Monoclonal antibodies for serotyping Leishmania strains

Development of monoclonal antibodies against axenic amastigotes of Leishmania infantum strain in Iran: implication for diagnosis of Kala-azar

OBJECTIVES

Leishmaniasis is endemic in 88 countries. Amastigote forms of Leishmania are experts at exploiting host cell processes to establish infection. Monoclonal antibodies are key reagents used in the diagnosis of infectious and non-infectious diseases. The aim of this study was to produce monoclonal antibodies against axenic amastigotes of the Leishmaniainfantum strain in Iran.

MATERIALS AND METHODS

First, standard strains were cultured and axenic amastigote antigens of L. infantum were obtained. Since then, BALB/c smice were immunized and antibody titers were determined. For hybridoma cell formation, lymphocytes isolated from spleen of immunized mice and myeloma cells were fused at a ratio of 10 to 1 in the presence of polyethylene glycol, followed by limiting dilution for the isolation of monoclones. Subsequently, antibody isotypes were determined by using the isotyping kit. The best clone was injected intraperitoneally to pristane-primed mice for large scale production of monoclonal antibodies. The specificity of antibody was determined with Western blotting.

RESULTS

Approximately 25 positive monoclones were obtained, of which four hybrids producing anti-amastigotes L. infantum monoclonal antibodies with high optical density (OD), selected and designated as 8D2 FVI6, 8D2 FVI3, 6G2 FV4 and 6G2 FV3. Results from isotype determination showed the IgG2b sub-class in 6G2FV2 and 8D2FVI6 monoclones.

CONCLUSION

This study produced monoclonal antibody against amastigotes of Iranian strain of L. infantum for the first time. These antibodies have reactivity against Iranian strain of L. infantum and can be used in the diagnosis of Kala-azar.

Epitope mapping of a common 57 kDa antigen of Leishmania species by monoclonal antibodies

BALB/c mice were immunized with freeze-thawed promastigote of Leishmania infantum. Five monoclonal antibodies (mAb) were selected, four IgM (designated as P1A9, P2G8, P5E3 and P6B3) and one IgG1 (P3D2). ELISA and Western blot analysis suggested that all monoclonal antibodies are specific to a band of 57 kDa antigen of L. infantum as well as other three Leishmania species (L. tropica, L. major and L. donovani). ELISA additivity tests revealed four epitopes on 57 kDa antigen as defined by four IgM monoclonal antibodies. Three distinct epitopes were recognized by P1A9, P2G8, and P6B3 antibodies and one epitope recognized by P5E3 antibody that shared with P2G8, and P6B3 epitopes. The 57 kDa protein was purified with affinity column and was shown to possess proteolytic activity. It seems that 57 kDa protein is the major surface Leishmania antigen (gp63) that has been used as subunit vaccine with appropriate adjuvant and induced protection against L. major infection in BALB/c mice.

The involvement of TLR2 in cytokine and reactive oxygen species (ROS) production by PBMCs in response to Leishmania major phosphoglycans (PGs)

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.

Cell biology of Leishmania

Leishmania are digenetic protozoa which inhabit two highly specific hosts, the sandfly, where they grow as motile flagellated promastigotes in the gut, and the mammalian macrophage, where they survive and grow intracellularly as non-flagellated amastigotes in the phagolysosome. Leishmaniasis is the outcome of an evolutionary 'arms race' between the host's immune system and the parasite's evasion mechanisms, which ensure survival and transmission in the population. The diverse spectrum of patterns and severity of disease reflect the varying contributions of parasite virulence factors and host responses, some of which act in a host protective manner while others exacerbate disease. This chapter describes the interaction of the Leishmania with their hosts, with emphasis on the molecules and mechanisms evolved by the parasites to avoid, subvert or exploit the environments in the sandfly and the macrophage, and to move from one to the other.

The Leishmania promastigote surface antigen 2 complex is differentially expressed during the parasite life cycle

The promastigote surface antigen 2 (PSA-2) complex comprises a family of antigenically similar polypeptides of M(r) 96,000, 80,000 and 50,000, anchored to the membrane with glycosylphosphatidylinositol. Although PSA-2 was initially detected only in promastigotes, Northern blot analysis indicated that mRNA transcripts are also present in amastigotes. Unlike the situation in promastigotes, where at least four major transcripts (2.6-5.3 kb) were detected, only one major (2.6 kb) and two minor transcripts were present in amastigotes. A cDNA clone encoding a member of the PSA-2 family expressed in amastigotes was isolated using DNA probes. The predicted protein sequence of M(r) 40,000 is distinct from promastigote sequences, but shows significant similarity to previously described members of the family from L major and L amazonensis. Antibodies to the carboxyl terminal sequence conserved in all L major PSA-2 studied to date, as well as antibodies affinity purified on the amastigote cDNA-derived polypeptide recognized a major M(r) 50,000 amastigote polypeptide. Immuno-electron microscopy localized both promastigote and amastigote PSA-2 to the cell surface. The expression of PSA-2 polypeptides during the transformation of amastigotes into promastigotes was ordered in a time-dependent manner, with the promastigote M(r) 80000 polypeptide appearing first, followed by the M(r) 96000 polypeptide. In contrast to the glycosylphosphatidylinositol anchor of promastigote PSA-2, which could be hydrolysed by phosphatidylinositol-specific phospholipase C, the amastigote form was resistant to this enzyme.

