Tsetse immune responses and trypanosome transmission: Implications for thedevelopment of tsetse-based strategies to reduce trypanosomiasis

Tsetse flies are the medically and agriculturally important vectors of Afri can trypanosomes. Information on the molecular and biochemical nature of th e tsetse/trypanosome interaction is lacking. Here we describe three antimic robial peptide genes, attacin, defensin, and diptericin, from tsetse fat bo dy tissue obtained by subtractive cloning after immune stimulation with Esc herichia coli and trypanosomes. Differential regulation of these genes show s the tsetse immune system can discriminate not only between molecular sign als specific for bacteria and trypanosome infections but also between diffe rent life stages of trypanosomes. The presence of trypanosomes either in th e hemolymph or in the gut early in the infection process does not induce tr anscription of attacin and defensin significantly. After parasite establish ment in the gut, however, both antimicrobial genes are expressed at high le vels in the fat body, apparently not affecting the viability of parasites i n the midgut. Unlike other insect immune systems, the antimicrobial peptide gene diptericin is constitutively expressed in both fat body and gut tissu e of normal and immune stimulated flies, possibly reflecting tsetse immune responses to the multiple Gram-negative symbionts it naturally harbors. Whe n flies were immune stimulated with bacteria before receiving a trypanosome containing bloodmeal, their ability to establish infections was severely b locked, indicating that up-regulation of some immune responsive genes early in infection can act to block parasite transmission. The results are discu ssed in relation to transgenic approaches proposed for modulating vector co mpetence in tsetse.