DNA plasmid coding for Phlebotomus sergenti salivary protein PsSP9, a member of the SP15 family of proteins, protects against Leishmania tropica

BACKGROUND

The vector-borne disease leishmaniasis is transmitted to humans by infected female sand flies, which transmits Leishmania parasites together with saliva during blood feeding. In Iran, cutaneous leishmaniasis (CL) is caused by Leishmania (L.) major and L. tropica, and their main vectors are Phlebotomus (Ph.) papatasi and Ph. sergenti, respectively. Previous studies have demonstrated that mice immunized with the salivary gland homogenate (SGH) of Ph. papatasi or subjected to bites from uninfected sand flies are protected against L. major infection.

METHODS AND RESULTS

In this work we tested the immune response in BALB/c mice to 14 different plasmids coding for the most abundant salivary proteins of Ph. sergenti. The plasmid coding for the salivary protein PsSP9 induced a DTH response in the presence of a significant increase of IFN-γ expression in draining lymph nodes (dLN) as compared to control plasmid and no detectable PsSP9 antibody response. Animals immunized with whole Ph. sergenti SGH developed only a saliva-specific antibody response and no DTH response. Mice immunized with whole Ph. sergenti saliva and challenged intradermally with L. tropica plus Ph. sergenti SGH in their ears, exhibited no protective effect. In contrast, PsSP9-immunized mice showed protection against L. tropica infection resulting in a reduction in nodule size, disease burden and parasite burden compared to controls. Two months post infection, protection was associated with a significant increase in the ratio of IFN-γ to IL-5 expression in the dLN compared to controls.

CONCLUSION

This study demonstrates that while immunity to the whole Ph. sergenti saliva does not induce a protective response against cutaneous leishmaniasis in BALB/c mice, PsSP9, a member of the PpSP15 family of Ph. sergenti salivary proteins, provides protection against L. tropica infection. These results suggest that this family of proteins in Ph. sergenti, Ph. duboscqi and Ph. papatasi may have similar immunogenic and protective properties against different Leishmania species. Indeed, this anti-saliva immunity may act as an adjuvant to accelerate the cell-mediated immune response to co-administered Leishmania antigens, or even cause the activation of infected macrophages to remove parasites more efficiently. These findings highlight the idea of applying arthropod saliva components in vaccination approaches for diseases caused by vector-borne pathogens.

Vaccination with whole-cell killed or recombinant leishmanial protein and toll-like receptor agonists against Leishmania tropica in BALB/c mice

One strategy to control leishmaniasis is vaccination with potent antigens alongside suitable adjuvants. The use of toll-like receptor (TLR) agonists as adjuvants is a promising approach in Leishmania vaccine research. Leishmania (L.) tropica is among the less-investigated Leishmania species and a causative agent of cutaneous and sometimes visceral leishmaniasis with no approved vaccine against it. In the present study, we assessed the adjuvant effects of a TLR4 agonist, monophosphoryl lipid A (MPL) and a TLR7/8 agonist, R848 beside two different types of Leishmania vaccine candidates; namely, whole-cell soluble L. tropica antigen (SLA) and recombinant L. tropica stress-inducible protein-1 (LtSTI1). BALB/c mice were vaccinated three times by the antigens (SLA or LtSTI1) with MPL or R848 and then were challenged by L. tropica. Delayed-type hypersensitivity (DTH), parasite load, disease progression and cytokines (IL-10 and IFN-γ) responses were assessed. In general compared to SLA, application of LtSTI1 resulted in higher DTH, higher IFN-γ response and lower lymph node parasite load. Also compared to R848, MPL as an adjuvant resulted in higher DTH and lower lymph node parasite load. Although, no outstanding ability for SLA and R848 in evoking immune responses of BALB/c mice against L. tropica infection could be observed, our data suggest that LtSTI1 and MPL have a better potential to control L. tropica infection and could be pursued for the development of effective vaccination strategies.

Specific K39 antibody response and its persistence after treatment in patients with imported leishmaniasis

The sensitivity of a K39 ELISA (Leishmania IgG, Virion/Serion) for the detection of antibodies in patients with imported leishmaniasis was compared with an immunofluorescence assay (IFA), which was applied as “golden standard”. The retrospective study comprised 93 IFA-positive or borderline sera from 42 patients with visceral (n = 16) or cutaneous (n = 26) leishmaniasis. Patients had acquired infection predominately in the Mediterranean area or the Middle East. The Leishmania species (Leishmania donovani/infantum, Leishmania tropica, Leishmania major) were identified by real-time PCR. The majority (94 %) of first samples from patients with visceral leishmaniasis (VL) tested positive by K39 ELISA. Antibody levels ranged from low to very high (33.19–1990.00 U/ml; median 596.66 U/ml) but did not correlate with the respective IFA titers. High K39 ELISA values correlated with acute infection in immunocompetent individuals. K39 antibodies declined in all individuals after clinically successful therapy, but time to seronegativity varied considerably (51 weeks to >6 years). In patients with cutaneous leishmaniasis (CL), the sensitivity of the K39 ELISA was low (23 %) compared to IFA (92 % positive). Antibody levels ranged from low to medium (10.85–524.77 U/ml; median 19.77 U/ml). The highest antibody concentrations were seen in L. infantum-infected individuals. Summarizing, a high K39 ELISA value indicates active VL. The assay is, like IFA, not a measure for effective therapy but may support post-treatment monitoring. Low level positivity can indicate subclinical, previous or clinically cured VL or even CL. The K39 ELISA can supplement highly sensitive screening tests in the diagnosis and follow-up of imported leishmaniasis.

The mechanism behind the antileishmanial effect of zinc sulphate. I. An in-vitro study

In an attempt to determine the possible mechanism(s) behind the antileishmanial activity of zinc sulphate, promastigotes, axenic amastigotes and intracellular amastigotes of both Leishmania major and L. tropica were incubated with different concentrations of the compound. For each of the two Leishmania species, all three forms were found to be inhibited by the zinc sulphate, in a dose-dependent manner, the promastigotes being the most resistant form, followed by the axenic amastigotes. These results indicate that zinc sulphate has a direct antileishmanial effect. Compared with macrophages from starch-treated mice, the macrophages recovered from mice that had been injected intraperitoneally with zinc sulphate (daily for the 4 days prior to the macrophage collection) or BCG (once, 4 days before the cell collection) showed increased phagocytosis and increased killing of L. major and L. tropica. As the effects of the zinc sulphate were not statistically different from those of the known immunomodulating agent BCG, zinc sulphate appears to have an immunomodulating effect, in addition to its direct antileishmanial effect.

