Leishmania donovaniinfluenced cytokines and Toll-like receptors expression among Sudanese visceral leishmaniasis patients

Toll-like Receptor-9 (TLR-9) Signaling Is Crucial for Inducing Protective Immunity following Immunization with Genetically Modified Live Attenuated Leishmania Parasites

No human vaccine is available for visceral leishmaniasis (VL). Live attenuated centrin gene-deleted L. donovani (LdCen−/−) parasite vaccine has been shown to induce robust innate immunity and provide protection in animal models. Toll-like receptors (TLRs) are expressed in innate immune cells and are essential for the early stages of Leishmania infection. Among TLRs, TLR-9 signaling has been reported to induce host protection during Leishmania infection. Importantly, TLR-9 ligands have been used as immune enhancers for non-live vaccination strategies against leishmaniasis. However, the function of TLR-9 in the generation of a protective immune response in live attenuated Leishmania vaccines remains unknown. In this study, we investigated the function of TLR-9 during LdCen−/− infection and found that it increased the expression of TLR-9 on DCs and macrophages from ear-draining lymph nodes and spleen. The increase in TLR-9 expression resulted in changes in downstream signaling in DCs mediated through signaling protein myeloid differentiation primary response 88 (MyD88), resulting in activation and nuclear translocation of nuclear factor-κB (NF-κB). This process resulted in an increase in the DC’s proinflammatory response, activation, and DC-mediated CD4+T cell proliferation. Further, LdCen−/− immunization in TLR-9−/− mice resulted in a significant loss of protective immunity. Thus, LdCen−/− vaccine naturally activates the TLR-9 signaling pathway to elicit protective immunity against virulent L. donovani challenge.

Unwinding the mechanism of macrophage repolarization potential of Oceanimonas sp. BPMS22-derived protein protease inhibitor through Toll-like receptor 4 against experimental visceral leishmaniasis

The Oceanimonas sp. BPMS22-derived protein protease inhibitor (PPI) has been proven to shift macrophages towards an inflammatory state and reduce Leishmania donovani infection in vitro and in vivo. The current study explored and validated the mechanistic aspects of the PPI and Toll-like receptor (TLR) interaction. The PPI exhibited the upregulation of TLR2, TLR4, and TLR6 during treatment which was proven to orchestrate parasite clearance effectively. An in silico study confirmed the high interaction with TLR4 and PPI. Immune blotting confirmed the significant upregulation of TLR4 in macrophages irrespective of L. donovani infection. Pharmacological inhibition and immune blot study confirmed the involvement of the PPI in TLR4-mediated phosphorylation of p38 MAPK and dephosphorylation of ERK1/2, repolarizing to pro-inflammatory macrophage state against experimental visceral leishmaniasis. In addition, in TLR4 knockdown condition, PPI treatment failed to diminish M2 phenotypical markers (CD68, Fizz1, Ym1, CD206, and MSR-2) and anti-inflammatory cytokines (IL-4, IL-10, and TGF-β). Simultaneously, the PPI failed to upregulate the M1 phenotypical markers and pro-inflammatory cytokines (IL-1β, IL-6, IL-12, and IFN-γ) (p < 0.001) during the TLR4 knockdown condition. In the absence of TLR4, the PPI also failed to reduce the parasite load and T-cell proliferation and impaired the delayed-type hypersensitivity response. The absence of pro-inflammatory cytokines was observed during a co-culture study with PPI-treated macrophages (in the TLR4 knockdown condition) with day 10 T-cell obtained from L. donovani-infected mice. This study supports the immunotherapeutic potential of the PPI as it interacted with TLR4 and promoted macrophage repolarization (M2-M1) to restrict the L. donovani parasite burden and helps in the mounting immune response against experimental visceral leishmaniasis.

Paradoxical immune response in leishmaniasis: the role of toll-like receptors in disease progression

Toll-like receptors (TLRs), members of pattern recognition receptors, are expressed on many cells of the innate immune system and their engagements with antigens regulates specific immune responses. TLRs signalling influences species-specific immune responses during Leishmania infection, thus, TLRs play a decisive role towards elimination or exacerbation of Leishmania infection. To date, there is no single therapeutic or prophylactic approach that fully effective against Leishmaniasis. An in-depth understanding of the mechanisms by which Leishmania species evade, or exploit host immune machinery could lead to the development of novel therapeutic approaches for the prevention and management of leishmaniasis. In this review, the role of TLRs in the induction of a paradoxical immune response in leishmaniasis was discussed. This review focuses on highlighting the novel interplay of TLR2/TLR9 driven resistance or susceptibility to 5 clinically important Leishmania species in human. The activation of TLR2/TLR9 can induce a diverse anti-Leishmania activities depending on the species of infecting Leishmania parasite. Infection with L. infantum and L. mexicana initiate TLR2/9 activation leading to host protective immune response while infection with L. major, L. donovani, and L. amazonensis trigger either a TLR2/9 related protective or non-protective immune responses. These findings suggest that TLR2 and TLR9 are targets worth pursuing either for modulation or blockage to trigger host protective immune response towards leishmaniasis.

