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Immunity
This document provides information about the immune system and how it protects the body from infection. It discusses the different lines of defense, including physical barriers, innate immunity through macrophages and natural killer cells, and adaptive immunity through B cells, T cells, antibodies, and the development of immunity either actively through vaccination or passively through transfer of antibodies. It also describes the types of pathogens that can cause infection, how pathogens are spread, and examples of diseases like tuberculosis, measles, mumps and rubella.
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Immunity
- 1. 1 of 41© Boardworks Ltd 2006
- 2. © Boardworks Ltd20062 of 41 • Pathogens • Microorganisms that cause diseases • Commensals • Those that live in harmony with the host without causing any damage to it
- 3. © Boardworks Ltd20063 of 41 INFECTION • Lodging and multiplication of pathogens in or on tissues of a host
- 4. © Boardworks Ltd20064 of 41 Primary infection • Infection that develops in an otherwise healthy host
- 5. © Boardworks Ltd20065 of 41 Re - infection • Infection by the same organism again in the same host
- 6. © Boardworks Ltd20066 of 41 Secondary infection • Infection in the host affected by primary infection by a new organism
- 7. © Boardworks Ltd20067 of 41 Disease-causing organisms Organisms that cause disease are called pathogens. bacteria fungi protozoa virus What are the four major types of pathogen?
- 8. © Boardworks Ltd20068 of 41 How do pathogens cause illness? Toxins Toxins are harmful substances produced by the pathogen that poison the body’s tissue and enzymes. Reproduction A rise in the number of pathogens can damage a cell, even causing it to burst. Some pathogens hijack resources that the cell needs to survive. Immune response Sites of infection often become swollen, sore and hot as a result of increased blood flow. Pathogens cause illness in three main ways:
- 9. © Boardworks Ltd20069 of 41 How are pathogens spread? Different pathogens have different transmission routes: direct contact indirect contact food and water airborne droplets insect bites
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- 11. © Boardworks Ltd200611 of 41 Fighting infection How does the body fight infection?
- 12. Immunity to Infection •Immunity is the acquired ability to defend against infection by disease-causing organisms.
- 13. Overview of yourimmune system • First line of defense: Physical barriers that viruses, bacteria must cross – skin covers ~2 m2 – Mucous membranes that line digestive, respiratory, reproductive tracts cover ~400 m2 • Second line of defense: Innate immune system (germline-encoded receptors -- no adaptation to specific pathogens) – Macrophages (Greek for “big eater”), neutrophils, natural killer (NK) cells • Third line of defense (vertebrates only): Adaptive immune system (adapts to defend against specific pathogens using variable receptors) – B cells make antibodies that vary -- can make an antibody specific for any new antigen – T cells mediate cellular responses using variable receptors (T cell receptors; TCRs)
- 14. © Boardworks Ltd200614 of 41 First line of defence
- 15. © Boardworks Ltd200615 of 41 Painkillers can relieve the symptoms of an infection but do not kill the pathogen. Invasion! A pathogen enters your body through direct or indirect contact. What happens next? Your immune system begins to mount an attack. The pathogen begins to reproduce and make toxins that destroy the body’s cells and make you feel unwell.
- 16. © Boardworks Ltd200616 of 41 Second line of defence – Innate immunity Macrophages
- 17. © Boardworks Ltd200617 of 41 Second line of defence - Natural killer (NK) cells • Can kill tumor cells, virus-infected cells, bacteria, parasites, fungi in tissues • Identify targets based on “missing self” – Two types of NK receptors: inhibitory and activating – If inhibitory receptor recognizes a self protein (a class I MHC molecule) on a target cell, the NK cell is turned OFF even if activating receptor binds a ligand on the same target cell – If activating receptor binds a ligand, but inhibitory receptor does not (target cell has down-regulated class I MHC proteins), NK cells kill – Many virally-infected cells and tumor cells down-regulate expression of class I MHC molecules (NK cells important for preventing cancers)
- 18. © Boardworks Ltd200618 of 41 Resisting attack TB bacteria have a number of adaptations that enable them to resist phagocytosis: They produce chemicals that prevent macrophages from being attracted to sites of infection. They have a waxy cell wall that resists enzyme attack and secretes chemicals that block lysosomes from fusing with phagosomes. How does the immune system deal with these bacteria?
- 19. © Boardworks Ltd200619 of 41 Third line of defence - Lymphocytes Lymphocytes are a type of white blood cell found in the blood or lymph nodes and made by bone marrow. There are several types of lymphocyte, including: T-lymphocytes – recognise antigens on pathogens and either attack them directly or co-ordinate the activity of other cells of the immune system. B-lymphocytes – recognise antigens and produce special chemicals called antibodies.
- 20. © Boardworks Ltd200620 of 41 B lymphocytes Antibodies are special Y-shaped proteins produced by B-lymphocytes in response to antigens. Antibodies work by binding to antigens on pathogens, ‘labelling’ them and causing them to clump together. The pathogen can then be destroyed by: the antibodies themselves. phagocytosis by macrophages T-lymphocytes
- 21. © Boardworks Ltd200621 of 41 Antibodies Each different type of antigen causes a different type of antibody to be produced. An antibody can only bind to the antigen that caused it to be produced.
- 22. © Boardworks Ltd200622 of 41 Delayed response The B-lymphocyte that produces the correct antibody for the antigen begins dividing to produce many more antibody- producing cells. It takes a few days to produce enough antibodies to destroy the pathogen. This means there is delay between infection and the person beginning to feel better. Once a pathogen has been destroyed, a few memory cells remain. These recognize the pathogen if it re-infects, and make the immune response much quicker and more effective. This is called active immunity.
