Evidence for a neotropical origin of Leishmania

Leishmania tarentolae: Taxonomic classification and its application as a promising biotechnological expression host

In this review, we summarize the current knowledge concerning the eukaryotic protozoan parasite Leishmania tarentolae, with a main focus on its potential for biotechnological applications. We will also discuss the genus, subgenus, and species-level classification of this parasite, its life cycle and geographical distribution, and similarities and differences to human-pathogenic species, as these aspects are relevant for the evaluation of biosafety aspects of L. tarentolae as host for recombinant DNA/protein applications. Studies indicate that strain LEM-125 but not strain TARII/UC of L. tarentolae might also be capable of infecting mammals, at least transiently. This could raise the question of whether the current biosafety level of this strain should be reevaluated. In addition, we will summarize the current state of biotechnological research involving L. tarentolae and explain why this eukaryotic parasite is an advantageous and promising human recombinant protein expression host. This summary includes overall biotechnological applications, insights into its protein expression machinery (especially on glycoprotein and antibody fragment expression), available expression vectors, cell culture conditions, and its potential as an immunotherapy agent for human leishmaniasis treatment. Furthermore, we will highlight useful online tools and, finally, discuss possible future applications such as the humanization of the glycosylation profile of L. tarentolae or the expression of mammalian recombinant proteins in amastigote-like cells of this species or in amastigotes of avirulent human-pathogenic Leishmania species.

The evolution of trypanosomatid taxonomy

Trypanosomatids are protozoan parasites of the class Kinetoplastida predominately restricted to invertebrate hosts (i.e. possess a monoxenous life-cycle). However, several genera are pathogenic to humans, animals and plants, and have an invertebrate vector that facilitates their transmission (i.e. possess a dixenous life-cycle). Phytomonas is one dixenous genus that includes several plant pathogens transmitted by phytophagous insects. Trypanosoma and Leishmania are dixenous genera that infect vertebrates, including humans, and are transmitted by hematophagous invertebrates. Traditionally, monoxenous trypanosomatids such as Leptomonas were distinguished from morphologically similar dixenous species based on their restriction to an invertebrate host. Nonetheless, this criterion is somewhat flawed as exemplified by Leptomonas seymouri which reportedly infects vertebrates opportunistically. Similarly, Novymonas and Zelonia are presumably monoxenous genera yet sit comfortably in the dixenous clade occupied by Leishmania. The isolation of Leishmania macropodum from a biting midge (Forcipomyia spp.) rather than a phlebotomine sand fly calls into question the exclusivity of the Leishmania-sand fly relationship, and its suitability for defining the Leishmania genus. It is now accepted that classic genus-defining characteristics based on parasite morphology and host range are insufficient to form the sole basis of trypanosomatid taxonomy as this has led to several instances of paraphyly. While improvements have been made, resolution of evolutionary relationships within the Trypanosomatidae is confounded by our incomplete knowledge of its true diversity. The known trypanosomatids probably represent a fraction of those that exist and isolation of new species will help resolve relationships in this group with greater accuracy. This review incites a dialogue on how our understanding of the relationships between certain trypanosomatids has shifted, and discusses new knowledge that informs the present taxonomy of these important parasites.

What pre-Columbian mummies could teach us about South American leishmaniases?

A recent report on the taxonomic profile of the human gut microbiome in pre-Columbian mummies (Santiago-Rodriguez et al. 2016) gives for the first time evidence of the presence of Leishmania DNA (sequences similar to Leishmania donovani according to the authors) that can be reminiscent of visceral leishmaniasis during the pre-Columbian era. It is commonly assumed that Leishmania infantum, the etiological agent of American visceral leishmaniasis (AVL) was introduced into the New World by the Iberian conquest. This finding is really surprising and must be put into perspective with what is known from an AVL epidemiological and historical point of view. Beside L. infantum, there are other species that are occasionally reported to cause AVL in the New World. Among these, L. colombiensis is present in the region of pre-Columbian mummies studied. Other explanations for these findings include a more ancient introduction of a visceral species of Leishmania from the Old World or the existence of a yet unidentified endemic species causing visceral leishmaniasis in South America. Unfortunately, very few molecular data are known about this very long pre-Columbian period concerning the circulating species of Leishmania and their diversity in America.

