Abstract
Leishmania infantum parasites cause a severe form of visceral leishmaniasis in human and viscerocutaneous leishmaniasis in dogs. Recently, we reported that immunization with an attenuated L. infantum cell line, lacking the hsp70-II gene, protects against the development of murine cutaneous leishmaniasis. In this work, we analyzed the vaccine potential of this cell line towards the long-term protection against murine visceral leishmaniasis. This model shows an organ-dependent evolution of the disease. The infection can resolve in the liver but chronically affect spleen and bone marrow. Twelve weeks after subcutaneous administration of attenuated L. infantum, Bagg Albino (BALB/c) mice were challenged with infective L. infantum parasites expressing the luciferase-encoding gene. Combining in vivo bioimaging techniques with limiting dilution experiments, we report that, in the initial phase of the disease, vaccinated animals presented lower parasite loads than unvaccinated animals. A reduction of the severity of liver damage was also detected. Protection was associated with the induction of rapid parasite-specific IFN-γ production by CD4+ and CD8+ T cells. However, the vaccine was unable to control the chronic phase of the disease, since we did not find differences in the parasite burdens nor in the immune response at that time point.
Highlights
Visceral leishmaniasis (VL), the more severe form of leishmaniasis, is caused by parasites of the species Leishmania donovani and Leishmania infantum
These data indicated that vaccination would be restricting parasite multiplication, at least in the liver, which only in the liver of the vaccinated mice, whereas similar numbers of parasites were found in the spleen and Bone Marrow (BM) in both mice groups (Figure 2, late)
Our results demonstrated that the Li∆HSP70-II-based vaccine, in addition to generating robust protection against L. major heterologous challenge [18,20], is capable of contributing to controlling the acute phase of the disease, characteristic of the experimental murine model of VL
Summary
Visceral leishmaniasis (VL), the more severe form of leishmaniasis, is caused by parasites of the species Leishmania donovani and Leishmania infantum. Infections in the Indian subcontinent and in the region of East Africa are caused by L. donovani, a species with an anthroponotic transmission cycle [1]. In some L. donovani patients, after apparent successful treatment, the infection evolves to a cutaneous clinical outcome, termed post-kala-azar dermal leishmaniasis (PKDL), which favors parasite dissemination by hematophagous sandflies [2]. Infected dogs are the principal reservoir for parasite transmission to humans [4]. In dogs, this species causes a severe disease, named viscerocutaneous canine leishmaniasis (CanL), which shows a wide range of clinical manifestations [5,6]
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