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

Mevalonate kinase of Leishmania donovani promotes its survival and plays a pivotal role in pathogenesis

The infectivity of Leishmania is determined by its ability to invade and evade host and its thriving capacity within the macrophage. Our study revealed the role of Leishmania donovani mevalonate kinase (MVK), an enzyme of mevalonate pathway in visceral leishmaniasis pathogenesis. Peritoneal exudate cells (PEC)-derived macrophages from BALB/c mice were infected with wild type (WT), MVK over expressing (MVK OE) and knockdown (KD) parasites and MVK OE parasites were found to be more infective than WT and MVK KD parasites. Incubation of macrophages with MVK OE parasites declined inducible nitric oxide synthase (iNOS) expression as well as nitric oxide (NO) production, both by 2 times in comparison to WT parasites. Moreover, ∼3 fold increase in Arginase1 expression indicated that MVK might induce polarization of macrophage towards M2, favouring the survival of parasite within the macrophages. Post 24 h infection of the macrophages with mutant strains, the levels of different cytokines (TNF-α, IL-12, IL-10 and IFN-γ) were measured. Infection of macrophages with MVK OE parasites showed an increase in the level of anti-inflammatory cytokine: IL-10 while infection with MVK KD parasites exhibited an increase in the level of pro-inflammatory cytokines: TNF-α, IL-12, and IFN-γ. Hence, Leishmania donovani mevalonate kinase (LdMVK) modulates macrophage functions and has a significant role in pathogenesis.

Potential biomarkers of immune protection in human leishmaniasis

Leishmaniasis is a vector-borne neglected tropical disease endemic in over 100 countries around the world. Available control measures are not always successful, therapeutic options are limited, and there is no vaccine available against human leishmaniasis, although several candidate antigens have been evaluated over the last decades. Plenty of studies have aimed to evaluate the immune response development and a diverse range of host immune factors have been described to be associated with protection or disease progression in leishmaniasis; however, to date, no comprehensive biomarker(s) have been identified as surrogate marker of protection or exacerbation, and lack of enough information remains a barrier for vaccine development. Most of the current understanding of the role of different markers of immune response in leishmaniasis has been collected from experimental animal models. Although the data generated from the animal models are crucial, it might not always be extrapolated to humans. Here, we briefly review the events during Leishmania invasion of host cells and the immune responses induced against Leishmania in animal models and humans and their potential role as a biomarker of protection against human leishmaniasis.

Regulation of macrophage subsets and cytokine production in leishmaniasis

Macrophages are host cells for parasites of the genus Leishmania where they multiply inside parasitophorous vacuoles. Paradoxically, macrophages are also the cells responsible for killing or controlling parasite growth, if appropriately activated. In this review, we will cover the patterns of macrophage activation and the mechanisms used by the parasite to circumvent being killed. We will highlight the impacts of the vector bite on macrophage activation. Finally, we will discuss the ontogeny of macrophages that are infected by Leishmania spp.

A historical review of the role of cytokines involved in leishmaniasis

Leishmaniasis is an infectious disease caused by the Leishmania genus, affecting millions of persons in the world. Despite increased studies, no vaccine has been developed against leishmaniasis, and drug resistance is evolving in some Leishmania species (spp). Innate and acquired immune cells and their associated cytokines interplay together to determine the immune responses related outcomes in leishmaniasis. Interferon (IFN)-γ or macrophage activating factor (MAF) is the first effective lymphokine (LK), with a related function to leishmaniasis, discovered in 1979. This review article discussed the history of cytokines involved in Leishmania infection, and it is the first report demonstrating the involvement in the disease by focusing on cutaneous leishmaniasis. Up to now, the role of many cytokines has been determined and the literature review showed that IL-35 is the latest known cytokine involved in leishmaniasis. This review revealed that the cytokines have pleiotropic effects, depending upon the cytokine environment, generated during the infection and the host genetic background or infecting Leishmania spp. Overall, advances in our knowledge of immune cells and their secreted cytokines, contributing to the protection or pathological process of leishmaniasis may help to reach new approaches for immunotherapy.

Gene expression profile of cytokines produced in biopsies from patients with American cutaneous leishmaniasis

American cutaneous leishmaniasis (ACL) causes a local inflammatory process, inducing expression of several cytokine genes. Particularly, IFN-γ can predict to disease susceptibility. Based in these data, this study was aimed to investigate the gene expression profile of IFN-γ, IL-10, IL-27, TNF-γ, TGF-β and IL-6 produced in biopsies from ACL patients; and whether the gene expression profile of IFN-γ could determine the disease evolution. Gene expression of 6 cytokines was investigated in 40 formalin-fixed paraffin embedded (FFPE) biopsies from patients with cutaneous leishmaniosis (CL); and 10 FFPE biopsies from patients with mucosal leishmaniasis (ML) (control). All 50 patients were infected with Leishmania (Viannia) braziliensis. Gene expression was determined by qPCR; and a normal control group was used for calculations (5 normal biopsies). Values were expressed as Relative Quantification (RQ). The 40 CL patients were classified into 2 groups. CLlowIFN-γ, 35 patients with RQ for IFN-γ below 100; and CLhighIFN-γ, 5 (12.5%) patients with RQ above 100. Significant increase of mRNA levels of IFN-γ, IL-10 and IL-27 was shown in CLhighIFN-γ group when compared with CLlowIFN-γ and ML groups. TNF-α levels in CLlowIFN-γ group were higher than CLhighIFN-γ and ML groups. TGF-β and IL-6 were similar in 3 groups. Comparison of cytokine expression/group showed that CLlowIFN-γ group had an equilibrium between the cytokines analyzed. In ML group, IFN-γ was over-expressed; but in CLhighIFN-γ group, besides IFN-γ, IL-27 was also over-expressed. The immune response to Leishmania induces to identification of some markers, which can be determined by analysis by gene expression of cytokines produced in biopsies.

IFN-γ-Dependent Recruitment of CD4(+) T Cells and Macrophages Contributes to Pathogenesis During Leishmania amazonensis Infection

Interferon gamma (IFN-γ) is a key factor in the protection of hosts against intracellular parasites. This cytokine induces parasite killing through nitric oxide and reactive oxygen species production by phagocytes. Surprisingly, during Leishmania amazonensis infection, IFN-γ plays controversial roles. During in vitro infections, IFN-γ induces the proliferation of the amastigote forms of L. amazonensis. However, this cytokine is not essential at the beginning of an in vivo infection. It is not clear why IFN-γ does not mediate protection during the early stages of infection. Thus, the aim of our study was to investigate the role of IFN-γ during L. amazonensis infection. We infected IFN-γ(-/-) mice in the footpad and followed the development of leishmaniasis in these mice compared with that in WT mice. CD4(+) T lymphocytes and macrophages migrated earlier to the site of infection in the WT mice, and the earlier migration of these 2 cell types was associated with lesion development and parasite growth, respectively. These differences in the infiltrate populations were explained by the increased expression of chemokines in the lesions of the WT mice. Thus, we propose that IFN-γ plays a dual role during L. amazonensis infection; it is an important inducer of effector mechanisms, particularly through inducible nitric oxide synthase expression, and conversely, it is a mediator of inflammation and pathogenesis through the induction of the expression of chemokines. Our data provided evidence for a pathogenic effect of IFN-γ production during leishmaniasis that was previously unknown.

