Toll-like receptor signaling: a perspective to develop vaccine against leishmaniasis

Recombinant guanosine-5'-triphosphate (GTP)-binding protein associated with Poloxamer 407-based polymeric micelles protects against Leishmania infantum infection

Leishmania virulence proteins should be considered as vaccine candidates against disease, since they are involved in developing infection in mammalian hosts. In a previous study, a Leishmania guanosine-5'-triphosphate (GTP)-binding protein was identified as a potential parasite virulence factor. In the present work, the gene encoding GTP was cloned and the recombinant protein (rGTP) was evaluated as a vaccine candidate against Leishmania infantum infection. The protein was associated with saponin (rGTP/Sap) or Poloxamer 407-based micelles (rGTP/Mic) as adjuvants, and protective efficacy was investigated in BALB/c mice after parasite challenge. Both rGTP/Sap and rGTP/Mic compositions induced a Th1-type immune response in vaccinated animals, with significantly higher levels of IFN-γ, IL-12, IL-2, TNF-α, GM-CSF, nitrite, specific IgG2a isotype antibody and positive lymphoproliferation, when compared to the control groups. This response was accompanied by significantly lower parasite load in the spleens, livers, bone marrows and draining lymph nodes of the animals. Immunological and parasitological evaluations indicated that rGTP/Mic induced a more polarized Th1-type response and higher reduction in the organ parasitism, and with lower hepatotoxicity, when compared to the use of rGTP/Sap. In conclusion, our preliminary data suggest that rGTP could be considered for further development as a vaccine candidate to protect against VL.

Toll-like receptor-7/8 agonist kill Leishmania amazonensis by acting as pro-oxidant and pro-inflammatory agent

OBJECTIVES

Evaluation of the anti-Leishmanial activity of imidazoquinoline-based TLR7/8 agonists.

METHODS

TLR7/8-active imidazoquinolines (2 and 3) were synthesized and assessed for activity against Leishmania amazonensis-intracellular amastigotes using mouse peritoneal macrophages. The production of reactive oxygen species (ROS), nitric oxide (NO) and cytokines was determined in infected and non-infected macrophages.

KEY FINDINGS

The imidazoquinolines, 2 and 3, were primarily agonists of TLR7 with compound 3 also showing modest TLR8 activity. Docking studies showed them to occupy the same binding pocket on TLR7 and 8 as the known agonists, imiquimod and resiquimod. Compounds 2 and 3 inhibited the growth of L. amazonensis-intracellular amastigotes with the most potent compound (3, IC50 = 5.93 µM) having an IC50 value close to miltefosine (IC50 = 4.05 µM), a known anti-Leishmanial drug. Compound 3 induced macrophages to produce ROS, NO and inflammatory cytokines that likely explain the anti-Leishmanial effects.

CONCLUSIONS

This study shows that activating TLR7 using compounds 2 or 3 induces anti-Leishmanial activity associated with induction of free radicals and inflammatory cytokines able to kill the parasites. While 2 and 3 had a very narrow cytotoxicity window for macrophages, this identifies the possibility to further develop this chemical scaffold to less cytotoxic TLR7/8 agonist for potential use as anti-Leishmanial drug.

Potential of TLR agonist as an adjuvant in Leishmania vaccine against visceral leishmaniasis in BALB/c mice

Morbid infection of leishmaniasis is posing threat to humankind due to its exacerbating prevalence in newer emerging areas. Moreover, the availability of limited drugs, their toxicity, limited efficacy, the emergence of drug resistance, and unavailability of vaccines are the major obstacles in its elimination. This implies the demand for a prophylactic vaccine candidate to prevent this infection and resulting fatal disease. We evaluated gardiquimod (a toll-like receptor-7 agonist) for its action as an adjuvant with the heat-killed antigen of Leishmania donovani. BALB/c mice were immunized with a vaccine either with or without adjuvant and given challenge infection. The results depicted the low parasite burden, higher delayed-type hypersensitivity response, and higher levels of IgG2a, Th1 cytokines, and NO in immunized mice in contrast to infected control mice. Low levels of Th2 cytokines and IgG1 were also noticed in the vaccinated mice than in infected mice. The mice immunized with a combination of gardiquimod and heat-killed antigen showed maximum efficacy. The results from the present study reflect the potential of tested vaccine candidate with gardiquimod as an adjuvant.

