Small Myristoylated Protein-3, Identified as a Potential Virulence Factor in Leishmania amazonensis, Proves to be a Protective Antigen against Visceral Leishmaniasis.

Marcelo Oliveira,Thaís Santos,Vívian Martins,Lourena Costa,Antônio Teixeira,Patrícia Ribeiro,Daniel Dias,Ricardo Machado-De-Ávila,Beatriz Salles,Miguel Chávez-Fumagalli,Fernanda Ramos,Daniela Lage,Eduardo Coelho,Mônica Schneider

doi:10.3390/ijms19010129

Abstract

In a proteomics approach conducted with Leishmania amazonensis, parasite proteins showed either an increase or a decrease in their expression content during extensive in vitro cultivation, and were related to the survival and the infectivity of the parasites, respectively. In the current study, a computational screening was performed to predict virulence factors among these molecules. Three proteins were selected, one of which presented no homology to human proteins. This candidate, namely small myristoylated protein-3 (SMP-3), was cloned, and its recombinant version (rSMP-3) was used to stimulate peripheral blood mononuclear cells (PBMCs) from healthy subjects living in an endemic area of leishmaniasis and from visceral leishmaniasis patients. Results showed high interferon-γ (IFN-γ) production and low levels of interleukin 10 (IL-10) in the cell supernatants. An in vivo experiment was then conducted on BALB/c mice, which were immunized with rSMP-3/saponin and later challenged with Leishmania infantum promastigotes. The rSMP-3/saponin combination induced high production of protein-specific IFN-γ, IL-12, and granulocyte-macrophage colony-stimulating factor (GM-CSF) by the spleen cells of the immunized mice. This pattern was associated with protection, which was characterized by a significant reduction in the parasite load in distinct organs of the animals. Altogether, these results have revealed that this new virulence factor is immunogenic in both mice and humans, and have proven its protective efficacy against visceral leishmaniasis in a murine model.

Highlights

Leishmaniasis is a vector-borne disease complex caused by protozoan parasites of the genus Leishmania, which presents a high morbidity and mortality worldwide
Together with the results of immunogenicity from in vitro experiments using peripheral blood mononuclear cells (PBMCs), we propose that rSMP-3 should be considered a promising antigen for the development of vaccines against visceral leishmaniasis (VL)
Statistical analysis of the in vitro stimulation of PBMCs and the vaccination experiments was performed by using the one-way analysis of variance (ANOVA)

Summary

Introduction

Leishmaniasis is a vector-borne disease complex caused by protozoan parasites of the genus Leishmania, which presents a high morbidity and mortality worldwide. Around 380 million people are at risk of infection in 98 countries, with approximately 1.5–2.0 million cases being registered annually [1]. The outcome of infection depends mainly of the immune response of the hosts and the virulence of the parasite strain [2]. About 54 Leishmania species are known, and at least 21 of these can cause human disease [4]. In Brazil, leishmaniasis is caused by at least six different Leishmania species. L. infantum is the main parasite species responsible for the cases of VL [7]

Objectives

Methods

Results

Discussion

Conclusion