In this work we reviewed historical and recent data on Leishmania spp. infection combining data collected in Turkmenistan, Uzbekistan, Kazakhstan, Kyrgyzstan, Iran, China and Mongolia. We specifically focused on a complex of co-existing species (Leishmania major, Leishmania turanica and Leishmania gerbilli) sharing the same animal reservoirs and vectors. In addition, we analysed the presence of dsRNA viruses in these species and discussed future research directions to identify species-specific traits, which may determine susceptibility of different Leishmania spp. to viral infection.

Leishmania rely heavily on glycans to complete their digenetic life cycle in both mammalian and phlebotomine sand fly hosts. Leishmania promastigotes secrete a proteophosphoglycan-rich gel (Promastigote Secretory Gel, PSG) that is regurgitated during transmission and can exacerbate infection in the skin. Here we explored the role of PSG from natural Leishmania-sand fly vector combinations by obtaining PSG from Leishmania (L.) major-infected Phlebotomus (P.) papatasi and P. duboscqi and L. tropica-infected P. arabicus. We found that, in addition to the vector's saliva, the PSG from L. major and L. tropica potently exacerbated cutaneous infection in BALB/c mice, improved the probability of developing a patent cutaneous lesion, parasite growth and the evolution of the lesion. Of note, the presence of PSG in the inoculum more than halved the prepatent period of cutaneous L. tropica infection from an average of 32 weeks to 13 weeks. In addition, L. major and L. tropica PSG extracted from the permissive experimental vector, Lutzomyia (Lu.) longipalpis, also exacerbated infections in mice. These results reinforce and extend the hypothesis that PSG is an important and evolutionarily conserved component of Leishmania infection that can be used to facilitate experimental infection for drug and vaccine screening.

The main goal of this work consisted in cloning, purifying and characterizing a protein phosphatase 2C (PP2C) from promastigotes of Leishmania major. The gene was cloned and amplified by PCR using specific oligonucleotides and the recombinant protein was purified by affinity chromatography. The peak with maximal protein concentration was analysed by sodium dodecyl sulphate-polyacrylamide gel electrophoresis and revealed a protein of 44·9 kDa with PP2C activity. This activity was dependent on divalent cations (Mg+2 and Mn+2) and was optimal at pH of 8·5, using phosphothreonine as the substrate. Sanguinarine inhibited the activity of the recombinant LmPP2C, while protein tyrosine phosphatase inhibitors had no effect. The recombinant LmPP2C was used to generate polyclonal antibodies. These antibodies recognized a protein of 44·9 kDa in different Leishmania species; the LmPP2C was localized in the flagellar pocket and the flagellum of promastigotes.

Synthesized lipophilic tyrosyl ester derivatives with increasing lipophilicity were effective against Leishmania (L.) major and Leishmania infantum species in vitro. These findings prompted us to test in vivo leishmanicidal properties of these molecules and their potential effect on the modulation of immune responses. The experimental BALB/c model of cutaneous leishmaniasis was used in this study. Mice were infected with L. major parasites and treated with three in vitro active tyrosyl esters derivatives.

Among these tested tyrosylcaprate (TyC) compounds, only TyC10 exhibited an in vivo anti-leishmanial activity, when injected sub-cutaneously (s.c.). TyC10 treatment of L. major-infected BALB/c mice resulted in a decrease of lesion development and parasite load. TyC10 s.c. treatment of non-infected mice induced an imbalance in interferon γ/interleukin 4 (IFN-γ/IL-4) ratio cytokines towards a Th1 response. Our results indicate that TyC10 s.c. treatment improves lesions’ healing and parasite clearance and may act on the cytokine balance towards a Th1 protective response by decreasing IL-4 and increasing IFN-γ transcripts. TyC10 is worthy of further investigation to uncover its mechanism of action that could lead to consider this molecule as a potential drug candidate.

