Unit 2C - cells and the immune system

Question 1

what are antigens?

Answer 1

they are molecules (usally proteins) that can generate an immune response when detected by the body.

Question 2

where do you find antigens and what do they do?

Answer 2

they are usually found on the surface of cells and are used by the immune system to identify pathogens, abnormal body cells, toxins and cells from other individuals of the same species.

Question 3

what are the 4 main stages to an immune response?

Answer 3

1) phagocytosis
2) phagocytes active T - cells
3) T-cells activate B-cells which divide plasma cells
4) plasma cells make more antibodies to a specific antigen

Question 4

what are the stages to phagocytosis?

Answer 4

1. chemotaxis
2. endocytosis
3. forms a phagosome
4. a lysosome joins the vesicle which makes a phagolysosome
5. enzyme digests the bacteria via a hydrolysis reaction
6. exocytosis
7. the white blood cell becomes a antigen presenting cell to trigger an immune response

Question 5

what happens when phagocytes activate T-cells

Answer 5

T lymphocytes is another type of white blood cell. it has receptor proteins on its surface that bind to complementary antigens presented to it by phagocytes. this activates the T-cell. different types of T-cell respond in different ways. e.g. helper T-cells release chemicals signals that activate and stimulate phagocytes and cytotoxic T-cells which kills abnormal and foreign cells. T helper cells also activate B-cells which secrete antibodies.

Question 6

how do T-cells activate B-cells which divide into plasma?

Answer 6

B lymphocytes are also a type of white blood cell. they’re covered with antibodies - proteins that bind antigens to form an antigen - antibody complex. each B-cell has a different shaped antibody on its membrane so different ones bind to different shaped antigens.
1)when the antibody on the surface of a B-cell meets a complementary shaped antigen, it binds to it.
2) this, together with substances released from helper T-cells activates the B-cell. this process is called clonal selection.
3) the activated B-cell divides into plasma cells

Question 7

how do plasma cells make more antibodies to a specific antigen?

Answer 7

plasma cells are identical to the B-cell (they’re clones). they secrete loads of antibodies specific to the antigen. these are called monoclonal antibodies. they bind to the antigens on the surface of the pathogen to form lots of antigen-antibody complexes.
an antibody has two binding sites, so can bind to two pathogens at the same time. this means that pathogens become clumped together - this is called agglutination. phagocytes then bind to the antibodies and phagocytes then bind to the antibodies and phagocytose many pathogens at once. this process leads to the destruction of pathogens carrying this antigen in the body.

Question 8

what is an antibody

Answer 8

they are proteins made up of chains of amino acids. the specificity of an antibody depends on its variable regions, which form the antigen binding sites. each antibody has a variable region which a unique tertiary structure (due to different amino acid sequences) that complementary to one specific antigen. all antibodies have the same constant regions.

Question 9

what is the cellular immune response?

Answer 9

the T cells and other immune system cells that they interact with e.g. phagocytes from the cellular response
an immune response that does not rely on the production of antibodies

Question 10

what is the humoral immune response?

Answer 10

this is the production of specific antibodies in response to a specific antigen that dissolves and travel in the body fluid

Question 11

what is the primary immune response

Answer 11

1) when an antigen enters the body for the first time it activates the immune system. this is called the primary response.
2)the primary response is slow because there aren’t many B-cells that can make the antibody needed to bind it.
3) eventually the body will produce enough of the right antibody to overcome the infection. meanwhile the infected person will show symptoms of the disease.
4) after being exposed to an antigen, both T and B cells produce memory cells. these memory cells remain in the body for a long time. memory T-cells remember the specific antigen and will recognise it a second time round. memory B-cells record the specific antibodies needed to bind the antigen.
5) the person is now immune - their immune system has the ability to respond quickly to a second infection.

Question 12

what is the secondary immune response?

