Toll like receptor 4 mediates the inhibitory effect of SARS-CoV-2 spike protein on proximal tubule albumin endocytosis.

Tubular proteinuria is a common feature in COVID-19 patients, even in the absence of established acute kidney injury. SARS-CoV-2 spike protein (S protein) was shown to inhibit megalin-mediated albumin endocytosis in proximal tubule epithelial cells (PTECs). Angiotensin-converting enzyme type 2 (ACE2) was not directly involved. Since Toll-like receptor 4 (TLR4) mediates S protein effects in various cell types, we hypothesized that TLR4 could be participating in the inhibition of PTECs albumin endocytosis elicited by S protein. Two different models of PTECs were used: porcine proximal tubule cells (LLC-PK1) and human embryonic kidney cells (HEK-293). S protein reduced Akt activity by specifically inhibiting of threonine 308 (Thr308) phosphorylation, a process mediated by phosphoinositide-dependent kinase 1 (PDK1). GSK2334470, a PDK1 inhibitor, decreased albumin endocytosis and megalin expression mimicking S protein effect. S protein did not change total TLR4 expression but decreased its surface expression. LPS-RS, a TLR4 antagonist, also counteracted the effects of the S protein on Akt phosphorylation at Thr308, albumin endocytosis, and megalin expression. Conversely, these effects of the S protein were replicated by LPS, an agonist of TLR4. Incubation of PTECs with a pseudovirus containing S protein inhibited albumin endocytosis. Null or VSV-G pseudovirus, used as control, had no effect. LPS-RS prevented the inhibitory impact of pseudovirus containing the S protein on albumin endocytosis but had no influence on virus internalization. Our findings demonstrate that the inhibitory effect of the S protein on albumin endocytosis in PTECs is mediated through TLR4, resulting from a reduction in megalin expression.

Contact System Activation in Plasma from Dengue Patients Might Harness Endothelial Virus Replication through the Signaling of Bradykinin Receptors.

Since exacerbated inflammation and microvascular leakage are hallmarks of dengue virus (DENV) infection, here we interrogated whether systemic activation of the contact/kallikrein-kinin system (KKS) might hamper endothelial function. In vitro assays showed that dextran sulfate, a potent contact activator, failed to generate appreciable levels of activated plasma kallikrein (PKa) in the large majority of samples from a dengue cohort (n = 70), irrespective of severity of clinical symptoms. Impaired formation of PKa in dengue-plasmas correlated with the presence of cleaved Factor XII and high molecular weight kininogen (HK), suggesting that the prothrombogenic contact system is frequently triggered during the course of infection. Using two pathogenic arboviruses, DENV or Zika virus (ZIKV), we then asked whether exogenous BK could influence the outcome of infection of human brain microvascular endothelial cells (HBMECs). Unlike the unresponsive phenotype of Zika-infected HBMECs, we found that BK, acting via B2R, vigorously stimulated DENV-2 replication by reverting nitric oxide-driven apoptosis of endothelial cells. Using the mouse model of cerebral dengue infection, we next demonstrated that B2R targeting by icatibant decreased viral load in brain tissues. In summary, our study suggests that contact/KKS activation followed by BK-induced enhancement of DENV replication in the endothelium may underlie microvascular pathology in dengue.

Critical role of CD4+ T cells and IFNγ signaling in antibody-mediated resistance to Zika virus infection.

Protective adaptive immunity to Zika virus (ZIKV) has been mainly attributed to cytotoxic CD8+ T cells and neutralizing antibodies, while the participation of CD4+ T cells in resistance has remained largely uncharacterized. Here, we show a neutralizing antibody response, dependent on CD4+ T cells and IFNγ signaling, which we detected during the first week of infection and is associated with reduced viral load in the brain, prevention of rapid disease onset and survival. We demonstrate participation of these components in the resistance to ZIKV during primary infection and in murine adoptive transfer models of heterologous ZIKV infection in a background of IFNR deficiency. The protective effect of adoptively transferred CD4+ T cells requires IFNγ signaling, CD8+ T cells and B lymphocytes in recipient mice. Together, this indicates the importance of CD4+ T cell responses in future vaccine design for ZIKV.

The potent cell permeable calpain inhibitor MDL28170 affects the interaction of Leishmania amazonensis with macrophages and shows anti-amastigote activity.

