Induction of cell-mediated immunity during early stages of infection with intracellular protozoa

Bottlenose dolphins (Tursiops truncatus) do also cast neutrophil extracellular traps against the apicomplexan parasite Neospora caninum

Neutrophil extracellular traps (NETs) are web-like structures composed of nuclear DNA decorated with histones and cytoplasmic peptides which antiparasitic properties have not previously been investigated in cetaceans. Polymorphonuclear neutrophils (PMN) were isolated from healthy bottlenose dolphins (Tursiops truncatus), and stimulated with Neospora caninum tachyzoites and the NETs-agonist zymosan. In vitro interactions of PMN with the tachyzoites resulted in rapid extrusion of NETs. For the demonstration and quantification of cetacean NETs, extracellular DNA was stained by using either Sytox Orange® or Pico Green®. Scanning electron microscopy (SEM) and fluorescence analyses demonstrated PMN-derived release of NETs upon exposure to tachyzoites of N. caninum. Co-localization studies of N. caninum induced cetacean NETs proved the presence of DNA adorned with histones (H1, H2A/H2B, H3, H4), neutrophil elastase (NE), myeloperoxidase (MPO) and pentraxin (PTX) confirming the molecular properties of mammalian NETosis. Dolphin-derived N. caninum-NETosis were efficiently suppressed by DNase I and diphenyleneiodonium (DPI) treatments. Our results indicate that cetacean-derived NETs represent an ancient, conserved and relevant defense effector mechanism of the host innate immune system against N. caninum and probably other related neozoan parasites circulating in the marine environment.

Molecular analyses on Neospora caninum-triggered NETosis in the caprine system

Neospora caninum is an obligate intracellular protozoan parasite causing serious reproductive disorders in large and small ruminants worldwide. Polymorphonuclear neutrophils (PMN) react against multiple invading pathogens through different mechanisms including the release of neutrophil extracellular traps (NETs). Here, in vitro interactions of caprine PMN and N. caninum tachyzoites were studied. Scanning electron microscopic- and immunofluorescence-analyses demonstrated that caprine PMN undergo NETosis upon contact with tachyzoites of N. caninum, extruding filaments that entrap parasites. Detailed co-localization studies of N. caninum tachyzoite-induced NETs revealed the presence of PMN-derived DNA being decorated with histones (H1, H2A/H2B, H3,H4) and neutrophil elastase (NE) corroborating the molecular characteristics of classical mammalian NETs. As a new result for parasite-induced NETosis, we identified pentraxin and cathepsin B in N. caninum-triggered NETs. Nonetheless, functional inhibition assays revealed that during caprine NET formation triggered by N. caninum different molecular signaling pathways are induced, when compared to other apicomplexan parasites or host species. As such, N. caninum-induced NETosis appears to be influenced by MPO but independent of NADPH oxidase, SOCE, ERK1/2 and p38 MAPK activities. Furthermore, the inhibition of PMN autophagy via blockage of the PI3K-mediated signaling pathway failed to influence tachyzoite-induced NETosis. Since N. caninum-tachyzoites induced caprine NETosis, this effector mechanism should be considered as an early host immune response during acute caprine neosporosis.

Bovine Polymorphonuclear Neutrophils Cast Neutrophil Extracellular Traps against the Abortive Parasite Neospora caninum