Serodiagnosis of anthroponotic cutaneous leishmaniasis (ACL) caused by Leishmania tropica in Sanliurfa Province, Turkey, where ACL Is highly endemic

In this study, we aimed to evaluate the validity of the conventional enzyme-linked immunosorbent assay (ELISA) and the Western blotting test for the diagnosis of anthroponotic cutaneous leishmaniasis (ACL) using serum samples obtained from 51 patients with parasitologically proven nontreated CL (NonT-CL patients) and 62 patients under treatment for CL (UT-CL patients). Additionally, 29 serum samples obtained from patients with parasitologically and serologically proven visceral leishmaniasis (VL) were also used as positive controls, and serum samples from 43 blood donors were used as negative controls. All sera were diluted to the same dilution (1/100). Leishmania infantum MON-1 was used as the antigen in the conventional ELISA. The sera of 27 (93.1%) of 29 VL patients were seropositive by ELISA, while the sera of 40 (78.4%) of 51 NonT-CL patients and 43 (69.3%) of 62 UT-CL patients were seropositive by the conventional ELISA. The absorbance values of the CL patients' sera were significantly lower than the absorbance values of the VL patients' sera. Bands between 15 and 118 kDa were detected in two groups of CL patients. Among all bands, the 63-kDa band was found to be more sensitive (88.5%). When we evaluated the Western blotting results for the presence of at least one of the diagnostic antigenic bands, the sensitivity was calculated to be 99.1%. By using serological tests, a measurable antibody response was detected in most of the CL patients in Sanliurfa, Turkey. It is also noted that this response can be changed according to the sizes, types, and numbers of lesions that the patient has. The Western blot test was found to be more sensitive and valid than the conventional ELISA for the serodiagnosis of ACL. In some instances, when it is very difficult to demonstrate the presence of parasites in the smears, immunodiagnosis can be a valuable alternative for the diagnosis of ACL.

Leishmania tropica infection, in comparison to Leishmania major, induces lower delayed type hypersensitivity in BALB/c mice

Leishmania tropica and L. major are etiologic agents of human cutaneous leishmaniasis. Delayed type hypersensitivity (DTH) is an immunologic response that has been frequently used as a correlate for protection against or sensitization to leishmania antigen. In BALB/c mice, L. tropica infection results in non-ulcerating disease, whereas L. major infection results in destructive lesions. In order to clarify the immunologic mechanisms of these 2 different outcomes, we compared the ability of these 2 leishmania species in induction of DTH response in this murine model. BALB/c mice were infected with L. major or L. tropica, and disease evolution and DTH responses were determined. The results show that the primary L. major infection can exacerbate the secondary L. major infection and is associated with DTH response. Higher doses of the primary L. major infection result in more disease exacerbation of the secondary L. major infection as well as higher DTH response. L. tropica infection induces lower DTH responses than L. major. We have previously reported that the primary L. tropica infection induces partial protection against the secondary L. major infection in BALB/c mice. Induction of lower DTH response by L. tropica suggests that the protection induced against L. major by prior L. tropica infection may be due to suppression of DTH response.

Cutaneous leishmaniasis caused by Leishmania tropica in Bikaner, India: parasite identification and characterization using molecular and immunologic tools

Identification of new foci of cutaneous leishmaniasis (CL), along with reports of Leishmania donovani causing the disease, is an issue of concern. Clinico-epidemiologic analysis of 98 cases in the endemic regions of Rajasthan state, India, suggested the preponderance of infection in men (62.24%) compared with women (37.75%). Species characterization by internal transcribed spacer 1 (ITS1) polymerase chain reaction (PCR)-restriction fragment length polymorphism (RFLP), kDNA-PCR, and immunofluorescence assay established L. tropica as the causative organism. When applied directly to 32 clinical samples, kDNA PCR had a sensitivity of 96.6%, whereas ITS1 PCR had a sensitivity of 82.75%, thus facilitating diagnosis and species identification. Either parasite culture or direct microscopy alone detected 48.2% and 65.5% of the positive samples, respectively, whereas culture and microscopy together improved overall sensitivity to 89.3% (25/28). Except for the kDNA PCR, all other assays were 100% specific. This study provides the first comprehensive molecular and immunologic studies of CL in India.

Leishmania major: Species specific delayed hypersensitivity reaction induced by exogenous secreted antigen in the guinea pig

The cellular response to Leishmania major (L. major) is usually evaluated in vivo by the delayed-type-hypersensitivity (DTH) test using leishmanin. Leishmanin can give false-positive reactions in areas where there is a background of leishmaniasis. In a previous study, it was shown that a 56 kDa antigen purified from promastigote and culture supernatant of L. major induce strong DTH reactions in sensitized guinea pigs. In this study, the species-specificity of this antigen was further investigated. Three groups of guinea pigs were sensitized with L. major, L. tropica, and L. infantum and both flanks of sensitized animal were injected intradermally with purified 56 kDa antigen or soluble leishmania antigen (SLA). The extent of indurations were measured after 24, 48, and 72 h. In animals which were sensitized with three species of leishmania, only those immunized with L. major showed skin reactions to purified antigen by an increase in skin thickness. Since complex antigen mixtures such as SLA and leishmanin show cross-reactivity and can be non-specific, the result obtained here suggest that 56 kDa antigen may be a useful diagnostic tool for species specific diagnosis in field studies of leishmaniasis.

[Cellular immune response of patients with anthroponotic cutaneous leishmaniasis in Sanliurfa]

Patients with cutaneous leishmaniasis (CL) have strong delayed-type hypersensitivity and in vitro proliferative responses to leishmanial antigens during active and cured diseases. To define the T cell response in patients with antroponotic CL infected with L. tropica is important to clarify the immunopathologic nature of the disease. T cell responses of acute and of already healed CL patients were defined using IFN-gamma, IL-5, IL-4, IL-10 cytokine measurement assays. In this study, while Th2 cell response was found to be dominant in active CL cases, Th1 cell response was more distinctive in the group of already healed CL cases. Differentiation of cellular response in the different stages of infection might be helpful in understanding the prognosis of leishmaniasis.

The effect of amphotericin b derivatives on Leishmania and immune functions

The effects of a water-soluble amphotericin B (AmB)-arabinogalactan (AG) conjugate on several immune functions were investigated. The experiments measured the effects of AmB-AG on (1) release of tumor necrosis factor-alpha (TNF-alpha), nitric oxide (NO), and interferon-gamma (IFN-gamma) from phagocytic cells and (2) cell-mediated immune responses. AmB-AG increased TNF-alpha release from mouse peritoneal macrophages and human monocytes but had no effect on IFN-gamma and NO release. A commercial preparation of nonconjugated AmB (Fungizone) also increased TNF-alpha production, but to a lesser extent than AmB-AG. AG alone had no effect on TNF-alpha production, proving that AmB caused the increased TNF-alpha production. AmB-AG and Fungizone were also tested for their effect on B- and T-cell proliferation. Neither compound altered T-lymphocyte responses to concanavalin A, but both inhibited the stimulation of B lymphocytes by lipopolysaccharides. However, Fungizone showed a stronger inhibitory effect on B cells. Allocytotoxicity was also inhibited by AmB-AG and more strongly by Fungizone. The increased production of TNF-alpha by cells treated with AmB-AG and the lower inhibitory effect of AmB-AG on lymphocyte stimulation and allocytotoxicity, as compared with Fungizone, explain the better therapeutic efficacy of the AmB-polysaccharide conjugate. AmB is active because of its preferential binding to ergosterol rather than cholesterol, the former sterol preferentially present in parasite surface membranes. This is also valid for the axenic amastigotes, which were sensitive to the AmB-AG. Overall, our results suggest that the antileishmanial activity of AmB-AG is mediated both directly and via modulation of immune functions.

