Maintaining the immunological balance in parasitic infections: a role for TGF-beta?

Dysregulation of cytokines expression in complicated falciparum malaria with increased TGF-β and IFN-γ and decreased IL-2 and IL-12

BACKGROUND

In Plasmodium falciparum infections, proinflammatory cytokine response is implicated in control of parasite multiplication as well as in disease pathogenesis. However, the regulation of proinflammatory and anti-inflammatory cytokine balance and its relation to disease severity remains poorly understood.

METHODS

We examined cytokines gene expression by quantitative real time-PCR technique in a case control study comprising of P. falciparum infected (n=58) and non infected (n=30) groups. P. falciparum infected were further stratified as complicated and uncomplicated as per WHO criterion and parasitaemia levels.

RESULTS

Higher expression of IL-2, IL-12α and TGF-β with decreased levels of IL-10 was seen in P. falciparum positivity. Complicated malaria was associated with enhanced expression of IFN-γ and TGF-β but lower IL-2 and IL-12α in comparison to uncomplicated malaria. Modeling of data suggested higher expression of IL-12α to be predictive of uncomplicated malaria [Odds ratio=3.074, 95% CI (1.254-7.536)] and was negatively associated with complicated malaria outcome (p=0.014). Interestingly, the probability of complicated malaria in males with elevated TNF-α expression was three times higher [p=0.05; Odds ratio=3.412, 95% CI (0.98-11.848)]. Age was also seen to be a factor with higher IL-8 in diseased young (p=0.012).

CONCLUSION

Our data suggested induction of balanced cytokine response in uncomplicated malaria while cytokine dysregulation with a role for TGF-β was indicated in complicated malaria. TH cells did not appear to be the source of increased IFN-γ expression associated with malaria severity.

In vivo, in vitro, and in silico studies suggest a conserved immune module that regulates malaria parasite transmission from mammals to mosquitoes

Human malaria can be caused by the parasite Plasmodium falciparum that is transmitted by female Anopheles mosquitoes. "Immunological crosstalk" between the mammalian and anopheline hosts for Plasmodium functions to control parasite numbers. Key to this process is the mammalian cytokine transforming growth factor-β1 (TGF-β1). In mammals, TGF-β1 regulates inducible nitric oxide (NO) synthase (iNOS) both positively and negatively. In some settings, high levels of NO activate latent TGF-β1, which in turn suppresses iNOS expression. In the mosquito, ingested TGF-β1 induces A. stephensi NOS (AsNOS), which limits parasite development and which in turn is suppressed by activation of the mosquito homolog of the mitogen-activated protein kinases MEK and ERK. Computational models linking TGF-β1, AsNOS, and MEK/ERK were developed to provide insights into this complex biology. An initial Boolean model suggested that, as occurs in mammalian cells, MEK/ERK and AsNOS would oscillate upon ingestion of TGF-β1. An ordinary differential equation (ODE) model further supported the hypothesis of TGF-β1-induced multiphasic behavior of MEK/ERK and AsNOS. To achieve this multiphasic behavior, the ODE model was predicated on the presence of constant levels of TGF-β1 in the mosquito midgut. Ingested TGF-β1, however, did not exhibit this behavior. Accordingly, we hypothesized and experimentally verified that ingested TGF-β1 induces the expression of the endogenous mosquito TGF-β superfamily ligand As60A. Computational simulation of these complex, cross-species interactions suggested that TGF-β1 and NO-mediated induction of As60A expression together may act to maintain multiphasic AsNOS expression via MEK/ERK-dependent signaling. We hypothesize that multiphasic behavior as represented in this model allows the mosquito to balance the conflicting demands of parasite killing and metabolic homeostasis in the face of damaging inflammation.

Expression of Tim-1 and Tim-3 in Plasmodium berghei ANKA infection

Cerebral malaria (CM) is a serious and often fatal complication of Plasmodium falciparum infections; however, the precise mechanisms leading to CM is poorly understood. Mouse malaria models have provided insight into the key events in pathogenesis of CM. T-cell immune response is known to play an important role in malaria infection, and members of the T-cell immunoglobulin- and mucin-domain-containing molecule (Tim) family have roles in T-cell-mediated immune responses. Tim-1 and Tim-3 are expressed on terminally differentiated Th2 and Th1 cells, respectively, and participate in the regulation of Th immune response. Until now, the role of Tim family proteins in Plasmodium infection remains unclear. In the present study, the mRNA levels of Tim-1, Tim-3, and some key Th1 and Th2 cytokines in the spleen of Kunming outbred mice infected with Plasmodium berghei ANKA (PbANKA) were determined using real-time polymerase chain reaction (qRT-PCR). Compared with uninfected controls, Tim-1 expression was significantly decreased in infected mice with CM at day 10 postinfection (p.i.) but significantly increased in infected mice with non-CM at day 22 p.i.; in contrast, Tim-3 expression was significantly increased in infected mice both with CM at day 10 p.i. and with non-CM at day 22 p.i. The expressions of IFN-γ, TNF-α, IL-10, and IL-12 were significantly increased but IL-4 was significantly decreased in infected mice with CM at days 10 p.i., whereas the expressions of IFN-γ, TNF-α, IL-4, IL-10, and TGF-β were significantly increased but IL-12 was significantly decreased in infected mice with non-CM at days 22 p.i. Furthermore, the expression of Tim-1 and Tim-3 could reflect Th2 and Th1 immune response in the spleen of PbANKA-infected mice, respectively. Our data suggest that PbANKA infection could inhibit the differentiation of T lymphocytes toward Th2 cells, promote the Th1 cell differentiation, and induce Th1-biased immune response in the early infective stage, whereas the infection could promote Th2 cell differentiation and induce Th2-biased immune response in the late infective stage. Our data indicate that both Tim-1 and Tim-3 may play a role in the process of PbANKA infection, which may represent a potential therapeutic target.

The effects of ingested mammalian blood factors on vector arthropod immunity and physiology

The blood feeding behavior of disease-transmitting arthropods creates a unique intersection between vertebrate and invertebrate physiology. Here, we review host blood-derived factors that persist through blood digestion to affect the lifespan, reproduction, and immune responses of some of the most common arthropod vectors of human disease.

Experimental murine fascioliasis derives early immune suppression with increased levels of TGF-β and IL-4

In fascioliasis, T-helper 2 (Th2) responses predominate, while little is known regarding early immune phenomenon. We herein analyzed early immunophenotype changes of BALB/c, C57BL/6, and C3H/He mice experimentally infected with 5 Fasciola hepatica metacercariae. A remarkable expansion of CD19(+) B cells was observed as early as week 1 post-infection while CD4(+)/CD8(+) T cells were down-regulated. Accumulation of Mac1(+) cells with time after infection correlated well with splenomegaly of all mice strains tested. The expression of tumor necrosis factor (TNF)-α mRNA in splenocytes significantly decreased while that of IL-4 up-regulated. IL-1β expression was down-modulated in BALB/c and C57BL/6 mice, but not in C3H/He. Serum levels of transforming growth factor (TGF)-β were considerably elevated in all mice during 3 weeks of infection period. These collective results suggest that experimental murine fascioliasis might derive immune suppression with elevated levels of TGF-β and IL-4 during the early stages of infection.

Cytokine and protein markers of leprosy reactions in skin and nerves: baseline results for the North Indian INFIR cohort

Background

Previous studies investigating the role of cytokines in the pathogenesis of leprosy have either been on only small numbers of patients or have not combined clinical and histological data. The INFIR Cohort study is a prospective study of 303 new multibacillary leprosy patients to identify risk factors for reaction and nerve damage. This study characterised the cellular infiltrate in skin and nerve biopsies using light microscopic and immunohistochemical techniques to identify any association of cytokine markers, nerve and cell markers with leprosy reactions.