Since the discovery of the28 first drugs used in leishmaniasis treatment up to now, the search for compounds with anti-Leishmania activity without toxic effects and able to overcome the emergency of resistant strains remains a major goal to combat this neglected disease. With this in mind, in the present work, we evaluated the effects of the calpain inhibitor MDL28170 on the interaction process of Leishmania amazonensis promastigote forms with murine peritoneal macrophages and on the intracellular amastigotes. Our results showed that the calpain inhibitor MDL28170 at 15 and 30µM significantly reduced the interaction process of promastigotes with macrophages by 16% and 41%, respectively. The inhibitor was also able to drastically reduce the number of infected macrophages in a time- and dose-dependent manner: after only 24h, MDL28170 was able to significantly diminish the infection rate, presenting an IC50 value of 18.2µM for amastigotes. The treatment with MDL28170 did not alter the nitric oxide production, but the production of TNF-α was significantly raised. Altogether, the results presented here contribute to the search of new proteolytic inhibitors able to act in a selective and effective manner against the diseases caused by trypanosomatids.

Zika Virus Infects, Activates, and Crosses Brain Microvascular Endothelial Cells, without Barrier Disruption.

Zika virus (ZIKV) has been associated to central nervous system (CNS) harm, and virus was detected in the brain and cerebrospinal fluids of microcephaly and meningoencephalitis cases. However, the mechanism by which the virus reaches the CNS is unclear. Here, we addressed the effects of ZIKV replication in human brain microvascular endothelial cells (HBMECs), as an in vitro model of blood brain barrier (BBB), and evaluated virus extravasation and BBB integrity in an in vivo mouse experimental model. HBMECs were productively infected by African and Brazilian ZIKV strains (ZIKVMR766 and ZIKVPE243), which induce increased production of type I and type III IFN, inflammatory cytokines and chemokines. Infection with ZIKVMR766 promoted earlier cellular death, in comparison to ZIKVPE243, but infection with either strain did not result in enhanced endothelial permeability. Despite the maintenance of endothelial integrity, infectious virus particles crossed the monolayer by endocytosis/exocytosis-dependent replication pathway or by transcytosis. Remarkably, both viruses' strains infected IFNAR deficient mice, with high viral load being detected in the brains, without BBB disruption, which was only detected at later time points after infection. These data suggest that ZIKV infects and activates endothelial cells, and might reach the CNS through basolateral release, transcytosis or transinfection processes. These findings further improve the current knowledge regarding ZIKV dissemination pathways.

Interplay between Inflammation and Cellular Stress Triggered by Flaviviridae Viruses.

The Flaviviridae family comprises several human pathogens, including Dengue, Zika, Yellow Fever, West Nile, Japanese Encephalitis viruses, and Hepatitis C Virus. Those are enveloped, single-stranded positive sense RNA viruses, which replicate mostly in intracellular compartments associated to endoplasmic reticulum (ER) and Golgi complex. Virus replication results in abundant viral RNAs and proteins, which are recognized by cellular mechanisms evolved to prevent virus infection, resulting in inflammation and stress responses. Virus RNA molecules are sensed by Toll-like receptors (TLRs), RIG-I-like receptors (RIG-I and MDA5) and RNA-dependent protein kinases (PKR), inducing the production of inflammatory mediators and interferons. Simultaneously, the synthesis of virus RNA and proteins are distinguished in different compartments such as mitochondria, ER and cytoplasmic granules, triggering intracellular stress pathways, including oxidative stress, unfolded protein response pathway, and stress granules assembly. Here, we review the new findings that connect the inflammatory pathways to cellular stress sensors and the strategies of Flaviviridae members to counteract these cellular mechanisms and escape immune response.

Dendritic cells primed with a chimeric plasmid containing HIV-1-gag associated with lysosomal-associated protein-1 (LAMP/gag) is a potential therapeutic vaccine against HIV.

