IB Biology ReviewImmune System

Immune System Vocab

PathogenAn organism or virus that causes a disease

AntigenAny foreign macromolecule (either proteins, polysaccharides or structures on the surface of bacteria) that triggers an immune response

AntibodyAntibodies are proteins that bind to particular antigens and mark them for elimination from the body

AntibioticsAny substance that is able to kill or inhibit a microorganism such as bacteria

Passive versus Active Immunity

Passive immunity is due to the acquisition of antibodies from another source Such as

when a developing fetus acquires antibodies from its mother when they are artificially injected into a person

Active immunity is when antibodies are produced by the person themselves after his or her immune system is triggered by antigens

Immune System Vocab cont.

VirusAn infective agent consisting of a protein coat surrounding an RNA or DNA coreAre not cells and do not possess membranes or organelles. They cannot manufacture their own proteins and must invade living cells to take over their protein production “machinery”

LeucocytesWhite blood cells

Phagocytic leucocytesSpecialized white blood cells that engulf foreign/invading pathogens and destroy them

Different Types of LeucocytesThe only ones we need to know are monocytes and macrophages, and lymphocytes

Why are antibiotics effective against bacteria, but not viruses?

Most antibiotics don’t kill bacteriaAntibiotics disrupt their reproduction (binary fission) by preventing formation of the bacterial cell wall in the “daughter cells” (a part of the cell’s metabolism)Since viruses aren’t cells and don’t produce cell walls, antibiotics are not effective against them

What are the different components

of the immune system?

Skin Mucous membranesPhagocytic leukocytesAntibodies

Skin and Mucous Membranes

These are a form of external defense preventing pathogens from entering the bodySkin forms a physical barrierMucous membranes surround invading pathogensBody senses excess mucous, induces coughingCoughing expels the mucous and the trapped pathogen

Phagocytic Leucocytes

A type of white blood cellFloat around the body in bloodPhagocyte surrounds the pathogen by endocytosisA vacuole containing the pathogen travels to a lysosome The membranes of the vacuole and lysosome fuseDigestive enzymes in the lysosome destroy the pathogenThe pathogen “debris” is released by exocytosis

Phagocytic Leucocyte Diagram

Antibodies

Proteins that recognize one kind of antigenSimilar to enzymes (lock and key)

Lock and key called “epitope”

React by binding to the antigenDestroys antigen

OrInactivates antigen

Antibody Production Pathogen is in the bodyPhagocytic leucocytes called macrophages ingest the pathogens Phagocytes “present” the antigens from the pathogens on their cell surface. T-helper cells (another type of leucocyte that is specific to that antigen) bind to the antigen presented by the macrophages and are activated/stimulatedMeanwhile, B-cells bind to the antigen, and present the antigen as the phagocytes did

Antibody Production cont.The activated T-helper cells then bind to B-cells and activate them;This triggers the B-cells to undergo mitosis to form memory cells and plasma cellsShort-lived Plasma B-cells secrete antibodies quickly that neutralize the pathogenMemory B-cells stay in the blood for a long time and enable a more rapid response by the immune system if the same pathogen invades in the future

HL Only: Monoclonal Antibodies

Monoclonal antibodies—large quantities of a single type of antibodyproduced in a laboratory

Hybridoma cellmemory B cell fused with a tumor celldivides uncontrollably, producing a large amount of antibodies

HL Only: Monoclonal Antibody Production

1. Antigens that correspond to a desired antibody are injected into an animal2. B-cells producing the desired antibody are harvested 3. Tumor cells are obtained from another source (tumor cells grow and divide endlessly)4. B-cells are fused with tumor cells, producing hybridoma cells that divide endlessly, providing the desired antibodies5. The hybridoma cells are cultured and the antibodies they produce are extracted and purified

HL Only: Application of Monoclonal Antibodies: Rabies

TreatmentRabies usually causes death in humans before the immune system can control it. Injecting monoclonal antibodies when a person gets infected will control the virusAt the same time, the person's body begins making its own antibodiesTriggers two-fold immune response