The history of leishmaniasis

In this review article the history of leishmaniasis is discussed regarding the origin of the genus Leishmania in the Mesozoic era and its subsequent geographical distribution, initial evidence of the disease in ancient times, first accounts of the infection in the Middle Ages, and the discovery of Leishmania parasites as causative agents of leishmaniasis in modern times. With respect to the origin and dispersal of Leishmania parasites, the three currently debated hypotheses (Palaearctic, Neotropical and supercontinental origin, respectively) are presented. Ancient documents and paleoparasitological data indicate that leishmaniasis was already widespread in antiquity. Identification of Leishmania parasites as etiological agents and sand flies as the transmission vectors of leishmaniasis started at the beginning of the 20^th century and the discovery of new Leishmania and sand fly species continued well into the 21^st century. Lately, the Syrian civil war and refugee crises have shown that leishmaniasis epidemics can happen any time in conflict areas and neighbouring regions where the disease was previously endemic.

Isolation of Novel Trypanosomatid, Zelonia australiensis sp. nov. (Kinetoplastida: Trypanosomatidae) Provides Support for a Gondwanan Origin of Dixenous Parasitism in the Leishmaniinae

The genus Leishmania includes approximately 53 species, 20 of which cause human leishmaniais; a significant albeit neglected tropical disease. Leishmaniasis has afflicted humans for millennia, but how ancient is Leishmania and where did it arise? These questions have been hotly debated for decades and several theories have been proposed. One theory suggests Leishmania originated in the Palearctic, and dispersed to the New World via the Bering land bridge. Others propose that Leishmania evolved in the Neotropics. The Multiple Origins theory suggests that separation of certain Old World and New World species occurred due to the opening of the Atlantic Ocean. Some suggest that the ancestor of the dixenous genera Leishmania, Endotrypanum and Porcisia evolved on Gondwana between 90 and 140 million years ago. In the present study a detailed molecular and morphological characterisation was performed on a novel Australian trypanosomatid following its isolation in Australia’s tropics from the native black fly, Simulium (Morops) dycei Colbo, 1976. Phylogenetic analyses were conducted and confirmed this parasite as a sibling to Zelonia costaricensis, a close relative of Leishmania previously isolated from a reduviid bug in Costa Rica. Consequently, this parasite was assigned the name Zelonia australiensis sp. nov. Assuming Z. costaricensis and Z. australiensis diverged when Australia and South America became completely separated, their divergence occurred between 36 and 41 million years ago at least. Using this vicariance event as a calibration point for a phylogenetic time tree, the common ancestor of the dixenous genera Leishmania, Endotrypanum and Porcisia appeared in Gondwana approximately 91 million years ago. Ultimately, this study contributes to our understanding of trypanosomatid diversity, and of Leishmania origins by providing support for a Gondwanan origin of dixenous parasitism in the Leishmaniinae.

The genus Leishmania includes approximately 53 species, 20 of which cause human leishmaniais, a significant disease that has afflicted humans for millennia. But how ancient is Leishmania and where did it arise? Some suggest Leishmania originated in the Palearctic. Others suggest it appeared in the Neotropics. The Multiple Origins theory proposes that separation of certain Old World and Neotropical species occurred following the opening of the Atlantic. Others suggest that an ancestor to the Euleishmania and Paraleishmania appeared on Gondwana 90 to 140 million years ago (MYA). We performed a detailed molecular and morphological characterisation of a novel Australian trypanosomatid. This parasite is a sibling to the Neotropical Zelonia costaricensis, a close relative of Leishmania, and designated as Zelonia australiensis sp. nov. Assuming Z. costaricensis and Z. australiensis split when Australia and South America separated, their divergence occurred between 36 and 41 MYA. Using this event as a calibration point for a phylogenetic time tree, an ancestor of the dixenous Leishmaniinae appeared in Gondwana ~ 91 MYA. This study contributes to our understanding of trypanosomatid diversity by describing a unique Australian trypanosomatid and to our understanding of Leishmania evolution by inferring a Gondwanan origin for dixenous parasitism in the Leishmaniinae.

