Immunization with LJM11 salivary protein protects against infection with Leishmania braziliensis in the presence of Lutzomyia longipalpis saliva

Leishmania is transmitted in the presence of sand fly saliva. Protective immunity generated by saliva has encouraged identification of a vector salivary-based vaccine. Previous studies have shown that immunization with LJM11, a salivary protein from Lutzomyia longipalpis, is able to induce a Th1 immune response and protect mice against bites of Leishmania major-infected Lutzomyia longipalpis. Here, we further investigate if immunization with LJM11 recombinant protein is able to confer cross-protection against infection with Leishmania braziliensis associated with salivary gland sonicate (SGS) from Lutzomyia intermedia or Lu. longipalpis. Mice immunized with LJM11 protein exhibited an increased production of anti-LJM11 IgG, IgG1 and IgG2a and a DTH response characterized by an inflammatory infiltrate with the presence of CD4⁺ IFN-γ⁺ T cells. LJM11-immunized mice were intradermally infected in the ear with L. braziliensis in the presence of Lu. longipalpis or Lu. intermedia SGS. A significant reduction of parasite numbers in the ear and lymph node in the group challenged with L. braziliensis plus Lu. longipalpis SGS was observed, but not when the challenge was performed with L. braziliensis plus Lu. intermedia SGS. A higher specific production of IFN-γ and absence of IL-10 by lymph node cells were only observed in LJM11 immunized mice after infection. After two weeks, a similar frequency of CD4⁺ IFN-γ⁺ T cells was detected in LJM11 and BSA groups challenged with L. braziliensis plus Lu. longipalpis SGS, suggesting that early events possibly triggered by immunization are essential for protection against Leishmania infection. Our findings support the specificity of saliva-mediated immune responses and reinforce the importance of identifying cross-protective salivary antigens.

Identification of Algerian Field-Caught Phlebotomine Sand Fly Vectors by MALDI-TOF MS

BACKGROUND

Phlebotomine sand flies are known to transmit Leishmania parasites, bacteria and viruses that affect humans and animals in many countries worldwide. Precise sand fly identification is essential to prevent phlebotomine-borne diseases. Over the past two decades, progress in matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) has emerged as an accurate tool for arthropod identification. The objective of the present study was to investigate the usefulness of MALDI-TOF MS as a tool for identifying field-caught phlebotomine.

METHODOLOGY/PRINCIPAL FINDINGS

Sand flies were captured in four sites in north Algeria. A subset was morphologically and genetically identified. Six species were found in these areas and a total of 28 stored frozen specimens were used for the creation of the reference spectrum database. The relevance of this original method for sand fly identification was validated by two successive blind tests including the morphological identification of 80 new specimens which were stored at -80°C, and 292 unknown specimens, including engorged specimens, which were preserved under different conditions. Intra-species reproducibility and inter-species specificity of the protein profiles were obtained, allowing us to distinguish specimens at the gender level. Querying of the sand fly database using the MS spectra from the blind test groups revealed concordant results between morphological and MALDI-TOF MS identification. However, MS identification results were less efficient for specimens which were engorged or stored in alcohol. Identification of 362 phlebotomine sand flies, captured at four Algerian sites, by MALDI-TOF MS, revealed that the subgenus Larroussius was predominant at all the study sites, except for in M'sila where P. (Phlebotomus) papatasi was the only sand fly species detected.

CONCLUSION

The present study highlights the application of MALDI-TOF MS for monitoring sand fly fauna captured in the field. The low cost, reliability and rapidity of MALDI-TOF MS analyses opens up new ways in the management of phlebotomine sand fly-borne diseases.

Evidence for a lectin specific for sulfated glycans in the salivary gland of the malaria vector, Anopheles gambiae

