Activation of Toll-like receptor-2 by glycosylphosphatidylinositol anchors from a protozoan parasite

Transcriptome-wide identification, molecular evolution and expression analysis of Toll-like receptor family in a Tibet fish, Gymnocypris przewalskii

Toll-like receptors (TLR) are key components of innate immunity that play significant roles in immune defense against pathogens invasion. Recent frequent outbreaks of the "white spot disease" caused by parasitic infection in farmed Tibetan fishes had resulted in great economic losses. However, to our knowledge, the roles of TLRs in mediating immune response to parasitic infection in Tibetan fishes remain to be determined. Here, we performed data-mining on a widely-farmed Tibetan fish (Gymnocypris przewalskii or Gp) transcriptome to determine the genetic variation and expression pattern of TLRs. We totally obtained 14 GpTLRs and identified 5 with a complete coding sequence. Phylogenetic analysis verified their identities and supported the classification of TLRs into six families as in other vertebrates. The TLR family motifs, such as leucine rich repeat (LRR) and Toll/interleukin (IL)-1 receptor (TIR) domain, are conserved in GpTLR1-5. Selective pressure test demonstrated that all known GpTLRs are under purifying selection, except GpTLR4 underwent positive selection. Further, site model analysis suggested that 11 positively selected sites are found in LRR domain of GpTLR4. Three positively selected sites are located on outside surface of TLR4 3D structure, indicating that function of GpTLR4 may be affected. Tissue specific expression analysis showed all GpTLRs are present in gill, head-kidney and spleen but the relative abundance varied among tissues. In response to parasite Ichthyophthirius multifiliis infection, 5 GpTLR (GpTLR1, -2, -4, -9 and -20) expressions were induced. Intriguingly, GpTLR4 was significantly up-regulated in gills, while GpTLR19 and GpTLR21 unexpectedly showed no any change. In summary, these results revealed the first genomic resources of TLR family and several parasitic infection responsive TLRs in Tibetan fish. These findings provide key information for future studies aiming to understand the molecular mechanisms underlying the immune response to pathogen invasion in Tibetan fishes.

Splenic Macrophage Subsets and Their Function during Blood-Borne Infections

The spleen is one of the major immunological sites for maintaining blood homeostasis. Previous studies showed that heterogeneous splenic macrophage populations contribute in complimentary ways to control blood-borne infections and induce effective immune responses. Marginal metallophilic macrophages (MMMΦs) and marginal zone macrophages (MZMΦs) are cells with great ability to internalize blood-borne pathogens such as virus or bacteria. Their localization adjacent to T- and B-cell-rich splenic areas favors the rapid contact between these macrophages and cells from adaptive immunity. Indeed, MMMΦs and MZMΦs are considered important bridges between innate and adaptive immunity. Although red pulp macrophages (RpMΦs) are mainly considered scavengers for senescent erythrocytes, several data indicate a role for RpMΦs in control of infections such as blood-stage malaria as well as in the induction of innate and adaptive immunity. Here, we review current data on how different macrophage subsets recognize and help eliminate blood-borne pathogens, and, in turn, how the inflammatory microenvironment in different phases of infection (acute, chronic, and after pathogen clearance) influences macrophage function and survival.

Toll-like receptor 9 signaling in dendritic cells regulates neutrophil recruitment to inflammatory foci following Leishmania infantum infection

Leishmania infantum is a protozoan parasite that causes visceral leishmaniasis (VL). This infection triggers dendritic cell (DC) activation through the recognition of microbial products by Toll-like receptors (TLRs). Among the TLRs, TLR9 is required for DC activation by different Leishmania species. We demonstrated that TLR9 is upregulated in vitro and in vivo during infection. We show that C57BL/6 mice deficient in TLR9 expression (TLR9(-/-) mice) are more susceptible to infection and display higher parasite numbers in the spleen and liver. The increased susceptibility of TLR9(-/-) mice was due to the impaired recruitment of neutrophils to the infection foci associated with reduced levels of neutrophil chemoattractants released by DCs in the target organs. Moreover, both Th1 and Th17 cells were also committed in TLR9(-/-) mice. TLR9-dependent neutrophil recruitment is mediated via the MyD88 signaling pathway but is TIR domain-containing adapter-inducing interferon beta (TRIF) independent. Furthermore, L. infantum failed to activate both plasmacytoid and myeloid DCs from TLR9(-/-) mice, which presented reduced surface costimulatory molecule expression and chemokine release. Interestingly, neutrophil chemotaxis was affected both in vitro and in vivo when DCs were derived from TLR9(-/-) mice. Our results suggest that TLR9 plays a critical role in neutrophil recruitment during the protective response against L. infantum infection that could be associated with DC activation.

Sympathetic glial cells and macrophages develop different responses to Trypanosoma cruzi infection or lipopolysaccharide stimulation

Nitric oxide (NO) participates in neuronal lesions in the digestive form of Chagas disease and the proximity of parasitised glial cells and neurons in damaged myenteric ganglia is a frequent finding. Glial cells have crucial roles in many neuropathological situations and are potential sources of NO. Here, we investigate peripheral glial cell response to Trypanosoma cruzi infection to clarify the role of these cells in the neuronal lesion pathogenesis of Chagas disease. We used primary glial cell cultures from superior cervical ganglion to investigate cell activation and NO production after T. cruzi infection or lipopolysaccharide (LPS) exposure in comparison to peritoneal macrophages. T. cruzi infection was greater in glial cells, despite similar levels of NO production in both cell types. Glial cells responded similarly to T. cruzi and LPS, but were less responsive to LPS than macrophages were. Our observations contribute to the understanding of Chagas disease pathogenesis, as based on the high susceptibility of autonomic glial cells to T. cruzi infection with subsequent NO production. Moreover, our findings will facilitate future research into the immune responses and activation mechanisms of peripheral glial cells, which are important for understanding the paradoxical responses of this cell type in neuronal lesions and neuroprotection.

Extracellular Vesicles: Role in Inflammatory Responses and Potential Uses in Vaccination in Cancer and Infectious Diseases

Almost all cells and organisms release membrane structures containing proteins, lipids, and nucleic acids called extracellular vesicles (EVs), which have a wide range of functions concerning intercellular communication and signaling events. Recently, the characterization and understanding of their biological role have become a main research area due to their potential role in vaccination, as biomarkers antigens, early diagnostic tools, and therapeutic applications. Here, we will overview the recent advances and studies of Evs shed by tumor cells, bacteria, parasites, and fungi, focusing on their inflammatory role and their potential use in vaccination and diagnostic of cancer and infectious diseases.

