Dendritic cells in Leishmania major-immune mice harbor persistent parasites and mediate an antigen-specific T cell immune response

Upon infection with Leishmania major, a cause of human cutaneous leishmaniasis, mice of resistant strains are able to control the infection, with lesions resolving spontaneously. A long-lasting cell-mediated immunity protects them from reinfection. Nevertheless, small numbers of viable parasites persist in the lymph nodes of these mice. We have recently documented that, in addition to macrophages, epidermal Langerhans cells can ingest L. major. Furthermore, Langerhans cells have the unique ability to transport viable parasites from the infected skin to the draining lymph node for presentation to antigen-specific T cells and initiation of the cellular immune response. During migration, Langerhans cells develop into dendritic cells. In the present study, we analyzed whether dendritic cells support the persistence of parasites in immune hosts. Immunohistological studies and assays in vitro showed that in the lymph nodes of mice that have recovered from infection with L. major, both macrophages and dendritic cells harbor viable parasites. However, only dendritic cells were able to induce a vigorous T-cell immune response to L. major in vitro in the absence of exogenous antigen. Tracking experiments conducted in vivo suggested that the infected dendritic cells in the lymph nodes are derived from Langerhans cells that have emigrated from the skin. The data demonstrate that L. major-infected dendritic cells and macrophages in lymph nodes of immune animals represent long-term host cells, but only dendritic cells have the ability to present endogenous parasite antigen to T cells. Long-term infected dendritic cells may thus allow the sustained stimulation of a population of parasite-specific T cells, protecting the mice from reinfection. Our results favor the hypothesis that the persistence of antigen supports the maintenance of T cell memory and that dendritic cells are critically involved in this process.

Soluble IL-4 receptor, potential for therapeutic and prophylactic intervention

Many bacterial, protozoal and viral infections trigger a cell-mediated immune response. Of special importance for the clinical outcome of disease, however, is the relative predominance of T helper (Th) cell populations (Th1 and Th2) secreting different patterns of lymphokines. Preferential development of one Th subset occurs apparent at the early stages of an infection, suggesting that the mechanisms driving the immune response in one direction or the other operate soon after exposure to the antigen. Cytokines are among the most important factors regulating T cell differentiation and expansion of the different T cell subtypes. As in experimental candidiasis, listeriosis, yersiniosis and murine retrovirus induced immunodeficiency syndrome (MAIDS), interleukin-4 (IL-4) is of central importance also for the clinical course of murine cutaneous leishmaniasis. It has been demonstrated that the presence of IL-4 is essential for the development of disease promoting Th2 cells whereas neutralization of IL-4 in vivo led to establishment of protective immunity against leishmania. A naturally occurring antagonist of IL-4 is the soluble IL-4 receptor (sIL-4R), which retains its ligand binding properties and binds IL-4 with high affinity. We therefore examined the immunomodulatory and therapeutic capacity of recombinant sIL-4R in murine cutaneous leishmaniasis. BALB/c mice were treated with recombinant sIL-4+ during the onset of the immune response. This treatment rendered BALB/c mice clinically resistant to Leishmania major (L. major), led to reduced parasite load, shifted the pattern of cytokines towards Th1 type and provided durable resistance against reinfection with L. major.(ABSTRACT TRUNCATED AT 250 WORDS)

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.

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.

Recombinant soluble interleukin-4 (IL-4) receptor acts as an antagonist of IL-4 in murine cutaneous Leishmaniasis

This study was performed to evaluate the soluble interleukin-4 receptor (sIL-4R) as a potential antagonist of interleukin-4 (IL-4) in an infectious disease. It is shown that antigen-triggered proliferation and cytokine secretion of Leishmania major-specific, cloned Th2 cells in vitro can be inhibited dose dependently by recombinant murine, but not control human, sIL-4R. In vivo, we found that endogenous synthesis of IL-4 mRNA is upregulated during the first week of infection, while an increase of IL-4R mRNA occurred later after infection of BALB/c mice with L. major. To interfere successfully with the IL-4 ligand-receptor interaction, we therefore chose to treat infected BALB/c mice with recombinant sIL-4R during the onset (e.g., days 0 to 7) of the immune response. Treatment with murine, but not with human, sIL-4R during the first week of infection rendered BALB/c mice clinically resistant to L. major, led to a 7- to 12-fold reduction of the parasite load in spleen and lymph nodes at 7 weeks of infection, shifted the pattern of cytokines towards a Th1 type, and provided durable resistance against reinfection. Thus, it could be demonstrated that the balance among sIL-4R, membrane-bound IL-4R, and their ligand IL-4 can be modulated in vivo, thereby modifying the antiparasitic immune response. These results suggest a therapeutic value of sIL-4R in diseases in which neutralization of IL-4 is desirable.