Leishmania priming of human dendritic cells for CD40 ligand-induced interleukin-12p70 secretion is strain and species dependent

A major question in the study of leishmaniasis is what dictates clinical disease expression produced by different Leishmania species, i.e., cutaneous versus systemic and healing versus nonhealing. Animal models using a Leishmania species associated with self-limiting cutaneous disease (L. major) have revealed that protective immunity requires CD40/CD40 ligand (CD40L)-dependent, interleukin-12 (IL-12)-driven Th1 responses. We recently showed that L. major can prime human dendritic cells (DCs) for CD40L-triggered IL-12p70 secretion and that these cells can drive a Th1 response in autologous T cells from sensitized individuals. Here we show that in contrast to L. major, Leishmania species responsible for visceral disease (L. donovani), as well as species associated with persistent, cutaneous lesions and occasional systemic disease (L. tropica), did not induce CD40L-dependent IL-12p70 production, despite comparable levels of uptake by DCs. Up-regulated surface expression of CD40 did not correlate with IL-12p70 production, and appreciable CD40L-induced IL-12p40 secretion was observed in uninfected as well as infected DCs, regardless of species. Reverse transcription-PCR analysis confirmed that the production of heterodimeric IL-12 was limited by expression of IL-12p35 mRNA, which was dependent on both a microbial priming signal and CD40 engagement for its high-level induction. The intrinsic differences in the ability of Leishmania species to prime DCs for CD40L-dependent IL-12p70 secretion may account, at least in part, for the evolution of healing and nonhealing forms of leishmanial disease.

Identification and characterization of T cell-stimulating antigens from Leishmania by CD4 T cell expression cloning

Persistent immunity against Leishmania: infections in humans is mediated predominantly by CD4(+) T cells of the Th1 phenotype. Herein we report the expression cloning of eight Leishmania: Ags using parasite-specific T cell lines derived from an immune donor. The Ags identified by this technique include the flagellar proteins alpha- and beta-tubulin, histone H2b, ribosomal protein S4, malate dehydrogenase, and elongation factor 2, as well as two novel parasite proteins. None of these proteins have been previously reported as T cell-stimulating Ags from Leishmania: beta-tubulin-specific T cell clones generated against Leishmania: major amastigotes responded to Leishmania:-infected macrophages and dendritic cells. IFN-gamma enzyme-linked immunospot analysis demonstrated the presence of T cells specific for several of these Ags in PBMC from self-healing cutaneous leishmaniasis patients infected with either Leishmania: tropica or L. major. The responses elicited by Leishmania: histone H2b were particularly striking in terms of frequency of histone-specific T cells in PBMC (1 T cell of 6000 PBMC) as well as the percentage of responding donors (86%, 6 of 7). Ags identified by T cells from immune donors might constitute potential vaccine candidates for leishmaniasis.

Comparison of adjuvants with Leishmania antigens in a guinea pig model to induce delayed-type hypersensitivity responses

BACKGROUND AND PURPOSE

Guinea pigs have been a traditional model for studies of delayed-type hypersensitivity. They are the natural host of Leishmania enriettii and have been experimentally infected with other species of Leishmania. They have been used as a skin-test model to screen potential antigens for use in diagnostic tests for Leishmania. Use of complete Freund's adjuvant (CFA), along with whole promastigote Leishmania antigen, was necessary to sensitize guinea pigs to invoke a sufficient cell-mediated immune response. However, use of CFA has come under scrutiny by Animal Care and Use Committees due to the pathologic changes associated with its use.

METHODS

Thirty-two specific-pathogen-free male Hartley guinea pigs were inoculated with Leishmania antigens alone or mixed with one of three adjuvants (CFA, TiterMax, and liposomes), and were skin tested 2 weeks later.

RESULTS

For the Leishmania antigens tested, guinea pigs that received liposomes as an adjuvant had skin-test responses comparable to those of guinea pigs that received CFA. TiterMax was also tested, but cellular responses at antigen test sites were poor.

CONCLUSIONS

Liposomes can be used in this model as a safe, effective adjuvant.

Cytologic features of "dry-type" cutaneous leishmaniasis

Exfoliative cytology smears from the lesions of 179 patients with cutaneous leishmaniasis due to Leishmania tropica were studied with specific reference to cellular reactions and their effect on the parasite. Aggregates of the parasite (so-called Leishmania Donovan bodies) were present within macrophages and in some fibroblasts. The nature of the inflammatory reaction to the disease was studied by performing differential counts of the inflammatory cells present in the smears. These were correlated with the number of Leishman Donovan bodies. There was an inverse relationship between the number of Leishman Donovan bodies and the percentage of small lymphocytes, neutrophils, and type I macrophages. It is postulated that aggregates of activated macrophages (designated types II and III) and the Leishmanian milieu (sticky matrix) protect the amastigote Leishmania parasites from being eradicated by the inflammatory and immune reaction. The cytoplasmic blebbing of the parasitophorous vacuoles and cell to cell connection of the activated histiocytes could be shown by the CD-68 immunostaining of the tissue biopsy.

Leishmania tropica: the identification and purification of metacyclic promastigotes and use in establishing mouse and hamster models of cutaneous and visceral disease

Few experimental studies on Leishmania tropica have been undertaken despite the importance of this parasite as the cause of cutaneous leishmaniasis, and now visceral disease, in the Old World. In part, this is due to the absence of convenient animals models, especially mice, for L. tropica infections. An anti-lipophosphoglycan (LPG) monoclonal antibody XCIV 1H2-A8 (T11), specific for L. tropica, was found to distinguish between culture-derived procyclic and metacyclic promastigotes. The antibody was used to negatively select for nonagglutinated metacyclic forms in stationary cultures, and the exceptional virulence of the purified metacyclics was verified by their infectivity for mouse macrophages in vitro and by their ability to produce cutaneous lesions in footpads of BALB/c mice. The lesions produced by three cutaneous isolates of L. tropica were nonulcerative and nonprogressive. Nonetheless, the lesions failed to heal, and high numbers of parasites could be recovered from footpads and draining lymph nodes up to 9 months after infection. Infections using L. tropica metacyclics purified from cutaneous, visceral and viscerotropic (Desert Storm) isolates of L. tropica were compared in both mouse and hamster models. Differences in disease progression were found that may reflect the parasite tissue tropism and virulence displayed by these strains in their human hosts. These findings suggest a role for parasite-related determinants in the clinical spectrum of disease.

