B7-H6, un membre de la famille B7, est exprimé sur diverses cellules tumorales humaines et active les cellules NK via NKp30. En revanche, B7-H6 n'est pas détecté à la surface d'aucunes cellules saines testées. Mon projet de thèse était d'identifier les mécanismes impliqués dans l'induction du gène B7-H6 et savoir si d'autres conditions que la transformation tumorale peuvent induire l'expression de B7-H6.Nous avons montré que B7-H6 est induit de façon sélective à la surface de neutrophiles et de monocytes CD14+CD16+, suite à des stimulations de type inflammatoire in vitro et in vivo. De plus, cette expression est de mauvais pronostic pour la survie de patients atteints de sepsis sévère. Nous avons également mis en évidence une forme soluble de B7-H6 produite, in vitro par des monocytes et des neutrophiles activés, et in vivo chez certains patients atteints de sepsis sévère à Gram négatif. Fait intéressant, cette forme soluble semble bloquer l'activité des cellules NK et avoir une tendance à être de mauvais pronostic pour la survie de ces patients.Par conséquent, mes travaux renforcent le concept immunologique selon lequel les ligands des récepteurs NK activateurs sont sous-exprimés dans les cellules saines et subissent une dérégulation qui les surexprime dans les cellules qui subissent. De plus, B7-H6 apparait comme un acteur potentiel dans l'immunité innée antibactérienne. La description systématique du profile de B7-H6 chez les patients atteins de sepsis pourrait permettre d'envisager de nouvelles prises en charge thérapeutiques basé sur les cellules NK et B7-H6 et aider à classer les patients en fonction de leur risque de développer une forme sévère de la maladie. / B7-H6, a new member of the B7 family, is expressed on several human tumor cells and triggers NKp30-mediated activation of human NK cells. However, B7-H6 is not detected in any normal cells tested. My thesis project was to identify the mechanisms causing the induction of B7-H6 gene and whether conditions other than tumor transformation could lead to B7-H6 expression. During my thesis, we showed that B7-H6 is selectively induced at the surface of neutrophils and CD14+CD16+ monocytes upon inflammatory stimulation in vitro and in vivo, these cells could also triggers NKp30-mediated activation of human NK cells in a context of inflammation. Moreover, this expression is a poor prognosis for survival of patients with severe sepsis. We also detected a soluble form of B7-H6 produced in vitro by activated neutrophils and monocytes, and in vivo in some patients with severe Gram-negative sepsis. Interestingly, this soluble form appears to block the activity of NK cells and have a tendency to be a poor prognosis for survival of these patients.Therefore, my work supports the immune concept that ligands of NK activating receptors are downregulated in normal cells and undergo deregulation that overexpressed in cells upon stress such as tumors, infection and inflammation. In addition, B7-H6 appears as a potential player in the antibacterial innate immunity. The systematic description of B7-H6 in patients with sepsis could allow to envisage new therapeutic treatment based on NK cells and B7-H6 and help classify patients according to their risk of developing a severe form of disease.

NK cells are important part of immune system, recognizing and eliminating tumor cells and cells infected by viruses. For the target cell recognition, binding of ligands by activating receptors plays a crucial role. Activating receptor NKp30, protein of family of natural cytotoxicity receptors, is able to bind multiple ligands either present on tumor cell surface or being part of some viruses. B7-H6 is one of the ligands of NKp30 and its specific constitutive expression on some tumor cells and cell lines makes it an interesting biological target. Although the NKp30/B7-H6 complex structure has been solved, structural basis of some important features of their binding is not explained yet. Soluble form of NKp30 receptor binding domain creates oligomers, presence of which is dependent on C-terminus length of its domain and its N-glycosylation; however, structural insight into formation of the oligomers and their significance is not known. Furthermore, binding affinity of NKp30 to its ligands is dependent on presence of its glycosylation and glycosylation type. We have already found out that NKp30 oligomerization is dependent on its glycosylation. In my work, I attempted to gain detailed functional and structural information about oligomerization of NKp30 and its binding to B7-H6 by multimethodical...