Resistance to Leishmania major infection correlates with the induction of nitric oxide synthase in murine macrophages

Inbred strains of mice differ considerably in their innate resistance to leishmanial infection. BALB/c mice are highly susceptible to cutaneous leishmaniasis caused by Leishmania major, whereas CBA mice are resistant. We now show that this resistance correlates with the ability of macrophages to synthesize nitric oxide (NO) following activation with interferon-gamma or tumor necrosis factor alpha. Furthermore, the larger amounts of NO generated by resistant macrophages are related to higher levels of NO synthase activity, a difference which is not attributable to the number or the affinity of the receptors for interferon-gamma on these cells. The level of NO synthesis by activated macrophages was also correlated to the resistance in a number of other inbred mouse strains tested; macrophages from the resistant B10.S, C57BL and C3H mice produced significantly higher levels of NO than the macrophages from the susceptible BALB.b and DBA/2 mice.

Comparison on the performance of Leishmania major-like and Leishmania braziliensis braziliensis as antigen for New World leishmaniasis IgG-immunofluorescence test

The performance of an antigen of L. major-like promastigotes for the serological diagnosis of mucocutaneous leishmaniasis in the IgG-immunofluorescent test was compared to that of an antigen of L.braziliensis braziliensis. Each antigen was used to test two hundred and twenty-four sera of etiologies such as mucocutaneous leishmaniasis, deep mycoses, toxoplasmosis, malaria. Chagas' disease, visceral leishmaniasis, anti-nuclear factor, schistosomiasis, rheumatoid factor and normal controls. Agreement between responses to each antigen was high: 77.2% of leishmaniases sera agreed on a positive or a negative result to both antigens and 91.1% of control sera. Cross reactivity was restricted to Chagas' disease sera, visceral leishmaniasis, anti-nuclear factor and paracoccidioidomycosis. The quantitative response of leishmaniasis and Chagas' disease sera to both antigens was evaluated by a linear regression; although the y-intercept and the slope were different for each antigen, neither was better than the other in the disclosure of anti-Leishmania antibodies. In the case of Chagas' disease sera the L.major-like antigen was better than L.b.braziliensis' to disclose cross-reacting antibodies.

IFN-gamma modulates the early development of Th1 and Th2 responses in a murine model of cutaneous leishmaniasis

Resistance to Leishmania major in mice is associated with the generation of distinct CD4+ Th subsets, termed TH1 and TH2. To define the factors contributing to the genesis of these Th cells, we first investigated when these subsets developed following L. major infection. Lymph node (LN) cells collected 3 days after infection of BALB/c mice secreted IL-4 and IL-5 in vitro, but little IFN-gamma, whereas LN cells from a resistant strain, C3H/HeN, secreted IFN-gamma and no IL-4 or IL-5. Cytokine production was eliminated in both cases by in vivo or in vitro depletion of CD4+ cells, but not after depletion of CD8+ cells. Similar responses were observed after inoculation of killed promastigotes or a soluble leishmanial Ag preparation. These data indicate that the development of Th1- and Th2-like responses can precede lesion formation and does not require a live infection. We next investigated whether IFN-gamma was important in the differentiation of Th1 and Th2 cells. C3H/HeN mice have previously been shown to be susceptible to leishmanial infection after treatment with anti-IFN-gamma. We confirmed this observation and found that the abrogation of resistance was associated with enhanced production of IL-4 and IL-5, and decreased production of IFN-gamma by cells taken from these mice. Conversely, LN cells from BALB/c mice inoculated with parasites plus IFN-gamma produced significantly higher levels of IFN-gamma, and decreased levels of IL-4 and IL-5, than mice infected with parasites alone. Finally, we determined if IFN-gamma might augment vaccine induced immunity. We found that s.c. immunization with soluble leishmanial Ag, the bacterial adjuvant, Corynebacterium parvum and IFN-gamma could protect mice against L. major infection, and that this protection was associated with induction of Th1 responses. From these data we conclude that levels of IFN-gamma at the time of infection or immunization dramatically alters the type of response elicited: high levels of IFN-gamma favor Th1 type responses, whereas low levels promote a Th2 response.

