Requirement of UNC93B1 reveals a critical role for TLR7 in host resistance to primary infection with Trypanosoma cruzi

The kallikrein-kinin system in experimental Chagas disease: a paradigm to investigate the impact of inflammatory edema on GPCR-mediated pathways of host cell invasion by Trypanosoma cruzi

Chronic chagasic myocarditis (CCM) depends on Trypanosoma cruzi persistence in the myocardium. Studies of the proteolytic mechanisms governing host/parasite balance in peripheral sites of T. cruzi infection revealed that tissue culture trypomastigotes (TCTs) elicit inflammatory edema and stimulate protective type-1 effector T cells through the activation of the kallikrein-kinin system. Molecular studies linked the proinflammatory phenotype of Dm28c TCTs to the synergistic activities of tGPI, a lipid anchor that functions as a Toll-like receptor 2 (TLR2) ligand, and cruzipain, a kinin-releasing cysteine protease. Analysis of the dynamics of inflammation revealed that TCTs activate innate sentinel cells via TLR2, releasing CXC chemokines, which in turn evoke neutrophil/CXCR2-dependent extravasation of plasma proteins, including high molecular weight kininogen (HK), in parasite-laden tissues. Further downstream, TCTs process surface bound HK, liberating lysyl-BK (LBK), which then propagates inflammatory edema via signaling of endothelial G-protein-coupled bradykinin B₂ receptors (BK₂R). Dm28 TCTs take advantage of the transient availability of infection-promoting peptides (e.g., bradykinin and endothelins) in inflamed tissues to invade cardiovascular cells via interdependent signaling of BKRs and endothelin receptors (ETRs). Herein we present a space-filling model whereby ceramide-enriched endocytic vesicles generated by the sphingomyelinase pathway might incorporate BK₂R and ETRs, which then trigger Ca²⁺-driven responses that optimize the housekeeping mechanism of plasma membrane repair from cell wounding. The hypothesis predicts that the NF-κB-inducible BKR (BK₁R) may integrate the multimolecular signaling platforms forged by ceramide rafts, as the chronic myocarditis progresses. Exploited as gateways for parasite invasion, BK₂R, BK₁R, ET_AR, ET_BR, and other G protein-coupled receptor partners may enable persistent myocardial parasitism in the edematous tissues at expense of adverse cardiac remodeling.

UNC93B1 and nucleic acid-sensing Toll-like receptors mediate host resistance to infection with Leishmania major

The mammalian homolog B1 of Unc-93 Caenorhabditis elegans known as UNC93B1 is a chaperone protein that mediates translocation of the nucleic acid-sensing Toll-like receptors (TLRs) from the endoplasmic reticulum to the endolysosomes. The triple deficient (UNC93B1 mutant) mice have a functional single point mutation in the UNC93B1 that results in non-functional TLR3, TLR7, and TLR9. Herein, we demonstrate that UNC93B1 mutant mice, in the C57BL/6 (resistant) genetic background, are highly susceptible to Leishmania major infection. Enhanced swelling of the footpad was associated with high levels of interleukin 10, decreased levels of interferon γ, and increased parasitism. None of the single TLR3, TLR7, and TLR9 knock-out (KO) mice resemble the UNC93B1 mutant phenotype upon infection with L. major. Whereas the double TLR7/TLR9 KO showed a partial phenotype, the triple TLR3/TLR7/TLR9 KO mice were as susceptible as the UNC93B1 mutant mice, when infected with Leishmania parasites. Finally, we demonstrate that treatment with either anti-interleukin 10 receptor monoclonal antibody or recombinant interleukin 12 restored a robust anti-parasite TH1 response and reverted the susceptible phenotype of UNC93B1 mutant mice. Altogether, our results indicate the redundant and essential role of nucleic acid-sensing TLR3, TLR7 and TLR9 in inducing interleukin 12, development of a TH1 response, and resistance to L. major infection in resistant C57BL/6 mice.