Co-expression of march5b and tlr7 in large yellow croaker Larimichthys crocea in response to Cryptocaryon irritans infection

In this study, molecular characteristics of march5b and co-expression of march5b and tlr7 in response to the infection of Cryptocaryon irritans in the large yellow croaker Larimichthys crocea were investigated. The full-length complementary (c)DNA of march5b was 1314 bp, including an open reading frame of 846 bp encoding a polypeptide of 281 amino acids, and the full-length genomic sequence was composed of 23,577 nucleotides, including six exons and five introns. The putative March5b protein contained a RINGv motif and four transmembrane domains. The march5b transcripts were broadly distributed in all detected tissues, with a strong expression in blood, brain and gills, and a weak expression in kidney by quantitative PCR analysis. The expression of march5b and tlr7 in the skin, gills, spleen and head kidney changed in the same manner at most time points post-primary infection with C. irritans. Significant increase was observed in the skin with march5b at days 2 and 3 by 26.10 and 6.88 fold, respectively, and with tlr7 at day 3 by 57.68 fold, when compared with the control. Their expressions, however, were decreased in the gills, especially at day 3 (march5b by 8.9%, tlr7 by 22.06%). In the spleen and head kidney, march5b and tlr7 transcripts were up-regulated early, then noticeably declined at day 3. These results suggested that march5b and tlr7 are co-expressed in response to parasite infection and March5b probably catalyses ubiquitination of some proteins of TLR7 signalling pathway.

Differential Activation of Human Monocytes and Lymphocytes by Distinct Strains of Trypanosoma cruzi

Background

Trypanosoma cruzi strains are currently classified into six discrete typing units (DTUs) named TcI to VI. It is known that these DTUs have different geographical distribution, as well as biological features. TcI and TcII are major DTUs found in patients from northern and southern Latin America, respectively. Our hypothesis is that upon infection of human peripheral blood cells, Y strain (Tc II) and Col cl1.7 (Tc I), cause distinct immunological changes, which might influence the clinical course of Chagas disease.

Methodology/Principal Findings

We evaluated the infectivity of CFSE-stained trypomastigotes of Col cl1.7 and Y strain in human monocytes for 15 and 72 hours, and determined the immunological profile of lymphocytes and monocytes exposed to the different isolates using multiparameter flow cytometry. Our results showed a similar percentage and intensity of monocyte infection by Y and Col cl1.7. We also observed an increased expression of CD80 and CD86 by monocytes infected with Col cl1.7, but not Y strain. IL-10 was significantly higher in monocytes infected with Col cl1.7, as compared to Y strain. Moreover, infection with Col cl1.7, but not Y strain, led to an increased expression of IL-17 by CD8+ T cells. On the other hand, we observed a positive correlation between the expression of TNF-alpha and granzyme A only after infection with Y strain.

Conclusion/Significance

Our study shows that while Col cl1.7 induces higher monocyte activation and, at the same time, production of IL-10, infection with Y strain leads to a lower monocyte activation but higher inflammatory profile. These results show that TcI and TcII have a distinct immunological impact on human cells during early infection, which might influence disease progression.

Chagas disease remains a major public health problem in Latin America with over 13 million people infected. It is believed that the host immune response and genetic diversity of the parasite play an important role in the progression of Chagas disease, which presents a variety of clinical forms ranging from indeterminate to cardiac and digestive forms. Since parasite genetic diversity may influence the development of Chagas disease, our study aims to understand the immune response of human peripheral blood cells upon infection with two T. cruzi strains with different genetic backgrounds (Col cl1.7 – Tc I, and Y strain – TcII). Our study showed differences in the expression of cytokines and activation molecules between cells infected with strains from Tc I (Col cl1.7) and Tc II (Y strain). These data show the importance of parasite strain in the development of the host response early in infection, which may influence the clinical progression of Chagas disease.

Polymorphisms in the TOLLIP Gene Influence Susceptibility to Cutaneous Leishmaniasis Caused by Leishmania guyanensis in the Amazonas State of Brazil

INTRODUCTION

The clinical outcome to Leishmania-infection is determined by the individual adaptive immune T helper cell responses and their interactions with parasitized host cells. An early development of a proinflammatory immune response (Th1 response) is necessary for Leishmania-infection resolution. The Toll-interacting protein (TOLLIP) regulates human Toll-like receptors signaling pathways by down regulating the proinflammatory cytokines interleukin-6 (IL-6) and tumor necrosis factor alpha (TNF-α) and inducing the ant-inflammatory cytokine interleukin-10 (IL-10). Polymorphisms in the TOLLIP gene are associated with infectious diseases.

MATERIAL AND METHODS

The polymorphisms rs5743899 and rs3750920 in the TOLLIP gene were genotyped by polymerase chain reaction and restriction fragment length polymorphism (RFLP) analysis in 631 patients with cutaneous leishmaniasis (CL) caused by L. guyanensis and 530 individuals with no history of leishmaniasis.

RESULTS

The G and T alleles of the rs5743899 and rs3750920 were more common in patients with CL than in healthy individuals (P = 2.6 x10(-8) ; odds ratio [OR], 1.7 [ 95% confidence interval (CI) 1.4-2.0] and P = 1.9 x10(-8) ; OR, 1.6 [95% CI 1.4-1.9] respectively). The r2 and D' linkage disequilibrium between the two polymorphisms are 0.05 and 0.473 with a confidence bounds of 0.37 to 0.57 respectively.

CONCLUSION

The two polymorphisms are independently associated with an increased risk of developing CL.

Immune-relevant thrombocytes of common carp undergo parasite-induced nitric oxide-mediated apoptosis

Common carp thrombocytes account for 30-40% of peripheral blood leukocytes and are abundant in the healthy animals' spleen, the thrombopoietic organ. We show that, ex vivo, thrombocytes from healthy carp express a large number of immune-relevant genes, among which several cytokines and Toll-like receptors, clearly pointing at immune functions of carp thrombocytes. Few studies have described the role of fish thrombocytes during infection. Carp are natural host to two different but related protozoan parasites, Trypanoplasma borreli and Trypanosoma carassii, which reside in the blood and tissue fluids. We used the two parasites to undertake controlled studies on the role of fish thrombocytes during these infections. In vivo, but only during infection with T. borreli, thrombocytes were massively depleted from the blood and spleen leading to severe thrombocytopenia. Ex vivo, addition of nitric oxide induced a clear and rapid apoptosis of thrombocytes from healthy carp, supporting a role for nitric oxide-mediated control of immune-relevant thrombocytes during infection with T. borreli. The potential advantage for parasites to selectively deplete the host of thrombocytes via nitric oxide-induced apoptosis is discussed.

SNP marker discovery in koala TLR genes

Toll-like receptors (TLRs) play a crucial role in the early defence against invading pathogens, yet our understanding of TLRs in marsupial immunity is limited. Here, we describe the characterisation of nine TLRs from a koala immune tissue transcriptome and one TLR from a draft sequence of the koala genome and the subsequent development of an assay to study genetic diversity in these genes. We surveyed genetic diversity in 20 koalas from New South Wales, Australia and showed that one gene, TLR10 is monomorphic, while the other nine TLR genes have between two and 12 alleles. 40 SNPs (16 non-synonymous) were identified across the ten TLR genes. These markers provide a springboard to future studies on innate immunity in the koala, a species under threat from two major infectious diseases.