Green fluorescent protein (GFP)-parasite transfectants have been widely used as a tool for studying disease pathogenesis in several protozoan models and their application in drug screening assays has increased rapidly. In the past decade, the expression of GFP has been established in several Leishmania species, mostly for in vitro studies. The current work reports generation of four transgenic parasites constitutively expressing GFP (Leishmania mexicana, Leishmania aethiopica, Leishmania tropica and Leishmania major) and their validation as a representative model of infection. This is the first report where stable expression of GFP has been achieved in L. aethiopica and L. tropica. Integration of GFP was accomplished through homologous recombination of the expression construct, pRib1.2αNEOαGFP downstream of the 18S rRNA promoter in all species. A homogeneous and high level expression of GFP was detected in both the promastigote and the intracellular amastigote stages. All transgenic species showed the same growth pattern, ability to infect mammalian host cells and sensitivity to reference drugs as their wild type counterparts. All four transgenic Leishmania are confirmed as models for in vitro and possibly in vivo infections and represent an ideal tool for medium throughput testing of compound libraries.

In the present study, we show for the first time that lipophosphoglycan (LPG) stimulated cytokine production by human peripheral blood mononuclear cells is also mediated via Toll-like receptor (TLR2). In addition, in order to verify if TLR2 is involved in recognition of the purified PGs, neutralizing mAbs against TLR2 and TLR4 were used to treat the cells before being stimulated with PGs. We found strong Th1-promoting cytokines induced by sLPG but not by mLPG which was blocked by presence of anti-TLR2 mAb. This finding reveals a mechanism by which the first encounter and recognition of L. major promastigotes by mLPG after interaction with TLR2 provides a cytokine milieu for consequent Th2 differentiation. Moreover, having shown the strong induction of Th1-promoting cytokines and low production of IL-10 in response to sLPG might have vaccine implication since it is recognized by TLR2 providing signals to professional antigen presenting cells that reside in the skin to promote effective T cell responses against Leishmania infection. In addition, it was shown that purified mLPG and sLPG activate reactive oxygen species (ROS) production which is also blocked by anti-TLR2 but not by anti-TLR4. However, no inhibition was seen in PPG-induced cytokine and ROS production in the presence of anti-TLR2 and anti-TLR4, implying involvement of other receptors.

Leishmania protozoa are obligate intracellular parasites that reside in the phagolysosome of host macrophages and cause a large spectrum of pathologies to humans known as leishmaniases. The outcome of the disease is highly dependent on the parasite species and on its ascribed virulence factors and the immune status of the host. Characterization of the genome composition of non-pathogenic species could ultimately open new horizons in Leishmania developmental biology and also the disease monitoring. Here, we provide evidence that the lizard non-pathogenic to humans Leishmania tarentolae species expresses an Amastin-like gene, cysteine protease B (CPB), lipophosphoglycan LPG3 and the leishmanolysin GP63, genes well-known for their potential role in the parasite virulence. These genes were expressed at levels comparable to those in L. major and L. infantum both at the level of mRNA and protein. Alignment of the L. tarentolae proteins with their counterparts in the pathogenic species demonstrated that the degree of similarity varied from 59% and 60% for Amastin, 89% for LPG3 and 71% and 68% for CPB, in L. major and L. infantum, respectively. Interestingly, the A2 gene, expressed specifically by the L. donovani complex which promotes visceralization, was absent in L. tarentolae. These findings suggest that the lack of pathogenicity in L. tarentolae is not associated with known virulence genes such as LPG3, CPB, GP63 and Amastin, and that other factors either unique to L. tarentolae or missing from this species may be responsible for the non-pathogenic potential of this lizard parasite.

