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Transcript
11.1 Week 11 Immune Responses Area of Study 2 Detecting and Responding Key knowledge Specific immune response: T-cell lymphocytes and cell-mediated response; B-cell lymphocytes and humoral response, antigen, antibodies; memory cells. Key skills Investigate and inquire scientifically Apply biological understandings Communicate biological information and understanding. Tasks this week relate to Outcome 2. Describe and explain coordination and regulation of an organism’s immune responses to antigens at the molecular level. Relevant websites – See online biology course environment. Go to the Links section. Glossary terms for Week 11 can be found here: http://quizlet.com/_sfd5 Introduction Read carefully through this Week’s work before completing the tasks. The Objectives By the end of this week you should be able to: Define and distinguish in finer detail, specific and adaptive defences. Please note: Last week (Week 10) you covered features of the nonspecific immune defences. This week you will focus on the specific immune defences, in more detail. 11.2 The clonal-selection theory of antibody production Courtesy of Nature of Biology by Jacaranda When an antigen enters the body it probably passes many B cells before it meets one with immunoglobulin with which it can combine. In effect, the antigen ‘selects’ the B cell that will lead to its death. The B cell selected by the antigen reproduces rapidly to give rise to a number of identical cells. Each of these cells also reproduces rapidly to produce a large clone of cells. This is called clonal expansion. Cells cloned in this way will all have exactly the same genetic material and the same immunoglobulins. Most of these cells then differentiate into plasma cells and produce the same kind of antibody (see figure 8.15). An Australian, Sir Macfarlane Burnet, first proposed the clonal selection theory in 1955. There is a delay in this type of immune response because clonal expansion is necessary before sufficiently large amounts of antibodies can be made. This means that, if the infecting bacteria are able to reproduce to form relatively large numbers, a person may become quite ill before antibodies are produced that can react with the bacteria. Some of the B cells produced differentiate into other cells called Bmemory cells. B-memory cells also have the same antibody–antigen specificity as the parent B cell. Plasma cells survive for only a few days but memory cells can survive for several years and, in some cases, for life. If a second infection of the bacterium occurs, the B-memory cells react faster and more vigorously than the initial B-cell reaction to the first infection. There is not usually a noticeable effect from a second infection by the same antigen because the body reacts very quickly to eliminate the 11.3 ‘non-self material’. The person is said to be immune to the particular disease. When recovery from infection is complete, fewer plasma cells and antibodies are produced. Because most of the cells produced by clonal expansion are no longer required after recovery from the infection, they die by apoptosis (important to note this!). The following text is courtesy of Heinemann Biology Two 4 th Edition Antigens and antibodies The highly efficient defence provided by the immune system is based on its two distinguishing features: the ability to respond specifically against a particular foreign substance (an antigen) and the ability to ‘remember’ a previous encounter with a foreign substance and react very rapidly if it is encountered again. Antigens By definition, antigens are molecules, usually proteins or carbohydrates, that are able to bind to antibodies (or T cell receptors) and stimulate production of antibodies. T cell receptors are antibody-like molecules located on the surface of T cells. Antigens are found on the surface of cells and the outer coats of viruses, and they may be released by bacteria as toxins. Part of the antigen molecule stimulates lymphocytes to begin the immune response. Antibodies Most antibodies are large globular glycoproteins, called immunoglobulins (lg), produced by lymphocytes and released into the blood plasma. They are highly selective and react with specific antigen molecules (in a similar way to the interaction between enzyme and substrate). Antibody molecules are basically Y-shaped, with two identical arms that bind two antigen molecules and a stem that recruits complement activation. They may act singly (monomers), in pairs (dimers) or in groups of five (pentamers). See the following table of the five main classes of antibody molecules that have been identified. Courtesy Heinemann Biology Two 4th Edition. 11.4 Read through pages 182 to 190 of your text book and complete the tasks or questions that follow. Use your own A4 paper or send work as MSWord documents attached to an email SEND… Questions 1. How does the innate immune response differ from the adaptive immune response? 2. Why is it that over 10 million different types of antibodies can be produced by our body? 3. Plasma B lymphocytes possess an extensive rough endoplasmic reticulum, many Golgi apparatuses and many mitochondria. Explain why. You may need to refer to the glossary on page 388 for some of these terms. 