Background: Immune responses to sandfly saliva have been shown to protect animals against Leishmania infection. Yet very little is known about the molecular characteristics of salivary proteins from different sandflies, particularly from vectors transmitting visceral leishmaniasis, the fatal form of the disease. Further knowledge of the repertoire of these salivary proteins will give us insights into the molecular evolution of these proteins and will help us select relevant antigens for the development of a vector based anti-Leishmania vaccine.

LJM11, an abundant salivary protein from the sand fly Lutzomyia longipalpis, belongs to the insect "yellow" family of proteins. In this study, we immunized mice with 17 plasmids encoding L. longiplapis salivary proteins and demonstrated that LJM11 confers protective immunity against Leishmania major infection. This protection correlates with a strong induction of a delayed type hypersensitivity (DTH) response following exposure to L. longipalpis saliva. Additionally, splenocytes of exposed mice produce IFN-␥ upon stimulation with LJM11, demonstrating the systemic induction of Th1 immunity by this protein. In contrast to LJM11, LJM111, another yellow protein from L. longipalpis saliva, does not produce a DTH response in these mice, suggesting that structural or functional features specific to LJM11 are important for the induction of a robust DTH response. To examine these features, we used calorimetric analysis to probe a possible ligand binding function for the salivary yellow proteins. LJM11, LJM111, and LJM17 all acted as high affinity binders of prohemostatic and proinflammatory biogenic amines, particularly serotonin, catecholamines, and histamine. We also determined the crystal structure of LJM11, revealing a six-bladed ␤-propeller fold with a single ligand binding pocket located in the central part of the propeller structure on one face of the molecule. A hypothetical model of LJM11 suggests a positive electrostatic potential on the face containing entry to the ligand binding pocket, whereas LJM111 is negative to neutral over its entire surface. This may be the reason for differences in antigenicity between the two proteins.The salivary secretions of blood-feeding insects contain a rich mixture of proteins that act to prevent host hemostatic and inflammatory responses (1, 2). Individual proteins in the saliva inhibit the essential processes of coagulation, platelet activation, vasoconstriction, inflammation, and mast cell function (2). Additionally, certain of these salivary proteins are immunogenic, conferring protection against cutaneous and visceral leishmaniasis in several animal models following exposure to sand fly bites or immunization with a salivary component (3-9). In most of these studies, protection correlates with a delayed type hypersensitivity (DTH) 3 response to saliva or to a protective salivary molecule in the host skin that alters the outcome of infection (10, 11). These studies have established the potential of salivary proteins as components of vaccines against leishmaniasis.A major protein family in the saliva of the sand fly genera Lutzomyia and Phlebotomus is related by sequence to the "yellow" protein of Drosophila melanogaster and the major royal jelly proteins (MRJPs) of bees. Immunization with LJM11, a yellow protein from saliva of Lutzomyia longipalpis, protects hamsters against visceral leishmaniasis up to 2 months postinfection (4). This partial protection was associated with the induction at the site of challenge of a DTH response composed mainly of a mononuclear infiltrate ...

BackgroundSand flies deliver Leishmania parasites to a host alongside salivary molecules that affect infection outcomes. Though some proteins are immunogenic and have potential as markers of vector exposure, their identity and vector specificity remain elusive.Methodology/Principal FindingsWe screened human, dog, and fox sera from endemic areas of visceral leishmaniasis to identify potential markers of specific exposure to saliva of Lutzomyia longipalpis. Human and dog sera were further tested against additional sand fly species. Recombinant proteins of nine transcripts encoding secreted salivary molecules of Lu. longipalpis were produced, purified, and tested for antigenicity and specificity. Use of recombinant proteins corresponding to immunogenic molecules in Lu. longipalpis saliva identified LJM17 and LJM11 as potential markers of exposure. LJM17 was recognized by human, dog, and fox sera; LJM11 by humans and dogs. Notably, LJM17 and LJM11 were specifically recognized by humans exposed to Lu. longipalpis but not by individuals exposed to Lu. intermedia.Conclusions/SignificanceSalivary recombinant proteins are of value as markers of vector exposure. In humans, LJM17 and LJM11 emerged as potential markers of specific exposure to Lu. longipalpis, the vector of Leishmania infantum chagasi in Latin America. In dogs, LJM17, LJM11, LJL13, LJL23, and LJL143 emerged as potential markers of sand fly exposure. Testing these recombinant proteins in large scale studies will validate their usefulness as specific markers of Lu. longipalpis exposure in humans and of sand fly exposure in dogs.

We characterized a cDNA from Phlebotomus papatasi, PpChit1, which encodes a midgut specific chitinase and show the presence of a functional, blood-induced chitinolytic system in sand flies. PpChit1 is detected only in the midgut and is regulated by blood feeding. A recombinant protein (rPpChit1) produced in HEK 293-F cells exhibited a similar activity profile to that found in the native protein against several specific substrates, including an oligomeric glycol chitin and synthetic 4-methyl-umbelliferone labelled substrates. Western blotting showed that the native protein is recognized by mouse polyclonal antibodies against rPpChit1. Additionally, the rPpChit1 and the native chitinase displayed similar retention times in a HPLC size fractionation column. When added to rPpChit1 or to midgut lysates, PpChit1 sera reduced chitinolytic activity by 65-70%.