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Summary Previous experiments have shown that the infectivity of virulent trypomastigotes in L-cell culture was much more intensive not only for macrophages but also for newly cultured fibroblasts from the mouse heart as compared to low-virulent trypomastigotes in L-cell culture which had been derived from the same strain. On the other hand, the infectivity of virulent trypomastigotes for L-cells was less intensive. In the present work, new fibroblasts derived from muscles, skin, heart and kidney of newborn mice and established fibroblasts from mouse muscles were examined in terms of their susceptibility to trypomastigotes of different virulence. A slight difference of susceptibility to virulent trypomastigotes among new fibroblasts from different sources was found, i. e. fibroblasts derived from muscles and skin were more susceptible than those from heart and kidney. Growth of low-virulent trypomastigotes was suppressed in all new fibroblasts. This suppression was explained by the result that amastigote proliferation of a low-virulent strain was much slower in new fibroblasts from mouse muscles in spite of a similar penetrative ability of both kinds of trypomastigotes. Furthermore, a slight decrease in the susceptibility of new fibroblasts to virulent trypomastigotes was found depending on the length of time fibroblasts had been maintained.

A simple, highly reproducible method of synchronizing cultured Plasmodium (P) falciparum was studied. When culture of P. falciparum was kept at 0°C for 48 hours, the parasites showed a stepwise multiplication curve in 37°C incubation, while nontreated parasites manifested a linear continuous propagation pattern. Morphological observation revealed that parasites grew synchronously after cold treatment. Only parasites at the stage of the young ring form survived after 0°C exposure, and this caused homogeneity of the developmental stage of treated parasites. Syn-chronicity of the treated parasites was also confirmed by boosted DNA and protein syntheses when parasites reached the late trophozoite stage. Several advantages over other synchronization methods are discussed.

In vitro drug sensitivity to chloroquine (CQ), mefloquine (MQ) and quinine was investigated in 60 culture-adapted Plasmodium falciparum isolates from malaria patients in Padrecocha, a village in the Amazonian Department of Loreto, Peru. All isolates showed resistance to CQ, decreased susceptibility to quinine, and sensitivity to MQ. These isolates were examined for mutations in the P. falciparum multidrug resistance 1 (pfmdr1) and chloroquine resistance transporter (pfcrt) genes previously linked to CQ resistance. The mutations N86Y and D1246Y, two of the five mutations commonly observed in the pfmdr1 gene of CQ-resistant clones, were not found. The pfcrt mutation K76T, associated with CQ resistance, was identified in all the isolates tested. Sequence analysis of codons 72-76 in the pfcrt gene showed the haplotypes SVMNT and CVMNT., American Journal of Tropical Medicine and Hygiene, 70(5), pp.461-466; 2004