Characterization of a Leishmania tropica antigen that detects immune responses in Desert Storm viscerotropic leishmaniasis patients

A chronic debilitating parasitic infection, viscerotropic leishmaniasis (VTL), has been described in Operation Desert Storm veterans. Diagnosis of this disease, caused by Leishmania tropica, has been difficult due to low or absent specific immune responses in traditional assays. We report the cloning and characterization of two genomic fragments encoding portions of a single 210-kDa L. tropica protein useful for the diagnosis of VTL in U.S. military personnel. The recombinant proteins encoded by these fragments, recombinant (r) Lt-1 and rLt-2, contain a 33-amino acid repeat that reacts with sera from Desert Storm VTL patients and with sera from L. tropica-infected patients with cutaneous leishmaniasis. Antibody reactivities to rLt-1 indicated a bias toward IgG2 in VTL patient sera. Peripheral blood mononuclear cells from VTL patients produced interferon gamma, but not interleukin 4 or 10, in response to rLt-1. No cytokine production was observed in response to parasite lysate. The results indicate that specific leishmanial antigens may be used to detect immune responses in VTL patients with chronic infections.

Mucosal leishmaniasis caused by Leishmania tropica in Saudi Arabia

Mucocutaneous leishmaniasis (MCL.) which is called Espundia, and Uta is confined to South and Central America. In this form of leishmaniasis, the reticulo-endothelial system of the mucous membrane of the mouth, nose and throat is parasitized. It causes chronic ulceration of the mucous membranes with destruction of the bone and cartilage of the nose and mouth. In this study, two cases of mucosal leishmaniasis were recorded in two boys. In one patient, a primary lesion was identified on the patient's neck. In the second patient, no lesion or scar of old lesion or even history of leishmaniasis was reported. The causative agent was typed biochemically and proved to be Leishmania tropica.

Helper T cells without CD4: control of leishmaniasis in CD4-deficient mice

Expression of either the CD4 or CD8 glycoproteins discriminates two functionally distinct lineages of T lymphocytes. A null mutation in the gene encoding CD4 impairs the development of the helper cell lineage that is normally defined by CD4 expression. Infection of CD4-null mice with Leishmania has revealed a population of functional helper T cells that develops despite the absence of CD4. These CD8- alpha beta T cell receptor+ T cells are major histocompatibility complex class II-restricted and produce interferon-gamma when challenged with parasite antigens. These results indicate that T lymphocyte lineage commitment and peripheral function need not depend on the function of CD4.

Gamma interferon response in secondary Leishmania major infection: role of CD8+ T cells

CD8+ T cells have been shown to contribute to the rapid resolution of secondary lesions developing in immune mice challenged with Leishmania major. In the present study, we assessed directly the participation of specific CD8+ T cells in the memory response induced in immune mice by reinfection. Lymphocyte populations from reinfected immune mice exhibit marked secondary gamma interferon (IFN-gamma) responses. The participation of IFN-gamma-producing CD8+ T cells in the memory response elicited by secondary infectious challenge was demonstrated in both genetically resistant immune CBA mice and genetically susceptible immune BALB/c mice that were rendered resistant by administration of anti-CD4 monoclonal antibody in the early phase of the primary infection. The protective function of CD8+ T cells in experimental murine cutaneous leishmaniasis might thus be explained in part by their ability to secrete IFN-gamma. In this context, the neutralization of IFN-gamma at the time of reinfection reduced the Leishmania-specific delayed-type hypersensitivity response, showing that this cytokine is involved in the recall of immunological memory to L. major in vivo.

Interleukin-7 enhances antimicrobial activity against Leishmania major in murine macrophages

Recently, it has been shown that interleukin-7 (IL-7) is able to induce secretion of cytokines and tumoricidal activity by human monocytes. This study shows that treatment of murine macrophages infected with Leishmania major with IL-7 without any other stimulus reduced the percentage of infected cells, as well as the parasite burden per cell, in a dose-dependent manner to a limited degree (45% reduction of the number of amastigotes per 100 macrophages). Simultaneous treatment of macrophages with gamma interferon and IL-7 led to nearly complete (> 99%) elimination of amastigotes. Addition of anti-tumor necrosis factor alpha or N omega-monomethyl-L-arginine acetate reversed the leishmanicidal effects of IL-7, and production of nitric oxide was induced in the presence of IL-7.

Targeted activation of CD8 cells and infection of beta 2-microglobulin-deficient mice fail to confirm a primary protective role for CD8 cells in experimental leishmaniasis

CD8+ T cells play an important role in the immunologic control of intracellular pathogens, particularly viruses. Leishmania are obligate intracellular parasites of macrophages in the mammalian host, and previous studies using deletion of CD8+ cells by administration of mAb to infected animals have suggested a protective role for these cells. Two complementary approaches were used to define more carefully the role of CD8+ cells in leishmaniasis. In BALB/c mice susceptible to Leishmania major (L. major) infection, targeted activation of CD8+ T cells was attempted by immunization with nonapeptides derived from the conserved major outer surface protein of the organism, gp63, that contained the consensus binding motif for MHC class I H-2Kd molecules. Two of the nonapeptides induced CTL activity in subsequently infected BALB/c mice that could be elicited against P815 cells pulsed either with peptide or lysates of L. major. Purified CD8+ T cells from immunized mice had elevated levels of IFN-gamma mRNA transcripts as compared to unimmunized mice. Despite evidence for activation of CD8+ cells, none of the mice immunized with nine different peptides alone or in combination were protected from progressive disease. In a second series of experiments, beta 2-microglobulin deficient mice that lack CD8+ cells were infected with L. major and the course of infection monitored. These mice cured disease as rapidly as beta 2-m +/- and +/+ littermates, and cure was associated with comparable levels of IFN-gamma mRNA in the draining lymph node population. Neither of these approaches was able to confirm a substantive role for CD8+ T cells in the primary protective response to L. major.

Interleukin-4 but not gamma interferon production correlates with the severity of murine cutaneous leishmaniasis

For murine cutaneous leishmaniasis, data to date suggest a correlation between the presence of gamma interferon (IFN-gamma) and resistance in C57BL/6 mice and the presence of interleukin-4 (IL-4) and disease in BALB/c mice. In this study, 13 inbred strains of mice covering the range of susceptibility to disease were infected with Leishmania major to determine whether the subsequent expression of IFN-gamma or IL-4 is a reliable indicator of cure or progressive disease. The presence of IL-4 and IFN-gamma mRNAs in the draining lymph nodes was examined 9 weeks after infection, when differences in disease severity became obvious. There were large differences in the levels of IL-4 mRNA among the different strains, whereas IFN-gamma mRNA was detected at similar levels in all strains. The levels of IL-4 mRNA correlated with lesion score, with susceptible and intermediate strains containing up to 100-fold more than any of the resistant strains. Differences in the levels of IFN-gamma mRNA were within only a fourfold range, with significant overlap among susceptible, intermediate, and resistant strains. Similarly, the levels of IFN-gamma secreted in vitro by lymph node cells from infected mice in response to L. major antigens were within a 10-fold range for most strains, and there was no correlation with lesion score. Analysis of Leishmania-specific antibody levels revealed a correlation between immunoglobulin G1 (IgG1) titers and lesion score, consistent with the role of IL-4 as a switch factor for IgG1. In contrast, there was no correlation between IgG2a titers and lesion score, supporting the notion that IFN-gamma synthesis (which promotes IgG2a production) is not correlated with disease state. These data suggest that along the spectrum of murine cutaneous leishmaniasis, IL-4 is a reliable indicator of disease, but IFN-gamma is not prognostic for resistance.