Answer 12

1) if the same pathogen enters the body again, the immune system will produce a quicker, stronger immune response - the secondary response.
2) clonal selection happens faster. memory B-cells are activated and divide into plasma cells that produce the right activated and divide into the correct type of T-cells to kill the cell and carrying the antigen
3) the secondary response often gets rid of the pathogen before you begin to show any symptoms (you are immune to the pathogen)

Question 13

whats a lymphocyte

Answer 13

small white blood cell with little cytoplasm and spherical nuclei, which originate from stem cells in the bone marrow.

Question 14

where do mature lymphocytes

Answer 14

in the spleen, lymph nodes, adenoids and tonsils as well as the lymphatic system and general circulation of the blood.

Question 15

what is the lymphatic system

Answer 15

• drains tissue fluid back into the blood
• removes waste material from around cells, including pathogen antigens
• transports digested fat to the blood system
• lymph nodes, thymus and spleen house lymphocytes
• transports APCs, T and B cells in search of match to an antigen

Question 16

types of phagocytes

Answer 16

• neutrophil - smaller, destroy any cells, short life span
• macrophage - larger engulf bacteria, infected cells etc
• dendritic cells - antigen presenting cells (APCs) communicate with the specific immune system

Question 17

2 types of lymphocytes

Answer 17

B cells - mature in bone marrow, migrate to lymph nodes = huoral response (antibodies)
T cells - mature in thymus gland and migrate to lymph nodes = cellular response

Question 18

what is autoimmune disease

Answer 18

if negative selection fails, some lymphocytes can survive and attack the body own tissue e.g. arthritis

Question 19

whats apoptosis

Answer 19

negative selection (programmed cell death) so immune system doesn’t attack cell tissue.

Question 20

what do T helper cells do?

Answer 20

messages other molecules to trigger next stages of immune responses - Tcytotoxic

Question 21

what do T killer cells do?

Answer 21

small molecules that causes cells to move and/or behave in a particular way
cytokines

Question 22

what is clonal selection

Answer 22

lymphocytes (specific) triggered by APC to do mitosis (B and T cells)

Question 23

whats the order of the immune response

Answer 23

1) phagocytosis
2) clonal selection
3) memory cells
4) the response is quicker
5) more T memory cells

Question 24

whats a non-specific defensive mechanisms?

Answer 24

response is immediate and the same for all pathogens
1) primary methods e.g. skin - physical barrier
2) secondary methods e.g. phagocytosis

Question 25

what a specific defence mechanisms?

Answer 25

response is slower and specific to each pathogen 1) cell - mediated response ---> T lymphocytes 2) humoral response --> B lymphocytes

Question 26

what are the first signs of an immune response?

Answer 26

- alarm chemicals (histamine) released --> signal further immune response -blood vesicles enlarge and capillaries become 'leaky' which allow white blood cells to move more freely - redness and swelling, heat and pain all cause by extra blood carrying immune system cells

Question 27

how do vaccinations work to stop the spread of a disease?

Answer 27

1) while your B-cells are busy dividing to build up their numbers to deal with a pathogen (i.e. the primary response) you suffer from the disease. vaccinations can help avoid this. 2) vaccines often contain antigens that cause your body to produce memory cells against a particular pathogen, without the pathogen causing disease. this means you can become immune without any symptoms 3) antigens in vaccinations may be free or attached to a dead or attenuated (weakened pathogen)

Question 28

what is heard immunity

Answer 28

vaccines can protect individuals that have them and because they reduce the occurrence of the disease, those not vaccinated are also less likely to catch the disease

Question 29

how can you take vaccinations and what are the disadvantages?

Answer 29

vaccinations may be injected or taken orally however when taken orally the disadvantage is that it could be Brocken down by enzymes in the gut or the molecules of the vaccine may be too large to be absorbed in the blood

Question 30

what is the use of a booster vaccines?

Answer 30

these can be given later on to make sure that memory cells are produced. this can be after several years

Question 31

how does antigenic variation work?

Answer 31

1) antigens on the surface of pathogens activate the primary response 2) when your infected a second time with the same pathogen (which has the same antigens on its surface) they activate the secondary response and you don't get ill. 3) however some sneaky pathogens can change their surface antigens . this antigen variability is called antigenic variation (different antigens are formed due to changes in the genes of a pathogen)

Question 32

how could antigenic variation affect the production of vaccines to help prevent people from catching influenza?