Neospora caninum represents a relevant apicomplexan parasite causing severe reproductive disorders in cattle worldwide. Neutrophil extracellular trap (NET) generation was recently described as an efficient defense mechanism of polymorphonuclear neutrophils (PMN) acting against different parasites. In vitro interactions of bovine PMN with N. caninum were analyzed at different ratios and time spans. Extracellular DNA staining was used to illustrate the typical molecules of NETs [i.e., histones (H3), neutrophil elastase (NE), myeloperoxidase (MPO), pentraxin] via antibody-based immunofluorescence analyses. Functional inhibitor treatments were applied to reveal the role of several enzymes [NADPH oxidase (NOX), NE, MPO, PAD4], ATP-dependent P2Y2 receptor, store-operated Ca⁺⁺entry (SOCE), CD11b receptor, ERK1/2- and p38 MAPK-mediated signaling pathway in tachyzoite-triggered NETosis. N. caninum tachyzoites triggered NETosis in a time- and dose-dependent manner. Scanning electron microscopy analyses revealed NET structures being released by bovine PMN and entrapping tachyzoites. N. caninum-induced NET formation was found not to be NOX-, NE-, MPO-, PAD4-, ERK1/2-, and p38 MAP kinase-dependent process since inhibition of these enzymes led to a slight decrease of NET formation. CD11b was also identified as a neutrophil receptor being involved in NETosis. Furthermore, N. caninum-triggered NETosis depends on Ca⁺⁺ influx as well as neutrophil metabolism since both the inhibition of SOCE and of P2Y2-mediated ATP uptake diminished NET formation. Host cell invasion assays indicated that PMN-derived NETosis hampered tachyzoites from active host cell invasion, thereby inhibiting further intracellular replication. NET formation represents an early and effective mechanism of response of the innate immune system, which might reduce initial infection rates during the acute phase of cattle neosporosis.

The leishmanicidal activity of oleuropein is selectively regulated through inflammation- and oxidative stress-related genes

Background

Much research effort has been focused on investigating new compounds derived from low-cost sources, such as natural products, for treating leishmaniasis. Oleuropein derived from numerous plants, particularly from the olive tree, Olea europaea L. (Oleaceae), is a biophenol with many biological activities. Our previous findings showed that oleuropein exhibits leishmanicidal effects against three Leishmania spp. in vitro, and minimizes the parasite burden in L. donovani-infected BALB/c mice. The aim of the present study is to investigate the possible mechanism(s) that mediate this leishmanicidal activity.

Methods

We determined the efficacy of oleuropein in elevating ROS and NO production in L. donovani-infected J774A.1 macrophages and in explanted splenocytes and hepatocytes obtained from L. donovani-infected BALB/c mice. We also assessed the expression of genes that are related to inflammation, T-cell polarization and antioxidant defense, in splenocytes. Finally, we determined the ratios of specific IgG2a/IgG1 antibodies and DTH reactions in L. donovani-infected BALB/c mice treated with oleuropein.

Results

Oleuropein was able to elevate ROS production in both in vitro and in vivo models of visceral leishmaniasis and raised NO production in ex vivo cultures of splenocytes and hepatocytes. The extensive oxidative stress found in oleuropein-treated mice was obviated by the upregulation of the host’s antioxidant enzyme (mGCLC) and the simultaneous downregulation of the corresponding enzyme of the parasite (LdGCLC). Moreover, oleuropein was able to mount a significant Th1 polarization characterized by the expression of immune genes (IL-12β, IL-10, TGF-β1, IFN-γ) and transcription factors (Tbx21 and GATA3). Moreover, this immunomodulatory effect was also correlated with an inhibitory effect on IL-1β gene expression, rather than with the expression of IL-1α, IL-1rn and TNF-α. Furthermore, oleuropein-treated BALB/c mice mounted a delayed-type hypersensitivity (DTH) response and an elevated Leishmania-specific IgG2a/IgG1 ratio that clearly demonstrated an in vivo protective mechanism.

Conclusion

The ability of Oleuropein to promote a Th1 type immune response in L. donovani-infected BALB/c mice points towards the candidacy of this bioactive compound as an immunomodulatory agent that may complement therapeutic approaches to leishmaniasis.

Cellular immune response in intraventricular experimental neurocysticercosis

Neurocysticercosis (NCC) is considered a neglected parasitic infection of the human central nervous system. Its pathogenesis is due to the host immune response, stage of evolution and location of the parasite. The aim of this study was to evaluate thein situand systemic immune response through cytokines dosage (IL-4, IL-10, IL-17 and IFN-γ) as well as the local inflammatory response of the experimental NCC withTaenia crassiceps. Thein situand systemic cellular and inflammatory immune response were evaluated through the cytokines quantification at 7, 30, 60 and 90 days after inoculation and histopathological analysis. All cysticerci were found within the cerebral ventricles. There was a discrete intensity of inflammatory cells of mixed immune profile, polymorphonuclear and mononuclear cells, at the beginning of the infection and predominance of mononuclear cells at the end. The systemic immune response showed a significant increase in all the analysed cytokines and predominance of the Th2 immune profile cytokines at the end of the infection. These results indicate that the location of the cysticerci may lead to ventriculomegaly. The acute phase of the infection showed a mixed Th1/Th17 profile accompanied by high levels of IL-10 while the late phase showed a Th2 immune profile.

