Depletion of NK cells in a murine polytrauma model is associated with improved outcome and a modulation of the inflammatory response

Sepsis and associated diseases such as systemic inflammatory response syndrome and multiple organ dysfunction syndrome represent common posttraumatic complications on intensive care units induced by a variety of body defense mechanisms. Natural killer (NK) cells are part of the innate immune system. They are thought to play an important role in the development of such syndromes by interplay with other immune cell types and subsequent activation of the inflammatory cascade. To test this hypothesis, NK cells were depleted by administration of antimouse asialo-GM1 antibody in a murine polytrauma model consisting of femur fracture, hemorrhagic shock, and subsequent sepsis. Mortality and immune parameters such as cytokine expression in lung and liver, lymphocyte phenotyping, lymphocyte apoptosis, and organ pathology were determined 96 h after sepsis induction. Survival values showed 50% in the control sepsis group and 100% after NK cell depletion. Thus, NK cell depletion resulted in 50% mortality reduction. Furthermore, we found reductions in the inflammatory response, represented by IL-6 expression in liver, and a decrease in infiltrating neutrophils in the liver and lung. In addition, lymphocyte apoptosis in spleen was decreased by depletion of NK cells. Taken together, these data demonstrate that NK cells contribute to the pathogenetic pathways in a murine polytrauma model. One main mechanism of action seems to be the induction of systemic inflammatory events. Thus, depletion of NK cells results in attenuated inflammation and an overall improvement in outcome. Therefore, NK cells can be considered as important targets for therapeutic strategies.