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Learn about the immune system, its different responses, lymphocytes, monoclonal antibodies, vaccination, and the MMR controversy. Discover how the immune system protects against diseases.
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What is the immune system? The immune system is a group of cells, tissues, organs and mechanisms that defend an organism against pathogens (disease-causing organisms) and other foreign substances. An immune response is a complex series of specific and non-specific processes involving a range of cells and chemicals. If the body successfully fights an infection, it will respond more quickly and effectively if the same pathogen is re-encountered.
Non-specific immune response The non-specific or innate immune response quickly targets a wide range of pathogens and foreign substances. Phagocytosis, inflammation and the antimicrobial proteins lysozyme and interferons are all part of this immune response. • Lysozymeis an enzyme that disrupts the cell walls of gram-positive bacteria by digesting the peptidoglycan. It is found in human tears, saliva and lysosomes. • Interferonsare proteins produced by virus-infected body cells in response to the virus. Interferons trigger the production of a second protein that inhibits viral replication by binding to mRNA coded by the virus.
Specific immune response The specific or adaptive immune responsecantarget a specific pathogen, although it is slower to act than the non-specific response. It features two main types of response to pathogens: • the cellular or cell-mediated response involves highly-specialized cells that target pathogens inside cells. • the humoral or antibody-mediated response targets pathogens in body fluids with antibodies.
What are lymphocytes? Lymphocytes are a type of white blood cell (leukocyte) found in the blood and lymph nodes. Lymphocytes recognise antigen molecules on the surface of pathogens, and co-ordinate the immune response against that pathogen. Collectively, lymphocytes can recognize millions of different antigens, due to the large variation of lymphocytes produced.
What are monoclonal antibodies? Polyclonal antibodiesare naturally produced in an immune response. Different plasma cells secrete antibodies, resulting in a variety of different antibodies against a specific antigen. Monoclonal antibodies (mAbs) are antibodies produced from clones of a single plasma cell and are therefore all identical. They have many important uses, such as: • the treatment of cancer and other diseases • drug screening • home pregnancy kits • scientific research.
Production of monoclonal antibodies Large quantities of mAbs can be produced using mice or rabbits. A specific antigen is injected into the animal, stimulating the production of plasma cells. The plasma cells are removed from the animal and fused with cancerous myeloma cells from normal mice. These form immortal hybridoma cells, which can produce a single type of antibody indefinitely.
Production of monoclonal antibodies The problem with using mouse-derived (murine) mAbs in humans is that they may be recognized as foreign. This will trigger an immune response, which quickly inactivates the mAbs. murine The immune response can be minimized by using genetic engineering to create humanizedmAbs. These consist of mainly human polypeptide chains, with only the amino acids at the antigen-binding site derived from mice. humanized
What is vaccination? Vaccinesstimulate the production of antibodies and memory cells against the target pathogen without causing illness. Why don’t vaccines cause illness? • They may contain an inactivated form of the pathogen, killed by heat treatment (which leaves the immune-stimulating antigens intact). • They may contain an attenuated (less virulent) form of the pathogen. • They may contain isolated antigens, such as cell surface proteins, from the pathogen.
Influenza vaccines New strains of the influenza virus are constantly emerging. This is because antigens displayed on the virus change due to mutation. This causes antigenic variation. Antigenic variation makes it hard to immunize a patient against the influenza virus for life with just a single vaccine. The government works with other organizations to identify current strains of influenza. An effective vaccine is developed each year.
The MMR controversy In 1998, a scientific paper was published in the medical journal The Lancet, speculating that the MMR vaccine could cause autism. The authors thought that the MMR vaccine could damage the bowel, allowing toxins that are normally destroyed in digestion to move into the blood. If these toxins travelled to the brain they might cause autism. The authors did not prove that this was the case but still recommended that doctors stop administering the MMR vaccine until more research was done.
The media’s role in the MMR controversy Many studies have concluded that the MMR vaccine is safe and only a few studies claim that it isn’t. However, this was not reflected by the media coverage. The majority of coverage centred on the possibility of a link between the MMR vaccine and autism, while the government insisted that the vaccine was safe. This mixed message caused confusion among the general public, leading to a drop in the number of children being given the combined vaccine. Should scientists be more careful about how they present their research or should the media be responsible for how they present controversial topics to society?
