Investigation of the antigenicity and protective efficacy of Leishmania promastigote membrane antigens in search of potential diagnostic and vaccine candidates against visceral leishmaniasis

Cellular mediators in human leishmaniasis: Critical determinants in parasite killing or disease progression

Data on cellular immunity mediators in the early phase of human leishmaniasis are still limited and controversial. In order to mimic the changes of humoral mediators during the early phase of human natural infection, some Th1, Th2, Treg, and Breg cytokines, MCP-1, and the nitric oxide (NO) from human PBMC, stimulated by Leishmania infantum, Leishmania major, Leishmania donovani and Leishmania tropica infective metacyclic promastigotes, were determined. After 4 h of L. major, L. donovani, and L. tropica challenge, TNFα, IL-1β, IL-6 levels were significantly higher than negative control cultures with saline (SF) instead of Leishmania promastigotes, unlike L. infantum-stimulated TNFα and L. major-stimulated IL-1β. We obtained higher levels of IL-4 and IL-10 cytokines after stimulation of human PBMCs by L. infantum and L. donovani, compared to those observed after the challenge of PBMCs by L. major and L. tropica. Regarding IL-35, such cytokine levels were significantly increased following infection with L. infantum and L. donovani, in contrast to L. major and L. tropica. Up to our knowledge, we are the first to study the effect of four different species of Leishmania on IL-35 levels in human cells. Our study highlights how several Leishmania species can up-regulate different groups of cytokines (Th1, Th2, Treg and Breg) and modulate NO release in a different way. This original aspect can be explained by different Leishmania cell products, such as LPG, obtained from different strains/species of live parasites. Our findings would contribute to the development of new therapeutics or vaccination strategies.

Deletion of MIF gene from live attenuated LdCen-/- parasites enhances protective CD4+ T cell immunity

Vaccination with live attenuated Leishmania parasites such as centrin deleted Leishmania donovani (LdCen^-/-) against visceral leishmaniasis has been reported extensively. The protection induced by LdCen^-/- parasites was mediated by both CD4⁺ and CD8⁺ T cells. While the host immune mediators of protection are known, parasite determinants that affect the CD4⁺ and CD8⁺ T cell populations remain unknown. Parasite encoded inflammatory cytokine MIF has been shown to modulate the T cell differentiation characteristics by altering the inflammation induced apoptosis during contraction phase in experimental infections with Leishmania or Plasmodium. Neutralization of parasite encoded MIF either by antibodies or gene deletion conferred protection in Plasmodium and Leishmania studies. We investigated if the immunogenicity and protection induced by LdCen^-/- parasites is affected by deleting MIF genes from this vaccine strain. Our results showed that LdCen^-/-MIF^-/- immunized group presented higher percentage of CD4⁺ and CD8⁺ central memory T cells, increased CD8⁺ T cell proliferation after challenge compared to LdCen^-/- immunization. LdCen^-/-MIF^-/- immunized group presented elevated production of IFN-γ⁺ and TNF-α⁺ CD4⁺ T cells concomitant with a reduced parasite load in spleen and liver compared to LdCen^-/-group following challenge with L. infantum. Our results demonstrate the role of parasite induced factors involved in protection and long-term immunity of vaccines against VL.

Development of Immunological Assays Based on Leishmania donovani Antigen for Diagnosis of Canine Visceral Leishmaniasis and Their Multicenter Evaluation in Brazil and Italy

Canine visceral leishmaniasis (CVL) due to Leishmania infantum infection is a zoonotic disease prevalent in the areas of South America and the Mediterranean. Infected dogs as reservoirs can contribute to disease transmission and can be a scourge to public health. Therefore, early diagnosis of infected dogs may play a pivotal role in circumscribing disease progression. Invasive tissue aspiration and insufficient serological methods impair a single assay for prompt CVL diagnosis. In the present study, we aimed to evaluate the potential of Leishmania donovani isolated membrane protein, LAg, for the diagnosis of CVL through immunological assays. Initially, enzyme-linked immunosorbent assay was done with Brazilian dog sera to evaluate the performance of LAg in diagnosing CVL and found sensitivity and specificity of 92.50% and 95%, respectively. The study further confirmed the diagnostic efficacy of LAg in a dipstick format. The dipstick test of canine sera from three centers in Brazil and one center in Italy collectively showed sensitivity values in the range of 53.33% to 100% in recognizing symptomatic dogs and specificity values between 75% and 100% to rule out healthy dogs. Moreover, a rapid immunochromatographic test was developed and optimized using LAg. This test was able to identify 94.73% of CVL of Brazilian origin with specificity of 97.29%. The current results highlight the reactive potential of the L. donovani antigen, LAg, for L. infantum CVL diagnosis and support our previous findings, which suggest the utility of LAg for the diagnosis of both L. donovani and L. infantum human VL in a variety of endemic regions. LAg as a diagnostic candidate may be employed to identify comprehensive CVL cases in epidemiological areas.