Natural killer cells are a source of interferon gamma that drives differentiation of CD4+ T cell subsets and induces early resistance to Leishmania major in mice

Infection of mice with the protozoan Leishmania major provides an excellent model to define the factors involved in T helper (Th) subset development, since Th1 cells confer protection in resistant strains of mice, whereas Th2 cells are associated with the fatal outcome of susceptible mice. We previously found that interferon gamma (IFN-gamma) was required for Th1 cell development after infection of mice with L. major. In this report, we evaluate the contribution of natural killer (NK) cells to IFN-gamma levels early in L. major infection. NK cell activity was higher in resistant C3H/HeN mice than in susceptible BALB/c mice during the first week of infection, and removal of NK cells significantly decreased IFN-gamma levels and promoted interleukin 4 (IL-4) production in both the draining lymph nodes and spleen. IFN-gamma production by NK cells required the presence of CD4+ T cells or IL-2, but not CD8+ T cells. Enhanced disease, as measured by parasite numbers and lesion development, was observed in NK cell-depleted mice. Furthermore, a comparison of the NK cell response and the subsequent parasite burden in several inbred strains of mice demonstrated that NK cells mediate early resistance to L. major. Together, these data indicate that the stimulation of NK cells, through the production of IFN-gamma, plays an important role in initiating Th1 cell differentiation in leishmaniasis and in controlling early resistance to L. major.

Leishmanin and tuberculin sensitivity in leishmaniasis in the Sudan, with special reference to kala-azar

The application of leishmanin and tuberculin skin tests was studied in patients with leishmaniasis in the Sudan. 35 cases of active kala-azar and 3 relapse cases were leishmanin negative. 81% of patients treated for kala-azar showed a positive reaction after 6 months. 17 of 29 patients with post kala-azar dermal leishmaniasis (PKDL) were leishmanin positive. 2 of 16 patients with kala-azar tested with tuberculin were positive; one was diagnosed as tuberculosis. In 7 initially tuberculin negative patients, the tuberculin test became positive after treatment. A new Leishmania major skin test antigen (Pasteur Institute, Iran) was more reactive than other antigens in patients with cutaneous leishmaniasis, mucocutaneous leishmaniasis and PKDL, but not in treated kala-azar cases. In a field study in an area of endemic kala-azar, the new L. major antigen proved more reactive both in individuals previously exposed to L. major (causing cutaneous leishmaniasis) and in those with past exposure to L. donovani. The literature concerning skin testing with leishmanin and tuberculin in kala-azar is reviewed.

Langerhans cells transport Leishmania major from the infected skin to the draining lymph node for presentation to antigen-specific T cells

Murine epidermal Langerhans cells (LC) have been shown to internalize Leishmania major, a cause of human cutaneous leishmaniasis, and to stimulate a vigorous parasite-specific T cell response. The present study emphasizes the critical role of LC in leishmaniasis by documenting directly that LC have the ability to transport L. major from the skin to the draining lymph node (LN). This was revealed by irreversible labeling of LC with a fluorescent cell linker and in vivo tracking. In contrast, no migration to the LN was seen with L. major-infected macrophages. These findings were consistent with the results of mixed labeling immunohistology showing that early in infection the expression of parasite antigen in the LN draining the lesion was confined to dendritic cells and could not be detected in macrophages. Furthermore, dendritic cells in LN draining the site of cutaneous infection stimulated L. major-primed T cells in vitro and, most notably, were able to activate unprimed T cells capable of mediating parasite-specific delayed-type hypersensitivity reactivity in vivo. Taken together, the results indicate that LC capture L. major in the skin and transport it to the regional LN for initiation of the specific T cell immune response.

Pre-exposure of murine macrophages to lipopolysaccharide inhibits the induction of nitric oxide synthase and reduces leishmanicidal activity

Murine macrophages produce nitric oxide (NO) from L-arginine on stimulation with lipopolysaccharide (LPS), alone or with interferon-gamma (IFN-gamma). The effect of incubation of macrophages with low concentrations of LPS on NO synthesis on subsequent stimulation was investigated, using a murine macrophage cell line, J774, and peritoneal macrophages from CBA mice. Cells which had been incubated with LPS produced significantly lower amounts of NO, and expressed lower levels of NO synthase activity, following stimulation with IFN-gamma and LPS, or with a high concentration of LPS. This effect was not reversed by tumor necrosis factor-alpha. The ability of CBA macrophages to kill the intracellular parasite Leishmania major was markedly reduced by pre-incubation with LPS. Reduced NO production by macrophages previously exposed to LPS is a manifestation of endotoxin tolerance, and may represent an important means of regulation of NO synthesis and thus a survival mechanism for intracellular parasites.

Leishmania major-specific, CD4+, major histocompatibility complex class II-restricted T cells derived in vitro from lymphoid tissues of naive mice

Several studies indicate that the outcome of experimental murine cutaneous leishmaniasis caused by Leishmania major (Lm) is determined by immunological events occurring shortly after infection. These events lead to outgrowth of either protective CD4+ T cells in the C57BL/6 mouse, which cures, or exacerbative cells in the BALB/c mouse, which succumbs to disease. Potential factors influencing the outgrowth of protective or exacerbative T cells include antigen-presenting cells (APC), cytokines, and parasite antigens. An in vitro system, in which one could precisely control the factors shaping early events in the T cell response to Lm, would be very useful. To this end, we have examined the in vitro response of naive lymphocytes to Lm promastigotes. The data presented here show that Lm-specific CD4+ T cell receptor alpha/beta + T cells can be generated in vitro from spleen and lymph node cell populations of naive mice. Furthermore, they can be obtained from the CD44low (unprimed) population of T lymphocytes, indicating that in vitro priming occurs. The ability to generate these T cells is dependent on the presence of live parasites and is not due to a parasite-derived nonspecific T cell mitogen. Restimulation, as assayed by proliferation, requires APC bearing syngeneic I-A. Optimal restimulation of the in vitro derived T cells is achieved only when live promastigotes are used. The T cells do not proliferate in response to a frozen-and-thawed lysate of promastigotes, yet they exhibit mild reactivity to lysates prepared from heat-shocked promastigotes. Furthermore, they do not recognize two predominant antigens on the promastigote surface, lipophosphoglycan and gp63. T cells derived in vitro with Lm show crossreactivity with live L. donovani, less crossreactivity with live L. mexicana, and no crossreactivity with live Bacillus-Calmette-Guerin or live Brugia malayi microfilariae. Finally, these early T cells, whether derived from healing C57BL/6 or nonhealing BALB/c mice, produce interleukin 2 (IL-2), IL-4, and interferon gamma.

