Switch from a type 2 to a type 1 T helper cell response and cure of established Leishmania major infection in mice is induced by combined therapy with interleukin 12 and Pentostam

Host-Directed Therapies for Cutaneous Leishmaniasis

Cutaneous leishmaniasis exhibits a wide spectrum of clinical presentations from self-resolving infections to severe chronic disease. Anti-parasitic drugs are often ineffective in the most severe forms of the disease, and in some cases the magnitude of the disease can result from an uncontrolled inflammatory response rather than unrestrained parasite replication. In these patients, host-directed therapies offer a novel approach to improve clinical outcome. Importantly, there are many anti-inflammatory drugs with known safety and efficacy profiles that are currently used for other inflammatory diseases and are readily available to be used for leishmaniasis. However, since leishmaniasis consists of a wide range of clinical entities, mediated by a diverse group of leishmanial species, host-directed therapies will need to be tailored for specific types of leishmaniasis. There is now substantial evidence that host-directed therapies are likely to be beneficial beyond autoimmune diseases and cancer and thus should be an important component in the armamentarium to modulate the severity of cutaneous leishmaniasis.

Protective Cellular Immune Response Induction for Cutaneous Leishmaniasis by a New Immunochemotherapy Schedule

The palladacycle complex DPPE 1.2 was previously shown to inhibit Leishmania (Leishmania) amazonensis infection in vitro and in vivo. The present study aimed to evaluate the effect of DPPE 1.2 associated with a recombinant cysteine proteinase, rLdccys1, and the adjuvant Propionibacterium acnes on L. (L.) amazonensis infection in two mouse strains, BALB/c, and C57BL/6. Treatment with this association potentiated the leishmanicidal effect of DPPE 1.2 resulting in a reduction of parasite load in both strains of mice which was higher compared to that found in groups treated with either DPPE 1.2 alone or associated with P. acnes or rLdccys1. The reduction of parasite load in both mice strains was followed by immunomodulation mediated by an increase of memory CD4⁺ and CD8⁺ T lymphocytes, IFN-γ levels and reduction of active TGF-β in treated animals. No infection relapse was observed 1 month after the end of treatment in mice which received DPPE 1.2 associated with rLdccys1 or rLdccys1 plus P. acnes in comparison to that exhibited by animals treated with DPPE 1.2 alone. Evaluation of serum levels of AST, ALT, urea, and creatinine showed no alterations among treated groups, indicating that this treatment schedule did not induce hepato or nephrotoxicity. These data indicate the potential use of this association as a therapeutic alternative for cutaneous leishmaniasis caused by L. (L) amazonensis.

Pomegranate (Punica granatum) Juice Shows Antioxidant Activity against Cutaneous Leishmaniasis-Induced Oxidative Stress in Female BALB/c Mice

Leishmania species are parasites that multiply within phagocytes and cause several clinical diseases characterized by single or multiple ulcerations. One of the complications that can induce tissue damage and the resulting scars is caused by secondary bacterial infections. Studies to find new, effective, and safe oral drugs for treating leishmaniasis are being conducted since several decades, owing to the problems associated with the use of antimonials available. Previously, the antiparasitic and antioxidant properties of Punica granatum (pomegranate, P. granatum) have been reported. Therefore, in the present study, we aimed to investigate the antileishmanial activity of pomegranate aqueous juice in vitro and in female BALB/c mice. A 3-(4.5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay in Leishmania major promastigotes and alterations in the antioxidant status, liver function, and skin histological changes in L. major-infected mice orally treated with pomegranate juice alone and in combination with the antibiotic ciprofloxacin, were used to investigate the in vitro and in vivo antileishmanial activity of pomegranate juice, respectively. Oral P. granatum juice treatment significantly reduced the average size of cutaneous leishmaniasis lesions compared with that of the untreated mice. This antileishmanial activity of P. granatum was associated with enhanced antioxidant enzyme activities. Histopathological evaluation proved the antileishmanial activity of P. granatum, but did not reveal changes in the treated animals, compared to the positive control. In conclusion, P. granatum shows high and fast antileishmanial activity probably by boosting the endogenous antioxidant activity.

Chemotherapy of leishmaniasis: present challenges

Cutaneous and visceral leishmaniasis are amongst the most devastating infectious diseases of our time, affecting millions of people worldwide. The treatment of these serious diseases rely on a few chemotherapeutic agents, most of which are of parenteral use and induce severe side-effects. Furthermore, rates of treatment failure are high and have been linked to drug resistance in some areas. Here, we reviewed data on current chemotherapy practice in leishmaniasis. Drug resistance and mechanisms of resistance are described as well as the prospects for applying drug combinations for leishmaniasis chemotherapy. It is clear that efforts for discovering new drugs applicable to leishmaniasis chemotherapy are essential. The main aspects on the various steps of drug discovery in the field are discussed.

Anti-Leishmanial Activity (In Vitro and In Vivo) of Allicin and Allicin Cream Using Leishmania major (Sub-strain Zymowme LON4) and Balb/c Mice

BACKGROUND

Leishmania is a unicellular protozoan parasite that produces several human diseases, ranging from localized self-healing cutaneous lesions to deadly visceral infections.

OBJECTIVE

The effect of allicin on the growth of Leishmania major (L. major) promastigotes was evaluated under in vitro conditions. Moreover, the efficacy of a topical allicin cream was examined in BALB/c (Bagg albino, laboratory-bred strain of the House Mouse) mice with cutaneous leishmanial lesions compared to the currently used drug, sodiumstibogluconate (pentostam).

METHODS

Cytotoxiciy and promastigote proliferation were measured. Different concentrations (50, 100, 150, and 200 μM) of liquid allicin were tested on L. major promastigotes twice: after 24 and 48 hours using an MTT colorimetric assay. In the in vivo condition, the efficacies of allicin cream and liquid allicin at two concentrations (0.15 μM/mouse and 0.30 μM/mouse) were evaluated. Serum factors of the control and treated groups were tested to evaluate the toxic effects of allicin on the liver and kidney.

RESULTS

Allicin at a concentration of 50 μM inhibited the growth of Leishmania promastigotes. Topical application of allicin cream reduced lesion sizes in mice. No significant differences in biochemical analysis were observed between the control and treated groups.

CONCLUSIONS

Allicin has antileishmanial effects under in vitro and in vivo conditions and may be used in clinical applications.

