Deficiency of Leishmania phosphoglycans influences the magnitude but does not affect the quality of secondary (memory) anti-Leishmania immunity

Quantitative single-cell analysis of Leishmania major amastigote differentiation demonstrates variably extended expression of the lipophosphoglycan (LPG) virulence factor in different host cell types

Immediately following their deposition into the mammalian host by an infected sand fly vector, Leishmania parasites encounter and are engulfed by a variety of cell types. From there, parasites may transit to other cell types, primarily macrophages or dendritic cells, where they replicate and induce pathology. During this time, Leishmania cells undergo a dramatic transformation from the motile non-replicating metacyclic stage to the non-motile replicative amastigote stage, a differentiative process that can be termed amastigogenesis. To follow this at the single cell level, we identified a suite of experimental 'landmarks' delineating different stages of amastigogenesis qualitatively or quantitatively, including new uses of amastigote-specific markers that showed interesting cellular localizations at the anterior or posterior ends. We compared amastigogenesis in synchronous infections of peritoneal and bone-marrow derived macrophages (PEM, BMM) or dendritic cells (BMDC). Overall, the marker suite expression showed an orderly transition post-infection with similar kinetics between host cell types, with the emergence of several amastigote traits within 12 hours, followed by parasite replication after 24 hours, with parasites in BMM or BMDC initiating DNA replication more slowly. Lipophosphoglycan (LPG) is a Leishmania virulence factor that facilitates metacyclic establishment in host cells but declines in amastigotes. Whereas LPG expression was lost by parasites within PEM by 48 hours, >40% of the parasites infecting BMM or BMDC retained metacyclic-level LPG expression at 72 hr. Thus L. major may prolong LPG expression in different intracellular environments, thereby extending its efficacy in promoting infectivity in situ and during cell-to-cell transfer of parasites expressing this key virulence factor.

Selective activity of Oleanolic and Maslinic Acids on the Amastigote form of Leishmania Spp

Leishmaniasis represents a serious threat to the health as one of the most important neglected tropical diseases as designated by the World Health Organization. The disease is endemic in 82 countries, among them Tunisia is an indigenous area for cutaneous Leishmaniasis. In a previous work, two tritepenic acids namely oleanolic and maslinic acids have been isolated from olive leaf extract. In the present paper, the in vitro activity against amastigotes stage of Leishmania (L.) infantum and Leishmania (L.) amazonensis was investigated. Maslinic acid showed the highest activity, against L. amazonensis, with an IC₅₀ of 1.417 ± 0.401 µg/mL and a selectivity index of 9.405. Although, the oleanolic acid exhibit a better activity against L. infantum with an IC₅₀ of 0.999 ± 0.089 µg/mL and selectivity index of 8.111.

Cutaneous Infection with Leishmania major Mediates Heterologous Protection against Visceral Infection with Leishmania infantum

Visceral leishmaniasis (VL) is a fatal disease of the internal organs caused by the eukaryotic parasite Leishmania. Control of VL would best be achieved through vaccination. However, this has proven to be difficult partly because the correlates of protective immunity are not fully understood. In contrast, protective immunity against nonfatal cutaneous leishmaniasis (CL) is well defined and mediated by rapidly recruited, IFN-γ-producing Ly6C(+)CD4(+) T cells at the dermal challenge site. Protection against CL is best achieved by prior infection or live vaccination with Leishmania major, termed leishmanization. A long-standing question is whether prior CL or leishmanization can protect against VL. Employing an intradermal challenge model in mice, we report that cutaneous infection with Leishmania major provides heterologous protection against visceral infection with Leishmania infantum. Protection was associated with a robust CD4(+) T cell response at the dermal challenge site and in the viscera. In vivo labeling of circulating cells revealed that increased frequencies of IFN-γ(+)CD4(+) T cells at sites of infection are due to recruitment or retention of cells in the tissue, rather than increased numbers of cells trapped in the vasculature. Shortly after challenge, IFN-γ-producing cells were highly enriched for Ly6C(+)T-bet(+) cells in the viscera. Surprisingly, this heterologous immunity was superior to homologous immunity mediated by prior infection with L. infantum. Our observations demonstrate a common mechanism of protection against different clinical forms of leishmaniasis. The efficacy of leishmanization against VL may warrant the introduction of the practice in VL endemic areas or during outbreaks of disease.

An overview on Leishmania vaccines: A narrative review article

Leishmaniasis is one of the major health problems and categorized as a class I disease (emerging and uncontrolled) by World Health Organization (WHO), causing highly significant morbidity and mortality. Indeed, more than 350 million individuals are at risk of Leishmania infection, and about 1.6 million new cases occur causing more than 50 thousands death annually. Because of the severe toxicity and drug resistance, present chemotherapy regimen against diverse forms of Leishmania infections is not totally worthwhile. However, sound immunity due to natural infection, implies that vigor cellular immunity against Leishmania parasites, via their live, attenuated or killed forms, can be developed in dogs and humans. Moreover, genetically conserved antigens (in most of Leishmania species), and components of sand fly saliva confer potential immunogenic molecules for Leishmania vaccination. Vaccines successes in animal studies and some clinical trials clearly justify more researches and investments illuminating opportunities in suitable vaccine designation.