Ex vivo culture of spleen cells from BALB/c mice infected with 2 × 106Leishmania major (L.major) promastigotes were cultured with ConcanavalinA (ConA) or leishmanial antigen (L. Ag) and tested for prostaglandin E2 (PGE2) and for leukotriene B4 (LTB4), in order to study their involvement in the evolution of cutaneous leishmaniasis and the connexion with lymphokine-mediated responses. The data were compared with those obtained in BALB/c mice protected against L. major by sublethal irradiation (550 rad; cured mice). In the unprotected BALB/c mice the levels of PGE2 that were responsible for the depression of interferon-γ (IFN-γ) and tumour necrosis factor-α (TNFα) Th1-associated cytokines and for the relative increase in the interleukin-4 (IL-4) became higher and higher as the lesion progressed. On the contrary, the cured mice produced levels of PGE2 similar to normal uninfected controls, high levels of TNFα and IFN-γ and low levels of IL-4. Elevated levels of LTB4 were detected in the early stage of infection in the unprotected mice compared to cured ones, a sign of more intense inflammation and a stimulus for the recruitment of inflammatory cells. The observation that exogenous LTB4 was able to enhance in vitro both Th1 cytokines in cured mice and Th2 cytokines in unprotected ones suggests that LTB4 could act in the recruitment of the T cells already committed to Th1 or Th2 phenotype.

We have investigated the effect of qinghaosu (QHS, artemisinin) and its derivatives on Leishmania major replication in vitro and on the disease development in mice infected with L. major. Artemisinin is effective against promastigotes in vitro, with an ED 50 (50% effective dose) at 7.5 × 10−7 m. Both artemisinin and artemether are leishmanicidal for amastigotes in infected murine macrophages in vitro, with ED50 at 3 × 10−5 m and 3 × 10−6 m respectively. These compounds have no effect on the viability of macrophages or on the phytohaemaglutinin-induced proliferation of normal spleen cells, even at 10−4 m. BALB/c mice infected in the footpad with L. major developed significantly smaller lesions and parasite loads when treated with the compounds. Intra-lesion injection of the compounds was the most effective route. The intramuscular and oral routes were also effective; however, intravenous injection with artesunate was not effective.

The need for a vaccine(s) against cutaneous leishmaniasis and the populations at risk for whom such vaccines should be developed are briefly discussed. The current human vaccine studies are reviewed, as are some experimental mouse studies with emphasis on Leishmania major infection relevant to vaccine development. Based on the information available from the mouse model and those data which are being sought in human studies, the benign nature of the cutaneous disease, the ease with which L. major can be manipulated to yield the required material, and the ongoing practice of leishmanization which allows rapid evaluation of candidate vaccine(s), it is suggested that a vaccine, at least against L. major, is imminent in the not too distant future.

In complex organisms, apoptosis is a constitutive cell death process that is involved in physiological regulation of cell numbers and that can also be induced in the course of inflammatory and immune responses. Neutrophils are among the first cells recruited during inflammation. Neutrophils constitutively die by apoptosis at inflamed sites, and are ingested by macrophages. Recent studies investigated how phagocytic clearance of senescent neutrophils influences the survival of intracellular protozoan parasites that have been phagocytosed by, or have invaded phagocytes. The results indicate that neutrophil clearance plays an unexpected role in regulation of intramacrophagic protozoan parasite infection.

PTPases have been reported as a virulence factor in different pathogens. Recent studies suggest that PTPases play a role in the pathogenesis of Leishmania infections through activation of macrophage PTPases by the parasite. We report here the presence of a membrane-bound PTPase in Leishmania major promastigotes. We detected differences in the PTPases present in the procyclic and metacyclic stages of promastigotes. In metacyclic promastigotes, the PTPase activity was totally inhibited by specific PTPase and serine/threonine inhibitors, whereas in procyclic promastigotes the PTPase activity was inhibited only with PTPase inhibitors. Two antibodies against the catalytic domains of the human placental PTPase1B and a PTPase from Trypanosoma brucei cross-reacted with a 55–60 kDa molecule present in the soluble detergent-extracted fraction of a Leishmania homogenate. Metacyclic promastigotes expressed more of this molecule than parasites in the procyclic stage. Yet the specific activity of the enzyme was lower in metacyclic than in procyclic promastigotes. Ultrastructural localization of the enzyme showed that it was more membrane-associated in metacyclic promastigotes, whereas in procyclic promastigotes it was scattered throughout the cytoplasm. This is the first demonstration of a PTPase present in Leishmania major promastigotes that differs in expression, activity and ultrastructural localization between the procyclic and metacyclic stages of the parasite's life-cycle.