The Pathogenicity and Virulence of Leishmania - interplay of virulence factors with host defenses

Leishmaniasis is a group of disease caused by the intracellular protozoan parasite of the genus Leishmania. Infection by different species of Leishmania results in various host immune responses, which usually lead to parasite clearance and may also contribute to pathogenesis and, hence, increasing the complexity of the disease. Interestingly, the parasite tends to reside within the unfriendly environment of the macrophages and has evolved various survival strategies to evade or modulate host immune defense. This can be attributed to the array of virulence factors of the vicious parasite, which target important host functioning and machineries. This review encompasses a holistic overview of leishmanial virulence factors, their role in assisting parasite-mediated evasion of host defense weaponries, and modulating epigenetic landscapes of host immune regulatory genes. Furthermore, the review also discusses the diagnostic potential of various leishmanial virulence factors and the advent of immunomodulators as futuristic antileishmanial drug therapy.

Intranasal vaccine from whole Leishmania donovani antigens provides protection and induces specific immune response against visceral leishmaniasis

Visceral leishmaniasis is a protozoan disease associated with high fatality rate in developing countries. Although the drug pipeline is constantly improving, available treatments are costly and live-threatening side effects are not uncommon. Moreover, an approved vaccine against human leishmaniasis does not exist yet. Using whole antigens from Leishmania donovani promastigotes (LdAg), we investigated the protective potential of a novel adjuvant-free vaccine strategy. Immunization of mice with LdAg via the intradermal or the intranasal route prior to infection decreases the parasitic burden in primary affected internal organs, including the liver, spleen, and bone marrow. Interestingly, the intranasal route is more efficient than the intradermal route, leading to better parasite clearance and remarkable induction of adaptive immune cells, notably the helper and cytotoxic T cells. In vitro restimulation experiments with Leishmania antigens led to significant IFN-γ secretion by splenocytes; therefore, exemplifying specificity of the adaptive immune response. To improve mucosal delivery and the immunogenic aspects of our vaccine strategy, we used polysaccharide-based nanoparticles (NP) that carry the antigens. The NP-LdAg formulation is remarkably taken up by dendritic cells and induces their maturation in vitro, as revealed by the increased expression of CD80, CD86 and MHC II. Intranasal immunization with NP-LdAg does not improve the parasite clearance in our experimental timeline; however, it does increase the percentage of effector and memory T helper cells in the spleen, suggesting a potential induction of long-term memory. Altogether, this study provides a simple and cost-effective vaccine strategy against visceral leishmaniasis based on LdAg administration via the intranasal route, which could be applicable to other parasitic diseases.

Visceral leishmaniasis is a neglected tropical disease caused by specific species of Leishmania parasites that affect internal organs including spleen, liver, and bone marrow. The infective stage called promastigote, is transmitted into the host skin via sandfly bites. Visceral leishmaniasis is usually associated with high mortality rate in poor and developing countries, lacking proper health assistance. Moreover, treatments are expensive while no approved vaccines exist to prevent infection and avoid disease outbreaks. This study suggests an affordable and adjuvant-free vaccine formulation made from the total lysate of promastigotes. Vaccine administration via the intranasal route, ensures a remarkable clearance of Leishmania parasites from the internal organs of infected experimental mice. In particular, intranasal route known to be not invasive, is efficient in inducing adequate immune response against the infective form of the parasite. Further studies are now required to improve this prophylactic vaccine and provide therefore the basis for a promising translational approach.

Development and Clinical Evaluation of Serum and Urine-Based Lateral Flow Tests for Diagnosis of Human Visceral Leishmaniasis

Visceral leishmaniasis (VL), a fatal parasitic infection, is categorized as being neglected among tropical diseases. The use of conventional tissue aspiration for diagnosis is not possible in every setting. The immunochromatography-based lateral flow assay (LFA) has attracted attention for a long time due to its ability to give results within a few minutes, mainly in resource-poor settings. In the present study, we optimized and developed the LFA to detect anti-Leishmania antibodies for VL diagnosis. The performance of the developed test was evaluated with serum and urine samples of Indian VL patients and Brazilian sera. The new test exploits well-studied and highly-sensitive purified antigens, LAg isolated from Leishmania donovani promastigotes and protein G conjugated colloidal-gold as a signal reporter. The intensity of the bands depicting the antigen-antibody complex was optimized under different experimental conditions and quantitatively analyzed by the ImageJ software. For the diagnosis of human VL in India, LFA was found to be 96.49% sensitive and 95% specific with serum, and 95.12% sensitive and 96.36% specific with urine samples, respectively. The sensitivity and specificity of LFA were 88.57% and 94.73%, respectively, for the diagnosis of Brazilian VL using patients' sera infected with Leishmania infantum. LFA is rapid and simple to apply, suitable for field usage where results can be interpreted visually and particularly sensitive and specific in the diagnosis of human VL. Serum and urine LFA may improve diagnostic outcomes and could be an alternative for VL diagnosis in settings where tissue aspiration is difficult to perform.