The decline in number and function of T cells is a hallmark of HIV infection, and preservation or restoration of HIV-specific cellular immune response is a major goal of AIDS treatment. Dendritic cells (DCs) play a key role in the initiation and maintenance of the immune response, and their use as a vaccine vehicle is a promising strategy for enhancing vaccine efficacy. We evaluated the potential of DC-mediated immunization with a DNA vaccine consisting of HIV-1-p55gag (gag, group-specific antigen) associated to lysosomal associated protein (LAMP) sequence (LAMP/gag vaccine). Immunization of mice with mouse DCs transfected with LAMP/gag (Lg-mDCs) stimulated more potent B- and T-cell responses than naked DNA or DCs pulsed with inactivated HIV. Anti-Gag antibody levels were sustained for at least 3 mo after immunization, and recall T-cell responses were also strongly detected at this time point. Human DCs transfected with LAMP/gag (Lg-hDCs) were also activated and able to stimulate greater T-cell response than native gag-transfected DCs. Coculture between Lg-hDCs and T lymphocytes obtained from patients with HIV resulted in upregulation of CD38, CD69, HLA-DR, and granzyme B by CD4(+) and CD8(+) T cells, and increased IFN-γ and TNF-α production. These results indicate that the use of LAMP/gag-DC may be an efficient strategy for enhancing immune function in patients with HIV.-Lucas, C. G. D. O., Matassoli, F. L., Peçanha, L. M. T., Santillo, B. T., Oliveira, L. M. D. S., Oshiro, T. M., Marques, E. T. D. A., Jr., Oxenius, A., de Arruda, L. B. Dendritic cells primed with a chimeric plasmid containing HIV-1-gag associated with lysosomal-associated protein-1 (LAMP/gag) is a potential therapeutic vaccine against HIV.

Genomic Analysis, Phenotype, and Virulence of the Historical Brazilian Smallpox Vaccine Strain IOC: Implications for the Origins and Evolutionary Relationships of Vaccinia Virus.

UNLABELLED: Smallpox was declared eradicated in 1980 after an intensive vaccination program using different strains of vaccinia virus (VACV; Poxviridae). VACV strain IOC (VACV-IOC) was the seed strain of the smallpox vaccine manufactured by the major vaccine producer in Brazil during the smallpox eradication program. However, little is known about the biological and immunological features as well as the phylogenetic relationships of this first-generation vaccine. In this work, we present a comprehensive characterization of two clones of VACV-IOC. Both clones had low virulence in infected mice and induced a protective immune response against a lethal infection comparable to the response of the licensed vaccine ACAM2000 and the parental strain VACV-IOC. Full-genome sequencing revealed the presence of several fragmented virulence genes that probably are nonfunctional, e.g., F1L, B13R, C10L, K3L, and C3L. Most notably, phylogenetic inference supported by the structural analysis of the genome ends provides evidence of a novel, independent cluster in VACV phylogeny formed by VACV-IOC, the Brazilian field strains Cantagalo (CTGV) and Serro 2 viruses, and horsepox virus, a VACV-like virus supposedly related to an ancestor of the VACV lineage. Our data strongly support the hypothesis that CTGV-like viruses represent feral VACV that evolved in parallel with VACV-IOC after splitting from a most recent common ancestor, probably an ancient smallpox vaccine strain related to horsepox virus. Our data, together with an interesting historical investigation, revisit the origins of VACV and propose new evolutionary relationships between ancient and extant VACV strains, mainly horsepox virus, VACV-IOC/CTGV-like viruses, and Dryvax strain. IMPORTANCE: First-generation vaccines used to eradicate smallpox had rates of adverse effects that are not acceptable by current health care standards. Moreover, these vaccines are genetically heterogeneous and consist of a pool of quasispecies of VACV. Therefore, the search for new-generation smallpox vaccines that combine low pathogenicity, immune protection, and genetic homogeneity is extremely important. In addition, the phylogenetic relationships and origins of VACV strains are quite nebulous. We show the characterization of two clones of VACV-IOC, a unique smallpox vaccine strain that contributed to smallpox eradication in Brazil. The immunogenicity and reduced virulence make the IOC clones good options for alternative second-generation smallpox vaccines. More importantly, this study reveals the phylogenetic relationship between VACV-IOC, feral VACV established in nature, and the ancestor-like horsepox virus. Our data expand the discussion on the origins and evolutionary connections of VACV lineages.

Warifteine, an alkaloid purified from Cissampelos sympodialis, inhibits neutrophil migration in vitro and in vivo.