Macrophage biology and their activation by protozoan-derived glycosylphosphatidylinositol anchors and hemozoin

Despite recent advances in medical technology and a global effort to improve public health and hygiene, parasitic infections remain a major health and economic burden worldwide. The World Health Organization estimates that about 1/3 of the world's population is currently infected with a soil-transmitted helminth, and millions more suffer from diseases caused by protozoan parasites including Plasmodium, Trypanosoma, and Leishmania species. Due to the selective pressure applied by parasitic and other infections, animals have evolved an intricate immune system; however, the current worldwide prevalence of parasitic infections clearly indicates that these pathogens have adapted equally well. Thus, developing a better understanding of the host-parasite relationship, particularly by focusing on the host immune response and the mechanisms by which parasites evade this response, is a critical first step in mitigating the detrimental effects of parasitic diseases. Macrophages are critical contributors during the host response to protozoan parasites, and the success or failure of these cells often tips the balance in favor of the host or parasite. Herein, we briefly discuss macrophage biology and provide an update on our current understanding of how these cells recognize glycosylphosphatidylinositol anchors from protozoan parasites as well as malarial hemozoin.

Leishmania lipophosphoglycan: how to establish structure-activity relationships for this highly complex and multifunctional glycoconjugate?

A key feature of many pathogenic microorganisms is the presence of a dense glycocalyx at their surface, composed of lipid-anchored glycoproteins and non-protein-bound polysaccharides. These surface glycolipids are important virulence factors for bacterial, fungal and protozoan pathogens. The highly complex glycoconjugate lipophosphoglycan (LPG) is one of the dominant surface macromolecules of the promastigote stage of all Leishmania parasitic species. LPG plays critical pleiotropic roles in parasite survival and infectivity in both the sandfly vector and the mammalian host. Here, we review the composition of the Leishmania glycocalyx, the chemical structure of LPG and what is currently known about its effects in the mammalian host, specifically. We will then discuss the current approaches employed to elucidate LPG functions. Finally, we will provide a viewpoint on future directions that this area of investigation could take to unravel in detail the biological activity of the specific molecular elements composing the structurally complex LPG.

The host response: Toll-like receptor expression in periprosthetic tissues as a biomarker for deep joint infection

BACKGROUND

Toll-like receptors (TLRs) 1 and 6 are consistent molecular indicators of the host inflammatory response against bacterial infection. Our aims were to determine whether TLR elevation could be detected in infected periprosthetic tissues and to assess the utility of these biomarkers as tests for detecting a periprosthetic joint infection.

METHODS

Fifty-nine patients undergoing revision total joint arthroplasty (twenty-seven hips and thirty-two knees) were prospectively evaluated for periprosthetic joint infection according to currently recommended diagnostic criteria. Nine patients were excluded because of insufficient work-up, leaving fifty available for study. Of these, twenty-one were categorized as infected and twenty-nine as noninfected. Periprosthetic tissues were collected intraoperatively, and total RNA was extracted by standard techniques. Expression of TLR messenger RNAs was assessed by first-strand complementary DNA synthesis from 1 μg of total RNA followed by real-time PCR (polymerase chain reaction). Results were normalized relative to the housekeeping gene GAPDH (glyceraldehyde 3-phosphate dehydrogenase). Expression of TLRs 1, 6, and 10 in the infected and noninfected groups was compared with use of the Student t test. The receiver operating characteristic curve, area under the curve (AUC), sensitivity, specificity, positive likelihood ratio (LR+), and negative likelihood ratio (LR-) were calculated to determine the accuracy of each TLR for predicting periprosthetic joint infection at its optimal diagnostic threshold.

RESULTS

Mean TLR1 mRNA expression was significantly elevated in infected compared with noninfected samples (0.600 compared with 0.005, p = 0.0003); the same was true of TLR6 (0.208 compared with 0.0165, p = 0.0059) but not of TLR10 (0.00019 compared with 0.00014, p = 0.6238). The AUC was 0.995 for TLR1, 0.883 for TLR6, and 0.546 for TLR10. The optimal threshold for diagnosing periprosthetic joint infection was 0.0924 for TLR1 (sensitivity = 95.2%, specificity = 100%, LR+ = 13.80, LR- = 0.91) and 0.0215 for TLR6 (sensitivity = 85.7%, specificity = 82.8%, LR+ = 4.98, LR- = 0.83).

CONCLUSIONS

In our pilot study, TLR1 expression in periprosthetic tissues most accurately predicted periprosthetic joint infection. This measure of the host response may be particularly helpful in detecting culture-negative infections and avoiding false positives resulting from contamination.

LEVEL OF EVIDENCE

Diagnostic Level III. See Instructions for Authors for a complete description of levels of evidence.

Fungal glycans and the innate immune recognition

Polysaccharides such as α- and β-glucans, chitin, and glycoproteins extensively modified with both N- and O-linked carbohydrates are the major components of fungal surfaces. The fungal cell wall is an excellent target for the action of antifungal agents, since most of its components are absent from mammalian cells. Recognition of these carbohydrate-containing molecules by the innate immune system triggers inflammatory responses and activation of microbicidal mechanisms by leukocytes. This review will discuss the structure of surface fungal glycoconjugates and polysaccharides and their recognition by innate immune receptors.

Immunomodulation by Trypanosoma cruzi: toward understanding the association of dendritic cells with infecting TcI and TcII populations

Dendritic cells (DCs) are major immune components, and depending on how these cells are modulated, the protective host immune response changes drastically. Trypanosoma cruzi is a parasite with high genetic variability and modulates DCs by interfering with their capacity for antigen recognition, migration, and maturation. Despite recent efforts, the association between DCs and T. cruzi I (TcI) and TcII populations is unknown. Herein, it was demonstrated that AQ1.7 and MUTUM TcI strains present low rates of invasion of bone marrow-derived DCs, whereas the 1849 and 2369 TcII strains present higher rates. Whereas the four strains similarly induced the expression of PD-L1, the production and expression of IL-10 and TLR-2, respectively, in DCs were differentially increased. The production of TNF-α, IL-12, IL-6, and CCL2 and the expression of CD40, CD80, MHC-II, CCR5, and CCR7 changed depending on the strain. The 2369 strain yielded the most remarkable results because greater invasion correlated with an increase in the levels of anti-inflammatory molecules IL-10 and PD-L1 but not with a change in the levels of TNF-α, MHC-II, or CD40 molecules. These results suggest that T. cruzi strains belonging to different populations have evolved specific evasion strategies that subvert DCs and consequently the host response.