TNF-alpha reverses the disease-exacerbating effect of subcutaneous immunization against murine cutaneous leishmaniasis

Earlier studies have demonstrated that mice injected subcutaneously or intramuscularly with leishmanial antigens develop significantly exacerbated disease compared with unimmunized controls when challenged with the cutaneous protozoan parasites Leishmania major. We report here that this disease enhancement can be prevented, and protective immunity induced, by the incorporation of recombinant tumour necrosis factor (TNF-alpha) in the immunizing inoculum. This effect of TNF-alpha is dose-dependent and is not evident when TNF-alpha and the antigens are injected into separate sites. Furthermore, TNF-alpha injected together with p183, a peptide known to preferentially stimulate Th2 cells and disease exacerbation in H-2d mice, activates spleen and lymph node cells secreting more interferon-gamma (IFN-gamma) and less interleukin-4 (IL-4) and induces a modest but significant degree of resistance against L. major infection in highly susceptible BALB/c mice.

Antileishmanial defense in macrophages triggered by tumor necrosis factor expressed on CD4+ T lymphocyte plasma membrane

In our studies of host defense to the intracellular protozoan Leishmania major, we uncovered a novel mechanism of antileishmanial defense that involves direct cell contact between effector CD4+ lymphocytes and Leishmania-infected macrophages. The mechanism is distinctive because it does not involve lymphokine secretion and induces no cytotoxic effects in the host cells; its expression is antigen-specific and genetically restricted. We now demonstrate that these effector CD4+ cells display tumor necrosis factor (TNF) on their surface and provide evidence that the membrane-associated TNF is involved in the activation of the antileishmanial defense. Using a Leishmania-specific cloned T-T cell hybridoma line (1B6; CD4+, T helper type 1) that activates antileishmanial defense in macrophages through cell contact and does not secrete TNF, we noted that only cells bearing surface TNF (TNF+), but not ones lacking surface TNF (TNF-), exerted these effects. Moreover, the antileishmanial effects excreted by TNF+ 1B6 cells as well as by lymph node CD4+ TNF+ lymphocytes could be blocked with anti-TNF antibody. We propose that membrane-associated TNF on CD4+ T cells may provide a mechanism of targeting activation signals to macrophages in an antigen-specific and genetically restricted manner.

A possible novel pathway of regulation by murine T helper type-2 (Th2) cells of a Th1 cell activity via the modulation of the induction of nitric oxide synthase on macrophages

Murine peritoneal macrophages activated with interferon (IFN)-gamma and lipopolysaccharide (LPS) produce high levels of nitric oxide (NO) and are efficient in killing the intracellular protozoan parasites Leishmania major in vitro. Earlier studies have shown that NO, whose synthesis in murine macrophages is catalyzed by an inducible enzyme NO synthase, plays a major effector role in the host resistance against microbial infection. We now shown that both the NO synthesis and the leishmanicidal activity can be inhibited by prior treatment of the cells with recombinant interleukin 4 (IL4). IL4 treatment had no effect on the binding of IFN-gamma to macrophages but prevented the induction of NO synthase in these cells activated with IFN-gamma and LPS. Since IFN-gamma is produced by murine T helper type-1 (Th1) cells, whereas IL4 is secreted by Th2 cells, these results suggest a novel pathway by which Th2 cells regulate an activity of Th1 cells, namely by inhibiting the induction of NO synthase. These results may also account for the mechanism by which the disease-promoting Th2 cells counteract the host-protective effect of Th1 cells in leishmaniasis and other intracellular parasitic diseases.

Structure and antigenicity of the lipophosphoglycan from Leishmania major amastigotes

The lipophosphoglycan (LPG) of the intracellular amastigote form of the protozoan parasite Leishmania major is chemically distinct from the LPG on the surface of the extracellular promastigote form. Amastigote LPG is composed of the monosaccharides galactose, glucose, mannose, glucosamine and inositol in the molar ratio 51:30:24:1:1; arabinose is absent. The lipid anchor comprises four alkylglycerols, with alkyl chain lengths 24:0, 22:0, 20:0 and 26:0 in the molar ratio 68:18:8:6. Phosphate is present at 4% w/w of total carbohydrate. HPLC gel permeation reveals LPG to be a polydisperse family of molecules Mr 100-6 kDa. The results from immunological studies with LPG-directed antibodies are consistent with amastigote LPG having the expected tripartite structure of GPI-anchor, a core glycan and the phosphorylated disaccharide repeat backbone. Human sera from L. major patients bound amastigote LPG in enzyme-linked immunosorbent assays.

