The immune system protects the body from most infections that breach the skin and the body's other primary defense barriers. Special cells, organs, and tissues make up the integral parts of the immune system. Phagocytes, lymphocytes, lymph nodes, the thymus, and the tonsils are just a few of the different parts of the immune system. Most cells that operate within the immune system are created in bone marrow. While most immune cells are designed to actively destroy any dangerous material that may enter the body, others serve the function of remembering and recognizing harmful materials to trigger defensive reactions quicker in the future.
The complement system component of the immune system consists of a group of proteins that react to antigens, which are foreign, potentially harmful substances. These proteins can react so quickly to an invasion because they circulate throughout the body within blood. They can trigger inflammation, kill intruders, or coat intruders with a material that encourages eater cells to devour and destroy them.
Granulocytes and macrophages are in a group of immune cells called phagocytes, which function to eat viruses, bacteria, and injured or dead body cells. The pus found in infected wounds consists mainly of dead granulocytes. These cells attack infections in large numbers until they die. While granulocytes often react to an infection before macrophages, the immune system's macrophages are larger, live longer, and offer greater capacities than granulocytes. They are also one of the types of immune cells that alert the other immune system components of invaders.
Like granulocytes and macrophages, dendritic cells are phagocytes. They help devour and process infections and intruders. These immune cells are parts of the immune system that also activate the rest of the immune system when an infection is present. Dendritic cells help filter bodily fluids, keeping them free of foreign organisms.
T cells and B cells are the two main types of lymphocytes. Helper T cells produce proteins that activate killer T cells, B cells and other types of immune cells. Killer T cells search for infected cells of the body and swiftly kill them. B cells divide when activated, producing plasma cells and memory B cells. Plasma cells produce antibodies, which destroy invaders and memory B cells are designed to recognize intruders and begin activating the immune system.
Lymph nodes are key parts of the immune system and they are located all over the body. After the various immune cells are created in the bone marrow, many are transported to lymph nodes where they are stationed until an infection is detected. The thymus can be found behind a person's sternum, in front of his or her heart. This organ functions to produce and developing T cells. The tonsils, located in the back of the throat, represent one of the body's primary defenses against ingesting or inhaling pathogens.