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6.3.3 - Outline the role of skin & mucous membranes 6.3.4 - Outline how phagocytic leucocytes ingest pathogens in the blood and in body tissues 6.3.5 - Distinguish between antigens & antibodies 6.3.6 - Explain antibody production http://www.youtube.com/watch?v=IWMJIMzsEMg The Body’s Defence antibodies actively made by the body physical and chemical barriers, e.g blood clotting Specific vs. Non-Specific Cure Prevents pathogens that have entered the body causing harm Immune system/leucoytes (phagocytotic & lymphocytes) Prevention Prevents pathogens entering the body Skin, mucus membranes, various other ‘fluids’ & structures Both can be artificially acquired The body’s defence: Non-specific • First line of defence: skin • Externally covered by keratinised protein of the dead cells - Tough and impervious • Folds in skin with moisture can lead to breaking barrier e.g. athlete’s foot • Diagram not required Non-specific immunity: summary • Complement system: 20 or so antimicrobial proteins in blood • Localised damage – inflammation: increased number of leucocytes. Mast cells secrete histamine which makes blood vessels ‘leaky’ – allowing complement to reach damaged tissue. • Blood clotting helps to seal off any wounds. Phagocytes – Non-Specific Secondary Defence Phagocytes are a type of leucocyte (white blood cell). They recognise the pathogen after it has been coated by an antibody and destroy it Phagocytes - Phagocytosis http://www.youtube.com/watch?v=KxTYyNEbVU4 v http://www.exploratorium.edu/imaging-station/gallery.php?Asset=Human+white+blood+cell+- SL Antibody Production What is the difference between an antibody and an antigen? Antigens vs. Antibodies FOREIGNERS RESPONSES TO THEM • Antigen (Ag)– molecule • Antibodies (Ab) – a globular recognised as foreign by the protein that recognises Ag immune system • The outer surface of microbes are covered in antigens • Antibodies are produced by special white blood cells called B-cell (Blymphocytes) • These are formed and matured in • Phagocytotic leucocytes may the bone marrow but are stored in present these on their outer the lymph nodes, where they come surface into contact with Ag SL Identify the antigen and antibody Structure of an antibody SL The blood contains two types of white blood cell or Leukocyte Phagocytes ingest bacteria by endocytosis… Lymphocytes produce antibodies… •There are many types of lymphocyte, you do not need to know them… but each has a very specific function within the immune system • CD4 lymphocyte deficiency is associated with AIDS and leads to reduced antibody and ‘killer’ production as this cell helps the others function SL Antibodies •Proteins that recognise and bind to specific antigens • Lock and key system • Antigens are foreign substances that stimulate production of antibodies •Many molecules on surface of viruses and bacteria are antigens SL •Antibodies are specific – they usually bind to only one specific antigen • Millions of different lymphocytes in the body, all with unique complement of antibodies to recognise the antigens Antibodies Antigen Microbe Est. a single humans is capable of generating ~10-billion different kinds of antibodies. Each type of antibody defends the body against a specific type of antigen. SL Production of Antibodies by Lymphocytes A lymphocyte can produce only one type of antibody so a huge number of different types are needed Each lymphocyte has some of its antibody on its surface… SL The antigens of a pathogen bind to the antibodies in the surface membrane of a lymphocyte… …This activates the lymphocyte. SL The active lymphocyte divides by mitosis to produce a clone of many identical cells MITOSIS The clone of cells starts to produce large quantities of the same antibody… … the same antibody needed to defend against the pathogen! SL Most microbes have more than one antigen on their surface, so… …they stimulate more than one type of lymphocyte… …resulting in the production of many different antibodies which will act against it. These are called polyclonal antibodies. SL Antigen Antigen Activate Lymphocyte (B-cell) Clone Memory Cell Activate Lymphocyte (Helper T-cell) Antibody Production: Summary Plasma Cell Macrophage/ Phagocyte Antibodies Immunity PacMan! • One PACMEN (phagocyte) You can eat things tagged with antibodies • Three + opposing pacmen (bacteria) You must be tagged – only then you can be destroyed • Three + fruits (lymphocytes) •Can tag the bacteria, making them recognisable to pacmen http://www.youtube.com/watch?v=ZbjTqkSuHeo Immunity Questions 1. 2. 3. 4. 5. 6. What is an antigen? [2] What is an antibody? [2] Where are leucocytes produced? [1] How are antibodies produced? [2] What is a memory cell? [2] What is meant by the ‘specificity’ of the immune response? [2] 7. How do antibodies kill antigens? [2] Marks out of 13: Immunity Answers 1. 2. 3. 4. 5. 6. 7. An antigen is a protein on the outside of a foreign cell that can be recognised as ‘foreign’ and can evoke an immune response A protein produced by certain leucocytes (B lymphocytes, plasma cells) in response to a specific antigen In the bone marrow Antibodies are produced by lymphocytes once they have come into contact with a complementary/specific antigen Memory cells are a type of lymphocyte that is produced during the primary/first immune response to an antigen (on a pathogen). They live for years and are responsible for the ‘immunity’ we develop after we have had a disease. Every WBC has a unique complement of antibodies. A specific antibodys only bind to specific antigens, thus a lymphocyte with a complementary antibody must come into contact with the antigen before an immune response happens The complementary ‘arm’ of the antibody binds to an antigen on the surface of a pathogen. Antibodies coat the pathogen, directly killing it or ‘tag’ it for phagocytosis/ ingestion by a phagocyte. Immunity Immunity multiple choice: 1. 2. 3. 4. 5. A B D B C Whiteboard Quiz http://www.cellsalive.com/quiz3.htm Question & Answer http://www.biology-questions-and-answers.com/the-immune-system.html Crash course biology (15 mins) http://www.youtube.com/watch?v=CeVtPDjJBPU SL SL SL Higher Level Details Antibody Production: The Primary Response Step 1: Antigen Presentation Antigen Macrophage Macrophages take in antigen by endocytosis The macrophage processes the antigen and attaches it to a membrane protein called a MHC protein The MHC protein is moved to the cell surface membrane by exocytosis so that the antigen is displayed on its surface. MHC protein Step 2: Activation of Helper T-cell Helper T-cells have receptors on their cell surface membranes which can bind to antigens presented by macrophages. receptor Helper T-cell Helper T-cell binds to macrophage presenting the antigen Macrophage sends a signal to activate the helper T-cell Step 3: Activation of B-lymphocytes B-cells have antibodies in their cell surface membranes Antigens bind to the antibodies in the surface membranes of B-cells Antigen Inactive B-cell Antibody An activated helper T-cell with receptors for the same antigen binds to the B-cell SIGNAL The helper T-cell sends a signal to the B-cell, activating the B-cell. Step 4: Proliferation The activated B-cell starts to divide by mitosis to form a clone of plasma cells. Plasma cells are activated B-cells with a very extensive network of rough endoplasmic reticulum. Plasma cells synthesis large amounts of antibody, which they excrete by exocytosis. The Secondary Response: Memory Cells • If an antigen invades your body a second time, a much faster response occurs which produces much larger quantity of the required antibody. •When activated B-cells are dividing during the primary response, some cells stop dividing and secreting antibody and become memory cells. • Large numbers of memory cells remain in the body for a long time… • …they are capable of producing large amounts of antibody very quickly when stimulated. Antigen Antigen Activate B-cell Clone Memory Cell Activate Helper T-cell Antibody Production: Summary Plasma Cell Macrophage Antibodies