Methodology/Principal Findings

TNF-α, TGF-β and iNOS protein in skin and nerve biopsies were detected using monoclonal antibody detection immunohistochemistry techniques in 299 skin biopsies and 68 nerve biopsies taken from patients at recruitment. The tissues were stained with hematoxylin and eosin, modified Fite Faraco, CD68 macrophage cell marker and S100.

Conclusions/Significance

Histological analysis of the biopsies showed that 43% had borderline tuberculoid (BT) leprosy, 27% borderline lepromatous leprosy, 9% lepromatous leprosy, 13% indeterminate leprosy types and 7% had no inflammation. Forty-six percent had histological evidence of a Type 1 Reaction (T1R) and 10% of Erythema Nodosum Leprosum. TNF-α was detected in 78% of skin biopsies (181/232), iNOS in 78% and TGF-β in 94%. All three molecules were detected at higher levels in patients with BT leprosy. TNF-α was localised within macrophages and epithelioid cells in the granuloma, in the epidermis and in dermal nerves in a few cases. TNF-α, iNOS and TGF-β were all significantly associated with T1R (p<0.001). Sixty-eight nerve biopsies were analysed. CD68, TNF-α and iNOS staining were detectable in 88%, 38% and 28% of the biopsies respectively. The three cytokines TNF-α, iNOS and TGF-β detected by immunohistochemistry showed a significant association with the presence of skin reaction. This study is the first to demonstrate an association of iNOS and TGF-β with T1R.

Leprosy affects skin and peripheral nerves. Although we have effective antibiotics to treat the mycobacterial infection, a key part of the disease process is the accompanying inflammation. This can worsen after starting antibacterial treatment with episodes of immune mediated inflammation, so called ‘reactions’. These reactions are associated with worsening of the nerve damage. We recruited a cohort of 303 newly diagnosed leprosy patients in North India with the aim of understanding and defining the pathological processes better. We took skin and nerve biopsies from patients and examined them to define which molecules and mediators of inflammation were present. We found high levels of the cytokines Tumour Necrosis Factor alpha, Transforming Growth Factor beta and inducible Nitric Oxide Synthase in biopsies from patients with reactions. We also found high levels of bacteria and inflammation in the nerves. These experiments tell us that we need to determine which other molecules are present and to explore ways of switching off the production of these pro-inflammatory molecules.

TGFB1 and IL8 gene polymorphisms and susceptibility to visceral leishmaniasis

Visceral leishmaniasis (VL) or Kala-azar is a serious protozoan infectious disease caused by an obligate intracellular parasite. Cytokines have a major role in determining progression and severity of clinical manifestations in VL. We investigated polymorphisms in the TGFB1and IL8 genes, which are cytokines known to have a role in onset and severity of the disease. Polymorphisms at TGFB1 -509 C/T and +869 T/C, and IL8 -251 A/T were analyzed by a PCR-RFLP technique, in 198 patients with VL, 98 individuals with asymptomatic infection positive for a delayed-type hypersensitivity test (DTH+) and in 101 individuals with no evidence of infection (DTH-). The presence of the T allele in position -509 of the TGFB1 gene conferred a two-fold risk to develop infection both when including those with clinical symptoms (DTH+ and VL, grouped) or when considering DTH+ only, respectively p = 0.007, OR = 1.9 [1.19-3.02] and p = 0.012, OR = 2.01 [1.17-3.79], when compared with DTH- individuals. In addition, occurrence of hemorrhage was associated with TGFB1 -509 T allele. We suggest that the -509 T allele of the TGFB1 gene, a cytokine with a biologically relevant role in the natural history of the disease, may contribute to overall susceptibility to infection by Leishmania and to severity of the clinical disease.

Transforming growth factor-β: activation by neuraminidase and role in highly pathogenic H5N1 influenza pathogenesis

Transforming growth factor-beta (TGF-β), a multifunctional cytokine regulating several immunologic processes, is expressed by virtually all cells as a biologically inactive molecule termed latent TGF-β (LTGF-β). We have previously shown that TGF-β activity increases during influenza virus infection in mice and suggested that the neuraminidase (NA) protein mediates this activation. In the current study, we determined the mechanism of activation of LTGF-β by NA from the influenza virus A/Gray Teal/Australia/2/1979 by mobility shift and enzyme inhibition assays. We also investigated whether exogenous TGF-β administered via a replication-deficient adenovirus vector provides protection from H5N1 influenza pathogenesis and whether depletion of TGF-β during virus infection increases morbidity in mice. We found that both the influenza and bacterial NA activate LTGF-β by removing sialic acid motifs from LTGF-β, each NA being specific for the sialic acid linkages cleaved. Further, NA likely activates LTGF-β primarily via its enzymatic activity, but proteases might also play a role in this process. Several influenza A virus subtypes (H1N1, H1N2, H3N2, H5N9, H6N1, and H7N3) except the highly pathogenic H5N1 strains activated LTGF-β in vitro and in vivo. Addition of exogenous TGF-β to H5N1 influenza virus-infected mice delayed mortality and reduced viral titers whereas neutralization of TGF-β during H5N1 and pandemic 2009 H1N1 infection increased morbidity. Together, these data show that microbe-associated NAs can directly activate LTGF-β and that TGF-β plays a pivotal role protecting the host from influenza pathogenesis.

Transforming growth factor beta 2 and heme oxygenase 1 genes are risk factors for the cerebral malaria syndrome in Angolan children

Background

Cerebral malaria (CM) represents a severe outcome of the Plasmodium falciparum infection. Recent genetic studies have correlated human genes with severe malaria susceptibility, but there is little data on genetic variants that increase the risk of developing specific malaria clinical complications. Nevertheless, susceptibility to experimental CM in the mouse has been linked to host genes including Transforming Growth Factor Beta 2 (TGFB2) and Heme oxygenase-1 (HMOX1). Here, we tested whether those genes were governing the risk of progressing to CM in patients with severe malaria syndromes.

Methodology/Principal Findings

We report that the clinical outcome of P. falciparum infection in a cohort of Angolan children (n = 430) correlated with nine TGFB2 SNPs that modify the risk of progression to CM as compared to other severe forms of malaria. This genetic effect was explained by two haplotypes harboring the CM-associated SNPs (Pcorrec. = 0.035 and 0.036). In addition, one HMOX1 haplotype composed of five CM-associated SNPs increased the risk of developing the CM syndrome (Pcorrec. = 0.002) and was under-transmitted to children with uncomplicated malaria (P = 0.036). Notably, the HMOX1-associated haplotype conferred increased HMOX1 mRNA expression in peripheral blood cells of CM patients (P = 0.012).

Conclusions/Significance

These results represent the first report on CM genetic risk factors in Angolan children and suggest the novel hypothesis that genetic variants of the TGFB2 and HMOX1 genes may contribute to confer a specific risk of developing the CM syndrome in patients with severe P. falciparum malaria. This work may provide motivation for future studies aiming to replicate our findings in larger populations and to confirm a role for these genes in determining the clinical course of malaria.

Alterations in early cytokine-mediated immune responses to Plasmodium falciparum infection in Tanzanian children with mineral element deficiencies: a cross-sectional survey

Background

Deficiencies in vitamins and mineral elements are important causes of morbidity in developing countries, possibly because they lead to defective immune responses to infection. The aim of the study was to assess the effects of mineral element deficiencies on early innate cytokine responses to Plasmodium falciparum malaria.

