Carbohydrate alters the trypanocidal activity of normal human serum with Trypanosoma brucei

Three categories of carbohydrates are distinguished based on their effects on the trypanocidal activity of normal human serum on Trypanosoma brucei. The first category includes carbohydrates such as glucose, mannose and fructose which are utilized by parasites as an energy source. These carbohydrates inhibit the trypanocidal activity in a concentration-dependent manner. The third category, represented by xylose and mannitol, are not energy sources to the parasites but inhibit the trypanocidal activity in a manner similar to the first category carbohydrate. However, at very high concentrations (approximately 140-150 mM), the inhibition is reversed. Glycerol is the only known carbohydrate belonging to the second category. Glycerol enhances the trypanocidal activity of normal human serum and of those sera which normally display no cytotoxic activity, although glycerol serves as an excellent energy source. On the basis of these results, the mechanisms by which these three categories of carbohydrate could alter the trypanocidal activity are discussed in terms of the interaction between a trypanocidal factor and the surface receptor.