4. Describe what is meant by ‘clonal selection’ using B cells as an example. 5. a. What type of compound is an antibody? b. How does an antibody differ from an antigen? c. List three ways that antibodies can act to fight off a pathogen. 6. Reorganise the boxes in Figure 11.1 below into a flow chart that could act as a battle plan for defence against an infection caused by Mycobacterium tuberculosis. You may present your flow chart in a branching form. It does not have to be a straight line. Figure 11.1 Complement proteins cause lysis of bacterial cells Phagocytes engulf bacterium destroyed by antibodies Histamines secreted by mast cells cause inflammation Antigens from bacterium bind with antibody on immature B cell T-helper cell secretes lymphokines to help B cells divide B cell divides to produce many plasma and memory cells Plasma cells produce many antibodies Antibodies bind with antigens on bacterium Mucous membrane lining trachea traps bacteria Memory cells migrate to lymph nodes to be ready to fight a second infection quickly Cilia lining trachea move mucus up and out of the body 11.5 7. Liver, heart and kidney transplants are now fairly common procedures in many hospitals. Recipients of these transplants, however, face the problem of rejection of these organs. a. Explain why the immune system rejects these organs. b. Organ recipients are usually treated with immunosuppressant drugs. What is the function of these drugs? c. What might be a negative effect of these drugs on the health of the patient? 8. It is advised that all children get immunised against the common childhood diseases, such as measles and polio. Figure 11.2 (on the next page) shows the effect of immunisation on antibody production. a. Explain the body’s primary response. b. Explain the trend shown following the second dose of antigen. Figure 11.2 The effect of immunisation on antibody production 9. a. b. c. d. Where are T cells originally formed and where do they mature? What type of response is produced by T cells? Describe the function of T-helper (TH) and cytotoxic T cells (TC). Explain the consequences of being born without T cells. 10. The life cycle of Trypanosoma brucei is described in Chapter 5. The parasite has a number of intermediate stages in both the tsetse fly and the human hosts. Explain, in terms of detection and response by the human immune system, why this is an advantage to the parasite. 11.6 11. Australia has many venomous snakes. One species, commonly called the death adder (Acanthophis antarticus), has one of the most dangerous bites in the world. The active component of the venom is an alpha-neutrotoxin that binds to the receptor sites for acetylcholine. Paralysis of muscles results and death can occur when the muscles of the diaphragm become paralysed and breathing is prevented. a. What type of substance is acetylcholine? b. What is the function of acetylcholine? c. Explain how the alpha-neurotoxin prevents the acetylcholine from working. d. Fortunately, there is an antivenom injection available to people who have been bitten by a death adder. If the antivenom is injected quickly enough it prevents the paralysis. The antivenom is prepared by injecting tiny amounts of snake venom into horses over a long period of time. The amounts of venom injected are so small that the horses are unaffected; however, there is a response by the horses’ immune system. What substances would the horse produce in order to counteract the snake venom in its body? e. What cells in the horse would be responsible for the formation of this substance? f. Explain why small amounts of venom are injected into the horse over a long period of time. g. Outline the steps involved in the formation of these substances. h. After 10-12 months blood is extracted from the horse and the plasma can be injected into snake-bite victims. What term is given to the use of horse plasma as a treatment for snakebite? i. How is this effective in treating the snake-bite victim? 12. Use the visual summary provided below. Write short phrases or words that could replace the lines that link the boxes – See the example I’ve provided below. Example: responses to entry of foreign material are important in identifying self. 11.7 Key Summary Points Specific defence is provided by an elaborate immune system. Vertebrate immune responses are characterised by specificity and memory. Immune responses involve lymphocytes (a particular group of white blood cells formed in the bone marrow and spleen.) Immune responses include both humoral (‘blood-borne’) and cellmediated mechanisms. In humoral immunity antibodies are released by B cells; in cell-mediated immunity, active destruction is carried out by T cells. Antigens are molecules able to bind to antibodies or T cell receptors. They stimulate lymphocytes to begin the immune response. Antibodies are specific proteins produced by lymphocytes that are able to react with particular antigen molecules. T cells are responsible for cell-mediated immune responses. Tc cells act against virus-infected cells, cancer cells and transplanted tissue. TH cells assist B cells and TC cells. B cells are lymphocytes that produce large quantities of antibodies when stimulated by particular antigens. This is the humoral immune response. The clonal selection theory explains how, using only a moderate amount of DNA, the immune