Using Recombinant Proteins from Lutzomyia longipalpis Saliva to Estimate Human Vector Exposure in Visceral Leishmaniasis Endemic Areas

Abstract

Background Leishmania is transmitted by female sand flies and deposited together with saliva, which contains a vast repertoire of pharmacologically active molecules that contribute to the establishment of the infection. The exposure to vector saliva induces an immune response against its components that can be used as a marker of exposure to the vector. Performing large-scale serological studies to detect vector exposure has been limited by the difficulty in obtaining sand fly saliva. Here, we validate the use of two sand fly salivary recombinant proteins as markers for vector exposure.Methodology/principal findingsELISA was used to screen human sera, collected in an area endemic for visceral leishmaniasis, against the salivary gland sonicate (SGS) or two recombinant proteins (rLJM11 and rLJM17) from Lutzomyia longipalpis saliva. Antibody levels before and after SGS seroconversion (n = 26) were compared using the Wilcoxon signed rank paired test. Human sera from an area endemic for VL which recognize Lu. longipalpis saliva in ELISA also recognize a combination of rLJM17 and rLJM11. We then extended the analysis to include 40 sera from individuals who were seropositive and 40 seronegative to Lu. longipalpis SGS. Each recombinant protein was able to detect anti-saliva seroconversion, whereas the two proteins combined increased the detection significantly. Additionally, we evaluated the specificity of the anti-Lu. longipalpis response by testing 40 sera positive to Lutzomyia intermedia SGS, and very limited (2/40) cross-reactivity was observed. Receiver-operator characteristics (ROC) curve analysis was used to identify the effectiveness of these proteins for the prediction of anti-SGS positivity. These ROC curves evidenced the superior performance of rLJM17+rLJM11. Predicted threshold levels were confirmed for rLJM17+rLJM11 using a large panel of 1,077 serum samples.ConclusionOur results show the possibility of substituting Lu. longipalpis SGS for two recombinant proteins, LJM17 and LJM11, in order to probe for vector exposure in individuals residing in endemic areas.

Immunity to Lutzomyia whitmani Saliva Protects against Experimental Leishmania braziliensis Infection

“…The antibodies developed by immunized mice recognized distinct salivary proteins (~45kDa,~36kDa, ~30kDaand ~28kDa). Further studies are needed to identify and characterize these molecules, an important aspect since identification of discrete salivary molecules recognized by naturally exposed individuals can contribute to the development of tools to monitor exposure to sand flies [24,25]. …”

The Anopheles gambiae cE5 salivary protein: a sensitive biomarker to evaluate the efficacy of insecticide-treated nets in malaria vector control

“…Moreover, salivary proteins may also be immunogenic and induce in vertebrates an antisaliva antibody (Ab) response that may be taken as a measure of exposure to vector bites. This strategy has been investigated for several vectors of human pathogens such as ticks [10], triatomine bugs [11e13], sand flies [14,15], tsetse flies [16,17] and mosquitoes [18e22]. More specifically, as far as malaria is concerned, it should be pointed out that IgG Ab response to Anopheles saliva or salivary gland extracts has been shown to represent an effective biomarker of human exposure to bites of malaria vectors [23e26].…”

Seroconversion of sentinel chickens as a biomarker for monitoring exposure to visceral Leishmaniasis

“…intermedia sand flies artificially fed on chicken blood spiked with Leishmania braziliensis 17. Recently, we demonstrated the possibility of evaluating anti-saliva antibody responses using recombinant proteins, circumventing the limitation of obtaining large quantities of sand fly salivary glands for large scale studies18. Although probing human immune responses to sand fly saliva may be a useful epidemiological marker of exposure, obtaining blood samples from the human population in the endemic areas may face cultural resistance.…”