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

IFN-gamma expression is up-regulated by peripheral blood mononuclear cells (PBMC) from non-exposed dogs upon Leishmania chagasi promastigote stimulation in vitro

While the response to Leishmania spp. is well characterized in mice and humans, much less is known concerning the canine immune response, particularly soon after exposure to the parasite. Early events are considered to be a determinant of infection outcome. To investigate the dog's early immune response to L. chagasi, an in vitro priming system (PIV) using dog naïve PBMC was established. Until now, dog PIV immune response to L. chagasi has not been assessed. We co-cultivated PBMC primarily stimulated with L. chagasiin vitro with autologous infected macrophages and found that IFN-γ mRNA is up-regulated in these cells compared to control unstimulated cells. IL-4 and IL-10 mRNA expression by L. chagasi-stimulated PBMC was similar to control unstimulated PBMC when incubated with infected macrophages. Surprisingly, correlation studies showed that a lower IFN-γ/IL-4 expression ratio correlated with a lower percentage of infection. We propose that the direct correlation between IFN-γ/IL-4 ratio and parasite load is dependent on the higher correlation of both IFN-γ and IL-4 expression with lower parasite infection. This PIV system was shown to be useful in evaluating the dog immune response to L. chagasi, and results indicate that a balance between IFN-γ and IL-4 is associated with control of parasite infection in vitro.

Leishmania major soluble exo-antigens (LmSEAgs) protect neonatal BALB/C mice from a subsequent challenge with L. major and stimulate cytokine production by Leishmania-naïve human peripheral blood mononuclear cells

The vaccine potential and immunogenicity of soluble Leishmania major exo-antigens (LmSEAgs), a potentially novel source for vaccine candidates for leishmaniasis, were evaluated in neonatal BALB/c mice and with human peripheral blood mononuclear cells. Vaccinated neonatal BALB/c mice resisted infection with L. major, and lymphoid cells from the mice proliferated when restimulation with LmSEAgs and produced interferon-gamma and some interleukin-4. In addition, LmSEAgs stimulated human peripheral blood mononuclear cells to produce large amounts of interferon-gamma and some interleukin-5. This finding suggests that LmSEAgs may be a vaccine candidate for leishmaniasis in humans.

Characterization of the T-cell receptor Vbeta repertoire in the human immune response against Leishmania parasites

In order to explore a possible presence of hyperreactive T-cell clones in human cutaneous leishmaniasis (CL), we have investigated, by flow cytometry, the expression of Vbeta chains of T-cell receptors (TCRs) in the following types of cells: (i) peripheral blood mononuclear cells (PBMCs) from CL patients, which were then compared to those from normal volunteers; (ii) unstimulated and soluble Leishmania antigen-stimulated draining lymph node cells from CL patients; (iii) PBMCs from volunteers before versus after Leishmania immunization; and (iv) PBMCs from healthy volunteers that were primed in vitro with live Leishmania parasites. Our results show a modulation in the TCR Vbeta repertoire during CL and after antigen stimulation of patients' cells. Vaccination, however, leads to a broad expansion of different Vbeta TCRs. We also observed an association between TCR Vbeta12 expression, T-cell activation, and gamma interferon production upon in vitro priming with Leishmania. Collectively, these results both indicate that infection with live parasites or exposure to parasite antigen can modulate the TCR Vbeta repertoire and suggest that TCR Vbeta12 may be implicated in the response to Leishmania.