Cissampelos sympodialis Eichl is a plant from the Northeast and Southeast of Brazil. Its root infusion is popularly used for treatment of inflammatory and allergic diseases. We investigated whether warifteine, its main alkaloid, would have anti-inflammatory effect due to a blockage of neutrophil function. In vivo warifteine treatment inhibited casein-induced neutrophil migration to the peritoneal cavity but did not inhibit neutrophil mobilization from the bone marrow. Analysis of the direct effect of warifteine upon neutrophil adherence and migration in vitro demonstrated that the alkaloid decreased cell adhesion to P and E-selectin-transfected cells. In addition, fLMP-induced neutrophil migration in a transwell system was blocked by warifteine; this effect was mimicked by cAMP mimetic/inducing substances, and warifteine increased intracellular cAMP levels in neutrophils. The production of DNA extracellular traps (NETs) was also blocked by warifteine but there was no alteration on PMA-induced oxidative burst or LPS-stimulated TNF α secretion. Taken together, our data indicate that the alkaloid warifteine is a potent anti-inflammatory substance and that it has an effect on neutrophil migration through a decrease in both cell adhesion and migration.

Synthetic 1,4-pyran naphthoquinones are potent inhibitors of dengue virus replication.

Dengue virus infection is a serious public health problem in endemic areas of the world where 2.5 billion people live. Clinical manifestations of the Dengue infection range from a mild fever to fatal cases of hemorrhagic fever. Although being the most rapidly spreading mosquito-borne viral infection in the world, until now no strategies are available for effective prevention or control of Dengue infection. In this scenario, the development of compounds that specifically inhibit viral replication with minimal effects to the human hosts will have a substantial effect in minimizing the symptoms of the disease and help to prevent viral transmission in the affected population. The aim of this study was to screen compounds with potential activity against dengue virus from a library of synthetic naphthoquinones. Several 1,2- and 1,4-pyran naphthoquinones were synthesized by a three-component reaction of lawsone, aldehyde (formaldehyde or arylaldehydes) and different dienophiles adequately substituted. These compounds were tested for the ability to inhibit the ATPase activity of the viral NS3 enzyme in in vitro assays and the replication of dengue virus in cultured cells. We have identified two 1,4-pyran naphthoquinones, which inhibited dengue virus replication in mammal cells by 99.0% and three others that reduced the dengue virus ATPase activity of NS3 by two-fold in in vitro assays.

IL-22 modulates IL-17A production and controls inflammation and tissue damage in experimental dengue infection.

Dengue virus (DENV), a mosquito-borne flavivirus, is a public health problem in many tropical countries. IL-22 and IL-17A are key cytokines in several infectious and inflammatory diseases. We have assessed the contribution of IL-22 and IL-17A in the pathogenesis of experimental dengue infection using a mouse-adapted DENV serotype 2 strain (P23085) that causes a disease that resembles severe dengue in humans. We show that IL-22 and IL-17A are produced upon DENV-2 infection in immune-competent mice. Infected IL-22(-/-) mice had increased lethality, neutrophil accumulation and pro-inflammatory cytokines in tissues, notably IL-17A. Viral load was increased in spleen and liver of infected IL-22(-/-) mice. There was also more severe liver injury, as seen by increased transaminases levels and tissue histopathology. γδ T cells and NK cells are sources of IL-17A and IL-22, respectively, in liver and spleen. We also show that DENV-infected HepG2 cells treated with rhIL-22 had reduced cell death and decreased IL-6 production. IL-17RA(-/-) mice were protected upon infection and IL-17A-neutralizing-Ab-treatment partially reversed the phenotype observed in IL-22(-/-) -infected mice. We suggest that disrupting the balance between IL-22 and IL-17A levels may represent an important strategy to reduce inflammation and tissue injury associated with severe dengue infection.

Bradykinin enhances Sindbis virus infection in human brain microvascular endothelial cells.

Sindbis virus (SINV) induces inflammatory and vasoactive responses that are associated with rash and arthritis in human infections. The mechanisms underlying infection-associated microvasculopathy are still unknown. We investigated whether endothelial cells infected by SINV are differentially responsive to bradykinin (BK), a potent inducer of inflammatory edema in a broad range of infectious diseases. Human endothelial cells (HBMECs) infected with SINV presented an upregulation of bradykinin B2 receptors (BK2R) expression. Also, BK reduced SINV-induced apoptosis and enhanced virus replication in HBMECs in a way dependent on BK2R, PI3 kinase and ERK signaling. Strikingly, intracerebral infection of mice in the presence of a BK2R antagonist reduced the local viral load. Our data suggest that SINV infection renders human endothelial cells hypersensitive to BK, which increases host cell survival and viral replication. Ongoing studies may clarify if the deregulation of the kinin pathway contributes to infection-associated vasculopathies in life-threatening arbovirus infections.

