Deficiency in the transcription factor interferon regulatory factor (IRF)-2 leads to severely compromised development of natural killer and T helper type 1 cells.

Interferon (IFN) regulatory factor (IRF)-2 was originally described as an antagonist of IRF-1-mediated transcriptional regulation of IFN-inducible genes. IRF-1(-/)- mice exhibit defective T helper type 1 (Th1) cell differentiation. We have used experimental leishmaniasis to show that, like IRF-1(-/)- mice, IRF-2(-/)- mice are susceptible to Leishmania major infection due to a defect in Th1 differentiation. Natural killer (NK) cell development is compromised in both IRF-1(-/)- and IRF-2(-/)- mice, but the underlying mechanism differs. NK (but not NK(+) T) cell numbers are decreased in IRF-2(-/)- mice, and the NK cells that are present are immature in phenotype. Therefore, like IRF-1, IRF-2 is required for normal generation of Th1 responses and for NK cell development in vivo. In this particular circumstance the absence of IRF-2 cannot be compensated for by the presence of IRF-1 alone. Mechanistically, IRF-2 may act as a functional agonist rather than antagonist of IRF-1 for some, but not all, IFN-stimulated regulatory element (ISRE)-responsive genes.

A multidrug-resistance protein (MRP)-like transmembrane pump is highly expressed by resting murine T helper (Th) 2, but not Th1 cells, and is induced to equal expression levels in Th1 and Th2 cells after antigenic stimulation in vivo.

A transmembrane pump for organic anions was identified in resting murine T helper (Th) 2, but not Th1 lymphocyte cell clones, as revealed by extrusion of a fluorescent dye. Dye extrusion inhibition studies suggested that the pump may be the multidrug-resistance protein (MRP). The different expression of the pump in resting Th1 and Th2 cell clones correlated with their respective levels of MRP mRNA. The pump was inducible in Th1 cells by antigenic stimulation in vitro leading to equal expression in activated Th1 and Th2 cell clones. This suggested that dye extrusion might allow the detection of Th2 (resting or activated) or of activated Th1 cells ex vivo based on a functional parameter. To test this, mice were infected with Leishmania major parasites to activate L. major-specific T cells of either Th1 (C57BL/6 mice) or Th2 (BALB/c mice) phenotype: 2-3% of CD4+ lymph node T cells of both strains of mice extruded the dye, defining a cell subset that did not coincide with subsets defined by other activation markers. Fluorescence-activated cell-sorting revealed that the lymphokine response (Th1 or Th2, respectively) to L. major antigens was restricted to this dye-extruding subset.

Coexistence of antigen-specific TH1 and TH2 cells in genetically susceptible BALB/c mice infected with Leishmania major.

CD4-positive T cell clones with specificity for the protozoan parasite Leishmania major (L. major) of both the protective TH1 and the disease-exacerbating TH2 subtype were isolated from a diseased L. major-infected mouse of the susceptible BALB/c strain. In addition, TH2 cells were isolated from the lesion-draining lymph nodes of an animal clinically healed nine months after sublethal irradiation and subsequent infection. Our data support the notion that the differential outcome of the disease in non-irradiated versus irradiated BALB/c mice reflects the regulation of the two CD4+ T cell subsets. These data also argue against the possibilities that: 1) TH2 cells and their precursors are totally eliminated by irradiation and that 2) TH2 cells are capable of completely hindering the expansion of TH1 cells in diseased animals.

Helicobacter pylori gastritis: a Th1 mediated disease?

Helicobacter pylori is now considered to be the main cause for most stomach diseases including ulcer, MALT lymphoma, adenocarcinoma and gastritis. The infection with this bacterium is chronic despite a local and systemic immune response towards it. Among the cellular infiltrate that arises during H. pylori-mediated gastritis, there is a considerable frequency of CD4+ Th1 cells producing IFNgamma, but not of Th2 cells producing IL-4. Since IFNgamma may induce binding of H. pylori to gastric epithelial cells followed by apoptosis of these cells, one may speculate that H. pylori-mediated diseases are in part autoimmune diseases initiated by H. pylori-specific Th1 cells infiltrating the gastric mucosa. Recent support for this hypothesis comes from an animal model in which mice are infected with H. pylori and display strongly reduced gastritis in the absence of IFNgamma.

