Mucosal pathogens have been studied especially, Helicobacter in a mouse model, Shigella in a rabbit model and Listeria in a guinea pig model combined with the use of transgenic mouse model.
* Helicobacter induces a chronic gastritis in the mouse model studied with the team of R. Ferrero and A. Labigne (Unité de Pathogénie Microbienne des Muqueuses). Outbred mice with long term Helicobacter felis infection develop gastric lymphoid tissue and glandular hyperplastic lesions. B lymphocytes are numerous in the lamina propria of the antrum, suggesting a chronic recruitment of polyclonal lymphocytes without argument of maltoma like lesions. No atypical and preneoplastic lesions of epithelial components have been seen. A study is in progress with high mutation rate mice.
* A Listeria model has been studied with the team of P. Cossart (M. Lecuit et al, Unité des Interactions Bactéries-Cellules). The work of histopathology Unit was to demonstrate the crossing of the epithelial barrier with Listeria monocytogenes. Using transgenic mice expressing human E-caherin, it has been demonstrated that internalin, is a critical and specific ligand of cadherin, allowing the invasion of enterocytes and translocation within the macrophages of deeper tissues.
* The team of P. Sansonetti (C. Wenneras, A. Phalipon, Unité de pathogénie microbienne moléculaire) is working on a rabbit model of shigellosis. In collaboration, we have investigated the role of CD-14 endotoxin and LPS receptor. Various animal species, lacking functionnal CD-14 were protected against endotoxin mediated shock, suggesting a decreased local inflammation. In the shigella model, the blockade of CD-14 increased Shigella-mediated invasion and tissue destruction, suggesting that CD-14 interfers with the defense mechanism.
We have investigated in several models of infectious diseases: dengue fever, Rift valley fever, West Nile virus, Human T cell leukaemia virus and lymphomas in HIV positive patients.
* In collaboration with the Pasteur Institute in Vietnam, five cases of dengue fever hepatitis in children have been studied. It has been demonstrated that the liver is a specific target for dengue virus showing midzonal necrosis, steatosis and Councilman bodies. Dengue virus antigens were detected using immunohistochemistry in hepatocytes. There is no recruitment of lymphocytes and polymorphonuclear cells, and the Councilman body is an apoptotic cell, as in the pathogenesis of yellow fever.
* Rift valley fever induces an acute hepatitis in human pathology and a mouse model is available, showing a reproducible acute hepatitis in three or four days.( Collaboration Michèle Bouloy, Unité des Arbovirus) The virus is detected in the Kuppfer cells and hepatocytes at the second day (confirmed by Immunohistochemistry and in situ hybridization) It has been demonstrated that interferon was essential to control virus replication.
* We are working with V. Deubel (Unité des Arbovirus et Fièvres Hémorragiques) on a murine model of West-Nile virus infection. We are interested in the physiopathology of this infection. West-Nile virus is Flavivirus (Arbovirus), transmitted by mosquitoes to numerous species of Vertebrates. Epidemics have broke out in last years in man, horse and birds. Recent letal cases in New York of West-Nile encephalitis have stimulated interest for this virus. We have studied the lesions induced by two different strains of West-Nile virus (Israel or Senegal). Different routes of inoculation wer compared (i.n., i.p., i.d.). We observed clear differents in the incidence and severity of central nervous system lesions and amount of antigen in infected cells according to the strain and the route of inoculation.
We have investigated two diseases due to protozoa: Cryptosporidium parvum colitis in HIV positive patients (Collaboration with N. Brousse,Laboratory of Pathology, Necker-Enfants Malades hospital) and Leishmania in a mouse model.( Collaboration with T. Lang, J.C. Antoine and G. Milon from the Unit of Immunophysiology and intracellular parasitism) Another collaborative program on experimental leishmaniasis is in progress with a team of pasteur Institute in Lille.
2) Analysis of genes expression and function in vivo
Inactivation of SFN5 and tumors.
We have studied 53 tumors that arised in SNF5+/- mice. hSNF5 is a chromatin remodeling factor. Numerous data lead to think that it is a tumor suppressor gene. Somatic or constitutive mutations of this gene are found most often in rhabdoid tumors, very agressive tumors in child. A loss-of function mutation has been generated by homologousrecombination in the laboratory of M. Yaniv (A. Yeivin, Unité des Virus Oncogènes). Inactivation of both alleles of SNF5 is letal during embryogenesis. In 32% of the heterozygotes of the age of 4 months to 15 months, tumors were detected with preferential locations: 30 % were intracranial, 27 % around the dorsal root ganglia of the cervical spinal cord. These tumors appeared microscopically as indifferentiated sarcomas, that contained in 30 % of cases a variable number of rhabdoid cells. The immuno-phenotype of the tumors was heterogeneous: all were vimentin +, and expressed PS 100, N.G.F.-R(p75), or G.F.A.P or not. These markers suggest that tumors cells are derived from the neural crest. Immuno-labelling against others markers was negative (cytokeratins, E.M.A., desmin, myosin, myoglobin, N.S.E).
Role of vHNF1 in liver differentiation.
We are interested in the consequences of vHNF1 inactivation in liver differentiation L. Gresh, M. Yaniv, Unité des Virus Oncogènes). vHNF1 is a transcription factor, early and strongly expressed during developpement and is implicated in epithelial differentiation. The inactivation of vHNF1 lethal at 7,5. Using the cre-lox system of conditional inactivation, C. Coffinier has obtained a loss of function of vHNF1 restricted to the liver. In this murine strain, biliary sytem and perilobular arteries are not normally developped.
Role of Vimentin in tumorigenesis
F. Langa, E. Collucci, S. Pournael and C. Babinet , Unité de Biologie du Développement)
Teratocarcinoma derived from ES cells were studied in transgenic mice without vimentin compared to wild type. It has been demonstrated that the absence of vimentin did not affect the growth rate of experimental tumors, the size, vascularization and differenciation of ectoderm, endoderm and mesoderm components in all possible combinations ( Vim -/- or +/+ ES cells into Vim-/- or Vim+/+ mice. These results demonstrates that vimentin is not essential for efficient tumor growth and differenciation in vivo. .