Use of glycoconjugates for trypanosomatid taxonomy

Glycoconjugates from five trypanosomatid genera--Crithidia, Herpetomonas, Endotrypanum, Leishmania, and Trypanosoma--were extracted with Triton X-114 and analyzed by sodium dodecyl sulfate polyacrylamide gel electrophoresis followed by periodic acid-Schiff staining. Most of the glycoconjugates were detected in the hydrophobic phase, indicating the presence of anchored glycoconjugates. All the trypanosomatids expressed a glycoconjugate with a low molecular weight (below 20 kDa) in this phase. In each species, however, a characteristic and specific pattern of glycoconjugates was also observed in both phases. In the hydrophobic phase: 14-29 kDa glycoconjugates in C. guilhermei; 24-70 kDa in C. fasciculata, C. luciliae, E. schaudinni, and T. cruzi Y and G strains; 45-66 kDa in C. oncopelti and H. samuelpessoai; above 36 kDa in T. dionisii; 20-24 kDa, 36-45 kDa, and 70 kDa in L. tarentolae and T. mega. In the hydrophilic phase, typical glycoproteins were observed in some trypanosomatids: 60 kDa in T. mega and T. cruzi Y strain; 70 kDa in H. samuelpessoai; 66 kDa in C. oncopelti; 20-70 kDa in C. luciliae. These findings suggest that Triton X-114-extracted glycoconjugates could be useful markers for trypanosomatid taxonomy.

Lipophosphoglycan blocks attachment of Leishmania major amastigotes to macrophages

Promastigotes of the intracellular protozoan parasite Leishmania major invade mononuclear phagocytes by a direct interaction between the cell surface lipophosphoglycan found on all Leishmania species and macrophage receptors. This interaction is mediated by phosphoglycan repeats containing oligomers of beta (1-3)Gal residues specific to L. major. We show here that although amastigotes also use lipophosphoglycan to bind to both primary macrophages and a cell line, this interaction is independent of the beta (1-3)Gal residues employed by promastigotes. Binding of amastigotes to macrophages could be blocked by intact lipophosphoglycan from L. major amastigotes as well as by lipophosphoglycan from promastigotes of several other Leishmania species, suggesting involvement of a conserved domain. Binding of amastigotes to macrophages could be blocked significantly by the monoclonal antibody WIC 108.3, directed to the lipophosphoglycan backbone. The glycan core of lipophosphoglycan could also inhibit attachment of amastigotes, but to a considerably lesser extent. The glycan core structure is also present in the type 2 glycoinositolphospholipids which are expressed on the surface of amastigotes at 100-fold-higher levels than lipophosphoglycan. However, their inhibitory effect could not be increased even when they were used at a 300-fold-higher concentration than lipophosphoglycan, indicating that lipophosphoglycan is the major macrophage-binding molecule on amastigotes of L. major. In the presence of complement, the attachment of amastigotes to macrophages was not altered, suggesting that lipophosphoglycan interacts directly with macrophage receptors.

Characterization of a polymorphic family of integral membrane proteins in promastigotes of different Leishmania species

Antibodies raised against a Leishmania major recombinant promastigote surface antigen 2 (PSA-2) fragment recognized three major polypeptides of approximate M(r) 96,000, 80,000 and 50,000 in promastigotes of three Israeli isolates of L. major including the cloned line LRC-L137-V121, but detected a different array of polypeptides in other L. major isolates. The pattern was different both in number of polypeptides detected and their molecular weight. The antibodies to L. major PSA-2 also recognized polypeptides in L. tropica, L. donovani and very weakly in L. mexicana promastigotes and in Crithidia lucilliae. The number and size of the polypeptides was different in each species. In addition to the membrane-bound PSA-2 polypeptides we identified water-soluble forms of PSA-2 released in promastigote culture supernatants. Peptide maps of the various L. major PSA-2 membrane polypeptides showed they were different from each other. N-terminal amino acid sequence of the three polypeptides expressed by L. major showed they are similar but distinct, consistent with being members of a polymorphic family. Because of the extensive sequence similarity between the PSA-2 genes it has been difficult to assign protein products to individual genes. As a first step towards solving this problem, we have transfected into L. mexicana a genomic clone of a L. major PSA-2 gene and shown that it produces a M(r) 35,000 polypeptide recognized by monoclonal and polyclonal antibodies to L. major PSA-2.