Neutrophils and Visceral Leishmaniasis: Impact on innate immune response and cross-talks with macrophages and dendritic cells

Neutrophils with their array of microbicidal activities are the first innate immune cells to guard against infection. They are also most crucial for the host's initial defense against Leishmania parasites which cause clinically diverse diseases ranging from self-healing cutaneous leishmaniasis (CL) to a more severe visceral form, visceral leishmaniasis (VL). Neutrophils are recruited in large numbers at the infection site after bite of sandfly, which is the vector for the disease. The initial interaction of neutrophils with the parasites may modulate the subsequent innate and adaptive immune responses and hence affect the disease outcome. The purpose of this review is to comprehensively appraise the role of neutrophils during the early stages of Leishmania infection with a focus on the visceral form of the disease. In the past decade, new insights regarding the role of neutrophils in VL have surfaced which have been extensively elaborated in the present review. In addition, since much of the information regarding neutrophil-Leishmania early interaction has accumulated through studies on mouse models of CL, these studies are also revisited. We begin by reviewing the factors which drive the recruitment of neutrophils at the site of injection by the sandfly. We then discuss the studies delineating the molecular mechanisms involved in the uptake of the Leishmania parasite by neutrophils and how the parasite subverts their microbicidal functions. In the end, the interaction of infected neutrophils with macrophages and dendritic cells is summarized.

Cytokine saga in visceral leishmaniasis

In humans, infection with Leishmania manifests into a spectrum of diseases. The manifestation of the diseases depend on the resultant evasion of the parasite to immune responses namely by macrophages, which is an exclusive host of Leishmania. The B cells valiantly mount antibody responses, however, to no avail as the Leishmania parasites occupy the intracellular niches of the macrophages and subvert the immune response. Extensive studies have been documented on the role of cell-mediated immunity (CMI) in protection and counter survival strategies of the parasites leading to downregulation of CMI. The present review attempts to discuss the cytokines in progression or resolution of visceral form of leishmaniasis or kala-azar, predominantly affecting the Indian subcontinent. The components/cytokine(s) responsible for the regulation of the critical balance of T helper cells and their subsets have been discussed in the perspective. Therefore, any strategy involving the treatment of visceral leishmania (VL) needs to consider the balance and regulation of T cell function.

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.

Leishmania species-dependent functional duality of toll-like receptor 2

Toll-like receptors (TLRs) are a subset of pattern recognition receptors (PRR) in innate immunity and act as a connecting link between innate and adaptive immune systems. During Leishmania infection, the activation of TLRs influences the pathogen-specific immune responses, which may play a decisive role in determining the outcome of infection, toward elimination or survival of the pathogen. Antigen-presenting cells (APCs) of the innate immune system such as macrophages, dendritic cells (DCs), neutrophils, natural killer (NK) cells, and NKT cells express TLR2, which plays a crucial role in the parasite recognition and elicitation of immune responses in Leishmania infection. Depending on the infecting Leishmania species, the TLR2 pathways may result in a host-protective or a disease-exacerbating response. While Leishmania major and Leishmania donovani infections trigger TLR2-related host-protective and non-protective immune responses, Leishmania mexicana and Leishmania infantum infections are reported to elicit TLR2-mediated host-protective responses and Leishmania amazonensis and Leishmania braziliensis infections are reported to evoke a disease-exacerbating response. These findings illustrate that TLR2-related effector functions are diverse and may be exerted in a species- or strain-dependent manner. TLR2 agonists or antagonists may have therapeutic potentials to trigger the desired immune response during leishmaniasis. In this review, we discuss the TLR2-related immune responses during leishmaniasis and highlight the novel insights into the possible role of TLR2-driven resistance or susceptibility to Leishmania.