Inhibitory effect of the alkaloid warifteine purified from Cissampelos sympodialis on B lymphocyte function in vitro and in vivo.

The aqueous fraction of the ethanolic extract of the plant CISSAMPELOS SYMPODIALIS (Menispermaceae) was previously described to inhibit B cell function. The alkaloid warifteine is the major component of this extract. In the present study we investigated the effect of warifteine on B lymphocyte function and characterized its mechanism of action. Purified splenic murine B lymphocytes were stimulated with either Toll-like receptor (TLR) ligands (LPS, Pam (3)Cys and CpG oligodeoxynucleotides) or anti-IgM antibody and the effect of warifteine on B cell response was investigated. Warifteine inhibited both the proliferative response and immunoglobulin (Ig) secretion induced by these stimuli. Kinetics studies demonstrated that warifteine blocked B cell function even when added after 24 h of a 72 h culture. The inhibitory effect of warifteine was also detected in cultures activated by phorbol myristate acetate and calcium ionophore. We investigated the signal transduction pathways blocked by warifteine. It did not modify the total protein phosphorylation pattern in LPS and anti-IgM-stimulated B cell cultures. It did, however, decrease the rise in intracellular calcium levels, the phosphorylation of the mitogen activated protein kinase (MAPK) ERK and the intranuclear levels of the transcription factor NFkappaB. Warifteine also induced an increase in cAMP and its effect on LPS-induced proliferation was mimicked by the control adenyl cyclase activator forskolin. IN VIVO Ig production induced by the TI-2 antigen TNP-ficoll was also inhibited by warifteine. Taking together, our data suggest that warifteine is a potent inhibitor of B cell response both IN VITRO and IN VIVO and that this effect may be due to the induction of increased intracellular cAMP levels, suggesting that this substance may be useful as a modulator of B cell function.

Cooperative activation of TLR2 and bradykinin B2 receptor is required for induction of type 1 immunity in a mouse model of subcutaneous infection by Trypanosoma cruzi.

We have previously reported that exogenous bradykinin activates immature dendritic cells (DCs) via the bradykinin B(2) receptor (B(2)R), thereby stimulating adaptive immunity. In this study, we show that these premises are met in a model of s.c. infection by Trypanosoma cruzi, a protozoan that liberates kinins from kininogens through its major protease, cruzipain. Intensity of B(2)R-dependent paw edema evoked by trypomastigotes correlated with levels of IL-12 produced by CD11c(+) dendritic cells isolated from draining lymph nodes. The IL-12 response induced by endogenously released kinins was vigorously increased in infected mice pretreated with inhibitors of angiotensin converting enzyme (ACE), a kinin-degrading metallopeptidase. Furthermore, these innate stimulatory effects were linked to B(2)R-dependent up-regulation of IFN-gamma production by Ag-specific T cells. Strikingly, the trypomastigotes failed to up-regulate type 1 immunity in TLR2(-/-) mice, irrespective of ACE inhibitor treatment. Analysis of the dynamics of inflammation revealed that TLR2 triggering by glycosylphosphatidylinositol-anchored mucins induces plasma extravasation, thereby favoring peripheral accumulation of kininogens in sites of infection. Further downstream, the parasites generate high levels of innate kinin signals in peripheral tissues through the activity of cruzipain. The demonstration that the deficient type 1 immune responses of TLR2(-/-) mice are rescued upon s.c. injection of exogenous kininogens, along with trypomastigotes, supports the notion that generation of kinin "danger" signals is intensified through cooperative activation of TLR2 and B(2)R. In summary, we have described a s.c. infection model where type 1 immunity is vigorously up-regulated by bradykinin, an innate signal whose levels in peripheral tissues are controlled by an intricate interplay of TLR2, B(2)R, and ACE.

Dendritic cell-lysosomal-associated membrane protein (LAMP) and LAMP-1-HIV-1 gag chimeras have distinct cellular trafficking pathways and prime T and B cell responses to a diverse repertoire of epitopes.