Epitope mapping of monoclonal antibodies directed against lipophosphoglycan of Leishmania major promastigotes

Monoclonal antibodies (MAbs) were generated against Leishmania major promastigote lipophosphoglycan (LPG) to use as tools in defining functional epitopes of this major cell surface glycoconjugate. Epitope mapping of four MAbs, designated 4A2-A2, 2G11-A3, 5E6-D10 and 5E10-F2, revealed that the phosphorylated oligosaccharide repeat unit PO4-6[Gal(beta 1-3)]Gal(beta 1-4)Man alpha 1-, P3, is a highly immunogenic epitope which has previously been demonstrated, by chemical analyses, to be a repeat unit specific to L. major. Two antibodies, 4A2-A2 and 5E10-F2, also recognised the repeat unit PO4-6[Ara(beta 1-2)Gal(beta 1-3)]Gal(beta 1-4)Man alpha 1-, 4Pa, with less affinity than P3, while 2G11-A3 recognised P4a with greater affinity than for P3. The L. major metacyclic-specific antibody 3F12 only recognised repeat units terminating with arabinose residues. In particular, 3F12 recognised P4a, which is upregulated in metacyclic LPG compared to the procyclic form of the molecule. The oligosaccharides P3, P4a and P5a are specific to L. major LPG. The epitopes of 4A2-A2, 2G11-A3, 5E6-D10 and 5E10-F2 were found on the cell surface and in the flagellar pocket of both procyclic and metacyclic V121 promastigotes, but were only detected at very low levels on amastigotes. The repeat unit P3 is able to inhibit attachment of procyclic promastigotes to the midgut of the sandfly vector, but neither Fab fragments of the four antibodies nor purified P3 could inhibit attachment of metacyclic promastigotes to the macrophage cell line J774. It was also shown that human sera from patients with cutaneous leishmaniasis recognised purified P3. The data suggests that while P3 is an immunogen in the natural course of infection of the human host, P3 plays no role in attachment and internalisation of promastigotes into the macrophages of the mammalian host.

Ricin-resistant mutants of Leishmania major which express modified lipophosphoglycan remain infective for mice

Glycosylation variants of the virulent Leishmania major clone V121 were generated by mutagenesis with N-methyl-N-nitroso-N-nitroguanidine and selected using the galactose-specific lectin Ricinus communis II (RCA II). Three mutants, 4B9, 1D1 and 1C12, which failed to bind RCA II, were found to have an altered expression of lipophosphoglycan (LPG), a molecule implicated in the attachment to host macrophages and survival within the phagolysosome. There were differences in the antigenicity, molecular weight and localization of LPG from mutant parasites as compared to V121. Expression of gp63, a surface molecule also implicated in attachment to macrophages, was unaltered. All 3 mutants caused disease when injected into genetically susceptible BALB/c mice but lesions developed at a much slower rate than those caused by the virulent V121 clone. This slow rate of lesion development did not correlate with promastigotes' ability to invade macrophages in vitro. Karyotype analysis showed that there was a reduction in the size of chromosome band number 2 in all 3 mutants. The differences in LPG and chromosome band 2 were retained by mutant clones following passage through mice, suggesting that these phenotypes are stable. Although the mutant parasites were infective and caused lesions, the changed structure of the LPG appeared to influence the virulence of the parasites.

Distribution of lipophosphoglycan-associated epitopes in different Leishmania species and in African trypanosomes

Monoclonal antibody (mAb) CA7AE binds specifically to the phosphorylated Gal-beta 1,4-Man disaccharide repeat epitope of Leishmania donovani lipophosphoglycan (LPG). This mAb detected the repeat epitope in most but not all of a wide variety of Leishmania species and strains examined. MAb CA7AE also bound to both glycoprotein and carbohydrate antigens in medium from L. donovani promastigote cultures. Specifically, mAb CA7AE bound the delipidated form of LPG, the phosphoglycan, and a glycoprotein both of which are released into the medium by the parasite indicating that both share a specific phosphorylated carbohydrate epitope. The epitope was detected in sera from L. donovani-infected (kala-azar positive) patients when mAb CA7AE was used in an antigen-capture enzyme-linked immunosorbent assay (ELISA). MAb L157 is specific for a protein that is found associated with L. donovani LPG, the lipophosphoglycan-associated protein (LPGAP). This mAb bound to molecules in all 19 strains (representing 9 species) of Leishmania promastigotes and to molecules in 2 species of Trypanosoma procyclic culture forms. This wide distribution of the LPGAP epitope implies that it may have a conserved function, for example, in the biochemistry or arrangement of parasite surface molecules. In addition, since the LPGAP is involved in the stimulation of T lymphocyte proliferation, its wide distribution amongst different Leishmania species suggests that it may be an ideal molecule for testing as a vaccine for leishmaniasis.