Passive through injectionActive through body’s production

HL Only: Application of Monoclonal Antibodies: Malaria

Diagnosis1. Monoclonal antibodies are made to bind to antigens in malarial parasites2. A test plate is covered with antibodies 3. The sample is left on the plate long enough for malaria antigens (if present) to bind to antibodies4. The sample is rinsed off Any bound antigens are detected using more monoclonal antibodies with attached color-changing enzyme

HL Only: Challenge and Response,

Clonal Selection, and Memory CellsB-cells make antibodies

The immune system can make 1015 different types of antibodies (but not all at once) A few of each type of B-cell are produced and they wait until the body is infected with an antigenWhen this occurs, they multiply to form many clonesThis is called clonal selectionA clone of B-cells can produces large amounts of antibodies quickly and give immunity to a disease

Only after the immune system is challenged by a diseaseThis is called the challenge and response system

Vaccination

A weakened or dead version of a pathogen is injected into the body, causing the immune system to mount a primary responseThis results in the production of B memory cells The B-cells "remember" the antibodies to produce in response to the pathogenWhen the real pathogen strikes, a secondary response occurs, aided by the memory cell production of pathogen-specific antibodiesThis response is much stronger than the primary response and prevents any ill effects

HL Only: Benefits and Dangers of Vaccines

Benefitsprevent disease and epidemicsresults in a healthier societyreduces long-term medical costsspeed up the body's response to a future disease by memory B-cells

Dangerspossible allergic reactionsdanger of side-effects

HIV and the Immune System

HIV virus kills Helper T-cellsHelper T-Cells tell B-cells there is a pathogenImmune system cannot mount an effective defense against invading pathogensPatients then succumb to secondary infections

Blood ClottingDamaged cells in the blood vessel release compounds called “clotting factors”These factors trigger the formation of the enzyme thrombinThrombin catalyzes the conversion of soluble fibrinogen in the blood to the fibrous protein fibrinFibrin forms threads which create an interwoven netPlatelets and blood cells get caught in the net and plug up the wound

Blood Clotting Diagram

1. Which is not true of active immunity? (1 mark)

A. It can be produced by exposure to a disease causing organism.

B. It can be produced artificially.C. It can be produced by a virus.D. It can be transferred via the

colostrum.

Correct answer: DIf you’ve never heard of it, it’s probably a trick question!

IB Exam Question

2. Describe how human skin and mucous membranes act as

barriers to pathogens.(4 marks)To receive full marks, responses must have two

answers for each.Skin

lower pH / acid to keep bacteria from growing / chemical barrier;fatty acids / waxes antimicrobial;physical barrier to prevent entry / dry skin inhibits bacterial growths;bacteria on skin / mucous membranes prevent other bacteria from growing;antimicrobial / lysozyme in sweat and saliva (mucous membrane) to keep bacterial growth in check;

Mucous membranesmucous traps bacteria / sticky / mucus slightly acidic i.e. vagina cilia sweep mucous up to be swallowed to kill bacteria;contain macrophages / phagocytes;

IB Exam Question

3. Outline how phagocytic leucocytes ingest pathogens in the blood and in

body tissues.

The phagocytic cell surround the pathogen by endocytosisA vacuole containing the pathogen travels to a lysosome and the membranes of the vacuole and lysosome fuseDigestive enzymes in the lysosome destroy the pathogenThe pathogen “debris” is released by exocytosis