Combined action of nucleic acid-sensing Toll-like receptors and TLR11/TLR12 heterodimers imparts resistance to Toxoplasma gondii in mice

"Triple-defective" (3d) mice carrying a mutation in UNC93B1, a chaperone for the endosomal nucleic acid-sensing (NAS) Toll-like receptors TLR3, TLR7, and TLR9, are highly susceptible to Toxoplasma gondii infection. However, none of the single or even the triple NAS-TLR-deficient animals recapitulated the 3d susceptible phenotype to experimental toxoplasmosis. Investigating this further, we found that while parasite RNA and DNA activate innate immune responses via TLR7 and TLR9, TLR11 and TLR12 working as heterodimers are required for sensing and responding to Toxoplasma profilin. Consequently, the triple TLR7/TLR9/TLR11-deficient mice are highly susceptible to T. gondii infection, recapitulating the phenotype of 3d mice. Humans lack functional TLR11 and TLR12 genes. Consistently, human cells produce high levels of proinflammatory cytokines in response to parasite-derived RNA and DNA, but not to Toxoplasma profilin, supporting a more critical role for NAS-TLRs in human toxoplasmosis.

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.

Recognition of fungal RNA by TLR7 has a nonredundant role in host defense against experimental candidiasis

Despite convincing evidence for involvement of members of the Toll-like receptor (TLR) family in fungal recognition, little is known of the functional role of individual TLRs in antifungal defenses. We found here that TLR7 was partially required for the induction of IL-12 (IL-12p70) by Candida albicans or Saccharomyces cerevisiae. Moreover, the IL-12p70 response was completely abrogated in cells from 3d mice, which are unable to mobilize TLRs to endosomal compartments, as well as in cells from mice lacking either the TLR adaptor MyD88 or the IRF1 transcription factor. Notably, purified fungal RNA recapitulated IL-12p70 induction by whole yeast. Although RNA could also induce moderate TLR7-dependent IL-23 and tumor necrosis factor-alpha (TNF-α) secretion, TLR7 and other endosomal TLRs were redundant for IL-23 or TNF-α induction by whole fungi. Importantly, mice lacking TLR7 or IRF1 were hypersusceptible to systemic C. albicans infection. Our data suggest that IRF1 is downstream of a novel, nonredundant fungal recognition pathway that has RNA as a major target and requires phagosomal recruitment of intracellular TLRs. This pathway differs from those involved in IL-23 or TNF-α responses, which we show here to be independent from translocation of intracellular TLRs, phagocytosis, or phagosomal acidification.

Trypanosoma cruzi adjuvants potentiate T cell-mediated immunity induced by a NY-ESO-1 based antitumor vaccine

Immunological adjuvants that induce T cell-mediate immunity (TCMI) with the least side effects are needed for the development of human vaccines. Glycoinositolphospholipids (GIPL) and CpGs oligodeoxynucleotides (CpG ODNs) derived from the protozoa parasite Trypanosoma cruzi induce potent pro-inflammatory reaction through activation of Toll-Like Receptor (TLR)4 and TLR9, respectively. Here, using mouse models, we tested the T. cruzi derived TLR agonists as immunological adjuvants in an antitumor vaccine. For comparison, we used well-established TLR agonists, such as the bacterial derived monophosphoryl lipid A (MPL), lipopeptide (Pam3Cys), and CpG ODN. All tested TLR agonists were comparable to induce antibody responses, whereas significant differences were noticed in their ability to elicit CD4(+) T and CD8(+) T cell responses. In particular, both GIPLs (GTH, and GY) and CpG ODNs (B344, B297 and B128) derived from T. cruzi elicited interferon-gamma (IFN-γ) production by CD4(+) T cells. On the other hand, the parasite derived CpG ODNs, but not GIPLs, elicited a potent IFN-γ response by CD8(+) T lymphocytes. The side effects were also evaluated by local pain (hypernociception). The intensity of hypernociception induced by vaccination was alleviated by administration of an analgesic drug without affecting protective immunity. Finally, the level of protective immunity against the NY-ESO-1 expressing melanoma was associated with the magnitude of both CD4(+) T and CD8(+) T cell responses elicited by a specific immunological adjuvant.

Pattern recognition receptors in infectious skin diseases

During the last decade, multiple pattern recognition receptors (PRRs) have been identified. These are involved in the innate immune response against a plethora of pathogens. However, PRR functioning can also be detrimental, even during infections. This review discusses the current knowledge on PRRs that recognize dermatotropic pathogens, and potential therapeutical implications.