Migratory CD103+ dendritic cells suppress helminth-driven type 2 immunity through constitutive expression of IL-12

Everts et al. use Batf3^−/− mice to examine the role of Batf3-dependent CD8α⁺ and CD103⁺ DCs in Th2 immunity in response to helminth infection. Loss of Batf3-dependent DCs resulted in rapid control of normally chronic infection with Heligmosomoides polygyrus, whereas liver fibrosis was exacerbated with Schistosoma mansoni infection. Mechanistically, steady-state IL-12 production by migratory CD103⁺ DCs was found to antagonize Th2 responses.

CD8α⁺ and CD103⁺ dendritic cells (DCs) play a central role in the development of type 1 immune responses. However, their role in type 2 immunity remains unclear. We examined this issue using Batf3^−/− mice, in which both of these DC subsets are missing. We found that Th2 cell responses, and related events such as eosinophilia, alternative macrophage activation, and immunoglobulin class switching to IgG1, were enhanced in Batf3^−/− mice responding to helminth parasites. This had beneficial or detrimental consequences depending on the context. For example, Batf3 deficiency converted a normally chronic intestinal infection with Heligmosomoides polygyrus into an infection that was rapidly controlled. However, liver fibrosis, an IL-13–mediated pathological consequence of wound healing in chronic schistosomiasis, was exacerbated in Batf3^−/− mice infected with Schistosoma mansoni. Mechanistically, steady-state production of IL-12 by migratory CD103⁺ DCs, independent of signals from commensals or TLR-initiated events, was necessary and sufficient to exert the suppressive effects on Th2 response development. These findings identify a previously unrecognized role for migratory CD103⁺ DCs in antagonizing type 2 immune responses.

Studies on the protective efficacy of second-generation vaccine along with standard antileishmanial drug in Leishmania donovani infected BALB/c mice

It is well established that visceral leishmaniasis (VL; also known as Kala azar) causes immunosuppression, and a successful drug treatment is associated with the development of cell-mediated immunity. Therefore combining a drug with an immune enhancer can provide a better approach for the treatment of the disease. Keeping this in mind, the in vivo antileishmanial efficacy of immunochemotherapy was evaluated with the use of a 78 kDa antigen with or without monophosphoryl lipid A (MPL-A) along with a traditional drug sodium stibogluconate (SSG) in Leishmania donovani infected BALB/c mice. Mice were infected intracardially with promastigotes of L. donovani, and 30 days after infection, these animals were given specific immunotherapy (78 kDa/78 kDa+MPL-A) or chemotherapy (SSG) or immunochemotherapy (SSG+78 kDa/SSG+78 kDa+MPL-A). Animals were euthanased on 1, 15 and 30 post-treatment days. The antileishmanial potential of the immunochemotherapy was revealed by significant reduction in the parasite burden (P<0·001). These animals were also found to exhibit increased delayed type hypersensitivity (DTH) responses, higher IgG2a levels, lower IgG1 levels and greater cytokine (IFN-γ and IL-2) concentrations compared with chemotherapy or immunotherapy alone, pointing towards the generation of a strong protective (Th1) type of immune response. Immunochemotherapy with SSG+78 kDa+MPL-A was found to be most effective in protecting mice against VL and therefore can be an alternative option for treatment of VL.

Combination therapy with paromomycin-associated stearylamine-bearing liposomes cures experimental visceral leishmaniasis through Th1-biased immunomodulation

Visceral leishmaniasis (VL) caused by the parasite Leishmania donovani is a potentially fatal disease. Available limited drugs are toxic, require prolonged treatment duration, and are costly. A low-cost parenteral formulation of paromomycin sulfate (PM) has recently been approved for the treatment of VL. Monotherapy with PM runs the risk of development of resistance. Hence, efforts are needed to develop a combination therapy of PM with other drugs to shorten the duration of treatment and prolong the effective life of the drug. PM was formulated with leishmanicidal stearylamine (SA)-bearing phosphatidylcholine (PC) liposomes for low-dose therapy. In vitro and in vivo antileishmanial effects of the combination drug were determined. The immunomodulatory role of PC-SA-PM was determined using enzyme-linked immunosorbent assay (ELISA) and flow cytometry. Excluding the spleen, for which the therapeutic effect was additive, a remarkable synergistic activity toward cure and prophylaxis with a single-shot low-dose treatment with PC-SA-associated PM was achieved with BALB/c mice. PC-SA-PM showed an immunomodulatory effect on CD4(+) and CD8(+) T cells for gamma interferon (IFN-γ) production and downregulated disease-associated interleukin-10 (IL-10) and transforming growth factor β (TGF-β) to almost negligible levels. Such combination chemotherapy may provide a promising alternative for the cure of leishmaniasis, with a plausible conversion of the host immune response from a disease-promoting pattern to a Th1-biased response indicative of long-term resistance.

Applying TLR synergy in immunotherapy: implications in cutaneous leishmaniasis

Therapy of intracellular pathogens can be complicated by drug toxicity, drug resistance, and the need for prolonged treatment regimens. One approach that has shown promise is immunotherapy. Leishmaniasis, a vector-borne disease ranked among the six most important tropical infectious diseases by the World Health Organization, has been treated clinically with crude or defined vaccine preparations or cytokines, such as IFN-gamma and GM-CSF, in combination with chemotherapy. We have attempted to develop an improved and defined immunotherapeutic using a mouse model of cutaneous leishmaniasis. We hypothesized that immunotherapy may be improved by using TLR synergy to enhance the parasite-specific immune response. We formulated L110f, a well-established Leishmania poly-protein vaccine candidate, in conjunction with either monophosphoryl lipid A, a TLR4 agonist, or CpG, a TLR9 agonist, or a combination of these, and evaluated anti-Leishmania immune responses in absence or presence of active disease. Only mice treated with L110f plus monophosphoryl lipid A-CpG were able to induce a strong effective T cell response during disease and subsequently cured lesions and reduced parasite burden when compared with mice treated with L110f and either single adjuvant. Our data help to define a correlate of protection during active infection and indicate TLR synergy to be a potentially valuable tool in treating intracellular infections.

Effect of gamma radiation on cytokine expression and cytokine-receptor mediated STAT activation

PURPOSE

The expression of cytokine mRNA and their related transcription factors was examined in order to assess the effects of gamma radiation on the immune function of murine splenocytes.

MATERIALS AND METHODS

Splenocytes were collected from seven-week-old female Balb/c mice, and then irradiated at a dose of 5 Gy of 60Co gamma-ray at a dose rate of 1.394 Gy/min. Total RNA was extracted from both irradiated and non-irradiated splenocytes at 1/2, 1, 3, 6, and 24 h and analysed by reverse transcription-polymerase chain reaction (RT-PCR).