THE PROCESS OF Leishmania INFECTION - DISEASE AND NEW PERSPECTIVES OF PALEOPARASITOLOGY

Species of the genus Leishmania (Kinetoplastida, Trypanosomatidae) are causative agents of leishmaniasis, a complex disease with variable clinical spectrum and epidemiological diversity, constituting, in some countries, a serious public health problem. The origin and evolution of leishmaniasis has been under discussion regarding some clinical and parasitological aspects. After the introduction of paleoparasitology, molecular methods and immunodiagnostic techniques have been applied allowing the recovery of parasite remains, as well as the diagnosis of past infections in humans and other hosts. The dating of archaeological samples has allowed the parasitological analysis in time and space. This manuscript presents the state of the art of leishmaniasis and prospects related to paleoparasitology studies and their contribution to the evolutionary and phylogenetic clarification of parasites belonging to the genus Leishmania, and the leishmaniasis caused by them.

A Historical Overview of the Classification, Evolution, and Dispersion of Leishmania Parasites and Sandflies

BACKGROUND

The aim of this study is to describe the major evolutionary historical events among Leishmania, sandflies, and the associated animal reservoirs in detail, in accordance with the geographical evolution of the Earth, which has not been previously discussed on a large scale.

METHODOLOGY AND PRINCIPAL FINDINGS

Leishmania and sandfly classification has always been a controversial matter, and the increasing number of species currently described further complicates this issue. Despite several hypotheses on the origin, evolution, and distribution of Leishmania and sandflies in the Old and New World, no consistent agreement exists regarding dissemination of the actors that play roles in leishmaniasis. For this purpose, we present here three centuries of research on sandflies and Leishmania descriptions, as well as a complete description of Leishmania and sandfly fossils and the emergence date of each Leishmania and sandfly group during different geographical periods, from 550 million years ago until now. We discuss critically the different approaches that were used for Leishmana and sandfly classification and their synonymies, proposing an updated classification for each species of Leishmania and sandfly. We update information on the current distribution and dispersion of different species of Leishmania (53), sandflies (more than 800 at genus or subgenus level), and animal reservoirs in each of the following geographical ecozones: Palearctic, Nearctic, Neotropic, Afrotropical, Oriental, Malagasy, and Australian. We propose an updated list of the potential and proven sandfly vectors for each Leishmania species in the Old and New World. Finally, we address a classical question about digenetic Leishmania evolution: which was the first host, a vertebrate or an invertebrate?

CONCLUSIONS AND SIGNIFICANCE

We propose an updated view of events that have played important roles in the geographical dispersion of sandflies, in relation to both the Leishmania species they transmit and the animal reservoirs of the parasites.

