Background and objectives: A most memorable scene in "Bram Stoker's Dracula" of Francis Ford Coppola sees Count Vlad II of Wallachia proclaim: The blood is the life! It is impossible to evaluate how much the Irish novelist, writer of the 1897 book the film was based upon, was influenced by the developments in blood transfusion that characterized the end of the 19(th) and the beginning of the 20(th) century, but the word "transfusion" figures prominently in his manuscript. Past centuries had been characterized by successful blood transfusions between animals, but success in human transfusions had been limited prior to Landsteiner's discovery of the red blood cell (RBC) membrane ABO antigens (1901) that permitted the establishment of safe blood transfusions. The application of refrigeration and anticoagulants to blood storage in the 1910s then paved the way to blood banking. Since those early days, developments in the RBC field have been tightly associated with technologies that changed science, allowing researchers to home into the detail (moving from blood to RBC and then to RBC membrane proteins) and had a huge impact on the quality of life. Today, proteomics technologies can be used to tackle important but neglected aspects of transfusion medicine, such as determining changes at the peptide and protein level during storage of blood products. Results: Studies have demonstrated that stored leucocyte-undepleted whole RBC populations release over 100 proteins compared to the few released by leucocyte-depleted blood units. The leucocyte-poor RBC predominantly released carbonic anhydrase and thioredoxin peroxidase B. The presence of oxygen, in this context, gives rise to extensive RBC surface modifications, which can be prevented by adding protease inhibitors. Proteins released during storage of leucocyte-depleted RBCs were found in form of microvesicles and nanovesicles enriched not only in integral membrane proteins, but specifically in oligomerized band 3, suggesting a preferential release of damaged cell components from otherwise functional RBCs. Flow cytometry was used in combination with proteomics to study storage of younger versus older RBCs. In leucocyte-depleted RBC stored for 42 days, phosphatidylserine exposure at the RBC membrane external surface did not increase and none of the surface markers studied decreased significantly, while the copy numbers of CD44, CD58, CD147 and glycophorin decreased and annexin release increased in RBC stored with leucocytes. A recent review summarizes the contribution of proteomics to transfusion medicine and puts forward a possible approach in form of a workflow for monitoring the quality of blood-based therapeutics by proteomics. Conclusions: Monitoring may be essential as more detailed analyses using state of the art mass spectrometry tools are likely to provide an even better insight into storage and environment-induced changes in the RBC that may be critical to optimize the quality of transfused RBC. Increasing our knowledge of the RBC protein make-up (low abundant proteins in particular); of their changes in health and disease and in the interplay with other blood cells/endothelial cells will also be beneficial in assessing changes in their quality, while the study of intra-species differences will be instrumental in the light of the passage from animal experimentation to clinical trials.
