b'Chapter 1The immune system is a finely coordinated collection of specialized cells communicating to each other via unique chemicals and specialized receptors. Immune cells have their own circulatory system, the lymphatic system. Lymphatic fluid bathes the body as it transports vital white blood cells to areas of infection, injury, or abnormal cell growth. Immune system cells are located in various lymph nodes strategically positioned throughout the body. The spleen, located in the upper left part of the abdomen, manufactures lymphocytes (white blood cells) and traps foreign antigens in order to trigger the immune response. The spleen also filters the blood and lymphatic system of cell debris, microorganisms, and old or damaged cells. To best understand how the body protects itself, we need to understand each of the agents of the immune system.Antigens:Anything that is foreign is known as an antigen. A harmful bacterium, for example, is an antigen. The immune response to any antigen is very specific to that antigen, and the response is stored into the memory of the immune system. That way, if we encounter the same antigen again, the immune system can react immediately to destroy the foreign substance. Phagocytes:The initial scouts of the immune system are phagocytic cells called dendritic cells, macrophages, and neutrophils. All of these phagocyte cells seek out, engulf, and kill antigenic invaders. 2IMMUNITY'