Sepsis is an exaggerated inflammatory syndrome involving cell, organ and system dysregulation. This dysregulation is detrimental to the patient, mainly as it causes imbalances in the immune system. Monocytes and neutrophils are key cell players in the pathogenesis of sepsis; Two populations that follow divergent apoptotic fates; most importantly delayed neutrophil apoptosis has been demonstrated in sepsis and may contribute to organ damage. These two subpopulations have recently been referred to as specific targets of leukocyte filtration, a noveltherapeutic approach in septic patients. As the molecular mechanisms driving the survival/death switches of these cells in sepsis is still controversial, we decided to investigate the role of a new family of proteins predicted to be involved in inflammation and cell death mechanisms; the ApoLs. We studied ApoL expression in whole blood leukocytes and purified populations of neutrophils and monocytes from healthy volunteers and patients with or without sepsis. We then correlated ApoL expression to the degree of inflammation (CRP levels) and cellular apoptosis. We showed a down regulation in ApoL expression in septic and non-septic patients as compared to healthy volunteers, whereas purified monocytes showed an up regulation of ApoL1 and ApoL2 expression in septic patients as compared to non-septic patients. Given that these cells behave differently in the septic frame, we aim to investigate and invalidate the role of ApoLs in conditions related to cell activation and death. Given the high degree of variability in human samples, we resorted to an in-vitro cell line, the PLB 985 myelomonoblastic cell line with granulocytic differentiation potential. Culturing these cells in RPMI 1640 in the presence of specific differentiation agents resulted in mature terminally differentiated cells with phenotypic and functional similarities to human neutrophils. This was determined by monitoring specific leukemic and granulocytic markers. This cell model will help us to better understand the role ofApoLs in regulating neutrophil half-life particularly in inflammatory conditions. It can also be employed to characterize “The cytokine(s)” that is inducing a change in ApoL expression and ultimately uncover the signaling pathway dictating both ApoL expression and apoptosis/survival. / Le sepsis est defini comme une reponse inflammatoire exageree, associee a une dysfonction d'organes faisant suite a un desequilibre du systeme immunitaire. En effet, les monocytes et les neutrophiles representent les acteurs cle dans la physiopathogenese du sepsis. Etant donne que les mecanismes moleculaires regulant la balance de survie / mort cellulaire de ces deux populations de cellules restent jusqu'a present controverses, nous nous sommes interesses a etudier l'implication d'une nouvelle famille de proteines: les apols, susceptibles d'intervenir dans le processus inflammatoire et de la mort cellulaire. Nous avons explore l'expression des apols dans les leucocytes totaux et dans les populations de neutrophiles et de monocytes purifiees a partir de donneurs sains et de patients septiques et non septiques. Par la suite, nous avons etablit le lien de correlation entre l'expression des apols, le degre d'inflammation systemique (dosage de la crp) et l'apoptose. Nos resultats ont demontre une baisse de l'expression des apols dans les leucocytes totaux el les neutrophiles purifies, chez les patients septiques et non septiques, en comparaison avec les donneurs sains. En revanche, nous remarquons une surexpression de l'apol1 et l'apol2 chez les patients septiques par rapport aux patients non septiques. Etant donne la grande variabilite dans les echantillons preleves, nous avons procede a la differenciation d'une lignee myelomonoblastique ayant un pouvoir de differenciation granulocytaire. La mise en culture de cette lignee dans les conditions de differenciation adequates, nous a permis d'obtenir des cellules ayant des similarites fonctionnelles et phenotypiques aux neutrophiles humains. Ce modele cellulaire va nous aider d'une part, a mieux comprendre l'implication des apols dans le controle de la viabilite cellulaire dans les conditions inflammatoires; et d'autre part, a caracteriser la / (les) cytokine(s) susceptibles de moduler l'expression des apols; et finalement a decortiquer la voie de signalisation impliquant les apols dans le controle du processus de survie ou de mort cellulaire. / Doctorat en Sciences / info:eu-repo/semantics/nonPublished