Phylogenomic reconstruction supports supercontinent origins for Leishmania

Leishmania, a genus of parasites transmitted to human hosts and mammalian/reptilian reservoirs by an insect vector, is the causative agent of the human disease complex leishmaniasis. The evolutionary relationships within the genus Leishmania and its origins are the source of ongoing debate, reflected in conflicting phylogenetic and biogeographic reconstructions. This study employs a recently described bioinformatics method, SISRS, to identify over 200,000 informative sites across the genome from newly sequenced and publicly available Leishmania data. This dataset is used to reconstruct the evolutionary relationships of this genus. Additionally, we constructed a large multi-gene dataset, using it to reconstruct the phylogeny and estimate divergence dates for species. We conclude that the genus Leishmania evolved at least 90-100 million years ago, supporting a modified version of the Multiple Origins hypothesis that we call the Supercontinent hypothesis. According to this scenario, separate Leishmania clades emerged prior to, and during, the breakup of Gondwana. Additionally, we confirm that reptile-infecting Leishmania are derived from mammalian forms and that the species that infect porcupines and sloths form a clade long separated from other species. Finally, we firmly place the guinea-pig infecting species, Leishmaniaenriettii, the globally dispersed Leishmaniasiamensis, and the newly identified Australian species from a kangaroo, as sibling species whose distribution arises from the ancient connection between Australia, Antarctica, and South America.

Evolutionary History of Terrestrial Pathogens and Endoparasites as Revealed in Fossils and Subfossils

The present work uses fossils and subfossils to decipher the origin and evolution of terrestrial pathogens and endoparasites. Fossils, as interpreted by morphology or specific features of their hosts, furnish minimum dates for the origin of infectious agents, coevolution with hosts, and geographical locations. Subfossils, those that can be C14 dated (roughly under 50,000 years) and are identified by morphology as well as molecular and immunological techniques, provide time periods when humans became infected with various diseases. The pathogen groups surveyed include viruses, bacteria, protozoa, fungi, and select multicellular endoparasites including nematodes, trematodes, cestodes, and insect parasitoids in the terrestrial environment.

Leishmania amazonensis promastigotes present two distinct modes of nucleus and kinetoplast segregation during cell cycle

Here, we show the morphological events associated with organelle segregation and their timing in the cell cycle of a reference strain of Leishmania (L.) amazonensis promastigotes, the main causative agent of Tegumentary leishmaniasis in the Americas. We show evidences that during the cell cycle, L. amazonensis promastigotes present two distinct modes of nucleus and kinetoplast segregation, which occur in different temporal order in different proportions of cells. We used DAPI-staining and EdU-labeling to monitor the segregation of DNA-containing organelles and DNA replication in wild-type parasites. The emergence of a new flagellum was observed using a specific monoclonal antibody. The results show that L. amazonensis cell cycle division is peculiar, with 65% of the dividing cells duplicating the kinetoplast before the nucleus, and the remaining 35% doing the opposite or duplicating both organelles concomitantly. In both cases, the new flagellum appeared during S to G2 phase in 1N1K cells and thus before the segregation of both DNA-containing organelles; however, we could not determine the exact timing of flagellar synthesis. Most of these results were confirmed by the synchronization of parasites using hydroxyurea. Altogether, our data show that during the cell cycle of L. amazonensis promastigotes, similarly to L. donovani, the segregation of nucleus and kinetoplast do not follow a specific order, especially when compared to other trypanosomatids, reinforcing the idea that this characteristic seems to be species-specific and may represent differences in cellular biology among members of the Leishmania genus.

Sequence analysis and PCR-RFLP profiling of the hsp70 gene as a valuable tool for identifying Leishmania species associated with human leishmaniasis in Brazil

Since the first report of the genus Leishmania, many species have been described. In Brazil, human leishmaniasis has been associated with eight Leishmania species, of which seven are responsible for cutaneous leishmaniasis (CL). In some endemic areas, CL is associated with only one species; however, in other areas, such as the Amazon, the etiology of CL can be assigned to many species. The multitude of highly similar Leishmania species in Brazil makes it difficult to develop an appropriate method of typing them. Most Leishmania species were first described based on epidemiological and biological characteristics, and these were later corroborated by Multilocus Enzyme Electrophoresis (MLEE), the gold standard technique for identifying Leishmania species. In an attempt to overcome the limitations of MLEE, many PCR-based methods have been developed and used for parasite identification. In the present study, we analyzed the sequence of the hsp70 gene in Leishmania species associated with human leishmaniasis in Brazil. This analysis led to the identification of restriction enzymes that could be used for PCR-RFLP-based identification. The results obtained were in complete agreement with those obtained by MLEE, suggesting that PCR-RFLP analysis of hsp70 could soon replace MLEE for routine Leishmania typing.