In situ expression of regulatory cytokines by heart inflammatory cells in Chagas' disease patients with heart failure

Chagas' disease is caused by the protozoan parasite Trypanosoma cruzi. The immune system plays an important role in the reduction of parasite load, but may also contribute to the development of lesions observed during the chronic phase of the disease. We analyzed cytokines produced by inflammatory heart cells in 21 autopsy samples obtained from patients with Chagas' disease divided according to the presence or absence of heart failure (HF). Left ventricular sections were analyzed by immunohistochemistry using antibodies against human IL-4, IFN-γ, TGF-β, TNF-α, and NOS2. In situ mRNA expression was quantified by a Low Density Array. The number of IFN-γ-positive cells was significantly higher than IL-4 positive cells. TNF-α, TGF-β and NOS2 were detected in 65%, 62% and 94% of samples respectively. There was an association between TNF-α-producing cells and the presence of HF. Subjects with HF presented higher levels of STAT4 mRNA, whereas FoxP3 and STAT6 levels were similar in the two groups. A Th1 cytokine pattern predominated in the cardiac inflammatory cell infiltrate of Chagas' disease patients associated with HF. High degree of fibrosis was associated with low NOS2 expression. These results support the idea that Th1 immune responses are involved in heart lesions of Chagas' disease patients.

Host cholesterol and inflammation as common key regulators of toxoplasmosis and artherosclerosis development

Atherosclerosis and toxoplasmosis are two widely prevalent diseases worldwide. The relationship between these diseases is now being elucidated. Atherosclerosis is a disease with three main components: increased blood lipoprotein/cholesterol and their deposition in the arterial wall, an important Th1-mediated proinflammatory reaction and thrombogenic status. Toxoplasma gondii, in turn, is dependent on host cholesterol for optimal intracellular growth and replication. As a result, host cholesterol will be cleared from the blood, reducing plasma low-density lipoprotein, a crucial atherosclerosis risk factor. On the other hand, T. gondii infection elicits an important Th1 systemic inflammatory response in the host. Therefore, this additional proinflammatory stimulus may impose an enhanced pro-atherogenic environment in the host. As result, the association between these two diseases in one individual could change the course of atherosclerosis. In this review, we demonstrate that the host-parasite relationship is complex and that the outcome of each disease is dependent on the availability of intracellular cholesterol, as well as the intensity of the inflammatory reaction triggered by the parasite. We also discuss the possible clinical implications of these studies.

UDP-Gal: N-acetylglucosamine beta 1-4 galactosyltransferase expressing live attenuated parasites as vaccine for visceral leishmaniasis

As compared to cutaneous leishmaniasis, vaccination against visceral leishmaniasis (VL) has received limited attention. In this study, we demonstrate for the first time that an UDP-Galactose: N-acetylglucosamine beta 1-4 galactosyltransferase (GenBank Accession No. EF159943) expressing attenuated LD clonal population (A-LD) is able to confer protection against the experimental challenge with the virulent LD AG83 parasite. A-LD was also effective in established leishmania infection. The vaccinated animals showed both cell mediated (in vitro T-cell proliferation, and DTH response) and humoral responses (Th1 type). These results demonstrate the potential of the attenuated clones as an immunotherapeutic and immunoprophylactic agent against visceral leishmaniasis.

Leishmania major: recruitment of Gr-1+ cells into draining lymph nodes during infection is important for early IL-12 and IFN gamma production

The production of interleukin-12 and interferon-gamma is a key event for controlling leishmaniasis. Here, we tested the hypothesis that after murine infection with Leishmania major, cell migration into draining lymph nodes is crucial for early production of those cytokines. We showed that inflammatory cells carrying the marker of recently migrated cells, the Gr-1 antigen, including polymorphonuclear and mononuclear cells, migrate rapidly into the site of promastigote infection and, subsequently, into draining lymph nodes. Treatment with RB6-8C5 monoclonal antibody reduced local inflammation and migration of Gr-1+ cells into the draining lymph nodes. This reduction was associated with a decrease of interleukin-12 production by draining lymph node cells from BALB/c mice but not C57BL/6 mice. Additionally, interferon-gamma was also reduced in both mouse strains after depletion of Gr-1+ cells, suggesting that these cells are important for early interleukin-12 and interferon-gamma production. Our findings suggest that recently migrated myeloid cells, more than resident cells, are the major source of the early IL-12 production after L. major infection.

