We apply a transdisciplinary approach to decipher the mechanisms of rupture, invasion and inflammatory destruction of mucosal barriers by pathogens, and host defenses.

Shigella, the agent of bacillary dysentery, invades epithelial cells and cause inflammation of the human colonic mucosa. We have identified the major virulence genes, their regulatory mechanisms, the mode of secretion and functions of encoded effectors. We develop imaging techniques to monitor infection in cells and tissues.

A « first wave » of polarly secreted effector molecules (i.e. Ipa proteins), causes characteristic phenotypes: bacterial macropinocytosis, escape into the cytoplasm and apoptotic killing of macrophages. We have established the fundamental role of c-src, upon its recruitment and activation by the Shigella protein IpaC, in the cytoskeletal remodelling leading to bacterial entry. IcsA causes actin dependent intra/intercellular spread. Cross-talks are amplified by paracrine signals (i.e. ATP) released through connexin-based channels. Very early steps of bacterial capture at cell surface through nanopodial structures have been unravelled and analyzed (Figure). Observation that Shigella invasion activates NF-κB in epithelial cells allowed us to identify Nod proteins as sensors of muropeptides released by intracellular bacteria. We are now showing that Shigella also strongly regulate the elicited innate response by expressing and secreting a « second wave » of effector molecules, Osp and IpaH. OspG is a kinase that binds and inhibits functions of the ubiquitinated ubiquitine-transfer enzymes E2 involved in the degradation of I-κB, thereby making it an anti-inflammatory protein. OspF translocates into the nucleus where it dephosphorylates MAPKinases (Erk1/2, P38), causes dephosphorylation of Histone H3 and suppresses accessibility to selected promoters like IL-8 to pro-inflammatory transcription factors, thereby acting as a potent regulator of neutrophils migration through the epithelium. OspF is also a potent regulator of adaptive immunity by suppressing expression of Th1 cytokines (i.e. IL-12 and IFNγ). IpaH molecules form a new family of E3 ubiquitine ligases whose targets are being identified. This is a new angle of analysis of the ways bacteria deceive host immunity, including epigenetic regulation of the innate response. Recent results demonstrate that these effectors suppress the expression of epithelial anti-microbial peptides and the trafficking of dendritic cells.

Based upon the fine analysis of Shigella virulence, we have recently opened a new line or research that aims at understanding how the commensal microbiota maintains the homeostasy of the gut crypt-villous axis (i.e. regulation of stern cell fate, control of epithelial proliferation) and differenciation) and how these homeostatic processes are disrupted by a pathogen like Shigella which was shown to regulate the major epithelial defense systems, including the mucins.

Development of vaccines : clinical trials are underway for S. flexneri 2a and S. dysenteriae1 oral candidates. We also develop a new approach based upon conjugated, chemically-synthetised O-polysaccharide antigens.

Klebsiellainfection : we study the cross-talks between Klebsiella pneumoniae with the tracheo-bronchial tree, and the functional genomics of closely-related K. pneumoniae and Klebsiella rhinoscleromatis expressing opposite infection strategies respectively acute, hyperinflammatory and chronic granulomatous.

Keywords: Shigella, inflammation, invasion, immunity, Klebsiella

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MOUNIER J, POPOFF MR, ENNINGA J, FRAME MC, SANSONETTI PJ, VAN NHIEU GT. The IpaC carboxyterminal effector domain mediates Src-dependent actin polymerization during Shigella invasion of epithelial cells. PLoS Pathog. 2009 Jan;5(1):e1000271.

PHALIPON A, TANGUY M, GRANDJEAN C, GUERREIRO C, BELOT F, COHEN D, SANSONETTI PJ, MULARD LA. A synthetic carbohydrate-protein conjugate vaccine candidate against Shigella flexneri 2a infection. J Immunol. 2009 Feb 15;182(4):2241-7.

DUPONT N, LACAS-GERVAIS S, BERTOUT J, PAZ I, FRECHE B, VAN NHIEU GT, VAN DER GOOT FG, SANSONETTI PJ, LAFONT F. Shigella phagocytic vacuolar membrane remnants participate in the cellular response to pathogen invasion and are regulated by autophagy. Cell Host Microbe. 2009 Aug 20;6(2):137-49.

PAZ I, SACHSE M, DUPONT N, MOUNIER J, CEDERFUR C, ENNINGA J, LEFFLER H, POIRIER F, PREVOST MC, LAFONT F, SANSONETTI P. Galectin-3, a marker for vacuole lysis by invasive pathogens. Cell Microbiol. 2009 Nov 27.