Interleukin-10 inhibits antimicrobial activity against Leishmania major in murine macrophages

The stimulation of macrophages is of importance to the defense against intracellularly replicating microorganisms such as Leishmania. In this study the direct effect of recombinant interleukin-10 (IL-10) on the leishmanicidal effector functions of murine peritoneal or bone marrow derived macrophages was investigated. IL-10 almost completely inhibited the killing of intracellular leishmania at concentrations above 10 ng/ml. This inhibitory effect was independent of the stimulus used as the activation of macrophages by IFN-gamma and IL-7, recently shown to possess macrophage activating properties, were suppressed by IL-10. Kinetic experiments revealed that IL-10 must be present during the process of macrophage activation and that the leishmanicidal effector function of fully activated macrophages was not influenced. Furthermore, in the absence of exogenously added IL-10, the addition of neutralizing antibodies against IL-10 or IL-10-specific antisense phosphorothioate DNA-oligonucleotide led to an enhanced killing of parasites after stimulation with either IFN-gamma or IL-7. In accordance with this, IL-10 mRNA was readily detectable in murine macrophages by PCR with reverse transcribed mRNA. These results indicate that IL-10, which is endogenously produced by macrophages, acts as an autocrine deactivating factor supporting the survival of the parasite.

Transcriptional and translational regulation of IL-1 alpha and IL-1 beta account for the control of IL-1 in experimental yersiniosis

Interleukin 1 (IL-1) gene expression was investigated in mice following oral infection with Yersinia enterocolitica 08. In Peyer's patches (PP), the primary site of bacterial invasion, induction of IL-1 alpha mRNA was delayed when compared to IL-1 beta mRNA. As shown by in situ hybridization. IL-1 alpha and IL-1 beta mRNA were found to be expressed within different cell types. These results indicate that expression of the two forms of IL-1 is regulated in a cell-specific manner at the transcriptional level. Moreover, IL-1 (alpha and beta) mRNA was increased in other organs such as spleen and lung. In spleens, IL-1 beta mRNA was found within the red pulp, and IL-1 alpha mRNA was located to the marginal zone confirming that differential expression of IL-1 alpha and IL-1 beta mRNA does not represent a tissue-specific event. However, as revealed by immunohistochemistry and measuring IL-1 activity in tissue homogenates, synthesis of IL-1 proteins was not detectable in spleens, unless mice were challenged with LPS. Because IL-1 synthesis was inducible in spleen cells following actinomycin D treatment, the results indicate that at distant sites of infection IL-1 (alpha and beta) mRNA is expressed but not translated into protein. It is concluded that cell-specific transcription of IL-1 alpha and IL-1 beta as well as dissociation between IL-1 mRNA and protein synthesis are two mechanisms effective in regulating the production of IL-1 during infection.

Tissue expression of inducible nitric oxide synthase is closely associated with resistance to Leishmania major

Previous studies with inhibitors of inducible nitric oxide synthase (iNOS) suggested that high-output production of nitric oxide (NO) is an important antimicrobial effector pathway in vitro and in vivo. Here, we investigated the tissue expression of iNOS in mice after infection with Leishmania major. Immunohistochemical staining with an iNOS-specific antiserum revealed that in the cutaneous lesion and draining lymph nodes (LN) of clinically resistant mice (C57BL/6), iNOS protein is found earlier during infection and in significantly higher amounts than in the nonhealing BALB/c strain. Similar differences were seen on the mRNA level as quantitated by competitive polymerase chain reaction. Anti-CD4 treatment of BALB/c mice not only induced resistance to disease, but also restored the expression of iNOS in the tissue. In situ, few or no parasites were found in those regions of the skin lesion and the draining LN which were highly positive for iNOS. By double labeling experiments, macrophages were identified as iNOS expressing cells in vivo. In the lesions of BALB/c mice, cells staining positively for transforming growth factor beta (TGF-beta), a potent inhibitor of iNOS in vitro, were strikingly more prominent than in C57BL/6, whereas no such difference was found for interleukin 4 or interferon gamma (IFN-gamma). In vitro, production of NO was approximately threefold higher in C57BL/6 than in BALB/c macrophages after stimulation with IFN-gamma. We conclude that the pronounced expression of iNOS in resistant mice is an important mechanism for the elimination of Leishmania in vivo. The relative lack of iNOS in susceptible mice might be a consequence of macrophage deactivation by TGF-beta and reduced responsiveness to IFN-gamma.