Characterization of effector functions of v-raf/mil- and v-myc-transformed murine splenic macrophage cell lines

We have characterized several of the cytocidal effector functions of a series of cell lines derived by recombinant retroviral transformation of individual clones of C3H/HeJ mouse splenic macrophages. The three cell lines described in this report (4.01, 4.07, 4.14) all expressed equivalent tumoricidal activity against P815 tumor target cells. However they differed in their high avidity binding of tumor cells (4.01 = 4.14 greater than 4.07), as well as in the killing of Leishmania major (4.01 = 4.07 greater than 4.14), the expression of antibody-dependent cellular cytotoxicity against chicken erythrocytes (4.14 greater than 4.01 greater than 4.07), and finally, in the tumor-stimulated release of tumor necrosis factor-alpha (4.01 = 4.14 greater than 4.07). The stable and restricted expression of distinct effector functions among these three cell lines makes them particularly valuable as models for establishing the precise mechanisms by which cytocidal functions are effected. In addition, they should also prove of value in understanding the basis for macrophage functional diversity.

Role of tumor necrosis factor in macrophage leishmanicidal activity in vitro and resistance to cutaneous leishmaniasis in vivo

Recombinant human tumor necrosis factor (TNF) and purified murine TNF were both able to activate macrophages to destroy intracellular Leishmania major in vitro. In addition, parasitizing macrophages with L. major markedly increased the ability of the cells to produce TNF. Finally, when mice were vaccinated with an avirulent form of L. major, the animals produced large amounts of TNF but no gamma interferon in response to infection with virulent L. major. Treating these mice with a neutralizing anti-TNF antibody led to partial but not complete inhibition of the resistant state, which suggests that factors other than TNF and gamma interferon contribute to resistance to L. major.

Metacyclogenesis of Leishmania spp: species-specific in vitro transformation, complement resistance, and cell surface carbohydrate and protein profiles

Metacyclic (stationary) and logarithmic (log) forms of promastigotes of Leishmania donovani and Leishmania major were characterized in several ways. The highly active metacyclic forms were larger with more protein and less carbohydrate. The flagellum increased in length 2.4 times in L. major as compared to 1.8 times in L. donovani. Resistance to complement-mediated lysis by normal human serum of in vitro grown Leishmania promastigotes was related to the species, the growth phase in culture, and also the temperature. Metacyclic forms of both species had a much increased resistance to killing by normal serum at different temperatures. Differences in membrane-exposed carbohydrates were detected by fluorescein-conjugated lectins. Peanut agglutinin and Ulex agglutinin I differentiated log and stationary phase promastigotes of L. major. Higher amounts of acid phosphatase were demonstrated in the metacyclic phase. Differences in polypeptides were detected by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Two polypeptides of approximately 51 and 114 kDa were found exclusively in metacyclic promastigotes of both species, whereas 38- and 23-kDa polypeptides were lost or reduced during transformation from log to metacyclic phase promastigotes of L. donovani. In addition, a 75-kDa polypeptide was expressed only in metacyclic promastigotes of L. major.

Evidence of genetic recombination in Leishmania

In the genus Leishmania there has been no convincing demonstration of genetic exchange, and it has been proposed that reproduction is clonal. However, preliminary characterization of two strains of Leishmania isolated from wild animals in a zoonotic focus of cutaneous leishmaniasis in the Eastern Province of Saudi Arabia, has suggested that they may represent hybrids of Leishmania major and Leishmania arabica. Evidence presented here strongly supports this hypothesis. Isoenzyme analysis and molecular karyotyping of cloned organisms indicated that the putative hybrids are distinct from other species of Leishmania, and possess characteristics of both L. major and L. arabica. Experiments using highly specific probes demonstrated that kinetoplast minicircle DNA from the putative hybrid contained L. major-specific, but not L. arabica-specific sequences. DNA fingerprinting data obtained using 6 genomic DNA probes were consistent in all cases with a L. major/L. arabica recombinant genotype, and implied both diploidy and allelic segregation. These observations suggest that sexual reproduction may generate genetic diversity within natural Leishmania populations.

