No abstract

Abstract. Correlations between the genetic diversity of Leishmania infantum (syn. L. chagasi) isolates and their respective geographic origins support the theoretic assumption that visceral leishmaniasis probably originated in the Old World. Because dogs are widely considered to be the main reservoir of this disease, the present study aimed to investigate the degree of genetic divergence among 44 leishmanial canine isolates from two Brazilian cities, Jequié and Campo Grande, located approximately 2,028 km from each other. We hypothesized that a low degree of genetic divergence would be observed among these isolates. In fact, statistical analyses found no significant differences between the isolates using both random amplified polymorphic DNA and multilocus microsatellite typing genotyping techniques with three and seven markers, respectively. These findings provide support for the recent introduction of L. infantum into the New World.

While the response to Leishmania spp. is well characterized in mice and humans, much less is known concerning the canine immune response, particularly soon after exposure to the parasite. Early events are considered to be a determinant of infection outcome. To investigate the dog's early immune response to L. chagasi, an in vitro priming system (PIV) using dog naïve PBMC was established. Until now, dog PIV immune response to L. chagasi has not been assessed. We co-cultivated PBMC primarily stimulated with L. chagasi in vitro with autologous infected macrophages and found that IFN-gamma mRNA is up-regulated in these cells compared to control unstimulated cells. IL-4 and IL-10 mRNA expression by L. chagasi-stimulated PBMC was similar to control unstimulated PBMC when incubated with infected macrophages. Surprisingly, correlation studies showed that a lower IFN-gamma/IL-4 expression ratio correlated with a lower percentage of infection. We propose that the direct correlation between IFN-gamma/IL-4 ratio and parasite load is dependent on the higher correlation of both IFN-gamma and IL-4 expression with lower parasite infection. This PIV system was shown to be useful in evaluating the dog immune response to L. chagasi, and results indicate that a balance between IFN-gamma and IL-4 is associated with control of parasite infection in vitro.