Optimisation of flow cytometric measurement of parasitaemia in plasmodium-infected mice

Mouse malaria is often used as a model for drug testing. The results of dru g trials are monitored by tedious (and consequently, sometimes inaccurate) microscopic counting of blood smears, or by flow cytometry. We suggest an i mproved, accurate and time-saving flow cytometric method for determination of parasitaemias in mice infected with Plasmodium vinckei petteri or Plasmo dium berghei. The method involves collection of drops of blood from the tai l vein, fixation, storage, permeabilisation. staining and analysis with a v isible range flow cytometer. Three nucleic acid dyes, YOYO-1, propidium iod ide and acridine orange were compared. YOYO-1 was found to be the best stai n for the discrimination of parasitised erythrocytes from non-infected ones . A good direct correlation was obtained between parasitaemia determined by conventional microscopy and parasitaemia measured by flow cytometry. Drug effects could be assessed by the cytometric method. For the detection of lo w level of parasitemia. parasitised cells were treated with RNAse to comple tely cancel RNA-derived signals originating from host reticulocytes. This p rocedure also revealed discrete peaks arising from red cells infected with multiple parasites or from parasites with different numbers of nuclei. (C) 2000 Published by Elsevier Science Ltd on behalf of the Australian Society for Parasitology Inc. All rights reserved.