Phagocytosis is a term used in cell biology to describe a specific process through which cells internalize solid particles. This is a key mechanism through which immune cells such as neutrophils and macrophages eliminate dead cells, pathogens, and foreign matter in the body. Phagocytosis assays are laboratory tests that are used to quantify how much a particular substrate is engulfed by cells and is commonly used in the development of antibodies and vaccines.