256 OLIVE OILS AND HEALTH IMMUNE SYSTEM A set of organs and cells working to defend the body against external agents (bacteria, viruses, fungi, parasites, toxins) or internal ones (cancer cells) which can promote infections and other illnesses. The protection conferred by the immune system is called immunity. The ORGANS involved are: two adenoid glands located in the upper airway, just behind the nasal cavity; bone marrow (a spongy, soft tissue in the centre of most bones); lymph nodes (throughout the body and interconnected by the lymphatic vessels, filtering and containing lymphocytes); lymphatic vessels, a network in which lymphocytes are conveyed to lymphoid organs and the bloodstream; Peyer’s patches, lymphatic tissue in the small intestine; the spleen (a lymphoid organ located on the left side of the abdomen, near the stomach, which produces lymphocytes, filters blood, stores blood cells, and destroys the old ones); the thymus (organ of the lymphatic system in the chest, between the lungs and behind the sternum); and the tonsils (lymphatic tissue masses located on both sides of the throat). The CELLS involved in the immune system are the leukocytes, dendritic cells, and those called natural killer cells. The white blood cells or leukocytes are highly specialised to protect the body against noxious agents. There are several types: granulocytes (neutrophils, eosinophils, and basophils), monocytes and macrophages, and lymphocytes (T and B cells). Lymphocytes: one of the main immune cells. Generated in the bone marrow, they regulate the immune response and produce antibodies which recognise specific parts of pathogens (antigens). They circulate throughout the body via the blood and lymphatic systems. There are two lymphocyte types, T and B, and two main types of T lymphocytes: CD8+ and CD4+. T lymphocytes, or T cells, are formed in the bone marrow, then migrate to the thymus, and accumulate in the lymph nodes and spleen. CD8+ T cells destroy cancerous or virus-infected cells. CD4+ T cells coordinate the immune response with other immune cells, such as macrophages and CD8+ T cells. B lymphocytes, or B cells, are also formed in the bone marrow, then migrate to the lymph nodes and other lymphoid areas. They produce antibodies that recognise foreign antigens and bind to them to either neutralise them directly or signal other immune cells, like T cells, to do so. Each antigen corresponds to a specific antibody. The immune system remembers these antigens, allowing it to respond more quickly upon re-exposure. Antibodies can also neutralise toxins and activate a group of proteins called the complement system, which helps destroy bacteria, viruses, and infected cells. Tonsils Thymus Lymph nodes Lymphatic vessels Spleen Peyer’s patches (in the small intestine) Bone marrow
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