According to WHO, leishmaniasis is endemic in 98 countries, and has been placed ninth in a global analysis of infectious diseases. Treatment of leishmaniasis is based on pentavalent antimonials but toxicity and developing resistance have been reported. Traditional medicine and scientific studies have shown that the extract of Galipea longiflora Krause (Evanta) exhibits antileishmanial activity. We hypothesized that the healing observed when using this plant might not only be due to the direct action on the parasite, but possibly to a parallel effect on the host immune response. We found that an alkaloid extract of Evanta (AEE) inhibited the growth of Leishmania braziliensis promastigotes while viability of eukaryotic cells was practically not affected. We also found that AEE interfered with polyclonal activation or Leishmania-specific re-stimulation of lymphocytes, as revealed by a reduction of in vitro cellular proliferation and IFN-g production. More important, AEE treatment of mice hosting L. braziliensis showed that AEE is able to control both inflammation and parasite load. Additionally, the healing process was improved when AEE and meglumine antimoniate were administered simultaneously. Dendritic cells (DCs) play a pivotal role in T-cell stimulation and polarization of naïve T cells. Therefore, we investigated if AEE could alter the activation of DCs and if allostimulatory DCs properties were altered if activated in the presence of AEE. DCs activated in the presence of AEE reduced the production of IL-12p40 and IL-23. When we analyzed the allostimulatory capacity of AEE-treated DCs, we found that allogeneic CD4+ T-cells secreted lower levels of IFN-γ. In conclusion, this thesis provides valuable insight into the effects of Evanta derived extract. The dual effect found for AEE, on Leishmania parasite and on the immune response, suggests that AEE may be useful in controlling the parasite burden and preventing over-production of inflammatory mediators and subsequently avoiding tissue damage. / <p>At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 2: Accepted. Paper 3: Submitted.</p>