Rhodnius prolixusInfected withTrypanosoma rangeli:In Vivoandin VitroExperiments

Abstract

Studies were carried out on the activation of the prophenoloxidase (proPO) in adults ofRhodnius prolixusinfected by short and long epimastigote forms ofTrypanosoma rangeli. Thein vitroactivation of the proPO cascade usingl-DOPA as substrate was very low in the absence of fat body extract, hemolymph, and parasites. On the other hand, a higher PO activity was observed when short, but not long, epimastigotes ofT. rangeliwere incubated with fresh hemolymph, fat body extract, andl-DOPA. Supernatant from lysed long epimastigotes increased the PO activity at levels identical to those observed with supernatants from lysed short epimastigotes. Similarly, the PO activity of hemolymph obtained from inoculated insects with long epimastigotes ofT. rangelishowed a very low activity when incubated withl-DOPA compared to the PO activity of hemolymph taken from insects inoculated with short epimastigotes ofT. rangeli.Control insects inoculated with sterile PBS showed no PO activity. These data indicate the presence of (a) factor(s) in the hemolymph as well as in the fat body extract that may be released (or induced) by the presence of short epimastigotes ofT. rangeliand which results in the activation of theR. prolixusproPO system. The implications of these findings are discussed in relation to the development ofT. rangeliand its ability to overcome the proPO system, survive, and successfully colonize the hemolymph ofR. prolixus.