Leishmanial CpG DNA nanovesicles: A propitious prophylactic approach against visceral leishmaniasis

Unmethylated CpG motifs with phosphothioate backbone trigger TLR9 to elicit innate immune response characterized by the production of Th1 cytokines. The use of CpG DNA as an adjuvant has established its role in potentiating the humoral and cell mediated vaccine specific immune response. However, none of the synthetic oligodeoxynucleotides (ODNs) know and used till date are associated with the parasite itself. Our group identified a novel CG rich sequence of 14 base pairs from Leishmania donovani genome (Ld CpG ODN) and established it as a TLR9 agonist. The present study was designed to ascertain the adjuvanticity of Ld CpG ODN with soluble leishmanial antigen in experimental model of L. donovani. During the study Schizophyllan (SPG), a fungal polymer was used for encapsulating Ld CpG ODN for efficient endosomal delivery. The synthesized nanovehicles were of nearly 100 nm and localized within endosomes as confirmed by confocal microscopy. Immunization studies displayed the superior ability of synthesized nanovehicles co-administered with parasite antigen in augmenting innate immune response in comparison to ODN, nanoparticles or soluble antigen alone. The response included generation of ROS, NO and iNOS expression followed by proinflammatory cytokine milieu with reduced parasitic load within liver, spleen and bone marrow. These immune-tailored particles in combination with parasitic antigens elicited significant generation of cell mediated response owing to the presence of high levels of CD8⁺ T-cells and lymphocyte proliferation. Moreover, vaccination regime with synthesized adjuvant also activated humoral immunity by escalating the levels of IgG2 followed by reduced levels of anti-leishmanial IgG and IgG1 antibodies. The findings support the efficacy of Ld CpG ODN as a potential adjuvant against visceral leishmaniasis.

Higher levels of TNF and IL-4 cytokines and low miR-182 expression in visceral leishmaniasis-HIV co-infected patients

AIMS

The aim of the present study was to assess serum cytokine and miRNA expression in visceral leishmaniasis-HIV (VL-HIV) co-infection and HIV mono-infection.

METHODS AND RESULTS

We analysed 113 serum samples from HIV patients in areas endemic for leishmaniasis. The diagnosis of VL was confirmed in 65 of these 113 samples. The VL-HIV and HIV groups presented significant differences regarding haemoglobin level (P < .0001), lymphocyte count (P = .0444), white blood cell count (P = .0108), weight loss (P = .0310), HIV load (P < .0001) and CD4+ T-lymphocytes count (P = .0003). Levels of IL-6 and IL-10, IFN-γ and IL-6, IFN-γ and IL-10, TNF and IL-2 were positively correlated in VL-HIV co-infection, indicating higher serum levels of TNF and IL-4 (P < .0001). In addition, miR-182 expression was found to be significantly higher in HIV (P = .009), miR-210 exhibited no statistically significant difference between groups, and nonexpression of miR-122 was found in both groups.

CONCLUSION

Together, TNF, IL-4 and miR-182 may represent circulatory biomarkers of VL-HIV co-infection.

The CD200-CD200R cross-talk helps Leishmania donovani to down regulate macrophage and CD4+CD44+ T cells effector functions in an NFκB independent manner

The lacuna in the knowledge of immunobiology, especially in visceral infections that are fatal if left untreated, are a major hurdle in getting a vaccine candidate for leishmaniasis. Till date, only a few drugs are available to combat human leishmaniasis and a vaccine candidate either prophylactic or preventive is still awaited. Therefore, identification of host and parasitic factors involved in the regulation of specific immune mechanisms are essentially needed. In this study, we observed that CD200-CD200R immune inhibitory axis regulates host macrophages effectors properties and helps antigen experienced T cells (CD4⁺CD44⁺ T cells) to acquire anti-inflammatory cytokines (IL-4, IL-10, TGF-β, IL-27) producing abilities in an NFkB independent manner. After CD200 blocking the macrophages effectively inhibited proliferation of Leishmania amastigotes and also induced the production of IL-12, IFN-γ, TNF-α and nitric oxide (NOx). Further, the blocking of CD200 signaling also restored macrophages MHC-II expression and helped CD4⁺CD44⁺ T cells to produce pro-inflammatory cytokines like IL-2, IL-12 and IFN-γ. The finding of this study suggested the importance of immune inhibitory mechanisms in controlling Leishmania growth and survival and therefore, requires more studies to understand its role in vaccine induced immunity.