Leishmania antigens presented by GM-CSF-derived macrophages protect susceptible mice against challenge with Leishmania major

Leishmania major, a causative agent of leishmaniasis, in humans is also capable of infecting mice. Several strains of mice, including the BALB/c strain, are unable to mount appropriate T cell responses to the parasite and develop a fatal, disseminated infection. We present evidence that injection of granulocyte-macrophage-CSF derived bone marrow macrophages (GMM phi), previously incubated with L. major antigens, into BALB/c mice before infection, induced a Th1-dominated response and subsequent healing. Injection of BALB/c mice with GMM phi pulsed with irrelevant Ag, or other macrophages pulsed with L. major Ag, failed to protect against L. major challenge. Protection induced by L. major Ag-bearing GMM phi correlated with the induction of a Th1-like response with the production of high levels of IFN-gamma, delayed-type hypersensitivity reactivity and long-lived resistance to reinfection. GMM phi-T cell interaction, rather than parasite killing by GMM phi, appeared to be a crucial step and there was a strong correlation between ability to function as APC in vitro and induction of protective immunity in vivo. These data suggest that presentation of Ag by a population of L. major Ag-bearing GMM phi can activate Th1 cells in BALB/c mice, leading to a protective immune response to parasite invasion. This implies that the nature of the APC population which presents Ag may influence the response to that Ag in vivo.

Repeated induction of nitric oxide synthase and leishmanicidal activity in murine macrophages

Murine macrophages express high levels of nitric oxide (NO) synthase and produce large amounts of NO when stimulated with interferon-gamma plus lipopolysaccharide in vitro. The expression of NO synthase peaks at 12 h after stimulation and declines rapidly to the background level by 72 h. These macrophages can be repeatedly reactivated to express similar levels of NO synthase. The reactivation is not due to newly divided cells since peritoneal macrophages which do not divide in vitro and J774 cells cultured in the presence of colchicine can also be restimulated to express NO synthase. The reactivation is accompanied by re-expression of NO synthase mRNA, as assessed by polymerase chain reaction analysis. Furthermore, the reactivated macrophages are fully capable of killing the intracellular protozoan parasite Leishmania major.

IL-2 is necessary for the progression of leishmaniasis in susceptible murine hosts

BALB/c mice are highly susceptible to disseminated infection with the intracellular protozoa Leishmania major. Progression of disease requires in vivo expansion of Th2 CD4+ lymphocytes and is reversed by treatment with anti-IL-4 monoclonal antibody. Inasmuch as IL-2 may be necessary for both the production of IL-4 and differentiation of Th2 cells, the possible contribution of IL-2 to progressive infection was examined. Four weekly injections of anti-IL-2 mAb (S4B6) cured more than 80% of BALB/c mice infected with L. major, as determined by diminished footpad swelling and decreased numbers of parasites in infected tissues. Multiple doses of S4B6 were necessary for benefit; a single dose given at the time of infection was ineffective. The anti-IL-2R mAb PC61 demonstrated a similar protective effect when administered twice weekly for 4 wk. Anti-IL-2-mediated cure of cutaneous leishmaniasis was associated with increased IFN-gamma and decreased IL-4 production by regional lymph node cells compared to untreated BALB/c mice with progressive illness. Both CD4+ and CD8+ T lymphocytes contributed to the increased expression of IFN-gamma mRNA in cured mice. These data suggest that levels of IL-2 suboptimal for Th2 expansion in vivo do not inhibit Th1 CD4+ and CD8+ T cell activation and IFN-gamma synthesis. Other cytokines or activation pathways that are either IL-2-independent or synergistic with low levels of IL-2 may account for the appearance of curative T cell responses during treatment with anti-IL-2 antibodies.

Immunological analysis of the zinc-binding peptides of surface metalloproteinase (gp63) of Leishmania major

The surface metalloproteinase, gp63, is highly conserved and immunogenic. A peptide spanning the zinc-binding region of the molecule is immunogenic and can induce protective immunity in mice against Leishmania major infection. We report here that the minimum length of the immunogenic peptide in this region is a heptapeptide, VVTHEMA, corresponding to residues 161-167. Optimal immunogenicity is conferred by a decapeptide, LVTVVTHEMA, corresponding to residues 158 to 167, where H and E are consensus zinc-binding residues. These two residues determine the specificity of the peptide. The next two residues, M and A are necessary for the immunogenicity of the peptide. These results suggest that the zinc-binding residues are recognized by the T-cell receptor complex, while the two adjacent residues are involved in the peptide presentation by the major histocompatibility complex (MHC) molecule.

Development of in vitro parameters of cell-mediated immunity in the course of human cutaneous leishmaniasis infection

The goal of the present study was to determine whether a correlation between the clinical stage of cutaneous leishmaniasis lesions and in vitro parameters of cell-mediated immunity could be established. For this purpose, we measured lymphocyte proliferation, using a total lymphocyte proliferation (TLP) blood assay, and leishmanicidal effector activity using peripheral blood mononuclear cells (PBMC) in a three-day assay. The parameters of leishmanicidal activity measured included percent infected monocytes and number of amastigotes per 100 infected monocytes 24 and 72 hr after infection. Three groups of people were studied: a group of patients in the course of the disease, a group of immune individuals, and unexposed controls. The results of the study suggested that the ability of PBMC to kill parasites increased in patients as the lesions cured, and was highest in immune individuals. In contrast, the TLP response once positive, did not increase after cure. In approximately 30% of the patients who were retested on several occasions during the course of the disease, a positive response reversed to negative both in the TLP and the effector assays while the lesions were still active. In approximately 50% of these cases, the response eventually became positive again. The data presented show that effector activity and proliferation correlate with immunity, and suggest that marked heterogeneity characterizes the immune response in the course of active disease.

Leishmania major interferes with antigen presentation by infected macrophages

Impairment of the Ag-presenting capacity of macrophages harboring intracellular Leishmania might represent one of the several mechanisms by which these parasites can evade host-protective T cell responses. Thus, the present study was designed to investigate the ability of macrophages, parasitized with Leishmania major, to present Ag to relevant T cell hybridomas. Results show that bone marrow-derived macrophages from BALB/c mice, after infection with L. major, have a greatly reduced capacity to present OVA, beta-galactosidase, and L. major-derived Ag to specific T cell hybrids derived from mice immunized with those Ag. In contrast, after pulsing with relevant peptide, macrophages containing L. major have a normal Ag-presenting capacity. The inhibition of presentation of native Ag did not appear to result from decreased endocytosis or catabolism. Inasmuch as the inhibition of presentation could not be attributed to an impaired processing of the Ag or an unavailability of MHC class II molecules on the surface of infected cells, these results could indicate that the presence of L. major interferes with the intracellular loading of MHC class II molecules with antigenic peptides.