Monoclonal antibodies directed against Leishmania secreted acid phosphatase and lipophosphoglycan. Partial characterization of private and public epitopes

Leishmania promastigotes, the stage of the parasite characteristic for the sandfly vector, express an abundant glycoconjugate, called lipophosphoglycan, at their surface. Lipophosphoglycan consists of lysoalkyl-sn-glycerophosphoinositol linked to a phosphosaccharide core conserved in all species, which is connected to PO4-6Gal beta 1,4Man alpha 1 repeats with species-specific substitutions at the Gal residue; the repeats are capped by conserved and species-specific oligosaccharides. Most Leishmania species also secrete an acid phosphatase, which, in Leishmania mexicana, is a filamentous complex composed of a phosphorylated glycoprotein and non-covalently associated proteo-(high-molecular-mass)phosphoglycan. The secreted acid phosphatase complex was used as an antigen to derive a panel of monoclonal antibodies (mAbs). A total of 25 mAbs (17 novel and 8 previously described) were tested by different techniques for their specificity against lipophosphoglycan and secreted acid phosphatase from several Leishmania species. This comparison and the modification of the antigens by chemical or enzymic treatments allowed a classification of the mAbs into several groups. First, from 25 mAbs examined, 22 recognize lipophosphoglycan and the enzyme complex of L. mexicana; only three are specific for secreted acid phosphatase. Two of the latter group are also directed against carbohydrate structures, whereas the third mAb recognizes the 100-kDa polypeptide of the complex. The secreted acid-phosphatase-specific class detects antigen in the flagellar pocket of promastigotes while all anti-lipophosphoglycan mAbs bind to the cell surface. Second, all 15 anti-lipophosphoglycan mAbs investigated in detail appear to be directed against the phosphosaccharide repeats or the cap structure rather than the phosphosaccharide core. Two mAbs recognize terminal cap-structures containing Man alpha 1,2Man residues. Four antibodies are specific for L. mexicana and are probably directed against PO4-6[Glc beta 1,3]Gal beta 1,4Man alpha 1 repeats while six mAbs react with the unmodified repeats. Two antibodies specific for Leishmania major recognize Gal beta 1,3-substituted repeats unique for lipophosphoglycan from this species. Analysis by immunoblotting indicates that the high-molecular-mass proteo-phosphoglycan of L. mexicana secreted acid phosphatase carries epitopes for all anti-lipophosphoglycan mAbs suggesting the presence of capped phosphosaccharide repeats while the enzymically active glycoprotein subunit is modified by caps but probably not by repeats. In the case of Leishmania donovani secreted acid phosphatase, the enzymically active polypeptide may be directly modified by repeats. The mAbs are used to characterize changes in lipophosphoglycan structure, which occur in culture during the transition of promastigotes from the logarithmic to the stationary growth phase.(ABSTRACT TRUNCATED AT 400 WORDS)

The structure, biosynthesis and function of glycosylated phosphatidylinositols in the parasitic protozoa and higher eukaryotes

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Expression of lipophosphoglycan, high-molecular weight phosphoglycan and glycoprotein 63 in promastigotes and amastigotes of Leishmania mexicana

The abundant surface glycoconjugate of Leishmania promastigotes, lipophosphoglycan (LPG), forms a blue-colored complex (lambda max = 649 nm) with the cationic dye Stains-all, which can be quantitated densitometrically on polyacrylamide gels of cell lysates. Promastigotes of Leishmania mexicana, Leishmania major and Leishmania donovani yield values of 1-3 x 10(6) LPG molecules cell-1. In amastigotes the LPG content is down-regulated below the detection limit (< 10(3) molecules cell-1) in L. mexicana and L. donovani, but remains significant in L. major (2 x 10(3) molecules cell-1). In the case of L. mexicana, these results are supported by immunological studies. Using several monoclonal and polyclonal antibodies, LPG is undetectable by immunoblotting in lysates of either amastigotes or infected macrophages and the amastigote surface is devoid of LPG as judged by immunofluorescence and immunoelectron microscopy. Immunoblotting experiments demonstrate that amastigotes synthesize hydrophilic high-molecular weight compounds which stain blue with Stains-all and cross-react with the monoclonal and polyvalent antibodies suggesting the presence of similar phosphoglycan structures as in LPG. The high-molecular weight phosphoglycan appears to be located in the lumen of the flagellar pocket of mouse lesion amastigotes and may be secreted from there into the lumen of the parasitophorous vacuole of parasitized macrophages. In L. mexicana promastigotes the surface protease gp63 is amphiphilic and comprises about 1% of the cellular proteins. In contrast, in amastigotes gp63-related proteins are predominantly hydrophilic; they amount to only about 0.1% of the cellular proteins and are mainly located in the lumen of the extended lysosomes (megasomes) characteristic for this species.

Persistence of virulent Leishmania major in murine cutaneous leishmaniasis: a possible hazard for the host

The persistence of Leishmania major parasites in mice resistant to infection was investigated by the polymerase chain reaction and in vitro culture methods. Parasite-specific DNA was detected in the lymph nodes, spleens, bone marrow, and livers of C57BL/6 mice 1 year after their recovery from infection. Live parasites were also recovered from these tissues (except liver tissues) and were used to establish in vitro isolates. Pulsed-field gel electrophoresis, Southern blotting, and Western blot (immunoblot) analyses showed that these isolates retained the karyotype and the phenotype of the original inoculum, including the levels of expression of gp63 and lipophosphoglycan, the two major surface molecules of Leishmania species. More importantly, these isolates were virulent and induced fatal disease when injected into susceptible BALB/c mice. Persistence was shown to be a more general phenomenon, since several different strains of mice which were resistant to L. major infection also harbored persistent parasites. The implications for the etiology of human leishmaniasis in immunocompromised individuals such as AIDS patients are discussed.