Research Progress of Mechanisms and Drug Therapy For Atherosclerosis on Toll-Like Receptor Pathway

Recent reports have established atherosclerosis (AS) as a major factor in the pathogenetic process of cardiovascular diseases such as ischemic stroke and coronary heart disease. Although the possible pathogenesis of AS remains to be elucidated, a large number of investigations strongly suggest that the inhibition of toll-like receptors (TLRs) alleviates the severity of AS to some extent by suppressing vascular inflammation and the formation of atherosclerotic plaques. As pattern recognition receptors, TLRs occupy a vital position in innate immunity, mediating various signaling pathways in infective and sterile inflammation. This review summarizes the available data on the research progress of AS and the latest antiatherosclerotic drugs associated with TLR pathway.

Leishmania donovani infection differentially regulates small G-proteins

Leishmania is a protozoan parasite that resides and replicates in macrophages and causes leishmaniasis. The parasite alters the signaling cascade in host macrophages and evades the host machinery. Small G-proteins are GTPases, grouped in 5 different families that play a crucial role in the regulation of cell proliferation, cell survival, apoptosis, intracellular trafficking, and transport. In particular, the Ras family of small G-proteins has been identified to play a significant role in the cellular functions mentioned before. Here, we studied the differential expression of the most important small G-proteins during Leishmania infection. We found major changes in the expression of different isoforms of Ras, mainly in N-Ras. We observed that Leishmania donovani infection led to enhanced N-Ras expression, whereas it inhibited K-Ras and H-Ras expression. Furthermore, an active N-Ras pull-down assay showed enhanced N-Ras activity. L donovani infection also increased extracellular signal-regulated kinase 1/2 phosphorylation and simultaneously decreased p38 phosphorylation. In contrast, pharmacological inhibition of Ras led to reduction in the phosphorylation of extracellular signal-regulated kinase 1/2 and enhanced the phosphorylation of p38 in Leishmania-infected cells, which could lead to increased interleukin-12 expression and decreased interleukin-10 expression. Indeed, farnesylthiosalicyclic acid (a Ras inhibitor), when used at the effective level in L donovani-infected macrophages, reduced amastigotes in the host macrophages. Thus, upregulated N-Ras expression during L donovani infection could be a novel immune evasion strategy of Leishmania and would be a potential target for antileishmanial immunotherapy.

Transcriptional Profiling of Immune-Related Genes in Leishmania infantum-Infected Mice: Identification of Potential Biomarkers of Infection and Progression of Disease

Leishmania spp. is a protozoan parasite that affects millions of people around the world. At present, there is no effective vaccine to prevent leishmaniases in humans. A major limitation in vaccine development is the lack of precise understanding of the particular immunological mechanisms that allow parasite survival in the host. The parasite-host cell interaction induces dramatic changes in transcriptome patterns in both organisms, therefore, a detailed analysis of gene expression in infected tissues will contribute to the evaluation of drug and vaccine candidates, the identification of potential biomarkers, and the understanding of the immunological pathways that lead to protection or progression of disease. In this large-scale analysis, differential expression of 112 immune-related genes has been analyzed using high-throughput qPCR in spleens of infected and naïve Balb/c mice at four different time points. This analysis revealed that early response against Leishmania infection is characterized by the upregulation of Th1 markers and M1-macrophage activation molecules such as Ifng, Stat1, Cxcl9, Cxcl10, Ccr5, Cxcr3, Xcl1, and Ccl3. This activation doesn't protect spleen from infection, since parasitic burden rises along time. This marked difference in gene expression between infected and control mice disappears during intermediate stages of infection, probably related to the strong anti-inflammatory and immunosuppresory signals that are activated early upon infection (Ctla4) or remain activated throughout the experiment (Il18bp). The overexpression of these Th1/M1 markers is restored later in the chronic phase (8 wpi), suggesting the generation of a classical "protective response" against leishmaniasis. Nonetheless, the parasitic burden rockets at this timepoint. This apparent contradiction can be explained by the generation of a regulatory immune response characterized by overexpression of Ifng, Tnfa, Il10, and downregulation Il4 that counteracts the Th1/M1 response. This large pool of data was also used to identify potential biomarkers of infection and parasitic burden in spleen, on the bases of two different regression models. Given the results, gene expression signature analysis appears as a useful tool to identify mechanisms involved in disease outcome and to establish a rational approach for the identification of potential biomarkers useful for monitoring disease progression, new therapies or vaccine development.

