Reims University Hospitals, Robert Debre Hospital 1 article published in JoVE Immunology and Infection Measuring Erythrocyte Complement Receptor 1 Using Flow Cytometry Aymric Kisserli1,2, Sandra Audonnet3, Valérie Duret2,4, Thierry Tabary2,4, Jacques Henri Max Cohen2, Rachid Mahmoudi5,6 1Oncogeriatric Coordination Unit, Reims University Hospitals, Maison Blanche Hospital, 2Faculty of Medicine, University of Reims Champagne-Ardenne, 3URCACyt, Flow cytometry technical platform, University of Reims Champagne-Ardenne, 4Department of Immunology, Reims University Hospitals, Robert Debre Hospital, 5Department of Internal Medicine and Geriatrics, Reims University Hospitals, Maison Blanche Hospital, 6Faculty of Medicine, University of Reims Champagne-Ardenne The aim of this method is to determine the CR1 density in the erythrocytes of any subject by comparing with three subjects whose erythrocyte CR1 density is known. The method uses flow cytometry after immunostaining of the subjects' erythrocytes by an anti-CR1 monoclonal antibody coupled to an amplified system using phycoerythrin (PE).