Identification of a macrophage-binding determinant on lipophosphoglycan from Leishmania major promastigotes

Leishmania are obligatory intracellular parasites in mammalian macrophages that gain entry by receptor-mediated phagocytosis. Their major cell surface glycoconjugate, lipophosphoglycan (LPG), has been implicated in this process. A monoclonal antibody specific for Leishmania major LPG (WIC 79.3), which has been shown to block promastigote attachment to macrophages, was used to identify a macrophage-binding determinant of LPG. WIC 79.3 bound exclusively to the phosphorylated repeats of LPG and not to the saccharide core or lipid anchor. Furthermore, the epitope recognized by WIC 79.3 mapped to the phosphorylated oligosaccharide P5b, PO4-6[Gal(beta 1-3)Gal(beta 1-3)Gal(beta 1-3)]Gal(beta 1-4)Man(alpha 1-, which is unique to the LPG of promastigotes of L.major. Phosphorylated oligosaccharides P3, PO4-6[Gal(beta 1-3)[Gal(beta 1-4) Man(alpha 1-, and P4b, PO4-6[Gal(beta 1-3)Gal(beta 1-3)] Gal(beta 1-4)Man(alpha 1-, were also recognized by WIC 79.3 but with considerably lower (approximately 100-fold) affinities. The phosphorylated oligosaccharide P5b inhibited attachment of promastigotes of L. major to the macrophage cell line J774 to the same degree as phosphoglycan (derived from LPG) and Fab fragments of WIC 79.3, suggesting that P5b is a site of L. major LPG that is recognized by macrophage receptor(s) and is an important determinant in the attachment of promastigotes to host macrophages and initiation of infection.

An antigenically distinct lipophosphoglycan on amastigotes of Leishmania major

We show that lipophosphoglycan (LPG) on the surface of amastigotes of Leishmania major is antigenically and biochemically distinct from promastigote LPG. A rabbit antiserum raised against the amastigote integral membrane fraction detected LPG spanning the region of Mr 55,000-100,000 on Western blots of the amastigote integral membrane fraction, but did not recognize the promastigote integral membrane fraction. WIC 79.3, a monoclonal antibody which recognizes L. major metacyclic promastigote LPG, did not recognize the amastigote integral membrane fraction on Western blots. The antigen recognized by this rabbit antiserum was shown to be LPG by its migration pattern on SDS-PAGE, the presence of terminal galactose residues, recognition by a monoclonal antibody to LPG, WIC 108.3, the biosynthetic incorporation of label from [3H]glucose and [32P]phosphate, a hydrophobic chromatography elution profile similar to promastigote LPG, and the presence of a lipid anchor sensitive to phosphatidylinositol-specific phospholipase C. The temporal regulation of LPG expression during parasite differentiation was studied in vitro. During amastigote-to-promastigote transformation, the amastigote-specific form of LPG disappeared after subculture at 48 h. The WIC 79.3 epitope was not detected by Western blotting on transforming parasites until 48 h in culture. During promastigote-to-amastigote transformation, the amastigote-specific form of LPG was detected 12 h after infection. WIC 79.3 epitopes gradually diminished over 48 h. The results demonstrate the developmentally regulated expression of an antigenically distinct LPG on amastigotes of L. major.

Lipophosphoglycan and secreted acid phosphatase of Leishmania tropica share species-specific epitopes

Several species-specific monoclonal antibodies (T11, T13-T15) which only react with Leishmania tropica, recognize phosphorlated carbohydrate epitopes on lipophosphoglycan and the structurally related molecule, phosphoglycan, which is shed by promastigotes into spent culture medium. During immunoaffinity isolation of [32P]orthophosphate-labeled phosphoglycan on monoclonal antibody T15 conjugated to Sepharose 4B, a high-Mr component (approx. 200,000) was co-purified. The latter material is metabolically labeled with [35S]methionine and [3H]glucosamine. This glycoprotein was separated from phosphoglycan by chromatography on lentil lectin resin. The glycoprotein exhibited a L-tatrate-sensitive acid phosphatase activity, typical of secreted acid phosphatase (EC 3.1.3.2) from Leishmania. Monospecific antibodies to Leishmania donovani-secreted acid phosphatase selectively precipitated the L. tropica enzyme from immunoaffinity purified mixtures of the two antigens, and monoclonal antibodies to lipophosphoglycan precipitate the pure enzyme. Species-specific monoclonal antibodies to L. major lipophosphoglycan also recognized both L. tropica antigens. Treatment of the acid phosphatase with periodate or phosphodiesterase I abolished binding by the monoclonal antibodies to the pure enzyme. These results demonstrate that the two major secreted glycoconjugates of Leishmania tropica, the lipophosphoglycan and the acid phosphatase, share species-specific phosphorylated carbohydrate epitope(s).