Leishmania amazonensis: participation of regulatory T and B cells in the in vitro priming (PIV) of CBA/J spleen cells susceptible response

CBA/J mice are resistant to Leishmania major and susceptible to Leishmania amazonensis. Early events determine infection outcome. Until now, PIV (in vitro priming) immune response to L. amazonensis has not been assessed. Herein, we have shown that compared to L. major, L. amazonensis induced higher parasite burden associated to similar IL-4, IFN-gamma, and TNF-alpha mRNA expressions and IFN-gamma and IL-10 levels. Although similar amounts of IL-10 were detected, the frequency of intracellular IL-10 positive B cells was enhanced in spleen cells stimulated with anti-CD3/anti-CD28, or anti-CD3/anti-CD28 and L. amazonensis, compared to L. major-stimulation. Interestingly, IL-10- producing B cells were reduced in response to anti-CD3/anti-CD28 stimulation combined with L. major compared to the other groups. L. amazonensis may favor T regulatory cell development, since 40% of all the CD4+CD25+ were CD25(high) cells. These data suggest that in PIV, susceptibility to L. amazonensis is not related to Th cell polarization, but to the presence and activity of regulatory T and B cells.

CD40 signaling induces reciprocal outcomes in Leishmania-infected macrophages; roles of host genotype and cytokine milieu

We investigated the influence of CD40-CD40 ligand-mediated signaling on induction of microbicidal activity against Leishmania major in macrophages from resistant (B6) and susceptible (BALB) mouse strains. CD40 engagement induced leishmanicidal activity in resistant macrophages, but increased parasite replication in susceptible macrophages. CD40 engagement induced comparable TNF-alpha production in macrophages from both strains. However, increased IL-10 production was restricted to susceptible macrophages. Increased parasite replication in susceptible macrophages was prevented by a neutralizing anti-IL-10 antibody. In the presence of IFN-gamma, CD40 engagement induced Leishmania killing by macrophages from both strains. Therefore, the outcome of CD40 signaling on effector responses against L. major depends on host genotype and the cytokine milieu, and a source of IFN-gamma is required for a protective response.

IFN-gamma-producing CD45RA+CD8+ and IL-10-producing CD45RA-CD4+ T cells generated in response to LACK in naive subjects never exposed to Leishmania

Leishmania guyanensis (L.g.)-specific CD8+ T cells can be isolated from PBMC of subjects who have never been previously exposed to Leishmania. Cells that produce IFN-gamma in response to live L.g. are generated from naive CD45RA+CD8+ T cells. The generation of L.g.-specific CD8+ T cells requires the presence of whole L.g. or UV-irradiated parasite but not the soluble antigens from L.g. promastigotes. The IFN-gamma-producing T cells recognize a specific antigen, the Leishmania homologue of receptors of activated C kinases (LACK) and this antigen but not live L.g. can produce a strong IL-10 response in CD45RA-CD4+ memory T cells from naive subjects. A single epitope (amino acid 156-173) is found to induce the IL-10 synthesis. While the IFN-gamma-producing cells are present among CD45RA+CD8+ T cells that are CD62L-CDR7- and CLA-, the LACK-reactive IL-10-producing cells are CD4+ T cells that are CD62L+CCR7- and CLA-.

Differences in gamma interferon production in vitro predict the pace of the in vivo response to Leishmania amazonensis in healthy volunteers

The initial encounter of Leishmania cells and cells from the immune system is fundamentally important in the outcome of infection and determines disease development or resistance. We evaluated the anti-Leishmania amazonensis response of naive volunteers by using an in vitro priming (IVP) system and comparing the responses following in vivo vaccination against the same parasite. In vitro stimulation allowed us to distinguish two groups of individuals, those who produced small amounts of gamma interferon (IFN-gamma) (n = 16) (low producers) and those who produced large amounts of this cytokine (n = 16) (high producers). IFN-gamma production was proportional to tumor necrosis factor alpha and interleukin 10 (IL-10) levels but did not correlate with IL-5 production. Volunteers who produced small amounts of IFN-gamma in vitro remained low producers 40 days after vaccination, whereas high producers exhibited increased IFN-gamma production. However, 6 months after vaccination, all individuals tested produced similarly high levels of IFN-gamma upon stimulation of their peripheral blood mononuclear cells with Leishmania promastigotes, indicating that low in vitro producers respond slowly in vivo to vaccination. In high IFN-gamma producers there was an increased frequency of activated CD8(+) T cells both in vitro and in vivo compared to the frequency in low producers, and such cells were positive for IFN-gamma as determined by intracellular staining. Such findings suggest that IVP responses can be used to predict the pace of postvaccination responses of test volunteers. Although all vaccinated individuals eventually have a potent anti-Leishmania cell-mediated immunity (CMI) response, a delay in mounting the CMI response may influence resistance against leishmaniasis.