Answer 32

1) the influenza (flu) vaccine changes every year. that's because the antigens on the surface of the influenza virus change regularly, forming new strains of the virus 2) memory cells produced from vaccination with one strain of the flu will not recognise other strains with different antigens. the strains are immunologically distinct 3) every year there are different strains of the influenza virus circulating in the population so a different vaccine has to be made 4) new vaccines are developed and one is chosen every year that is the most effective against the recently circulating influenza viruses 5) governments and health authorities then implement a programme of vaccination using the most suitable vaccine

Question 33

what does it mean if your infected again for the second time but antigenic variation has taken place?

Answer 33

1) memory cells produced from the first infection will not recognise the different antigens. so the immune system has to start from scratch and carry out a primary response against these new antigens 2) this primary response takes time to get rid of the infection which is why you get ill again 3) antigenic variation also makes it difficult to develop vaccines against some pathogens for the same reason. this includes HIV and the influenza virus

Question 34

what is active immunity?

Answer 34

this is a type of immunity you get when your immune system makes its own antibodies after being stimulated by an antigen.

Question 35

what are both types of active immunity?

Answer 35

1) natural - this is when you become immune after catching a disease 2) artificial- this is when you become immune after you've been given a vaccination containing a harmless dose of antigen

Question 36

what is passive immunity?

Answer 36

this is a type of immunity you get from being given antibodies made by a different organism - your immune system doesn't produce any antibodies of its own.

Question 37

what is both types of passive immunity?

Answer 37

1) natural - this is when a baby becomes immune due to the antibodies it receives from its mother, through the placenta and in breast milk 2) artificial - this is when you become immune after being injected with antibodies from someone else. e.g. if you contract tetanus you can be injected with antibodies against the tetanus toxin, collected from the blood donations

Question 38

what is the difference between active and passive immunity?

Answer 38

active immunity : requires exposure to antigen it takes a while for protection to develop memory cells are produced protection is long term because the antibody is produced (after activation of memory cells) in response to complementary antigen being present in the body passive immunity: doesn't require exposure to antigen protection is immediate memory cells aren't produced protection is short term because the antibodies given are Brocken down

Question 39

what is an attenuated microorganism?

Answer 39

Weakened or thinned. Attenuated strains of disease-causing bacteria and viruses are often used as vaccines. The weakened strains are used as vaccines because they stimulate a protective immune response while causing no disease or only mild disease in the person receiving the vaccine.

Question 40

what are monoclonal antibodies?

Answer 40

antibodies produced from a single group of genetically identical B-cells (plasma cells). this means that they're all identical in structure

Question 41

why are monoclonal antibodies useful?

Answer 41

you can make monoclonal antibodies that bind to anything you want e.g. a cell antigen or other substance and they will only bind to this molecule

Question 42

how can you use monoclonal antibodies for targeting drugs to a particular cell type - cancer cells?

Answer 42

1) different cells in the body have different surface antigens 2) cancer cells have antigens called tumour markers that are not found on normal body cells 3) monoclonal antibodies can be made that will bind to the tumour markers 4) you can also attach anti-cancer drugs to the antibodies 5) when the antibodies come into contact with the cancer cells they will bind to the tumour makers 6) this means the drug will only accumulate in the body where there are cancer cells 7) so, the side effects of an antibody based drug are lower than other drugs because they accumulate near specific cells

Question 43

how can you use monoclonal antibodies for targeting a particular - pregnancy testing

Answer 43

pregnancy tests detect the hormone human chorionic gonadotropin (hCG) that found in the urine of pregnant women 1) the application area contains antibodies for hCG will bind to the antibody on the bead (blue) 2) when urine is applied to the application area any hCG will bind to the antibody on the beads, forming an antigen-antibody complex 3) the urine moves up the stick to the test strip, carrying any beads with it 4) the test strip contains antibodies to the hGC that are stuck in place (immobilised) 5) if there is hCG present the test strip turns blue because the immobilised antibody binds to any hCG - concentrating immobilised antibody complex with the blue beads attached. if no hCG is present, the beads will pass through the test area without binding to anything and so it wont go blue

Question 44

what are ELISA tests and what can they used for?