Parasitism of epidermal Langerhans cells in experimental cutaneous leishmaniasis with Leishmania major

Murine epidermal Langerhans cells (LC) have been demonstrated to stimulate a vigorous T cell response to Leishmania major, a cause of human cutaneous leishmaniasis. It was therefore of interest to analyze whether LC can take up viable parasites. Epidermal cells were obtained from mouse ear skin for incubation with L. major and subsequent detection of intracellular parasites by cytochemistry. Freshly isolated LC, but not cultured LC, phagocytosed L. major and the uptake was inhibited by antibodies to the complement receptor type 3. Electron microscopic studies revealed the presence of viable amastigotes within LC. Moreover, with double-labeling techniques, L. major-containing LC could also be detected in infected skin. The results demonstrate that LC can internalize L. major. Since the number of organisms per infected LC remained consistently low, the prime task of LC may not be the promotion of parasite spreading but the presentation of L. major antigen to T cells and, thus, the regulation of the cellular immunity during cutaneous leishmaniasis.

Interleukin-4 transgenic mice of resistant background are susceptible to Leishmania major infection

The outcome of cutaneous leishmaniasis is dependent on the balance of Th1 and Th2 cells. In the murine model, Th1 cells are host-protective whereas the Th2 cells are disease-promoting. However, the in vivo role of interleukin-4 (IL-4), a signature product of Th2 cells, is uncertain. We compared the course of Leishmania major infection in the genetically resistant 129/Sv mice and the mutant 129/Sv mice transgenic for the murine IL-4 gene under the control of the immunoglobulin heavy chain enhancer and promoter. We report here that in contrast to their wild-type parents, the IL-4 transgenic mice are susceptible to L. major infection. This is associated with the development of inexorably progressive lesions and parasite loads. Spleen cells from infected transgenic mice produced significantly higher levels of IL-4 but lower amounts of interferon-gamma when stimulated in vitro with leishmanial antigens compared to those from infected normal 129/Sv mice. Furthermore, sera from the infected transgenic mice contained higher levels of IL-4 and IgE than the sera of infected normal 129/Sv mice. These results, therefore, establish in a new animal model that IL-4 promotes disease development in murine cutaneous leishmaniasis.

Vaccine development against cutaneous leishmaniasis. Subcutaneous administration of radioattenuated parasites protects CBA mice against virulent Leishmania major challenge

Experiments described in this paper were aimed at determining whether subcutaneous inoculation of live, avirulent Leishmania major would protect mice against infection by the virulent parasite. To this effect, promastigotes or amastigotes of a highly virulent strain of L. major (MRHO/IR/76), used in human trials of leishmanization, and which induces non-healing skin lesions in both CBA and BALB/c mice, were rendered non-pathogenic by gamma irradiation. A dose of 150 krad was required to abrogate the virulence of the parasite as tested on BALB/c mice. Strikingly, however, not all leishmanias were completely inactivated by this procedure since live parasites were detected in the footpads and/or the inguinal lymph nodes as long as 28 days (CBA) or 18 weeks (BALB/c) after injection. Furthermore, 150 krad-irradiated promastigotes retained the capacity to transform into amastigotes intracellularly in vitro. Subcutaneous inoculation of this irradiated 'vaccine' conferred onto CBA mice a high degree of protection against challenge by both the homologous and a heterologous (MRHO/SU/59/P) strains of L. major. Lymph node cells from protected animals acquired the capacity to activate infected macrophages in vitro to kill intracellular L. major. To allow for maximum development of immunoprotection, the irradiated promastigotes had to remain viable, perhaps reflecting a requirement for transformation into amastigotes in the vaccinated host.

[The current aspects of seroepidemiological research in combined foci of leishmaniasis]

The authors analyze the results of C-ELISA, used in screening of the population in combined foci of zoonotic cutaneous leishmaniasis and visceral leishmaniasis in two types of landscapes in Turkmenistan. In the deltas, on the plains [correction of planes] and oases, where the incidence of zoonotic cutaneous leishmaniasis is very high, 1.6% of the examinees were found to have antibody to L. major. The antibodies in this condition are detectable only during the acute stage of the disease and persist for just a few months after convalescence. The share of the positive sera with antibody to L. donovani sensu lato was the minimal (0.48%) in the population of the alluvial plain [correction of plane] at the Kopet-Dag hills, the highest share (4%) of the population with such antibodies lived in the sandy deserts in the interfluvial areas of southern-eastern Turkmenistan. The authors have validated the criteria for the assessment of the endemicity level of leishmaniasis foci with due consideration for various incidence rates of visceral and zoonotic cutaneous leishmaniases and the specific features of the immune response in these nosologic forms. They suggest that a positive serologic response be considered as the basic criterion of a visceral leishmaniasis focus, and the disease incidence and the number of subjects who had had this disease in the focus--the basic criterion for the assessment of a zoonotic cutaneous leishmaniasis focus endemicity.

Role of T cell subsets during the recall of immunologic memory toLeishmania major

The contributions of different T cell subpopulations to the maintenance of immunity during secondary Leishmania major infections were analyzed in healed, resistant animals by depletion of T cell subsets in vivo. The strong delayed-type hypersensitivity mounted in immune genetically resistant mice upon challenge with viable promastigotes was mediated by both CD4+ and CD8+ T cells. Each T cell subpopulation alone contributes, although to a different extent, to the resolution of secondary lesions; both subsets, however, are required for an efficient and rapid healing of the secondary lesions and the decrease in the parasite burden in infected tissues. The results indicate that in immune, genetically resistant CBA mice, the activity of both T cell subsets is required for successful resistance to reinfection and an efficient maintenance of immunity.

Immunology of leishmaniasis

Resolution of leishmanial infections requires the expansion of specific type 1 T helper cells that secrete or express on their membrane lymphokines capable of activating macrophages that contain these parasites to a microbicidal state. Specific CD8+ T cells, which are triggered during infection, also appear to play a role in protective immunity, possibly through their ability to secrete interferon-gamma. In the mouse model of infection with Leishmania major, the expansion of specific type 2 T helper cells exacerbates disease, an effect that appears to result from the properties of type 2 T helper derived lymphokines to deactivate macrophages and inhibit release of activating cytokines by type 1 T helper cells. In the mouse, destruction of intracellular Leishmania by activated macrophages depends upon the L-arginine-dependent production of nitrogen oxides. Molecules from the parasite that can induce, and are the target of, the protective T-cell response are being characterized.

