Post‐traumatic immunosuppression is reversed by anti‐coagulated salvaged blood transfusion: deductions from studying immune status after knee arthroplasty

Summary Major trauma increases vulnerability to systemic infections due to poorly defined immunosuppressive mechanisms. It confers no evolutionary advantage. Our objective was to develop better biomarkers of post‐traumatic immunosuppression (PTI) and to extend our observation that PTI was reversed by anti‐coagulated salvaged blood transfusion, in the knowledge that others have shown that non‐anti‐coagulated (fibrinolysed) salvaged blood was immunosuppressive. A prospective non‐randomized cohort study of patients undergoing primary total knee arthroplasty included 25 who received salvaged blood transfusions collected post‐operatively into acid–citrate–dextrose anti‐coagulant (ASBT cohort), and 18 non‐transfused patients (NSBT cohort). Biomarkers of sterile trauma included haematological values, damage‐associated molecular patterns (DAMPs), cytokines and chemokines. Salvaged blood was analysed within 1 and 6 h after commencing collection. Biomarkers were expressed as fold‐changes over preoperative values. Certain biomarkers of sterile trauma were common to all 43 patients, including supranormal levels of: interleukin (IL)‐6, IL‐1‐receptor‐antagonist, IL‐8, heat shock protein‐70 and calgranulin‐S100‐A8/9. Other proinflammatory biomarkers which were subnormal in NSBT became supranormal in ASBT patients, including IL‐1β, IL‐2, IL‐17A, interferon (IFN)‐γ, tumour necrosis factor (TNF)‐α and annexin‐A2. Furthermore, ASBT exhibited subnormal levels of anti‐inflammatory biomarkers: IL‐4, IL‐5, IL‐10 and IL‐13. Salvaged blood analyses revealed sustained high levels of IL‐9, IL‐10 and certain DAMPs, including calgranulin‐S100‐A8/9, alpha‐defensin and heat shock proteins 27, 60 and 70. Active synthesis during salvaged blood collection yielded increasingly elevated levels of annexin‐A2, IL‐1β, Il‐1‐receptor‐antagonist, IL‐2, IL‐4, IL‐6, IL‐8, IL‐10, IL‐12p70, IL‐17A, IFN‐γ, TNF‐α, transforming growth factor (TGF)‐β1, monocyte chemotactic protein‐1 and macrophage inflammatory protein‐1α. Elevated levels of high‐mobility group‐box protein‐1 decreased. In conclusion, we demonstrated that anti‐coagulated salvaged blood reversed PTI, and was attributed to immune stimulants generated during salvaged blood collection.