Mouse macrophage galactose-type lectin (mMGL) is critical for host resistance against Trypanosoma cruzi infection

The C-type lectin receptor mMGL is expressed exclusively by myeloid antigen presenting cells (APC) such as dendritic cells (DC) and macrophages (Mφ), and it mediates binding to glycoproteins carrying terminal galactose and α- or β-N-acetylgalactosamine (Gal/GalNAc) residues. Trypanosoma cruzi (T. cruzi) expresses large amounts of mucin (TcMUC)-like glycoproteins. Here, we show by lectin-blot that galactose moieties are also expressed on the surface of T. cruzi. Male mMGL knockout (-/-) and wild-type (WT) C57BL/6 mice were infected intraperitoneally with 10⁴T. cruzi trypomastigotes (Queretaro strain). Following T. cruzi infection, mMGL-/- mice developed higher parasitemia and higher mortality rates compared with WT mice. Although hearts from T. cruzi-infected WT mice presented few amastigote nests, mMGL-/- mice displayed higher numbers of amastigote nests. Compared with WT, Mφ from mMGL-/- mice had low production of nitric oxide (NO), interleukin (IL)-12 and tumor necrosis factor (TNF)-α in response to soluble T. cruzi antigens (TcAg). Interestingly, upon in vitro T. cruzi infection, mMGL-/- Mφ expressed lower levels of MHC-II and TLR-4 and harbored higher numbers of parasites, even when mMGL-/- Mφ were previously primed with IFN-γ or LPS/IFN-γ. These data suggest that mMGL plays an important role during T. cruzi infection, is required for optimal Mφ activation, and may synergize with TLR-4-induced pathways to produce TNF-α, IL-1β and NO during the early phase of infection.

Trypanosoma cruzi infection in genetically selected mouse lines: genetic linkage with quantitative trait locus controlling antibody response

Trypanosoma cruzi infection was studied in mouse lines selected for maximal (AIRmax) or minimal (AIRmin) acute inflammatory reaction and for high (H_III) or low (L_III) antibody (Ab) responses to complex antigens. Resistance was associated with gender (females) and strain—the high responder lines AIRmax and H_III were resistant. The higher resistance of H_III as compared to L_III mice extended to higher infective doses and was correlated with enhanced production of IFN-γ and nitric oxide production by peritoneal and lymph node cells, in H_III males and females. We also analyzed the involvement of previously mapped Ab and T. cruzi response QTL with the survival of Selection III mice to T. cruzi infections in a segregating backcross [F1(H_III×L_III) ×L_III] population. An Ab production QTL marker mapping to mouse chromosome 1 (34.8 cM) significantly cosegregated with survival after acute T. cruzi infections, indicating that this region also harbors genes whose alleles modulate resistance to acute T. cruzi infection.

Cervical and vaginal fluid soluble Toll-like receptor 2 in pregnancies complicated by preterm prelabor rupture of membranes

OBJECTIVE

To determine the cervical and vaginal fluid soluble Toll-like receptor-2 (sTLR2) levels in pregnancies complicated by preterm prelabor rupture of membranes (PPROM) and their correlation to microbial invasion of the amniotic cavity (MIAC) and/or histological chorioamnionitis (HCA).

METHODS

Sixty-eight women with singleton pregnancies complicated by PPROM were included in this study. Cervical and vaginal fluid was collected at the time of admission, and levels of sTLR2 in the cervical and vaginal fluid were determined using enzyme-linked immunosorbent assay.

RESULT

Women with MIAC and both MIAC and HCA did not have different cervical and vaginal fluid sTLR2 levels compared to those without MIAC and without both MIAC and HCA. Women with HCA had higher cervical fluid sTLR2 levels in crude analysis (with HCA: median 11.6 pg/mL versus without HCA: median 5.5 pg/mL; p = 0.04) but not after adjustment for gestational age at sampling (p = 0.19). No difference in vaginal fluid sTLR2 levels between women with and without HCA was found. A positive correlation between cervical and vaginal fluid sTLR2 levels was identified (rho = 0.54; p < 0.0001).

CONCLUSIONS

Cervical and vaginal fluid sTLR2 levels did not reflect the presence of MIAC and/or HCA.

Induction of IL-12 production in human peripheral monocytes by Trypanosoma cruzi Is mediated by glycosylphosphatidylinositol-anchored mucin-like glycoproteins and potentiated by IFN- γ and CD40-CD40L interactions

Chagas disease, caused by the protozoan parasite Trypanosoma cruzi (T. cruzi), is characterized by immunopathology driven by IFN-γ secreting Th1-like T cells. T. cruzi has a thick coat of mucin-like glycoproteins covering its surface, which plays an important role in parasite invasion and host immunomodulation. It has been extensively described that T. cruzi or its products—like GPI anchors isolated from GPI-anchored mucins from the trypomastigote life cycle stage (tGPI-mucins)—are potent inducers of proinflammatory responses (i.e., cytokines and NO production) by IFN-γ primed murine macrophages. However, little is known about whether T. cruzi or GPI-mucins exert a similar action in human cells. We therefore decided to further investigate the in vitro cytokine production profile from human mononuclear cells from uninfected donors exposed to T. cruzi as well as tGPI-mucins. We observed that both living T. cruzi trypomastigotes and tGPI-mucins are potent inducers of IL-12 by human peripheral blood monocytes and this effect depends on CD40-CD40L interaction and IFN-γ. Our findings suggest that the polarized T1-type cytokine profile seen in T. cruzi infected patients might be a long-term effect of IL-12 production induced by lifelong exposure to T. cruzi tGPI-mucins.

Chagas disease: still many unsolved issues

Over the past 20 years, the immune effector mechanisms involved in the control of Trypanosoma cruzi, as well as the receptors participating in parasite recognition by cells of the innate immune system, have been largely described. However, the main questions on the physiopathology of Chagas disease remain unanswered: “Why does the host immune system fail to provide sterile immunity?” and “Why do only a proportion of infected individuals develop chronic pathology?” In this review, we describe the mechanisms proposed to explain the inability of the immune system to eradicate the parasite and the elements that allow the development of chronic heart disease. Moreover, we discuss the possibility that the inability of infected cardiomyocytes to sense intracellular T. cruzi contributes to parasite persistence in the heart and the development of chronic pathology.

Perpetual expression of PAMPs necessary for optimal immune control and clearance of a persistent pathogen

Pathogen-associated molecular patterns (PAMPs) are known to be fundamental in instigating immune responses, but their role in influencing these responses beyond their initiation is less well understood. Here, using the protozoan parasite Trypanosoma cruzi, which is deficient in strong PAMPs, we demonstrate a requirement for the continuous expression of PAMPs for optimal anti-pathogen immunity. Although co-inoculating with, temporary anchoring of and transgenic expression of exogenous PAMPs all result in enhanced early adaptive immune responses, only the continuous expression of bacterial PAMPs on transgenic T. cruzi sustains these responses, resulting in enhanced pathogen clearance. These findings demonstrate that PAMPs function to potentiate adaptive immune responses well beyond their initiation and may determine the efficiency of control of pathogens capable of long-term persistence.

Cytokine profiling in Chagas disease: towards understanding the association with infecting Trypanosoma cruzi discrete typing units (a BENEFIT TRIAL sub-study)

BACKGROUND

Chagas disease caused by the protozoan Trypanosoma cruzi is an important public health problem in Latin America. The immunological mechanisms involved in Chagas disease pathogenesis remain incompletely elucidated. The aim of this study was to explore cytokine profiles and their possible association to the infecting DTU and the pathogenesis of Chagas disease.

METHODS

109 sero-positive T. cruzi patients and 21 negative controls from Bolivia and Colombia, were included. Flow cytometry assays for 13 cytokines were conducted on human sera. Patients were divided into two groups: in one we compared the quantification of cytokines between patients with and without chronic cardiomyopathy; in second group we compared the levels of cytokines and the genetic variability of T. cruzi.