Experimental murine leishmaniasis and the Th1/Th2 cell concept.

Herein, the current knowledge about the immune response during murine cutaneous leishmaniasis is summarized. Special regard is given to the characteristics and generation of Th1 and Th2 cells during this disease. Originally established on the basis of different cytokines produced by T cell clones, it is now known that the Th1/Th2 concept really defines totally different immune pathways that affect most, if not all cells of the immune system. Murine experimental leishmaniasis was the first model to confirm the relevance of the Th1/Th2 concept in vivo. In particular, data from this laboratory will be presented on the role of different IL-4 receptor allotypes, on the role of the transcription factor interferon-regulatory-factor-1 (IRF-1) and the importance of the enzyme inducible NO synthase (iNOS). This work was supported by the SFB 263 and the Fonds der Chemischen Industrie.

IRF4 and BATF are critical for CD8⁺ T-cell function following infection with LCMV.

CD8(+) T-cell functions are critical for preventing chronic viral infections by eliminating infected cells. For healthy immune responses, beneficial destruction of infected cells must be balanced against immunopathology resulting from collateral damage to tissues. These processes are regulated by factors controlling CD8(+) T-cell function, which are still incompletely understood. Here, we show that the interferon regulatory factor 4 (IRF4) and its cooperating binding partner B-cell-activating transcription factor (BATF) are necessary for sustained CD8(+) T-cell effector function. Although Irf4(-/-) CD8(+) T cells were initially capable of proliferation, IRF4 deficiency resulted in limited CD8(+) T-cell responses after infection with the lymphocytic choriomeningitis virus. Consequently, Irf4(-/-) mice established chronic infections, but were protected from fatal immunopathology. Absence of BATF also resulted in reduced CD8(+) T-cell function, limited immunopathology, and promotion of viral persistence. These data identify the transcription factors IRF4 and BATF as major regulators of antiviral cytotoxic T-cell immunity.

[Sepsis-like disease in an immunocompromised patient with a travel history to Mallorca]. / Sepsisähnliches Krankheitsbild bei Immunsuppression nach früherem Mallorcaurlaub.

In immunosuppressed patients, a high rate of complications due to opportunistic infection is known. We report the case of a 36 year old patient with ulcerative colitis and a septic complication with ongoing pancytopenia. Due to colonic perforation, colectomy had to be performed. Despite this intervention, the septic constellation persisted. The pancytopenia in peripheral blood counts also persisted with the necessity of repetitive transfusions. A bone marrow biopsy showed an infiltration with Leishmania bodies in macrophages. Tissue culture allowed for typing of the parasites as belonging to the L. donovani/infantum complex, DNA sequencing confirmed infection with L. infantum. This infection must have been contracted during a vacation on Mallorca about 1.5 years earlier. Administration of liposomal amphotericin B cured the patient. Surprisingly, histological examination of the resected colon reveiled the presence of an immunoblastic B-cell lymphoma. In this case, immunosuppression was a prerequisite for the manifestation of leishmaniosis.

Signaling via CD28 costimulates lymphokine production, but does not reverse unresponsiveness to interleukin-2 in anti-CD3 triggered Th1 cells.

Previously, it has been described that the ability of murine Th1 cells to proliferate in response to exogenous interleukin (IL)-2 is blocked when these cells are exposed to immobilized anti-CD3 antibodies. In the present study we examined whether simultaneous triggering of the T cell antigen CD28 can prevent the induction of unresponsiveness to IL-2 in Th1 cells. We report that costimulation of Th1 cells with anti-CD28 monoclonal antibodies (mAb) did not overcome unresponsiveness to IL-2 induced by various amounts of immobilized anti-CD3 antibodies. However, stimulation with anti-CD28 mAb strongly augmented IL-2 and interferon-gamma production in anti-CD3-exposed Th1 cells. Thus, despite the fact that anti-CD28 mAb is a potent costimulus for lymphokine production, signaling through CD28 does not seem to be sufficient to trigger proliferation in Th1 cells activated via the T cell receptor. These data suggest the existence of at least three signals to trigger Th1 cell activation. The first is mediated by ligation of the T cell receptor. One cosignal, delivered by the CD28 molecule, leads to IL-2 production. A third, still undefined, signal is required for proliferation in response to IL-2.