Age modifies the immunologic response and clinical presentation of American tegumentary leishmaniasis

Leishmania (Viannia) braziliensis is the main causal agent of American tegumentary leishmaniasis (ATL) that may present as cutaneous, mucosal, or disseminated cutaneous leishmaniasis. The disease is highly prevalent in young males and there is a lack of studies of ATL in the elderly. Herein, we compared clinical manifestations, immunologic response, and response to antimony therapy between patients > 60 years of age (N = 58) and patients who were 21-30 years of age (N = 187). The study was performed in Corte de Pedra, Bahia, Brazil, a well-known area of L. braziliensis transmission. Cytokine production by cultured peripheral blood mononuclear cells stimulated with soluble Leishmania antigen was performed. Elderly subjects more frequently had a previous history of cutaneous leishmaniasis, large lesions, or mucosal leishmaniasis, and they were less likely to have lymphadenopathy. There was no difference regarding gender and response to therapy. Peripheral blood mononuclear cells from elderly subjects produced a similar amount of tumor necrosis factor than young patients but they produced less interferon-gamma and more interleukin-10 than young subjects. We concluded that elderly patients with cutaneous leishmaniasis should be searched for mucosal or disseminated leishmaniasis. The decreased interferon-gamma production and increase in interleukin-10 observed in elderly patients may contribute to parasite persistence and L. braziliensis infection dissemination.

Role of hemodialysis with high cut-off membranes in a patient with a non-recognized leishmaniasis

BACKGROUND

We report here a case of a woman affected by fever, weight loss, splenomegaly, and leucopenia associated with trombocytopenia, transferred to the intensive care unit with acute kidney injury and septic shock.

METHODS

Patient was treated with high cut-off continuous veno-venous hemodialysis (HCO-CVVHD).

RESULTS

During treatment, the patient experienced a stable improvement in the hemodynamic, pulmonary function and tissue perfusion parameters. After 48 h of treatment, significant reductions in SOFA score (from 12, before starting the procedure, to 6) and in serum inflammatory mediators (as IL-6, from 599-568 pg/ml) were observed. Leishmania infection was identified as responsible of the septic condition only 48 h after removing hemodialysis. Antiprotozoal therapy was begun and the patient discharged.

CONCLUSIONS

By supporting the renal function and reducing systemic inflammation, HCO-CVVHD could be a useful bridge therapy. This procedure allowed the medical team to gain sufficient time to diagnose the type of infection and begin an etiological therapy.

Morita-Baylis-Hillman adduct shows in vitro activity against Leishmania (Viannia) braziliensis associated with a reduction in IL-6 and IL-10 but independent of nitric oxide

Current treatments for different clinical forms of leishmaniasis are unsatisfactory, highly toxic and associated with increasing failure rates resulting from the emergence of resistant parasites. Leishmania (Viannia) braziliensis is the main aetiological agent of different clinical forms of American tegumentary leishmaniasis, including the mucosal form for which treatment has high failure rates. The aim of this work was to investigate the activity of the Morita-Baylis-Hillman adduct, methyl 2-{2-[hydroxy(2-nitrophenyl)methyl])acryloyloxy} benzoate in vitro against isolates of L. (V.) braziliensis obtained from patients with different clinical manifestations of tegumentary leishmaniasis: localized cutaneous leishmaniasis, mucosal leishmaniasis and disseminated cutaneous leishmaniasis. The adduct effectively inhibited the growth of promastigotes of the different isolates of L. (V.) braziliensis (IC50 ⩽ 7·77 μg/ml), as well as reduced the infection rate of macrophages infected with these parasites (EC50 ⩽ 1·37 μg/ml). It is remarkable to state that the adduct was more effective against intracellular amastigotes (P ⩽ 0·0045). The anti-amastigote activity correlated with an immunomodulatory effect, since the adduct was able to decrease the production of IL-6 and IL-10 by the infected macrophages. However, its effect was independent of nitric oxide production. This work demonstrates the anti-leishmanial activity of methyl 2-{2-[hydroxy(2-nitrophenyl)methyl])acryloyloxy} benzoate and suggests its potential in the treatment of human infections caused by L. (V.) braziliensis.

A MATHEMATICAL MODEL OF IMMUNE RESPONSE IN CUTANEOUS LEISHMANIASIS

The TH1/TH2 paradigm has been largely used in the interpretation of several diseases, particularly in leishmaniasis. As far as we know there is no mathematical description of this model related to leishmaniasis. We have extended and modified a previous published set of equations1in order to adapt it to leishmanial disease particularities. The main modifications were: (1) the analysis of logistic and exponential parasite growth curves, (2) the assumption of the TH2 arm of the immune response having a positive action on parasite growth. The set of three simultaneous differential equations describing the TH1 arm, TH2 arm and parasite growth were analyzed for conditions of existence and stability of the solutions.

Stable solutions valid for the logistic and exponential parasite growth models, with its possible clinical correlations, were obtained in the following situations: (1) parasite and TH2 extinction [TH1 cure], (2) parasite extinction and TH1/TH2 co-existence [TH1/TH2 cure], (3) TH1 and parasite co-existence, TH2 extinction [stable TH1 infection], and (4) TH1, TH2 and parasite co-existence [stable TH1/TH2 infection]. TH2 and parasite co-existence associated to TH1 extinction [stable TH2 infection] was obtained only with the logistic growth model. The model also provides an alternative hypothesis for TH1 bias in resistant mice and emphazises the importance of natural immunity for the existence of chronic states.

The hydroxy-naphthoquinone lapachol arrests mycobacterial growth and immunomodulates host macrophages

The present study reports the anti-mycobacterial activity of 2-hydroxy-3-(3-methyl-2-butenyl)-1,4-naphthoquinone (lapachol) as well as its influence on macrophage functions. Lapachol (L) did not induce apoptosis/necrosis of THP-1 macrophages at ≤32 μg/mL. Mycobacterium avium liquid growth was arrested by ≥32 μg/mL and intra-macrophage proliferation by ≥16 μg/mL lapachol. The main immuno-modulatory effects of lapachol observed were an up-regulation of interferon-γ-receptor 1 (IFN-γR1) and major histocompatibility complex class II (MHCII) surface expression, and a marked inhibition of IL-10 secretion. Lapachol did not affect resting, IFN-γ- or toll-like receptor 2 (TLR2)-induced levels of oxygen and nitrogen metabolism key proteins nor the TLR2-mediated secretion of TNF-α, nor induced either oxidative or endoplasmic reticulum (ER) stress. Lapachol inhibited the surface expression of the co-stimulatory molecule CD86 but not that of CD80 and CD83. The results obtained indicate that the substituted naphthoquinone lapachol exhibits an anti-mycobacterial activity that is more efficient intra- than extra-cellularly, and exerts immuno-modulatory effects some of which may enhance the capacity of the host cell to control mycobacterial growth. The immune-modulatory action of lapachol could contribute to its more efficient intra-macrophage anti-mycobacterial activity.

Intrinsic antibody-dependent enhancement of microbial infection in macrophages: disease regulation by immune complexes

A wide range of microorganisms can replicate in macrophages, and cell entry of these pathogens via non-neutralising IgG antibody complexes can result in increased intracellular infection through idiosyncratic Fcγ-receptor signalling. The activation of Fcγ receptors usually leads to phagocytosis. Paradoxically, the ligation of monocyte or macrophage Fcγ receptors by IgG immune complexes, rather than aiding host defences, can suppress innate immunity, increase production of interleukin 10, and bias T-helper-1 (Th1) responses to Th2 responses, leading to increased infectious output by infected cells. This intrinsic antibody-dependent enhancement (ADE) of infection modulates the severity of diseases as disparate as dengue haemorrhagic fever and leishmaniasis. Intrinsic ADE is distinct from extrinsic ADE, whereby complexes of infectious agents with non-neutralising antibodies lead to an increased number of infected cells. Intrinsic ADE might be involved in many protozoan, bacterial, and viral infections. We review insights into intracellular mechanisms and implications of enhanced pathogenesis after ligation of macrophage Fcγ receptors by infectious immune complexes.

Leishmania interferes with host cell signaling to devise a survival strategy

The protozoan parasite Leishmania spp. exists as extracellular promastigotes in its vector whereas it resides and replicates as amastigotes within the macrophages of its mammalian host. As a survival strategy, Leishmania modulates macrophage functions directly or indirectly. The direct interference includes prevention of oxidative burst and the effector functions that lead to its elimination. The indirect effects include the antigen presentation and modulation of T cell functions in such a way that the effector T cells help the parasite survive by macrophage deactivation. Most of these direct and indirect effects are regulated by host cell receptor signaling that occurs through cycles of phosphorylation and dephosphorylation in cascades of kinases and phosphatases. This review highlights how Leishmania selectively manipulates the different signaling pathways to ensure its survival.

