Regulation of pro-and anti-inflammatory host responses.

Sepsis is a very heterogeneous clinical syndrome broadly defined as the systemic host response to an infection. Until recently, the concept that mortality is the consequence of an uncontrolled hyperinflammatory response of the host was widely accepted. However, although some patients may die rapidly from septic shock accompanied by an overwhelming systemic inflammatory response syndrome triggered by a highly virulent pathogen, most patients survive the initial phase of sepsis, showing multiple organ failure days or weeks later. These patients often demonstrate signs of immune suppression rather than enhanced inflammation. As such, sepsis is now considered a misbalance between proinflammatory reactions (designed to kill invading pathogens but at the same time responsible for tissue damage) and anti-inflammatory responses (designed to limit excessive inflammation, but at the same time making the host more vulnerable for secondary infections). This chapter discusses key components of the pro- and anti-inflammatory response to sepsis and the regulation thereof.