Leishmania parasites are able to survive in host macrophages despite the harsh phagolysosomal vacuoles conditions. This could reflect, in part, their capacity to secrete proteins that may play an essential role in the establishment of infection and serve as targets for cellular immune responses. To characterize Leishmania major proteins excreted/secreted early after promastigote entry into the host macrophage, we have generated antibodies against culture supernatants of stationary-phase promastigotes collected 6 h after incubation in conditions that partially reproduce those prevailing in the parasitophorous vacuole. The screening of an L. major cDNA library with these antibodies led us to isolate 33 different cDNA clones that we report here. Sequence analysis revealed that the corresponding proteins could be classified in 3 groups: 9 proteins have been previously described as excreted/secreted in Leishmania and/or other species; 11 correspond to known proteins already characterized in Leishmania and/or other species although it is unknown whether they are excreted/secreted and 13 code for unknown proteins. Interestingly, the latter are transcribed as shown by RT-PCR and some of them are stage regulated. The L. major excreted/secreted proteins may constitute putative virulence factors, vaccine candidates and/or new drug targets.

In order to investigate the importance of the host microbiota on differentiation of T cell subsets in response to infection, Swiss/NIH germ-free mice and conventional (microbiota-bearing) mice were infected with Leishmania major, and lesion development, parasite loads, and cytokine production were assessed. Germ-free mice failed to heal lesions and presented a higher number of parasites at the site of infection than their conventional counterparts. In addition, histopathological analysis indicated a higher density of parasitized macrophages in lesions from germ-free mice than in conventional mice. The initial production of interleukin (IL)-12 and interferon-gamma (IFN-γ) in germ-free mice was comparable to the conventional controls. Also, germ-free mice produced elevated levels of IFN-γ and lower levels of IL-4 throughout the course of infection, suggesting the development of a Th1 response. Macrophages from germ-free mice exposed to IFN-γ and infected with amastigotes in vitro were not as efficient at killing parasites as macrophages from conventional animals. These observations indicate that the microbiota is not essential for the development of Th1 immune responses, but seems to be important for macrophage activation.

While purine transport has been widely studied in protozoa, almost nothing is known about their capacity to salvage pyrimidines. Here, we report a Leishmania major transporter with high affinity for uracil (Km=0·32±0·07 μM) which we designated LmU1. This transporter displayed a high degree of specificity, as it had virtually no affinity for cytosine, thymine or purine nucleobases, nor did it transport pyrimidine nucleosides. Highest affinity was for 5-fluorouracil. The results show that the permeant binding site of LmU1 interacts strongly with the keto groups of uracil, as shown by a low affinity for 2-thio- and 4-thiouracil. LmU1 appears to further bind uracil through a weak hydrogen bond with N(1)H of the pyrimidine ring in addition to a stronger H-bond with N(3)H. Substrate binding and selectivity were strikingly similar to that of the U1 transporter in the related kinetoplastid Trypanosoma brucei. Uracil analogues likely to be transported by LmU1 were also screened for antileishmanial activity, with 5-fluorouracil displaying strong activity against promastigotes and intracellular amastigotes. Overall, the results show that, like purine nucleobase transport, pyrimidine nucleobase transport function is very similar in L. major and T. brucei insect forms.