Methods

Peripheral blood mononuclear cells from 304 Tanzanian children aged 6-72 months were stimulated with P. falciparum-parasitized erythrocytes obtained from in vitro cultures.

Results

The results showed a significant increase by 74% in geometric mean of TNF production in malaria-infected individuals with zinc deficiency (11% to 240%; 95% CI). Iron deficiency anaemia was associated with increased TNF production in infected individuals and overall with increased IL-10 production, while magnesium deficiency induced increased production of IL-10 by 46% (13% to 144%) in uninfected donors. All donors showed a response towards IL-1β production, drawing special attention for its possible protective role in early innate immune responses to malaria.

Conclusions

In view of these results, the findings show plasticity in cytokine profiles of mononuclear cells reacting to malaria infection under conditions of different micronutrient deficiencies. These findings lay the foundations for future inclusion of a combination of precisely selected set of micronutrients rather than single nutrients as part of malaria vaccine intervention programmes in endemic countries.

Interleukin-10 but not Transforming Growth Factor beta inhibits murine activated macrophages Paracoccidioides brasiliensis killing: effect on H2O2 and NO production

Paracoccidioidomycosis is caused by the thermally dimorphic fungus Paracoccidioides brasiliensis (P. brasiliensis). Most often, this mycosis runs as a chronic progressive course affecting preferentially the lungs. In vitro fungicidal activity against a high virulent strain of P. brasiliensis by murine peritoneal macrophages preactivated with IFN-gamma or TNF-alpha is high and correlates with increased NO and H2O2 production. Within this context, the purpose of this work was to study the role of suppressor cytokines, such as IL-10 and TGF-beta, in this process. Incubation of either IFN-gamma or TNF-alpha with IL-10 inhibits fungicidal activity of these cells. However, TGF-beta had no effect on fungicidal activity of IFN-gamma or TNF-alpha-activated macrophages. The suppression of fungicidal activity by IL-10 correlated with the inhibition of NO and H2O2 production supporting the involvement of these metabolites in P. brasiliensis killing. These results suggest that IL-10 production in vivo could represent an evasion mechanism of the fungus to avoid host immune response.

Limited role of CD4+Foxp3+ regulatory T cells in the control of experimental cerebral malaria

Cerebral malaria (CM) associated with Plasmodium berghei ANKA (PbA) infection is an accepted model of human CM. CM during PbA infection critically depends on sequestration of T cells into the brain. Several studies aimed to address the role of regulatory T cells (T(reg)) in modulating this pathogenic T cell response. However, these studies are principally hampered due to the fact that until recently no reagents were available to deplete Foxp3(+) T(reg) specifically. To study the function of T(reg) in the genesis of CM, we used depletion of T(reg) mice that are transgenic for a bacterial artificial chromosome expressing a diphtheria toxin receptor-enhanced GFP fusion protein under the control of the foxp3 gene locus. These mice allow for a selective depletion of Foxp3(+) T(reg) by diphtheria toxin injection, and also their specific detection and purification during an ongoing infection. Using depletion of T(reg) mice, we found only a small increase in the absolute numbers of Foxp3(+) T(reg) during PbA infection and, consequently, the ratio of T(reg) to T effector cells (T(eff)) decreased due to the rapid expansion of T(eff). Although the latter sequester in the brains of infected mice, almost no T(reg) were found in the brains of infected mice. Furthermore, we demonstrate that depletion of T(reg) has no influence on sequestration of T(eff) and on the clinical outcome, and only minor influence on T cell activation. Using ex vivo analysis of purified T(reg) from either naive mice or PbA-infected mice, we found that both exhibit similar inhibitory capacity on T(eff).

Bioactive TGF-beta levels can be preserved in plasma samples collected into heparin but not EDTA

Quantifying TGF-beta is important for many research areas since its effects often are dose-dependently bidirectional. The post-transcriptional control of TGF-beta bioavailability points out the need to determine TGF-beta at the protein level. Studies measuring TGF-beta in peripheral blood have to avoid contamination with platelet-derived TGF-beta. Techniques to obtain platelet-poor plasma have been suggested, however, the impact of different anti-coagulants on artificial TGF-beta contamination has not been studied in detail. Here, we compare TGF-beta levels in blood samples collected into heparin and EDTA tubes, stored for 0.5-18 h at various temperatures. We show that contamination with latent TGF-beta can only be prevented by collecting the sample on ice. Importantly, levels of bioactive TGF-beta in blood collected into heparin but not EDTA tubes remained stable up to 18 h, even when kept at RT. Further in vitro experiments indicate that heparin prevents the activation of latent TGF-beta into its bioactive form probably by virtue of accelerating the complex-formation between AT-III and thrombin. Where precise measurement of latent TGF-beta in blood samples is required, samples need to be collected on ice; bioactive TGF-beta can be detected reliably in samples collected into heparin tubes even when stored at RT.

Dynamics of hepatic stellate cells, collagen types I and III synthesis and gene expression of selected cytokines during hepatic fibrogenesis following Mesocestoides vogae (Cestoda) infection in mice

In the present study, the relationship between progression of Mesocestoides vogae infection in the liver of mice, the accumulation rate of collagen types I and III, gene expression of fibrogenic factors and cytokines was examined within 6weeks p.i. Due to asexual multiplication, the total number of larvae in the liver increased considerably and 63.4% were found in collagen capsules on day 42 p.i. Intense staining for both collagens was recorded in the activated hepatic stellate cells (HSCs) throughout the period of this study in the inflammatory lesions. With progressing infection, cellular expression of both collagens was confined to the flat cells, myofibroblasts, which were scattered among collagen fibres in parenchymal lesions and capsules. Collagen-positive areas mirrored immunostaining of alpha-smooth muscle actin (alpha-SMA) in HSCs and myofibroblasts. Gene expression of both collagens increased rapidly within 14days p.i. and their expression pattern resembled that for pro-fibrotic cytokine transforming growth factor (TGF)-beta1 and alpha-SMA protein. IL-10 cytokine expression was up-regulated following day 14 p.i. and that of IL-13 was up-regulated early p.i., then transcription elevated gradually mirroring the activity of other pro-fibrotic markers. In contrast, transcription activity of TNF-alpha and IFN-gamma was elevated shortly after infection, followed by the partial down-regulation of gene expression, indicating the lack of larval killing, enhanced granulomatous inflammation and the perpetuation of hepatic fibrosis. Histomorphometric analysis of the parenchymal fibrous lesions, surface areas of larvae surrounded with the inflammatory infiltrates and surface areas of developing or mature larva-containing granulomas, correlated with the proportion of free and encapsulated larvae, immunostaining and gene expression patterns of collagens and pro-fibrotic markers. At a later stage of infection (day 28 p.i. onwards) collagen I-positive areas occupied a greater surface area and formed mature larval capsules and scars in the liver. In contrast, collagen III was less abundant and was localised mainly in the fibrous lesions in damaged parenchyma, suggesting their specific up-regulation as the part of host-protecting and tissue-healing responses.

Malaria and vitamin A deficiency in African children: a vicious circle?

Vitamin A deficiency and malaria are both highly prevalent health problems in Africa. Vitamin A deficiency affects over 30 million children, most of whom are in the age-group (under five years) most affected by malaria. Vitamin A deficiency increases all-cause mortality in this part of the population, and malaria is an important cause of death in children at this age. A low serum retinol concentration (a marker of vitamin A deficiency) is commonly found in children suffering from malaria, but it is not certain whether this represents pre-existing vitamin A deficiency, a contribution of malaria to vitamin A deficiency, or merely an acute effect of malaria on retinol metabolism or binding. In this paper, available evidence in support of a causal relationship in each direction between vitamin A deficiency and malaria is reviewed. If such a relationship exists, and especially if this is bidirectional, interventions against either disease may convey an amplified benefit for health.

