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Lewis-Hughes P. H. and Howell M. J. 1984. In vitro culture of Plasmodium yoelii blood stages. International Journal for Parasitology 14: 447–451. Plasmodium yoelii infected reticulocytes were cultured for 72 h at either 37 or 20°C in MEM (Eagle's modification) medium containing, in addition, glucose, para-aminobenzoic acid and 5% foetal calf serum, buffered at pH 7.3 with sodium bicarbonate/ HEPES and maintained under 10% CO 2 in air. Red blood cell numbers were more stable at 20°C than at 37°C. Culture at both temperatures resulted in an increase in parasitaemia of the reticulocyte population over the initial 36 h at 37°C and for at least 72 h at 20°C. The effects of different temperatures appeared to be related to the continued presence of target cells. Parasites were not detected after 72 h culture at 37°C, but persisted for up to 120 h at 20°C. Increasing parasitaemia at both temperatures was associated with changes in the numbers of some parasite development types. Early falls in schizont numbers were associated with an increase in the numbers of ring forms. Trophozoite numbers tended to remain constant throughout the culture period. Viability of parasites cultured for 36 h was confirmed by their infectivity to CBA mice. In addition, parasites progressively incorporated H 3 -leucine into TCA-precipitable material over the initial 36 h of culture.

During the course of rodent malaria a marked decrease in the numbers of circulating lymphocytes within the peripheral blood occurred 2-4 days post-infection. Monocytes and polymorphs did not show the same degree of decline. For both avirulent Plasmodium yoelii and lethal Plasmodium berghei infections lymphocyte numbers returned to control levels by day 6-8 post-infection. While these levels were maintained until clearance of P. yoelii infection, a sustained and abnormal increase occurred during P. berghei infection. Early lymphocyte depletion was also observed following Babesia microti and Plasmodium vinckei petteri infections, and could be induced by freeze-thawed P. yoelii infected blood and its particulate, but not soluble, fraction. Corynebacterium parvum and sheep red blood cells had no depressant effect on peripheral blood lymphocyte counts. Cell trapping experiments indicated that peripheral blood lymphocytes were preferentially recruited to the spleen in the initial stages of infection. Cell surface marker tests showed that the major cell type involved was Thy-1.2+ T-lymphocytes.

The protection of mouse erythrocytes (RBC) parasitized with Plasmodium vinckei vinckei against activated oxygen species was examined in relation to the intraerythrocytic parasite load. RBC from highly infected animals were separated by density gradient centrifugation into six bands with increasing parasite content and with parasitemias ranging from 17% to 100%. Increase in parasite load was accompanied by a decrease in the activities of the enzymes superoxide dismutase (EC 1.15.1.1), catalase (EC 1.11.1.6), glutathione peroxidase (EC 1.11.1.9), glutathione reductase [NAD(P)H] (EC 1.6.4.2), and NADH-methemoglobin reductase (EC 1.6.2.2; NADH:ferricytochrome b5 oxidoreductase) in the RBC lysates. In contrast, the total amount of reduced glutathione increased in the highly parasitized bands. Furthermore, the vitamin E content of all RBC bands, including the one that contained mainly nonparasitized erythrocytes, was 3- to 5-fold higher than that of control noninfected RBC. Increasing parasite load was accompanied by an increase in the production of malonyldialdehyde, indicating enhanced lipid peroxidation. Our results indicate that oxidative stress is experienced by all RBC during a malarial infection and is accompanied by a variety of changes in the antioxidant defense mechanisms of the host and the parasite. Furthermore, it appears that the plasma membrane of the host cell is better protected against oxidative injury than are the membranes surrounding the parasite.