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.

Cutaneous leishmaniasis: co-ordinate expression of granzyme A and lymphokines by CD4+ T cells from susceptible mice

We have recently demonstrated that the frequency of T cells expressing granzyme A is significantly higher in skin lesions and spleens of susceptible BALB/c mice compared with resistant C57BL/6 mice infected with Leishmania major, a cause of human cutaneous leishmaniasis. In the present study, we have performed in vitro studies to characterize the subpopulation, the antigen responsiveness and the lymphokine production pattern of granzyme A-expressing T cells in L. major-infected mice. Using a limiting dilution system for functional analysis of selected T cells at the clonal level, we could show that granzyme A activity in infected BALB/c mice can be assigned to L. major-reactive CD4+ T cells secreting interleukin-2 (IL-2) and IL-4. Granzyme A production was most pronounced in the early phase of infection. On the other hand, granzyme A expression could not be detected in C57BL/6-derived T cells responding to L. major. The data support the suggestion that granzyme A is produced by L. major-responsive CD4+ T cells facilitating lesion formation and the dissemination of infection.

Leishmania major parasites share an epitope with the murine CD3-T cell receptor complex

After immunization of BALB/c mice with a low molecular mass fraction (FrD; < or = 31 kDa) isolated from a soluble extract of Leishmania major promastigotes, a panel of monoclonal antibodies (mAb) was obtained. One of these antibodies (mAb 9C) recognized a cytosol-associated antigen from L. major of approximately 21 kDa as shown by Western blot and immunoprecipitation. In addition, mAb 9C reacted with surface structures of murine splenic T cells and T cell clones. Reactivity was confined to murine cells, but was not strain restricted. Immunoprecipitation studies and surface-labeling experiments with CD4+ T cell clones and the T cell receptor (TCR)-CD3-T cell line TG40 transfected with V alpha/beta chains from human TCR and concomitant co-expression of murine CD3 suggested that mAb 9C binds to an epitope located within the murine CD3-TCR complex. In addition, mAb 9C induced strong T cell proliferation. We conclude that L. major parasites share an epitope with the murine CD3-TCR complex which is functionally important for T cell activation.

V beta gene repertoires in T cells expanded in local self-healing and lethal systemic murine cutaneous leishmaniasis

Inbred mice infected with Leishmania major promastigotes display two different courses of leishmaniasis: resistant strains develop self-healing local sores, while susceptible strains show progressive systemic disease with lethal outcome. Resistance predominantly correlates with the production of T helper type 1 (TH1) lymphokines and susceptibility with production of TH2-type lymphokines. Here, we analyzed whether this TH phenotype difference correlates with expression of particular T cell receptor V beta chains. Our results show that T cells expand strongly during infection in all groups of mice and invariantly express the same V beta gene families as prior to infection. Our data indicate that TH1 and TH2 cells use similar V beta gene families, and argue against the engagement of a restricted set of V beta by dominant determinants associated with L. major.

Differential regulation of IL-9-expression after infection with Leishmania major in susceptible and resistant mice