Immunological and genetic evidence for a crucial role of IL-10 in cutaneous lesions in humans infected with Leishmania braziliensis

In populations exposed to Leishmania braziliensis, certain subjects develop skin ulcers, whereas others are naturally protected against cutaneous leishmaniasis. We have evaluated which cytokines are most crucial in the development of skin lesions. We found that active lesions occur in subjects with polarized Th2 or mixed Th1/Th2 responses, both associated with elevated IL-10 production. IL-10 was strongly associated (p = 0.004, odd ratio (OR) = 6.8, confidence interval = 1.9-25) with lesions, excluding IFN-gamma, IL-12, TNF, IL-13, and IL-4 from the regression model. IL-10 was produced by blood monocytes and CD4(+)CD25(+) T lymphocytes (mostly Foxp3(+)). However, we did not observe any difference between the number of these cells present in the blood of subjects with active lesions and those present in resistant subjects. Genetic analysis of the IL10-819C/T polymorphism, located in the IL10 promoter, showed that the C allele increased the risk of lesions (OR = 2.5 (1.12-5.7), p = 0.003). Functional analysis of these variants showed allele-specific binding of nuclear factors. The IL10-819C/C genotype was associated with higher levels of IL-10 than C/T and T/T genotypes. These observations demonstrate an important role for IL-10 in skin lesions in humans infected with L. braziliensis, and identify circulating monocytes and Tregs as principal sources of IL-10 in these patients.

Deletion of IL-4Ralpha on CD4 T cells renders BALB/c mice resistant to Leishmania major infection

Effector responses induced by polarized CD4⁺ T helper 2 (Th2) cells drive nonhealing responses in BALB/c mice infected with Leishmania major. Th2 cytokines IL-4 and IL-13 are known susceptibility factors for L. major infection in BALB/c mice and induce their biological functions through a common receptor, the IL-4 receptor α chain (IL-4Rα). IL-4Rα–deficient BALB/c mice, however, remain susceptible to L. major infection, indicating that IL-4/IL-13 may induce protective responses. Therefore, the roles of polarized Th2 CD4⁺ T cells and IL-4/IL-13 responsiveness of non-CD4⁺ T cells in inducing nonhealer or healer responses have yet to be elucidated. CD4⁺ T cell–specific IL-4Rα (Lck^creIL-4Rα^−/lox) deficient BALB/c mice were generated and characterized to elucidate the importance of IL-4Rα signaling during cutaneous leishmaniasis in the absence of IL-4–responsive CD4⁺ T cells. Efficient deletion was confirmed by loss of IL-4Rα expression on CD4⁺ T cells and impaired IL-4–induced CD4⁺ T cell proliferation and Th2 differentiation. CD8⁺, γδ⁺, and NK–T cells expressed residual IL-4Rα, and representative non–T cell populations maintained IL-4/IL-13 responsiveness. In contrast to IL-4Rα^−/lox BALB/c mice, which developed ulcerating lesions following infection with L. major, Lck^creIL-4Rα^−/lox mice were resistant and showed protection to rechallenge, similar to healer C57BL/6 mice. Resistance to L. major in Lck^creIL-4Rα^−/lox mice correlated with reduced numbers of IL-10–secreting cells and early IL-12p35 mRNA induction, leading to increased delayed type hypersensitivity responses, interferon-γ production, and elevated ratios of inducible nitric oxide synthase mRNA/parasite, similar to C57BL/6 mice. These data demonstrate that abrogation of IL-4 signaling in CD4⁺ T cells is required to transform nonhealer BALB/c mice to a healer phenotype. Furthermore, a beneficial role for IL-4Rα signaling in L. major infection is revealed in which IL-4/IL-13–responsive non-CD4⁺ T cells induce protective responses.

Leishmaniasis is a disease induced by a protozoan parasite and transmitted by the sandfly. Several forms of infection are identified, and the different diseases have wide-ranging symptoms from localized cutaneous sores to visceral disease affecting many internal organs. Animal models of human cutaneous leishmaniasis have been established in which disease is induced by infecting mice subcutaneously with Leishmania major. Different strains of inbred mice have been found to be susceptible or resistant to L. major infection. “Healer” C57BL/6 mice control infection with transient lesion development. The protective response to infection in this strain is dominated by type 1 cytokines inducing parasite killing by nitric oxide. Conversely, “nonhealer” BALB/c mice are unable to control infection and develop nonhealing lesions associated with a dominant type 2 immune response driven by cytokines IL-4 and IL-13. However, mice deficient in IL-4/IL-13 signaling are not protected against development of cutaneous leishmaniasis. Here we describe a BALB/c mouse where the ability to polarize to a dominant type 2 response is removed by cell-specific deletion of the receptor for IL-4/IL-13 on CD4⁺ T cells. These mice are resistant to L. major infection similar to C57BL/6 mice, which highlights the role of T helper 2 cells in driving susceptibility and the protective role of IL-4/IL-13 signaling in non-CD4⁺ T cells in BALB/c mice.

Real-time reverse transcription-PCR quantification of cytokine mRNA expression in golden Syrian hamster infected with Leishmania infantum and treated with a new amphotericin B formulation

A real-time quantitative reverse transcription-PCR assay was developed for the quantification of cytokine mRNA expression in the golden Syrian hamster Mesocricetus auratus infected with Leishmania infantum and treated with amphotericin B (AMB) formulated in microspheres made of human serum albumin (HSA). Treatment was administered intravenously on days 69, 71, and 73 postinfection (p.i.) with 10(7) metacyclic promastigotes, at doses of 2 and 40 mg/kg of AMB. High infection levels were recorded for untreated animals by day 76 p.i., with parasite loads always about 2 log10 per gram higher in the liver than in the spleen. Treatment was highly effective with both doses, but at 40 mg/kg, almost complete parasite elimination was achieved. mRNA expression of gamma interferon (IFN-gamma) and, to a lesser extent, tumor necrosis factor alpha (TNF-alpha) and transforming growth factor beta (TGF-beta) in spleen cells was up-regulated in most animals of the untreated group. The mRNA expression of interleukin-4 was strongly down-regulated in untreated as well as treated infected animals. Treatment with the lower dose of AMB-HSA down-regulated the mRNA expression of IFN-gamma and TNF-alpha, with no effect on the deactivating cytokine TGF-beta. In contrast, treatment with the higher dose (40 mg/kg) of the formulation caused moderate up-regulation of IFN-gamma and TNF-alpha and strong suppression of TGF-beta. Treatment of noninfected animals did not alter the cytokine expression pattern with regard to untreated controls. Our results suggest that treatment of L. infantum-infected Syrian hamsters with highly effective nontoxic doses of AMB-HSA causes deactivation of the anti-inflammatory cytokine TGF-beta, which in turn results in up-regulation of the Th1 cytokines IFN-gamma and TNF-alpha.

Tuning of macrophage responses by Stat3-inducing cytokines: molecular mechanisms and consequences in infection

A successful response to pathogen challenge requires that a balance is achieved between the induction of efficient anti-microbial effector mechanisms and the avoidance of detrimental tissue damage. While the Toll-like receptor (TLR) system is innate immunity's sensor of infectious danger, macrophages receive activating as well as inhibitory signals via the Jak-Stat pathway. IFNgamma is key to the control of infection particularly with intracellular pathogens and depends on functional Stat1 signal transduction. Stat3 signalling is activated by a range of cytokines, including IL-10, IL-6 and IL-27. Here, recent progress in understanding the regulation of macrophage function in inflammation and infection by Stat3-activating cytokines is reviewed. The use of targeted mouse mutants of these cytokines, their receptors or signalling components, revealed the importance of the Stat3 axis in the control of infection and immunopathology. Genome-wide transcriptome analyses of macrophages under the influence of these cytokines have contributed to advances in defining the molecular mechanisms of macrophage activation and deactivation. Functional characterization of Stat3-target genes should now identify the molecular mediators of impaired pathogen control and tissue protection.

