Understanding The Immune System

Allergen trigers B cell to make IgE antibody, which attaches to mast cell. When that allergen reappears, it binds to the IgE and triggers the mast cell to release it chemicals. Autoimmune Diseases

some scientists suspect that it developed as a defense against infection by parasitic worms. The first time an allergy-prone person is exposed to an allergen, he or she make large amounts of the corresponding IgE antibody These IgE molecules attach to the surfaces of mast cells (in tissue) or basophils (in the circulation). Mast cells are plentiful in the lungs, skin, tongue, and linings of the nose and intestinal tract. When an IgE antibody sitting on a mast cell or basophil encounters its specific allergen, the IgE antibody signals the mast cell or basophil to release the powerful chemicals stored within its granules. These chemicals include histamine, heparin, and substances that activate blood platelets and attract secondary cells such as eosinophils and neutrophils. The activated mast cell or basophil also synthesizes new mediators, including prostaglandins and leukotrienes, on the spot. It is such chemical mediators that cause the symptoms of allergy including wheezing, sneezing, runny eyes, and itching. They can also produce anaphylactic shock, a life-threatening allergic reaction characterized by swelling of body tissues, including the throat, and a sudden fall in blood pressure. Sometimes the immune system's recognition apparatus breaks down, and the body begins to manufacture antibodies and T cells directed against the body's own constituents-cells, cell components, or specific organs. Such antibodies are known as autoantibodies, and the diseases they produce are called autoimmune diseases. (Not all autoantibodies are harmful, some types appear to be integral to the immune system's regulatory scheme.)   Autoimmune reactions contribute to many enigmatic diseases. For instance, autoantibodies to red blood cells can cause anemia, autoantibodies to pancreas cells contribute to juvenile diabetes, and autoantibodies to nerve and muscle cells are found in patients with the chronic muscle weakness known as myasthenia gravis. Autoantibody known as rheumatoid factor is common in persons with rheumatoid arthritis. Persons with systemic lupus erythematosus (SLE), whose symptoms encompass many systems, have antibodies to many types of cells and cellular components. These include antibodies directed against substances found in the cell's nucleus-DNA, RNA, or proteins-which are known as antinuclear antibodies, or ANAs. These antibodies can cause serious damage when they link up with self antigens to form circulating