Rhodnius prolixus infected with Trypanosoma rangeli: In vivo and in vitro experiments

Studies mere carried out on the activation of the prophenoloxidase (proPO) in adults of Rhodnius prolixus infected by short and long epimastigote form s of Trypanosoma rangeli. The in vitro activation of the proPO cascade usin g L-DOPA as substrate was very low in the absence of fat body extract, hemo lymph, and parasites. On the other hand, a higher PO activity was observed when short, but not long, epimastigotes of T. rangeli mere incubated with f resh hemolymph, fat body extract, and L-DOPA, Supernatant from lysed long e pimastigotes increased the PO activity at levels identical to those observe d with supernatants from lysed short epimastigotes, Similarly the PO activi ty of hemolymph obtained from inoculated insects with long epimastigotes of T. rangeli showed a very lo cv activity when incubated with L-DOPA compare d to the PO activity of hemolymph taken from insects inoculated with short epimastigotes of T. rangeli. Control insects inoculated with sterile PBS sh owed no PO activity These data indicate the presence of (a) factor(s) in th e hemolymph as well as in the fat body extract that may be released (or ind uced) by the presence of short epimastigotes of T. rangeli and which result s in the activation of the R. prolixus proPO system. The implications of th ese findings are discussed in relation to the development of T. rangeli and its ability to overcome the proPO system, survive, and successfully coloni ze the hemolymph of R. prolixus. (C) 1999 Academic Press.