Systems Analysis of Antigen Presenting Cells in Human Sepsis

Sepsis is a common life-threatening inflammatory response to infection and is the leading cause of death in the intensive care unit. Septic patients exhibit a complex immunosuppressive response affecting both innate and adaptive components of immunity, with a possible link to nosocomial infections. However, the molecular and cellular mechanisms resulting in secondary immunosuppression remain poorly understood, but may involve the antigen-presenting cells (APC, including dendritic cells and monocytes/macrophages) that link innate and adaptive immunity. Furthermore, the increasing phenotypic and functional heterogeneity of APC subsets raise the question of their respective role in sepsis. We propose to address the pathophysiologal role of APC using systems biology approaches in human sepsis. The objective is to go from low- to high-resolution analysis of APC subset diversity and underlying molecular and functional features in sepsis. The global objective will be reached through: 1. Systematic description and phenotypic analysis of circulating APC subsets in sepsis 2. Association of APC subsets distribution, phenotype and function with severe sepsis physiopathology and relevant clinical outcomes (ICU-acquired infections and death) 3. High-resolution molecular profiling of circulating APC subsets using population level and single cell RNAseq. To this aim, the investigator designed a prospective interventional study in order to collect blood samples at significant time points in patients with sepsis or septic shock (the population of interest) and relevant control subjects, either critically ill patients with non-septic acute circulatory failure or age-matched healthy subjects. The study's intervention is limited to additional blood samples. The risks and constraints are related to additional blood samples (maximum 120mL), which will be performed either from an arterial catheter when present in ICU patients, or from a venous puncture for patients without arterial cath