The respiratory syncytial virus fusion protein formulated with a polymer-based adjuvant induces multiple signaling pathways in macrophages

Respiratory syncytial virus (RSV) causes acute respiratory tract infections in infants, the elderly and immunocompromised individuals. No licensed vaccine is available against RSV. We previously reported that intranasal immunization of rodents and lambs with a RSV vaccine candidate (ΔF/TriAdj) induces protective immunity with a good safety profile. ΔF/TriAdj promoted innate immune responses in respiratory mucosal tissues in vivo, by local chemokine and cytokine production, as well as infiltration and activation of immune cells including macrophages. The macrophage is an important cell type in context of both innate and adaptive immune responses against RSV. Therefore, we characterized the effects of ΔF/TriAdj on a murine macrophage cell line, RAW264.7, and bone marrow-derived macrophages (BMMs). A gene expression study of pattern recognition receptors (PRRs) revealed induction of endosomal and cytosolic receptors in RAW264.7 cells and BMMs by ΔF/TriAdj, but no up-regulation by ΔF in PBS. As a secondary response to the PRR gene expression, induction of several chemokines and pro-inflammatory cytokines, as well as up-regulation of MHC-II and co-stimulatory immune markers, was observed. To further investigate the mechanisms involved in ΔF/TriAdj-mediated secondary responses, we used relevant signal transduction pathway inhibitors. Based on inhibition studies at both transcript and protein levels, JNK, ERK1/2, CaMKII, PI3K and JAK pathways were clearly responsible for ΔF/TriAdj-mediated chemokine and pro-inflammatory cytokine responses, while the p38 and NF-κB pathways appeared to be not or minimally involved. ΔF/TriAdj induced IFN-β, which may participate in the JAK-STAT pathway to further amplify CXCL-10 production, which was strongly up-regulated. Blocking this pathway by a JAK inhibitor almost completely abrogated CXCL-10 production and caused a significant reduction in the cell surface expression of MHC-II and co-stimulatory immune markers. These data demonstrate that ΔF/TriAdj induces multiple signaling pathways in macrophages.

Modulating toll-like receptor-mediated inflammatory responses following exposure of whole cell and lipopolysaccharide component from Porphyromonas gingivalis in wistar rat models

Objective:

To explore host innate inflammatory response and the signal pathway induced by Porphyromonas gingivalis by measuring level of toll-like receptor 2 (TLR2) and TLR4 activity.

Materials and Methods:

Animal experimental study with pretest-posttest controlled group design were done between January 1 and December 10, 2016.. Total of 28 wistar rats had been used, randomized into 7 groups, each were given various dose of intra-sulcural injection of Porphyromonas gingivalis lipopolysaccharide.

Statistical Analysis:

Normality were measured by Shapiro–Wilk test, while statistical analysis made by ANOVA, t test, Pearson, and linear regression model..

Results:

At day 0, no significant difference TLR2 and TLR4 level were measured. At day 4, there is a slight difference between TLR2 and TLR4 level in each group. At day 11, there is a significant difference between TLR2 and TLR4 level in each group. Group with exposure of whole cell will develop greater TLR2 but lower TLR4 level. In the contrary, group with exposure of LPS will develop greater TLR4 but lower TLR2 level.

Conclusion:

Our data supported that P. gingivalis played a vital role in the pathogenesis of pathogen-induced inflammatory responses in which TLR2 and TLR4 have different molecular mechanisms following recognition of pathogens and inflammatory response.