Virulent or avirulent (dhfr-ts-) Leishmania major elicit predominantly a type-1 cytokine response by human cells in vitro

In this study we have compared the immune response of normal human cells cultured in vitro to two virulent strains of Leishmania major (CC1 and LV39), and to an avirulent vaccine strain (dhfr-ts-) made by targeted deletion of the essential gene DHFR-TS. We utilized an in vitro system in which naive T cells from normal human donors were primed with autologous Leishmania-infected macrophages. All three parasites infected macrophages and transformed into amastigotes within the cells. However, whereas LV39 and CC1 replicated in macrophages, dhfr-ts- did not. When peripheral blood lymphocytes (PBL) were stimulated with autologous macrophages infected with any of the three parasites, the lymphocytes produced a type-1-biased cytokine response. Finally, addition of IL-12 during the first stimulation period increased the production of interferon-gamma but decreased IL-5 secretion. On the other hand, anti-IL-12 resulted in the opposite effect.

Priming of a beta-galactosidase (beta-GAL)-specific type 1 response in BALB/c mice infected with beta-GAL-transfected Leishmania major

To determine whether an ongoing response to Leishmania major would affect the response to a non-cross-reacting, non-leishmanial antigen, susceptible BALB/c mice and resistant C3H mice were infected with L. major parasites expressing Escherichia coli beta-galactosidase (beta-GAL); this parasite was designated L. major-betaGAL. BALB/c and C3H mice responded to infection with L. major-betaGAL by mounting a CD4 T-cell response to both parasite antigens and to the reporter antigen, beta-GAL. The phenotypes of these T cells were characterized after generating T-cell lines from infected mice. As expected, BALB/c mice responded to infection with L. major-betaGAL by producing interleukin 4 in response to the parasite and C3H mice produced gamma interferon (IFN-gamma) in response to the parasite and beta-GAL. Interestingly, however, BALB/c mice produced IFN-gamma in response to beta-GAL. Taken together, these results demonstrate that priming of IFN-gamma-producing cells can occur in BALB/c mice despite the fact the animals are simultaneously mounting a potent Th2 response to L. major.

Murine dendritic cells internalize Leishmania major promastigotes, produce IL-12 p40 and stimulate primary T cell proliferation in vitro

Metacyclic Leishmania promastigotes (PM), transmitted by sand-fly bite, are likely to interact initially with cells of the dendritic cell (DC) lineage(s) in the epidermis or dermis. Epidermal Langerhans cells internalize L. major amastigotes (AM) and transport them to draining lymph nodes (Moll, H., Fuchs, H., Blank, C. and Röllinghoff, M., Eur. J. Immunol. 1993. 23: 1595) but little is known about the interaction of DC with PM. The present study demonstrates that DC are able to internalize PM and that the fate of the parasites within DC differs from that within macrophages (Mphi). DC took up small numbers of PM which did not differentiate into AM but appeared to be degraded; Mphi internalized large numbers of PM into parasitophorous vacuoles where they differentiated into AM. In response to direct stimulation with PM, DC from both C3H ("resistant" to L. major infection) and BALB/c ("susceptible") up-regulated production of IL-12 p40. In contrast, IL-12 production by Mphi was not detected. DC exposed to either metacyclic PM or PM culture supernatants were also able to stimulate proliferative responses in lymph node T cells from naive mice. These data indicate that DC have the capacity to promote protective Th1 immune responses in Leishmania infection and suggest that DC exposed to PM may be useful in immunotherapy and vaccination.