Does the Leishmania major paradigm of pathogenesis and protection hold for New World cutaneous leishmaniases or the visceral disease?

Parasitic protozoa of the genus Leishmania have provided a useful perspective for immunologists in terms of host defense mechanisms critical for the resolution of infection caused by intracellular pathogens. These organisms, which normally reside in a late endosomal, major histocompatibility complex (MHC) class II(+) compartment within host macrophages cells, require CD4(+) T-cell responses for the control of disease. The paradigm for the CD4(+) T-helper 1 (Th1)/Th2 dichotomy is largely based on the curing/non-curing responses, respectively, to Leishmania major infection. However, this genus of parasitic protozoa is evolutionarily diverse, with the cutaneous disease-causing organisms of the Old World (L. major) and New World (Leishmania mexicana/ Leishmania amazonensis) having diverged 40-80 million years ago. Further adaptations to survive within the visceral organs (for Leishmania donovani, Leishmania chagasi, and Leishmania infantum) must have been required. Consequently, significant differences in host-parasite interactions have evolved. Different virulence factors have been identified for distinct Leishmania species, and there are profound differences in the immune mechanisms that mediate susceptibility/resistance to infection and in the pathology associated with disease. These variations not only point to interesting features of the host-pathogen interaction and immunobiology of this genus of parasitic protozoa, but also have important implications for immunotherapy and vaccine development.

Sand fly saliva enhances Leishmania amazonensis infection by modulating interleukin-10 production

After transmission through the bite of female sand flies, Leishmania spp. can cause a broad spectrum of disease manifestations collectively known as leishmaniases. L. amazonensis is endemic in South America, where it causes cutaneous, diffuse cutaneous, and visceral leishmaniasis. In this study, we have provided evidence that salivary gland extracts (SGE) of Lutzomyia longipalpis enhances L. amazonensis infection. BALB/c mice infected intradermally in the ear with 10(5) metacyclic promastigotes of L. amazonensis together with SGE (equivalent to 0.5 gland) showed an early onset of disease and larger lesions that contained approximately 3-log-units more parasites than did controls. To determine the potential mechanism underlying this enhancement, we assessed cytokine production via reverse transcriptase PCR and enzyme-linked immunosorbent assay. Mice coinjected with parasites and SGE displayed higher levels of interleukin-10 (IL-10) mRNA in the ear tissues, as well as higher levels of IL-10 in supernatants of restimulated draining lymph node (LN) cells, than did controls. Flow cytometric analysis revealed high frequencies of IL-10-producing CD4(+) and CD8(+) T cells in the draining LN of mice coinjected with the parasite and SGE. In addition, we examined bone marrow derived-macrophage cultures and detected increased IL-10 but decreased nitric oxide (NO) production in cells exposed to SGE prior to infection with L. amazonensis. Together, these results imply that the sand fly saliva facilitates Leishmania evasion of the host immune system by modulating IL-10 production.

Enhanced replication of Leishmania amazonensis amastigotes in gamma interferon-stimulated murine macrophages: implications for the pathogenesis of cutaneous leishmaniasis

During Leishmania major infection in mice, gamma interferon (IFN-gamma) plays an essential role in controlling parasite growth and disease progression. In studies designed to ascertain the role of IFN-gamma in Leishmania amazonensis infection, we were surprised to find that IFN-gamma could promote L. amazonensis amastigote replication in macrophages (Mphis), although it activated Mphis to kill promastigotes. The replication-promoting effect of IFN-gamma on amastigotes was independent of the source and genetic background of Mphis, was apparently not affected by surface opsonization of amastigotes, was not mediated by interleukin-10 or transforming growth factor beta, and was observed at different temperatures. Consistent with the different fates of promastigotes and amastigotes in IFN-gamma-stimulated Mphis, L. amazonensis-specific Th1 transfer helped recipient mice control L. amazonensis infection established by promastigotes but not L. amazonensis infection established by amastigotes. On the other hand, IFN-gamma could stimulate Mphis to limit amastigote replication when it was coupled with lipopolysaccharides but not when it was coupled with tumor necrosis factor alpha. Thus, IFN-gamma may play a bidirectional role at the level of parasite-Mphi interactions; when it is optimally coupled with other factors, it has a protective effect against infection, and in the absence of such synergy it promotes amastigote growth. These results reveal a quite unexpected aspect of the L. amazonensis parasite and have important implications for understanding the pathogenesis of the disease and for developing vaccines and immunotherapies.

The site of cutaneous infection influences the immunological response and clinical outcome of hamsters infected with Leishmania panamensis

We determined that the site of inoculation (foot or snout) influences the clinical evolution and immune responses of hamsters infected with Leishmania (Viannia) panamensis. Hamsters infected in the snout showed (i) a more rapid and severe lesion evolution at multiple time points (P < 0.05), (ii) a more extensive inflammatory infiltrate and tissue necrosis, (iii) a higher tissue parasite burden, (iv) a higher antibody titre (P < 0.01), but lower antigen-specific spleen cell proliferative response (P = 0.02), and (v) a slower response to anti-leishmanial drug treatment (P < 0.002). In both inoculation groups there was co-expression of type 1 (IFN-gamma and IL-12) and some type 2 (IL-10 and TGF-beta, but not IL-4) cytokines in the cutaneous lesions and spleen. Early in the course of infection, hamsters infected in the snout showed higher expression of splenic IL-10 (P = 0.04) and intra-lesional IFN-gamma (P = 0.02) than foot infections. No expression of IL-12p40 or IL-4 was detected. During the chronic phase, snout lesions expressed more IFN-gamma (P = 0.001), IL-12p40 (P = 0.01), IL-10 (P = 0.009) and TGF-beta (P = 0.001), and the level of expression of each of these cytokines correlated with lesion size (P < or = 0.01). These results suggest that the site of infection influences the clinical outcome in experimental cutaneous leishmaniasis, and that the expression of macrophage-deactivating type 2 cytokines and/or an exaggerated type 1 proinflammatory cytokine response may contribute to lesion severity.

IL-10 leads to a higher parasite persistence in a resistant mouse model of Leishmania major infection

IL-10 is a cytokine secreted by a wide variety of cell types and has pleiotropic activities, mainly as a modulator of the immune response. In this study, we tested in a direct way the influence of IL-10 expression on Leishmania major infection in resistant mice. We report that C57BL/6 mice treated with a single inoculation of recombinant adenovirus vector-expressing viral IL-10 (Ad-vIL-10), 1 day before parasitic challenge, exhibited a dual effect on footpad swelling, characterized by a decrease on lesion size at the early stage of the infection, followed by a rapid increase of these lesions that attained the complete healing later in infection. The reduction in lesion swelling in vIL-10 treated mice was accompanied by a decrease cellular infiltration of lymphocytes and monocytes at the site of parasite inoculation. Most significantly, vIL-10 administration led to a higher parasite burden in the draining popliteal lymph nodes late during infection, when the complete healing of the lesions was already achieved. RT-PCR analysis showed no important modification of cytokine transcripts in vIL-10 treated mice, early in infection, indicating no changes in mouse phenotype from resistant to susceptible status. Therefore, IL-10 administration influenced the outcome of the disease by modifying the inflammation and local cell recruitment at the site of parasite penetration and by leading to an enhanced residual parasite load in popliteal lymph nodes later in infection. The implication of IL-10 on the host immune status and the establishment and outcome of the infection is discussed.