Leishmania donovani infection activates Toll-like receptor 2, 4 expressions and Transforming growth factor-beta mediated apoptosis in renal tissues

The present study was aimed to identify the underlying mechanisms of improper renal function in Leishmania donovani infection that causes VL. Mice (BALB/c) were infected with L. donovani and different parameters for proteinuria were assessed. The levels of superoxide anion (O₂⁻), hydrogen peroxide (H₂O₂), lipid peroxidation (MDA), inflammatory cytokines, and toll-like receptor (TLR) 2 and 4 expression were found significantly elevated at 60th day in these animals and declined at 90th day post infection. However, TGF-β and caspase 3 activities were higher at 90th day in comparison to 60th day post infection. These findings suggested that exacerbated inflammatory conditions correlate with abnormal renal functions in L. donovani infection, which is further augmented by activated TLRs expressions by circulating leishmanial antigens. Further, the increased levels of TGF-β and caspase 3 at 90th day suggested TGF-β mediated apoptotic cell death of renal and other cells during later stages of disease that may eventually result in release of host and parasitic factors in urine during visceral leishmaniasis.

Identification and Characterization of miRNAs in Response to Leishmania donovani Infection: Delineation of Their Roles in Macrophage Dysfunction

The outcome of Leishmania infection depends on parasite abilities to evade host immune response and its survival in hostile environment of host macrophages. Despite a wealth of gained crucial information, parasite strategies by which it dampens host macrophage functions remain poorly understood. Micro RNAs (miRNAs) are evolutionarily conserved class of endogenous 22-nucleotide small non-coding RNA gene products, described to participate in the regulation of almost every cellular process investigated so far. In this study, we identified 940 miRNAs in Leishmania donovani infected macrophages by de novo sequencing out of which levels of 85 miRNAs were found to be consistently modified by parasite infection. Herein, we report the functional characteristics of 10 miRNAs i.e., mir-3620, mir-6385, mir-6973a, mir-6996, mir-328, mir-8113, mir-3473f, mir-763, mir-6540, and mir-1264 that were differentially but constantly regulated in infected macrophages for their role in regulation of macrophage effector functions. The target gene prediction and biological interaction analysis revealed involvement of these miRNAs in various biological processes such as apoptosis inhibition, phagocytosis, drug response, and T cell phenotypic transitions. These findings could contribute for the better understanding of macrophages dysfunction and leishmanial pathogenesis. Further, the identified miRNAs could also be used as biomarker/s in diagnosis, prognosis, and therapeutics of Leishmania infection.

Effect of smoking on the genetic makeup of toll-like receptors 2 and 6

Background

Cigarette smoking is a major risk factor for lung cancer, asthma, and oral cancer, and is central to the altered innate immune responsiveness to infection. Many hypotheses have provided evidence that cigarette smoking induces more genetic changes in genes involved in the development of many cigarette-related diseases. This alteration may be from single-nucleotide polymorphisms (SNPs) in innate immunity genes, especially the toll-like receptors (TLRs).

Objective

In this study, the genotype frequencies of TLR2 and TLR6 in smoking and nonsmoking population were examined.

Methods

Saliva samples were collected from 177 smokers and 126 nonsmokers. The SNPs used were rs3804100 (1350 T/C, Ser450Ser) and rs3804099 (597 T/C, Asn199Asn) for TLR2 and rs3796508 (979 G/A, Val327Met) and rs5743810 (745 T/C, Ser249Pro) for TLR6.

Results

Results showed that TLR2 rs3804100 has a significant effect in short-term smokers (OR =2.63; P=0.04), and this effect is not observed in long-term smokers (>5 years of smoking). Therefore, this early mutation may be repaired by the DNA repair system. For TLR2 rs3804099, the variation in genotype frequencies between the smokers and control patients was due to a late mutation, and its protective role appears only in long-term smokers (OR =0.40, P=0.018). In TLR6 rs5743810, the TT genotype is significantly higher in smokers than in nonsmokers (OR =6.90). The effect of this SNP is observed in long-term smokers, regardless of the smoking regime per day.