Susceptibility and resistance to Leishmania amazonensis in H-2q syngeneic high and low antibody responder mice (Biozzi mice)

H-2 syngeneic H and L (Biozzi) mice provide a model to study Leishmania infections in which polar resistant and susceptible phenotypes are independent from H-2 differences. High-Ab-responder (H) and low-Ab-responder (L) mice syngeneic at the H-2 locus (H-2q) were, respectively, susceptible and highly resistant to Leishmania amazonensis infection. L-mice resistance was associated with high IFN-gamma and transient IL-4 production by lymph node (LN) cells, in contrast with sustained IL-4 and decreasing IFN-gamma production by susceptible H mice. IL-12 production could be detected only in LN from resistant mice. The cytokine production pattern was consistent with preferential progression to a Th1-type response in resistant L-mice, and to a Th2-type response in susceptible H-mice. We also investigated whether this shift towards Th1- or Th2-type cytokine responses was dependent upon H or L antigen presenting cells' (APC) intrinsic ability to preferentially stimulate either T-cell subset. To this end, LN-derived T-cell lines were grown from 12-day infected mice, when both strains produced IFN-gamma and IL-4. L-derived T-cell lines developed a Th2 cytokine pattern whereas H-derived T-cell lines produced IFN-gamma, IL-4 and IL-10 whatever the APC origin (H or L) used for their derivation. This work constitutes the first characterization of cellular immune responses to the intracellular parasite, L. amazonensis in H-2 syngeneic mice, an infection model in which polar resistant and susceptible phenotypes are determined by non-MHC genes.

Analysis of the immune responses of mice to infection with Leishmania braziliensis

Leishmania major and Leishmania braziliensis both cause cutaneous leishmaniasis, but the former kills BALB/c mice while the latter is killed by the mice. This killing of L. braziliensis occurred by a gamma interferon-dependent mechanism, potentially made possible by the observed lack of high interleukin-4 production.

An in vitro model for infection with Leishmania major that mimics the immune response in mice

By using a primary in vitro response specific for Leishmania major, normal T cells from resistant CBA/CaH-T6J and susceptible BALB/c mice commit to a Th1 and a Th2 response, respectively. Since commitment occurred, we measured the production of gamma interferon (IFN-gamma), interleukin-1 (IL-1), IL-2, IL-4, IL-5, IL-10, and IL-12, prostaglandin E2 (PGE2), transforming growth factor beta (TGF-beta), and nitric oxide in the first 7 days of the response to identify factors that are critical for Th1 and Th2 development. While cells from resistant CBA mice produced more IFN-gamma, IL-10, and nitric oxide, cells from susceptible BALB/c mice produced more IL-1alpha, IL-5, PGE2, and TGF-beta. Although substantial amounts of IL-12 were detected, IL-12 did not associate with either Th1 or Th2 development. We did not anticipate that cells from resistant CBA mice would make more IL-10 in vitro. However, this also occurred in vivo since CBA mice produced substantial amounts of IL-10 following infection with L. major. Moreover, adding anti-IL-10 to primary in vitro responses enhanced production of IFN-gamma and nitric oxide by cells from CBA and BALB/c mice. Therefore, IL-10 cannot be regarded as a cytokine that associates with susceptibility to infection with L. major. Finally, the data presented here suggest that a collection of factors that can be produced by accessory cells influence Th commitment (e.g., IL-1, PGE2, and TGF-beta favor Th2 development).

An enhanced immune response in mice lacking the transcription factor NFAT1

Transcription factors of the NFAT family are thought to play a major role in regulating the expression of cytokine genes and other inducible genes during the immune response. The role of NFAT1 was investigated by targeted disruption of the NFAT1 gene. Unexpectedly, cells from NFAT1 -/- mice showed increased primary responses to Leishmania major and mounted increased secondary responses to ovalbumin in vitro. In an in vivo model of allergic inflammation, the accumulation of eosinophils and levels of serum immunoglobulin E were increased in NFAT1 -/- mice. These results suggest that NFAT1 exerts a negative regulatory influence on the immune response.

