Phagocytes are derived from monocytes in the human body. When monocytes escape from the blood vessels and reach the tissues, they become phagocytes by deforming their morphology and increasing in size. The role of phagocytes is manifested in two main aspects the first one is non-specific phagocytosis. Phagocytes can engulf pathogenic microorganisms that enter the body. These include bacteria, viruses, parasites, protozoa, etc. Also, phagocytes can engulf aging cells in the body, as well as various cellular debris. The second aspect of their role is the occurrence of specific immune effects. After phagocytes have engulfed pathogenic microorganisms, they can transmit information about the pathogenic microorganisms to the body’s B-lymphocytes; they stimulate B-lymphocytes to proliferate and transform into plasma cells. At the same time, plasma cells then produce specific antibodies against pathogenic microorganisms and exert humoral immunity.