The involvement of CD4+CD25+ T cells in the acute phase of Trypanosoma cruzi infection

The infection with Trypanosoma cruzi leads to a vigorous and apparently uncontrolled inflammatory response in the heart. Although the parasites trigger specific immune response, the infection is not completely cleared out, a phenomenon that in other parasitic infections has been attributed to CD4+CD25+ T cells (Tregs). Then, we examined the role of natural Tregs and its signaling through CD25 and GITR in the resistance against infection with T. cruzi. Mice were treated with mAb against CD25 and GITR and the parasitemia, mortality and heart pathology analyzed. First, we demonstrated that CD4+CD25+GITR+Foxp3+ T cells migrate to the heart of infected mice. The treatment with anti-CD25 or anti-GITR resulted in increased mortality of these infected animals. Moreover, the treatment with anti-GITR enhanced the myocarditis, with increased migration of CD4+, CD8+, and CCR5+ leukocytes, TNF-alpha production, and tissue parasitism, although it did not change the systemic nitric oxide synthesis. These data showed a limited role for CD25 signaling in controlling the inflammatory response during this protozoan infection. Also, the data suggested that signaling through GITR is determinant to control of the heart inflammation, parasite replication, and host resistance against the infection.

Immunohistochemical characterization of mononuclear cells and MHC II expression in the brain of horses with experimental chronic Trypanosoma evansi infection

An histochemical and immunohistochemical study was carried out to evaluate the mechanisms of immune response of horses experimentally infected by Trypanosoma evansi. For this purpose the HE histochemical stain and the avidin biotin peroxidase method were used. To determine the presence and immunoreactivity of immune cells we used anti-major histocompatibility complex II antibodies. Cellular infiltration phenotype was characterized with the aid of anti-CD3 antibody for T lymphocytes and by anti-BLA 36 antibodies for B lymphocytes. Macrophages were marked with an antibody against myeloid/histyocites antigen (clone Mac387). Lesions in the CNS of experimentally infected horses were those of a wide spread non suppurative encephalomyelitis and meningomyelitis. The severity of lesions varied in different parts of the nervous system, reflecting an irregular distribution of inflammatory vascular changes. Lymphoid perivascular cuffs and meningeal infiltrations were of predominantly composed of T and B cells. The parasite, T. evansi, was not identified in these horses tissues.

Chorionic gonadotropin can enhance innate immunity by stimulating macrophage function

Human chorionic gonadotropin (hCG) is a placental glycoprotein, mainly secreted by trophoblasts during pregnancy. Its function in endocrine regulation has been well documented, but its immunological role is still largely unclear. For a successful pregnancy, an effective innate immunity is needed to protect the mother and fetus against infection, while maintaining tolerance against the paternal antigens of the fetus. The aim of this study was to investigate the effect of hCG on the function of macrophages (Mvarphi), which are major players in the innate response. hCG treatment of IFN-gamma-primed Mvarphi resulted in increased production of NO, reactive oxygen species, IL-6 and IL-12p40, and enhanced phagocytosis of apoptotic cells. hCG treatment did not affect the induction of allogeneic T cell proliferation by IFN-gamma-primed Mvarphi. The observed effects were receptor-mediated and involved the protein kinase A signaling pathway, as indicated by blocking studies using specific inhibitors. In vivo thioglycollate-elicited Mvarphi also exhibited increased phagocytic ability upon IFN-gamma activation and hCG treatment. In conclusion, hCG enhances Mvarphi functions involved in innate immunity, while the capacity to stimulate allogeneic T cells remains unchanged.