RESULTS

The mRNA level of interferon (IFN)-gamma, which is a Th1-type (T helper cell type 1) cytokine, was reduced after 3 h post-irradiation, whereas the interleukin (IL)-2 mRNA in the naïve splenocytes had no significant changes within the 24 h after irradiation. Moreover, IFN-gamma and IL-2 mRNA expression in concanavalin A (Con A, 2.5 mug/ml) activated-splenocytes was significantly reduced by gamma irradiation. On the other hand, the mRNA level of the Th2 type (T helper cell type 2) cytokines, such as IL-4, IL-5 and IL-10, was increased both in naïve and activated splenocytes, and pro-inflammatory cytokines were also rapidly induced in response to irradiation in naïve splenocytes. Interestingly, gamma irradiation had no effect on transforming growth factor (TGF)-beta mRNA expression. Moreover, the mRNA levels of the leucine zipper trqnscription factor c-Maf and GATA binding protein-3 (GATA-3), which regulate IL-4 and IL-5 transcription, were found to have been up-regulated. However, the mRNA coding for interferon regulatory factor (IRF)-1, which is involved in IFN-gamma production, was reduced 6 h post-irradiation. The level of signal transducers and activators of transcription (Stat)-1 and Stat-4 phosphorylation, which are activated by IFN-gamma and IL-12, respectively, was significantly reduced by gamma irradiation, but IL-4 receptor mediated Stat-6 activation remained unchanged.

CONCLUSIONS

These results suggest that gamma irradiation may play a role in Th1 and Th2 cytokine expression, via regulation of the level of cytokine-mediators through transcriptional modulation and Stat signaling. These results are helpful to understand general profile of cytokine expression in response to gamma irradiation.

Low dose oral administration of cytokines for treatment of allergic asthma

Many inflammatory diseases are characterized by an imbalance among lymphocyte populations, in particular Th1, Th2 and the recently described Th17 cells. The Th1/Th2 imbalance is linked to many factors, but certainly the role of cytokines is essential. In Th2 diseases IL-4 expression is predominant, while Th1 pathologies are characterized by high expression of IFN-gamma and IL-12. Though today the therapeutical proposal for many inflammatory diseases aims to re-establish normal levels of Th1/Th2 cytokines, the pharmacological use of cytokines, which are very active molecules, is limited by the possible collateral effects. Therefore, our study aims to determine, in a murine model of allergic asthma, the possible therapeutic activity of low dose cytokines solutions, mechanically activated. We found that oral administration of low doses IL-12 plus IFN-gamma is able to solve the bronchial hyperresponsiveness condition of mice, establishing normal cytokine levels. The anti-asthma activity was confirmed by histological analysis of lungs and broncho-alveolar lavage fluid cell count. Serum ovalbumin-specific IgE was also significantly inhibited by treatment with low dose activated cytokines solution. These findings may suggest a novel approach to diseases which involve a Th1/Th2 imbalance.

The central memory CD4+ T cell population generated during Leishmania major infection requires IL-12 to produce IFN-gamma

Central memory CD4(+) T cells provide a pool of lymph node-homing, Ag-experienced cells that are capable of responding rapidly after a secondary infection. We have previously described a population of central memory CD4(+) T cells in Leishmania major-infected mice that were capable of mediating immunity to a secondary infection. In this study, we show that the Leishmania-specific central memory CD4(+) T cells require IL-12 to produce IFN-gamma, demonstrating that this population needs additional signals to develop into Th1 cells. In contrast, effector cells isolated from immune mice produced IFN-gamma in vitro or in vivo in the absence of IL-12. In addition, we found that when central memory CD4(+) T cells were adoptively transferred into IL-12-deficient hosts, many of the cells became IL-4 producers. These studies indicate that the central memory CD4(+) T cell population generated during L. major infection is capable of developing into either Th1 or Th2 effectors. Thus, continued IL-12 production may be required to ensure the development of Th1 cells from this central memory T cell pool, a finding that has direct relevance to the design of vaccines dependent upon central memory CD4(+) T cells.

Reversal of polarized T helper 1 and T helper 2 cell populations in murine leishmaniasis

T helper 1 (Th1) and Th2 cells are the major subsets of fully differentiated CD4+ T cells in the mouse. The spectrum of cytokines characteristic of each subset determines the distinctive regulatory and effector functions mediated by each subset. We have used the murine model of Leishmania major infection to study the question of whether highly polarized populations of normal T cells are as stable in their cytokine phenotype as Th clones or whether the phenotype can be altered with regulatory cytokines. Interleukin 4 (IL-4) appears to be a key cytokine for Th2 responses as it is necessary for both the initial differentiation of Th responses to L. major and the stability of ongoing responses. Furthermore, IL-4 is capable of converting highly polarized Th1 responses to Th2 responses either in vitro or when adoptively transferred to severe combined immunodeficiency mice.

The two faces of interleukin 12: a pro-inflammatory cytokine and a key immunoregulatory molecule produced by antigen-presenting cells

Interleukin 12 (IL-12) is produced by phagocytic cells, antigen-presenting cells and B lymphocytes in response to bacteria or intracellular parasites. IL-12 acts on T and natural killer (NK) cells inducing: production of cytokines, particularly gamma-interferon (IFN-gamma); proliferation; and enhancement of cell-mediated cytotoxicity. Early in infection, IL-12 acts as a proinflammatory cytokine and induces IFN-gamma production by NK and T cells. IFN-gamma activates the phagocytes and increases their ability to produce IL-12. Unlike IFN-gamma, IL-10, IL-4, IL-13 and transforming growth factor beta are negative regulators of the production and activity of IL-12. IL-12 sets the stage for the ensuing adaptive immune response by stimulating the generation of T helper 1 (Th1) cells. It is likely that the balance between IL-12 (favouring a Th1 response) and IL-4 (favouring a Th2 response) determines the eventual outcome of the Th1/Th2 dichotomy during an immune response. HIV-infected patients have a deficient production of IL-12, even at early stages of the disease. However, exogenous IL-12 can improve the deficient immune responsiveness of these patients' T and NK cells in vitro, suggesting a possible role of the IL-12 deficiency in HIV disease pathogenesis and a potential therapeutic role of IL-12 both against opportunistic pathogens and HIV infection itself.

