Establishment of
Leishmania infection inside macrophages requires deactivation of various signaling pathways that are dispensable for effective immune responses against the parasite. In the present study, we provide evidence that Leishmania infantum promastigotes attachment on the surface of peritoneal macrophages, internalization and transformation to amastigotes abrogated the activation of extracellular signal-regulated
protein kinases (ERK) 1/2,
p38 mitogen activated protein kinases (MAPK) and c-Jun NH2-terminal
kinases (JNK) and the production of pro-inflammatory
cytokines IL-12 and
TNFalpha. Subsequent macrophage stimulation with
lipopolysaccharide (LPS) during the first hours of exposure to parasite or
infection resulted in restoration of MAPK phosphorylation. However, LPS-mediated MAPK activation required parasite internalization (uptake) since
cytochalasin-D pretreated macrophages did not responded to LPS stimulation.
IL-12,
TNFalpha, and NO production was positively regulated with MAPK phosphorylation in contrast to
nuclear factor-kappaB (
NF-kB) which was MAPK independent. Specifically, inhibition of MAPK activation with specific inhibitors revealed that
IL-12 production required
p38 MAPK activation, whereas
TNFalpha and NO production required all three MAPK. The restoration of NO production resulted in decrease of
infection rates. Hence, these results suggest that in contrast to phagocytosis of L. infantum promastigotes, establishment of
infection does not desensitize macrophages to subsequent stimulation with LPS, resulting in parasite elimination through MAPK and NF-κB activation and partial restoration of
IL-12,
TNFalpha and NO synthesis.