RESULTS

Significant difference in anti-inflammatory and pro-inflammatory cytokines profiles was observed between the two groups cardiac and non-cardiac. Moreover, serum levels of IFN-γ, IL-12, IL-22 and IL-10 presented an association with the genetic variability of T.cruzi, with significant differences in TcI and mixed infections TcI/TcII.

CONCLUSION

Expression of anti-inflammatory and pro-inflammatory cytokines may play a relevant role in determining the clinical presentation of chronic patients with Chagas disease and suggests the occurrence of specific immune responses, probably associated to different T. cruzi DTUs.

TLR2, TLR4 and CD14 recognize venom-associated molecular patterns from Tityus serrulatus to induce macrophage-derived inflammatory mediators

Scorpion sting-induced human envenomation provokes an intense inflammatory reaction. However, the mechanisms behind the recognition of scorpion venom and the induction of mediator release in mammalian cells are unknown. We demonstrated that TLR2, TLR4 and CD14 receptors sense Tityus serrulatus venom (TsV) and its major component, toxin 1 (Ts1), to mediate cytokine and lipid mediator production. Additionally, we demonstrated that TsV induces TLR2- and TLR4/MyD88-dependent NF-κB activation and TLR4-dependent and TLR2/MyD88-independent c-Jun activation. Similar to TsV, Ts1 induces MyD88-dependent NF-κB phosphorylation via TLR2 and TLR4 receptors, while c-Jun activation is dependent on neither TLR2 nor TLR4/MyD88. Therefore, we propose the term venom-associated molecular pattern (VAMP) to refer to molecules that are introduced into the host by stings and are recognized by PRRs, resulting in inflammation.

Do you see what I see: Recognition of protozoan parasites by Toll-like receptors

Toll-like receptors (TLRs) are important for recognizing a variety of pathogens, including protozoan parasites, and initiating innate immune responses against them. TLRs are localized on the cell surface as well as in the endosome, and are implicated in innate sensing of these parasites. In this review, we will discuss recent findings on the identification of parasite-derived pathogen associated molecular patterns and the TLRs that bind them. The role of these TLRs in initiating the immune response against protozoan parasitic infections in vivo will be presented in the context of murine models of infection utilizing TLR-deficient mice. Additionally, we will explore evidence that TLRs and genetic variants of TLRs may impact the outcome of these parasitic infections in humans.

Schistosoma japonicum infection induces macrophage polarization

The role of macrophages (Mφ) as the first line of host defense is well accepted. These cells play a central role in orchestrating crucial functions during schistosomal infection. Thus, understanding the functional diversity of these cells in the process of infection as well as the mechanisms underlying these events is crucial for developing disease control strategies. In this study, we adopted a Mφ polarization recognition system. M1 macrophage was characterized by expressing CD16/32, IL-12 and iNOS. M2 macrophage was characterized by expressing CD206, IL-10 and arg-1. In vivo (mouse peritoneal macrophages of different infection stages were obtained) and in vitro (different S. japonicum antigens were used to stimulate RAW264.7) were characterized by using the above mentioned system. NCA and ACA stimulated RAW264.7 express significantly higher levels of IL-12 while significantly higher levels of IL-10 were detected after soluble egg antigen (SEA) stimulation. The results showed that dramatic changes of antigen in the microenvironment before and after egg production led to macrophage polarization. Furthermore, through TLR blocking experiments, the TLR4 signaling pathway was found to play a role in the process of macrophage polarization toward M1. Our data suggest that macrophage polarization during S. japonicum infection had significant effects on host immune responses to S. japonicum.

NLRP3 controls Trypanosoma cruzi infection through a caspase-1-dependent IL-1R-independent NO production

Trypanosoma cruzi (T. cruzi) is an intracellular protozoan parasite and the etiological agent of Chagas disease, a chronic infectious illness that affects millions of people worldwide. Although the role of TLR and Nod1 in the control of T. cruzi infection is well-established, the involvement of inflammasomes remains to be elucidated. Herein, we demonstrate for the first time that T. cruzi infection induces IL-1β production in an NLRP3- and caspase-1-dependent manner. Cathepsin B appears to be required for NLRP3 activation in response to infection with T. cruzi, as pharmacological inhibition of cathepsin B abrogates IL-1β secretion. NLRP3^−/− and caspase1^−/− mice exhibited high numbers of T. cruzi parasites, with a magnitude of peak parasitemia comparable to MyD88^−/− and iNOS^−/− mice (which are susceptible models for T. cruzi infection), indicating the involvement of NLRP3 inflammasome in the control of the acute phase of T. cruzi infection. Although the inflammatory cytokines IL-6 and IFN-γ were found in spleen cells from NLRP3^−/− and caspase1^−/− mice infected with T. cruzi, these mice exhibited severe defects in nitric oxide (NO) production and an impairment in macrophage-mediated parasite killing. Interestingly, neutralization of IL-1β and IL-18, and IL-1R genetic deficiency demonstrate that these cytokines have a minor effect on NO secretion and the capacity of macrophages to control T. cruzi infection. In contrast, inhibition of caspase-1 with z-YVAD-fmk abrogated NO production by WT and MyD88^−/− macrophages and rendered them as susceptible to T. cruzi infection as NLRP3^−/− and caspase-1^−/− macrophages. Taken together, our results demonstrate a role for the NLRP3 inflammasome in the control of T. cruzi infection and identify NLRP3-mediated, caspase-1-dependent and IL-1R-independent NO production as a novel effector mechanism for these innate receptors.

Inflammasomes are cytosolic innate receptors that are emerging as central effectors in the control of infections and inflammatory pathologies. NLRP3 is the most studied member of inflammasomes with established role in the control of bacterial and viral infections. This manuscript describes original studies on the involvement of NLRP3 inflammasome in the control of Trypanosoma cruzi, the etiological agent of Chagas disease, a chronic infectious illness that affects millions of people in the world. T. cruzi activates NLRP3 inflammasome by a mechanism involving cathepsin B. NLRP3^−/− and caspase1^−/− mice display high parasitemia during acute phase of T. cruzi infection, which could be explained by a severe defect in the production of nitric oxide (NO) and in the impairment of their macrophages to control intracellular parasites. Interestingly, inhibition of caspase-1, but not the neutralization of IL-1β and IL-18, the best-studied caspase-1 substrates, abrogated NO production by WT and MyD88^−/− macrophages and rendered them as susceptible to T. cruzi infection as NLRP3^−/− macrophages. Together, our results indicate a caspase-1-dependent and IL-1β and IL-18-independent pathway for NO production as a new effector mechanism played by NLRP3 to control T. cruzi infection.