IL-9 is a pleiotropic lymphokine, one of its activities being the growth stimulation of certain CD4+ T lymphocytes. In murine cutaneous leishmaniasis, depending on the genetic background of the host mouse strain, vigorous proliferation of either mainly Th1 in resistant C57BL/6 mice or Th2-type CD4+ T cells in susceptible BALB/c mice occurs after infection with Leishmania major (L. major). Since little is known about the involvement of IL-9, the possible role of this cytokine with regard to its immunregulatory function was evaluated by comparing its presence in the serum and its expression kinetics in spleen and lymph nodes in resistant and susceptible mice. To this sera of L. major-infected mice were tested functionally for IL-9. In addition the PCR-aided detection of IL-9 mRNA in organs of mice and measurement of the lymphokine in supernatants of restimulated lymph node and spleen cell cultures were used. We show here that although no functionally active IL-9 was detected in sera of both BALB/c and C57BL/6 mice, IL-9 is produced after in vitro antigenic restimulation and its mRNA was found to be expressed in lymph nodes and spleens during an immune response against L. major. Shortly after infection no principal differences in the kinetics of IL-9 expression could be observed, which had its maximum between day 5 and 7 after infection. The rate of production however was higher in the susceptible BALB/c mice. In athymic BALB/c nu/nu mice and in mice depleted of CD4+ T cells no IL-9 production was detectable in vivo at the level of mRNA and no IL-9 was produced after stimulation with L. major antigen in vitro. Treatment of infected mice with cyclosporin A ablates antigen-specific IL-9 production when tested in vitro without affecting its production after polyclonal T cell stimulation. Positively selected, purified CD4+ T cells were fully capable of producing IL-9. From 4 weeks after infection, IL-9 synthesis was observed only in BALB/c mice, correlating with the expansion of antigen-specific Th2 type T helper cells in these mice. Treatment of BALB/c mice with neutralizing anti-IL-4 mAb, a regimen known to lead to subsequent cure of infected BALB/c mice, suppressed late IL-9 synthesis.

Cytokines in leishmaniasis: a complex network of stimulatory and inhibitory interactions

The work of immunologists, cell biologists and parasitologists in the field of leishmaniasis has not only provided important insights into the immunopathogenesis of this disease, but also yielded fundamental contributions to our understanding of basic immunological phenomena and of host-parasite interactions. The ability of recombinant interferon-gamma to induce the microbicidal activity of phagocytes and the opposite effect of inhibitory cytokines was first demonstrated with Leishmania-infected macrophages. The selective development of protective and disease-mediating CD4+ T lymphocytes as well as their differential influence on the course of the disease has been long investigated in the murine Leishmania major model and now represents one of the best examples for the in vivo induction of type 1 versus type 2 T helper lymphocytes. At the same time, this model has also been extensively used for immunization studies and cytokine therapy, which shed light on the functions of cytokines in vivo as well as on the mechanism(s) of disease resistance and susceptibility. In this review we will discuss the present picture of the cytokine network in murine L. major infections.

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.

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

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

Natural killer cells participate in the early defense against Leishmania major infection in mice

In this study the role of natural killer (NK) cells in the course of experimental Leishmania major infection was investigated. NK cells in genetically resistant C57BL/6 mice were depleted by in vivo administration of anti-asialo-GM1 or anti-NK1.1 antibodies. A marked exacerbation of the infection was found in the NK-depleted mice within the first two weeks of infection. Both the local tissue swelling and the number of parasites in the lesions were significantly higher than in normal animals. Lymph node cells taken from infected NK-depleted mice released less interferon-gamma (IFN-gamma) when cultured in vitro. As an alternate approach we have used poly I:C treatment in order to activate NK cell activity in vivo in BALB/c mice, which are genetically susceptible to L. major infection. Poly I:C treatment led to milder symptoms and to a significantly lower parasite burden in the early course of infection. Lymph node cells from infected and poly I:C-treated BALB/c mice released higher amount of IFN-gamma in vitro than cells from control mice. These data show that NK cells are active participants in the non-specific phase of anti-leishmanial activity in the control of parasite multiplication early in the course of L. major infection in mice.

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

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

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

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

[Persistence and transient conjunctival pathogen colonization before planned intraocular interventions]

The risk of a postoperative endophthalmitis is influenced by the presence of a significant bacterial colonisation of the conjunctiva before intraocular surgery. Between February and August 1990 we performed conjunctival smears in 481 patients 1) on the eve of the operation and 2) just before planned intraocular surgery, to evaluate a persistent or transient microbial colonisation of the conjunctiva. 352 patients showed insignificant ("negative") and 129 patients a significant ("positive") bacterial growth in the first conjunctival smear. 96% of the patients (n = 336) had a negative result in both smears. 30% of the patients (n = 37) with a positive conjunctival smear showed a persisting bacterial colonisation, whereas 70% of the patients (n = 92) had a transient colonisation of the conjunctiva with a negative second smear. As a persisting microbial colonisation of the conjunctiva may be an important factor for the development of postoperative endophthalmitis, we recommend prophylactic conjunctival smears before surgery to diminish the risk of intraocular infections after surgery.

