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Antibodies How does your body fight infections? Introduction • The body has to be ready to fight off anything which could do damage to it • One of the ways that it can do this is by releasing lots of chemicals that will destroy anything in their path • However, there’s an even more specific system that has been designed to target particular bugs that might get in – and this is where antibodies come in Outline • What is an antibody? • What does an antibody do? • Types of antibodies What is an antibody? • An antibody is a special group of proteins that acts like a label • They are the main part of the humoral immune system, and they are produced by a special kind of cell called a plasma cell – Plasma cells are mature B lymphocytes What is an antibody? • Each antibody is made up of – light chains – heavy chains – connected by disulphide bonds • The structure of the antibody is split into the Fab regions and the Fc region. What is an antibody? • The Fab regions – “Fragment antigenbinding” – Connect to enemy proteins – Different on different antibodies What is an antibody? • The Fc region – “Fragment crystallisable” – Connect to normal cells – Alerts immune cells to the presence of an invader What is an antibody? Immune cell Fc region antibody Fab region surface proteins invader What do antibodies do? • Antibodies are able to help prevent invasion from bacteria, viruses and other enemies in several ways – Neutralisation – Flagging – Opsonisation What do antibodies do? • Neutralisation – Invaders use proteins on their surface to get into cells and cause damage – Antibodies which coat surface proteins stop them from having this action What do antibodies do? • Flagging – By coating an invader, the antibody acts like a flag to alert circulating immune cells to the present danger – Immune cells connect to the Fc region of the antibody What do antibodies do? • Opsonisation – If an enemy is coated in certain molecules, macrophages and other similar cells will eat up the invader – Antibodies can cause this, and they can also stimulate complement, which is particularly good at causing it Types of antibodies • Antibodies exist in several different types • These are called isotypes • Each different type has a different type of heavy chain • IgA • This is used in areas where there is a layer of cells producing mucus, to stop infections growing in that area • E.g. gut, respiratory tract and urogenital tract, saliva etc. • Goes around in a pair (i.e. a dimer) Types of antibodies • Antibodies exist in several different types • These are called isotypes • Each different type has a different type of heavy chain • IgD • This usually acts as a receptor on the surface of B lymphocytes • It goes around on the surface of these cells on its own (i.e. a monomer) Types of antibodies • Antibodies exist in several different types • These are called isotypes • Each different type has a different type of heavy chain • IgE • Responds to things that the body is allergic to (e.g. pollen) • Activates basophils and mast cells to release histamine • Goes around alone (i.e. a monomer) Types of antibodies • Antibodies exist in several different types • These are called isotypes • Each different type has a different type of heavy chain • IgG • This is the main antibody needed to fight infection, causing autoimmunity and recognising re-infection • The only antibody to cross the placenta • Shows if you have ever been exposed to a particular infection • Goes around alone (i.e. a monomer) Types of antibodies • Antibodies exist in several different types • These are called isotypes • Each different type has a different type of heavy chain • IgM • The antibody used mostly in the ‘acute phase’ immediate response, before a rise in IgG • Shows whether you currently have a particular infection • Goes around in group of five (i.e. a pentamer) Types of antibodies Summary IgA Acts wherever there’s mucus, to fight infection (e.g. gut, lungs, genitourinary tract) Dimer IgD Forms a receptor on the surface of B-lymphocytes Monomer IgE Responds to things that the body is allergic to (e.g. pollen) Monomer IgG This is the main antibody needed to fight infection, causing autoimmunity, and recognising re-infection Monomer IgM The antibody used mostly in the ‘acute phase’ immediate response, before a rise in IgG Pentamer Conclusion • Humoral immunity is an important way in which the body fights off infection • It is based around antibodies, which are groups of proteins that act like labels on invaders • Antibodies fight infection in three major ways: neutralising enemies, flagging them up to immune cells, and coating them to help them get eaten • Different isotypes of antibodies work in different ways and in different locations in the body Any questions? Further reading: • DeFranco AL, Locksley RM, Roberston M (2007) Immunity: The Immune Response in Infectious and Inflammatory Disease. 5th Ed. Oxford University Press • Frank SA. (2002) Immunology and Evolution of Infectious Disease. Princeton University Press • Janeway CA Jr. (1993) How the immune system recognizes invaders. Scientific American. 269(3):72-79 For more information, don’t forget to visit www.blobs.org