Down regulation of IL-10 and TGF-β1 mRNA expression associated with reduced inflammatory process correlates with control of parasitism in the liver after treating L. infantum infected dogs with the LBMPL vaccine therapy.

Abstract

The liver plays an important role in human and canine visceral leishmaniasis, then it is considered as target to understand the mechanisms involved in the parasite control and a parameter to assess therapeutic responses. In this sense, our study focuses on evaluating the major alterations in the liver by histological (morphometric parenchyma inflammation/semi-quantitative portal inflammation), immunohistochemical assays (parasitism), and qPCR (parasitism and cytokine gene expression) in Leishmania infantum naturally infected dogs and treated with LBMPL vaccine. Animals were divided in four groups: NI group (n = 5): uninfected and untreated dogs; INT group (n = 7): L. infantum-infected dogs and not treated; MPL group (n = 6): L. infantum-infected dogs that received only monophosphoryl lipid A adjuvant, and LBMPL group (n = 10): L. infantum-infected dogs that received treatment with the vaccine composed by L. braziliensis disrupted promastigotes associated with MPL adjuvant. Ninety days after the end of treatments, the dogs were euthanized, and the liver was collected for the proposed evaluations. Significantly lower portal inflammatory reactions, and lower parenchyma inflammation were observed in the LBMPL group compared to INT and MPL groups. iNOS mRNA expression was higher in LBMPL group and in contrast, IL-10 and TGF-β1 mRNA expression was lower in this group when compared to INT group. Immunohistochemical and qPCR analysis showed significant parasite load reduction in LBMPL group compared to INT and MPL animals. Our data suggest that in naturally Leishmania-infected dogs, LBMPL vaccine reduces the damage in the hepatic tissue, being able to attenuate the type 2 immune response. It could be associated with a marked reduction in the parasitism decreasing liver inflammation in treated dogs. Along with previously obtained data, our results suggest that LBMPL vaccine can significantly contribute to the therapy strategy for L. infantum infected dogs.