Sweeten PAMPs: Role of Sugar Complexed PAMPs in Innate Immunity and Vaccine Biology

Innate sensors play a critical role in the early innate immune responses to invading pathogens through sensing of diverse biochemical signatures also known as pathogen associated molecular patterns (PAMPs). These biochemical signatures primarily consist of a major family of biomolecules such as proteins, lipids, nitrogen bases, and sugar and its complexes, which are distinct from host molecules and exclusively expressed in pathogens and essential to their survival. The family of sensors known as pattern recognition receptors (PRRs) are germ-line encoded, evolutionarily conserved molecules, and consist of Toll-like receptors (TLRs), RIG-I-like receptors (RLRs), NOD-like receptors (NLRs), C-type lectin-like receptors (CLRs), and DNA sensors. Sensing of PAMP by PRR initiates the cascade of signaling leading to the activation of transcription factors, such as NF-κB and interferon regulatory factors (IRFs), resulting in a variety of cellular responses, including the production of interferons (IFNs) and pro-inflammatory cytokines. In this review, we discuss sensing of different types of glycosylated PAMPs such as β-glucan (a polymeric sugar) or lipopolysaccharides, nucleic acid, and so on (sugar complex PAMPs) by different families of sensors, its role in pathogenesis, and its application in development of potential vaccine and vaccine adjuvants.

Expression profiles of toll-like receptors in channel catfish (Ictalurus punctatus) after infection with Ichthyophthirius multifiliis

Toll-like receptors (TLRs) play a crucial role in the innate immune system, but to date the roles of fish TLRs in response to parasitic infection are still poorly understood. In the present study, we used channel catfish (Ictalurus punctatus) and the ciliate parasite Ichthyophthirius multifiliis as a model to investigate whether and which fish TLRs play important roles in the immune response against parasitic pathogens by detecting the expression profiles of a complete set of TLRs in catfish at different time points after infection with I. multifiliis. The expression profiles of TLR1 and TLR2 were similar, and both were significantly up-regulated in the skin and head kidney at most time points after infection. Furthermore, the expression of TLR2 was also up-regulated in the gill and spleen. TLR9 was induced in the skin and gill, whereas TLR21 was induced in the head kidney and spleen after infection. For TLR19, significant up-regulation was observed in the skin and gill, but significant down-regulation was detected in the head kidney and spleen. In contrast to TLR19, TLR25 was significantly up-regulated in the head kidney and spleen at some time points. No significant changes were observed for the rest of the TLRs at most time points. The results indicated that some TLRs may play essential roles in catfish defense against I. multifiliis infection.

Grass carp (Ctenopharyngodon idella) TRAF6 and TAK1: molecular cloning and expression analysis after Ichthyophthirius multifiliis infection

Ichthyophthirius multifiliis, a pathogenic ciliate parasite, infects almost all freshwater fish species and causes significant economic losses. Tumor necrosis factor receptor-associated factor 6 (TRAF6) and transforming growth factor-β-activated kinase 1 (TAK1) are two important signaling molecules involved in toll-like receptor (TLR) signal transduction. To date, the roles of TRAF6 and TAK1 in host defense against fish parasites are still poorly understood. In the present study, TRAF6 (CiTRAF6) and TAK1 (CiTAK1) were identified from grass carp (Ctenopharyngodon idella). The full-length cDNA sequence of CiTRAF6 (2250 bp) includes an open reading frame (ORF) of 1629 bp, which shows a high similarity to that of Cyprinus carpio TRAF6 and encodes a putative protein of 542 amino acids containing one RING domain, two zinc fingers, one coiled-coil region, and one MATH domain. The full-length CiTAK1 cDNA sequence is 2768 bp and includes an ORF of 1626 bp that encodes a putative protein of 541 amino acids containing a conserved serine/threonine protein kinase catalytic domain and a coiled-coil region. Phylogenetic analysis showed that CiTRAF6 and CiTAK1 were clustered with TRAF6 and TAK1 of other teleosts, respectively. CiTRAF6 and CiTAK1 were both constitutively expressed in all examined tissues but with varied expression levels. The highest expressions of CiTRAF6 and CiTAK1 were in the head kidney and spleen, respectively. The expression profiles of CiTRAF6 and CiTAK1 were detected in grass carp after I. multifiliis infection. Expressions of both genes were significantly up-regulated in the skin, gill, head kidney, and spleen at most time points after infection, indicating that CiTRAF6 and CiTAK1 may play essential roles in grass carp defense against I. multifiliis.

Kudoa septempunctata was recognised by toll-like receptor 2 produced by a RAW 264 macrophage-like cell line

Kudoa septempunctata is a myxosporean parasite that infects Paralichthys olivaceus (olive flounder). Previously, we reported that the consumption of raw P. olivaceus meat containing a high concentration of K. septempunctata spores induces transient but severe diarrhoea and emesis. In this study, we investigated the cytokine production of mouse macrophage-like RAW 264 cells stimulated with K. septempunctata. When the RAW 264 cells were incubated with the spores of K. septempunctata for 24 h, they secreted tumour necrosis factor α (TNF-α) and several chemokines, such as IP-10, MIP-1β, and MIP-2. The secretion of TNF-α was induced in a dose-dependent manner in a bioassay using L929 cells and mouse TNF-α-specific enzyme-linked immunosorbent assay (ELISA). To identify the macrophage receptor of K. septempunctata, activation of HEK 293 cells expressing one of the Toll-like receptors (TLR) was measured using an NF-κB-dependent reporter assay. TLR2-expressing HEK 293 cells were strongly activated following stimulation with the spores. These results suggested that K. septempunctata was recognised by TLR2 on the macrophages, which were then activated and produced TNF-α.

Differential use of TLR2 and TLR9 in the regulation of immune responses during the infection with Trypanosoma cruzi

Pathogens express ligands for several TLRs that may play a role in the induction or control of the inflammatory response during infection. Concerning Trypanosoma cruzi, the agent of Chagas disease, we have previously characterized glycosylphosphatidylinositol (GPI) anchored mucin-like glycoproteins (tGPI-mucin) and unmethylated CpG DNA sequences as TLR2 and TLR9 agonists, respectively. Here we sought to determine how these TLRs may modulate the inflammatory response in the following cell populations: F4/80⁺CD11b⁺ (macrophages), F4/80^lowCD11b⁺ (monocytes) and MHCII⁺CD11c^high (dendritic cells). For this purpose, TLR2^−/− and TLR9^−/− mice were infected with Y strain of T. cruzi and different immunological parameters were evaluated. According to our previous data, a crucial role of TLR9 was evidenced in the establishment of Th1 response, whereas TLR2 appeared to act as immunoregulator in the early stage of infection. More precisely, we demonstrated here that TLR2 was mainly used by F4/80⁺CD11b⁺ cells for the production of TNF-α. In the absence of TLR2, an increased production of IL-12/IL-23p40 and IFN-γ was noted suggesting that TLR2 negatively controls the Th1 response. In contrast, TLR9 was committed to IL-12/IL-23p40 production by MHCII⁺CD11c^high cells that constitute the main source of IL-12/IL-23p40 during infection. Importantly, a down-regulation of TLR9 response was observed in F4/80⁺CD11b⁺ and F4/80^lowCD11b⁺ populations that correlated with the decreased TLR9 expression level in these cells. Interestingly, these cells recovered their capacity to respond to TLR9 agonist when MHCII⁺CD11c^high cells were impeded from producing IL-12/IL-23p40, thereby indicating possible cross-talk between these populations. The differential use of TLR2 and TLR9 by the immune cells during the acute phase of the infection explains why TLR9- but not TLR2-deficient mice are susceptible to T. cruzi infection.

