Role of superoxide and reactive nitrogen intermediates in Rhodnius prolixus (reduviidae)/Trypanosoma rangeli interactions

This study compares aspects of the superoxide, nitric oxide and prophenolox idase pathways in Rhodnius prolixas hemolymph, measured in parallel, in res ponse to Trypanosoma rangeli inoculation. Responses to two strains of I: ra ngeli, and two developmental forms, were studied, and the results obtained were correlated with the ability of the parasites to survive, multiply, and complete their life cycles in the hemolymph of the host. T. rangeli H14 st rain parasites, which fail to complete their life cycle in Rhodnius by inva ding the salivary glands, stimulated high levels of superoxide and propheno loxidase activity, which peaked 24 h after inoculation. Simultaneously, the concentration of hemolymph nitrites and nitrates increased, indicative of nitric oxide activity, but parasite numbers remained low T. rangeli Choachi strain parasite inoculation also stimulated superoxide and prophenoloxidas e activity, which, though significantly lower than the equivalent responses to the H14 strain, also peaked at 24 h. However, nitrate and nitrite level s in Choachi strain-inoculated hemolymph rem;tined low, and this parasite s train multiplied rapidly, especially following peak superoxide activity, an d eventually invaded the salivary glands for transmission to a vertebrate h ost, in both strains, short form epimastigotes stimulated greater superoxid e and prophenoloxidase responses than long form epimastigotes. Injection of the NADPH oxidase inhibitor N-ethylmaleimide or the inducible nitric oxide synthase inhibitor S-methyl isothiourea sulfate caused significantly highe r insect mortalities in groups of R. prolixus inoculated with either parasi te strain compared with those of uninfected control insects. This indicates that both NADPH oxidase and nitric oxide synthase activity may be involved in the immune response of R. prolixus to infection by I: rangeli. Finally, Western blotting of R. prolixus hemocyte lysates revealed the presence of a protein immunologically related to the human NADPH oxidase complex, the i nitiator enzyme of the respiratory burst. (C) 2001 Academic Press.