Interferon-gamma inhibits the efficacy of interleukin 1 to generate a Th2-cell biased immune response induced by Leishmania major

Splenic adherent cells from L. major-infected resistant and susceptible mice were restimulated in vitro and analyzed for the expression of IL-1 activity. Three weeks or later after infection, cells from parasite infected susceptible BALB/c mice produced substantially more IL-1 activity than those from non-infected controls or from L. major-infected resistant C57BL/6 animals. More than 95% of the IL-1 bioactivity was mediated by IL-1 alpha, as determined by blocking experiments with an anti-IL-1 alpha antiserum. The strain-specific differences in IL-1 production correlated with different accumulation of IL-1 producing adherent cells in the spleens of infected animals, but also with different IL-1 producing capacity on a per cell basis. When adherent cells were mixed with syngeneic IFN-gamma producing CD4+ T lymphocytes from L. major-infected C57BL mice or from animals that had been pretreated with anti-CD4 monoclonal antibody prior to infection, the level of detectable IL-1 decreased depending on the number of T cells added. This inhibition could be blocked completely with an anti-IFN-gamma antibody. No such effect was seen, when CD4+ cells were used that were derived from parasite-infected BALB/c mice and did not produce IFN-gamma. In contrast to L. major, L. donovani antigen not only failed to induce IL-1 production, but also dose-dependently suppressed the IL-1 activity elaborated by L. major antigen. We conclude from these data that IFN-gamma effectively inhibits the efficacy to IL-1 to generate to Th2-cell biased immune response induced by L. major. A T cell independent and as yet unknown mechanism to inhibit the IL-1 response is used by L. donovani.

Establishment of resistance to Leishmania major infection in susceptible BALB/c mice requires parasite-specific CD8+ T cells

Although CD4+ T cells are generally accepted to be responsible for the determination of resistance to infection in experimental murine cutaneous leishmaniasis, a contribution of CD8+ lymphocytes to immunity can be demonstrated under certain well-defined conditions. Normally highly susceptible BALB/c mice can be rendered resistant to infection with Leishmania major promastigotes by a single injection of monoclonal anti-CD4 antibodies at the beginning of infection. Mice treated in such a way can heal their primary cutaneous lesions and acquire immunity to subsequent challenge infection. Both the resolution of the primary infection and the induced state of immunity to reinfection in these mice is shown to be dependent upon the anti-leishmanial effector functions of CD8+ T cells. Furthermore, in contrast to control infected BALB/c mice, which are unable to mount a delayed-type hypersensitivity (DTH) response to viable parasites, mice cured as a result of treatment with anti-CD4 antibodies in vivo exhibit a strong DTH response, which can be significantly reduced by injection of either anti-CD4 or anti-CD8 monoclonal antibodies prior to antigenic challenge with viable promastigotes. Moreover, increased numbers of specific CD8+ T cells, able to transfer Leishmania-specific DTH responses, were found in lymphoid organs of BALB/c mice rendered resistant to infection by immunointervention with anti-CD4 monoclonal antibodies at the beginning of infection. Neutralization in vivo of interleukin 4 during the course of infection in BALB/c mice also enables these otherwise susceptible mice to resolve their cutaneous lesions and to decrease the parasite burden in infected tissues. CD8+ T cells are required for both of these beneficial effects. Taken together, these results indicate that in the immune BALB/c mouse, as in the normally resistant CBA mouse, CD8+ lymphocytes are involved in the elimination of L. major and in the establishment and maintenance of immunity against infection with this parasite.

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.

Differential susceptibility of activated macrophage cytotoxic effector reactions to the suppressive effects of transforming growth factor-beta 1

We examined the effects of TGF-beta 1 on induction of several activated macrophage antimicrobial activities against the protozoan parasite Leishmania, and on induction of tumoricidal activity against the fibrosarcoma tumor target 1023. TGF-beta by itself did not affect the viability of either the intracellular or extracellular target in concentrations up to 200 ng/ml. As little as 1 ng/ml TGF-beta, however, suppressed more than 70% of the intracellular killing activity of macrophages treated with lymphokines. In contrast, more than 100 ng/ml TGF-beta was required to suppress intracellular killing by cells activated with an equivalent amount of recombinant IFN-gamma. Addition of TGF-beta for up to 30 min after exposure to activation factors significantly reduced macrophage killing of intracellular parasites. Pretreatment of macrophages with TGF-beta was even more effective: treatment of cells with TGF-beta for 4 h before addition of activation factors abolished all macrophage intracellular killing activity. Regardless of treatment sequence, however, TGF-beta had absolutely no effect, at any concentration tested, on activated macrophage resistance to infection induced by lymphokines or by the cooperative interaction of IFN-gamma and IL-4. Effects of TGF-beta on tumoricidal activity of activated macrophages was intermediate to that of its effects on intracellular killing or resistance to infection. Lymphokine-induced tumor cytotoxicity was marginally (25%) affected by TGF-beta; 200 ng/ml was able to suppress IFN-gamma-induced tumoricidal activity by 40%. Thus, TGF-beta dramatically suppressed certain activated macrophage cytotoxic effector reactions, but was only partially or not at all effective against others, even when the same activation agent (IFN-gamma) was used. The biochemical target for TGF-beta suppressive activity in these reactions may be the pathway for nitric oxide production from L-arginine, because TGF-beta also inhibited the generation of nitric oxide by cytokine-activated macrophages.