Cryptosporidium parvum antigens induce mouse and human dendritic cells to generate Th1-enhancing cytokines

Cryptosporidium parvum is an opportunistic intracellular parasite that causes mild to severe diarrhoea, which can be life-threatening in an immunocompromised host. To increase our understanding of the mechanisms that play a role in host immune responses, we investigated the effects of C. parvum antigens on the phenotype of mouse and human dendritic cells (DCs). Cryptosporidium parvum antigens induced DC activation as indicated by upregulation of the maturation marker CD209, as well as by the production of the cytokines interleukin-12 p70, IL-2, IL-1beta, IL-6. In particular, significant increases in the expression of IL-12 p70 were observed from mouse DCs derived from bone marrow in response to solubilized sporozoite antigen and the recombinant cryptosporidial antigens, Cp40 and Cp23. We observed a small but significant increase in IL-18 expression following the exposure to Cp40. We found that the induction of Th1 cytokines was MyD88 dependent (MyD88 knockout mouse DCs were unresponsive). Additionally, both sporozoite preparations (solubilized and live) significantly induced IL-12 production by human monocytic dendritic cells (MoDCs). This finding indicates that solubilized as well as recombinant antigens can induce the maturation of DCs and subsequently initiate an innate immune response.

Transmission and epidemiology of zoonotic protozoal diseases of companion animals

Over 77 million dogs and 93 million cats share our households in the United States. Multiple studies have demonstrated the importance of pets in their owners' physical and mental health. Given the large number of companion animals in the United States and the proximity and bond of these animals with their owners, understanding and preventing the diseases that these companions bring with them are of paramount importance. Zoonotic protozoal parasites, including toxoplasmosis, Chagas' disease, babesiosis, giardiasis, and leishmaniasis, can cause insidious infections, with asymptomatic animals being capable of transmitting disease. Giardia and Toxoplasma gondii, endemic to the United States, have high prevalences in companion animals. Leishmania and Trypanosoma cruzi are found regionally within the United States. These diseases have lower prevalences but are significant sources of human disease globally and are expanding their companion animal distribution. Thankfully, healthy individuals in the United States are protected by intact immune systems and bolstered by good nutrition, sanitation, and hygiene. Immunocompromised individuals, including the growing number of obese and/or diabetic people, are at a much higher risk of developing zoonoses. Awareness of these often neglected diseases in all health communities is important for protecting pets and owners. To provide this awareness, this review is focused on zoonotic protozoal mechanisms of virulence, epidemiology, and the transmission of pathogens of consequence to pet owners in the United States.

Toll-like receptor 4 (TLR4) polymorphisms in Iranian patients with visceral leishmaniasis

The role of Toll-like receptor (TLR) 4 in visceral leishmaniasis (VL), a disease caused by an obligate intracellular protozoan parasites belonging to the genus Leishmania, has been shown in the recent leishmaniasis experimental studies. As genetic host factors play an important role in the susceptibility and/or resistance to VL, the association between TLR4 gene mutations [A896G and C1196T single nucleotide polymorphisms (SNPs)] and VL was investigated. Genotyping of A896G (Asp299Gly) and C1196T (Thr399Ile) SNPs was performed in the patients with VL (N = 122) and ethnically matched controls (N = 155) using polymerase chain reaction-restriction fragment length polymorphism method. When VL patients and the controls were compared, no statistically significant differences were observed in A896G and C1196T alleles and genotypes (P > 0.05). The TLR4 A896G and C1196T were in moderate linkage disequilibrium in the controls and patients (r (2) = 0.497, 0.548 and D' = 0.705, 0.808, respectively), and haplotypes reconstructed from these SNPs were not significantly different between the aforementioned study groups. In conclusion, based on the results, TLR4 gene polymorphisms at the positions 896 and 1196 cannot be regarded as the major contributors to VL susceptibility among the Iranian population.

Intraspecies variation in Trypanosoma cruzi GPI-mucins: biological activities and differential expression of α-galactosyl residues

The glycosylphosphatidylinositol (GPI)-anchored mucins of Trypanosoma cruzi trypomastigotes play an important immunomodulatory role during the course of Chagas disease. Here, some biological activities of tGPI-mucins from four T. cruzi isolates, including benznidazole-susceptible (BZS-Y), benznidazole-resistant (BZR-Y), CL, and Colombiana, were evaluated. GPI-mucins were able to differentially trigger the production of interleukin-12 and nitric oxide in BALB/c macrophages and modulate LLC-MK2 cell invasion. The significance of these variations was assessed after analysis of the terminal α-galactosyl residues. Enzymatic treatment with α-galactosidase indicated a differential expression of O-linked α-galactosyl residues among the strains, with higher expression of this sugar in BZS-Y and BZR-Y T. cruzi populations followed by Colombiana and CL. Unweighted pair group method analysis of the carbohydrate anchor profile and biological parameters allowed the clustering of two groups. One group includes Y and CL strains (T. cruzi II and VI), and the other group is represented by Colombiana strain (T. cruzi I).

Regulatory cells and immunosuppressive cytokines: parasite-derived factors induce immune polarization

Parasitic infections are prevalent in both tropical and subtropical areas. Most of the affected and/or exposed populations are living in developing countries where control measures are lacking or inadequately applied. Although significant progress has been made in our understanding of the immune response to parasites, no definitive step has yet been successfully done in terms of operational vaccines against parasitic diseases. Evidence accumulated during the past few years suggests that the pathology observed during parasitic infections is in part due to deregulation of normal components of the immune system, mainly cytokines, antibodies, and immune effector cell populations. A large number of studies that illustrate how parasites can modify the host immune system for their own benefit have been reported in both metazoan and protozoan parasites. The first line of defense against foreign organisms is barrier tissue such as skin, humoral factors, for instance the complement system and pentraxin, which upon activation of the complement cascade facilitate pathogen recognition by cells of innate immunity such as macrophages and DC. However, all the major groups of parasites studied have been shown to contain and/or to release factors, which interfere with both arms of the host immune system. Even some astonishing observations relate to the production by some parasites of orthologues of mammalian cytokines. Furthermore, chronic parasitic infections have led to the immunosuppressive environment that correlates with increased levels of myeloid and T suppressor cells that may limit the success of immunotherapeutic strategies based on vaccination. This minireview briefly analyzes some of the current data related to the regulatory cells and molecules derived from parasites that affect cellular function and contribute to the polarization of the immune response of the host. Special attention is given to some of the data from our laboratory illustrating the role of immunomodulatory factors released by protozoan parasites, in the induction and perpetuation of chronic disease.

