Leishmania Promastigotes Research Articles

Evaluation of Antileishmanial Activity of Selected Brazilian Plants and Identification of the Active Principles

This study evaluated extracts, fractions, and isolated compounds from some selected Brazilian medicinal plants against strains of promastigotes of Leishmania amazonensis and L. brasiliensis in vitro. The cell viability was determined, comparing the results with reference standards. The dichloromethane fractions of the roots, stems, and leaves of Allamanda schottii showed IC50 values between 14.0 and 2.0 μg/mL. Plumericin was the main active compound, with IC50 of 0.3 and 0.04 μg/mL against the two species of Leishmania analyzed. The hexane extract of Eugenia umbelliflora fruits showed IC50 of 14.3 and 5.7 μg/mL against L. amazonensis and L. brasiliensis, respectively. The methanolic extracts of the seeds of Garcinia achachairu and guttiferone A presented IC50 values of 35.9 and 10.4 μg/mL, against L. amazonensis, respectively. The ethanolic extracts of the stem barks of Rapanea ferruginea and the isolated compound, myrsinoic acid B, presented activity against L. brasiliensis with IC50 of 24.1 and 6.1 μg/mL. Chloroform fraction of Solanum sisymbriifolium exhibited IC50 of 33.8 and 20.5 μg/mL, and cilistol A was the main active principle, with IC50 of 6.6 and 3.1 μg/mL against L. amazonensis and L. brasiliensis, respectively. It is concluded that the analyzed plants are promising as new and effective antiparasitic agents.

Cutaneous leishmaniasis and rickettsial African tick‐bite fever: a combination of exotic traveler’s diseases in the same patient

Cutaneous leishmaniasis and rickettsial African tick-bite fever are two zoonoses increasingly diagnosed in industrialized nations due to more international travel to endemic areas. A 52-year-old American nurse was evaluated for a 0.5 cm well-demarcated, tender, shallow ulcer on her wrist, nonproductive cough, fever, chills, and night sweats, all of which began three weeks after travel to Botswana and a visit to a game reserve, where she reported being scratched on the ankle by a cheetah. This cutaneous finding was strongly suggestive of leishmaniasis, but the systemic symptoms were perplexing. Although excisional biopsy showed only nonspecific changes, a specimen sent to the United States Centers for Disease Control revealed leishmania promastigotes of L. tropica. Initial Rickettsia typhi titers and many other serologic tests were negative. However, four weeks after admission, R. typhi IgG titer was 1 : 64 and R. rickettsii IgG was 1 : 1024. Thus, our patient had two tropical diseases simultaneously.

Application of Serial Analysis of Gene Expression to the Study of the Gene Expression Profile ofLeishmania infantum chagasiPromastigote

This study describes the application of the LongSAGE methodology to study the gene expression profile in promastigotes of Leishmania infantum chagasi. A tag library was created using the LongSAGE method and consisted of 14,208 tags of 17 bases. Of these, 8,427 (59.3%) were distinct. BLAST research of the 1,645 most abundant tags showed that 12.8% of them identified the coding sequences of genes, while 82% (1,349/1,645) identified one or more genomic sequences that did not correspond with open reading frames. Only 5.2% (84/1,645) of the tags were not aligned to any position in the L. infantum genome. The UTR size of Leishmania and the lack of CATG sites in some transcripts were decisive for the generation of tags in these regions. Additional analysis will allow a better understanding of the expression profile and discovering the key genes in this life cycle.

