Sepsis is one of the leading causes of death among critically ill patients and develops in approximately 1.8 million people worldwide annually. Major efforts have been undertaken in recent years to treat severe sepsis early and aggressively. However, the death rate remains high. An improved understanding of the immunopathology of sepsis and additional strategic approaches are urgently warranted. Macrophages are central cells of the body that regulate tissue homeostasis and immunity in all issues of the body. Macrophages engulf and then digest cellular debris, apoptotic cells, or foreign pathogens and consequently induce tissue regeneration, wound healing or anti-pathogenic immune responses. Dysregulation of these responses in macrophages can lead to fatal outcomes such as sepsis, autoimmunity, chronic lung disease, atherosclerosis or cancer. In this project, a close to nature in vivo blood vessel shall be colonized with macrophages in order to investigate the interaction of endothelial cells and mesenchymal stem cells and to study the influence of the modulation of the immune response. The aim is to expand our understanding of how macrophages regulate and control the immune response during sepsis. Additional, the influence of modulation of macrophage function in the pathogenesis of sepsis by the use of mesenchymal stem cells regarding new therapeutic possibilities will be investigated.