Effect of autologous salvaged blood on postoperative natural killer cell precursor frequency

Immunosuppression after major surgery increases the risk of infections. Natural killer cells play a pivotal part in defence against infection. We aimed to investigate the immunomodulatory effects of different types of postoperative blood transfusion by use of a new assay for measuring the frequency of peripheral blood natural killer precursor cells (NKpf assay). Methods We measured the natural killer cell precursor (NKp) frequency before and 5 days after surgery in 120 patients undergoing joint replacement surgery. The patients were assigned to one of five groups according to the type of transfusion received: non-transfused (n=32), allogeneic non-leukodepleted blood (eight), allogeneic leukodepleted blood (30), autologous predeposited blood (ten), and autologous salvaged blood collected within the first 24 h after surgery (40). We also measured interferon γ and interleukin 10 concentrations before and after surgery. Findings The mean postoperative NKp frequency for all patients was lower than the preoperative values, except in patients receiving autologous salvaged blood, which was higher than all other groups (p<0·0001). Postoperative NKp frequencies for patients receiving allogeneic or autologous predeposited blood responded similarly (p=0·99), but these patients had lower NKp frequencies than did the non-transfused group (p<0·0001). Postoperative interferon γ concentrations were higher in the autologous salvaged blood group (p<0·0001) than in other groups, which did not differ from each other. Interleukin 10 concentrations were similar across all groups (p=0·49). Interpretation Immunosuppression associated with surgery and blood loss was reflected in a reduced frequency of NKp and decreased interferon γ. This immunosuppression was reversed by transfusion of autologous salvaged blood, suggesting that this fluid contained immunostimulants.