First Report on Sergentomyia sintoni and Sergentomyia clydei (Diptera: Psychodidae): Their Natural Promastigote Infection and Some Aspects of Biology in Sistan-Baluchistan Province, Southeastern Iran

ObjectiveTo This paper has explained initial survey on two vectors of lizard leishmania promastigote in south-east of Iran. MethodsTotally 333 S. sintoni and 475 S. clydei were collected from rodent burrows by sticky traps in three villages of Chabahar County. Sand flies were dissected in a drop of normal saline. ResultsNatural leptomonad infection rate involved %2.1 S. sintoni and %5 S. clydei. The finding about seasonal variation was showed the highest infection rate in two vectors in the first week of August. The highest population of gravid and semi-gravid of main vectors of Lizard leishmaniasis, S. sintoni and S. clydei, were observed in the last week of September and the lowest were in the last week of July. The examination of accessory glands showed that the maximum population of parous was observed in the last week of September and the last week of July it was at least. This is the first report of leptomonad (promastigote) infection in S. sintoni and S. clydei in Sistan-Baluchistan Province, southeastern Iran. ConclusionsA further study with more focus on biology of Sergentomyia genus is suggested.

Differential Microbicidal Effects of Human Histone Proteins H2A and H2B on Leishmania Promastigotes and Amastigotes

Recent studies have shown that histone proteins can act as antimicrobial peptides in host defense against extracellular bacteria, fungi, and Leishmania promastigotes. In this study, we used human recombinant histone proteins to further study their leishmaniacidal effects and the underlying mechanisms. We found that the histones H2A and H2B (but not H1(0)) could directly and efficiently kill promastigotes of Leishmania amazonensis, L. major, L. braziliensis, and L. mexicana in a treatment dose-dependent manner. Scanning electron microscopy revealed surface disruption of histone-treated promastigotes. More importantly, the preexposure of promastigotes to histone proteins markedly decreased the infectivity of promastigotes to murine macrophages (Mφs) in vitro. However, axenic and lesion-derived amastigotes of L. amazonensis and L. mexicana were relatively resistant to histone treatment, which correlated with the low levels of intracellular H2A in treated amastigotes. To understand the mechanisms underlying these differential responses, we investigated the role of promastigote surface molecules in histone-mediated killing. Compared with the corresponding controls, transgenic L. amazonensis promastigotes expressing lower levels of surface gp63 proteins were more susceptible to histone H2A, while L. major and L. mexicana promastigotes with targeted deletion of the lipophosphoglycan 2 (lpg2) gene (but not the lpg1 gene) were more resistant to histone H2A. We discuss the influence of promastigote major surface molecules in the leishmaniacidal effect of histone proteins. This study provides new information on host innate immunity to different developmental stages of Leishmania parasites.

GC-MS analysis and antileishmanial activities of two Turkish propolis types

Propolis is a honeybee product with a very complex chemical composition and various pharmacological properties. This study was aimed to investigate antileishmanial activities of "Bursa" and "Hatay" propolis samples against Leishmania infantum and Leishmania tropica strains. Propolis samples were analysed with the gas chromatography-mass spectrometry technique. Promastigotes were incubated in Roswell Park Memorial Institute culture medium in the absence and presence of several concentrations (50, 100, 250, 500, 750, and 1,000μg/mL) of each propolis sample. The viability and cell morphology of promastigotes in each concentration were examined after 24, 48, 72, and 96h of incubation. The growth of leishmania parasites was significantly suppressed in the presence of 500, 750, and 1,000μg/mL of Hatay propolis. Bursa propolis was found to be efficient in inhibiting the growth of leishmania promastigotes in culture media at these concentrations, 250, 500, 750, and 1,000μg/mL. Thus, the in vitro results showed that the Hatay and Bursa propolis samples decreased significantly the proliferation of L. infantum and L. tropica parasites (p < 0.001); however, Bursa propolis was found to be more effective than Hatay propolis against leishmania promastigotes. These two natural products may be useful agents in the prevention of leishmanial infections.

