Étude des mécanismes de régulation négative utilisés par Leishmania pour contrer la réponse immunitaire innée

Authors: Forget, Geneviève
Advisor: Olivier, Martin
Abstract: The intracellular protozoan parasite Leishmania has been known for its ability to evade its host immune response principally by inhibiting phagocyte functions. Indeed, infected macrophages show a loss of microbicidal (NO, oxygen intermediates) and immunological activities (IL-1, IL-12, MHC). This allows for its replication and invasion of the host. These dysfunctions are correlated by alterations in signalling cascades depending on Ca2+, PKC, JAK2/STAT1α and MAPK ERK1/2. It has also been reported that Leishmania infection could induce the macrophage phosphotyrosine phosphatase (PTP) activity and more specifically that of PTP SHP-1, a strong negative regulator of tyrosine kinase-dependent pathways. Moreover, the use of PTP inhibitors showed their essential role in parasite survival both in vivo and in vitro. These results suggested a potential role for SHP-1 in parasite survival and in the inhibition of macrophages. To address this issue, SHP-1-deficient mice, the viable motheaten mice, and their bone marrow-derived macrophages were infected with Leishmania. Results show that footpad inflammation was virtually absent in SHP-1-deficient mice and depended on inducible nitric oxide synthase increased activity as well as inflammatory cells recruitment, especially neutrophils. This recruitment seemed to be due to increases in pro-inflammatory cytokines expression and secretion and in chemokine gene expression. SHP-1-deficient mice had both more inflammatory cells numbers and a higher ratio of neutrophils, recognized for their microbicidal action against Leishmania. In vitro, SHP-1 activity seemed essential for parasite survival by allowing the attenuation of NO-dependent and -independent mechanisms. Furthermore, its alteration of NO generation in infected cells was due to the dephosphorylation of JAK2 and ERK1/2 as well as inhibition of transcription factors NF-κB and AP-1. However, SHP-1 was not responsible for the inhibition of transcription factor STAT1α seen in infected macrophages. This phenomenon seemed due to specific proteasomal degradation of the protein. Overall, the present thesis demonstrates that Leishmania is a versatile parasite able to use several strategies to alter its host responsiveness, two of them being the essential activation of SHP-1 and the targeting of STAT1α to the proteasomal degradation pathway.
Document Type: Thèse de doctorat
Issue Date: 2004
Open Access Date: 11 April 2018
Permalink: http://hdl.handle.net/20.500.11794/17871
Grantor: Université Laval
Collection:Thèses et mémoires

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