Salivary gland homogenate (SGH) from the female mosquitoes Anopheles gambiae, An. stephensi, An. freeborni, An. dirus and An. albimanus were found to exhibit hemagglutinating (lectin) activity. Lectin activity was not found for male An. gambiae, or female Ae aegypti, Culex quinquefasciatus, Phlebotomus duboscqi, and Lutzomyia longipalpis. With respect to species-specificity, An. gambiae SGH agglutinates red blood cells (RBC) from humans, horse, sheep, goat, pig, and cow; it is less active for rats RBC, and not detectable for guinea-pigs or chicken RBC. Notably, lectin activity was inhibited by low concentrations of dextran sulfate 50–500 K, fucoidan, heparin, laminin, heparin sulfate proteoglycan, sialyl-containing glycans (e.g. 3′-sialyl Lewis X, and 6′-sialyl lactose), and gangliosides (e.g. GM3, GD1, GD1b, GTB1, GM1, GQ1B), but not by simple sugars. These results imply that molecule(s) in the salivary gland target sulfated glycans. SGH from An. gambiae was also found to promote agglutination of HL-60 cells which are rich in sialyl Lewis X, a glycan that decorates PSGL-1, the neutrophils receptor that interacts with endothelial cell P-selectin. Accordingly, SGH interferes with HL-60 cells adhesion to immobilized P-selectin. Because An. gambiae SGH expresses galectins, one member of this family (herein named Agalectin) was expressed in E. coli. Recombinant Agalectin behaves as a non-covalent homodimer. It does not display lectin activity, and does not interact with 500 candidates tested in a Glycan microarray. Gel-filtration chromatography of the SGH of An. gambiae identified a fraction with hemagglutinating activity, which was analyzed by 1D PAGE followed by in-gel tryptic digestion, and nano-LC MS/MS. This approach identified several genes which emerge as candidates for a lectin targeting sulfated glycans, the first with this selectivity to be reported in the SGH of a blood-sucking arthropod. The role of salivary molecules (sialogenins) with lectin activity is discussed in the context of inflammation, and parasite-vector-host interactions.

Functional characterization of a salivary apyrase from the sand fly, Phlebotomus duboscqi, a vector of Leishmania major

Two transcripts coding for proteins homologous to apyrases were identified by massive sequencing of a Phlebotomus (P.) duboscqi salivary gland cDNA library. The sequence analysis revealed that the amino acids important for enzymatic activity including nucleotidase activity and the binding of calcium and nucleotides were well conserved in these molecules. A recombinant P. duboscqi salivary apyrase was expressed in Escherichia coli and purified. The resulting protein efficiently hydrolyzed ADP and ATP, but not AMP, GDP, CDP or UDP, in a calcium-dependent manner. Further, the recombinant protein inhibited ADP- and collagen-induced platelet aggregation. The results indicated that this salivary protein plays an important role in the blood-feeding process in P. duboscqi. Its unique enzymatic activity makes the salivary apyrase an attractive candidate as a therapeutic agent for the treatment of thrombotic pathologies as well as a reagent for a wide variety of research purposes.

Evaluation of rhodamine B as an orally delivered biomarker for rodents and a feed-through transtadial biomarker for phlebotomine sand flies (Diptera: Psychodidae)

The purpose of this study was to evaluate the use of rhodamine B as an orally delivered biomarker for rodents and a feed-through transtadial biomarker for phlebotomine sand flies (Diptera: Psychodidae). Rhodamine B-treated hamsters were visibly marked for up to 8 wk, and their feces were fluorescent when examined under a fluorescence microscope. The development and survival of sand fly larvae fed feces of rhodamine B-treated hamsters were not significantly different from control sand flies. Adult male and female sand flies, that had been fed as larvae the feces of rhodamine B-treated hamsters, were fluorescent when examined using fluorescent microscopy and could be distinguished from control sand flies. Adult female sand flies that took bloodmeals from rhodamine B-treated hamsters were fluorescent when examined immediately after feeding. Rhodamine B incorporated rodent baits could be used to detect adult male and female sand flies that fed on the feces of baited rodents as larvae, or adult female sand flies that have taken a bloodmeal from bait-fed rodents. This would allow the delineation of specific foci with rodent-sand fly associations that would be susceptible to control by using feed-through or systemic insecticides.

Sand fly specificity of saliva-mediated protective immunity in Leishmania amazonensis-BALB/c mouse model

Immune response of BALB/c mice to the salivary antigens of sand flies was found to vary with different species used, i.e. Phlebotomus papatasi, Phlebotomus sergenti and Lutzomyia longipalpis. Exposure of mice to bites of these sand flies elicits production of antibodies, which are largely specific to different saliva antigens previously identified as unique to the respective fly species. When immunized intradermally (i.d.) with salivary gland lysates (SGL) of L. longipalpis, BALB/c mice developed partial protective immunity against challenges in the contralateral ears with Leishmania amazonensis plus the gland lysates. Preimmunization of these mice with the lysates from the other two species was ineffective, further indicative of the specificity of saliva-mediated immune response. The partial protective immunity observed is significant, although it is not as dramatic as reported previously in a different sand fly-mouse model. There is a correlation of this immunity with a lower number of mononuclear and polymorphonuclear phagocytes at the site of parasite inoculation. Vector species-specificity of this immunity implies its elicitation by unique saliva antigen-an issue which requires attention when designing saliva-based vaccines against leishmaniasis.