9-O-acetylated sialic acids enhance entry of virulentLeishmania donovanipromastigotes into macrophages

Distribution of 9-O-acetylated sialic acids (9-O-AcSA) on Leishmania donovani has been previously reported. Considering their role in recognition, the differential distribution of sialic acids especially 9-O-acetylated sialic acids in avirulent (UR6) versus virulent (AG83 and GE1) promastigotes of Leishmania donovani and its role in entry into macrophages was explored. Fluorimetric-HPLC, fluorimetric determination and ELISA revealed 14-, 8- and 5-fold lower sialic acids in UR6 as compared to AG83. Interestingly, on UR6, flow cytometry indicated lower (alpha2-->6)-linked sialoglycoproteins along with minimal 9-O-acetylated sialoglycoproteins by Scatchard analysis. Further, UR6 demonstrated a 9- and 14.5-fold lower infectivity and phagocytic index than AG83. Additionally, de-O-acetylation and de-sialylation of AG83 demonstrated a 3- and 1.5-fold reduced phagocytic index. The role of 9-O-AcSA in entry was further confirmed by pre-blocking the macrophage surface with a cocktail of sugars followed by microscopic quantification. The phagocytic index of AG83 exclusively through 9-O-AcSA was significantly high. Interestingly, AG83 produced higher metacyclic promastigotes containing increased 9-O-AcSA as compared to avirulent UR6 supporting its virulent nature. Taken together; our results conclusively demonstrate the increased presence of 9-O-acetylated sialic acid on promastigotes of virulent Leishmania donovani as compared to avirulent UR6 and their subsequent role in entry within macrophages.

Dichotomy of the T cell response to Leishmania antigens in patients suffering from cutaneous leishmaniasis; absence or scarcity of Th1 activity is associated with severe infections.

The T cell response was studied in 25 patients suffering from cutaneous leishmaniasis caused by Leishmania major with severe (n = 10) and mild (n = 15) disease manifestations. Peripheral blood mononuclear cells (PBMC) from the patients were activated by sonicates of Leishmania promastigotes (LMP) and amastigotes (LDA), and the surface protease gp63. The proliferative responses to Leishmania antigens were lower in patients with severe disease than in patients with mild disease (P = 0.01-0.05), and such a difference was not observed in the response to purified protein derivative of tuberculin (PPD) or tetanus toxoid (TT). LMP-induced interferon-gamma (IFN-gamma) production was lower in patients with severe than in patients with mild disease (P < 0.05). When the IL-4 and IFN-gamma responses of each patient were considered, two response patterns were observed in the cultures activated by the Leishmania sonicates. One response pattern was characterized by high production of IFN-gamma without production of IL-4 (a Th1-like pattern), the other was characterized by low IFN-gamma levels which in most cases were associated with IL-4 production (not a Th1-like pattern). These patterns could not be distinguished when the cells from the same donors were stimulated by TT and PPD. The percentages of patients with a Th1-like response pattern after stimulation by LMP in patients with severe and mild disease manifestations were 30% and 80%, respectively. This difference was statistically significant (P = 0.034).

Aloe vera leaf exudate induces a caspase-independent cell death in Leishmania donovani promastigotes

Leishmaniasis constitutes a complex of diseases with clinical and epidemiological diversity and includes visceral leishmaniasis, a disease that is fatal when left untreated. In earlier studies, the authors reported that Aloe vera leaf exudate (AVL) is a potent antileishmanial agent effective in promastigotes of Leishmania braziliensis, Leishmania mexicana, Leishmania tropica, Leishmania major and Leishmania infantum and also in axenic amastigotes of Leishmania donovani. In the present study, it has been demonstrated that, in promastigotes of L. donovani (IC(50) = 110 microg ml(-1)), AVL mediates this leishmanicidal effect by triggering a programmed cell death. Incubation of promastigotes with AVL caused translocation of phosphatidylserine to the outer leaflet of the plasma membrane as measured by annexin V binding, which was accompanied by loss of mitochondrial membrane potential, release of cytochrome c into the cytosol and concomitant nuclear alterations that included chromatin condensation, deoxynucleotidyltransferase-mediated dUTP end labelling and DNA laddering. As this AVL-induced leishmanicidal effect could not be inhibited by protease inhibitors including Z-Val-Ala-dl-Asp (methoxy)-fluoromethylketone, a broad-spectrum caspase inhibitor, non-involvement of caspases and major proteases was suggested. Additionally, AVL treatment caused no increase in cytosolic Ca(2+) or generation of reactive oxygen species, indicating that although promastigote death was induced by an apoptotic-like mechanism similar to metazoan apoptosis, the pathways of induction and/or execution differed at the molecular level.