Redundant and regulatory roles for Toll-like receptors in Leishmania infection

Toll-like receptors (TLRs) are germline-encoded, non-clonal innate immune receptors, which are often the first receptors to recognize the molecular patterns on pathogens. Therefore, the immune response initiated by TLRs has far-reaching consequences on the outcome of an infection. As soon as the cell surface TLRs and other receptors recognize a pathogen, the pathogen is phagocytosed. Inclusion of TLRs in the phagosome results in quicker phagosomal maturation and stronger adaptive immune response, as TLRs influence co-stimulatory molecule expression and determinant selection by major histocompatibility complex (MHC) class II and MHC class I for cross-presentation. The signals delivered by the TCR-peptide-MHC complex and co-stimulatory molecules are indispensable for optimal T cell activation. In addition, the cytokines induced by TLRs can skew the differentiation of activated T cells to different effector T cell subsets. However, the potential of TLRs to influence adaptive immune response into different patterns is severely restricted by multiple factors: gross specificity for the molecular patterns, lack of receptor rearrangements, sharing of limited number of adaptors that assemble signalling complexes and redundancy in ligand recognition. These features of apparent redundancy and regulation in the functioning of TLRs characterize them as important and probable contributory factors in the resistance or susceptibility to an infection.

Ex vivo infection of human placental chorionic villi explants with Trypanosoma cruzi and Toxoplasma gondii induces different Toll-like receptor expression and cytokine/chemokine profiles

PROBLEM

Trypanosoma cruzi and Toxoplasma gondii present, respectively, low and high congenital transmission rates. The placenta as an immune regulatory organ expresses TLRs, leading to the secretion of cytokines. Both parasites are recognized by TLR-2, TLR-4, and TLR-9. Here, we studied if the parasites induce differences in TLR protein expression, cytokine profiles, and whether receptor inhibition is related to parasite infection.

METHOD OF STUDY

Placental tissue explants were infected ex vivo with each parasite, TLRs protein expression, cytokine profile and parasite infection were determined by Western blotting, ELISA and qPCR.

RESULTS

Trypanosoma cruzi and Toxoplasma gondii infection is related to TLR-2 and TLR-4/TLR-9, respectively. Trypanosoma cruzi elicits an increase in TNF-α, IL-1β, IL-6, IL-8 and IL-10 cytokine secretion whereas T. gondii only increases the secretion of IL-8.

CONCLUSION

The susceptibility of the placenta to each parasite is mediated partially by the innate immune response.

TLR-2 and TLR-4 transcriptions in unstimulated blood from dogs with leishmaniosis due to Leishmania infantum at the time of diagnosis and during follow-up treatment

Innate immunity, in particular, the role of toll-like receptors (TLRs), has not been extensively studied in canine L. infantum infection. The main aim of this study was to determine the transcription of TLR2 and TLR4 in the blood of dogs with natural clinical leishmaniosis at the time of diagnosis and during treatment follow-up and subsequently correlate these findings with clinical, serological and parasitological data. Forty-six Leishmania-seropositive sick dogs with a high antibody level at the time of diagnosis were studied and compared with 34 healthy seronegative dogs. Twenty-two of these sick dogs were treated with meglumine antimoniate and allopurinol and followed-up at 30, 180 and 365days following the start of treatment. Clinical status was defined by a thorough physical examination, complete blood count, biochemistry profile, electrophoresis of serum proteins, and urinary protein/creatinine ratio (UPC). EDTA blood was stored in RNAlater^® solution before RNA extraction and cDNA production were performed. TLR2, TLR4 and three reference genes (HPRT-1, CG14980 and SDHA) were studied in each blood sample by real time PCR. The relative quantification of TLR2 was higher (mean 3.5) in sick dogs when compared with seronegative healthy dogs (mean 1.3; P=0.0001) while the relative quantification of TLR4 was similar in both groups. In addition, the relative quantification of TLR2 significantly decreased during follow-up at all time points compared with day 0 whereas no changes were observed with TLR4 transcription. A significant positive correlation was noted between TLR2 and UPC, total protein, beta and gamma globulins, specific L. infantum antibodies and blood parasite load while a negative correlation was observed with albumin, albumin/globulin ratio, hematocrit and hemoglobin. TLR4 transcript did not correlate with any parameter. These findings indicate an up-regulation of TLR2 transcription in unstimulated blood in naturally infected sick dogs as compared to healthy dogs suggesting active innate immune and proinflammatory responses. In addition, TLR2 transcription is reduced with clinical improvement during treatment. In contrast, TLR4 transcription appears to be similar among groups at the time of diagnosis with no changes during treatment follow-up suggesting a less important role for this TLR in clinical canine leishmaniosis.