The role of interleukin (IL)-10 in the persistence of Leishmania major in the skin after healing and the therapeutic potential of anti-IL-10 receptor antibody for sterile cure

Some pathogens (e.g., Mycobacterium tuberculosis, Toxoplasma gondii, Leishmania spp) have been shown to persist in their host after clinical cure, establishing the risk of disease reactivation. We analyzed the conditions necessary for the long term maintenance of Leishmania major in genetically resistant C57BL/6 mice after spontaneous healing of their dermal lesions. Interleukin (IL)-10 was found to play an essential role in parasite persistence as sterile cure was achieved in IL-10-deficient and IL-4/IL-10 double-deficient mice. The requirement for IL-10 in establishing latency associated with natural infection was confirmed in IL-10-deficient mice challenged by bite of infected sand flies. The host-parasite equilibrium was maintained by CD4+ and CD8+ T cells which were each able to release IL-10 or interferon (IFN)-gamma, and were found to accumulate in chronic sites of infection, including the skin and draining lymph node. A high frequency of the dermal CD4+ T cells released both IL-10 and IFN-gamma. Wild-type mice treated transiently during the chronic phase with anti-IL-10 receptor antibodies achieved sterile cure, suggesting a novel therapeutic approach to eliminate latency, infection reservoirs, and the risk of reactivation disease.

Interdependency of interleukin-10 and interleukin-12 in regulation of T-cell differentiation and effector function of monocytes in response to stimulation with Cryptococcus neoformans

We previously demonstrated that the principal component of capsular material of Cryptococcus neoformans, glucuronoxylomannan (GXM), induces interleukin-10 (IL-10) secretion from human monocytes. Here we report that encapsulation of the yeast with GXM is able to down-regulate interleukin-12 (IL-12) production by monocytes that would normally occur in the absence of encapsulation. This phenomenon appeared to be the result of inhibition of the phagocytic process by encapsulation with GXM as well as of negative signals such as IL-10 secretion produced by interaction of GXM with leukocytes. Decreased secretion of IL-12 correlated with decreased release of gamma interferon (IFN-gamma) from T cells, suggesting a role for encapsulation with GXM in hindering a T helper type 1 (Th1) response. This is supported by the ability of encapsulation with GXM to limit increased expression of B7-1 costimulatory molecules that otherwise might limit IL-10 secretion. Endogenous IL-10 played a critical role in modulatory activity associated with encapsulation with GXM. Blocking IL-10 with monoclonal antibody to IL-10 resulted in increased (i) IL-12 secretion, (ii) IFN-gamma release from T cells, and (iii) killing of C. neoformans by monocytes. These results suggest that encapsulation with GXM limits development of a protective Th1-type response, an inhibitory process in which IL-10 plays a critical role. Scavengers of GXM and/or IL-10 could be useful in a protective Th1-type response in patients with cryptococcosis.

Leishmania donovani: evolution and architecture of the splenic cellular immune response related to control of infection

Infection with the protozoan Leishmania donovani in humans is usually subclinical. Parasites probably persist for the life of the host and the low-level infection is controlled by the cellular immune response. To better understand the mechanisms related to the control of infection, we studied the evolution and architecture of the splenic cellular immune response in a murine model that is most representative of human subclinical infection. Following systemic inoculation with L. donovani, the parasites were primarily localized to the macrophage-rich splenic red pulp. There was an initial increase in the numbers of T cells and dendritic cells in the periarteriolar lymphoid sheath and marginal zone, but the red pulp (where parasitized macrophages were prominent) remained free of these cells until later in the course of infection. Thus, T cells did not colocalize with parasitized red pulp macrophages until later in the course of infection. Early in the course of infection, IL-10 production within the marginal zone and TGF-beta production by cells in the red pulp were prominent. These macrophage-inhibitory cytokines may contribute to the establishment of the infection and early parasite replication. By day 28 of infection, when the visceral parasite burden began to decline, the number of IL-10-producing spleen cells was back to the baseline level, but IFN-gamma production was higher and the number of IL-12-producing cells was increased dramatically. At this time T cells and dendritic cells had moved out of the lymphoid follicle and marginal zone into the red pulp where the parasites were located. These findings therefore suggest that control of infection is associated with IFN-gamma and IL-12 production and migration of T cells and dendritic cells to the site of chronic parasitism.

Anti-inflammatory response in patients with obstructive jaundice caused by biliary malignancy

BACKGROUND

Obstructive jaundice potentially modulates the host defense mechanism resulting in perioperative infection. It has been reported that a systemic inflammatory response occurs in patients with obstructive jaundice. An anti-inflammatory response was studied in 29 jaundiced patients undergoing biliary drainage.

RESULTS

Plasma concentrations of interleukin (IL)-10, soluble tumor necrosis factor receptor (STNFR) p55, STNFR p75, IL-1 receptor antagonist (IL-1ra), IL-6 and soluble CD14 (sCD14) were measured by using immunoassay. Plasma concentrations of IL-10, STNFR p55, STNFR p75, IL-1ra, IL-6 and sCD14 were significantly higher in jaundiced patients than in the controls (P < 0.01). After biliary drainage, the concentrations of IL-10, the three cytokine antagonists, and IL-6 decreased significantly (P < 0.05). The sCD14 concentration did not decrease. At the time of drainage, the concentrations of STNFR p55 and STNFR p75 were significantly higher in 10 patients with positive bile cultures than in 19 patients with negative bile cultures (P < 0.05). Bile cultures became positive 14 days after drainage in 10 patients, and remained negative in nine. The concentration of STNFR p55 before drainage was significantly higher in the former group (P = 0.05). The plasma concentrations of IL-10 and STNFRs were significantly correlated with the IL-6 concentration, body temperature and the white blood cell count (P < 0.05). Serum total bilirubin levels did not affect plasma levels of anti-inflammatory mediators, and sCD14.

CONCLUSION

Jaundiced patients exhibited an anti-inflammatory immune response that potentially modulates the host defense mechanism and results in anergy and increased susceptibility to infection. Biliary infection may be one of the major stimuli of the immune response.

Immunomodulatory role of interleukin-10 in visceral leishmaniasis: defective activation of protein kinase C-mediated signal transduction events

Leishmania donovani, an intracellular protozoan parasite, challenges host defense mechanisms by impairing the signal transduction of macrophages. In this study we investigated whether interleukin-10 (IL-10)-mediated alteration of signaling events in a murine model of visceral leishmaniasis is associated with macrophage deactivation. Primary in vitro cultures of macrophages infected with leishmanial parasites markedly elevated the endogenous release of IL-10. Treatment with either L. donovani or recombinant IL-10 (rIL-10) inhibited both the activity and expression of the Ca2+-dependent protein kinase C (PKC) isoform. However, preincubation with neutralizing anti-IL-10 monoclonal antibody (MAb) restored the PKC activity in the parasitized macrophage. Furthermore, we observed that coincubation of macrophages with rIL-10 and L. donovani increased the intracellular parasite burden, which was abrogated by anti-IL-10 MAb. Consistent with these observations, generation of superoxide (O2-) and nitric oxide and the release of murine tumor necrosis factor-alpha were attenuated in response to L. donovani or rIL-10 treatment. On the other hand, preincubation of the infected macrophages with neutralizing anti-IL-10 MAb significantly blocked the inhibition of nitric oxide and murine tumor necrosis factor-alpha release by the infected macrophages. These findings imply that infection with L. donovani induces endogenous secretion of murine IL-10, which in turn facilitates the intracellular survival of the protozoan and orchestrates several immunomodulatory roles via selective impairment of PKC-mediated signal transduction.

The role of IL-10 in promoting disease progression in leishmaniasis

To determine the role of IL-10 in cutaneous leishmaniasis, we examined lesion development following Leishmania major infection of genetically susceptible BALB/c mice lacking IL-10. Whereas normal BALB/c mice developed progressive nonhealing lesions with numerous parasites within them, IL-10(-/-) BALB/c mice controlled disease progression, and had relatively small lesions with 1000-fold fewer parasites within them by the fifth week of infection. We also examined a mechanism whereby Leishmania induced the production of IL-10 from macrophages. We show that surface IgG on Leishmania amastigotes allows them to ligate Fc gamma receptors on inflammatory macrophages to preferentially induce the production of high amounts of IL-10. The IL-10 produced by infected macrophages prevented macrophage activation and diminished their production of IL-12 and TNF-alpha. In vitro survival assays confirmed the importance of IL-10 in preventing parasite killing by activated macrophages. Pretreatment of monolayers with either rIL-10 or supernatants from amastigote-infected macrophages resulted in a dramatic enhancement in parasite intracellular survival. These studies indicate that amastigotes of Leishmania use an unusual and unexpected virulence factor, host IgG. This IgG allows amastigotes to exploit the antiinflammatory effects of Fc gamma R ligation to induce the production of IL-10, which renders macrophages refractory to the activating effects of IFN-gamma.

