IMMUNITY AND DISEASE:

Immunological processes are normally beneficial. However, development of inappropriate immunity can cause disease or at least adverse clinical effects. The breakdown of tolerance to self can result in autoimmune diseases, such as rheumatoid arthritis, primary biliary cirrhosis, systemic lupus erythematosus, Hashimoto’s thyroiditis, myasthenia gravis, and insulin-dependent diabetes mellitus. Production of antibodies against sperm can result in a woman’s inability to conceive. Excessive aggressive immune reactivity (hypersensitivity) can result in conditions like anaphylaxis, allergy, and asthma. An impaired immune response occurs in a group of pathological conditions known as immunodeficiencies. Such conditions can affect innate or acquired immunity and may involve humoral or cellular responses. They vary in severity. Bruton’s congenital agammaglobulinaemia results in a grossly impaired ability to produce immunoglobulins. Common variable immunodeficiency is the most frequently occurring immunodeficiency disease and involves a defect in B-cell function such that the cells cannot secrete antibodies. DiGeorge and Nezelof syndromes involve defects in T-cell development. Severe combined immunodeficiency results in total lack of ability to mount humoral and cellular immune responses. The underlying basis for such conditions is often genetic, but in several cases is unclear. Other immunodeficiencies are caused by viruses. The acquired immune deficiency syndrome (AIDS) results from infection with the human immunodeficiency virus (HIV); this virus destroys CD4-positive T-cells, causing dramatic immunosuppression. Immunosuppressive disorders result in an inability to cope with infections and, in some cases, the spontaneous growth of tumours. Severe illness or death often results.