Riboprinting is one of several molecular methods that can generate comparative data independently of the complexity of the organism's morphology. Restriction fragment length polymorphism (RFLP) profiles derived from digestion of polymerase chain reaction (PCR) products of the ribosomal 18S from Leishmania spp. yields a typical ‘riboprint’ profile that can vary intraspecifically. A selection of 76 stocks of L. major and L. tropica, isolated from patients with cutaneous leishmaniasis, was analysed by riboprinting to assess divergence within and between species. L. major and L. tropica could be easily differentiated from each other. Analysis of PCR–RFLP profiles indicated that stocks of Leishmania spp. could be broadly partitioned into 2 species corresponding to L. major and L. tropica. To test if ribosomal 18S sequences were homogeneous within each species, several isolates of each of the Leishmania spp. were digested. Interpretation of the riboprint profiles of the 18S independently amplified by PCR, there would appear to be one restriction pattern present within each Leishmania spp. Homogeneity within copies of the ribosomal 18S within a single genome has, therefore, been demonstrated. The species designation established by riboprinting results were in agreement with the zymodeme analysis of the same isolates. The restriction patterns produced were simple, reproducible and easy to interpret.

Cytokine responses to Leishmania infection begin very early in infection, and differ between susceptible and resistant mice. Susceptibility to chronic Leishmania infection has been associated with increased haematopoiesis. To analyse the effect that acute infection with L. major has on bone-marrow haematopoiesis in susceptible (BALB/c) and resistant (CBA) mice, we enumerated erythroid progenitors and granulocyte-monocyte progenitors 3 days after infection. We found that haematopoiesis was stimulated in BALB/c mice infected with L. major, while haematopoiesis was inhibited in CBA mice. We found that this effect could be partially explained by cytokine production: interleukin-4 was involved in stimulation of BALB/c haematopoiesis and tumour necrosis factor-α was involved in inhibition of CBA haematopoiesis. Our conclusions are that haematopoietic changes occur shortly after L. major infection, and may be related to disease outcome.

Phlebotomus papatasi sand flies, the vectors of Leishmania major, differ genetically in their susceptibility to the pathogens. The costs of infection appear to be so great that selection against Leishmania-susceptible flies could presumably occur, unless susceptibility is compensated for by some advantage. Foci of P. papatasi-transmitted L. major are mainly found in arid habitats where seasonal stress of dehydration and heat reduces the quantity of sugar in plant leaves. The sand flies feed on these leaves and with the lack of essential sugar only a few survive long enough to deposit eggs and transmit Leishmania. This association suggested that susceptibility to L. major infection may be linked with advantageous tolerance of sugar deprivation. Here we show that desert sand flies, provided with excess sugar, became progressively resistant to infection. Selection for survival under sugar-poor conditions increased the susceptibility of parent and first-generation offspring by more than 2-fold. The leaves of plants, on which flies naturally feed, contain more sugar in irrigated than in arid habitats. About 85% of first-generation flies colonized from a desert habitat retain experimental Leishmania infection compared to 25% of offspring of flies from irrigated sites.

The aim of this investigation was to examine whether macrophage and Leishmania major glutathione were involved in either host or parasite protection against NO cytotoxicity. Buthionine sulfoximine (BSO), an inhibitor of γ-glutamyl-cysteine synthase, caused a complete and irreversible depletion of macrophage glutathione, but only a 20% and reversible decrease in L. major glutathione. Glutathione-depleted macrophages, when activated with IFN-γ/LPS, released less than 60% of the NO produced by untreated macrophages, resulting in a corresponding decrease in their leishmanicidal activity. BSO-treated macrophages were more susceptible to the cytotoxic effects of the NO donor SNAP. Treatment of macrophages with 1,3-bis(chloroethyl)-1-nitrosourea (BCNU), an inhibitor of glutathione reductase and trypanothione reductase or with Br-Octane, a glutathione-S-transferase substrate, resulted in a transient decrease in glutathione levels and did not increase the susceptibility of the macrophages to SNAP. Treatment of the promastigote forms of L. major with BCNU resulted in an 80% decrease in total glutathione concentration with no concomitant change in viability. However, this treatment rendered the parasites more susceptible to SNAP. Finally, macrophage glutathione protected the internalized L. major from SNAP. Overall, these results demonstrate that glutathione is an essential protective component against NO cytotoxicity on both macrophages and parasites.

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.