The immune system consists of a vast collection of cells, including lymphocytes and cell-devouring phagocytes. Some of these cells attack all foreign invaders (antigens), while others attack only specific targets. In defending the human body against disease, the immune system cells need to function cooperatively. All immune cells begin as immature pluripotent stem cells in the bone marrow. Cells of the immune system are essential to maintain harmful invaders out from the human system.
Lymphocytes are white blood cells (leukocytes) that carry antibodies attached to their cellular membranes. The principle types of lymphocytes are B cells and T cells. B cells differentiate to form plasma cells, which are identical copies of a specific antibody, secreting them into the fluids of the human body and identifying and destroying pathogens. They also differentiate into memory cells which provide immunity from a familiar pathogen in future pathogen attacks. B cells can produce over 10 million copies of antibody molecules every hour.
T cells help maintain the immune system defenses in two principle ways: by regulating the complex internal mechanisms of the immune response; and by directly identifying and destroying infected cells. The surfaces of T cells contain antibody receptors that bind to the receptors of antigens. Helper T cells (Th or CD4 cells) help activate other immune cells, including B cells and other T cells. Cytotoxic T cells (killer T or CD8 cells) kill cells that have been infected by a virus or cells that have become cancerous by injecting perforin into the plasma membranes of the infected cell. Killer cells also attack cells from other tissues, as in tissue and organ transplants.
Killer cells and natural killer cells (NK), another type of T cell, contain granules filled with lethal chemicals, and both of them kill upon contact; however, killer cells only recognize an antigen when it is carried on the surface of a cell by one major histocompatibility complex (MHC) molecule, while NK recognize cells lacking MHC molecules. NK have the potential to destroy many types of
Phagocytes are types of immune cells that can engulf and digest (phagocytose) antigens. Phagocytes include monocytes, macrophages, dendritic cells, and neutrophils. Monocytes circulate in the blood; when they travel to other tissues and organs, they transform into macrophages. Macrophages, besides devouring antigens, secrete chemical messengers known as cytokines which are essential in the immune response.
Granulocytes are another type of white blood cells that contain microscopic granules, containing killer chemicals. Eosophils and basophils, which are granulocytes, spray these chemicals onto their enemy targets. Neutrophils, which are the most abundant type of phagocyte, are both phagocytes and granulocytes, meaning, they can devour, as well as spray granules onto their enemies. Platelets, cell fragments containing granules, promote blood clotting and wound repair. In addition, they activate some immune responses.
Dendritic cells, characterized by having long extensions, engulf antigens from microbes, such as bacteria, viruses, and other microorganisms and present them to T cells for an initial immune response. Dendritic cells are found mostly in the external tissues of the body, including the skin, stomach, intestines, the inner linning of the nose, and lungs. When dendritic cells travel to the lymphoid tissues, they activate T cells which differentiate into cytotoxic or helper T cells, influencing an immune response.
A healthy immune system can prevent the invasion of harmful pathogens, thus, preventing many Immune disorders. The cells in the immune system are essential living components of the human body; therefore, it is important to support your immune system by implementing a healthy diet along with regular physical exercise. healthiest foods gives some useful recommendations to maintain a healthy immune system.