Lutzomyia adiketis sp. n. (Diptera: Phlebotomidae), a vector of Paleoleishmania neotropicum sp. n. (Kinetoplastida: Trypanosomatidae) in Dominican amber

BACKGROUND

Amber fossils can be used to trace the history of disease-vector associations because microorganisms are preserved "in situ" inside the alimentary tract and body cavity of blood-sucking insects.

RESULTS

Lutzomyia adiketis sp. n. (Phlebotomidae: Diptera) is described from Dominican amber as a vector of Paleoleishmania neotropicum sp. n. (Kinetoplastida: Trypanosomatidae). The fossil sand fly differs from all previously described extinct and extant members of the genus by the following combination of characters: Sc forked with the branches meeting the costa and radius veins; wing L/W value of 4.1; a delta value of 18; a ratio beta/alpha value of 0.86, and the shape and size of the spatulate rods on the ninth sternite. The trypanosomatid is characterized by the structure of its promastigotes, amastigotes and paramastigotes and its transmission by an extinct species of sand fly.

CONCLUSION

Morphological characters show that the fossil sand fly is a new extinct species and that it is host to a digenetic species of trypanosomatid. This study provides the first fossil evidence that Neotropical sand flies were vectors of trypanosomatids in the mid-Tertiary (20-30 mya).

Leishmania: origin, evolution and future since the Precambrian

This brief review discusses the history of leishmaniasis, considering its origin from the Paleoartic, Neoartic or Neotropic. We reassess some of the theories of the likely origin of this protozoan since the beginning of life on Earth, passing through the Mesozoic and continuing to the appearance of humans. The relationship between this parasite or its ancestors, possible vectors and hosts with regard to ecological modifications is discussed. Recent molecular techniques have helped to elucidate some of the evolutionary questions regarding Leishmania, but have also brought doubts about the origin and evolution of this human parasite. PCR has been used for studies in the new discipline of paleoparasitology, helping to elucidate some of the remaining evolutionary questions. Understanding of this global condition is fundamental in determining the best approach to use against the parasite, specifically for the development of an efficient vaccine.

A quantitative synthesis of the medicinal ethnobotany of the Malinké of Mali and the Asháninka of Peru, with a new theoretical framework

BACKGROUND

Although ethnomedically and taxonomically guided searches for new medicinal plants can improve the percentage of plants found containing active compounds when compared to random sampling, ethnobotany has fulfilled little of its promise in the last few decades to deliver a bounty of new, laboratory-proven medicinal plants and compounds. It is quite difficult to test, isolate, and elucidate the structure and mechanism of compounds from the plethora of new medicinal plant uses described each year with limited laboratory time and resources and the high cost of clinical trials of new drug candidates.

METHODS

A new quantitative theoretical framework of mathematical formulas called "relational efficacy" is proposed that should narrow down this search for new plant-derived medicines based on the hypothesis that closely related plants used to treat closely related diseases in distantly related cultures have a higher probability of being effective because they are more likely to be independent discoveries of similar plant compounds and disease mechanisms. A prerequisite to this hypothesis, the idea that empirical testing in traditional medicine will lead to choosing similar medicinal plants and therefore the medicinal flora of two distant cultures will prove to be more similar than their general flora, is tested using resampling statistics on cross-cultural field data of the plants used by the Malinké of Mali and the Asháninka of Peru to treat the diseases malaria, African sleeping sickness, Chagas' disease, leishmaniasis, diabetes, eczema, asthma, and uterine fibroids.

RESULTS

In this case, the similarity of the medicinal floras is found to be significantly greater than the similarity of the general floras, but only when the diseases in question are grouped into the categories of parasitic and autoimmune diseases.