Sugars in the gut of the sandfly Phlebotomus orientalis from Dinder National Park, Eastern Sudan

The sandfly Phlebotomus orientalis Parrot (Diptera: Psychodidae) is the vector of visceral leishmaniasis in eastern and Upper Nile regions of Sudan, where vector infection rates of over 7% have been reported. Sugars are known to be important for development of the parasite and for increasing the survival and oviposition rates of several species of sandflies. In the present study we have analysed the sugars present in the guts of individuals and groups of male and female P. orientalis and compared these with sugars from several potential local plant sources: Acacia seyal, Balanites aegyptiaca and Combretum kordofanum. The distribution of these trees in Sudan is closely correlated with that of P. orientalis. Only 20% of individually analysed female sandflies had significant amounts of sugars present suggesting that P. orientalis either digest their sugar meal quickly or do not require regular sugar meals. Interestingly, the sugars present in the males were significantly different to those found in the females, indicating that they had fed on different sugar sources. There was evidence that fruit sugars from Balanites aegyptiaca, Combretum kordofanum and aphid or coccid honeydew are utilized by male and female P. orientalis. There was evidence to indicate that female P. orientalis feeds directly on honeydew. There was no evidence to indicate that direct feeding on leaves is a typical source for the sugar meal. There was no melizitose and only a very small amount of turanose present in the male, suggesting that honeydew was not an important sugar source for males.

Adenosine, AMP, and protein phosphatase activity in sandfly saliva

As they probe the skin for blood, sand flies inject saliva that prevents hemostasis. Sand fly saliva also promotes leishmaniasis by suppressing immunologic functions of macrophages. Saliva of Phlebotomus papatasi, the vector of Old World cutaneous leishmaniasis, contains adenosine and AMP. We show that Ph. papatasi saliva as well as pure adenosine down-regulate the expression of the inducible nitric oxide (NO) synthase gene in activated macrophages. In addition Ph. papatasi, but not Lutzomyia longipalpis, saliva inhibits the production of NO. Taken together, these data suggest that salivary adenosine is responsible for the down-regulation of NO synthesis. Saliva of both genera Phlebotomus and Lutzomyia contains significant levels of endogenous protein phosphatase-1/2A-like activity that is heat labile, inhibitable by okadaic acid and calyculine a, and does not require divalent cations.

Intra-species and stage-specific polymorphisms in lipophosphoglycan structure control Leishmania donovani-sand fly interactions

The Leishmania lipophosphoglycan conveys the ability for the parasites to avoid destruction in diverse host environments. During its life cycle within the sand fly vector, the parasite differentiates from a dividing procyclic promastigote stage that avoids expulsion from the midgut by attaching to the gut wall, to a nondividing metacyclic promastigote stage that is unable to attach to the midgut and migrates to the mouth parts for reinfection of a mammalian host. Lipophosphoglycan plays an integral role during this transition. Structurally, lipophosphoglycan is a multidomain glycoconjugate whose polymorphisms among species lie in the backbone Gal(beta 1,4)Man(alpha 1)-PO(4) repeating units and the oligosaccharide cap. We have characterized the lipophosphoglycan from an Indian L. donovani isolate. Unlike East African isolates, which express unsubstituted repeats and a galactose- and mannose-terminating cap, procyclic lipophosphoglycan from the Indian isolate consists of beta1,3-linked glucose residues that branch off the backbone repeats (n approximately 17) and also terminate the cap. Of biological significance, metacyclic lipophosphoglycan lacks the glucose residues while doubling the number of repeats. The importance of these developmental modifications in lipophosphoglycan structure was determined using binding experiments to Phlebotomus argentipes midguts. Procyclic promastigotes and procyclic LPG were able to bind to sand fly midguts in vitro whereas metacyclic parasites and LPG lost this capacity. These results demonstrate that the Leishmania adapts the synthesis of terminally exposed sugars of its LPG to manipulate parasite-sand fly interactions.

Detection of Leishmania lipophosphoglycan binding proteins in the gut of the sandfly vector

Binding to the midgut microvillar surface in the sandfly Phlebotomus papatasi is a prerequisite for successful development of Leishmania major within the gut of the vector. This paper describes a method for detecting microvillar-associated proteins which act as ligands for the parasite surface glycoconjugate lipophosphoglycan (LPG). Adhesion of LPG to midgut proteins was visualized by probing midgut extracts with LPG using a Western ligand blotting technique. Procyclic L. major LPG bound to a microvillar polypeptide band of 65 kDa (estimated in the non-reduced state) and bound variably to several lower molecular weight bands, probably degradation products or subunits of the primary binding polypeptides. Specificity of binding was confirmed by co-incubating biotinylated LPG with an LPG-specific mAb which resulted in a great reduction in binding.