Field adaptable tests for kala-azar

Leishmaniasis is endemic in the tropical and subtropical regions. 12 million cases occur worldwide with 1 to 1.5 million cutaneous and 500,000 visceral leishmaniasis (kala-azar, VL) occuring fresh every year. Leishmania-HIV coinfection is emerging in southern Europe where 25 to 70% of adults with VL have AIDS as well. In the Indian subcontinent, the disease is almost exclusively caused by L donovani. Diagnosis of kala azar (VL) is by demonstration of amastigotes in splenic or bone marrow smears or by culture of leishmania promastigotes from clinical specimen. While the sensitivity of splenic smears could be as high as > 95%, it carries the risk of severe/fatal haemorrhage. Bone marrow aspiration is painful, cumbersome and has a low sensitivity (60-85%). Culture can not be used for routine clinical diagnosis as it requires expensive equipment and expertise [1].

Activity of a killer peptide on the growth and ultrastructure of leishmaniae

An engineered killer decapeptide (KP) has been recently synthesized based on the sequence of a recombinant, single‐chain anti‐idiotypic antibody acting as a functional internal image of a yeast killer toxin. This KP exerts a microbicidal activity by an interaction with β‐glucan present in the surface of many microorganisms, in particular fungi. The activity of KP against the “in vitro” growth and vitality of promastigotes of two Leishmania species has been evaluated and compared with the activity due to a “scramble” irrelevant decapeptide (SP). The IC50 of KP corresponds to 7.2 × 10−5mol/litre for Leishmania infantum, whereas both the inhibitory and leishmanicidal activity is superior on Leishmania major. Moreover, an increase of activity was observed by treating protozoa again with KP; SP is inactive. Structural damages of promastigotes were revealed by transmission electron microscopic studies; the treatment with KP induces a cell death via a non‐apoptotic process. In particular, intracellular damage including cytoplasmic degeneration without disruption of the plasma membrane was noted. The activity of KP on leishmania promastigotes seems governed by ionic and/or electrostatic interactions with the glycoconjugates present on the surface of the parasite inducing an authophagic cell degeneration.

Isolation of integral membrane proteins of Leishmania promastigotes and evaluation of their prophylactic potential in hamsters against experimental visceral leishmaniasis

The integral membrane proteins (IMP's) of promastigotes of two virulent strain of Leishmania (L.) donovani Dd8 and Leishmania (L.) infantum LV9 and one avirulent viscerotropic strain Leishmania tropica UR6 were extracted by phase separation technique using a non-ionic detergent “Triton X-114”. This detergent is homogeneous at 0 °C but divides in an aqueous phase and a detergent phase at above 20 °C. The phase partition resulted in solubilisation of hydrophilic proteins in aqueous phase, and IMP's with an amphiphilic nature were recovered in the detergent phase. The strain wise quantitative recovery rates of IMP's were estimated. These proteins were purified by chill methanol centrifugation and used as vaccinogen, alone or in combination with adjuvant against L. donovani challenge in hamster model. Among all the combinations, hamsters immunised with IMP of L. donovani (Dd8) in combination with CFA resulted in 75% parasite inhibition in spleen ( P < 0.001), however, 61.14% ( P < 0.001) and 77.60% ( P < 0.001) parasitic inhibition was achieved in liver and bone marrow respectively as compared to their unvaccinated counter part. Similar combinations with UR6 and LV9 strain inhibited the parasite establishment up to 65.12% ( P < 0.001) and 66.87% ( P < 0.001), respectively on splenic site. The specific IgG level against (Dd8 strain) soluble leishmania promastigote antigen was monitored at different stages by enzyme linked immunosorbent assay (ELISA) corresponds to the level of parasitic establishment. Similar observations were made in cases of LV9 and UR6 strains. However, significant lymphoproliferative response to IMPs of Dd8 strain (SI 3.5–4.9, P < 0.001) was noticed in all IMP + CFA vaccinated animals. Thus, this study will provide a lead for more manipulative trials to develop a subunit vaccine against the fatal disease.