Conclusion

TLR2 (rs3804100 and rs3804099) and TLR6 (rs5743810) can be used as a potential index in the diagnosis and prevention of more diseases caused by smoking.

Differential Immune Response against Recombinant Leishmania donovani Peroxidoxin 1 and Peroxidoxin 2 Proteins in BALB/c Mice

We assessed the immune response against recombinant proteins of two related, albeit functionally different, peroxidoxins from Leishmania donovani: peroxidoxin 1 (LdPxn1) and peroxidoxin 2 (LdPxn2) in BALB/c mice. We also evaluated the effect of coadministration of TLR agonists (CpG ODN and GLA-SE) on the antigen-specific immune response. Immunization with recombinant LdPxn1 alone induced a predominantly Th2 type immune response that is associated with the production of high level of IgG1 and no IgG2a isotype while rLdPxn2 resulted in a mixed Th1/Th2 response characterized by the production of antigen-specific IgG2a in addition to IgG1 isotype. Antigen-stimulated spleen cells from mice that were immunized with rLdPxn1 produced low level of IL-10 and IL-4 and no IFN-γ, whereas cells from mice immunized with rLdPxn2 secreted high level of IFN-γ, low IL-4, and no IL-10. Coadministration of CpG ODN or GLA-SE with rLdPxn1 skewed the immune response towards a Th 1 type as indicated by robust production of IgG2a isotype. Furthermore, the presence of TLR agonists together with rLdPxn1 antigen enhanced the production of IFN-γ and to a lesser extent of IL-10. TLR agonists also enhanced a more polarized Th 1 type immune response against rLdPxn2.

Enhanced expression of Toll-like receptors 2 and 4, but not 9, in spleen tissue from patients with visceral leishmaniasis

Toll-like receptor (TLR) signalling is involved in first-line defence against Leishmania parasites by triggering NF-κB activation and downstream production of proinflammatory cytokines. Experimental models of visceral leishmaniasis (VL) support a protective role for TLRs 2, 4 and 9 in host immune responses to Leishmania infection. There are limited data available on expression of these TLRs in human VL, particularly in sites of infection, such as the spleen. This study aimed to determine whether the expression of mRNA encoding the expression of TLRs 2, 4 and 9 was altered in VL and compare expression patterns in splenic biopsies and peripheral blood mononuclear cells.

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.

Regulatory actions of Toll-like receptor 2 (TLR2) and TLR4 in Leishmania donovani infection in the liver

In livers of susceptible but self-curing C57BL/6 mice, intracellular Leishmania donovani infection enhanced Toll-like receptor 4 (TLR4) and TLR2 gene expression. In the liver, infected TLR4(-/-) mice showed reduced gamma interferon (IFN-γ), tumor necrosis factor (TNF), and inducible nitric oxide synthase (iNOS) mRNA expression, higher-level and slowly resolving infection, delayed granuloma formation, and little response to low-dose chemotherapy; in serum, the ratio of IFN-γ to interleukin 10 (IL-10) activity was decreased by 50%. In contrast, in TLR2(-/-) mice, control of liver infection, parasite killing, and granuloma assembly were accelerated and chemotherapy's efficacy enhanced. In livers of infected TLR2(-/-) mice, mRNA expression was not increased for inflammatory cytokines or iNOS or decreased for IL-10; however, the serum IFN-γ/IL-10 ratio was increased 6.5-fold and minimal responses to IL-10 receptor blockade suggested downregulated IL-10. In established infection in wild-type mice, blockading TLR2 induced parasite killing and triggering TLR4 strengthened resistance and promoted chemotherapy's effect. Thus, in experimental L. donovani infection in the liver, TLR4 signaling upregulates and TLR2 signaling downregulates macrophage antileishmanial activity, making both receptors potential therapeutic targets in visceral leishmaniasis for engagement (TLR4) or blockade (TLR2).

