Abstract Background Immune response of triatomines plays an important role in the success or failure of transmission of T. cruzi . Studies on parasite–vector interaction have shown the presence of trypanolytic factors and have been observed to be differentially expressed among triatomines, which affects the transmission of some T. cruzi strains or DTUs (Discrete Typing Units). Methodology/Principal Findings Trypanolytic factors were detected in the hemolymph and saliva of R. prolixus against epimastigotes and trypomastigotes of T. cruzi II. To identify the components of the immune response that could be involved in this lytic activity, a comparative proteomic analysis was carried out, detecting 120 proteins in the hemolymph of R. prolixus and 107 in R. colombiensis . In salivary glands, 1103 proteins were detected in R. prolixus and 853 in R. colombiensis . A higher relative abundance of lysozyme, prolixin, nitrophorins, and serpin as immune response proteins was detected in the hemolymph of R. prolixus . Among the R. prolixus salivary proteins, a higher relative abundance of nitrophorins, lipocalins, and triabins was detected. The higher relative abundance of these immune factors in R. prolixus supports their participation in the lytic activity on T. cruzi II, but not on T. cruzi I, which is resistant to lysis by hemolymph and salivary proteins of R. prolixus due to mechanisms of evading oxidative stress caused by immune factors. Conclusions/Significance T. cruzi I is a DTU distributed from the southern United States to the center of Chile and Argentina, and its successful spread across this range could be related to resistance to oxidative stress in vectors. Future proteomic and transcriptomic studies on vectors and the interactions of the intestinal microbiota with parasites will help to confirm the determinants of successful or failed vector transmission of T. cruzi DTUs in different parts of the Western Hemisphere. Author summary Some factors can facilitate or prevent T. cruzi transmission, i.e. vector immunity. Our work has managed to detect a stronger immune response against T. cruzi II in R. prolixus saliva and haemolymph, compared to that of R. colombiensis . Proteins from both species’ saliva and haemolymph were analysed for studying factors which might have been involved in such response; most proteins were detected in both species’ haemolymph, thereby indicating common immune mechanisms. Three proteins having oxidative immune activity were only expressed in R. prolixus . Lipocalin diversity and abundance predominated in R. prolixus saliva; these proteins are involved in nitric oxide metabolism and their role in immunity could be key in host defence against T. cruzi . Recognising the components modulating parasite transmission in a vector helps in understanding how such factors act independently and how they would act synergistically against T. cruzi , thereby enabling us to establish tools regarding Chaga’s disease epidemiology, aimed at predicting T. cruzi distribution and creating transmission control mechanisms.

Comparative proteomic analysis of the hemolymph and salivary glands ofRhodnius prolixusandR. colombiensisreveals candidates associated with differential lytic activity againstTrypanosoma cruziI andT. cruziII