Comparative analysis of biological aspects of Leishmania infantum isolates

Abstract

Leishmania infantum infantum (LII) is one of the species that causes visceral leishmaniasis (VL) in the Old World, while L. infantum chagasi (LIC), and is present in the New World. Few studies address the biological differences, as well as the behaviour of these strains during infection. These parasites live inside the cells of their hosts, continuously evading the microbicidal mechanisms and modulating the immune response of these cells. One of the mechanisms used by these protozoa involves the L-arginine metabolism. Given the importance of the understanding of differences between Leishmania species, as well as establishing a better murine model to study leishmaniases, the objectives of this work were to analyse the biological and molecular differences between two Leishmania infantum strains (LII and LIC) and the degree of susceptibility of mice with different genetic backgrounds to infection, as well as to understand the role of arginase (ARG)/nitric oxide synthase (NOS) in the parasite-host relationship. The infectivity in vivo and in vitro of LII and LIC was performed in BALB/c and Swiss Webster mice, as well the NOS and ARG activities. The LII strain showed more infective than the LIC strain both in vivo and in vitro. In animals infected by both strains, a difference in NOS and ARG activities occurred. In vitro, promastigotes of LII isolated from BALB/c and Swiss Webster mice showed higher ARG activity than the LIC during the growth curve, however, no difference was observed in intracellular NO production by promastigotes between these strains. A comparison of the sequences of the ARG gene was made and both strains were identical. However, despite the similarity, the strains showed different expression of this gene. It can be concluded that although L. chagasi strains are considered identical to L. infantum strains, both have different biological behaviour.