Carbohydrate-binding specificities and physico-chemical properties of lectins in various tissue of phlebotominae sandflies

Physico-chemical properties and carbohydrate-binding specificity of hemagglutination activity (HA) were compared in tissue lysates and haemolymph of unfed and bloodfed females of five sandfly species. Sandfly gut lectins were found to be heat-labile, sensitive to dithiotreitol treatment, freezing/thawing procedures and were affected by divalent cations. The pH optimum of HA ranged between 7.0-7.5. Specificity of gut HA of all species studied was directed towards aminosugars and some glycoconjugates, mainly lipopolysaccharide from Escherichia coli K-235, heparin and fetuin. Gut HA of Phlebotomus papatasi (Scopoli, 1786) was strongly inhibited by lipophosphoglycan (LPG) from Leishmania major promastigotes. In females, that took blood, the HA was higher but the carbohydrate-binding specificity remained the same; this suggests that the same lectin molecule was present, at different levels, both in unfed and fed flies. High HA was found in ovaries of fed females of Lutzomyia longipalpis (Lutz et Nieva, 1912), P. papatasi and P. duboscqi Neveu-Lemaire, 1906. In P. papatasi and P. duboscqi the HA was present also in the haemolymph and head lysates of both fed and unfed females. Carbohydrate-binding specificity of HA present in these tissues was similar with the gut lectin.

Agglutination of Leishmania promastigotes by midgut lectins from various species of phlebotomine sandflies

Lectins which agglutinate Leishmania promastigotes were demonstrated in gut lysates from laboratory colonies of five Phlebotomus and two Lutzomyia species. In general, the highest agglutination titres were found in P. halepensis and Lu. longipalpis (Jacobina). Marked differences were found in the agglutination of promastigotes of various Leishmania species and strains and high agglutination titres were observed in some natural vector-parasite combinations, such as Phlebotomus argentipes and Le. donovani. Intraspecific variability, in agglutination of Le. major strains, could be related to the varying infectivity of the strains to laboratory animals. Similar carbohydrates, of which the most effective were D-mannosamine and N-acetyl-D-glucosamine, inhibited the agglutination of Le. major and Le. donovani promastigotes by midgut extracts from P. papatasi and Lu. longipalpis. D-Mannosamine and N-acetyl-D-glucosamine inhibited agglutination of promastigotes in all vector-parasite combinations. The results of the carbohydrate-inhibition tests indicate that the lectin specificities in Phlebotomus are similar to those in Lutzomyia.

Aspects of sandfly biology in southern Switzerland

During three field surveys of phlebotomine sandflies in the region of Sessa, Minor Malcantone, southern Switzerland, annually 1987-89, Phlebotomus perniciosus and P. mascittii were caught regularly by means of light traps, but only when the traps were in close association with humans. The most productive catching sites were in the middle of Sessa village, in basements or partially closed shelters in the immediate vicinity of human dwellings. All catching sites outside the village were negative. The only other sandfly species caught was Sergentomyia minuta, four specimens only. P.perniciosus and P.mascittii always occurred together and were found to feed--at least occasionally--on human blood. Glucose and fructose were identified in wild-caught sandflies of both species. A breeding place of P. mascittii was identified in the basement of a house in the middle of Sessa. Analyses of soil samples revealed moderately loamy humus with a slightly acidic pH (5.6).

Free amino acids in wild-caught Phlebotomus perniciosus and P. perfiliewi (Diptera: Psychodidae)

Free amino acids occurring in wild Phlebotomus perniciosus and P. perfiliewi were analyzed using high performance liquid chromatography. For both species the total concentration of amino acids, per unit weight, is over three times greater in females than in males. Qualitative inter-sex differences in amino acid compositions were also discovered: the most significant involving higher proportions of taurine and gamma-aminobutyric acid in females and higher proportions of arginine and glutamic acid in males. Although amino acid composition is consistent between females of both species, there are significant differences between males. The most important difference between males is an increase in tyrosine levels, at the expense of taurine, in P. perniciosus (as compared with P. perfiliewi). It is suggested that the intra- and inter-specific variation in amino acid composition identified in these studies could be due to ecological factors, such as differences in the sandflies natural amino acid sources (honeydew and/or plants), although a physiological explanation is not ruled out.