- 23. © Boardworks Ltd200623 of 41 Antibody levels during infection
- 24. © Boardworks Ltd200624 of 41 T cells How does the body deal with pathogens that are inside cells? Viruses and bacteria that infect cells leave antigens on the surface of the cell they infect. T-lymphocytes recognize these antigens by receptors on their surface and destroy the whole infected cell. infected cell T-cell antigen receptor
- 25. © Boardworks Ltd200625 of 41 Types of Immunity Artificially acquired Passive immunityActive immunity Naturally acquired Naturally acquired Artificially acquired
- 26. © Boardworks Ltd200626 of 41 Types of Immunity • Natural immunity is the result of a body’s previous encounter with an organism. • Artificial immunity results from the injection of a vaccine or an antibody. Vaccines stimulate active immunity whereas injection antibody or antiserum is an example of passive immunity.
- 27. © Boardworks Ltd200627 of 41 Types of Immunity • Active immunity is when the immune system encounters and antigen and is primed to recognise it and destroy it quickly the next time it is encountered. This is active immunity because the body’s immune system prepares itself for future challenges. • Passive immunity is short-term and involves the transfer of immunity from one individual to another via antibody-rich serum. This may be artificial as is the case with anti-venom or natural, as in antibodies crossing the placenta to protect the developing foetus.
- 28. © Boardworks Ltd200628 of 41 Immunity Active immunity Production of a person’s own antibodies. Long lasting Passive immunity An individual is given antibodies by another Short-term resistance (weeks- 6months) Natural Active When pathogen enters body in the normal way, we make antibodies Natural Passive Baby in utero (placenta) Breast-fed babies Artificial Passive Gamma globulin injection Extremely fast, but short lived (e.g. snake venom) Edward Jenner Artificial Active Vaccination – usually contains a safe antigen from the pathogen. Person makes antibodies without becoming ill
- 29. © Boardworks Ltd200629 of 41 Passive immunity Many snakes produce a powerful nerve toxin that can be lethal to humans. Antivenin contains antibodies to give instant immunity. It is produced by injecting horses with small, non-lethal doses of venom. Over time, the horses produce antibodies, which are extracted and processed. People bitten by poisonous snakes can be treated with antivenin. Because the person didn’t make the antibodies themselves, this is called passive immunity.
- 30. © Boardworks Ltd200630 of 41 Vaccines contain a small amount of dead or weakened pathogen particles. What are vaccines? A vaccine stimulates the production of antibodies and memory cells against the target pathogen, without making the person ill. If a vaccinated person is later infected by the same pathogen, their immune system can destroy it very quickly. Parents of two-year-old children are offered a combined measles, mumps and rubella (MMR) vaccine to protect their child. What has happened to MMR vaccination rates recently?
- 31. © Boardworks Ltd200631 of 41 Measles, mumps and rubella MMR vaccination rates used to be high, but fell following a media scare story. The media reported on controversial research speculating that MMR could cause autism, a behavioural disorder causing learning and communication difficulties.
- 32. © Boardworks Ltd200632 of 41 Glossary (1/2) antibiotic – A drug that can destroy or prevent the growth of bacteria. antibody – A Y-shaped protein produced by the body that binds to antigens. antigen – A substance on pathogens that stimulates the production of antibodies. B-lymphocyte – A white blood cell that produces antibodies. immunization – The process of protecting against infection by using a vaccine. immune response – The body’s defence against foreign material such as pathogens.
- 33. © Boardworks Ltd200633 of 41 Glossary (2/2) immunity – The ability to fight infection by pathogens. It can be active or passive. pathogen – A disease-causing micro-organism. phagocytosis – The process where a type of white blood cell called a macrophage ingests and destroys a pathogen. T-lymphocyte – A type of white blood cell that recognises and destroys pathogens, and co-ordinates the immune response. tuberculosis – A serious bacterial disease that mainly affects the respiratory system. vaccine – A small amount of dead or weakened pathogen that stimulates antibody production.
- 34. © Boardworks Ltd200634 of 41 Multiple-choice quiz
- 35. © Boardworks Ltd200635 of 41 • Please read after going back • Things here are highly volatile
Editor's Notes
- #12 Teacher notes This illustration contains several discussion points relating to the immune response. Pathogens inside the building are holding a couple of white blood cells hostage. Outside, one of the pathogens has been caught (i.e. recognized) by a T-cell, who is co-ordinating the attack (immune response) on the rest of the pathogens. B-cells ( the riot police) are awaiting instructions from the T-cell. The clubs held by the B-cells represent antibodies that they will use to attack the pathogens.
- #17 Teacher notes This five-stage animation illustrates the process of phagocytosis of a bacterium by a macrophage. Suitable prompts could include: How does the macrophage know to ingest the bacterium? How does the macrophage envelop the bacterium? How could the macrophage safely destroy the bacterium?
- #24 Teacher notes Students could be asked to draw predicted graphs on mini whiteboards and then compare them with these graphs to consolidate their understanding of the previous slide.
- #29 Gamma globulin – from animals
- #30 Photo credit: © 2006 Jupiterimages Corporation
- #32 Photo credit: © 2006 Jupiterimages Corporation
- #35 Teacher notes This multiple-choice quiz could be used as a plenary activity to assess students’ understanding of infections and immunity. The questions can be skipped through without answering by clicking “next”. Students could be asked to complete the questions in their books and the activity could be concluded by the completion on the IWB.