We focused on the mode of action of CD8+ T cells in murine visceral leishmaniasis and their contribution to the clearance of the parasite. Genetically curative C57BL/6 and non-curative ΒΑLB/c mice were infected with L. infantum, the most common cause of visceral leishmaniasis in the Mediterranean basin. It has been showed that the spleen of infected BALB/c mice contained parasite-specific CD8+ lymphocytes shared a TC1 pattern of differentiation in an environment of compromised TH1 response. These cells had up regulated the CD25 and CD69 surface antigens and were capable to lyse target cells pulsed with Leishmania peptides and Leishmania-infected macrophages through the perforin pathway of cytotoxicity. TC lymphocytes had also the ability to kill target cells by apoptosis, as they over expressed FasL. An equally important function of this cell subset in visceral leishmaniasis was the production of massive amount of cytokines (IFN-γ and TNFα) and C-C chemokines (MIP-1α and RANTES).
On the other hand, in cure C57BL/6 mice the role of TC lymphocytes was of markedly lesser importance, as the number of parasite-specific CD8+ T cells remained very low, cytotoxicity was limited to the first weeks of infection, TNF production was virtually absent and chemokine (especially RANTES) production was limited. However, they retained the ability to secrete IFN-γ, and were thus characterized as TC1 cells. Experiments in TNF-/- mice showed that the major mediator of apoptosis was TNF. Infection of β2-microglobulin-/- mice allowed us to assess the in vivo contribution of CD8+ T cells in the resolution of visceral leishmaniasis in the curative experimental model.
  
 
Impact of L. infantum infection οn macrophage function: role of MAP kinases 
   
MAP kinases – ERK1/2, JNK and p38 – differentially regulate iNOS and IL-12 gene expression in LPS-stimulated macrophages. In vitro infection of LPS-stimulated macrophages obtained from BALB/c mice, with L. infantum, led to the phosphorylation of MAP kinases and the iNOS and IL-12 genes transcription resulting in the reduction of parasite load. Use of MAP kinase inhibitors demonstrated that JNK and p38 MAP kinases play an important role in the induction of iNOS, while ERK1/2 does not. In addition, p38 MAP kinase induces IL-12 gene transcription, in contrast to ERK1/2 and JNK activation which abrogate IL-12 production. These findings indicate that NO and IL-12 inhibition by Leishmania parasites is JNK- and p38 MAP kinase-mediated, suggesting these molecules as candidate targets for immune intervation.
 
 
DCs and their role in the induction of protective immunity in L. major infection 
 
In the context of DC-based vaccination strategy, we investigated the capability of bone marrow derived DCs-pulsed with Leishmania gp63 peptides to induce protective immunity against L. major infection. To this end, susceptible BALB/c mice were vaccinated with DCs-pulsed with gp63 epitopes 154-169aa and 467-482aa and subsequently challenged with L. major promastigotes.  DCs pulsed with gp63 epitope 154-169aa triggered antigen-specific immune responses able to reduce lesion formation and parasite load in BALB/c mice. This effect was accompanied by a modulation of the immune response towards Th1 type as confirmed by the cytokine secretion (IFN-γ vs IL 4) and parasite-specific antibodies profile (IgG2a vs IgG1). DCs-pulsed with gp63 epitopes 467-482aa failed to instruct Th1 response.
In contrast, vaccination of resistant CBA mice with DCs-pulsed with gp63 epitopes 467-482aa resulted in a shift towards a Th2 cellular immune response that justified the exacerbation of lesions. These findings suggest that vaccination with DCs pulsed with defined peptides could be a strategy against infectious diseases. Peptide selection is a prerequisite as they can differentially regulate the type of immune response in susceptible or resistant hosts.
Other attempts to explore novel vaccination approaches included vaccination of BALB/c mice with a plasmid carrying a truncated gp63 cDNA resulted in the exacerbation of the local inflammatory reaction. In contrast, the co-administration of this plasmid with another encoding CD40L induced protection in