Exacerbation of experimental murine cutaneous leishmaniasis with CD4+ Leishmania major-specific T cell lines or clones which secrete interferon-gamma and mediate parasite-specific delayed-type hypersensitivity

Leishmania major-specific T cell lines were derived from mice sensitized to the parasite. The cells were of the CD4+ T cell lineage and, upon adoptive transfer, were found to be capable of inducing parasite-specific delayed-type hypersensitivity. Adoptive transfer of these L. major-specific T cells to syngeneic recipients which were either normal, T cell deficient or B cell and antibody deficient led to exacerbation of infection upon subsequent challenge with L. major. This suggested that host T cells, B cells and antibody were not required for the L. major-specific T cells to exert their exacerbative effect on the course of cutaneous leishmaniasis. Additional studies revealed that the adoptive transfer of graded doses of these L. major-specific T cells always resulted in exacerbation of infection. Study of the localization pattern of the cells following transfer showed that they migrate preferentially to the site of the lesions. Furthermore, although the induction phase of this phenomenon was immunologically specific, its effector phase was not. Finally, T cell clones were derived from the L. major-specific T cell lines. The T cell clones were phenotypically and functionally identical to the T cell lines from which they were derived. Adoptive transfer of these parasite-specific T cell clones to normal syngeneic recipients induced an exacerbated course of infection with L. major. Interestingly, when these cloned T cells were specifically activated in vitro, the cells produced interleukin 2 and interferon-gamma, but no interleukin 4, indicating that they belong to the murine Th1 subset of CD4+ T cells.

Administration of beta-glucan following Leishmania major infection suppresses disease progression in mice

The potential of beta-glucan (glucan) to suppress the progression of lesions caused by virulent strains of Leishmania major in genetically susceptible BALB/c mice when administered post challenge was evaluated. Glucan particles (glucanp) prepared from Saccharomyces cerevisiae were injected i.v. at 7-day intervals starting 7 days after parasite challenge. Four injections gave a more rapid and a higher extent of suppression than 1, 2 or 3 injections. Mice receiving only parasites, a glucose solution, starch particles or glucanp by the i.p. route showed a progressive increase in footpad thickness and developed ulcerating lesions. An alkali solubilized glucan (glucanas) was injected (50 micrograms, 200 micrograms and 400 micrograms/mouse) 4 times at 4 day intervals either i.v. or i.p. starting four days post parasite challenge. Glucanas injection by either route blocked lesion development; the 50 micrograms treatment had already substantial effects and 400 micrograms in the i.p. route prevented even the initial stages of lesion formation. Touch prints from the lesion area and from the liver of mice receiving 200 micrograms glucanas were amastigote free. The anti Leishmania antibody titre of glucanas treated mice was lower and their sera recognized fewer antigens than that of control Leishmania bearing mice.

Th2 lymphocyte clone can activate macrophage antileishmanial defense by a lymphokine-independent mechanism in vitro and can augment parasite attrition in vivo

Antileishmanial defense has been ascribed to the antimicrobial effects induced by soluble macrophage-activating lymphokines (MAFs), such as interferon-gamma and granulocyte-macrophage colony-stimulating factor. Recently, we identified an additional mechanism of T cell-mediated macrophage activation of defense against Leishmania that is apparently lymphokine independent, requires cell-cell contact, and is not cytotoxic to host cells. By employing antigen-specific murine T cell hybridoma lines, we observed that this property was associated with CD4+ subpopulations possessing the characteristics of the Th1 subset. In the present study, we address the question of whether contact-mediated macrophage activation can also be induced by Th2 lymphocytes. We employed as T effector cells in antileishmanial defense assays the Th2 cell line D10.G1.4 (D10) which is specific for conalbumin. We observed that D10 cells were able to induce activation of Leishmania-infected macrophages only when the macrophages were also primed with conalbumin, and that this activation apparently occurred by a mechanism without the secretion of MAF. Moreover, when mice infected with L. major were injected into footpad lesions with conalbumin and D10 cells, in situ parasite replication was partially inhibited. The expression of this antimicrobial mechanism by Th1 as well as Th2 clones suggests that the property of contact-mediated (lymphokine-independent) activation may be shared by certain lymphocytes in both Th1 and Th2 subpopulations. We hypothesize that this activation mechanism may involve the interaction of a lymphocyte membrane-associated MAF (such as tumor necrosis factor) and its receptor on the infected macrophage, resulting in the induction of antimicrobial effects but not cytotoxicity to the host cell.