[The role of interleukin 1 in infection and sepsis]

Interleukin(IL-)-1 is the prototype of a proinflammatory cytokine, produced in response to infection and other forms of trauma. At low concentrations IL-1 brings about increases in a number of defense mechanisms, particularly immunologic and inflammatory responses. However, over- or continued production of IL-1, as seen for example during septic infection, significantly contributes to pathological reactions such as hemodynamic shock. Thus, it is not surprising that IL-1 activities are tightly regulated, most notably at the levels of transcription and secretion. Additional regulation is provided by the action of a protein, that blocks the binding of IL-1 to its receptors. This protein, termed IL-1-receptor antagonist (IL-1ra) has been cloned recently, and may provide the possibility of specific therapeutic measures.

Transition from interleukin 1 beta (IL-1 beta) to IL-1 alpha production during maturation of inflammatory macrophages in vivo

In situ production of interleukin 1 alpha (IL-1 alpha) and IL-1 beta was investigated in Peyer's patches (PP) of mice undergoing an acute bacterial infection with Yersinia enterocolitica O8. Synthesis of IL-1 beta, as determined by immunohistochemistry, was found primarily in monocytes migrating into the inflamed PP. In comparison, synthesis of IL-1 alpha was temporarily delayed by at least 24 h and was only found in mature macrophages, which did not produce detectable levels of IL-1 beta. This indicates a transition from IL-1 beta to IL-1 alpha production during maturation of monocytes into inflammatory macrophages, and further emphasizes a dichotomy between IL-1 alpha and IL-1 beta.

Murine epidermal Langerhans cells are potent stimulators of an antigen-specific T cell response to Leishmania major, the cause of cutaneous leishmaniasis

Cutaneous leishmaniasis is initiated by the bite of an infected sandfly and inoculation of Leishmania major parasites into the mammalian skin. Macrophages are known to play a central role in the course of infection because they are the prime host cells and function as antigen-presenting cells (APC) for induction of the cell-mediated immune response. However, in addition to macrophages in the dermis, the skin contains epidermal Langerhans cells (LC) which can present antigen (Ag) to T cells. Therefore, using a murine model of cutaneous leishmaniasis, we analyzed the ability of epidermal cells to induce a T cell response to L.major. The results demonstrated that freshly isolated LC, but not cultured LC, are highly active in presenting L.major Ag in vitro to T cells from primed mice and to a L.major-specific T cell clone. Furthermore, freshly isolated LC had the ability to retain L.major Ag in immunogenic form for at least 2 days. Their efficiency was much greater than that of irradiated spleen cells, a standard population of APC. LC stimulated both T cell proliferation and production of the lymphokines interleukin (IL)-2 and IL-4. The response was Ag specific and could be induced by lysate of L.major parasites and by live organisms. The data suggest that epidermal LC are important APC in cutaneous leishmaniasis. They may perform a critical function by capturing L.major Ag in the skin and presenting it either to quiescent T cells circulating through the draining lymph node or locally to T effector cells infiltrating the cutaneous lesion.

Immunoblotting as a valuable tool to differentiate human visceral leishmaniasis from lymphoproliferative disorders and other clinically similar diseases

Diseases presenting with splenomegaly, fever and pancytopenia require intensive differential diagnostic considerations. These diseases include lymphoproliferative and autoimmune diseases, but also chronic infections like mansonian schistosomiasis or visceral leishmaniasis (kala-azar). Diagnosis for the latter is usually performed by testing for the presence of antileishmanial antibodies using the immunofluorescence test (IFT) or the enzyme-linked immunosorbent assay (ELISA) technique. Here, we report on patients who displayed positive antileishmanial antibody titres in the IFT and/or ELISA, but did not develop kala-azar and were eventually diagnosed as having one of the non-kala-azar diseases listed above. These false-positive sera proved to be seronegative when tested on a Leishmania immunoblot. Our studies lead us to recommend the immunoblot technique as a confirmatory test in cases with doubtful IFT or ELISA antibody titres.

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.