T cell and non-T cell compartments can independently determine resistance to Leishmania major

In experimental murine cutaneous leishmaniasis caused by Leishmania major (Lm), the cellular determinants governing development of protective or exacerbative T cells are not well understood. We, therefore, attempted to determine the influence of T cell and non-T cell compartments on disease outcome. To this end, T cell chimeric mice were constructed using adult thymectomized lethally irradiated, bone marrow-reconstituted (ATXBM) animals of genetically resistant, C57BL/6, or susceptible, BALB/c, backgrounds. These hosts were engrafted with naive T cell populations from H-2-congenic susceptible, BALB.B6-H-2b, or resistant, C57BL/6.C-H-2d, animals, respectively. Chimeric mice were then infected with Lm, and disease outcome was monitored. BALB/c T cell chimeric mice, BALB/c ATXBM hosts given naive C57BL/6.C-H-2d T cells, resolved their infections as indicated by reductions in both lesion size and parasite numbers. Furthermore, the mice developed typical Th1 (interferon[IFN]-gamma hiinterleukin[IL]-4lo) cytokine patterns. In contrast, both sham chimeric, BALB/c ATXBM hosts given naive BALB/c T cells, and control irradiated euthymic mice succumbed to infection, producing Th2 profiles (IFN-gamma loIL-4hiIL-10hi). C57BL/6 T cell chimeras, C57BL/6 ATXBM hosts given naive BALB.B6-H-2b T cells, resolved their infections as did C57BL/6 sham chimeras and euthymic controls. Interestingly, whereas C57BL/6 control animals produced Th1 cytokines, chimeric animals progressed from Th0 (IFN-gamma hiIL-4hiIL-10hi) to Th2 (IFN-gamma loIL-4hiIL-10hi) cytokine profiles as cure ensued. Both reconstitution and chimeric status of all mice were confirmed by flow cytometry. In addition, T cell receptor V beta usage of Lm-specific blasts was determined. In all cases, V beta use was multiclonal, involving primarily V beta 2, 4, 6, 8.1, 8.2, 8.3, 10, and 14, with relative V beta frequencies differing between H-2b and H-2d animals. Most importantly, however, these differences did not segregate between cure and noncure outcomes. These findings indicate that: (a) genetic traits determining cure in Lm infection can direct disease outcome from both T cell and non-T cell compartments; (b) the presence of the curing genotype in only one compartment is sufficient to confer cure; (c) curing genotype T cells autonomously assume a Th1 cytokine profile-mediating cure; (d) noncuring genotype T cells can mediate cure in a curing environment, despite the onset of Th2 cytokine production; and lastly, (e) antigen specificity of responding T cells, as assessed by V beta T cell receptor diversity, is not a critical determinant of disease outcome.

Saliva of the Lyme disease vector, Ixodes dammini, blocks cell activation by a nonprostaglandin E2-dependent mechanism

Tick-borne pathogens would appear to be vulnerable to vertebrate host immune responses during the protracted duration of feeding required by their vectors. However, tick salivary components deposited during feeding may inhibit hemostasis and induce immunosuppression. The mode of action and the nature of immunosuppressive salivary components remains poorly described. We determined that saliva from the main vector of the agent of Lyme disease, Ixodes dammini, profoundly inhibited splenic T cell proliferation in response to stimulation with concanavalin A or phytohemagglutin, in a dose-dependent manner. In addition, interleukin 2 secretion by the T cells was markedly diminished by saliva. Tick saliva also profoundly suppressed nitric oxide production by macrophages stimulated with lipopolysaccharide. Finally, we analyzed the molecular basis for the immunosuppressive effects of saliva and discovered that the molecule in saliva responsible for our observations was not PGE2, as hypothesized by others, but rather, was a protein of 5,000 mol wt or higher.