Decision‐making by the immune response

Decisions by uncommitted cells to differentiate down one lineage pathway or another is fundamental to developmental biology. In the immune system, lymphocyte precursors commit to T- or B-cell lineages and T-cell precursors to CD4 or CD8 independently of foreign antigen. T and B cells must also decide whether or not to respond to antigen and when a response is initiated, what sort of response to make such as the type of antibody, CD4 or CD8, and CD4 Th1 or Th2. The two basic mechanisms for these decision-making processes are selection and instruction. Selection depends on prior stochastic production of precommitted cells, which are then selected to respond by an appropriate signal; for example, CD8 and CD4 responses selected by peptide presented in association with major histocompatibility complex class I or II. In contrast, instruction occurs when an uncommitted precursor embarks upon a differentiation pathway in response to a particular set of signals; for example, Th1 and Th2 lineage commitment. In this paper, the signals that determine Th1 and Th2 differentiation are examined with a mathematical model and shown to act as a bistable switch permitting either Tbet or Gata3 to be expressed in an individual cell but not both. The model is used to show how the Tbet Gata3 network within an individual cell interacts with cytokine signals between cells and suggests how Th1 and Th2 lineage commitment can become irreversible. These considerations provide an example of how mathematical models can be used to gain a better understanding of lymphocyte differentiation in an immune response.

Cutaneous Leishmania infection: progress in pathogenesis research and experimental therapy

Studies in murine experimental Leishmania major infection have helped to understand the requirements for efficient development of T helper (Th)1/cytotoxic T (Tc)1-mediated protection against the parasite. As such they have revealed that Fc gamma receptor (Fc gamma R)I and Fc gamma RIII-mediated uptake of L. major amastigotes by dendritic cells (DC) is an important prerequisite for Th1 development. In addition, DC-derived cytokines contribute to adequate T-cell education. DC-based vaccines may thus provide an important tool for both the development of a prophylactic vaccine against leishmaniasis and - together with leishmanicidal drugs - for eliciting immune-deviating functions towards protective immunity in non-healing leishmaniasis. This review highlights recent advances in the understanding of the role of DC for the induction of Th1/Tc1-predominant immunity against L. major and how this knowledge may translate into clinical approaches.

Nanodisk-associated amphotericin B clears Leishmania major cutaneous infection in susceptible BALB/c mice

Nanometer-scale, apolipoprotein-stabilized phospholipid bilayer disk complexes (nanodisks [ND]) harboring the toxic and poorly soluble antileishmanial agent amphotericin B (AMB) were examined for efficacy in treatment of Leishmania major-infected BALB/c mice (Mus musculus). L. major-infected mice were intraperitoneally (i.p.) treated with AMB-ND in 0-, 1-, and 5-mg/kg doses at 24 h, 48 h, and 4, 7, 14, and 21 days postinfection in two experiments. L. major-infected mice were i.p. treated with phosphate-buffered saline, 5 mg/kg AMB-ND, or 5 mg/kg lipid-associated amphotericin B (liposomal amphotericin B, AmBisome) at 24 h, 48 h, and 10, 20, 30, and 40 days postinfection in one experiment. Parasite numbers, footpad lesion size progression, and development of cytokine responses were assayed at days 7, 15, 30, 50, 140, and 250 or at days 14, 30, 50, 95, and 140 postinfection. Mice administered AMB-ND in 1- or 5-mg/kg doses were significantly protected from L. major, displaying decreases in lesion size and parasite burden, particularly at the 5-mg/kg dosage level. In contrast to the i.p. treated AmBisome group, BALB/c mice treated with i.p. AMB-ND completely cleared an L. major infection by 140 to 250 days postinfection, with no lesions remaining and no parasites isolated from infected animals. Restimulated mixed lymphocyte culture cytokine responses (interleukin-4 [IL-4], IL-12, IL-10, NO, and gamma interferon) were unchanged by AMB-ND administration compared to controls. The marked clearance of Leishmania parasites from a susceptible strain of mice without an appreciable change in the cytokine response suggests that AMB-ND represent a potentially useful formulation for treatment of intrahistiocytic organisms.

Novel compounds active against Leishmania major

Leishmania major is an important trypanosomatid pathogen that causes leishmaniasis, which is a serious disease in much of the Old World. Current treatments include a small number of antimony compounds that, while somewhat effective, are limited by serious side effects. We have screened a small portion of a unique chemical library and have found at least three novel compounds that are effective against L. tarentolae and L. major in vitro and in a murine macrophage model of L. major infection. These compounds were effective in both assays at doses significantly lower than those of sodium stibogluconate (Pentostam) and represent possible candidates for drug development.

Lamivudine plus interleukin-12 combination therapy in chronic hepatitis B: antiviral and immunological activity

Interleukin-12 (IL-12) is an immunomodulatory cytokine that promotes cellular immunity. Pre-clinical data suggest that IL-12 inhibits hepatitis B virus (HBV) replication by stimulating interferon-gamma (IFN-gamma) production. We investigated whether a combination treatment with lamivudine plus recombinant human interleukin-12 (rhIL-12) will result in a greater and prolonged suppression of HBV replication in comparison with lamivudine monotherapy. Fifteen patients with HBeAg-positive chronic hepatitis B were randomized to receive either lamivudine alone for 24 weeks (group 1); combination of lamivudine for 16 weeks and rhIL-12 (200 ng/kg twice weekly), starting 4 weeks after initiation of lamivudine, for 20 weeks (group 2), or the same schedule as for group 2, with lamivudine and a higher dose of rhIL-12 (500 ng/kg, group 3). Serum HBV DNA levels, T-cell proliferation, frequency of virus-specific T-cells, and IFN-gamma production were evaluated serially during and 24 weeks posttreatment. Lamivudine plus rhIL-12/500 showed greater antiviral activity than lamivudine monotherapy. However, after stopping lamivudine in groups 2 and 3, serum HBV DNA increased significantly despite continuing rhIL-12 administration. Lamivudine plus rhIL-12 treatment was associated with a greater increase in virus-specific T-cell reactivity, IFN-gamma production, and an inverse correlation between the frequency of IFN-gamma-producing CD4+ T-cells and viremia. The T-cell proliferative response to HBcAg did not differ between the three groups. In conclusion, the addition of IL-12 to lamivudine enhances T-cell reactivity to HBV and IFN-gamma production. However, IL-12 does not abolish HBV replication in HBeAg-positive patients and does not maintain inhibition of HBV replication after lamivudine withdrawal.

Immunology and mathematics: crossing the divide

'It's high time molecular biology became quantitative, it cries out to a physicist ... for modeling. Modeling isn't a crutch, it's the opposite; it's a way of suggesting experiments to do, to fill gaps in your understanding.' John Maddox, Editor of Nature 1966-73, and 1980-95.