Dynamics of transcription of immunomodulatory genes in endothelial cells infected with different coccidian parasites

Sporozoites of Eimeria bovis and tachyzoites of Neospora caninum and Toxoplasma gondii are able to invade and to replicate in endothelial cells. Here we report on responses of bovine umbilical vein endothelial cells (BUVEC) in vitro to these coccidial infections by determining mRNA levels of the CXC chemokines GRO-alpha, IL-8 and IP-10, the CC chemokines MCP-1 and RANTES and of GM-CSF, COX-2 and iNOS relative to the level of housekeeping gene (GAPDH) transcription. T. gondii and N. caninum tachyzoites caused profound transcriptional upregulation of all genes in question. In general, upregulation started 2-4 h p.i. and maximum transcript levels were observed 4 h p.i. GRO-alpha and IL-8 gene transcription had decreased to almost control levels by 12 h p.i.; in the case of the other chemokines enhanced transcript levels persisted longer or showed a biphasic time-course. A similar time-course to CC chemokines was observed for GM-CSF mRNA, whilst COX-2 gene transcript peaks were detected at 2-4 h p.i. and 48-72 h p.i. iNOS mRNA levels increased from 4 to 48 h p.i. In contrast, E. bovis sporozoites failed to induce the transcription of CXC chemokine genes and of COX-2, and only caused moderate transcription upregulation of the other genes considered. In conclusion, infections of BUVEC with these coccidian parasites result in host cell activation associated with enhanced transcription of genes encoding for proinflammatory and immunomodulatory molecules, which are important for innate immune reactions and the transition to adaptive immunity. Differences between E. bovis versus T. gondii and N. caninum may illustrate a particular evasion strategy of E. bovis sporozoites, which is related to their need to persist in the host cell for a long period of time and to the avoidance of inflammatory process-induction.

Macrophage migration inhibitory factor contributes to host defense against acute Trypanosoma cruzi infection

Macrophage migration inhibitory factor (MIF) is a proinflammatory cytokine that is involved in the host defense against several pathogens. Here we used MIF-/- mice to determine the role of endogenous MIF in the regulation of the host immune response against Trypanosoma cruzi infection. MIF-/- mice displayed high levels of blood and tissue parasitemia, developed severe heart and skeletal muscle immunopathology, and succumbed to T. cruzi infection faster than MIF+/+ mice. The enhanced susceptibility of MIF-/- mice to T. cruzi was associated with reduced levels of proinflammatory cytokines, such as tumor necrosis factor alpha, interleukin-12 (IL-12), IL-18, gamma interferon (IFN-gamma), and IL-1beta, in their sera and reduced production of IL-12, IFN-gamma, and IL-4 by spleen cells during the early phase of infection. At all time points, antigen-stimulated splenocytes from MIF+/+ and MIF-/- mice produced comparable levels of IL-10. MIF-/- mice also produced significantly less Th1-associated antigen-specific immunoglobulin G2a (IgG2a) throughout the infection, but both groups produced comparable levels of Th2-associated IgG1. Lastly, inflamed hearts from T. cruzi-infected MIF-/- mice expressed increased transcripts for IFN-gamma, but fewer for IL-12 p35, IL-12 p40, IL-23, and inducible nitric oxide synthase, compared to MIF+/+ mice. Taken together, our findings show that MIF plays a role in controlling acute T. cruzi infection.

Toxoplasma gondii and Neospora caninum infections of bovine endothelial cells induce endothelial adhesion molecule gene transcription and subsequent PMN adhesion

Toxoplasma gondii and Neospora caninum are important, closely related coccidian parasites infecting a broad spectrum of hosts and host cells. Infections underly a complex immunological regulation; however, little is known on innate immune reactions to these parasites. To investigate interactions between infected cells and polymorphonuclear neutrophil cells (PMN), PMN adhesion to tachyzoite-infected bovine umbilical vein endothelial cells (BUVECs) under physiological flow conditions and adhesion molecule (E-selectin, P-selectin, VCAM-1, ICAM-1) gene transcription in infected BUVECs were examined in vitro for 72h post-infection (p.i.). BUVECs were rapidly invaded by T. gondii and N. caninum; in general 10-15% of the cells became infected. Tachyzoites were released from 24 and 48h p.i. onwards, for T. gondii and N. caninum, respectively. PMN adhesion to infected cell layers increased early (4h) after infection with both parasites, reached maximum levels 16-24h p.i., but remained enhanced throughout the observation period. PMN adhered to both, infected and non-infected cells within one cell layer, suggesting parasites induced paracrine activation of the BUVECs. Semiquantitative Realtime RT-PCR showed upregulated transcription of the E- and P-selectin genes in BUVECs within 1h p.i. and of ICAM-1 and VCAM-1 genes within 2h p.i. Maximum transcript levels were observed at 4-6h p.i.; the 24h p.i. gene transcription had declined to control levels. In general, T. gondii more strongly induced PMN adhesion and adhesion molecule gene transcription than N. caninum. The data suggest an effective role of PMN in innate immune reactions to these parasites.