Ag processing is a critical step in defining the repertoire of epitope-specific immune responses. In the present study, HIV-1 p55Gag Ag was synthesized as a DNA plasmid with either lysosomal-associated membrane protein-1 (LAMP/gag) or human dendritic cell-LAMP (DC-LAMP/gag) and used to immunize mice. Analysis of the cellular trafficking of these two chimeras demonstrated that both molecules colocalized with MHC class II molecules but differed in their overall trafficking to endosomal/lysosomal compartments. Following DNA immunization, both chimeras elicited potent Gag-specific T and B cell immune responses in mice but differ markedly in their IL-4 and IgG1/IgG2a responses. The DC-LAMP chimera induced a stronger Th type 1 response. ELISPOT analysis of T cell responses to 122 individual peptides encompassing the entire p55gag sequence (15-aa peptides overlapping by 11 residues) showed that DNA immunization with native gag, LAMP/gag, or DC-LAMP/gag induced responses to identical immunodominant CD4+ and CD8+ peptides. However, LAMP/gag and DC-LAMP/gag plasmids also elicited significant responses to 23 additional cryptic epitopes that were not recognized after immunization with native gag DNA. The three plasmids induced T cell responses to a total of 39 distinct peptide sequences, 13 of which were induced by all three DNA constructs. Individually, DC-LAMP/gag elicited the most diverse response, with a specific T cell response against 35 peptides. In addition, immunization with LAMP/gag and DC-LAMP/gag chimeras also promoted Ab secretion to an increased number of epitopes. These data indicate that LAMP-1 and DC-LAMP Ag chimeras follow different trafficking pathways, induce distinct modulatory immune responses, and are able to present cryptic epitopes.

LASSBio-468: a new achiral thalidomide analogue which modulates TNF-alpha and NO production and inhibits endotoxic shock and arthritis in an animal model.

As part of a program researching the synthesis and immunopharmacological evaluation of novel synthetic compounds, we have described the immune modulatory profile of the new achiral thalidomide analogue LASSBio-468 in the present work. This compound was planned as an N-substituted phthalimide derivate, structurally designed as a hybrid of thalidomide and aryl sulfonamides, which were previously described as tumor necrosis factor-alpha (TNF-alpha) and PDE4 inhibitors. LASSBio-468 was recently demonstrated to inhibit the TNF-alpha production induced by lipopolysaccharide (LPS), in vivo. Here, we investigated whether this compound would affect chronic inflammation processes associated with the production of this pro-inflammatory cytokine. Treatment with LASSBio-468 before a lethal dose injection of LPS in animals greatly inhibited endotoxic shock. This effect seems to be mediated by a specific down regulation of TNF-alpha and nitric oxide production, regulated mainly at the RNA level. In another model, histopathological analysis indicated that this compound also inhibited adjuvant-induced arthritis in rats. Taken together, our data demonstrated a potent anti-inflammatory effect of LASSBio-468, suggesting its use as a potential drug against chronic inflammatory diseases.

Expression of functional TLR4 confers proinflammatory responsiveness to Trypanosoma cruzi glycoinositolphospholipids and higher resistance to infection with T. cruzi.

TLRs function as pattern recognition receptors in mammals and play an essential role in the recognition of microbial components. We found that the injection of glycoinositolphospholipids (GIPLs) from Trypanosoma cruzi into the peritoneal cavity of mice induced neutrophil recruitment in a TLR4-dependent manner: the injection of GIPL in the TLR4-deficient strain of mice (C57BL/10ScCr) caused no inflammatory response. In contrast, in TLR2 knockout mice, neutrophil chemoattraction did not differ significantly from that seen in wild-type controls. GIPL-induced neutrophil attraction and MIP-2 production were also severely affected in TLR4-mutant C3H/HeJ mice. The role of TLR4 was confirmed in vitro by testing genetically engineered mutants derived from TLR2-deficient Chinese hamster ovary (CHO)-K1 fibroblasts that were transfected with CD14 (CHO/CD14). Wild-type CHO/CD14 cells express the hamster TLR4 molecule and the mutant line, in addition, expresses a nonfunctional form of MD-2. In comparison to wild-type cells, mutant CHO/CD14 cells failed to respond to GIPLs, indicating a necessity for a functional TLR4/MD-2 complex in GIPL-induced NF-kappaB activation. Finally, we found that TLR4-mutant mice were hypersusceptible to T. cruzi infection, as evidenced by a higher parasitemia and earlier mortality. These results demonstrate that natural resistance to T. cruzi is TLR4 dependent, most likely due to TLR4 recognition of their GIPLs.