Homeostatic regulation of T effector to Treg ratios in an area of seasonal malaria transmission

An important aspect of clinical immunity to malaria is the ability to down-regulate inflammatory responses, once parasitaemia is under control, in order to avoid immune-mediated pathology. The role of classical (CD4(+)CD25(+)CD127(lo/-)FOXP3(+)) Treg in this process, however, remains controversial. Thus, we have characterized the frequency, phenotype and function of Treg populations, over time, in healthy individuals in The Gambia. We observed that both the percentage and the absolute number of CD4(+)FOXP3(+)CD127(lo/-) T cells were higher among individuals living in a rural village with highly seasonal malaria transmission than among individuals living in an urban area where malaria rarely occurs. These CD4(+)FOXP3(+)CD127(lo/-) T cells exhibited an effector memory and apoptosis-prone phenotype and suppressed cytokine production in response to malaria antigen. Cells from individuals exposed to malaria expressed significantly higher levels of mRNA for forkhead box P3 and T-box 21 (T-BET) at the end of the malaria transmission season than at the end of the non-transmission season. Importantly, the ratio of T-BET to forkhead box P3 was remarkably consistent between populations and over time, indicating that in healthy individuals, a transient increase in Th1 responses during the malaria transmission season is balanced by a commensurate Treg response, ensuring that immune homeostasis is maintained.

MAPK ERK signaling regulates the TGF-beta1-dependent mosquito response to Plasmodium falciparum

Malaria is caused by infection with intraerythrocytic protozoa of the genus Plasmodium that are transmitted by Anopheles mosquitoes. Although a variety of anti-parasite effector genes have been identified in anopheline mosquitoes, little is known about the signaling pathways that regulate these responses during parasite development. Here we demonstrate that the MEK-ERK signaling pathway in Anopheles is controlled by ingested human TGF-beta1 and finely tunes mosquito innate immunity to parasite infection. Specifically, MEK-ERK signaling was dose-dependently induced in response to TGF-beta1 in immortalized cells in vitro and in the A. stephensi midgut epithelium in vivo. At the highest treatment dose of TGF-beta1, inhibition of ERK phosphorylation increased TGF-beta1-induced expression of the anti-parasite effector gene nitric oxide synthase (NOS), suggesting that increasing levels of ERK activation negatively feed back on induced NOS expression. At infection levels similar to those found in nature, inhibition of ERK activation reduced P. falciparum oocyst loads and infection prevalence in A. stephensi and enhanced TGF-beta1-mediated control of P. falciparum development. Taken together, our data demonstrate that malaria parasite development in the mosquito is regulated by a conserved MAPK signaling pathway that mediates the effects of an ingested cytokine.

IL-10 and TGF-beta redundantly protect against severe liver injury and mortality during acute schistosomiasis

The cytokines IL-10 and TGF-beta regulate immunity and inflammation. IL-10 is known to suppress the extent of hepatic damage caused by parasite ova during natural infection with Schistosoma mansoni, but the role of TGF-beta is less clear. Cytokine blockade studies in mice revealed that anti-IL-10R mAb treatment during acute infection modestly increased cytokine production and liver damage, whereas selective anti-TGF-beta mAb treatment had marginal effects. In contrast, mice administered both mAbs developed severe hepatic inflammation, with enlarged, necrotic liver granulomas, cachexia, and >80% mortality by 8 wk postinfection, despite increased numbers of CD4(+)CD25(+)Foxp3(+) T regulatory cells. Blocking both IL-10 and TGF-beta at the onset of egg production also significantly increased IL-4, IL-6, TNF, IFN-gamma, and IL-17 production and markedly increased hepatic, peritoneal, and splenic neutrophilia. In contrast, coadministration of anti-IL-10R and TGF-beta mAbs had little effect upon parasite ova-induced intestinal pathology or development of alternatively activated macrophages, which are required to suppress intestinal pathology. This suggests that inflammation is controlled during acute S. mansoni infection by two distinct, organ-specific mechanisms: TGF-beta and IL-10 redundantly suppress hepatic inflammation while intestinal inflammation is regulated by alternatively activated macrophages.

Pivotal role for TGF-beta in infectious heart disease: The case of Trypanosoma cruzi infection and consequent Chagasic myocardiopathy

This paper summarizes recent data from the literature suggesting that transforming growth factor-beta (TGF-beta) participates at least in four different processes influencing development of myocardiopathy in Chagas disease, a major parasitic illness caused by Trypanosoma cruzi infection: (a) invasion of cardiac fibroblasts and myocytes; (b) intracellular parasite cycle; (c) regulation of inflammation and immune response; (d) fibrosis and heart remodeling during acute and chronic disease. All these effects point to an important role of TGF-beta in Chagas disease myocardiopathy and suggest that monitoring the circulating levels of this cytokine could be of help in clinical prognosis and management of patients. Moreover, TGF-beta-interfering therapies appear as interesting adjuvant interventions during acute and chronic phases of T. cruzi infection.

Suppressive action of melatonin on the TH-2 immune response in rats infected with Trypanosoma cruzi

Control of the acute phase of Trypanosoma cruzi infection is critically dependent on cytokine-mediated macrophage activation to intracellular killing, natural killer (NK) cells, CD4(+) T cells, CD8(+) T cells and B cells. Cell-mediated immunity in T. cruzi infection is also modulated by cytokines, but in addition to parasite-specific responses, autoimmunity can be also triggered. Importantly, cytokines may also play a role in the cell-mediated immunity of infected subjects. Here we studied the role of cytokines in the regulation of innate and adaptive immunity during the acute phase of T. cruzi infection in Wistar rats. Melatonin is an effective regulator of the immune system. Macrophages and T lymphocytes, which have melatonin receptors, are target cells for the immunomodulatory function of melatonin. In this paper melatonin was orally given via two protocols: prior to and concomitant with infection. Both treatments were highly effective against T. cruzi with enhanced action for the concomitant treatment. The data suggest an up-regulation of the TH-1 immune response as all analyzed parameters, interleukin (IL)-4, IL-10, transforming growth factor-beta1 and splenocyte proliferation, displayed reduced levels as compared with the untreated counterparts. However, the direct effects of melatonin on immune cells have not been fully investigated during T. cruzi infection. We conclude that in light of the current results, melatonin exerted important therapeutic benefits through its immune regulatory effects.

Immunopathology and cytokine responses in broiler chickens coinfected with Eimeria maxima and Clostridium perfringens with the use of an animal model of necrotic enteritis

The incidence of necrotic enteritis (NE) due to Clostridium perfringens (CP) infection in commercial poultry has been increasing at an alarming rate. Although pre-exposure of chickens to coccidia infections is believed to be one of the major risk factors leading to NE, the underlying mechanisms of CP virulence remain undefined. The objectives of this study were to utilize an experimental model of NE produced by Eimeria maxima (EM) and CP coinfection to investigate the pathologic and immunologic parameters of the disease. Broilers coinfected with EM plus CP exhibited more severe gut pathology compared with animals given EM or CP alone. Additionally, EM/CP coinfection increased the numbers of intestinal CP bacteria compared with chickens exposed to an identical challenge of CP alone. Coinfection with EM and CP repressed nitric oxide synthase gene expression that was induced by EM alone, leading to lower plasma NO levels. Intestinal expression of a panel of cytokine and chemokine genes following EM/CP coinfection showed a mixed response depending on the transcript analyzed and the time following infection. In general, IFN-alpha, IFN-gamma, IL-1beta, IL-2, IL-12, IL-13, IL-17, and TGF-beta4 were repressed, whereas IL-8, IL-10, IL-15, and LITAF were increased during coinfection compared with challenge by EM or CP alone. These results are discussed in the context of EM and CP to act synergistically to create a more severe disease phenotype leading to an altered cytokine/chemokine response than that produced by infection with the individual pathogens.