CONCLUSION

If the central theoretical framework of this hypothesis is shown to be true, it will allow the synthesis of medicinal plant information from around the world to pinpoint the species with the highest potential efficacy to take into the laboratory and analyze further, ultimately saving much field and laboratory time and resources.

Comparative analysis of megasomes in members of the Leishmania mexicana complex

Megasomes are large lysosome-like structures, previously described in amastigote forms of Leishmania belonging to the mexicana complex, whose major constituents are the cysteine proteinases. Routine observation of thin sections of amastigotes obtained from species of the mexicana complex revealed variations in size and number of megasomes according to the species, and also between amastigotes obtained from axenic cultures and from infected animals. Three-dimensional reconstruction of amastigotes, stereology and immunocytochemical localization of cysteine proteinase revealed significant differences between the three Leishmania species examined, L. amazonensis, L. mexicana and L. pifanoi. The relative volume of megasomes in lesion-derived amastigotes was higher than in axenic amastigotes of L. amazonensis and L. mexicana. The relative volume of megasomes from lesion-derived amastigotes of L. mexicana was 2-3 times higher than in L. amazonensis. Axenic amastigotes of L. pifanoi showed a small relative volume of megasomes and low cysteine proteinase activity, and were not able to produce lesions in the animals, whereas axenic amastigotes of L. mexicana and L. amazonensis did. There were significant differences in the structural organization, distribution within the cell, size and number of megasomes, and in the characteristics of cysteine proteinases found in the amastigotes of the three Leishmania species. These results suggest that these organelles and their constituents may be involved in the infectivity and virulence of Leishmania species.

Transmembrane molecules for phylogenetic analyses of pathogenic protists: Leishmania-specific informative sites in hydrophilic loops of trans- endoplasmic reticulum N-acetylglucosamine-1-phosphate transferase

A sequence database was created for the Leishmania N-acetylglucosamine-1-phosphate transferase (nagt) gene from 193 independent isolates. PCR products of this single-copy gene were analyzed for restriction fragment length polymorphism based on seven nagt sequences initially available. We subsequently sequenced 77 samples and found 19 new variants (genotypes). Alignment of all 26 nagt sequences is gap free, except for a single codon addition or deletion. Phylogenetic analyses of the sequences allow grouping the isolates into three subgenera, each consisting of recognized species complexes, i.e., subgenus Leishmania (L. amazonensis-L. mexicana, L. donovani-L. infantum, L. tropica, L. major, and L. turanica-L. gerbilli), subgenus Viannia (L. braziliensis, L. panamensis), and one unclassified (L. enriettii) species. This hierarchy of grouping is also supported by sequence analyses of selected samples for additional single-copy genes present on different chromosomes. Intraspecies divergence of nagt varies considerably with different species complexes. Interestingly, species complexes with less subspecies divergence are more widely distributed than those that are more divergent. The relevance of this to Leishmania evolutionary adaptation is discussed. Heterozygosity of subspecies variants contributes to intraspecies diversity, which is prominent in L. tropica but not in L. donovani-L. infantum. This disparity is thought to result from the genetic recombination of the respective species at different times as a rare event during their predominantly clonal evolution. Phylogenetically useful sites of nagt are restricted largely to several extended hydrophilic loops predicted from hypothetical models of Leishmania NAGT as an endoplasmic reticulum transmembrane protein. In silico analyses of nagt from fungi and other protozoa further illustrate the potential value of this and, perhaps, other similar transmembrane molecules for phylogenetic analyses of single-cell eukaryotes.