Regulatory mechanisms and their therapeutic implications of interleukin-12 production in immune cells

Studies with neutralizing anti-interleukin (IL)-12 antibodies and IL-12-deficient mice have suggested that endogenous IL-12 plays an important role in the normal host defense against infection by a variety of intracellular microorganisms. However, IL-12 also appears to play a central role in the pathogenesis of autoimmune diseases such as multiple sclerosis or rheumatic arthritis. Therefore, it is crucial to understand how IL-12 is produced and its production is regulated at the molecular level. IL-12 production is differentially regulated through multiple pathways, which can be classified as follows: nuclear factor-kappaB (NF-kappaB) and other transcription factors, p38 mitogen-activated protein (MAP) kinase, cyclic adenosine monophosphate (cyclic AMP)-modulating molecules, cell membrane ion channels and pumps, nitric oxide (NO), and receptors. In this review we describe the regulatory mechanisms of IL-12 production in immune cells and also some agents to control IL-12 production for the treatment of immune-related diseases.

Intratumoral administration of recombinant human interleukin 12 in head and neck squamous cell carcinoma patients elicits a T-helper 1 profile in the locoregional lymph nodes

The objective of this Phase II study was to evaluate the pharmacodynamic and immune effects of intratumorally administered recombinant human interleukin-12 (IL-12) on regional lymph nodes, primary tumor, and peripheral blood. Ten previously untreated patients with head and neck squamous cell carcinoma were injected in the primary tumor two to three times, once/week, at two dose levels of 100 or 300 ng/kg, before surgery. We compared these patients with 20 control (non-IL-12-treated) patients. Toxicity was high, with unexpected dose-limiting toxicities at the 300 ng/kg dose level. Dose-dependent plasma IFN-gamma and IL-10 increments were detected. These cytokine levels were higher after the first injection than after the subsequent injections. A rapid, transient reduction in lymphocytes, monocytes, and all lymphocyte subsets, especially natural killer cells, was observed, due to a redistribution to the lymph nodes. In the enlarged lymph nodes of the IL-12-treated patients, a higher percentage of natural killer cells and a lower percentage of T-helper cells were found compared with control patients. The same pattern was detected in the infiltrate in the primary tumor. Real-time semiquantitative PCR analysis of peripheral blood mononuclear cells in the peripheral blood showed a transient decrease of T-bet mRNA. Interestingly, the peripheral blood mononuclear cells in the lymph nodes showed a 128-fold (mean) increase of IFN-gamma mRNA. A switch from the Th2 to a Th1 profile in the lymph nodes compared with the peripheral blood occurred in the IL-12-treated patients. In conclusion, in previously untreated head and neck squamous cell carcinoma patients, recombinant human IL-12 intratumorally showed dose-limiting toxicities at the dose level of 300 ng/kg and resulted in measurable immunological responses locoregionally at both dose levels.

The development of effector and memory T cells in cutaneous leishmaniasis: the implications for vaccine development

Leishmania major infections induce the development of a CD4(+) T-helper 1 (Th1) response that not only controls the primary infection but also results in life-long immunity to reinfection. How that immunity is maintained is unknown, although because of the existence of infection-induced immunity, there has been an assumption that the development of a vaccine against leishmaniasis would be relatively easy. This has turned out not to be the case. One problem has been the finding that a large part of the immunity induced by a primary infection depends upon the presence of persistent parasites. Nevertheless, there are ample situations where immunologic memory persists without the continued presence of antigen, providing the prospect that a non-live vaccine for leishmaniasis can be developed. To do so will require an understanding of the events involved in the development of an effective protective T-cell response and, more importantly, an understanding of how to maintain that response. Here, we review work from our laboratory, describing how Th1 cells develop in L. major-infected mice, the nature of the memory T cells that provide protection to reinfection, and how that information may be utilized in the development of vaccines.

Promising immunotherapies with Th1-related cytokines against infectious diseases

In recent years, there has been an increase in the number of individuals with compromised immune systems. This is due to the rise in the numbers of aging people, patients receiving immunosuppressive treatment after organ transplantation, patients with hematological malignancies, and patients with AIDS. These individuals frequently fall into helper T cell (Th)1-Th2 cytokine imbalance due to a shift towards a Th2-dominant condition. Such a pathological condition puts them at a high risk for developing infectious diseases caused by a variety of microbial pathogens which are often refractory to conventional chemotherapy. Therefore, the administration of Th1-related cytokines is expected to be promising immunotherapy against these intractable infectious diseases. In a series of investigations, we have demonstrated the effectiveness of treatment with Th1-related cytokines, such as interferon (IFN)-gamma, interleukin (IL)-12, and IL-18, in protecting animals from experimental infectious diseases caused by Mycobacterium tuberculosis and Cryptococcus neoformans. Recently, several investigators reported successful clinical treatment with IFN-gamma or IL-12 in patients with intractable tuberculous and nontuberculous mycobacteriosis. Thus, now is an appropriate time for scientific evaluation to clinically confirm the effectiveness of these novel immunotherapies.

STAT1 and STAT3 alpha/beta splice form activation predicts host responses in mouse hepatitis virus type 3 infection

Signal transducer and activator of transcription 1alpha (STAT1 alpha) is reported to be essential for IFN-gamma and IFN-alpha regulated gene expression, while STAT1 beta, an alternate splice-form, mediates only IFN-alpha-dependent gene expression. STAT3 alpha and STAT3 beta splice forms are also differentially activated in response to cytokines including IL-6 and IL-10. The aim of this study was to investigate whether the STAT activation will predict the host immune response to viral infection and possibly a therapeutic target for the treatment of viral infection. Mouse hepatitis virus type 3 (MHV-3) resistant strain (A/J) and sensitive mouse strains (BalB/cJ) were infected intraperitoneally (i.p.) with 100 plaque form units (pfu) of MHV-3. The mice were sacrificed at the indicated times, and livers and spleens were immediately frozen in liquid nitrogen. Nuclear extracts proteins were detected by immunoblotting. STAT1 and STAT3 activation in spleen increased 24 to 72 hr following MHV-3 infections in both sensitive and resistant mouse strains. However, over this time period, the ratio of activated alpha to beta splice-form for STAT1 and STAT3 increased above 1.0 in resistant A/J mice, while the ratio fell to <0.3 in MHV-3 sensitive Balb/cJ and C3H/HeJ strains. Activated STAT1 alpha/beta and STAT3 alpha/beta ratio in liver were similar in resistant and sensitive mouse strains. Treatment of sensitive Balb/cJ mice with neutralizing anti-TGF-beta antibody could increase the STAT1 alpha/beta ratio to <1.0 in spleens, predicting enhanced rates of survival. These results suggested that ratio of activated STAT1 alpha/beta and STAT3 alpha/beta in mixed leukocytes from spleen predict the outcome to MHV-3 infection, and may be an important marker and therapeutic target for modification of host immune response to virus infection.