Enhanced expression of transforming growth factor-beta 1 in inflammatory cells, alpha-smooth muscle actin in stellate cells, and collagen accumulation in experimental granulomatous hepatitis caused by Toxocara canis in mice

Although toxocaral granulomatous hepatitis (TGH) characterized with a dominant-Th2 type immune response is a self-limiting disease, little is known concerning the role of fibrosis-related cytokine transforming growth factor-beta 1 (TGF-beta 1) in pathogenesis of TGH. A detailed histological and quantitatively immunohistochemical analysis of TGF-beta 1, alpha-smooth muscle actins (alpha-SMA), and collagen was performed on the liver tissues from mice infected with Toxocara canis as assessed between day 1 and 42 weeks post-infection (DPI or WPI). TGF-beta1 was detected mainly in infiltrating leukocytes in lesions with strong expressions from 4 to 16 WPI. Larvae per se also exhibited strong TGF-beta 1-like molecule expressions in the trial. Alpha-SMA was detected predominantly in hepatic stellate cells (HSC) which surrounded the lesions with moderate expressions largely throughout the period of the entire experiment. Collagen was observed to accumulate in inflammatory lesions and biliary basement with moderate to strong expressions from 1 WPI onwards in the trial. Since many evidences have indicated that leukocytes have the potential to influence HSC by producing TGF-beta 1 which can affect HSC to increase collagen synthesis in various liver diseases, we may propose that persistently elevated TGF-beta 1 expression in infiltrating leukocytes and active HSC with marked alpha-SMA expressions may contribute to healing of injured sites through up-stimulation of collagen deposition; in contrast, abnormally persistent collagen accumulation may cause irreversible fibrotic injury in the TGH.

IL-10 from CD4CD25Foxp3CD127 adaptive regulatory T cells modulates parasite clearance and pathology during malaria infection

The outcome of malaria infection is determined, in part, by the balance of pro-inflammatory and regulatory immune responses. Failure to develop an effective pro-inflammatory response can lead to unrestricted parasite replication, whilst failure to regulate this response leads to the development of severe immunopathology. IL-10 and TGF-β are known to be important components of the regulatory response, but the cellular source of these cytokines is still unknown. Here we have examined the role of natural and adaptive regulatory T cells in the control of malaria infection and find that classical CD4⁺CD25^hi (and Foxp3⁺) regulatory T cells do not significantly influence the outcome of infections with the lethal (17XL) strain of Plasmodium yoelii (PyL). In contrast, we find that adaptive IL-10-producing, CD4⁺ T cells (which are CD25⁻, Foxp3⁻, and CD127⁻ and do not produce Th1, Th2, or Th17 associated cytokines) that are generated during both PyL and non-lethal P. yoelii 17X (PyNL) infections are able to down-regulate pro-inflammatory responses and impede parasite clearance. In summary, we have identified a population of induced Foxp3⁻ regulatory (Tr1) T cells, characterised by production of IL-10 and down regulation of IL-7Rα, that modulates the inflammatory response to malaria.

Much of the pathology of malaria infection is due to an excessive inflammatory response to the parasite. The regulatory cytokine IL-10 is known to control inflammation during malaria infections and thus protect against immunopathology, but, in so doing, it reduces the effectiveness of other immune mechanisms which remove the parasites. In order to try to dissociate these two effects of IL-10, to allow simultaneous control of infection and avoidance of pathology, we need a better understanding of the processes leading to IL-10 production, the timing of its production, and the cells that produce it. In this study we have found that the major source of IL-10 during malaria (Plasmodium yoelii) infection is adaptive regulatory CD4⁺ T cells. This population is distinct from natural regulatory T cells and classical effector T cells. IL-10 derived from these adaptive CD4⁺ T cells prevents hepatic immunopathology but also suppresses the effector T cell response, preventing parasite clearance. Further work is now required to determine how these two key cell types (anti-parasitic effector T cells and IL-10-producing regulatory T cells) are induced, so that vaccines can be designed that will induce optimal numbers of each cell type at appropriate stages of the infection.

Hepatosplenomegaly is associated with low regulatory and Th2 responses to schistosome antigens in childhood schistosomiasis and malaria coinfection

Hepatosplenomegaly among Kenyan schoolchildren has been shown to be exacerbated where there is transmission of both Schistosoma mansoni and Plasmodium falciparum. This highly prevalent and chronic morbidity often occurs in the absence of ultrasound-detectable periportal fibrosis and may be due to immunological inflammation. For a cohort of school-age children, whole-blood cultures were stimulated with S. mansoni soluble egg antigen (SEA) or soluble worm antigen (SWA). Responses to SWA were found to be predominantly Th2 cytokines; however, they were not significantly associated with either hepatosplenomegaly or infection with S. mansoni or P. falciparum. In comparison, SEA-specific Th2 cytokine responses were low, and the levels were negatively correlated with S. mansoni infection intensities and were lower among children who were coinfected with P. falciparum. Tumor necrosis factor alpha levels in response to stimulation with SEA were high, and a negative association between presentation with hepatomegaly and the levels of the regulatory cytokines interleukin-6 and transforming growth factor beta(1) suggests that a possible mechanism for childhood hepatomegaly in areas where both malaria and schistosomiasis are endemic is poor regulation of an inflammatory response to schistosome eggs.

Low levels of mammalian TGF-beta1 are protective against malaria parasite infection, a paradox clarified in the mosquito host

Nitric oxide (NO), derived from catalysis of inducible NO synthase (iNOS), limits malaria parasite growth in mammals. Transforming growth factor (TGF)-beta1 suppresses iNOS in cells in vitro as well as in vivo in mice, but paradoxically severe malaria in humans is associated with low levels of TGF-beta1. We hypothesized that this paradox is a universal feature of infection and occurs in the mosquito Anopheles stephensi, an invertebrate host for Plasmodium that also regulates parasite development with inducible NO synthase (AsNOS). We show that exogenous human TGF-beta1 dose-dependently regulates mosquito AsNOS expression and that parasite killing by low dose TGF-beta1 depends on AsNOS catalysis. Furthermore, induction of AsNOS expression by TGF-beta1 is regulated by NO synthesis. These results suggest that TGF-beta1 plays similar roles during parasite infection in mammals and mosquitoes and that this role is linked to the effects of TGF-beta1 on inducible NO synthesis.

Disruption of CD36 impairs cytokine response to Plasmodium falciparum glycosylphosphatidylinositol and confers susceptibility to severe and fatal malaria in vivo

CD36 is a scavenger receptor that has been implicated in malaria pathogenesis as well as innate defense against blood-stage infection. Inflammatory responses to Plasmodium falciparum GPI (pfGPI) anchors are believed to play an important role in innate immune response to malaria. We investigated the role of CD36 in pfGPI-induced MAPK activation and proinflammatory cytokine secretion. Furthermore, we explored the role of this receptor in an experimental model of acute malaria in vivo. We demonstrate that ERK1/2, JNK, p38, and c-Jun became phosphorylated in pfGPI-stimulated macrophages. In contrast, pfGPI-induced phosphorylation of JNK, ERK1/2, and c-Jun was reduced in Cd36(-/-) macrophages and Cd36(-/-) macrophages secreted significantly less TNF-alpha in response to pfGPI than their wild-type counterparts. In addition, we demonstrate a role for CD36 in innate immune response to malaria in vivo. Compared with wild-type mice, Cd36(-/-) mice experienced more severe and fatal malaria when challenged with Plasmodium chabaudi chabaudi AS. Cd36(-/-) mice displayed a combined defect in cytokine induction and parasite clearance with a dysregulated cytokine response to infection, earlier peak parasitemias, higher parasite densities, and higher mortality rates than wild-type mice. These results provide direct evidence that pfGPI induces TNF-alpha secretion in a CD36-dependent manner and support a role for CD36 in modulating host cytokine response and innate control of acute blood-stage malaria infection in vivo.