Miltefosine induces apoptosis-like death in Leishmania donovani promastigotes.

Miltefosine (hexadecylphosphocholine [HePC]) has proved to be a potent oral treatment for human visceral leishmaniasis due to Leishmania donovani. The molecular mechanisms that contribute to the antileishmanial activity of HePC are still unknown. We report that in wild-type promastigotes of Leishmania donovani HePC is able to induce a cell death process with numerous cytoplasmic, nuclear, and membrane features of metazoan apoptosis, including cell shrinkage, DNA fragmentation into oligonucleosome-sized fragments, and phosphatidylserine exposure. None of these changes were detected in an HePC-resistant clone treated with the same drug concentration. Therefore, HePC does not appear to kill L. donovani promastigotes by a direct toxic mechanism but, rather, kills the promastigotes by an indirect one. Pretreatment of wild-type promastigotes with two broad caspase inhibitors, z-Val-Ala-DL-Asp(methoxy)-fluoromethylketone and Boc-Asp(methoxy)-fluoromethylketone, as well as a broad protease inhibitor, calpain inhibitor I, prior to drug exposure interfered with DNA fragmentation but did not prevent cell shrinkage or phosphatidylserine externalization. These data suggest that at least part of the apoptotic machinery operating in wild-type promastigotes involves proteases. Identification of the death-signaling pathways activated in HePC-sensitive parasites appears to be essential for a better understanding of the molecular mechanisms of action and resistance in these parasites.

Molecular and functional characterization of adenylate kinase 2 gene from Leishmania donovani.

ATP-regenerating enzymes may have an important role in maintaining ATP levels in mitochondria-like kinetoplast organelle and glycosomes in parasitic protozoa. Adenylate kinase (AK) (ATP:AMP phosphotransferase) catalyses the reversible transfer of the gamma-phosphate group from ATP to AMP, releasing two molecules of ADP. This study describes cloning and functional characterization of the gene encoding AK2 from a genomic library of Leishmania donovani and also its expression in leishmania promastigote cultures. AK2 was localized on an approximately 1.9-Mb chromosomal band as a single copy gene. L. donovani AK2 gene is expressed as a single 1.9-kb mRNA transcript that is developmentally regulated and accumulated during the early log phase. The overexpression of L. donovani AKgene in Escherichia coli yielded a 26-kDa polypeptide that could be refolded to a functional protein with AK activity. The recombinant protein was purified to apparent homogeneity. Kinetic analysis of purified L. donovani AK showed hyperbolic behaviour for both ATP and AMP, with Km values of 104 and 74 microM, respectively. The maximum enzyme activity (Vmax) was 0.18 micromol.min(-1).mg(-1) protein. P1,P5-(bis adenosine)-5'-pentaphosphate (Ap5A), the specific inhibitor of AK, competitively inhibited activity of the recombinant enzymes with estimated Ki values of 190 nM and 160 nM for ATP and AMP, respectively. Ap5A also inhibited the growth of L. donovani promastigotes in vitro which could be only partially reversed by the addition of ADP. Thus, presence of a highly regulated AK2, which may have role in maintenance of ADP/ATP levels in L. donovani, has been demonstrated.

The major surface protease (MSP or GP63) of Leishmania sp. Biosynthesis, regulation of expression, and function.