A soluble form of the murine common gamma chain is present at high concentrations in vivo and suppresses cytokine signaling

The common gamma-chain (gammac) is a component of the receptors for IL-2, IL-4, IL-7, IL-9, and IL-15 and is essential for their signal transduction. Western blotting and a newly established enzyme-linked immunosorbent assay detected substantial constitutive levels (50-250 ng/mL) of soluble gammac (sgammac) in sera of murine inbred strains. It was demonstrated that purified immune cells, such as T, B, and natural killer cells, and macrophages released this protein after activation. Transfection experiments with cDNA encoding the full-length gammac showed that shedding of the transmembrane receptor led to the release of sgammac. The shedding enzymes, however, appeared to be distinct from those cleaving other cytokine receptors because inhibitors of metalloproteases (eg, TAPI) did not influence sgammac release. In vivo, superantigen-induced stimulation of T cells enhanced sgammac serum concentrations up to 10-fold within 6 hours. Because these findings demonstrated regulated expression of a yet unknown molecule in the immune response, further experiments were performed to assess the possible function(s) of sgammac. A physiological role of sgammac was indicated by its capacity to specifically inhibit cell growth induced by gammac-dependent cytokines. Mutational analysis revealed that the C-terminus and the WSKWS motif are essential for the cytokine inhibitory effect of the sgammac and for binding of the molecule to cytokine receptor-expressing cells. Thus, competitive displacement of the transmembrane gammac by excess sgammac is the most likely mechanism of cell growth inhibition. It was implied that naturally produced sgammac is a negative modulator of gammac-dependent cytokines.

Protection of trinitrobenzene sulfonic acid-induced colitis by an interleukin 2-IgG2b fusion protein in mice

BACKGROUND & AIMS

We have shown in previous studies that an interleukin 2 (IL-2)-IgG2b fusion protein suppresses both humoral and cellular immune reactions in a murine model of DTH reaction. We now analyze the effects of IL-2-IgG2b in a model of intestinal inflammation in mice induced by the hapten reagent 2,4, 6-trinitrobenzene sulfonic acid (TNBS) that mimics immunologic characteristics of human Crohn's disease.

METHODS

In TNBS-induced colitis, colonic and splenic T-cell subsets were characterized by immunohistochemistry and flow cytometry. Cytokine synthesis was studied by semiquantitative reverse-transcription polymerase chain reaction and intracellular cytokine staining in CD4(+) T cells.

RESULTS

When mice were treated with IL-2-IgG2b, improvement in both wasting disease and histopathologic signs of colonic inflammation was observed. An increase in the number of colonic CD4(+)/CD25(+) T cells and increased synthesis of the immunosuppressive cytokine IL-10 also occurred. The protective role of IL-10 was demonstrated by the finding that neutralization of IL-10 in vivo using IL-10-specific antibodies inhibited the IL-2-IgG2b effects in TNBS-induced colitis.

CONCLUSIONS

These studies show for the first time that the IL-2-IgG2b fusion protein can abrogate experimental colitis by local induction of IL-10-secreting T cells.

A Transgenic Model to Analyze the Immunoregulatory Role of IL-10 Secreted by Antigen-Presenting Cells

IL-10 is a cytokine secreted by a wide variety of cells type that has pleiotropic stimulatory and suppressive activities on both lymphoid and myeloid cells in vitro. To analyze the consequences of high IL-10 secretion by APCs in immune responses, we produced transgenic mice expressing human IL-10 directed by the MHC class II Ea promoter. Despite alterations in the development of T and B cells, no gross abnormalities were detected in peripheral lymphocyte populations or serum Ig levels. However, when immunized using conditions that give either a Th2-type or a Th1-type response, IL-10 transgenic mice failed to mount a significant T or B cell immune response to OVA. IL-10 transgenic mice were also highly susceptible to infection with intracellular pathogens like Listeria monocytogenes or Leishmania major, in contrast to IL-10 transgenic mice, where the transgene was express in T cells. Finally, the recently described stimulatory effect of IL-10 on CD8+ T cells was confirmed by the ability of IL-10 transgenic mice to limit the growth of immunogenic tumors by a CTL-mediated mechanism. These results demonstrate, that, depending on the type of immune response, IL-10 can mediate immunosuppressive or immunostimulatory activities in vivo.

Leishmania donovani infection of a susceptible host results in apoptosis of Th1-like cells: rescue of anti-leishmanial CMI by providing Th1-specific bystander costimulation

A protective immune response against Leishmania donovani infection is mediated by T-helper type 1 (Th1) cells. Th1 induced cell-mediated immunity (CMI), as assessed by anti-leishmanial DTH response, is lost in a susceptible host such as BALB/c mice. Although the impaired Th1 function eventuates in unhindered parasite growth and in manifestation of the susceptible phenotype, the mechanism of down-regulation of the Th1 function is yet to be elucidated. Here, we provide evidence that the parasite down-regulates the expression of a Th1-specific costimulatory molecule, M150, on the surface of infected BALB/c mice-derived macrophages. Th cells are rendered unresponsive to anti-CD3 Ab-mediated stimulation after interaction with infected macrophages. The anergized T cells produce much less IL-2, IL-4 and IFN-gamma compared to those T cells which were costimulated using normal macrophages. The defect in proliferation, anti-CD3 Ab induced unresponsiveness and IFN-gamma but not IL-4 production can be restored by providing bystander costimulation through M150. These results not only unfold a novel immune evasion strategy used by the parasite but also clarify the mechanism of Th1 cell debilitation during the disease. Recovery of Th1 cytokine production by bystander costimulation through M150 may help in formulating a new strategy for the elimination of intracellular parasites.

Migration Inhibitory Factor Induces Killing of Leishmania major by Macrophages: Dependence on Reactive Nitrogen Intermediates and Endogenous TNF-α

Macrophage migration inhibitory factor (MIF) is a product of activated T cells, anterior pituitary cells, and macrophages. MIF plays an important role in LPS-induced shock and delayed-type hypersensitivity. Furthermore, MIF exhibits a proinflammatory spectrum of action, promoting TNF-α production by macrophages, and counter-regulates glucocorticoid suppression of cytokine production. Here, we report that purified recombinant MIF activates murine macrophages to kill Leishmania major, with maximal effects at concentrations above 1 μg/ml. This MIF-mediated activation is specific, since it can be blocked completely by anti-MIF mAb. The MIF-mediated activation is dependent on TNF-α produced endogenously by macrophages, because the administration of anti-TNF-α antiserum markedly reduced the MIF effect. No MIF-mediated activation was observed in macrophages derived from TNF receptor p55 knockout mice, thus demonstrating the requirement of the smaller TNF receptor molecule for autocrine TNF-α signaling. A highly specific inhibitor of the inducible nitric oxide synthase (iNOS), l-N6-(1-iminoethyl)lysine, dihydrochloride, also inhibited the action of MIF, suggesting an important role for iNOS in the antiparasitic properties of MIF. In line with this, no MIF-mediated activation was detected analyzing macrophages derived from iNOS-deficient mice. The effect of MIF was blocked completely by the macrophage-deactivating cytokines IL-10, IL-13, and TGF-β. Finally, the expression of MIF mRNA and protein was up-regulated in lymph nodes of mice during the first week after infection with L. major. MIF therefore represents a cytokine involved not only in the recruitment of proinflammatory cells during infection but also in the complex regulation of the antimicrobial activity of these cells.

