Human
sepsis is characterized by a set of systemic reactions in response to intensive and massive
infection that failed to be locally contained by the host. Currently,
sepsis ranks among the top ten causes of mortality in the USA intensive care units. During
sepsis there are two established haemodynamic phases that may overlap. The initial phase (hyperdynamic) is defined as a massive production of proinflammatory
cytokines and
reactive oxygen species by macrophages and neutrophils that affects vascular permeability (leading to
hypotension), cardiac function and induces metabolic changes culminating in tissue
necrosis and organ failure. Consequently, the most common cause of mortality is
acute kidney injury. The second phase (hypodynamic) is an anti-inflammatory process involving altered monocyte antigen presentation, decreased lymphocyte proliferation and function and increased apoptosis. This state known as immunosuppression or immune depression sharply increases the risk of nocosomial
infections and ultimately, death. The mechanisms of these pathophysiological processes are not well characterized. Because both phases of
sepsis may cause irreversible and irreparable damage, it is essential to determine the immunological and physiological status of the patient. This is the main reason why many therapeutic drugs have failed. The same drug given at different stages of
sepsis may be therapeutic or otherwise harmful or have no effect. To understand
sepsis at various levels it is crucial to have a suitable and comprehensive animal model that reproduces the
clinical course of the disease. It is important to characterize the pathophysiological mechanisms occurring during
sepsis and control the model conditions for testing potential therapeutic agents. To study the etiology of human
sepsis researchers have developed different animal models. The most widely used clinical model is cecal
ligation and
puncture (CLP). The CLP model consists of the perforation of the cecum allowing the release of fecal material into the peritoneal cavity to generate an exacerbated immune response induced by
polymicrobial infection. This model fulfills the human condition that is clinically relevant. As in humans, mice that undergo CLP with fluid
resuscitation show the first (early) hyperdynamic phase that in time progresses to the second (late) hypodynamic phase. In addition, the
cytokine profile is similar to that seen in human
sepsis where there is increased lymphocyte apoptosis (reviewed in). Due to the multiple and overlapping mechanisms involved in
sepsis, researchers need a suitable
sepsis model of controlled severity in order to obtain consistent and reproducible results.