Trypanosoma cruzi invades host cells through the activation of endothelin and bradykinin receptors: a converging pathway leading to chagasic vasculopathy

BACKGROUND AND PURPOSE

Independent studies in experimental models of Trypanosoma cruzi appointed different roles for endothelin-1 (ET-1) and bradykinin (BK) in the immunopathogenesis of Chagas disease. Here, we addressed the hypothesis that pathogenic outcome is influenced by functional interplay between endothelin receptors (ET(A)R and ET(B)R) and bradykinin B(2) receptors (B(2)R).

EXPERIMENTAL APPROACH

Intravital microscopy was used to determine whether ETR/B(2)R drives the accumulation of rhodamine-labelled leucocytes in the hamster cheek pouch (HCP). Inflammatory oedema was measured in the infected BALB/c paw of mice. Parasite invasion was assessed in CHO over-expressing ETRs, mouse cardiomyocytes, endothelium (human umbilical vein endothelial cells) or smooth muscle cells (HSMCs), in the presence/absence of antagonists of B(2)R (HOE-140), ET(A)R (BQ-123) and ET(B)R (BQ-788), specific IgG antibodies to each GPCRs; cholesterol or calcium-depleting drugs. RNA interference (ET(A)R or ET(B)R genes) in parasite infectivity was investigated in HSMCs.

KEY RESULTS

BQ-123, BQ-788 and HOE-140 reduced leucocyte accumulation in HCP topically exposed to trypomastigotes and blocked inflammatory oedema in infected mice. Acting synergistically, ET(A)R and ET(B)R antagonists reduced parasite invasion of HSMCs to the same extent as HOE-140. Exogenous ET-1 potentiated T. cruzi uptake by HSMCs via ETRs/B(2)R, whereas RNA interference of ET(A)R and ET(B)R genes conversely reduced parasite internalization. ETRs/B(2)R-driven infection in HSMCs was reduced in HSMC pretreated with methyl-β-cyclodextrin, a cholesterol-depleting drug, or in thapsigargin- or verapamil-treated target cells.

CONCLUSIONS AND IMPLICATIONS

Our findings suggest that plasma leakage, a neutrophil-driven inflammatory response evoked by trypomastigotes via the kinin/endothelin pathways, may offer a window of opportunity for enhanced parasite invasion of cardiovascular cells.

The role of NF-κB activation during protection against Leishmania infection

Members of the nuclear factor-κB (NF-κB) family of transcription factors regulate a variety of molecules involved in host defense against pathogens. A prominent role of NF-κB in innate and adoptive immunity is based on the regulation of inducible transcription of various genes whose products are essential components of the immune response such as cytokines, chemokines, and adhesion molecules. Since the discovery of the five members of the NF-κB transcription factor family, RelA, c-Rel, RelB, p50 and p52, considerable progress has been made toward better understanding how the different NF-κB homo- and heterodimers regulate such distinct subsets of target genes. All of the NF-κB molecules are activated by various infectious stimuli; however, there are still open questions related to the selective functions of individual NF-κB family members during a coordinated immune response to infection. Diverse parasites such as Toxoplasma gondii, Leishmania donovani, Leishmania major, and Trichuris muris have been reported to activate NF-κB signaling cascades, and a number of distinct parasite-derived molecules may actively interfere with the pathways that lead to NF-κB activation. In this review, we provide an overview on the role of NF-κB activation in leishmaniasis and discuss how individual NF-κB family members might perform their distinct and non-overlapping functions in the regulation of protective immunity to Leishmania infection.

Vesicles as carriers of virulence factors in parasitic protozoan diseases

Different types of shed vesicles as, for example, exosomes, plasma-membrane-derived vesicles or microparticles, are the focus of intense research in view of their potential role in cell-cell communication and under the perspective that they might be good tools for immunotherapy, vaccination or diagnostic purposes. This review discusses ways employed by pathogenic trypanosomatids to interact with the host by shedding vesicles that contain molecules important for the establishment of infection, as opposed to previous beliefs considering them as a waste of cellular metabolism. Trypanosomatids are compared with Apicomplexa, which circulate parasite antigens bound to vesicles shed by host cells. The knowledge of the origin and chemical composition of these different vesicles might lead to the understanding of the mechanisms that determine their biological function.

GM-CSF priming drives bone marrow-derived macrophages to a pro-inflammatory pattern and downmodulates PGE2 in response to TLR2 ligands

In response to pathogen recognition by Toll-like receptors (TLRs) on their cell surface, macrophages release lipid mediators and cytokines that are widely distributed throughout the body and play essential roles in host responses. Granulocyte macrophage colony-stimulating factor (GM-CSF) is important for the immune response during infections to improve the clearance of microorganisms. In this study, we examined the release of mediators in response to TLR2 ligands by bone marrow-derived macrophages (BMDMs) primed with GM-CSF. We demonstrated that when stimulated with TLR2 ligands, non-primed BMDMs preferentially produced PGE₂ in greater amounts than LTB₄. However, GM-CSF priming shifted the release of lipid mediators by BMDMs, resulting in a significant decrease of PGE₂ production in response to the same stimuli. The decrease of PGE₂ production from primed BMDMs was accompanied by a decrease in PGE-synthase mRNA expression and an increase in TNF-α and nitric oxide (NO) production. Moreover, some GM-CSF effects were potentiated by the addition of IFN-γ. Using a variety of TLR2 ligands, we established that PGE₂ release by GM-CSF-primed BMDMs was dependent on TLR2 co-receptors (TLR1, TLR6), CD14, MyD88 and the nuclear translocation of NFκB but was not dependent on peroxisome proliferator-activated receptor-γ (PPAR-γ) activation. Indeed, GM-CSF priming enhanced TLR2, TLR4 and MyD88 mRNA expression and phospho-IκBα formation. These findings demonstrate that GM-CSF drives BMDMs to present a profile relevant to the host during infections.

CD36 c.1264 T>G null mutation impairs acquisition of IgG antibodies to Plasmodium falciparum MSP1₁₉ antigen and is associated with higher malaria incidences in Tanzanian children

Polymorphisms in genes that encode crucial signalling molecules have been proposed as factors that influence susceptibility to, and outcome of malaria. We studied the role of a mutation, c.1264 T>G, that causes CD36 deficiency on IgG responses to MSP-1₁₉ antigen and malaria incidence. Children were genotyped for the c.1264 T>G mutation at the beginning of the study using PCR-RFLP. IgG levels [optical density (OD) readings] and per cent seropositivity to MSP-1₁₉ were determined at baseline by ELISA. Children were followed for 12 months for acquisition of anti-MSP-1₁₉ IgG antibody and malaria incidence. We observed a significant increase in the production of anti-MSP-1₁₉ IgG antibody in normal and heterozygous children during the 12 months of follow-up, but not in homozygous mutants. Normal children had a significantly lower malaria incidence rate compared to other genotypes (χ² = 115.59; P < 0.01). We conclude that the presence of the c.1264 T>G mutation that leads to CD36 deficiency is closely associated with reduced IgG production and higher malaria incidence. It is most likely that deficiency of CD36 which is known to modulate dendritic cell function suppresses the production of protective IgG antibodies directed to Plasmodium falciparum MSP-1₁₉ antigen, which predisposes to the acquisition of clinical malaria in children.