Microscopy-Based Methods for Measuring Platelet and Red Blood Cell Phagocytosis

Phagocytosis plays a pivotal role in diseases involving the accelerated removal of platelets and erythrocytes from the circulation and can be mediated by antibodies through the mononuclear phagocyte system. In autoimmune conditions such as immune thrombocytopenia and autoimmune hemolytic anemia, autoantibodies target self-antigens on platelets or red blood cells. Similarly, in alloimmune diseases like fetal and neonatal alloimmune thrombocytopenia and hemolytic disease of the fetus and newborn, maternal alloantibodies can target platelet or erythrocyte antigens, leading to cytopenias. Phagocytosis can be facilitated by Fc gamma receptors on macrophages, which bind to the Fc region of IgG that sensitizes these platelets or erythrocytes. Understanding the mechanisms of phagocytosis is crucial, as it can significantly drive the pathophysiology of autoimmune and alloimmune diseases. In this chapter, we detail confocal and phase contrast microscopy-based methods for quantifying antibody-mediated phagocytosis of platelets and erythrocytes, respectively.