Answer 44

the ELISA test allows you to see if a patient has any antibodies to a certain antigen. it can be used to test for pathogenic infections for allergies and for just about anything you can make an antibody for.

Question 45

what is the process of an ELISA test?

Answer 45

1) in an ELISA test, an antibody is used which has an enzyme attached to it. this enzyme can react with a substrate to produce a coloured product. this causes the solution in the reaction vessel to change colour so its a physical change. 2) if there is a colour change, it demonstrates that the antigen or antibody of interest is present in the sample being tested (e.g. blood plasma). in some types of ELISA, the quantity of this antigen/ antibody can be worked out from the intensity of the colour change.

Question 46

using information about indirect ELIAS tests, refer it to an example of HIV

Answer 46

1) HIV antigen is bound to the bottom of a well in a well plate (a plastic tray with loads of little circular pits in it) 2) a sample of the patients blood plasma, which might contain several different antibodies, i added to the well. if there are any HIV- specific antibodies (i.e. antibodies against HIV) these will bind to the HIV antigen stuck to the bottom of the well. the well is then washed out to remove any unbound antibodies. 3) a secondary antibody, that has a specific enzyme attached to it, is added to the well. this secondary antibody can bind to the HIV-specific antibody (which is also called the primary antibody). the well is washed out again to remove any unbound secondary antibody. if theres no primary antibody in the sample, all of the secondary antibody will be washed away. 4) a solution is added to the well. this solution contains a substrate, which is able to react with the enzyme attached to the secondary antibody and produce a coloured product. if the solution chamges colour, it indicates that a patient has HIV-specific antibodies in their blood and is infected with HIV.

Question 47

what is the difference between direct and indirect ELISA tests?

Answer 47

there are several different types of ELISA. direct ELISA uses a single antibody that is complementary to the antigen your testing for. indirect ELISA is different because it uses two different antibodies. this is used to test for HIV

Question 48

why is washing important an important step within ELIZA tests?

Answer 48

washing makes sure unbound antibodies aren't left in the well which could affect the results. e.g. unbound secondary antibodies could cause the test to appear positive when there are no HIV antibodies present.

Question 49

what are ethical issues surrounding vaccinations?

Answer 49

1) all vaccines are tested on animals before being tested on humans - some people disagree with animal testing. also, animal based substances may be used to produce a vaccine, which some people disagree with. 2) testing vaccinations on humans can be tricky , e.g. volunteers may put themselves at unnecessary risk of contracting the disease because they think they are fully protected (e.g. may have unprotected sex because they think they are safe from HIV) 3) some people don't want to take the vaccine due to the risk of side effects, but they are still protected because of herd immunity - other people think this is unfair. 4) if there was an epidemic of a new disease there would be a rush to receive a vaccine and difficult decisions would have to be made about who would be the first to receive it.

Question 50

what are ethical issues surrounding monoclonal antibody therapy?

Answer 50

they often involve animal right issues. animals are used to produce the cells from which the monoclonal antibodies are produced. some people disagree with the use of animals in this way.

Question 51

what is HIV?

Answer 51

a virus that affects the immune system. it eventually leads to acquired immune deficiency syndrome (AIDS)

Question 52

what is AIDS?

Answer 52

AIDS is a condition where the immune system deteriorates and eventually fails. this makes someone with AIDS more vulnerable to other infections, like pneumonia

Question 53

what happens after you have been infected by HIV?

Answer 53

HIV infects and eventually kills helper T-cells, which act as the host cells for the virus. helper T-cells send chemical signals that acitvate phagocytes, cytotoxic T-cells and B-cells so they're hugely important cells in the immune response. without enough T-helper cells the immuen system is unable to mount an effective response to infections because other immune system cells dont behave how they should.

