Lectin signalling of maturation of T. congolense infections in tsetse.

The process of maturation of Trypanosoma congolense Broden in tsetse has been shown to be initiated by lectin secreted in the fly midgut. In the present study the duration of lectin signal required to induce maturation was determined by the sequential addition or removal of a specific lectin inhibitor (D+glucosamine) to the diet of infected male Glossina morsitans Westwood. An established midgut infection of T.congolense was found to require, at most, 72 h exposure to midgut lectin to begin the process of maturation. Longer exposure to midgut lectin increased the frequency of maturation, suggesting clonal variation in response to lectin stimulation occurs within trypanosome stocks. It is suggested that this variation corresponds to differences in lectin binding sites on the trypanosome surface. Midgut trypanosomes retained their ability to mature throughout their life in the fly; when lectin activity in the midgut was inhibited, the trypanosomes remained as procyclic forms but when this inhibition was removed maturation was able to proceed. This indicates that the process of maturation is dependent upon a signal from the fly and is not predetermined by the trypanosomes undergoing a fixed number of division cycles. The possible role of lectins in the maturation of trypanosomes in vitro is discussed.