Thesis Elena Kostova

Summary

The red blood cell (RBC) is a unique cell type which has evolved as specialized oxygen carrier. RBC are transfused when improvement of tissue oxygenation is required, which usually occurs in the context of anemia and severe blood loss. Although the beneficial effects of transfusing RBC are clear, the use of RBC can also have adverse effects. RBC undergo considerable changes during storage, which leads to alterations in the function and lifespan of RBC in vivo post transfusion. We investigated the changes observed in long-stored RBC and we found that potassium leakage primes stored erythrocytes for phosphatidylserine (PS) exposure and subsequent shedding of vesicles. Thus, the shedding of vesicles, which promotes coagulation and other adverse phenomena, may contribute to the deleterious side effects associated with transfusion. To further study the signaling pathways involved in vesiculation, we established a screening method using the Ca2+ ionophore ionomycin. We screened two libraries of pharmacological inhibitors for their effects on RBC from healthy donors and we identified novel signaling pathways involved in vesiculation. Furthermore, we investigated the role of RBC in immune adherence clearance (IAC). Interestingly, RBC are capable of binding complement-opsonized pathogens via complement receptor 1. It has been suggested that immune adherence and immobilization of bacteria on RBC facilitate pathogen phagocytosis via IAC. To understand the underlying mechanisms of IAC, we developed an assay to monitor the transfer of opsonized pathogens from RBC to human monocytes/macrophages under flow conditions.