IB Exam Question

4. Which of the following represents the correct sequence of events when the body is

responding to a bacterial infection? (1 mark)I. Antigen presentation by

macrophagesII. Activation of B-cellsIII. Activation of helper T-cells

A. I, II, IIIB. I, III, IIC. III, II, ID. II, III, I

Correct answer: B

IB Exam Question

5. Explain antibody production. A vaccine is injected into body This vaccine contains killed / weakened pathogen or fragments of pathogens Phagocytic leucocytes called macrophages ingest the pathogens and “present” the antigens from the pathogens on their cell surface. Helper-T cells (another type of leucocyte that is specific to that antigen) bind to the antigen presented by the macrophages and are activated/stimulatedMeanwhile, B-cells bind to the antigen, and present the antigen as the T cells didThe activated T-helper cells then bind to B-cells and activate them;This triggers the B-cells to undergo mitosis to form memory cells and plasma cellsShort-lived Plasma B-cells secrete antibodies quickly that neutralize the pathogenMemory B-cells stay in the blood for a long time and enable a more rapid response by the immune system if the same pathogen invades in the future

IB Exam Question

6. Which type of cell is responsible for secondary immune responses to a

pathogen? (1 mark)

A. Cytotoxic T-cellsB. PhagocytesC. MacrophagesD. Memory cells

Correct answer: D

IB Exam Question

HL Only: 7. Outline the principles of challenge and response, clonal selection, and memory cells as the

basis of immunity. B-cells make antibodiesThe immune system can make 1015 different types of antibodies (but not all at once)A few of each type of B-cell are produced and they wait until the body is infected with an antigen When this occurs, they multiply to form many clones; this is called clonal selectionA clone of B-cells can produces large amounts of antibodies quickly and give immunity to a disease, only after the immune system is challenged by a diseaseThis is called the challenge and response system

IB Exam Question

8. Which type of immunity usually results from vaccination? (1 mark)

A. active, naturalB. active, artificialC. passive, naturalD. passive, artificial

Correct answer: B

IB Exam Question

9. Discuss the benefits and dangers of vaccination. (8 marks)

Benefits [5 max]prevent disease;eliminate diseases: like smallpox prevent epidemics;healthier society;reduce medical cost;disease free cattle / more food;

Dangers [3 max]allergic reactions / anaphylactic shock;weakened virus becomes virulent / causes the disease;harmful side-effects;

IB Exam Question

10. Which curve shows the response of the immune system to a vaccine, followed

by an infection?

(1 mark)

Correct answer: B

IB Exam Question

HL Only: 11. Describe the production of monoclonal antibodies along with one use of them in diagnosis and one use in treatment.Monoclonal antibodies - large quantities of a single

type of antibody, produced using the procedure outlined below. 1. Antigens that correspond to a desired antibody are injected into an animal. 2. B-cells producing the desired antibody are extracted. 3. Tumor cells are obtained from another source (tumor cells grow and divide endlessly). 4. B-cells are fused with tumor cells, producing hybridoma cells that divide endlessly, providing the desired antibodies. 5. The hybridoma cells are cultured and antibodies they produce are extracted and purified.

IB Exam Question

HL Only: 11. Describe the production of monoclonal antibodies along with one use of them in diagnosis and one use in treatment. cont.Treatment of rabies

Rabies usually causes death in humans before the immune system can control it. Injecting monoclonal antibodies when a person gets infected will control the virus and at the same time, the person's body begins making its own antibodies.

Diagnosis of malaria 1. Monoclonal antibodies are made to bind to antigens in malarial parasites. 2. A test plate is covered with antibodies. 3. The sample to be tested is left on the plate long enough for malaria antigens (if present) to bind to antibodies. 4. The sample is rinsed off and any bound antigens are detected using more monoclonal antibodies with attached color-changing enzyme.

IB Exam Question

12. Outline the effect of HIV on the immune system.

The HIV virus results in the death of Helper T-cellsTherefore, the immune system of the infected individual cannot mount an effective defense against invading pathogensPatients can then succumb to secondary infections

IB Exam Question

13. Describe the process of blood clotting.

Damaged cells in the blood vessel release compounds called “clotting factors”These factors trigger the formation of the enzyme thrombinThrombin catalyzes the conversion of soluble fibrinogen in the blood to the fibrous protein fibrinFibrin forms threads which create an interwoven net. Platelets and blood cells get caught in the net and plug the open cut

IB Exam Question