Stress and murine NK cell function: the role of blood loss

It has been previously reported that NK cell function decreases following surgery in mice. To explore the basis of this observation, we compared the relative influence of anesthesia, surgical amputation and bleeding on NK cell cytotoxicity in C57BL/6 mice. After hind limb amputation, including with blood loss, there was a statistically significant decrease in NK cell cytotoxicity and the appearance of splenomegaly on the 4th day postoperative day. The increase in spleen size appeared to be due to either the surgical stress-induced expansion of splenic erythroblasts or erythroblast generation following blood loss. In contrast, if blood loss was minimal there was no suppression of NK cell cytotoxicity following hind limb amputation. Moreover, there was a statistically significant correlation of NK cell activity and the quantitation of total blood loss. Interestingly, the decrement in NK cell activity was not observed if blood transfusion was made, even in the presence of surgical amputation. These observations are important for defining the immune suppression reported following surgery and suggest that in human, chronic blood loss may also be associated with immune suppression.