Macrophages at intermediate stage of maturation produce high levels of IL-12 p40 upon stimulation with Leishmania

IL-12 is one of the main cytokines driving the immune response to a resistant phenotype in leishmaniasis and in several other diseases involving intracellular microbes. In this study, we investigated IL-12 production by mononuclear phagocytes at several developmental stages when stimulated with Leishmania major, L. amazonensis or L. chagasi. Bone marrow cells were cultured for 4-6 days in vitro in the presence of M-CSF, GM-CSF or IL-3. After density separation, only cells banding at the 40-50% Percoll interface, but not those at 20-40% or 50-80% interfaces, produced large amounts of IL-12 p40 when stimulated with LPS or live Leishmania promastigotes. However, only low levels of IL-12 p70 were produced under these conditions. The high IL-12 p40-producing cells could be similarly derived from mouse strains with different susceptibility to Leishmania. Quantitative analysis of monocyte/macrophage lineage marker expression, in combination with positive and negative selection, led to the conclusion that the high IL-12 p40-producing cells are macrophages at an intermediate stage of maturation between immature and fully differentiated cells, expressing ER-HR3 but only low levels of the mature markers, scavenger receptor and CD11b/Mac-1. They do not express any of the precursor markers CD31/ER-MP12, Ly-6C/ER-MP20 or ER-MP58. Because recruitment of monocytes to an infection site and its draining lymph node is a general phenomenon, the notion that, developing from these monocytes, a population of mononuclear phagocytes at an intermediate maturation stage has the capacity to synthesize large amounts of IL-12 p40 has significant bearing on our understanding of immune regulation in leishmaniasis and also in infections by other pathogens.

Immature macrophages derived from mouse bone marrow produce large amounts of IL-12p40 after LPS stimulation

Production of IL-12 is an important indicator of the macrophage's ability to regulate immune responses. In this study, we investigated the IL-12 production by macrophages in different developmental stages. To this end, macrophages were generated in vitro from precursors stimulated with M-CSF, GM-CSF or IL-3. Density separation yielded populations enriched in different maturation stages. Invariably, only cells banding at the 40-50% Percoll interface produced large amounts of IL-12p40 when stimulated with LPS, whereas only low levels of IL-12p70 were produced. These cells represented immature macrophages, as indicated by the absence of precursor markers CD31/ER-MP12, Ly-6C/ER-MP20 and ER-MP58, and by the low level of expression of mature-cell markers like ER-HR3, scavenger receptor and CD11b/Mac-1. Upon further maturation, the macrophages' ability to produce IL-12p40 decreased, coinciding with increased nitric oxide production upon LPS stimulation. These results show that immature macrophages produce high levels of IL-12p40 and thus may either contribute to IL-12p70 production or regulate it.

Pathology of toxoplasmosis in captive new world primates

Clinical information was available for 32 of 33 New World primates with fatal toxoplasmosis, all of which were subjected to a variable number of pathological observations. Death without apparent clinical signs occurred in 43.7% of cases. The most common clinical findings were malaise (40.6%), dyspnoea (18.7%), hypothermia (15.6%) and a sero-sanguinous or foamy nasal discharge (12.5%). Nutritional status was good in 71.8%, average in 18.7% and poor in 9.4%. The most common post-mortem findings were pulmonary congestion (78.8%), pulmonary oedema (75.8%), splenomegaly (57.6%) and mesenteric lymphadenitis (54.6%). The most common histopathological findings were multifocal necrotic hepatitis (97%), lymphadenitis (95.4%), interstitial pneumonia (90.3%) and necrotic splenitis (71.4%). The gross post-mortem changes in cebids were more variable than those observed in callitrichids, a fact that may complicate the diagnosis of toxoplasmosis in cebids.