Adaptive immunity to nontypeable Haemophilus influenzae

Nontypeable Haemophilus influenzae (NTHi) colonizes the upper respiratory tract of most healthy people and is also a major cause of infection in chronic obstructive lung disease. The immune response to this bacterium has not been well characterized. We tested the hypothesis that recurrent airway infection with NTHi may be associated with nonclearing adaptive immunity. Study subjects were healthy control subjects and patients with idiopathic bronchiectasis who had severe chronic infection with H. influenzae. We established that all subjects in both groups had detectable antibody to NTHi, suggesting that most normal people have developed an adaptive immune response. To characterize the nature of the immune response, we measured antigen-specific production of T helper cell cytokines and CD40 ligand by flow cytometry and immunoglobulin subclass levels in peripheral blood. We found that normal control subjects made Th1 response to NTHi with distinct CD40 ligand production. In contrast, subjects with bronchiectasis had predominant production of Th2 cytokines, decreased expression of CD40 ligand, and different immunoglobulin G subclass production. Therefore, chronic infection with NTHi in bronchiectasis is associated with a change in adaptive immunity that may be important in the pathogenesis of bronchial infection.

Combined treatment with interleukin-12 and indomethacin promotes increased resistance in BALB/c mice with established Leishmania major infections

Following infection of susceptible BALB/c mice with Leishmania major, early production of interleukin-4 (IL-4) is associated with the development of a nonprotective Th2 response and the development of progressive disease. Treatment of mice with IL-12 at the time of infection can promote the activation of a protective Th1 response; however, IL-12 treatment of mice with established infections has little effect on the progress of lesion development. This may be due to a down-regulation of the IL-12 receptor beta2 chain (IL-12Rbeta2) that accompanies the expansion of IL-4-producing Th2 cells. We have examined whether prostaglandins function to regulate in vivo responsiveness to IL-12. Mice treated with indomethacin are responsive to treatment with exogenous IL-12 through at least the first 2 weeks of infection and, unlike control mice treated with IL-12, develop an enhanced Th1-type response associated with increased enhanced resistance to infection. Cells from indomethacin-treated mice also exhibit enhanced production of gamma interferon (IFN-gamma) following in vitro stimulation with IL-12. Although in vivo indomethacin treatment did not appear to influence IL-12 production in infected mice, cells from indomethacin-treated mice did express higher levels of IL-12Rbeta2, suggesting that prostaglandins may play a role in the loss of IL-12 responsiveness observed during nonhealing L. major infections.

Skin-derived macrophages from Leishmania major-susceptible mice exhibit interleukin-12- and interferon-gamma-independent nitric oxide production and parasite killing after treatment with immunostimulatory DNA

Co-administration of CpG-containing immunostimulatory oligodeoxynucleotides and parasite antigen protects susceptible BALB/c mice from otherwise progressive infection with Leishmania major. Although the protective effect of CpG-containing immunostimulatory oligodeoxynucleotides is clearly dependent on endogenous interleukin-12 and interferon-gamma production, the source of these Th1-promoting cytokines in infected mice is unknown. In contrast to macrophages from Leishmania-resistant C57BL/6 mice, macrophages from susceptible BALB/c mice are hyporesponsive to stimulation with lipopolysaccharide and interferon-gamma. While studying interactions of various antigen-presenting cells with Leishmania, we found that BALB/c inflammatory skin macrophages, whether Leishmania-infected or uninfected, produced large amounts of interleukin-12 when treated with CpG-containing immunostimulatory oligodeoxynucleotides. Like lipopolysaccharide, CpG-containing immunostimulatory oligodeoxynucleotides induced production of interferon-gamma and release of nitric oxide by skin macrophages. Studies using skin macrophages from interleukin-12- and interferon-gamma-deficient BALB/c mice demonstrated that nitric oxide release was not dependent on interleukin-12 and interferon-gamma production. Approximately 44% and 27% of intracellular Leishmania major amastigotes were killed by infected skin macrophages within 72 h upon stimulation with CpG-containing immunostimulatory oligodeoxynucleotides and lipopolysaccharide, respectively. Parasite killing by macrophages was independent of endogenous interferon-gamma production, but was strongly enhanced by exogenous interferon-gamma. Parasite elimination was dependent on the induction of nitric oxide, however. In vivo, injection of CpG-containing immunostimulatory oligodeoxynucleotides into lesional skin reduced the parasite burden approximately 50-fold within the first 5 d of infection prior to full generation of a Th response. These results suggest that skin macrophages, constituting the principal reservoir of parasites in infected susceptible mice, produce Th1-promoting cytokines in response to CpG-containing immunostimulatory oligodeoxynucleotides. In addition, CpG-containing immunostimulatory oligodeoxynucleotides may also act locally on skin macrophages to facilitate Leishmania clearance by inducing nitric oxide production.

In vitro activities of iboga alkaloid congeners coronaridine and 18-methoxycoronaridine against Leishmania amazonensis

In previous studies, we demonstrated the leishmanicide effect of coronaridine, a natural indole alkaloid isolated from stem bark of Peschiera australis (Delorenzi et al., Antimicrob. Agents Chemother. 45:1349-1354, 2001). In this study we show the leishmanicidal effect of the synthetic coronaridine and its racemic 18-methoxylated analog, 18-methoxycoronaridine. Both alkaloids revealed a potent leishmanicide effect against Leishmania amazonensis, a causative agent of cutaneous and diffuse cutaneous leishmaniasis in the New World. Despite their potent leishmanicide effect, both alkaloids were neither toxic to murine macrophages nor did they modulate their oxidative or cytokine production responses.

Immunoregulation of CNS autoimmunity by helminth and mycobacterial infections

The 'hygiene hypothesis' has been proposed to explain apparent increases in autoimmune disease and allergy in areas of the world with improved health care and sanitation. This hypothesis proposes that the lack of serious childhood infections impairs development of an appropriately educated immune response. Imbalance of Th1 and Th2 responses and lack of regulatory T-cell populations are two of many proposed potential mechanisms for immune failures such as autoimmunity and allergy. We summarize the literature evidence for the influence of infectious organisms on autoimmunity with focus on helminth and mycobacterial infections. We also demonstrate that Schistosoma mansoni ova pretreatment, Mycobacterium bovis (BCG) infection, and lyophilized Mycobacterium tuberculosis all modify the course of clinical disease in mice induced for experimental autoimmune encephalomyelitis (a mouse model for human multiple sclerosis (MS)). Our data supports the applicability of the hygiene hypothesis to CNS autoimmune disease.