system responds quickly to an almost unlimited array of foreign antigens. Challenging Activity: Mnemonic Activity Choose one or more terms from the list given on page 199 of your textbook and create a memory aid to help you remember the definition of that term. You may use drawings, poetry, song, sound, whatever works for you! Share your ‘mnemonic’ (memory aid) with the other students of your class via the chat room. Feel free to discuss your ideas with me. Use the glossary found on page 388 for definitions of terms. Log on to the www.decvonline.vic.edu.au check out the back of your DECV book for your login details if you have forgotten. Click on the link to the Unit 3 Biology course. Click on the button “Discussion Room” Place your Mnemonic as a comment to the Discussion post titled Mnemonics Week 11. Make sure you check out the other Mnemonics left by your classmates and leave them a comment. 11.8 Challenging Activity: Personal Reflection Log on to the VCE Biology Course. Place your Personal Reflection in the Biology Blog as outlined on 0.7 in the introduction of this book. Exam Practice Exercise Past Exam Questions Each week you will get at least one question which relates to the weeks work, which comes from a past VCE exam paper. The purpose of this task is to familiarize yourself with the type of questions you will encounter during the exam and the timing you should devote to each. Timing You should allow 1 minute and ten seconds per mark assigned to the question. Question 1 (Q20, 2000) Non-specific immunity in mammals includes A. the action of lysozymes in tears and saliva. B. the production of antibodies after infection. C. the production of memory cells. D. the action of T helper cells. 1 marks Question 2 (Q7, 2001) A bacterium with two different proteins on its surface can be represented as follows: Antibodies produced against this bacterium include: 11.9 1 marks Question 3 (Q8, 2001) Specific immunity in a person includes: A. ingestion of bacteria by phagocytes. B. involvement of helper T cells and B cells. C. development of inflammation around a cut. D. production of lysozymes in tears. 1 marks Question 4 (Q22, 2002) In humans, non-specific immunity includes: A. production of antibodies by plasma cells. B. different responses for different bacteria. C. destruction of bacteria by enzymes in saliva. D. presentation of material to a T cell by a phagocyte. 1 marks (Total 4 marks) Checklist This week you should have sent this work to me. Please tick the items you have sent, and keep this as your record: Responses to Questions 1-12 At least one mnemonic of a biological term left online Your personal Reflection left online Don’t forget to drink plenty of water! 11.10 Feedback What if anything needs to be improved, corrected, cleared up or presented better from the materials presented in this week? Your honesty is appreciated. Write your comments on the back of the cover sheet. Answers to Past Exam Questions Question 1 Non-specific immunity in mammals includes: A. The action of lysozymes in tears and saliva. All the other alternatives mention elements of specific immunity. Question 2 Antibodies produced against this bacterium include: C. (Alternatives B and D can be eliminated because their antigen binding sites do not fit either of the proteins on the surface of the bacterium. Alternative A is incorrect as it shows an antibody with 2 different antigenbinding sites. One antibody has 2 identical antigen-binding sites. Question 3 Specific immunity in a person includes: B. Involvement of helper T cells and B cells. All other alternatives are examples of non-specific immunity. Question 4 In humans, non-specific immunity includes: C. Destruction of bacteria by enzymes in saliva. A, B and D are all part of specific immunity. END OF WEEK 11 11.11 315 Clarendon Street, Thornbury 3071 Telephone (03) 8480 0000 FAX (03) 9416 8371 (Despatch) Toll free (1800) 133 511 Fix your student barcode label over this space. SCHOOL NO. 64811 [64811] STUDENT NUMBER ___________________ SCHOOL NAME _______________________ STUDENT NAME ______________________ SUBJECT Biology Unit 3 YEAR/LEVEL TEACHER 12 WEEK 11 ________________________ [ZX] PLEASE ATTACH WORK TO BE SENT. NOTE: Please write your number on each page of your work which is attached to this page. SEND Please check that you have attached: Response to Questions 1-12 At least one mnemonic of a biological term left online Your Personal Reflection for week 11 If you have not included any of these items, please explain why not. _____________________________________________________________________________ _____________________________________________________________________________ _____________________________________________________________________________ Use the space on the back of this sheet if you have any questions you would like to ask, or problems with your work that you would like to share with your teacher. 11.12 YOUR QUESTIONS AND COMMENTS Please provide the following information: Were you able to complete the tasks in the time frame allocated? ____________________ Roughly how long did it take for you to complete this week of work? _____________ Use this space for any queries or comments you have, (or maybe errors you’ve found). DISTANCE EDUCATION CENTRE TEACHER’S COMMENTS DISTANCE EDUCATION CENTRE TEACHER