The Immune Response to Trypanosoma cruzi: Role of Toll-Like Receptors and Perspectives for Vaccine Development

In the past ten years, studies have shown the recognition of Trypanosoma cruzi-associated molecular patterns by members of the Toll-like receptor (TLR) family and demonstrated the crucial participation of different TLRs during the experimental infection with this parasite. In the present review, we will focus on the role of TLR-activated pathways in the modulation of both innate and acquired immune responses to T. cruzi infection, as well as discuss the state of the art of vaccine research and development against the causative agent of Chagas disease (or American trypanosomiasis).

IL-10 limits parasite burden and protects against fatal myocarditis in a mouse model of Trypanosoma cruzi infection

Chagas' disease is a zoonosis prevalent in Latin America that is caused by the protozoan Trypanosoma cruzi. The immunopathogenesis of cardiomyopathy, the main clinical problem in Chagas' disease, has been extensively studied but is still poorly understood. In this study, we systematically compared clinical, microbiologic, pathologic, immunologic, and molecular parameters in two mouse models with opposite susceptibility to acute myocarditis caused by the myotropic Colombiana strain of T. cruzi: C3H/HeSnJ (100% mortality, uncontrolled parasitism) and C57BL/6J (<10% mortality, controlled parasitism). T. cruzi induced differential polarization of immunoregulatory cytokine mRNA expression in the hearts of C57BL/6J versus C3H/HeSnJ mice; however, most differences were small. The difference in IL-10 expression was exceptional (C57BL/6J 8.7-fold greater than C3H/HeSnJ). Consistent with this, hearts from infected C57BL/6J mice, but not C3H/HeSnJ mice, had a high frequency of total IL-10-producing CD8(+) T cells and both CD4(+) and CD8(+) subsets of IFN-γ(+)IL-10(+) double-producing T cells. Furthermore, T. cruzi infection of IL-10(-/-) C57BL/6J mice phenocopied fatal infection in wild-type C3H/HeSnJ mice with complete loss of parasite control. Adoptive transfer experiments indicated that T cells were a source of protective IL-10. Thus, in this system, IL-10 production by T cells promotes T. cruzi control and protection from fatal acute myocarditis.

The role of Toll-like receptors and adaptive immunity in the development of protective or pathological immune response triggered by the Trypanosoma cruzi protozoan

Trypanosoma cruzi, the causal agent of Chagas disease, is an intracellular protozoan parasite that predominantly invades macrophages and cardiomyocytes, leading to persistent infection. Several members of the Toll-like receptor family are crucial for innate immunity to infection and are involved in maintaining tissue homeostasis. This review focuses on recent experimental findings of the innate and adaptive immune response in controlling the parasite and/or in generating heart and liver tissue injury. We also describe the importance of the host’s genetic background in the outcome of the disease and emphasize the importance of studying the response to specific parasite antigens. Understanding the dual participation of the immune response may contribute to the design of new therapies for Chagas disease.

Trypanosoma cruzi as an effective cancer antigen delivery vector

One of the main challenges in cancer research is the development of vaccines that induce effective and long-lived protective immunity against tumors. Significant progress has been made in identifying members of the cancer testis antigen family as potential vaccine candidates. However, an ideal form for antigen delivery that induces robust and sustainable antigen-specific T-cell responses, and in particular of CD8(+) T lymphocytes, remains to be developed. Here we report the use of a recombinant nonpathogenic clone of Trypanosoma cruzi as a vaccine vector to induce vigorous and long-term T cell-mediated immunity. The rationale for using the highly attenuated T. cruzi clone was (i) the ability of the parasite to persist in host tissues and therefore to induce a long-term antigen-specific immune response; (ii) the existence of intrinsic parasite agonists for Toll-like receptors and consequent induction of highly polarized T helper cell type 1 responses; and (iii) the parasite replication in the host cell cytoplasm, leading to direct antigen presentation through the endogenous pathway and consequent induction of antigen-specific CD8(+) T cells. Importantly, we found that parasites expressing a cancer testis antigen (NY-ESO-1) were able to elicit human antigen-specific T-cell responses in vitro and solid protection against melanoma in a mouse model. Furthermore, in a therapeutic protocol, the parasites expressing NY-ESO-1 delayed the rate of tumor development in mice. We conclude that the T. cruzi vector is highly efficient in inducing T cell-mediated immunity and protection against cancer cells. More broadly, this strategy could be used to elicit a long-term T cell-mediated immunity and used for prophylaxis or therapy of chronic infectious diseases.