Pharmacodynamics of pentoxifylline and/or praziquantel in murine schistosomiasis mansoni

Pentoxifylline (PTX) was proved to exert both anti-inflammatory and anti-fibrotic effects, and was used therapeutically in this experimental model to investigate its role alone or with praziquantel (PZQ) in Schistosoma mansoni-infected mice, and to explore its impact on the tissue expression of transforming growth factor-beta1 (TGF-beta1). S. mansoni-infected mice were divided into seven groups: Control untreated (I), treated with curative dose of PZQ, 500 mg/kg/day for 2 consecutive days (II), or subcurative dose, 100 mg/kg/day for 2 consecutive days (III), treated with PTX (10 mg/kg/day for 5 days/wk) alone for 4 weeks (IV) or in addition to subcurative dose of PZQ (V), and treated with PTX alone for 8 weeks (VI) or in addition to subcurative dose of PZQ (VII). All animals were killed 10 weeks post infection. Parasitological assessment of worm burden, tissue egg load and oogram pattern was carried out. The degree of granulomatous fibrosis and eosinophilic cell population was quantified in Sirius-red-stained sections and tissue transforming growth factor beta-1 expression was estimated immunohistochemically. Serum ALAT and GGT, as well as hepatic content of reduced GSH, were measured. The results revealed the highest percent of worm reduction and dead ova in groups (II) and (VII) accompanied by significant diminution in granulomatous parameters, collagen content and TGF-beta1 tissue expression. Moreover, treatments with PTX and/or PZQ ameliorated the liver functions. In conclusion, prolonged treatment with PTX has a potent anti-fibrogenic role especially when used in the early stages of infection, with limited toxic effects on schistosome worms and eggs. Thus, PTX can be used as an adjuvant therapeutic tool with anti-helminthic drugs in the treatment of human schistosomiasis.

Incomplete depletion and rapid regeneration of Foxp3+ regulatory T cells following anti-CD25 treatment in malaria-infected mice

Investigation of the role of regulatory T cells (Treg) in model systems is facilitated by their depletion using anti-CD25 Abs, but there has been considerable debate about the effectiveness of this strategy. In this study, we have compared the depletion and repopulation of CD4+CD25+Foxp3+ Treg in uninfected and malaria-infected mice using 7D4 and/or PC61 anti-CD25 Abs. We find that numbers and percentages of CD25(high) cells, but not Foxp3+ cells, are transiently reduced after 7D4 treatment, whereas treatment with PC61 alone or in combination with 7D4 (7D4 plus PC61) reduces but does not eliminate Foxp3+ cells for up to 2 wk. Importantly, all protocols fail to eliminate significant populations of CD25-Foxp3+ or CD25(low)Foxp3+ cells, which retain potent regulatory capacity. By adoptive transfer we show that repopulation of the spleen by CD25(high)Foxp3+ cells results from the re-expression of CD25 on peripheral populations of CD25-Foxp3+ but not from the conversion of peripheral Foxp3-) cells. CD25(high)Foxp3+ repopulation occurs more rapidly in 7D4-treated mice than in 7D4 plus PC61-treated mice, reflecting ongoing clearance of emergent CD25+Foxp3+ cells by persistent PC61 Ab. However, in 7D4 plus PC61-treated mice undergoing acute malaria infection, repopulation of the spleen by CD25+Foxp3+ cells occurs extremely rapidly, with malaria infection driving proliferation and CD25 expression in peripheral CD4+CD25-Foxp3+ cells and/or conversion of CD4+CD25-Foxp3- cells. Finally, we reveal an essential role for IL-2 for the re-expression of CD25 by Foxp3+ cells after anti-CD25 treatment and observe that TGF-beta is required, in the absence of CD25 and IL-2, to maintain splenic Foxp3+ cell numbers and a normal ratio of Treg:non-Treg cells.

Leishmania infantum: Mixed T-helper-1/T-helper-2 immune response in experimentally infected BALB/c mice

The main goal of the present study was to characterise the course of infection and immunological responses developed by Leishmania infantum infected BALB/c mice. Parasite load was determined by Real-time TaqMan PCR while cytokine and Immunoglobulin G (IgG) production were assessed by ELISA. Leishmania DNA was detected in spleen and liver as soon as day 1 post-inoculation (pi) and the parasitism was sustained until the end of the experiment. The cytokine kinetics in spleen and liver was generally associated with the oscillations of parasite load. Overall, it was not observed a distinct Th1 or Th2 pattern of cytokine production during the time of experiment. The infected mice developed a mixed immune response, with concomitant production of IFN-gamma, IL-4 and IL-10, both in spleen and liver, and both IgG isotypes. However, our results suggest that, compared to liver, the spleen is more susceptible to L. infantum infection.

Immunomodulatory role of chloroquine and pyrimethamine in Plasmodium yoelii 17XL infected mice

Chloroquine (CLQ) and Pyrimethamine (PYR) are used for the treatment of malaria and some autoimmune diseases; although their mechanism of action is only partially understood, their therapeutic effectiveness in the second case has been attributed to their ability to increase apoptosis of T lymphocytes. In view of the potential for immunomodulation during malaria chemotherapy, we investigated the effects of CLQ and PYR treatment on lymphocyte apoptosis and cytokine expression during infection with blood-stage Plasmodium. This work shows that infection of BALB/c mice with Plasmodium yoelii 17XL (Py17XL) reduced apoptosis in spleen cells but when infected mice were treated with CLQ, apoptosis of B and T lymphocytes increased significantly via a Fas-mRNA expression independent mechanism associated with downregulation of Bcl-2 expression, whereas treatment with PYR increased apoptosis to a lesser extent and only in B lymphocytes. CLQ treatment of Py17XL infected mice upregulated tumour necrosis factor-alpha mRNA expression, while PYR treatment increased interferon-gamma mRNA expression. In infected mice, treatment with CLQ downregulated expression of the anti-inflammatory cytokines, interleukin-10 and transforming growth factor-beta (TGF-beta), while PYR treatment upregulated TGF-beta. Thus, in addition to their anti-malarial effects, both drugs modulate the immune response in malaria by increasing apoptosis and modulating the mRNA expression of cytokines involved in parasite elimination and regulation of inflammatory responses.

Effects of exogenous transforming growth factor beta on Trypanosoma congolense infection in mice

The socioeconomic implications of trypanosomosis in sub-Saharan Africa and the limitations of its current control regimes have stimulated research into alternative control methods. Considering the pro- and anti-inflammatory properties of transforming growth factor beta1 (TGF-beta1) and its potential to enhance immunity against protozoan parasites, we examined the effects of intraperitoneally delivered TGF-beta1 in C57BL/6 mice infected with Trypanosoma congolense, the hemoprotozoan parasite causing nagana in cattle. A triple dose of 10 ng TGF-beta1 significantly reduced the first parasitemic peak and delayed mortality of infected mice. Furthermore, exogenous TGF-beta1 significantly decreased the development of trypanosome-induced anemia and splenomegaly. The apparent TGF-beta1-induced antitrypanosome protection, occurring mainly during the early stage of infection, correlated with an enhanced parasite antigen-specific Th1 cell response characterized by a skewed type I cytokine response and a concomitant stronger antitrypanosome immunoglobulin G2a antibody response. Infected TGF-beta1-pretreated mice exhibited a significant reduction in the trypanosome-induced hyperexpansion of B cells. Furthermore, evidence is provided herein that exogenous TGF-beta1 activates macrophages that may contribute to parasite control. Collectively, these data indicate that exogenous TGF-beta1 is immunostimulative, inducing partial protection against T. congolense infection, possibly through mechanisms involving innate immune responses.