Trace elements, innate immune response and parasites

Micronutrient deficiencies and infectious disease often coexist and show complex interactions leading to mutually reinforced detrimental clinical effects. Such a combination is predominantly observed in underprivileged people of developing countries, particularly in rural regions. Several micronutrients such as trace elements (zinc, iron, selenium) modulate immune function and influence the susceptibility of the host to infection. Nevertheless, the effect of individual micronutrients on components of innate immunity is difficult to design and interpret. Micronutrient deficiency, in general, has a widespread effect on nearly all components of the innate immune response. Chagas' disease is a pertinent model to study interaction of nutrition, immunity and infection, as it implies many components of innate immunity. An important question is whether alterations on micronutrient intake modify the course of infection. Some interactions of trace elements with innate immunity and acute inflammatory response are reviewed in this article with a special focus on selenium deficiency and Trypanosoma cruzi infection.

Evidence that development of severe cardiomyopathy in human Chagas' disease is due to a Th1-specific immune response

The role of interleukin 10 (IL-10) and gamma interferon (IFN-gamma) on the development of pathology in human Chagas' disease was investigated. Two categories of patients, low and high producers of IFN-gamma, were identified based on the levels of secretion of this cytokine in the supernatant of peripheral blood mononuclear cell (PBMC) cultures. Eighty-three percent of the patients presenting with cardiac disease (CARD) of different degrees and 59% of the patients with the indeterminate form of disease (IND) were identified as high IFN-gamma producers. PBMC from IND patients classified as low IFN-gamma producers secreted significantly higher amounts of IL-10 than did those from other groups. Flow cytometry analysis demonstrated that in PBMC from the IND group, the majority of the IL-10-producing cells were monocytes (CD14(High+) cells), whereas in the CARD group, the major sources of IFN-gamma were T lymphocytes (CD3(+) CD4(+) cells). These results suggest an association between the production of IFN-gamma by CD3(+) CD4(+) cells and morbidity in Chagas' disease, whereas the production of IL-10 by macrophages/monocytes leads to regulation of the immune response in IND patients. We hypothesize that an exacerbated production of IFN-gamma against Trypanosoma cruzi antigens favors the development of a strong Th1 response in CARD patients, which leads to progression of heart disease.

Trypanosoma cruzi down-regulates lipopolysaccharide-induced MHC class I on human dendritic cells and impairs antigen presentation to specific CD8(+) T lymphocytes

Trypanosoma cruzi, the etiological agent of Chagas' disease, may persist for many years in its mammalian host. This suggests escape from the immune response and particularly a suboptimal CD8(+) T cell response, since these cells are involved in infection control. In this report, we show that T. cruzi inhibits the lipopolysaccharide (LPS)-induced up-regulation of MHC class I molecules at the surface of human dendritic cells (DC). To further investigate the functional consequences of this inhibition, a trypomastigote surface antigen-derived peptide (TSA-1(514-522) peptide) was selected for its stable binding to HLA-A*0201 molecules and used to generate a primary T. cruzi-specific human CD8(+) T cell line in vitro. We observed that DC infected with T. cruzi or treated with T. cruzi-conditioned medium (TCM) had a weaker capacity to present this peptide to the specific CD8(+) T cell line as shown in an IFN-gamma ELISPOT assay. Interestingly, T. cruzi or TCM also reduced the antigen presentation capacity of DC to CD8(+) T cell lines specific for the influenza virus M(58-66) or HIV RT(476-484) epitopes. This dysfunction appears to be linked essentially to reduced MHC class I molecule expression since the stimulation of the RT(476-484) peptide-specific CD8(+) T cell line was shown to depend mainly on the MHC class I-TCR interaction and not on the co-stimulatory signals which, however, were also inhibited by T. cruzi. This impairment of DC function may represent a novel mechanism reducing in vivo the host's ability to combat efficiently T. cruzi infection.