Specific inhibition of interleukin-10 production in murine macrophage-like cells by phosphorothioate antisense oligonucleotides

The effects of phosphorothioate antisense oligonucleotides (AS-S-oligos) directed against murine interleukin-10 (IL-10) mRNA on IL-10 production in RAW264.7 cells, a murine macrophage-like cell line, when stimulated by lipopolysaccharide (LPS) were examined. Of the six AS-S-oligos used, AS-S-oligos directed against the 3'-untranslated region (3'-UTR) of IL-10 mRNA (AS6-S-oligo) showed the strongest inhibitory effect on IL-10 production, and this inhibition was dose and time dependent. Reverse transcription-polymerase chain reaction (RT-PCR) revealed that the antisense effect originated from a specific reduction of target IL-10 mRNA by hybridization with AS6-S-oligo. In addition, AS6-S-oligo did not affect tumor necrosis factor-alpha (TNF-alpha) production in cells stimulated by LPS, and S-oligos with control sequences did not affect IL-10 production. These findings suggested that AS6-S-oligo most powerfully inhibited IL-10 production in macrophages by an antisense mechanism.

Disulfide analysis reveals a role for macrophage migration inhibitory factor (MIF) as thiol-protein oxidoreductase

The molecular mechanism of action of macrophage migration inhibitory factor (MIF), a cytokine with a critical role in the immune and inflammatory response, has not yet been identified. Here we report that MIF can function as an enzyme exhibiting thiol-protein oxidoreductase activity. Using a decapeptide fragment of MIF (MF1) spanning the conserved cysteine sequence motif Cys57-Ala-Leu-Cys60 (CALC), Cys-->Ser mutants (C57S MIF, C60S MIF, and C57S/C60S MIF) of human MIF (wtMIF), and alkylated wtMIF, we show that this activity is mediated by the CALC region and is important for the macrophage-activating properties of MIF. Both wtMIF and MF1 were demonstrated to form an intramolecular disulfide bridge. Using two common oxidoreductase assays, MIF was shown to enzymatically catalyze the reduction of insulin and 2-hydroxyethyldisulfide (HED). Examination of wtMIF and the mutants by far-UV circular dichroism spectroscopy (CD) together with denaturation studies showed that substituting or reducing the cysteine residues of CALC led to a reduced conformational stability of MIF but did not significantly change its overall conformation. A functional role for the CALC region was revealed by subjecting the mutants and alkylated wtMIF to the enzymatic assays. Mutant C60S did not have any enzymatic activity while mutant C57S had a reduced activity. Thiol-modified wtMIF that was alkylated under oxidizing conditions was found to have full enzymatic activity, whereas alkylation of wtMIF under reducing conditions completely eliminated MIF-mediated redox activity. Importantly, further physiological relevance of the disulfide motif was obtained by examining the mutants and alkylated MIF in an immunological assay that involved the macrophage-activating properties of MIF. In this test, mutant C60S was essentially inactive and mutant C57S was partly active, indicating together that at least some of the cytokine-like biological activities of MIF are dependent on the presence of cysteine 57 and 60. Again, use of the alkylated MIF species confirmed the role of the cysteine motif for this MIF activity. In conclusion, our results argue (a) that MIF exhibits enzymatic oxidoreductase activity, (b) that this activity is dependent on the presence of the catalytic center that is formed by cysteine residues 57 and 60, and (c) that certain MIF-mediated immune processes are due to the cysteine-mediated redox mechanism.

Cloning of Syrian hamster (Mesocricetus auratus) cytokine cDNAs and analysis of cytokine mRNA expression in experimental visceral leishmaniasis

The Syrian golden hamster (Mesocricetus auratus) is uniquely susceptible to a variety of intracellular pathogens and is an excellent model for a number of human infectious diseases. The molecular basis for this high level of susceptibility is unknown, and immunological studies related to this model have been limited by the lack of available reagents. In this report we describe the cloning and sequence analysis of portions of the Syrian hamster interleukin 2 (IL-2), IL-4, gamma interferon (IFN-gamma), tumor necrosis factor alpha, IL-10, IL-12p40, and transforming growth factor beta cDNAs. In addition, we examined the cytokine response to infection with the intracellular protozoan Leishmania donovani in this animal model. Sequence analysis of the hamster cytokines revealed 69 to 93% homology with the corresponding mouse, rat, and human nucleotide sequences and 48 to 100% homology with the deduced amino acid sequences. The hamster IFN-gamma, compared with the mouse and rat homologs, had an additional 17 amino acids at the C terminus that could decrease the biological activity of this molecule and thus contribute to the extreme susceptibility of this animal to intracellular pathogens. The splenic expression of these genes in response to infection with L. donovani, the cause of visceral leishmaniasis (VL), was determined by Northern blotting. VL in the hamster is a progressive, lethal disease which very closely mimics active human disease. In this model there was pronounced expression of the Th1 cytokine mRNAs, with transcripts being detected as early as 1 week postinfection. Basal expression of IL-4 in uninfected hamsters was prominent but did not increase in response to infection with L. donovani. IL-12 transcript expression was detected at low levels in infected animals and paralleled the expression of IFN-gamma. Expression of IL-10, a potent macrophage deactivator, increased throughout the course of infection and could contribute to the progressive nature of this infection. These initial studies are the first to examine the molecular immunopathogenesis of a hamster model of VL infection and indicate that progressive disease in this model of VL is not associated with early polarization of the splenic cellular immune response toward a Th2 phenotype and away from a Th1 phenotype.

Exogenous interleukin-10 fails to decrease the mortality or morbidity of sepsis

OBJECTIVE

To determine if exogenous interleukin (IL)-10 will decrease the morbidity or mortality of sepsis induced by cecal ligation and puncture.

DESIGN

Prospective, randomized, controlled study.

SETTING

University research laboratory.

SUBJECTS

Adult, female, Balb¿c mice.

INTERVENTIONS

Balb¿c mice were subjected to cecal ligation and puncture with an 18- or 23-gauge needle and treated with triple antibiotics. Mice were injected subcutaneously with recombinant human IL-10 (diluted in normal saline with 0.1% mouse serum albumin) and followed until death. In a separate experiment, IL-10 was also injected subcutaneously and lipopolysaccharide (LPS) injected intraperitoneally and plasma tumor necrosis factor concentrations measured 90 mins later.

MEASUREMENTS AND MAIN RESULTS

In the LPS experiments, IL-10 decreased tumor necrosis factor (TNF) production by nearly 90%. For the cecal ligation and puncture experiments, temperature and movement were recorded continuously via implanted transmitters. Studies on mortality indicated that exogenous IL-10 given at 0, +6 and +12 hrs after surgery failed to increase survival when using an 18-gauge needle (alive:total cecal ligation and puncture alone 4:21; IL-10 10 microg/mouse 2:12; 1 microg/mouse 8:25; 0.1 microg/mouse 1:12) or a 23-gauge needle (cecal ligation and puncture alone 13:29; IL-10 1 microg 18:30). There was no difference in the number of hours to death between the groups. IL-10 did not prevent the hypothermia after cecal ligation and puncture or increase the animals' activity. To examine parameters of inflammation, mice were killed 8 hrs after 18-gauge cecal ligation and puncture. IL-10 (1 microg/mL) failed to reduce pulmonary neutrophil sequestration (lung myeloperoxidase, cecal ligation and puncture 107 +/- 10 [SEM], IL-10 107 +/- 5) or recruitment of neutrophils to the peritoneum (neutrophils x 10(6), cecal ligation and puncture 3.72 +/- 0.62; IL-10 3.49 +/- 0.37). IL-10 also failed to reduce the appearance of TNF or IL-6 in the plasma or peritoneal fluid. The chemokine KC was reduced in the peritoneal fluid but not the plasma and endogenous IL-10 production was not reduced in the peritoneum.

CONCLUSION

Our data indicate that exogenous IL-10 fails to improve morbidity or mortality in the clinically relevant cecal ligation and puncture model of sepsis.