Innate Immune Responses to Human Malaria: Heterogeneous Cytokine Responses to Blood-Stage Plasmodium falciparum Correlate with Parasitological and Clinical Outcomes

Taking advantage of a sporozoite challenge model established to evaluate the efficacy of new malaria vaccine candidates, we have explored the kinetics of systemic cytokine responses during the prepatent period of Plasmodium falciparum infection in 18 unvaccinated, previously malaria-naive subjects, using a highly sensitive, bead-based multiplex assay, and relate these data to peripheral parasite densities as measured by quantitative real-time PCR. These data are complemented with the analysis of cytokine production measured in vitro from whole blood or PBMC, stimulated with P. falciparum-infected RBC. We found considerable qualitative and quantitative interindividual variability in the innate responses, with subjects falling into three groups according to the strength of their inflammatory response. One group secreted moderate levels of IFN-gamma and IL-10, but no detectable IL-12p70. A second group produced detectable levels of circulating IL-12p70 and developed very high levels of IFN-gamma and IL-10. The third group failed to up-regulate any significant proinflammatory responses, but showed the highest levels of TGF-beta. Proinflammatory responses were associated with more rapid control of parasite growth but only at the cost of developing clinical symptoms, suggesting that the initial innate response may have far-reaching consequences on disease outcome. Furthermore, the in vitro observations on cytokine kinetics presented here, suggest that intact schizont-stage infected RBC can trigger innate responses before rupture of the infected RBC.

Vitamin A supplementation increases ratios of proinflammatory to anti-inflammatory cytokine responses in pregnancy and lactation

Vitamin A supplementation reduces child mortality in populations at risk of vitamin A deficiency and may also reduce maternal mortality. One possible explanation for this is that vitamin A deficiency is associated with altered immune function and cytokine dysregulation. Vitamin A deficiency in pregnancy may thus compound the pregnancy-associated bias of cellular immune responses towards Th-2-like responses and exacerbate susceptibility to intracellular pathogens. We assessed mitogen and antigen-induced cytokine responses during pregnancy and lactation in Ghanaian primigravidae receiving either vitamin A supplementation or placebo. This was a double-blind, randomized, placebo-controlled trial of weekly vitamin A supplementation in pregnant and lactating women. Pregnancy compared to postpartum was associated with a suppression of cytokine responses, in particular of the proinflammatory cytokines interferon (IFN)-gamma and tumour necrosis factor (TNF)-alpha. Mitogen-induced TNF-alpha responses were associated with a decreased risk of peripheral parasitaemia during pregnancy. Furthermore, vitamin A supplementation was significantly associated with an increased ratio of mitogen-induced proinflammatory cytokine (IFN-gamma) to anti-inflammatory cytokine (IL-10) during pregnancy and in the postpartum period. The results of this study indicate that suppression of proinflammatory type 1 immune responses and hence immunity to intracellular infections, resulting from the combined effects of pregnancy and vitamin A deficiency, might be ameliorated by vitamin A supplementation.

Transforming growth factor-beta regulation of immune responses

Transforming growth factor-beta (TGF-beta) is a potent regulatory cytokine with diverse effects on hemopoietic cells. The pivotal function of TGF-beta in the immune system is to maintain tolerance via the regulation of lymphocyte proliferation, differentiation, and survival. In addition, TGF-beta controls the initiation and resolution of inflammatory responses through the regulation of chemotaxis, activation, and survival of lymphocytes, natural killer cells, dendritic cells, macrophages, mast cells, and granulocytes. The regulatory activity of TGF-beta is modulated by the cell differentiation state and by the presence of inflammatory cytokines and costimulatory molecules. Collectively, TGF-beta inhibits the development of immunopathology to self or nonharmful antigens without compromising immune responses to pathogens. This review highlights the findings that have advanced our understanding of TGF-beta in the immune system and in disease.

Reduced protective efficacy of a blood-stage malaria vaccine by concurrent nematode infection

Helminth infections, which are prevalent in areas where malaria is endemic, have been shown to modulate immune responses to unrelated pathogens and have been implicated in poor efficacy of malaria vaccines in humans. We established a murine coinfection model involving blood-stage Plasmodium chabaudi AS malaria and a gastrointestinal nematode, Heligmosomoides polygyrus, to investigate the impact of nematode infection on the protective efficacy of a malaria vaccine. C57BL/6 mice immunized with crude blood-stage P. chabaudi AS antigen in TiterMax adjuvant developed strong protection against malaria challenge. The same immunization protocol failed to induce strong protection in H. polygyrus-infected mice. Immunized nematode-infected mice produced significantly lower levels of malaria-specific antibody than nematode-free mice produced. In response to nematode and malarial antigens, spleen cells from immunized nematode-infected mice produced significantly lower levels of gamma interferon but more interleukin-4 (IL-4), IL-13, and IL-10 in vitro than spleen cells from immunized nematode-free mice produced. Furthermore, H. polygyrus infection also induced a strong transforming growth factor beta1 response in vivo and in vitro. Deworming treatment of H. polygyrus-infected mice before antimalarial immunization, but not deworming treatment after antimalarial immunization, restored the protective immunity to malaria challenge. These results demonstrate that concurrent nematode infection strongly modulates immune responses induced by an experimental malaria vaccine and consequently suppresses the protective efficacy of the vaccine against malaria challenge.

Growth factor receptors in helminth parasites: Signalling and host-parasite relationships

Parasitic helminths remain major pathogens of both humans and animals throughout the world. The success of helminth infections depends on the capacity of the parasite to counteract host immune responses but also to exploit host-derived signal molecules for its development. Recent progress has been made in the characterization of growth factor receptors of various nematode and flatworm parasites with the demonstration that transforming growth factor beta (TGF-beta), epidermal growth factor (EGF) and insulin receptor signalling pathways are conserved in helminth parasites and potentially implicated in the host-parasite molecular dialogue and parasite development.

TGF-β1 Released from Activated Platelets Can Induce TNF-Stimulated Human Brain Endothelium Apoptosis: A New Mechanism for Microvascular Lesion during Cerebral Malaria

Platelets have recently been shown to accumulate in brain microvessels of patients with cerebral malaria and to modulate the binding of Plasmodium falciparum-infected red cells to human brain endothelium in vitro. In the present study we used a platelet-endothelial cell coculture model to investigate the mechanisms by which platelets modify the function of human brain microvascular endothelial cells (HBEC). Platelets were found to have a proapoptotic effect on TNF-activated HBEC, and this was contact-dependent, as inhibiting platelet binding prevented endothelial cell killing. We also showed that the supernatants of thrombin-activated platelets killed TNF-stimulated HBEC and that TGF-beta1 was the main molecule involved in endothelial cell death, because its inhibition completely abrogated the activated-platelet supernatant effect. Our data illustrate another aspect of the duality of TGF-beta1 in malaria and may provide new insights into the pathogenesis of cerebral malaria.