Cytokine interactions in experimental cutaneous leishmaniasis. Interleukin 4 synergizes with interferon-gamma to activate murine macrophages for killing of Leishmania major amastigotes

We investigated the effect of recombinant murine interleukin 4 (IL 4) in the absence or presence of recombinant murine interferon-gamma (IFN-gamma) on adherent bone-marrow macrophages (M phi), peritoneal exudate and resident peritoneal M phi from susceptible BALB/c M phi, which were pulse-infected with Leishmania major amastigotes (AM), IL 4 (5-100 U/ml) failed to activate any of these M phi populations for killing of intracellular AM. However, in the presence of low concentrations of IFN-gamma (10-20 U/ml), which alone caused only a slight or intermediate reduction of the number of intracellular parasites. IL 4 led to a dramatic increase of the parasite elimination by all M phi populations. In the case of resident peritoneal M phi, the synergism of IFN-gamma and IL 4 required the incubation of the M phi with both cytokines or with IFN-gamma alone for at least 10 h prior to infection; adding both cytokines after infection of the M phi did not cause a significant reduction of the intracellular parasite burden. The synergistic effect of IL 4 and IFN-gamma was completely abrogated in the presence of anti-IL 4 antibodies. Furthermore, there was no significant difference between M phi derived from either susceptible BALB/c or from resistant C57BL/6 mice. Evidence is presented that the synergistic action of IL 4 and IFN-gamma occurs via an L-arginine-dependent killing pathway. From these data we conclude that IL 4 provides a strong stimulus for the killing of intracellular L. major AM provided low concentrations of IFN-gamma are present. Also, IFN-gamma is apparently an important priming signal for the activation of resident M phi to eliminate intracellular AM.

T-cell reactivity to purified lipophosphoglycan from Leishmania major: a model for analysis of the cellular immune response to microbial carbohydrates

The major macromolecule on the surface of Leishmania major promastigotes is a lipophosphoglycan (LPG). This glycoconjugate plays a key role in determining infectivity and survival of parasites in the mammalian host cell. In addition, L. major LPG is able to induce a host-protective immune response. In this article, we summarise the evidence for recognition of highly purified LPG by T cells and we discuss the potential mechanisms of T-cell stimulation by this non-protein antigen.

Polyclonal B-cell stimulation by T-cells in a parasitic disease

Polyclonal B-cell stimulation resulting in B-cell proliferation and antibody production occurs in many infectious diseases. Here, we review our data showing that CD4-positive T-cells are instrumental for such polyclonal B-cell stimulation in a chronic parasitic infection, namely murine cutaneous leishmaniasis. The mechanism used by the T-cells involves a membrane interaction between B-cells and activated T-cells which can take place in the absence of antigen, as well as the action of lymphokines such as IL-4. The membrane interaction does not seem to involve the CD4 molecule on T-cells and MHC class II molecules on B-cells, as it is the case in cognate interaction during antigen-specific stimulation of B-cells by CD4 positive T-helper cells. Whether or not adhesion molecules, e.g. of the integrin family, play a role in the triggering process, is currently under investigation.

Activation of human T lymphocytes by Leishmania lipophosphoglycan

This study describes Leishmania antigen-induced activation of lymphocytes isolated from Kenyan donors, previously treated for visceral leishmaniasis, and from Danish and Kenyan controls. Peripheral blood mononuclear cells (PBMC) from cured Kala-Azar patients proliferated and produced Interferon-gamma in vitro in response to lipophosphoglycan (LPG) isolated from Leishmania major. The proliferative response was mainly due to activation of CD2-positive T cells. PBMC from controls did not respond to LPG, but to sonicates prepared from both L. major and L. donovani promastigotes. The surface glycoprotein GP 63 failed to activate PBMC from any of the donors tested. These results show that the individuals cured from visceral leishmaniasis had expanded T-cell clones recognizing LPG, conceivably as a result of Leishmania infection. The LPG preparation was without detectable protein contamination. Thus, the results suggest that human T lymphocytes can respond to glycolipid antigens.