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.

Murine IL-4 antagonizes the protective effects of IFN on virus-mediated lysis of murine L929 fibroblast cells.

IFN-alpha, -beta, and -gamma protect murine fibroblasts from lysis by vesicular stomatitis virus. In this report we show that culture supernatants derived from a Th cell clone of the TH2-type completely block the protective effects of the IFN. The active component in inhibiting IFN is identified to be IL-4. rIL-4 has similar effects as the T cell supernatant.

Suppressive effect of interferon-gamma on the BCL1 cell-dependent interleukin 5 bioassay.

Proliferation of BCL1 cells, generally used for the measurement of murine interleukin (IL)5, is shown to be strongly suppressed by interferon (IFN)-gamma. This effect can be abrogated by the addition of anti-IFN-gamma antibodies. Thus, the IL5 activity of culture supernatants derived from T cells simultaneously producing IFN-gamma and IL5, can only be seen with BCL1 cells in the presence of anti-IFN-gamma antibodies. If anti-IFN-gamma antibodies are omitted, T cells which produce both, IFN-gamma and IL5, may mistakenly be grouped into the TH1 subtype producing only IFN-gamma, but no IL5.

Polyclonal B-cell stimulation by L3T4+ T cells in experimental leishmaniasis.

The well-established polyclonal B-cell stimulation in the lymphoid organs in mice infected with Leishmania major is thought to be dependent on T cells. Here we present clear experimental evidence that this is indeed the case by showing that BALB/c-derived, L3T4-positive L. major-specific T cells induce syngeneic B cells to polyclonal proliferation and immunoglobulin production.

Two signals are involved in polyclonal B cell stimulation by T helper type 2 cells: a role for LFA-1 molecules and interleukin 4.

T helper cell type 2 (Th2) cells when triggered by antibodies to CD3 acquire the capacity to stimulate the polyclonal proliferation of syngeneic, resting B cells. Here, we tested the ability of various monoclonal antibodies (mAb) to block the B cell proliferation-inducing potential of such activated Th2 cells. We demonstrate that anti-interleukin 4, as well as anti-LFA-1 antibodies interfere with the T-B cell interaction. In kinetic studies, anti-LFA-1 was found to be operative during the first half and anti-interleukin 4 during the second half of the 48-h culture period. This defines at least two different steps in B cell triggering by Th2 cells. In addition, the data imply that the T-B cell interaction involves an additional structure, namely an activation molecule, on the T cell surface.

CD44 plays a co-stimulatory role in murine T cell activation: ligation of CD44 selectively co-stimulates IL-2 production, but not proliferation in TCR-stimulated murine Th1 cells.

The murine CD44 receptor family is thought to be involved in a variety of lymphocyte functions, including lymphopoesis, lymphocyte homing and cell migration. Herein, we show that murine CD44 also plays a role as a co-stimulatory molecule for the activation of CD4+ T cells. Ligation of CD44 by mAb enhanced IL-2 production of long-term cultured, anti-CD3-stimulated Th1 cell lines. Moreover, anti-CD44 mAb synergized with anti-CD28 mAb in exerting this effect. A synergism of anti-CD28 and anti-CD44 mAb to co-stimulate IL-2 production was also observed in anti-CD3-triggered, freshly isolated splenic CD4+ T cells. Blocking experiments with cyclosporin A indicated that the intracellular pathways used by the CD28 and CD44 molecules appear to be different. In contrast to the effects on the IL-2 production of Th1 cells, neither anti-CD44 mAb alone nor the combination of anti-CD44 with anti-CD28 were able to induce proliferation of anti-CD3-triggered Th1 cells. In accordance, triggering of CD44 and/or CD28 by mAb was not sufficient to reverse the previously described 'proliferative block'. This term describes the unresponsiveness of Th1 cells against IL-2, which occurs when Th1 cells are triggered by anti-CD3 in the absence of co-signals. These data lead us to propose a model of Th1 cell activation which includes two functionally different types of co-signals: one for IL-2 production and a separate one for proliferation.

Demonstration of organic anion transport in T lymphocytes. L-lactate and fluo-3 are target molecules.