Question 54

when does AIDS develop?

Answer 54

AIDS develops when the helper T-cell numbers in their body reach a critically low level

Question 55

describe the structure of HIV

Answer 55

1) a core that contains the genetic material (RNA) and some proteins (including the enzyme reverse transcriptase, which is needed for virus replication) 2) an outer coating of protein called a capsid 3) an extra outer layer called an envelope. this is made of membrane stolen from the cell membrane of a previous host cell 4) sticking out from the envelope are loads of copies of an attachment protein that help HIV attach to the host helper T-cells

Question 56

describe the process of HIV replicating inside the host helper t cells

Answer 56

cant replicate on its own as it doesn't have the right equipment including enzymes and ribosomes. s1) the attachment protein attaches to a receptor molecule on the cell membrane of the host helper T-cell s2) the capsid is released into the cell, where it uncoats and releases the genetic material (RNA) into the cells cytoplasm s3) inside the cell, reverse transcriptase is used to make a complementary strand of DNA from the viral RNA template 4) from this, double stranded DNA is made and inserted into the human DNA 5) host cell enzymes are used to make viral proteins from the viral DNA found within the human DNA 6) the viral proteins are assembled into new viruses, which bud from the cell and go on to infect other cells

Question 57

what are stages of AIDS until death (sometimes)

Answer 57

1) the initial symptoms of AIDS include minor infections of mucous membranes (e.g. the inside of the nose, ears and genitals) and recurring respiratory infections 2) as AIDS progresses the number of immune system cells decrease further. patients become susceptible to more serious infections including chronic diarrhoea, severe bacterial infections and tuberculosis 3) during the late stages of AIDS patients have a very low number of immune system cells and can develop a range of serious infections such as toxoplasmosis of the brain (a parasite infection) and candidiasis of the respiratory system (fungal infection). its these serious infections that kill AIDS patients not HIV itself

Question 58

why don't antibiotics work against a virus?

Answer 58

1) antibiotics kill bacteria by interfering with their metabolic reactions. they target the bacterial enzymes and ribosomes used in these reactions. 2) bacterial enzymes and ribosomes are different from human enzymes and ribosomes. antibiotics are designed to only target the bacterial ones so they dont damage human cells. 3) viruses don't have their own enzymes and ribosomes - they use the ones in the host cells. so because human viruses use human enzymes and ribosomes to replicate , antibiotics cant inhibit them because they dont target human processes 4) most antiviral drugs are designed to target the few virus-specific enzymes (enzymes that only the virus uses) that exist. e.g. HIV uses reverse transcriptase to replicate. human cells don't use this enzyme so drugs can be designed to inhibit it without affecting the host cell. these drugs are called reverse transcriptase inhibitors

Question 59

what do antiviral drugs designed to target? how is this used in HIV cases?

Answer 59

most antiviral drugs are designed to target the few virus-specific enzymes (enzymes that only the virus uses) that exist. e.g. HIV uses reverse transcriptase to replicate. human cells don't use this enzyme so drugs can be designed to inhibit it without affecting the host cell. these drugs are called reverse transcriptase inhibitors

Question 60

why is there no cure for HIV?

Answer 60

theirs currently no cure or vaccine for HIV but antiviral drugs can be used to slow down the progression of HIV infection and AIDS in an infected person

Question 61

what is the latency period of HIV?

Answer 61

HIV replicates rapidly and the infected person may experience severe flu-like symptoms. after this period, HIV replication drops to a lower level. this is the latency period. during the latency period (which can last for years) the infected person wont experience any symptoms

Question 62

how is HIV spread and how do you control it?

Answer 62

the best way to control HIV infection in a population is by reducing its spread. HIV can be spread via unprotected sexual intercourse, through infected bodily fluids and from a HIV positive mother to her foetus. not all babied from HIV-positive mothers are born infected with HIV and taking antiviral drugs during pregnancy can reduce the chance of the baby being HIV- positive.