Regulation of immune response by Plasmodium-infected red blood cells

During the asexual blood stage infection of the human malaria parasite, Plasmodium falciparum, parasite-derived proteins are inserted onto the surface of the host red blood cell membrane. These proteins are highly variable and were originally thought only to mediate antigenic variation, and sequestration of parasites from peripheral circulation, thus enabling immune evasion. Recent studies have revealed that PfEMP-1 and other molecules on the P. falciparum-infected red blood cell (PfRBC) activate and modulate the immune response. In this review, we discuss how PfRBCs interact with antigen-presenting cells (APCs) and other cells of the immune system, and how such interactions could modulate the host response to Plasmodium infections.

The beneficial helminth parasite?

There is unequivocal evidence that parasites influence the immune activity of their hosts, and many of the classical examples of this are drawn from assessment of helminth infections of their mammalian hosts. Thus, helminth infections can impact on the induction or course of other diseases that the host might be subjected to. Epidemiological studies demonstrate that world regions with high rates of helminth infections consistently have reduced incidences of autoimmune and other allergic/inflammatory-type conditions. Here I review and assess the possible ways by which helminth infections can block or modulate concomitant disease processes. There is much to be learned from careful analysis of immuno-regulation in helminth-infected rodents and from an understanding of the immune status of acutely and chronically infected humans. The ultimate reward from this type of investigation will likely be a more comprehensive knowledge of immunity, novel ways to intervene in the immune response to alleviate autoimmune and allergic diseases (growing concerns in economically developed areas), and perhaps the development of helminth therapy for patients suffering from specific inflammatory, autoimmune or allergic disorders.

Participation of cytokines in the necrotic-inflammatory lesions in the heart and skeletal muscles of Calomys callosus infected with Trypanosoma cruzi

Calomys callosus, a sylvatic reservoir of Trypanosoma cruzi, when infected with the Colombian strain (Biodeme Type III, T. cruzi I ) develops necrotic-inflammatory lesions and intense early fibrogenesis in the heart and skeletal muscles, that spontaneously regress. Participation of pro-inflammatory and pro-fibrogenic cytokines, such as tumor necrosis factor-alpha (TNF-alpha), gamma interferon (IFN-gamma) , and tumor growth factor-beta (TGF-beta), in the pathogenesis of the lesions is herein studied. Eighty C. callosus weighing 20 to 30 g were used. Seventy of them were inoculated with the Colombian strain (10(5) blood forms) and 10 were maintained as intact non-infected controls. After infection, C. callosus were sacrificed at different time-points from 15 to 70 days. The heart and skeletal muscle were processed for histopathology and cryopreserved for immunohistochemistry. Early necrotic lesions of parasitized skeletal muscle and myocardium with intense inflammatory lesions were present. Search for the in situ presence of TNF-alpha and IFN-gamma, was performed using rat-IgG anti-mouse antibodies against these cytokines. For the in situ search of TGF-beta, rabbit IgG anti-mouse antibodies were used. Immunolabeling of the cytokines in tissues of infected C. callosus was successful. The cytokines TNF-alpha, IFN-gamma , and TGF-beta were detected in the cytoplasm of macrophages and in the necrotic material from 15 to 45 days post-infection, decreasing their intensity until complete disappearance by the 65th day, which correlated with subsiding histopathological lesions. These findings suggest the participation of these cytokines in the control of parasite multiplication, in the development of an early fibrogenesis and in the regression of fibrotic-inflammatory lesions observed in C. callosus.

Impairment of protective immunity to blood-stage malaria by concurrent nematode infection

Helminthiases, which are highly prevalent in areas where malaria is endemic, have been shown to modulate or suppress the immune response to unrelated antigens or pathogens. In this study, we established a murine model of coinfection with a gastrointestinal nematode parasite, Heligmosomoides polygyrus, and the blood-stage malaria parasite Plasmodium chabaudi AS in order to investigate the modulation of antimalarial immunity by concurrent nematode infection. Chronic infection with the nematode for 2, 3, or 5 weeks before P. chabaudi AS infection severely impaired the ability of C57BL/6 mice to control malaria, as demonstrated by severe mortality and significantly increased malaria peak parasitemia levels. Coinfected mice produced significantly lower levels of gamma interferon (IFN-gamma) during P. chabaudi AS infection than mice infected with malaria alone. Concurrent nematode infection also suppressed production of type 1-associated, malaria-specific immunoglobulin G2a. Mice either infected with the nematode alone or coinfected with the nematode and malaria had high transforming growth factor beta1 (TGF-beta1) levels, and concurrent nematode and malaria infections resulted in high levels of interleukin-10 in vivo. Splenic CD11c(+) dendritic cells (DC) from mice infected with malaria alone and coinfected mice showed similarly increased expression of CD40, CD80, and CD86, but DC from coinfected mice were unable to induce CD4(+) T-cell proliferation and optimal IFN-gamma production in response to the malaria antigen in vitro. Importantly, treatment of nematode-infected mice with an anthelmintic drug prior to malaria infection fully restored protective antimalarial immunity and reduced TGF-beta1 levels. These results demonstrate that concurrent nematode infection strongly modulates multiple aspects of immunity to blood-stage malaria and consequently impairs the development of protective antimalarial immunity.

Effects of prednisolone treatment on cytokine expression in patients with leprosy type 1 reactions

Leprosy type 1 reactions (T1R) are due to increased cell-mediated immunity and result in localized tissue damage. The anti-inflammatory drug prednisolone is used for treatment, but there is little good in vivo data on the molecular actions of prednisolone. We investigated the effect of prednisolone treatment on tumor necrosis factor alpha (TNF-alpha), interleukin-1beta (IL-1beta), IL-10, and transforming growth factor beta1 (TGF-beta1) mRNA and protein expression in blood and skin biopsies from 30 patients with T1R in India. After 1 month of prednisolone treatment the sizes of the skin granulomas were reduced, as were the grades of cells positive for TNF-alpha and IL-10 in skin lesions. Increased production of TGF-beta1 was seen in skin lesions after 6 months of prednisolone treatment. Expression of mRNA for TNF-alpha, IL-1beta, and TGF-beta1 was reduced, whereas no change in IL-10 mRNA expression was detected during treatment. The circulating cytokine profiles were similar in patients with and without T1R, and prednisolone treatment had no detectable effects on cytokine expression in the blood. The data emphasize the compartmentalization of pathology in T1R and the importance of the immune response in the skin. Clinical improvement and cytokine expression were compared. Surprisingly, patients with improved skin and nerve function and patients with nonimproved skin and nerve function had similar cytokine profiles, suggesting that clinical improvement is not directly mediated by the cytokines studied here. This in vivo well-controlled study of the immunosuppressive effects of prednisolone showed that the drug does not switch off cytokine responses effectively.

Human African trypanosomiasis: clinical presentation and immune response

Human African trypanosomiasis or sleeping sickness is caused by infection with two subspecies of the tsetse-fly-vectored haemoflagellate parasite Trypanosoma brucei. Historically, epidemic sleeping sickness has caused massive loss of life, and related animal diseases have had a crucial impact on development in sub-Saharan Africa. After a period of moderately successful control during the mid-part of the 20th century, sleeping sickness incidence is currently rising, and control is hampered by a combination of factors, including civil unrest and the possible development of drug resistance by the parasites. The prevailing view is that the disease is invariably fatal without anti-trypanosomal drug treatment. However, there have also been intriguing reports of wide variations in disease severity as well as evidence of asymptomatic carriers of trypanosomes. These differences in the presentation of the disease will be discussed in the context of our knowledge of the immunology of trypanosomiasis. The impact of dysregulated inflammatory responses in both systemic and CNS pathology will be examined and the potential for host genotype variation in disease severity and control will be discussed.