A strategy to improve the efficacy of vaccination against tuberculosis and leprosy

The pathogens responsible for leprosy, tuberculosis and the leishmaniases can induce different classes of immunity, but protection is provided only by a cell-mediated response. Here, Peter Bretscher proposes a strategy to achieve an immunological imprint that ensures a stable cell-mediated response upon natural infection.

Humoral antibody response in Leishmania tropica infection

A small epidemic of Leishmania tropica infection was detected in Rajasthan, India. Most cases were in the 21-25 years age group and were possibly related to outdoor activity. Nearly one third of the patients had more than five lesions, the maximum number of lesions being confined to the face, neck and extremities. As determined by ELISA, 90% cases had leishmania antibodies with an OD range of 0.8-1.1. The serum of 60% of patients was positive by CIEP against L. tropica promastigote soluble antigen. By immunofluorescence, 96% persons were positive when L. tropica promastigotes were used as the substrate. The prevalence of infection with L. tropica appears to be much higher than that reported earlier.

[Antibody detection in zoonotic cutaneous leishmaniasis by using the indirect immunofluorescence reaction and C-ELISA in different clinical manifestations of the disease]

189 sera from patients with ZCL of different stages were studied by means of RNIF and C-ELISA. A high significant correlation between RNIF and C-ELISA indices was shown, but the latter test was proved to be more sensitive and therefore more effective. In patients with ZCL, a significant direct correlation between the duration of the process and the antibody titer was established by means of C-ELISA. In patients with ZCL at the third (final) stage (reduction and granulation of lesions), the C-ELISA liter of specific antibodies was higher than at the second stage (rapidly progressing ulceration of lesions). The findings indicate the presence of clinical and serological parallels in ZCL and show it expedient to compare the dynamics of antibody genesis and cell immunity indices in further studies.

Cellular and humoral immune responses in a population from the Baringo District, Kenya to Leishmania promastigote lipophosphoglycan

In a cross-sectional house-to-house study in a leishmaniasis-endemic area in Kenya, the cellular and humoral immune response to Leishmania lipophosphoglycan (LPG) was determined. Clinical data, peripheral blood mononuclear cells, and plasma were obtained from 50 individuals over the age of eight years. Lymphoproliferation and interferon-gamma (IFN-gamma) production by these cells were examined. It was shown that cells from all six individuals in the population with a history of kala-azar responded to LPG in the lymphocyte proliferation assay, and four of these six responded in the IFN-gamma assay. In contrast, cells from 12 of 44 individuals from the study area with no history of kala-azar and none of the five Danish control samples responded to LPG. Antibodies against LPG were detected by enzyme-linked immunosorbent assay in 45 of 50 plasma samples. Our findings clearly show that mononuclear cells from kala-azar patients cured of infection were able to respond to the LPG preparation. The finding of a specific cellular immune response to LPG in 12 of 44 individuals with no history of kala-azar is consistent with previous epidemiologic studies, in which it has been shown that a proportion of L. donovani infections run a subclinical course. The high frequency of individuals with antibodies against LPG might indicate that a majority of the population had been exposed to the parasite.(ABSTRACT TRUNCATED AT 250 WORDS)

[The serological examination of the population for leishmaniasis and the detection of Leishmania in rodents in the Republic of Guinea]

A serological study on leishmaniasis in human population of Guinea revealed the percentage of seropositive persons varying in different parts of the country from 0.84 to 4.76 (according to C-ELISA) and from 1.0 to 5.1 (according to IFAT). The majority of sera positively reacting in C-ELISA with the antigen of Leishmania major in dilutions of 1:800 and higher were received from Kundara District (northwestern part of the country), and with the antigen of L. donovani sensu lato from Sigiri and Kankan districts (northeastern part of the country). All the districts were situated in the savanna zone. The amastigotes of Leishmania were found in the liver and spleen of Tatera gambiana caught near Kindia. These data suggest the circulation of Leishmania over the territory of Guinea.

Immunobiology of experimental leishmaniasis

Self-cure versus uncontrolled disease progression in experimental murine cutaneous leishmaniasis depends upon a delicate interplay among various activated cells of the host's immune system. Susceptibility or resistance to infection with Leishmania major is correlated with the ability of different inbred strains of mice to produce the characteristic spectra of lymphokines upon infection. Appropriate experimental interventions now allow the modulation of these responses, providing the possibility to render genetically susceptible mice resistant to infection and, vice versa, to cause genotypically "healer" strains to express a "non-healer" phenotype. These experimental manipulations have proven to be powerful tools in the dissection of the underlying immune mechanisms and cellular parameters responsible for susceptibility and resistance, and will perhaps allow the identification of molecules of parasite origin that induce deleterious immune responses to infection with Leishmania, and thus to exclude them from future vaccines. More importantly, rational immune intervention could permit the diversion of established host-damaging immune responses to host-protective immunization.

IL-4 induces a Th2 response in Leishmania major-infected mice

The infection of mice with Leishmania major can cause either a fatal disseminated disease or a localized healing disease, depending on the genetic background of the mice. A strong correlation has been shown between disease outcome and the nature of the T cell response, with healer strains developing a Th1-like response and nonhealer strains a Th2-like response. The treatment of nonhealer BALB/c mice with a single dose of an anti-IL-4 antibody, given at the time of infection with L. major, allowed these mice to develop healing Th1-like responses, suggesting that IL-4 is required in BALB/c mice for the differentiation of Th cells into Th2 cells. Anti-IL-4 had to be present during the first 2 wk of infection to have this effect. Anti-IL-4 caused a marked shift from a Th2 to a Th1 pattern of cytokine expression within 4 days, in vivo, and injections of IL-4 had the opposite effect on the early response in healer C3H/HeN mice. These findings demonstrate that IL-4 can induce the development of Th2 response to L. major infection in vivo.

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.

Catalase inhibits nitric oxide synthesis and the killing of intracellular Leishmania major in murine macrophages

Mouse peritoneal macrophages activated with interferon-gamma (IFN-gamma) and lipopolysaccharide produce substantial amounts of nitric oxide (NO), which correlates with the elimination of the intracellular protozoan parasite Leishmania major. Both the production of NO and the leishmanicidal function of the activated macrophages can be significantly inhibited by catalase in a dose- and time-dependent manner. These results could not be interpreted by the reduction of H2O2 by catalase since the removal of H2O2 by the addition of glutathione peroxidase had no effect on the NO synthesis or the leishmanicidal function of activated macrophages. Furthermore, catalase did not affect the induction of NO synthase in IFN-gamma-activated macrophages. In contrast, the inhibition of NO synthesis and leishmanicidal activity by catalase was reversed in a dose-dependent manner by the addition of tetrahydrobiopterin, a cofactor of NO synthase. Taken together, these results not only further support the central role of NO as the cytotoxic moiety, but also suggest that hydrogen peroxide may interfere with NO production by affecting the levels of cofactor needed for its synthesis.