dose rate of 2 gray/min (1 gray /Gy = 100 rad). Parasitized and nonparasitized RBC were exposed to gamma-irradiation at 10000, 15000 and 20000 CGy. After irradiation the following crossings were realized before exposure to culture: A) irradiated parasitized RBC plus irradiated nonparasitized RBC; B) irradiated parasitized RBC plus nonparasitized RBC; C) parasitized RBC plus irradiated nonparasitized RBC; and D) parasitized RBC plus nonparasitized RBC. The sensitivity of P. falciparum to gamma-irradiation was measured by daily parasitemia calculation, as previously described (MF Ferreira-da-Cruz et al. 1995 Parasite 2: 23-29). Similar results were observed with both 10000 and 15000 CGy irradiations: groups A and B showed a reduction of parasitemia till days 6 (group A) or 7 (group B) when viable forms arised followed by an increase of parasitemia levels reaching 4.5% (group A) or 3.5% (group B) around day 11. As expected, in control groups (C and D) the parasitemia developed reaching around 7% at day 2 for both groups. In the 20000 CGy irradiation experiment it was possible to observe a reduction of parasitemia levels beginning at day 2 for both groups (A and B). Around day 4, the microscopic examination was negative and no parasites were detected till day 11. Control groups showed standard growth curves ( Fig.). The hemoglobin profile, evaluated by electrophoresis, and the initial and complete osmotic fragility tests (Bronstein Laboratory, Rio de Janeiro, Brazil) did not reveal any alteration in irradiated RBC that presented the same profile of non irradiated ones.
Acknowledgments: to the National Cancer Institute's staff and to all patients for their kindness and generous collaboration.
Copyright 1996 Fundacao Oswaldo Cruz The following images related to this document are available:Photo images[oc97029f1.jpg]Line drawing images[oc97029a.gif] |
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