Novel approaches for the treatment of food allergy

At present there is no effective therapy for IgE-mediated food allergy, and patients must rely upon food-allergen avoidance. Unfortunately, the accidental ingestion of allergen-containing foods leading to potentially severe reactions is common. Definitive therapies for food allergy are desperately needed. Although rush immunotherapy has been reported to induce tolerance in some patients, the rate of maintenance of tolerance was low, and there was an undesirably high incidence of adverse reactions. New knowledge of the immunological mechanisms underlying allergic disease has expanded the potential therapeutic options for food allergy. The establishment of animal models of food hypersensitivity, which include sensitization by the oral route and anaphylaxis upon oral challenge, have facilitated the investigation of therapies for food allergy. Novel approaches under investigation include the reduction of IgE by the infusion of anti-IgE antibodies, vaccination with plasmid DNA, the use of anti-allergy immunostimulatory sequences, cytokines and bacterial agents, immunotherapy with mutated proteins and peptides, and complementary medicine such as Chinese herbs.

Stimulation of both humoral and cellular immune responses to HIV-1 gp120 by interleukin-12 in Rhesus macaques

The adjuvant effect of recombinant Rhesus macaque interleukin-12 (RhIL-12) on the induction of cellular and humoral immune responses elicited by the HIV-1 subunit vaccine protein gp120 in Rhesus macaques was examined. RhIL-12 in conjunction with gp120 was given at day 0, 28 and 84 intramuscularly. Coadministration resulted in an approximate 10-fold increase in plasma anti-gp120 antibody levels as compared to levels generated in control monkeys receiving gp120 alone. Potentiation of the humoral arm of the immune response was evident by both ELISA and an antiviral bioassay. In addition, RhIL-12 was found to produce a significant increase in gp120-specific proliferative responses and in the frequency of antigen-specific IFN-gamma and IL-2 producing T cells after restimulation of PBMC with gp120 in vitro indicating that RhIL-12 potentiates cell-mediated immune responses as well. A critical finding was that during the course of the study, RhIL-12 did not induce a neutralizing antibody response to the administered cytokine. The doses of RhIL-12 were well tolerated and no detectable adverse side-effects on hematopoietic and hepatic parameters were noted. The data revealed that IL-12, when coadministered intramuscularly, acts as a potent adjuvant which is able to enhance not only cellular but also humoral immune responses to gp120 in non-human primates and may have to be considered in future HIV vaccine strategies.

Influence of parasite load on the ability of type 1 T cells to control Leishmania major infection

BALB/c mice infected with Leishmania major developed a type 2 immune response which failed to control parasite replication. We found that scid mice that received splenocytes from BALB/c mice that had been infected for 3 weeks with L. major (a type 2 cell population) and that were subsequently infected with L. major were protected when they were treated with interleukin 12 (IL-12). In contrast, IL-12 was ineffective at protecting BALB/c mice infected for 3 weeks, suggesting that a high parasite load regulates the development of protective immunity. To determine how this regulation operates, we performed a series of adoptive transfers of naïve, type 1 or type 2 splenocytes into scid mice. The recipient scid mice were infected either for 5 weeks prior to cell transfer (and thus had a high parasite load) or at the time of cell transfer. scid mice that were infected for 5 weeks and received a type 1 cell population were able to cure their lesions. However, when 5-week-infected scid mice received both type 1 and 2 cell populations, they were unable to control their infections. In contrast, the same type 1 and 2 cells transferred to naïve scid mice, which were subsequently infected, provided protection. In addition, we found that naïve cells mediated protection in scid mice with established lesions. These results show that high parasite numbers do not block type 1 protective responses or the development of type 1 responses. Instead, the influence of a high parasite load is dependent on the presence of a type 2 cell population.

Oral administration of IL-12 suppresses anaphylactic reactions in a murine model of peanut hypersensitivity

There is no satisfactory therapeutic intervention for peanut allergy, which accounts for most life-threatening food allergic reactions. Since IL-12 has been found to inhibit allergic airway responses in a mouse model of asthma and to cure Th2 cytokine-mediated murine schistosomiasis, we hypothesized that IL-12 treatment might also inhibit peanut allergic reactions. Consequently, we investigated the effects of oral IL-12 treatment in a murine model of peanut allergy and found that oral administration of liposome encapsulated rIL-12 could both prevent and reverse peanut hypersensitivity and could reduce histamine release, peanut-specific serum IgE and IgG1, and fecal IgA levels. Oral IL-12 treatment also increased IFN-gamma but did not decrease IL-4 or IL-5 levels. We conclude that oral rIL-12 treatment has therapeutic as well as preventive effects on peanut allergy, which are associated with increased IFN-gamma production.

Differentiation of resting human peripheral blood gamma delta T cells toward Th1- or Th2-phenotype

Depending on the microenvironment, murine gamma delta T cells differentiate into either Th1 (IFN-gamma-producing) or Th2 (IL-4-producing) cells. It is unclear, however, whether circulating human peripheral blood gamma delta T cells can be driven into Th1 or Th2 cells by modulation of the priming cytokine milieu. In this study, peripheral blood gamma delta T cells were stimulated by phosphoantigen (isopentenyl pyrophosphate) or Daudi lymphoma cells in the presence of Th1-priming (rIL-12, anti-IL-4 Ab) or Th2-priming (rIL-4, anti-IL-12 Ab) conditions. Single-cell analysis of cytokine secretion (IFN-gamma and IL-4) was performed by flow cytometry after 18 h and after restimulation of expanded gamma delta T cells. The early activation of resting gamma delta T cells was characterized by the induction of IFN-gamma. Priming under Th1 conditions induced a Th1 profile characterized by increased secretion of IFN-gamma and TNF-alpha, while Th2 conditions caused increased production of IL-4 (Th2 profile) by the gamma delta T cells. These results indicate that the major subset of human gamma delta T cells can be polarized into either Th1 or Th2 cytokine pattern depending on the cytokine milieu in which contact with antigen occurs.

Immunochemotherapy in American cutaneous leishmaniasis: immunological aspects before and after treatment

In this study, we evaluated the immune response of patients suffering from cutaneous leishmaniasis treated with two distinct protocols. One group was treated with conventional chemotherapy using pentavalent antimonium salts and the other with immunochemotherapy where a vaccine against cutaneous leishmaniasis was combined with the antimonium salt. Our results show that, although no differences were observed in the necessary time for complete healing of the lesions between the two treatments, peripheral blood mononuclear cells from patients treated by chemotherapy showed smaller lymphoproliferative responses at the end of the treatment than those from patients in the immunochemotherapy group. Furthermore, IFN-gamma production was also different between the two groups. While cells from patients in the chemotherapy group produced more IFN-gamma at the end of treatment, a significant decrease in this cytokine production was associated with healing in the immunochemotherapy group. In addition, IL-10 production was also less intense in this latter group. Finally, an increase in CD8+ -IFN-gamma producing cells was detected in the chemotherapy group. Together these results point to an alternative treatment protocol where healing can be induced with a decreased production of a potentially toxic cytokine.

