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

Abstract

Tsetse flies are the medically and agriculturally important vectors of African trypanosomes. Information on the molecular and biochemical nature of the tsetse͞trypanosome interaction is lacking. Here we describe three antimicrobial peptide genes, attacin, defensin, and diptericin, from tsetse fat body tissue obtained by subtractive cloning after immune stimulation with Escherichia coli and trypanosomes. Differential regulation of these genes shows the tsetse immune system can discriminate not only between molecular signals specific for bacteria and trypanosome infections but also between different life stages of trypanosomes. The presence of trypanosomes either in the hemolymph or in the gut early in the infection process does not induce transcription of attacin and defensin significantly. After parasite establishment in the gut, however, both antimicrobial genes are expressed at high levels in the fat body, apparently not affecting the viability of parasites in the midgut. Unlike other insect immune systems, the antimicrobial peptide gene diptericin is constitutively expressed in both fat body and gut tissue of normal and immune stimulated flies, possibly reflecting tsetse immune responses to the multiple Gram-negative symbionts it naturally harbors. When flies were immune stimulated with bacteria before receiving a trypanosome containing bloodmeal, their ability to establish infections was severely blocked, indicating that up-regulation of some immune responsive genes early in infection can act to block parasite transmission. The results are discussed in relation to transgenic approaches proposed for modulating vector competence in tsetse.Glossina ͉ insect immunity ͉ vector control ͉ transgenesis ͉ symbiosis T he life cycle of the parasitic African trypanosomes (Euglenozoa: Kinetoplastida) in their insect vector, the tsetse fly (Diptera: Glossinidae), begins when it feeds from an infected mammalian host. For successful transmission, the parasite undergoes two stages of differentiation in the fly: first, establishment in midgut and then maturation in the mouthparts or salivary glands. In the midgut, the mammalian bloodstream parasites rapidly differentiate to procyclic forms and begin to replicate (establishment). Once established in the midgut, trypanosomes migrate forwards to the proventriculus and the mouthparts, where they begin to differentiate into epimastigotes and eventually colonize the proboscis or salivary glands, depending on the parasite species (1). Here they differentiate into metacyclic forms infective to mammals (maturation) and can be transmitted to the next host during blood feeding by the fly (2). It is generally thought that during normal development in the fly, there are no intracellular stages, although reports of intracellular Trypanosoma brucei rhodesiense (3, 4) and Trypanosoma congolense (5) in the anterior midgut cells have been published. It is also thought that during normal infection, trypanosomes do not cross an epithelial barrier to enter the fly, although there are several repo...

Activation of host constitutive immune defence by an intestinal trypanosome parasite of bumble bees

“…Surprisingly, we found that infection by this non-invasive parasite produced an increase in the constitutive 10 15 pro-Phenoloxidase immune system present in the haemolymph, a previously unreported aspect of the invertebrate immune function in this particular in vivo context. However, in contrast to other recent studies 20 (Boulanger, et al, 2001;Hao, et al, 2001;Boulanger, et al, 2002), we found no evidence for a similar increase in the production of inducible antibacterial peptides.…”

“…This 20 adds to recent evidence that such infections can induce the production of antibacterial peptides (Boulanger, et al, 2001;Hao, et al, 2001;Boulanger, et al, 2002). Together these results There is indeed accumulating evidence that local infection of the gut triggers a systemic immune response and, vice versa, a systemic 17 response induces a local response (Lehane et al, PNAS 1997, Nakajima et al…”

“…It has been suspected that immune messengers connecting gut tissue and the fat body (a prime site of the immune system) inlcude nitric oxide or cytokine-like molecules (Hao, et al, 2001;) , Antibacterial activity 0.0 ± 0.00 1.7 ± 1.20 1.9 ± 1.20 0.6 ± 0.56 0.0 ± 0.00 3.4 ± 2.26 2.2 ± 1.18 3.1 ± 1.27…”

“…The main defences of insects against such parasites are thought to be lectins, the peritrophic matrix, lysis, and melanisation and encapsulation above the basal lamina of the gut (reviewed in Kaslow & Welburn (1996)). Recent work, however, suggests that interactions between gut parasites and the invertebrate immune system may be more complex than previously suspected (Kaaya, Flyg & Boman, 1987;Richman, et al, 1997;Lowenberger, et al, 1999;Boulanger, et al, 2001;Hao, et al, 2001;Boulanger, et al, 2002). Invertebrates possess an innate immune system, which has been the focus of much recent study (for reviews, see Hoffmann, Reichhart & Hetru (1996) ;Hoffmann & Reichhart, (1997) ;Hoffmann, et al (1999)).…”

Preliminary characterization of a Rhodnius prolixus hemolymph trypanolytic protein, this being a determinant of Trypanosoma rangeli KP1(+) and KP1(-) subpopulations' vectorial ability

“…(Hao et al 2001) and stomoxyn isolated from S. calcitrans against T. brucei rhodesiense (Boulanger et al 2002b). …”