Regional differences in the cellular immune response to experimental cutaneous or visceral infection with Leishmania donovani

Infection with the protozoan Leishmania donovani can cause serious visceral disease or subclinical infection in humans. To better understand the pathogenesis of this dichotomy, we have investigated the host cellular immune response to cutaneous or visceral infection in a murine model. Mice infected in the skin developed no detectable visceral parasitism, whereas intravenous inoculation resulted in hepatosplenomegaly and an increasing visceral parasite burden. Spleen cells from mice with locally controlled cutaneous infection showed strong parasite-specific proliferative and gamma interferon (IFN-gamma) responses, but spleen cells from systemically infected mice were unresponsive to parasite antigens. The in situ expression of IFN-gamma, interleukin-4 (IL-4), IL-10, IL-12, and inducible nitric oxide synthase (iNOS) mRNAs was determined in the spleen, draining lymph node (LN), and cutaneous site of inoculation. There was considerably greater expression of IFN-gamma and IL-12 p40 mRNAs in the LN draining a locally controlled cutaneous infection than in the spleen following systemic infection. Similarly, there was a high level of IFN-gamma production by LN cells following subcutaneous infection but no IFN-gamma production by spleen cells following systemic infection. Splenic IL-4 expression was transiently increased early after systemic infection, but splenic IL-10 transcripts increased throughout the course of visceral infection. IL-4 and IL-10 mRNAs were also increased in the LN following cutaneous infection. iNOS mRNA was detected earlier in the LN draining a cutaneous site of infection compared to the spleen following systemic challenge. Thus, locally controlled cutaneous infection was associated with antigen-specific spleen cell responsiveness and markedly increased levels of IFN-gamma, IL-12, and iNOS mRNA in the draining LN. Progressive splenic parasitism was associated with an early IL-4 response, markedly increased IL-10 but minimal IL-12 expression, and delayed expression of iNOS.

Structure activity studies of the cytokine macrophage migration inhibitory factor (MIF) reveal a critical role for its carboxy terminus

Carboxy-truncated mutants of human MIF (MIF(1-104) and MIF(1-109)) were used in structure activity studies. CD spectroscopy revealed an overall structural similarity between the mutants and MIF. Denaturant-induced unfolding demonstrated that the C-terminus contributed significantly to the conformational stability of MIF. This appears to be due to the formation of two C-terminal beta-strands. The mutants were enzymatically active, exhibiting half of the enzymatic redox activity of MIF. However, immunological analysis showed that deletion of both 5 and 10 C-terminal residues resulted in loss of the macrophage activating properties of MIF, providing functional evidence that the C-terminus is important for immunological activity and trimer formation. A more detailed study of the C-terminus may assist in identifying the molecular basis for the immunological and enzymatic activities of MIF.

Changes in swine macrophage phenotype after infection with African swine fever virus: cytokine production and responsiveness to interferon-gamma and lipopolysaccharide

Cytokines produced by cells of the immune system, including macrophages, can influence inflammatory responses to viral infection. This has been exploited by viruses, which have developed strategies to direct the immune response towards ineffective responses. African swine fever virus (ASFV) is a double-stranded DNA virus that infects macrophages of domestic swine. In this study, primary cells of monocyte macrophage lineage were obtained from the lungs, peritoneum or blood of domestic swine and, after infection with ASFV, supernatants were tested for cytokines using biological assays. The cytokine transforming growth factor-beta (TGF-beta) was detected after infection of macrophage preparations, but tumour necrosis factor (TNF) and interleukin-1 (IL-1) were not detected. ASFV-infected and uninfected macrophage populations were also tested to assess their ability to respond to cytokines by enhancing production of superoxide in the respiratory burst mechanism. Responses to interferon-gamma (IFN-gamma) and lipopolysaccharide (LPS) were suppressed in macrophage populations infected with virus, even at low multiplicities of infection. Addition of TGF-beta to uninfected macrophages resulted in a similar suppression of response, but antibody to TGF-beta did not prevent suppression induced by virus. These results are discussed in relation to the pathology of African swine fever.

Repeated Chlamydia trachomatis infection of Macaca nemestrina fallopian tubes produces a Th1-like cytokine response associated with fibrosis and scarring

Chlamydia trachomatis-associated female infertility and ectopic pregnancy are caused by postinflammatory fibrosis and scarring of the upper genital tract. Scarring of the upper genital tract is associated with multiple infectious episodes with C. trachomatis. To study the immune response that occurs with multiple infections of C. trachomatis in the female upper genital tract, a Macaca nemestrina model was used. Subcutaneous pockets containing autologous salpingeal tissue implants were inoculated three times with C. trachomatis. The inflammation after three inoculations was associated with a mononuclear infiltrate dominated by CD8 T-cell lymphocytes. Perforin mRNA was induced in infected pockets, demonstrating that activated cytolytic lymphocytes were present in the lesions. Fibrosis, as evidenced by fibroblast proliferation and connective tissue deposition, was observed by the third infection. Cytokine mRNAs induced by repeated chlamydial infection included gamma interferon, interleukin-2 (IL-2), IL-6, and IL-10 mRNAs, but IL-4 mRNA was not induced. Nearly identical findings were found in macaque fallopian tubes infected in situ repeatedly with C. trachomatis, validating the subcutaneous pocket model of chlamydial salpingitis. However, it was not possible to evaluate if there was an induction of perforin mRNA in infected salpingeal tubes in situ, because there was a high basal level of perforin mRNA in these tissues. These results suggest that repeated chlamydial infection of the female upper genital tract leads to CD8 T-cell predominance, a Th1-like cytokine milieu, and these inflammatory changes are associated with progression to fibrosis associated with female infertility.

Resistance to Leishmania major is linked to the H2 region on chromosome 17 and to chromosome 9

In Leishmaniasis, as in many infectious diseases, clinical manifestations are determined by the interaction between the genetics of the host and of the parasite. Here we describe studies mapping two loci controlling resistance to murine cutaneous leishmaniasis. Mice infected with L. major show marked genetic differences in disease manifestations: BALB/c mice are susceptible, exhibiting enlarging lesions that progress to systemic disease and death, whereas C57BL/6 are resistant, developing small, self-healing lesions. F2 animals from a C57BL/6 X BALB/c cross showed a continuous distribution of lesion score. Quantitative trait loci (QTL) have been mapped after a non-parametric QTL analysis on a genome-wide scan on 199 animals. QTLs identified were confirmed in a second cross of 271 animals. Linkage was confirmed to a chromosome 9 locus (D9Mit67-D9Mit71) and to a region including the H2 locus on chromosome 17. These have been named Imr2 and Imr1, respectively.

Role of nitric oxide in parasitic infections

Nitric oxide is produced by a number of different cell types in response to cytokine stimulation and thus has been found to play a role in immunologically mediated protection against a growing list of protozoan and helminth parasites in vitro and in animal models. The biochemical basis of its effects on the parasite targets appears to involve primarily inactivation of enzymes crucial to energy metabolism and growth, although it has other biologic activities as well. NO is produced not only by macrophages and macrophage-like cells commonly associated with the effector arm of cell-mediated immune reactivity but also by cells commonly considered to lie outside the immunologic network, such as hepatocytes and endothelial cells, which are intimately involved in the life cycle of a number of parasites. NO production is stimulated by gamma interferon in combination with tumor necrosis factor alpha or other secondary activation signals and is regulated by a number of cytokines (especially interleukin-4, interleukin-10, and transforming growth factor beta) and other mediators, as well as through its own inherent inhibitory activity. The potential for design of prevention and/or intervention approaches against parasitic infection (e.g., vaccination or combination chemo- and immunotherapy strategies) on the basis of induction of cell-mediated immunity and NO production appears to be great, but the possible pathogenic consequences of overproduction of NO must be taken into account. Moreover, more research on the role and regulation of NO in human parasitic infection is needed before its possible clinical relevance can be determined.