Leishmania sp. are digenetic protozoa that cause an estimated 1.5-2 million new cases of leishmaniasis per year worldwide. Among the molecular factors that contribute to Leishmania sp. virulence and pathogenesis is the major surface protease, alternately called MSP, GP63, leishmanolysin, EC3.4.24.36, and PSP, which is the most abundant surface protein of leishmania promastigotes. Recent studies using gene knockout, antisense RNA and overexpression mutants have demonstrated a role for MSP in resistance of promastigotes to complement-mediated lysis and either a direct or indirect role in receptor-mediated uptake of leishmania. The MSP gene clusters in different Leishmania sp. include multiple distinct MSPs that tend to fall into three classes, which can be distinguished by their sequences and by their differential expression in parasite life stages. Regulated expression of MSP class gene products during the parasite life cycle occurs at several levels involving both mRNA and protein metabolism. In this review we summarize advances in MSP research over the past decade, including organization of the gene families, crystal structure of the protein, regulation of mRNA and protein expression, biosynthesis and possible functions. The MSPs exquisitely demonstrate the multiple levels of post-transcriptional gene regulation that occur in Leishmania sp. and other trypanosomatid protozoa.

Sensitivity of Leishmania viannia panamensis to pentavalent antimony is correlated with the formation of cleavable DNA-protein complexes.

The emergence of Leishmania less sensitive to pentavalent antimonial agents (SbVs), the report of inhibition of purified topoisomerase I of Leishmania donovani by sodium stibogluconate (Pentostam), and the uncertain mechanism of action of antimonial drugs prompted an evaluation of SbVs in the stabilization of cleavable complexes in promastigotes of Leishmania (Viannia). The effect of camptothecin, an inhibitor of topoisomerase, and additive-free meglumine antimoniate (Glucantime) on the stabilization of cleavable DNA-protein complexes associated with the inhibition of topoisomerase was assessed in the human promonocytic cell line U-937, promastigotes of L. (Viannia) panamensis selected for SbV resistance in vitro, and the corresponding wild-type strain. The stabilization of cleavable complexes and the 50% effective dose (ED50) of SbVs for parasites isolated from patients with relapses were also evaluated. The median ED50 for the wild-type strain was 16. 7 microg of SbV/ml, while that of the line selected for resistance was 209.5 microg of SbV/ml. Treatment with both meglumine antimoniate and sodium stibogluconate (20 to 200 microg of SbV/ml) stabilized DNA-protein complexes in the wild-type strain but not the resistant line. The ED50s of the SbVs for Leishmania strains from patients with relapses was comparable to those for the line selected for in vitro resistance, and DNA-protein complexes were not stabilized by exposure to meglumine antimoniate. Cleavable complexes were observed in all Leishmania strains treated with camptothecin. Camptothecin stabilized cleavable complexes in U-937 cells; SbVs did not. The selective effect of the SbVs on the stabilization of DNA-protein complexes in Leishmania and the loss of this effect in naturally resistant or experimentally derived SbV-resistant Leishmania suggest that topoisomerase may be a target of antimonial drugs.

Insulin like growth factor-I -induced growth response in leishmania promastigotes involves a 185KD phosphorylation substrate molecule antigenically homologous to the human insulin receptor substrate-1 (IRS-1)

Insulin like growth factor-I -induced growth response in leishmania promastigotes involves a 185KD phosphorylation substrate molecule antigenically homologous to the human insulin receptor substrate-1 (IRS-1)

