TRYPANOSOMA-BRUCEI-RHODESIENSE - THE INHIBITION OF HL-60 CELL-GROWTH BY THE AFRICAN TRYPANOSOMES IN-VITRO

Trypanosomiasis is of major public health importance in Africa where the disease affects man and livestock. In order to explore the underlying mechanisms of pathogenesis in African trypanosomiasis, we studied the inhibition of host cell (human promyelocytic HL-60 cells) growth by Trypanosoma brucei rhodesiense using an in vitro system. This inhibition was not due to changes in pH or nutritional depletion of the culture medium by the trypanosomes as inhibitory activity was still observed in cultures that had been supplemented with glucose or fresh culture medium. Our study suggests that the African trypanosomes produce a soluble factor which inhibits the growth of HL-60 cells. This growth inhibitor does not appear to kill the HL-60 cells as determined by the trypan blue dye exclusion test. The production of this factor does not require host cell contact nor does it require a host cell cofactor. The trypanosome growth inhibitor is strictly a trypanosome product. Estimation of the molecular weight of the trypanosome growth inhibitor with Amicon filters revealed that the factor is greater than 30,000 Da in size. Protease and heat treatment of the factor resulted in the depletion of inhibitory activity. These results indicate that the African trypanosomes produce a large-molecular-weight protein growth inhibitory factor which could play a role in the pathogenesis of the disease. © 1993 Academic press, Inc.