Specific Immune System

Lymphocytes are the white blood cells involved in the specific immune response There are two types of lymphocytes - B lymphocytes and T lymphocytes. Lymphocytes respond to specific antigens on invading pathogens Antigens are molecules, often proteins located on the cell surface that trigger a specific immune response

Lymphocytes have a single type of membrane receptor which is specific for one antigen Antigen binding leads to repeated lymphocyte division resulting in the formation of a clonal population of identical lymphocytes

B lymphocytes produce antibodies against antigens and this leads to the destruction of a pathogen Antibodies are Y shaped proteins that have receptor binding sites specific to a particular antigen on a pathogen Antibodies become bound to antigens, inactivating the pathogen. The resulting antigen-antibody complex can then be destroyed by phagocytosis

B lymphocytes can respond to antigens or substances that are harmless to the body e.g. pollen This hypersensitive response is called and allergic reaction

T lymphocytes destroy infected body cells by recognising antigens of the pathogen on the cell membrane and inducing apoptosis. Apoptosis is programmed cell death T lymphocytes attach onto infected cells and release proteins. These proteins diffuse into the infected cells causing production of self destructive enzymes which cause cell death The remains of the cell are then removed by phagocytosis

T lymphocytes can normally distinguish between self antigens on the body’s own cells and non self antigens on infected cells Failure of the regulation of the immune system leads to T lymphocytes responding to self antigens. This causes autoimmune diseases In autoimmunity, the T lymphocytes attack the body’s own cells. This causes autoimmune diseases such as type 1 diabetes and rheumatoid arthritis

Some of the cloned B and T lymphocytes survive long term as memory cells When a secondary exposure to the same antigen occurs, these memory cells rapidly give rise to a new clone of specific lymphocytes During secondary response, antibody production is greater and more rapid than during the primary response. These destroy the invading pathogens before the individual shows symptoms

The human immunodeficiency virus (HIV) attacks and destroys T lymphocytes HIV causes depletion of T lymphocytes which leads to the development of AIDS (acquired immune deficiency syndrome) Individuals with AIDS have a weakened immune system and so are more vulnerable to opportunistic infections