In this paper, we describe for the first time the existence of organic anion transport in T lymphocytes, exemplified by the transmembrane transport of the anions L-lactate and the Ca2+ indicator fluo-3. The transport of either anion was found to be inhibitable by probenecid, a common blocker of organic anion transport. Transport of L-lactate was observed in long-term cultured T cell lines, as well as in freshly ex vivo isolated T cells, and occurred via a saturable, pH-dependent, and stereospecific process. L-Lactate uptake was dependent on the activation state of the T cells, because activation of T cells by Con A strongly enhanced accumulation of L-lactate from the medium. Because L-lactate may be transported bidirectionally through the T cell membrane in vivo, different physiologic roles of L-lactate transport are discussed. L-Lactate uptake may serve as an alternative source of energy in an inflamed, glucose-deficient tissue or may represent a prerequisite for the earlier-published immunoregulatory function of this molecule on T cells. On the other hand, release of L-lactate emerging from glycolysis could be necessary to avoid acidification of the cell. The fact that the Ca2+ indicator fluo-3 is also transported through the cellular membranes of long-term cultured T cells via organic anion transport has important implications for the determination of Ca2+ influx into T cells. Even though the transport of both molecules, L-lactate and fluo-3, represents organic anion transport, evidence is presented that confirms that the respective transport systems are different.

The Xid defect determines an improved clinical course of murine leishmaniasis in susceptible mice.

The course of Leishmania major infection in B cell-defective BALB.Xid mice was investigated. Infected BALB.Xid mice showed a significantly slower lesion development compared with BALB/c controls accompanied by a 10- to 30-fold lower parasite burden in lymphatic organs. The B cell immune response, as quantified by anti-leishmanial antibody production and B cell numbers in lymphatic organs, remained significantly lower in BALB.Xid mice as compared with BALB/c control mice. In accordance with disease development, CD4+ T cells from lymph nodes of infected BALB.Xid mice produced 6- to 10-fold more IFN-gamma than the respective T cells of BALB/c mice, when stimulated with leishmanial antigen in vitro. B cells from lymph nodes and the peritoneal cavities of BALB/c mice could be induced to produce 3- to 8-fold more IL-10 than the respective cells from B cell-defective BALB.Xid mice. The data thus indicate that the Xid mutation allows for the development of Th1 cells which confer resistance to infection with L. major. Moreover, the data suggest that B cells contribute to susceptibility to L. major infection in BALB/c mice by skewing the Th cell network towards a Th2 phenotype. Since the difference in B cell-derived IL-10 production between BALB/c and BALB.Xid mice was more prominent in peritoneal B cells, the data support the notion that the skewing of the T cell response may be predominantly mediated by the B1 cell subset.

The Th1/Th2 paradigm and experimental murine leishmaniasis.

In recent years, the Th1/Th2 concept has become of prime importance in the understanding of heterogeneous responses of the immune system and implications thereof for infectious and autoimmune diseases. Originally established on the basis of different cytokines produced by T cell clones, it is now known that the Th1/Th2 concept really defines totally different immune pathways that affect most if not all cells of the immune system. Murine experimental leishmaniasis was the first model to confirm the relevance of the Th1/Th2 concept in vivo. Herein, we summarize the current knowledge on the characteristics and generation of Th1 and Th2 cells, as well as on recent advances of the application of this concept to murine cutaneous leishmaniasis.

Studies on the mechanism of polyclonal B cell stimulation by TH2 cells.

Recently, it has been shown that cloned L1/1 T helper cells of type 2 (TH2-cells), when stimulated with antigen, are able to induce polyclonal B cell proliferation. Here we present evidence that this process is dependent on direct cell-cell interaction between T and B cells, which in the effector phase, i.e., during stimulation of the B cells by activated T cells, can be mediated by a mechanism other than cognate interaction. This conclusion is derived from experiments in which highly purified, small B cells of high density were polyclonally stimulated by L1/1 T cells triggered by an anti-T3 monoclonal antibody in the absence of antigen. The triggering process was independent of the presence of the Fc part of the antibody and occurred in cultures devoid of macrophages. Thus, the well-established cognate recognition does not appear to be the only mechanism of B cell induction by T helper cells.