Lipophosphoglycan expression and virulence in ricin-resistant variants of Leishmania major

Lipophosphoglycan (LPG) of Leishmania is a polymorphic molecule comprising an alkylglycerol anchor, a conserved oligosaccharide core and a species-specific polymer of oligosaccharide repeats jointed by phosphodiester bonds. This molecule, together with the membrane polypeptide gp63, has been implicated as a parasite receptor for host macrophages. To examine the role of LPG in parasite infectivity glycosylation variants of Leishmania major were generated by chemical mutagenesis of a virulent cloned line V121 and variants with modified LPG selected using the galactose-specific lectin Ricinus communis II (RCA II). Twenty RCA II-resistant primary clones were generated. Analysis of LPG profile by immunoblotting using LPG-specific monoclonal and polyclonal antibodies revealed that some of the clones were LPG-deficient. Three clones that did not bind any LPG-specific antibodies but expressed normal levels of the Mr 63,000 glycoprotein (gp63), a second parasite receptor for host, were chosen for detailed studies. All three clones expressed, at least to some extent, a surface molecule which could be labeled by mild periodate oxidation and sodium borotritide and behaved like LPG by hydrophobic interaction chromatography. All clones also bound a well-characterized monoclonal antibody L157 directed to the core oligosaccharide of LPG, but did not bind another monoclonal antibody, CA7AE, to an epitope on a repeating unit shared by Leishmania donovani and L. major LPG. A third monoclonal antibody, 5E6, recognizing LPG on the surface of wild-type V121 promastigotes bound only to RCA II-resistant clone 3A2-C3 and was restricted to an internal structure. The LPG molecule that this clone expressed was a form of LPG by its chromatographic behavior and by its monosaccharide and alkylglycerol composition. Clone 3A2-C3 was the only one to infect mice in vivo and survive in macrophages in vitro, albeit at a much reduced rate compared to wild-type V121 promastigotes. The data suggest that some form of LPG may be necessary to ensure parasite infectivity.

Leishmania tropica: characterization of a lipophosphoglycan-like antigen recognized by species-specific monoclonal antibodies

Species-specific monoclonal antibodies to Leishmania tropica, T11 and T13-15, recognize membranal and secreted antigens. The membrane form of the antigen migrates on sodium dodecyl sulfate-polyacrylamide gels with a diffuse molecular weight from 15 to 50 kDa and can be labeled with palmitic acid, myoinositol, galactose, glucosamine, and inorganic phosphate. Both phosphate and sugar-labeled material were isolated from metabolically labeled promastigotes by affinity chromatography on antibodies coupled to Sepharose 4B. No binding to Ricinus communis agglutinin was observed. This material behaves like lipophosphoglycans from other Leishmania but contains unique species-specific epitopes. It is susceptible to cleavage by phospholipase C and after digestion no longer partitions into the detergent phase following a Triton X-114 extraction. All four monoclonal antibodies appear to recognize a carbohydrate epitope on the lipophosphoglycan since periodate treatment of this material bound to nitrocellulose essentially eliminated antibody binding. In addition, T15 binding could be blocked by 5 mM mannose-6-PO4 and fructose-1- or 6-PO4, but not by mannose, glucose, fructose, or the additional PO4 derivatives examined. The antibodies recognize a similar but not identical epitope, as demonstrated by a competitive radioimmunoassay using 125I-labeled T11, T13, and T15. Expression of surface antigen is elevated during the promastigote stationary phase.

The immunochemical structure and surface arrangement of Leishmania donovani lipophosphoglycan determined using monoclonal antibodies

Using intact Leishmania donovani promastigotes or purified L. donovani lipophosphoglycan (LPG) as immunogens, we have derived four LPG-specific monoclonal antibodies (MAbs). Two of these MAbs recognize an epitope consisting of the repeating phosphorylated galactose beta-1,4-mannose disaccharide portion of the molecule and cross-reacted with LPG from Leishmania major. These MAbs bound to the surface of living promastigotes of both species. The two other MAbs bound to the phosphosaccharide core structure of LPG and did not bind to the surface of living parasites, presumably due to masking of the core region. Experiments using all four MAbs with an LPG-deficient promastigote mutant indicated that both the repeat epitope and phosphosaccharide core were present in these cells, suggesting that incomplete assembly was responsible for the absence of intact LPG.

The lipophosphoglycan of Leishmania

The major cell surface glycoconjugate of leishmanial parasites is lipophosphoglycan (LPG). Its relative abundance, unique structure, and cellular location suggest one or more important roles in interactions between parasites and host cells. In this article, Sam Turco examines current information about this novel glycoconjugate and its significance.

