Lipophosphoglycan-3 protein from Leishmania infantum chagasi plus saponin adjuvant: A new promising vaccine against visceral leishmaniasis.

Visceral leishmaniasis (VL) is a serious neglected tropical disease that affects humans and dogs in urban areas. There are no vaccines against human VL, and few licensed canine VL vaccines are currently available, which instigates the search for new antigens and vaccine formulations with prophylactic potential against VL in these hosts. In this study, we evaluated the immunization using the native and recombinant Leishmania infantum chagasi (L. chagasi) lipophosphoglycan-3 (LPG3) and the adjuvants saponin (SAP) and incomplete Freund adjuvant (IFA) against L. chagasi infection in BALB/c mice. The native LPG3 vaccine was immunogenic, inducing splenic IFN-γ and IL-10 production, and mixed Th1/Th2 response when associated with IFA. However, only mice vaccinated with LPG3-IFA presented a reduction in the splenic parasite load (96% in comparison to the PBS control group), but without a significant reduction in the hepatic parasitism. On the other hand, mice immunized with the LPG3-SAP vaccine presented a reduction of approximately 98% in both splenic and hepatic parasite load, accompanied by a Th1/Th17 response and IL-10 production by L. chagasi antigen (AgLc)-stimulated splenic cells. Importantly, vaccination with recombinant LPG3 (rLPG3)-SAP presented similar results to the native LPG3-SAP vaccine. Therefore, the rLPG3-SAP vaccine is qualified to be used in future tests in canine and human models, considering the technical and economic advantages of the recombinant protein production compared to the native protein and the results obtained in the murine model.

Lipophosphoglycan 3 From Leishmania infantum chagasi Binds Heparin With Micromolar Affinity.

Leishmania infantum chagasi is an intracellular protozoan parasite responsible for visceral leishmaniasis, a fatal disease in humans. Heparin-binding proteins (HBPs) are proteins that bind to carbohydrates present in glycoproteins or glycolipids. Evidence suggests that HBPs present on Leishmania surface participate in the adhesion and invasion of parasites to tissues of both invertebrate and vertebrate hosts. In this study, we identified the product with an HSP90 (heat shock protein 90) domain encoded by lipophosphoglycan (LPG3) gene as a L infantum chagasi HBP (HBPLc). Structural analysis using the LPG3 recombinant protein suggests that it is organized as a tetramer. Binding analysis confirms that it is capable of binding heparin with micromolar affinity. Inhibition of adenosine triphosphatase activity in the presence of heparin, molecular modeling, and in silico docking analysis suggests that heparin-binding site superimposes with the adenosine triphosphate-binding site. Together, these results show new properties of LPG3 and suggest an important role in leishmaniasis.

Extracellular nucleotide metabolism in Leishmania: influence of adenosine in the establishment of infection.

Leishmaniasis is a parasitic disease with a variety of clinical forms, which are related to the Leishmania species involved. In the murine model, Leishmania amazonensis causes chronic non-healing lesions in Leishmania braziliensis- or Leishmania major-resistant mouse strains. In this study, we investigated the involvement of the pathway of extracellular nucleotide hydrolysis, with special focus on the role of extracellular adenosine, in the establishment of Leishmania infection. Our results show that the more virulent parasite--L. amazonensis--hydrolyzes higher amounts of ATP, ADP and AMP than the two other species, probably due to the higher expression of membrane NTPDase. Corroborating the idea that increased production of adenosine is important to lesion development and establishment of tissue parasitism, we observed that increased 5'-nucleotidase activity in L. braziliensis or addition of adenosine at the moment of infection with this parasite resulted in an increase in lesion size and parasitism as well as a delay in lesion healing. Furthermore, inhibition of adenosine receptor A2B led to decreased lesion size and parasitism. Thus, our results suggest that the conversion of ATP, a molecule with pro-inflammatory activity, into adenosine, which possesses immunomodulatory properties, may contribute to the establishment of infection by Leishmania.