Transcript Immunity
Immunity Immunity is the protection against disease provided by the body’s defence or immune system. Immune Response not one single mechanism Innate immunity, which does not require previous exposure to the invading microbe, Acquired immunity, where the immune system "remembers" how to deal with a microbe that it has dealt with before. The key to a healthy immune system is its remarkable ability to distinguish between the body’s own cells, recognized as “self,” and foreign cells, or “nonself.” Antigen - a chemical feature (a protein) which is unique to any given type of invading organism. When it wrongly identifies self as nonself it causes an autoimmune disease such as rheumatoid arthritis or systemic lupus erythematosus. Phagocytes Produced by bone marrow Scavengers Non-specific Two types: Neutrophils – small, short-lived Macrophages – large, long-lived Mode of action engulf pathogen and create enzymes to neutralize it This process is called phagocytosis, literally "eating cells." Macrophages use phagocytosis to collect antigens which they present to helper T-cells, alerting the T-cells to the fact that there is a foreign invader in the body, and triggering an immune response. Lymphocytes Made in bone marrow before birth Stored in lymphoid system Specific Secrete antibodies Two groups: T lymphocytes B lymphocytes T lymphocytes Mature in thymus gland Specific surface receptors called T cell receptors and glycoprotein receptors called CD receptors. T Cells provide Cell Mediated Immunity T cells have several functions. They can be: Helper T cells, which control other cells, such as B cells or Macrophages, directing them to carry out their task. Suppressor T cells, which dampen down the immune response when it is no longer needed. Cytotoxic T cells, which destroy host cells that have become infected with the invading organism. (Killer T) B Lymphocytes Mature in bone marrow Each one has a specific receptor 10 million different variants These code for the different antibodies Mode of action B Cells provide "Humoral Immunity". Each B cell secretes a unique antibody, which acts against a particular antigen. When B cells meet an invading organism for which they have the antibody, they do one of two things. They may turn into antibody factories and start manufacturing as many copies of their antibody as they can. They may clone themselves increasing the numbers of antibody factories, Memory Cells When B cells and T cells are activated some will become memory cells. Upon interaction with a previously encountered antigen, the appropriate memory cells are selected and activated. The second and subsequent exposures to an antigen produce a stronger and faster immune response. Antibodies Each antibody consists of four polypeptides– two heavy chains and two light chains joined to form a "Y" shaped molecule. The amino acid sequence in the tips of the "Y" varies greatly among different antibodies. This variable region, composed of 110-130 amino acids, give the antibody its specificity for binding to the antigen. The constant region determines the mechanism used to destroy the antigen. Active Immunity Naturally acquired active immunity occurs when the person is exposed to a live pathogen, develops the disease, and becomes immune as a result of the primary immune response. Artificially acquired active immunity can be induced by a vaccine, a substance that contains the antigen. A vaccine stimulates a primary response against the antigen without causing symptoms of the disease Passive Immunity Passive memory is usually short-term, lasting between a few days and several months. Newborn infants have had no prior exposure to microbes and are particularly vulnerable to infection. At birth, human babies have high levels of antibodies, with the same range of antigens as their mother. This is passive immunity because the fetus does not actually make any memory cells or antibodies, it only borrows them. Short-term passive immunity can also be transferred artificially from one individual to another via antibody-rich serum. Vaccination Immunization or vaccination is the deliberate induction of an immune response. Immunizations are successful because they utilize the immune system's natural specificity as well as its inducibility. An antigen, derived from a disease-causing organism, is injected and it stimulates the immune system to develop protective immunity against that organism, but the antigen does not itself cause the pathogenic effects of that organism. Most viral vaccines are based on live attenuated viruses, while many bacterial vaccines are based on avarious components of microorganisms, including harmless chemical components. Disease Eradication Smallpox was eradicated in 1980 because: Virus did not mutate, so one vaccine always worked. Easy to identify infected people Does not linger in the body to reinfect later. Vaccine could be freeze dried for use in the tropics (did not need to be refrigerated). Other diseases are no so easy to readicate, such as….. Cholera Malaria Sickle-Cell anaemia TB Measles Chart on page 232 explains why. Monoclonal antibodies Identical antibodies produced to be effective against a single, specific antigen. Problem with producing them – B lymphocytes that produce antibodies don’t divide, and B lymphocytes that divide (making plasma cells) don’t produce antibodies! HAT medium is hypoxanthine aminopterin thymidine. Only hybridomas survive. Myeloma and normal cells die. Plasma cells are fused with cancerous cells which go on dividing indefinitely. This formed a hybridoma which divides and secretes antibodies. Using monoclonal Antibodies 1. Pregnancy Tests The monoclonal antibodies are made that bind with the human hormone human chorionic gonadotrophin (hCG), which is produced in pregnancy. The antibody is attached to a dipstick. The dipstick is dipped into a urine sample. Any hCG in the urine will bind to the antibody and will be carried up the stick with the urine. Another antibody is made which will bind with the hCG-antibody complex. This is placed further up the stick and immobilised. As the hCG-antibody reaches the immobilised antibody it binds and a pink colour forms. (or blue, depending on the brand) To check whether the stick is working, another chemical is attached to it that will change colour even if there is no hGC present. One band: Negative, as there was no hCG. Two bands: Positive, as some of the mouse antibody has hCG bound to it. Monoclonal antibodies in diagnosis and treatment Diagnosis. Blood clots:Fibrin (protein found in blood clots) injected into a mouse, and monoclonal antibodies against fibrin are produced as previously discribed. The antibodies are labelled with a radioactive chemical so that they can be traced. The monoclonal antibodies are then injected into the patient, and bind to the fibrin in their blood clots. The radiation then shows the doctors where the blood clots are. Cancer cells can be tracked down in a similar way to identify the location of a tumour. Treatment: Monoclonal antibodies are made to be bind on to cancer cells. An anti-cancer drug is then joined to them. These “magic-bullets” are then injected into a patient, and the anti-cancer drug is taken to the cancer cell by the monoclonal antibody, and the cancer cell is destroyed.