Identification of monomeric and oligomeric forms of a major Leishmania infantum antigen by using monoclonal antibodies

Ten monoclonal antibodies (MAbs) produced against isolated Leishmania infantum membranes were used as probes of L. infantum membrane antigens. Western blots of L. infantum membranes, sodium dodecyl sulfate solubilized and heated at 100 degrees C before analysis by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, showed that all 10 MAbs recognized a band at 58 kilodaltons (kDa). However, when solubilized membranes were not heated, 2 of the 10 MAbs recognized, in addition to the 58-kDa band, bands of higher molecular weight. Limited digestion of heated or nonheated membranes showed that both groups of MAbs (i.e., not capable or capable of binding to the high-molecular-weight bands) recognized the same proteolytic digests. Hydrophilic forms of the above proteins, possessing proteolytic activity, were detected and isolated by gel filtration. Protein staining of the isolated monomer analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, under reducing and heating conditions, revealed incomplete reduction of the 58-kDa protein. The reduced form of the 58-kDa protein migrated at 63 to 65 kDa and was not recognized by the MAbs. These results suggest the existence of a monomeric and an oligomeric form of the 58-kDa antigen. The observed inhibition of Leishmania promastigote-macrophage binding caused by MAbs representative of the two groups (capable of oligomeric and/or monomeric antigen recognition) suggest that the 58-kDa monomer and oligomer play an important role in promastigote-macrophage interaction. We suggest that the 58-kDa L. infantum antigen is the major surface Leishmania antigen (p63) identified by others.

Heterologous protection in murine cutaneous leishmaniasis

Mice immunized with a glycolipid antigen (GL) of Leishmania major plus adjuvant are relatively resistant to subsequent infection with this protozoan parasite. The GL is affinity purified on the monoclonal antibody WIC-79.3 which is L. major-specific and does not react with L. donovani. When another monoclonal, WIC-108.3, which cross-reacts with several Leishmania species, is used to affinity purify GL from L. donovani, the eluted material can partially protect genetically resistant mice against L. major. Thus, GL cross-reactions may in part underlie the known protective effects of crude L. donovani antigens against L. major infection. Experiments with live parasites of the L. major isolate LRC-L119, that is non-pathogenic in mice, that does not survive long in macrophages in vitro, and that has not been shown to contain any WIC-79.3 reactive GL, indicated that this isolate will very effectively protect mice against subsequent infection. This raises the possibility that GL is only one of at least two different classes of vaccinating antigen capable of protectively immunizing mice in this cutaneous leishmaniasis model.

In situ detection of amastigotes in American cutaneous leishmaniasis, using monoclonal antibodies

Using an immunoperoxidase technique we have applied monoclonal antibodies against American Leishmania for the detection of amastigotes in biopsies from cutaneous leishmaniasis patients. The immunocytochemical procedure was notably superior to conventional histological staining in terms of the visualization and definition of the amastigotes. This technique could eventually prove to be of value in epidemiological studies, and possibly have prognostic importance, by allowing the in situ characterization of the species of infecting organism.

Nitrocellulose-based assays for the detection of glycolipids and other antigens: mechanism of binding to nitrocellulose

A variety of simple and rapid assays for the detection of glycolipids by direct binding to nitrocellulose or binding to antibody-coated nitrocellulose, and probing with monoclonal antibodies are described. These include dot-blotting, charge shift electrophoresis and electroblotting. It is shown that the direct binding of the Leishmania major glycolipid to nitrocellulose is dependent on its lipid moiety, indicating that the mechanism of binding is probably via hydrophobic interactions. However, the L. major glycolipid from which the lipid moiety has been removed can still be detected by blotting onto nitrocellulose precoated with a monoclonal antibody directed to a carbohydrate epitope. The general approach of blotting onto antibody-coated nitrocellulose thus extends the usefulness of these techniques to cases in which the antigen to be detected does not bind directly to nitrocellulose.

Immunization with Leishmania receptor for macrophages protects mice against cutaneous leishmaniasis

The Leishmania major receptor for macrophages is a lipid-containing glycoconjugate that is recognized by the monoclonal antibody WIC-79.3. When L. major promastigotes were incubated with Fab fragments of WIC-79.3 prior to injection into genetically susceptible mice, their infectivity was decreased. Fab fragments from an irrelevant control antibody of the same class had no effect. The L. major glycolipid was purified from detergent-solubilized promastigotes by affinity chromatography on immobilized WIC-79.3 and used to vaccinate mice that are genetically resistant or susceptible to disease. Genetically resistant mice could be protected totally from cutaneous disease with as little as 5 micrograms of glycolipid. A high but not absolute level of resistance was also induced in the susceptible mice, in which the disease is otherwise fatal. No protection was obtained with the carbohydrate fragment of the glycolipid alone or by injection of the glycolipid in the absence of adjuvant. Genetically susceptible mice, immunized and protected from disease as a result of multiple injections of live avirulent cloned promastigotes of L. major, produced antibodies to the glycolipid of L. major. No antibodies were detected in serum from chronically diseased mice. The data suggest that this functionally important antigen of L. major is a candidate vaccine against cutaneous leishmaniasis.