Chemokines in host–protozoan-parasite interactions

Here, we review the interactions between parasites and chemokines and chemokine receptors in toxoplasmosis, trypanosomiasis, leishmaniasis, malaria and other diseases caused by protozoan parasites. The potential roles of chemokines after infection by these intracellular pathogens include host defence functions such as leukocyte recruitment, participation in cell-mediated immunity and antiprotozoal activity. However, these interactions can also help the parasite in, for example, the penetration of host cells.

Toxoplasma gondii induces the secretion of monocyte chemotactic protein-1 in human fibroblasts, in vitro

Secretion of Monocyte Chemotactic Protein-1 (MCP-1) by fibroblasts infected with Toxoplasma gondii was studied in vitro. A significantly higher MCP-1 secretion was observed 24 h after infection by live tachyzoites. Analysis of chemokine mRNA transcripts by RNase protection assay revealed that this MCP-1 secretion seems associated with increased MCP-1 mRNA expression. However, these increased levels of MCP-1 secretion and expression were not obtained after stimulation by heat-killed tachyzoites or parasites pre-treated by a specific inhibitor of phosphatidylcholine-specific phospholipase C (D609). Inhibition of parasite multiplication by pyrimethamine did not modify MCP-1 secretion. Thus, it appeared that the active penetration of T. gondii in cells was of major importance in the induction of MCP-1 secretion. None of the other chemokines studied by RNase protection assay (lymphotactin, RANTES, IP-10, MIP-1alpha, MIP-1beta, IL-8, and I-309) were expressed after infection by live tachyzoites. We also found that MCP-1 secretion induced by live T. gondii is blocked by inhibitors of nuclear factor (NF)-kappaB activation, ALLN and MG132. Such data indicate that NF-kappaB could be involved in T. gondii-induced MCP-1 production. MCP-1 secretion may contribute to the recruitment of monocytes and lymphocytes and thus participate in the control of T. gondii infection and in its pathogenesis.

Paralysis of dendritic cell IL-12 production by microbial products prevents infection-induced immunopathology

Interleukin-12 plays a major role in immunity to intracellular pathogens by governing the development of IFNgamma-dependent host resistance. Nevertheless, unregulated IL-12 synthesis can lead to immunopathology, an outcome prevented by the concurrent expression of interleukin-10. Dendritic cells (DC) are an important source of the initial IL-12 stimulated by microbial agents. Here, we show that, following systemic triggering, DC can no longer be restimulated to produce IL-12 in vivo while continuing to respond in vitro. When infected with Toxoplasma gondii during this refractory state, mice mount impaired acute IFNgamma responses and, in the case of IL-10-deficient animals, are protected from cytokine-induced mortality. These findings demonstrate a previously unrecognized form of immunologic paralysis involving DC that can protect from infection-induced immunopathology.

Protection against toxoplasmosis in mice immunized with different antigens of Toxoplasma gondii incorporated into liposomes

Different toxoplasma antigens were entrapped within liposomes and evaluated, in this form, for their ability to protect Swiss mice against toxoplasma infection: soluble tachyzoite antigen (L/TAg), tissue cyst (L/CAg), tachyzoite plus tissue cyst (L/TCAg) or purified antigen of tachyzoite (L/pTAg). The protein used in L/pTAg was purified from tachyzoites using a stage-specific monoclonal antibody which reacted at a molecular weight of 32 kD in SDS PAGE and silver stain using reduced condition. To compare the immuno-adjuvant action of liposomes and of Freund's Complete Adjuvant (FCA), another group of mice was immunized with soluble tachyzoite antigen (STAg) emulsified in FCA (FCA/TAg). Control groups were inoculated with (STAg) alone, phosphate-buffered saline (PBS), FCA with PBS (FCA/PBS) and empty liposomes (L/PBS). Mice were inoculated subcutaneously with these antigens six, four and two weeks before a challenge with 80 tissue cysts of the P strain of Toxoplasma gondii orally. All mice immunized with or without adjuvant showed a humoral response, as measured by Elisa. However, no correlation was found between antibody titer and protection against the challenge. All mice immunized with L/pTAg or L/TCAg survived (100), whereas 80% and 90% of mice from groups which received respectively PBS or FCA/PBS and L/PBS died. All mice immunized with antigens entrapped within liposomes (L/TAg, L/CAg, L/TCAg and L/pTAg) showed low numbers of intracerebral cysts.