Molecular trees of trypanosomes incongruent with fossil records of hosts

Molecular trees of trypanosomes have confirmed conventionally accepted genera, but often produce topologies that are incongruent with knowledge of the evolution, systematics, and biogeography of hosts and vectors. These distorted topologies result largely from incorrect assumptions about molecular clocks. A host-based phylogenetic tree could serve as a broad outline against which the reasonability of molecular phylogenies could be evaluated. The host-based tree of trypanosomes presented here supports the " invertebrate first " hypothesis of trypanosome evolution, supports the monophyly of Trypanosomatidae, and indicates the digenetic lifestyle arose three times. An area cladogram of Leishmania supports origination in the Palaearctic during the Palaeocene.

Comparison of the A2 gene locus in Leishmania donovani and Leishmania major and its control over cutaneous infection

In Old World Leishmania infections, Leishmania donovani is responsible for fatal visceral leishmaniasis, and L. major is responsible for non-fatal cutaneous leishmaniasis in humans. The genetic differences between these species which govern the pathology or site of infection are not known. We have therefore carried out detailed analysis of the A2 loci in L. major and L. donovani because A2 is expressed in L. donovani but not L. major, and A2 is required for survival in visceral organs by L. donovani. We demonstrate that although L. major contains A2 gene regulatory sequences, the multiple repeats that exist in L. donovani A2 protein coding regions are absent in L. major, and the remaining corresponding A2 sequences appear to represent non-expressed pseudogenes. It was possible to restore amastigote-specific A2 expression to L. major, confirming that A2 regulatory sequences remain functional in L. major. Although L. major is a cutaneous parasite in rodents and humans, restoring A2 expression to L. major inhibited its ability to establish a cutaneous infection in susceptible BALB/c or resistant C57BL6 mice, a phenotype typical of L. donovani. There was no detectable cellular immune response against L. major after cutaneous infection with A2-expressing L. major, suggesting that the lack of growth was not attributable to acquired host resistance but to an A2-mediated suppression of parasite survival in skin macrophages. These observations argue that the lack of A2 expression in L. major contributed to its divergence from L. donovani with respect to the pathology of infection.

Relationships of new world phlebotomine sand flies (Diptera: Psychodidae) based on fossil evidence

The fossil record and systematics of phlebotomid sand flies, vectors of leishmaniasis and arbovirus in several regions of the world, strongly support that living genera existed long before the Oligocene (38 million years, myr). A common Phlebotominae ancestor was present in the Triassic period before the separations of continents (248 myr).

Proteome mapping of the protozoan parasite Leishmania and application to the study of drug targets and resistance mechanisms

Leishmania is a protozoan parasite responsible for significant morbidity and mortality worldwide. Few parasites have been subjected to proteomic analysis to date, but a genome sequencing project for Leishmania major is currently underway, making these studies possible. Here we present a high resolution proteome for L. major comprising almost 3700 spots, making it the most complete two-dimensional gel representation of a parasite proteome generated to date. We have identified a number of landmark proteins by mass spectrometry and show that several of these are valid for the related species Leishmania donovani infantum. We have also observed several forms and fragments of alpha- and beta-tubulins and show that the number and amount of these fragments increase with the age of the parasite culture. Trypanothione reductase (TRYR), which replaces glutathione reductase in trypanosomatid parasites, is an essential protein specific to these parasites and as such is under considerable scrutiny as a drug target. Two-dimensional gel analysis of a L. major strain overexpressing TRYR revealed increased amounts of five spots, all at the predicted molecular weight for TRYR and differing by 0.08 pH units in pI. Mass spectrometry identified four of these as TRYR, leading to the novel suggestion that it could be post-translationally modified. Finally quantitative comparative analysis of a methotrexate-resistant mutant of L. major generated in vitro found that a known primary resistance mediator, the pteridine reductase PTR1, was overexpressed. This constitutes the first proteomic analysis of drug resistance in a parasite and also the clearest identification of a primary drug resistance mechanism using this approach. Together these results provide a framework for further proteomic studies of Leishmania species and demonstrate that these tools are valuable for the essential study of potential drug targets and drug resistance mechanisms.