A COLORIMETRIC ASSAY FOR TRYPANOSOME VIABILITY AND METABOLIC FUNCTION

We have adapted a tetrazolium salt (MTT) colorimetric cytotoxicity ass ay to the assessment of viability and metabolic function in cultured A frican trypanosomes. Trypomastigotes of Trypanosoma congolense and T. brucei rhodesianse were harvested from the blood of parasitemic rats a nd cultured under axenic conditions that support trypanosome viability and growth. Analysis of serial dilutions of these bloodstream forms i ndicated that the assay could detect 10(4) parasites. To assess the ef fect of lymphoid cytokines on trypomastigote viability, 10(5) freshly harvested parasites were cultured with a wide range of dilutions of hu man recombinant IL-1, IL-3, IL-6, interferon-gamma (IFNgamma) or tumor necrosis factor-alpha (TNFalpha), or bovine recombinant IFNgamma or T NFalpha for 24, 48 or 96 h. These cytokines had no apparent growth enh ancing or inhibitory effect on the trypomastigotes compared with growt h in supplemented medium alone. This assay has several advantages over traditional counting methods, including increased sensitivity and rap id, repeatable quantitation. This adaptation of the MTT colorimetric a ssay should be useful in screening drugs and host-derived factors for growth-modulating effects on trypanosomes and other extracellular prot ozoan parasites.