Modulation of host responses to blood-stage malaria by interleukin-12: from therapy to adjuvant activity

This review focuses on the role of interleukin (IL)-12, a proinflammatory cytokine with pleiotropic effects as a potent immunoregulatory molecule and hematopoietic growth factor, in infection with Plasmodium parasites, the causative agents of malaria. IL-12 has been demonstrated to have profound effects on the immune response to blood-stage malaria, to induce protection, and to alleviate malarial anemia. In combination with an anti-malarial drug, IL-12 is effective in an established malaria infection. This cytokine also has potent immune effects as a malaria vaccine adjuvant. However, IL-12 can also mediate pathology during blood-stage malaria.

Type 1/Type 2 immunity in infectious diseases

T helper type 1 (Th1) lymphocytes secrete secrete interleukin (IL)-2, interferon-gamma, and lymphotoxin-alpha and stimulate type 1 immunity, which is characterized by intense phagocytic activity. Conversely, Th2 cells secrete IL-4, IL-5, IL-9, IL-10, and IL-13 and stimulate type 2 immunity, which is characterized by high antibody titers. Type 1 and type 2 immunity are not strictly synonymous with cell-mediated and humoral immunity, because Th1 cells also stimulate moderate levels of antibody production, whereas Th2 cells actively suppress phagocytosis. For most infections, save those caused by large eukaryotic pathogens, type 1 immunity is protective, whereas type 2 responses assist with the resolution of cell-mediated inflammation. Severe systemic stress, immunosuppression, or overwhelming microbial inoculation causes the immune system to mount a type 2 response to an infection normally controlled by type 1 immunity. In such cases, administration of antimicrobial chemotherapy and exogenous cytokines restores systemic balance, which allows successful immune responses to clear the infection.

T-helper type 2 cell-directed therapy for asthma

Asthma is a chronic inflammatory disease of the bronchial airways. Current research in humans and animals suggests that T-helper type 2 (Th2) cells and the cytokines they elaborate cause many of the pathophysiologic abnormalities characteristic of the disease. We review the evidence implicating Th2 cells in asthma and discuss the cellular and molecular mechanisms that control Th2 cell differentiation in the respiratory tract. Based on the steps in Th cell development, we discuss how traditional therapies can modulate Th2 cell function. Furthermore, we explore newer immunomodulatory strategies to inhibit Th2 cell effects, including therapies that may block Th2 cell differentiation, neutralize cytokines, and redirect immune responses towards Th1 and away from Th2.

Cytokine-modulated regulation of helper T cell populations

Helper T (Th) cells are a crucial component of the adaptive immune system and are of fundamental importance in orchestrating the appropriate response to pathogenic challenge. They fall into two broad categories defined by the cytokines each produces. Th1 cells produce interferon- gamma and are required for effective immunity to intracellular bacteria, viruses and protozoa whereas Th2 produce IL-4 and are required for optimal antibody production to T-dependent antigens. A great deal of experimental data on the regulation of Th1 and Th2 differentiation have been obtained but many essential features of this complex system are still not understood. Here we present a mathematical model of Th1/Th2 differentiation and cross regulation. We model Fas-mediated activation-induced cell death (AICD) as this process has been identified as an important mechanism for limiting clonal expansion and resolving T cell responses. We conclude that Th2 susceptibility to AICD is important for stabilizing the two polarized arms of the T helper response, and that cell-cell killing, not suicide, is the dominant mechanism for Fas-mediated death of Th1 effectors. We find that the combination of the anti-proliferative effect of the cytokine TGF- beta and the inhibiting influence of IL-10 on T cell activation are crucial controls for Th2 populations. We see that the strengths of the activation signals for each T helper cell subset, which are dependent on the antigen dose, co-stimulatory signals and the cytokine environment, critically determine the dominant helper subset. Switches from Th1- to Th2-dominance may be important in chronic infection and we show that this phenomenon can arise from differential AICD susceptibility of T helper subsets, and asymmetries in the nature of the cross-suppressive cytokine interactions. Our model suggests that in some senses a predominantly type 2 reaction may well be the "default" pathway for an antigen-specific immune response, due to these asymmetries.

IL-10 and IL-12 are the main regulatory cytokines in visceral leishmaniasis

Visceral leishmaniasis (VL) is characterized by the absence of cytokines such as IFN-gamma and IL-12. Cure of VL is associated with a restoration of the ability to make these cytokines. The aim of the present study was to evaluate the role of IL-12 in the recovery of the ability to produce IFN-gamma and to test whether or not IL-4 IL-10 and/or TGF-beta could suppress IFN-gamma production by PBMC from treated VL patients. High stimulation index (SI) of proliferation was observed in PBMC from subjects stimulated with Leishmania chagasi antigen (181+/-83). Neutralizing IL-12 inhibited lymphoproliferation [stimulation index (SI) of 210+/-114 to 1+/-0.6 (P<0.01)] and/or the production of IFN-gamma [2792+/-402 pg/ml to 407+/-449 pg/ml (P<0.01)]. Recombinant IL-10 abrogated the lymphoproliferation (SI=2+/-3) while recombinant IL-4 or TGF-beta had no effect on this response (147+/-22 and 194+/-12 respectively). IFN-gamma was high when PBMCs were stimulated with L. chagasi (873+/-400 pg/ml) and this was abrogated by the addition of IL-10 (5+/-2 pg/ml). In contrast neither IL-4 or TGF-beta suppressed IFN-gamma production (837+/-244 pg/ml and 759+/-523 pg/ml). These results indicate that IL-12 plays an important role in the ability of treated VL patients to make IFN-gamma and that IL-10 but not IL-4 or TGF-beta inhibits this response.

Immunology at the maternal-fetal interface: lessons for T cell tolerance and suppression

Mammalian reproduction poses an immunological paradox because fetal alloantigens encoded by genes inherited from the father should provoke responses by maternal T cells leading to fetal loss. Current understanding of T cell immunobiology and the critical role of inflammatory processes during pregnancy is reviewed and discussed. Lessons derived from studies on the regulation of T cell responsiveness during mammalian gestation are considered in the wider context of T cell tolerance toward some microbial infections and tumors, avoidance of autoimmunity, and tissue allograft rejection.