The Leishmania receptor for macrophages is a lipid-containing glycoconjugate

The glycoconjugate of Leishmania major recognized by the monoclonal antibody WIC-79.3 exists in two forms. The cellular form associated with the promastigote is a population of amphipathic molecules consistent with membrane insertion. In contrast, the extracellular form mainly consists of hydrophilic molecules, and probably arises by cleavage of the cellular form by an endogenous phospholipase. The hydrophilic population of extracellular glycoconjugate molecules binds specifically to macrophages but not to T or B lymphoid cells. Binding of the glycoconjugate and also intact promastigotes to macrophages in vitro is specifically inhibited by Fab fragments of WIC-79.3. These data indicate that the L. major glycoconjugate is the parasite receptor for macrophages, and hence the molecule directly involved in the initiation of infection.

Phenotypic diversity of cloned lines of Leishmania major promastigotes

In vitro cultured promastigotes of virulent (V) and avirulent (A) cloned lines of Leishmania major, and the parental isolate LRC-L137, were examined with respect to morphology, cell size, growth rate, and apparent DNA content. Growth rates of all lines were comparable and both virulent (V121, LRC-L137) and avirulent parasites (A12, A52, A59) exhibited a progressive decrease in apparent DNA content with time in culture, as measured by incorporation of Hoechst Dye 33342. The four cloned lines and the parental isolate showed differences in the content of morphological variants and in the mean body length. Morphologically, there were similarities between A12 and A52 and between A59 and V121. Promastigote populations were also examined for the expression of the target antigen of a previously characterized monoclonal antibody, WIC-79.3. This antibody binds to a membrane antigen that is also present in culture supernatants of Leishmania of A1 serotype. Three different assays with culture supernatants all showed that V121, A59, and A12 were high producers with LRC-L137 and A52, low producers. Similar variation in expression of the 79.3 target antigen was detected in intact organisms of the various lines by immunofluorescence with flow cytometry. No simple correlation was found between the expression or release of the WIC-79.3 target antigen and virulence. The virulence or avirulence of all cloned lines for BALB/c mice remained stable. The data are discussed in terms of differentiation stages of L. major promastigotes and the continuing search for morphological and biochemical markers of virulence.

Leishmania tropica: protective response in C3H mice vaccinated with excreted factor crosslinked with the synthetic adjuvant, muramyl dipeptide

Excreted factor, an immunosuppressive, acidic polysaccharide released by promastigotes of Leishmania tropica major in culture, was chemically crosslinked to the synthetic adjuvant muramyl dipeptide via the bifunctional imidoester dimethyladipimidate and poly-L-lysine. This conjugate, an uncrosslinked mixture of the components, or each of the components alone were injected one to three times into different groups of 8- to 12-week-old C3H mice. The mice were challenged 2 weeks after the last injection with 2 X 10(6) promastigotes of L. t. major in the base of the tail. For the next 5 weeks, the animals were monitored for number of parasites and size of the lesion which developed at the site of the challenge. Mice receiving one intraperitoneal injection of the conjugate were partially protected against challenge. Treated animals had higher initial parasite numbers but showed a more rapid clearing of the parasites. Furthermore, the treated animals developed smaller lesions that healed quicker than did those of the control groups. Multiple injections, or injection into a footpad, rather than intraperitoneally, reduced the ability to elicit a protective response. On the other hand, muramyl dipeptide injected into a footpad was partially protective. Antibody production to excreted factor, which was measured by indirect hemagglutination of sensitized erythrocytes, was detected after challenge in mice which had received conjugate or conjugate components. A delayed hypersensitivity reaction (measured by skin testing) was not detected in any of the groups prior to challenge.

An amphipathic sulphated glycoconjugate of Leishmania: characterization with monoclonal antibodies

A major glycoconjugate of Leishmania tropica major identified by two monoclonal antibodies was shown to be an externally oriented, amphipathic membrane antigen shed into the culture medium in which the parasites grow. This molecule could be labelled metabolically with [3H]glucose, [3H]galactose, [32P]phosphate and [35S]sulphate. It migrated as a polydisperse band upon electrophoresis in SDS-polyacrylamide gels, spanning the region of the gel corresponding to an apparent mol. wt. of 20 000-67 000 daltons. An apparently identical family of molecules could be labelled on the surface of living promastigotes using galactose oxidase and [3H]-sodium borohydride. This molecule was shown to be released into the supernatant over a period of several hours. Detection of the 3H- or 35S-labelled molecule required several days exposure of autoradiographs, but a novel blotting technique using nitrocellulose coated with monoclonal antibody allowed rapid detection of the molecule in charge shift electrophoresis, Western blotting and dot blotting. The electrophoretic mobility of the glycoconjugate in agarose relative to its mobility in Triton X-100 was increased in the presence of deoxycholate, and decreased in the presence of cetyl trimethyl-ammonium bromide, indicating amphipathic properties consistent with insertion into the lipid bilayer of the membrane. Using the dot-blotting technique the glycoconjugate was detected in all virulent and avirulent clones of LRC-L137 and in two additional isolates of L. tropica major (LRC-L287 and LRC-L251), but not in L. donovani or L. mexicana, consistent with the previously described specificity of the antibodies. However, the general approaches used in this paper showed that L. donovani (LRC-L52) and L. mexicana (LRC-L94) synthesize a similar, but antigenically distinct glycoconjugate.