Toxoplasma gondii possesses a superantigen activity that selectively expands murine T cell receptor V beta 5-bearing CD8+ lymphocytes

To investigate early immune responses to the intracellular parasite Toxoplasma gondii, we examined the capacity of nonimmune splenocytes to respond in vitro to intact tachyzoites and soluble tachyzoite antigen (Ag). Both types of stimuli induced high levels of proliferation as well as interferon gamma (IFN-gamma) secretion. Based on several key criteria, the response appeared to be driven by a superantigen present in the parasite. Thus, stimulation of C57BL/6 spleen cells with T. gondii resulted in a preferential threefold expansion of a T cell population expressing the V beta 5 chain of the T cell receptor, and a survey of different inbred mouse strains revealed an inverse correlation between Ag-induced proliferation and genetic deletion of V beta 5. Moreover, proliferation was induced using irradiated Ag-pulsed and infected splenic adherent cells, and was blocked by a major histocompatibility complex class II-specific monoclonal antibody. Furthermore, paraformaldehyde-fixed IAb-, IAk-, and IEk-transfected fibroblast lines were able to specifically bind T. gondii Ag and drive proliferation of T lymphocytes, demonstrating that the response can be mediated by allogeneic class II molecules, and that it does not require cellular Ag processing. It is interesting to note that after 1 wk of culture with Ag, up to 70% of the expanded V beta 5-expressing cells were CD8+. These results provide the first description of a superantigen activity in a protozoan pathogen. In the case of T. gondii, superantigen-driven expansion of IFN-gamma-secreting CD8+ lymphocytes may play a role in the development of the dominant IFN-gamma-dependent, cell-mediated immunity characteristic of infection with this parasite.

Interleukin-12 but not interferon-gamma production correlates with induction of T helper type-1 phenotype in murine candidiasis

By means of polymerase chain reaction-assisted mRNA amplification, we have monitored message levels of interleukin (IL)-12 in splenic macrophages and of interferon-gamma (IFN-gamma), IL-4, and IL-10 in CD4+ and CD8+ T cells using Candida albicans/host combinations that result either in a T helper type-1 (Th1)-associated self-limiting infection ("healer mice") or in a Th2-associated progressive disease ("nonhealer mice"). The timing and pattern of message detection did not differ qualitatively by the expression of IFN-gamma or IL-10 mRNA in CD4+ and CD8+ cells from healer (i.e. PCA-2 into CD2F1) vs. nonhealer (i.e. CA-6 into CD2F1 or PCA-2 into DBA/2) mice. In contrast, IL-4 mRNA was uniquely expressed by CD4+ cells from nonhealer animals. IL-12p40 was readily detected in macrophages from healer mice but was detected only early in infection in mice with progressive disease. Cytokine levels were measured in sera, and antigen-driven cytokine production by CD4+ and CD8+ cells was assessed in vitro, while IFN-gamma-producing cells were enumerated in CD4- CD8- cell fractions. Overall, our results showed that (i) antigen-specific secretion of IFN-gamma protein in vitro by CD4+ cells occurred only in healing infection; (ii) IL-4- and IL-10-producing CD4+ cells would expand in nonhealer mice in the face of high levels of circulating IFN-gamma, likely released by CD4- CD8- lymphocytes; (iii) a finely regulated IFN-gamma production correlated in the healer mice with IL-12 mRNA detection, and IL-12 was required in vitro for yeast-induced development of IFN-gamma-producing CD4+ cells. Although the mutually exclusive production of IL-4/IL-10 and IFN-gamma by early CD4+ cells may be the major discriminative factor of cure and noncure responses in candidiasis, IL-12 rather than IFN-gamma production may be an indicator of Th1 differentiation.