Adjuvant effects of TLR agonist gardiquimod admixed with Leishmania vaccine in mice model of visceral leishmaniasis

Tropical and subtropical areas of the world are affected by leishmaniasis, which is caused by Leishmania spp. It has been categorized as an NTD (neglected tropical disease) because of its negligence. The sand fly of genus Phlebotomus acts as the vector for the transmission of the promastigote form of this protozoan parasite to the mammalian host where it converts to amastigote form in the macrophages. Visceral form of leishmaniasis (VL) is a deadly infection in the endothelial system of the human and other mammals. Only a few chemotherapeutic agents are available for the treatment of this infectious disease whereas no vaccine is available for the control of leishmanial infection. Therefore in the current study, we have tested the effects of gardiquimod (a TLR agonist) as an adjuvant in combination with the formalin-killed antigen of L. donovani as a vaccine. The mice were vaccinated thrice at an interval of 2 weeks and challenged with L. donovani promastigotes after 2 weeks of the last vaccination. We assessed the parasite load, delayed-type hypersensitivity (DTH) responses, humoral and cell-mediated immune response in BALB/c mice before and after challenge infection with L. donovani. Immunized mice were found to have the least parasite load, high DTH response, elevated levels of Th1 cytokines, IgG2a, and nitric oxide than non-immunized and infected control mice. The efficacy of the vaccine was boosted with the use of adjuvant gardiquimod that depicts its potential as an adjuvant in this study. Our study is reporting the adjuvant effects of gardiquimod for the first time. Further studies using other Leishmania species can be performed to signify its role.

Laboratory Diagnosis of Cutaneous and Visceral Leishmaniasis: Current and Future Methods

Leishmaniasis is a neglected tropical disease with two main clinical forms: cutaneous and visceral leishmaniasis. Diagnosis of leishmaniasis is still a challenge, concerning the detection and correct identification of the species of the parasite, mainly in endemic areas where the absence of appropriate resources is still a problem. Most accessible methods for diagnosis, particularly in these areas, do not include the identification of each one of more than 20 species responsible for the disease. Here, we summarize the main methods used for the detection and identification of leishmaniasis that can be performed by demonstration of the parasite in biological samples from the patient through microscopic examination, by in vitro culture or animal inoculation; by molecular methods through the detection of parasite DNA; or by immunological methods through the detection of parasite antigens that may be present in urine or through the detection of specific antibodies against the parasite. Potential new methods that can be applied for laboratory diagnosis of leishmaniasis are also discussed.

Evaluation of Cysteine Protease C of Leishmania donovani in Comparison with Glycoprotein 63 and Elongation Factor 1α for Diagnosis of Human Visceral Leishmaniasis and for Posttreatment Follow-Up Response

Visceral leishmaniasis (VL) is a threat in many developing countries. Much effort has been put to eliminating this disease, for which serodiagnosis remains the mainstay for VL control programs. New and improved antigens as diagnostic candidates are required, though, as the available antigens fail to demonstrate equal optimum performance in all areas of endemicity. Moreover, these diagnoses are dependent on invasive serum sampling. In the current study, we cloned and expressed Leishmania donovani cysteine protease C (CPC) and evaluated its diagnostic and test-of-cure possibilities by detecting the antibody levels in human serum and urine through ELISA and immunoblot assays. Two immunodominant antigens, recombinant glycoprotein 63 (GP63) and elongation factor 1α (EF1α), identified earlier by our group, were also assessed by employing human serum and urine samples. Of these three antigens in ELISAs, CPC demonstrated the highest sensitivities of 98.15% and 96% positive testing in serum and urine of VL patients, respectively. Moreover, CPC yielded 100% specificity with serum and urine of nonendemic healthy controls compared to GP63 and EF1α. Urine samples were found to be more specific than serum for distinguishing endemic healthy controls and other diseases by means of all three antigens. In all cases, CPC gave the most promising results. Unlike serum, urine tests demonstrated a significant decrease in antibody levels for CPC, GP63, and EF1α after 6 months of treatment. The diagnostic and test-of-cure performances of CPC in the immunoblot assay were found to be better than those of GP63 and EF1α. In conclusion, CPC, followed by GP63 and EF1α, may be utilized as candidates for diagnosis of VL and to assess treatment response.