Identification and functional characterization of Leishmania donovani secretory peroxidase: delineating its role in NRAMP1 regulation

Leishmania silently evades host immune system and establish in the hostile environment of host macrophage phagolysosomes. For differentiation, growth and division parasite acquires divalent cations especially iron from the host nutritive pool. Natural resistance associated with macrophage protein1 (NRAMP1), a cation transporter that effluxes out divalent cations specifically iron from phagosomal milieu to the cytosol, to create ions deprived status for pathogenic microorganisms. The mechanisms of NRAMP1 regulation are largely unknown in leishmanial infections. In the present study, we identified a secretory Leishmania donovani peroxidase (Prx) that showed peroxidoxin like peroxidase activity and significantly reduced H₂O₂, O₂.⁻ and NO levels in LPS activated macrophages. Further, we also observed down regulated Nramp1 expression and concomitantly declined labile iron pool in activated macrophages treated with identified peroxidase. Prx also decreased levels of TNF-α, IFN-γ and IL-12 in LPS activated macrophages. These observations indicate a bifunctional protective role of secretory Prx; first it reduces redox activation of macrophages, and secondly it allows iron access to Leishmania by down regulating NRAMP1 expression.

Whole cigarette smoke increased the expression of TLRs, HBDs, and proinflammory cytokines by human gingival epithelial cells through different signaling pathways

The gingival epithelium is becoming known as a regulator of the oral innate immune responses to a variety of insults such as bacteria and chemicals, including those chemicals found in cigarette smoke. We investigated the effects of whole cigarette smoke on cell-surface-expressed Toll-like receptors (TLR)-2, -4 and -6, human β-defensin (HBD) and proinflammatory cytokine expression and production in primary human gingival epithelial cells. Whole cigarette smoke was shown to increase TLR2, TLR4 and TLR6 expression. Cigarette smoke led to ERK1/2, p38 and JNK phosphorylation in conjunction with nuclear factor-κB (NFκB) translocation into the nucleus. TLR expression following cigarette smoke exposure was down regulated by the use of ERK1/2, p38, JNK MAP kinases, and NFκB inhibitors, suggesting the involvement of these signaling pathways in the cellular response against cigarette smoke. Cigarette smoke also promoted HBD2, HBD3, IL-1β, and IL-6 expression through the ERK1/2 and NFκB pathways. Interestingly, the modulation of TLR, HBD, and cytokine expression was maintained long after the gingival epithelial cells were exposed to smoke. By promoting TLR, HBDs, and proinflammatory cytokine expression and production, cigarette smoke may contribute to innate immunity dysregulation, which may have a negative effect on human health.

Leishmania RNA virus: when the host pays the toll

The presence of an RNA virus in a South American subgenus of the Leishmania parasite, L. (Viannia), was detected several decades ago but its role in leishmanial virulence and metastasis was only recently described. In Leishmania guyanensis, the nucleic acid of Leishmania RNA virus (LRV1) acts as a potent innate immunogen, eliciting a hyper-inflammatory immune response through toll-like receptor 3 (TLR3). The resultant inflammatory cascade has been shown to increase disease severity, parasite persistence, and perhaps even resistance to anti-leishmanial drugs. Curiously, LRVs were found mostly in clinical isolates prone to infectious metastasis in both their human source and experimental animal model, suggesting an association between the viral hyperpathogen and metastatic complications such as mucocutaneous leishmaniasis (MCL). MCL presents as chronic secondary lesions in the mucosa of the mouth and nose, debilitatingly inflamed and notoriously refractory to treatment. Immunologically, this outcome has many of the same hallmarks associated with the reaction to LRV: production of type 1 interferons, bias toward a chronic Th1 inflammatory state and an impaired ability of host cells to eliminate parasites through oxidative stress. More intriguing, is that the risk of developing MCL is found almost exclusively in infections of the L. (Viannia) subtype, further indication that leishmanial metastasis is caused, at least in part, by a parasitic component. LRV present in this subgenus may contribute to the destructive inflammation of metastatic disease either by acting in concert with other intrinsic "metastatic factors" or by independently preying on host TLR3 hypersensitivity. Because LRV amplifies parasite virulence, its presence may provide a unique target for diagnostic and clinical intervention of metastatic leishmaniasis. Taking examples from other members of the Totiviridae virus family, this paper reviews the benefits and costs of endosymbiosis, specifically for the maintenance of LRV infection in Leishmania parasites, which is often at the expense of its human host.