Leishmania (Leishmania) amazonensis:Purification and Enzymatic Characterization of a Soluble Serine Oligopeptidase from Promastigotes

de Andrade, A. S. R., Santoro, M. M., de Melo, M. N., and Mares-Guia, M. 1998.Leishmania (Leishmania) amazonensis: Purification and enzymatic characterization of a soluble serine oligopeptidase from promastigotes.Experimental Parasitology89, 153–160. A soluble proteinase was purified 90-fold from extracts of promastigotes ofLeishmania (Leishmania) amazonensisusing a combination of ion-exchange chromatography in Q-Sepharose Fast Flow, gel filtration chromatography in Sephacryl HR S-200, and chromatofocusing. The enzyme appeared as a single band with an apparent molecular weight of 101 kDa by silver staining following SDS—PAGE, under both reducing and nonreducing conditions. The proteinase has a pH optimum between 8.0 and 8.5 and an isoelectric point between 5.12 and 5.23, belongs to the serine proteinase class, and is inhibited by Mg2+, Ca2+, and K+. The primary specificity determined using synthetic substrates is for basic amino acids. The kinetic parameters for the Bz-l-Arg-Nam substrate areKm= 26 μM,kcat= 32 min−1, andKsi= 1270 μM (the proteinase showed inhibition by excess substrate). The enzyme does not hydrolyze casein, albumin, and gelatin or large peptides like the oxidized insulin B chain, but hydrolyzes small peptides like bradykinin and fragment 4–10 of the adrenocorticotropic hormone, at the carboxyl side of basic residues and aromatic residues preceding basic residues. The enzyme appears, thus, to be restricted in its action, cleaving only small peptide substrates, which characterizes the proteinase as an oligopeptidase. This is the first report of purification of a serine peptidase fromLeishmaniaspecies and it increases the short list of known oligopeptidases.

Macrophage mannosyl fucosyl receptor: its role in invasion of virulent and avirulent L. donovani promastigotes.

The interaction of leishmania parasites with macrophages is known to be receptor mediated. Previous study from this laboratory (J. Parasitol. 82:632, 1996) showed the significant involvement of LPG and gp63 receptors in the recognition of virulent strains onto the macrophages. The role of carbohydrate receptors the other major receptors besides LPG and gp63 receptors, in the recognition of both virulent (strains AG83 and GE1) and avirulent (strain UR6) leishmania onto the host macrophages has been the major focus of the present investigation. Various neoglycoproteins were used as efficient ligands to preblock the carbohydrate receptors on the macrophage surface. Similarly, various sugar specific lectins were used to preblock the corresponding carbohydrate ligands on the parasite surface. When these preblocked macrophages or parasites were used to study their mode of recognition, it was obvious from the findings that avirulent leishmania promastigotes possibly use the mannosyl fucosyl receptors (MFR) more avidly for their initial attachment and subsequent internalization into the macrophages whereas the virulent leishmania exhibits limited use of this receptor. When a macrophage-like cell line (J774), lacking in MFR, was purposely selected to test the previous findings, as expected, the attachment of avirulent promastigotes (UR6) onto the cell line was found to be negligible when compared to the peritoneal macrophages. Thus, it appears that avirulent leishmania promastigotes probably utilize MFR significantly for their initial recognition and subsequent internalization by macrophages.

Leishmania, macrophages and complement: a tale of subversion and exploitation.

Leishmania are intracellular protozoan parasites which reside primarily, if not exclusively, in host mononuclear phagocytes. Several studies have demonstrated that infectious promastigotes rapidly and efficiently fix complement when they encounter serum components during their transmission to the mammalian host. Activation of the complement system by a microorganism can have 3 distinct biological effects. First, fixation of the terminal complement components can result in complement-mediated lysis. Second, fixation of the 3rd component of complement can lead to opsonization of the organism for uptake by phagocytic cells. Finally, the elaboration of the complement anaphylotoxins, C3a and C5a, can lead to inflammation. In the present chapter, we discuss the interaction of leishmania promastigotes with the complement system. We show that infectious promastigotes avoid the lytic effects of complement and resist fixation of the terminal complement components. At the same time, however, these organisms depend on fixation of opsonic complement to invade host mononuclear phagocytes efficiently. We discuss the mechanisms which allow metacyclic leishmania promastigotes to exploit the opsonic properties of complement and the receptors on macrophages involved in leishmania recognition. The role of complement mediated inflammatory processes in the host response to leishmania infection is an area which requires additional study.