Unit two 2C - cells and the immune system Flashcards
what are antigens?
they are molecules (usally proteins) that can generate an immune response when detected by the body.
where do you find antigens and what do they do?
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.
what are the 4 main stages to an immune response?
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
what are the stages to phagocytosis?
- chemotaxis
- endocytosis
- forms a phagosome
- a lysosome joins the vesicle which makes a phagolysosome
- enzyme digests the bacteria via a hydrolysis reaction
- exocytosis
- the white blood cell becomes a antigen presenting cell to trigger an immune response
what happens when phagocytes activate T-cells
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.
how do T-cells activate B-cells which divide into plasma?
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
how do plasma cells make more antibodies to a specific antigen?
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.
what is an antibody
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.
what is the cellular immune response?
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
what is the humoral immune response?
this is the production of specific antibodies in response to a specific antigen that dissolves and travel in the body fluid
what is the primary immune response
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.
what is the secondary immune response?
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)
whats a lymphocyte
small white blood cell with little cytoplasm and spherical nuclei, which originate from stem cells in the bone marrow.
where do mature lymphocytes
in the spleen, lymph nodes, adenoids and tonsils as well as the lymphatic system and general circulation of the blood.
what is the lymphatic system
- 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
types of phagocytes
- 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
2 types of lymphocytes
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
what is autoimmune disease
if negative selection fails, some lymphocytes can survive and attack the body own tissue e.g. arthritis
whats apoptosis
negative selection (programmed cell death) so immune system doesn’t attack cell tissue.
what do T helper cells do?
messages other molecules to trigger next stages of immune responses - Tcytotoxic
what do T killer cells do?
small molecules that causes cells to move and/or behave in a particular way
cytokines
what is clonal selection
lymphocytes (specific) triggered by APC to do mitosis (B and T cells)
whats the order of the immune response
1) phagocytosis
2) clonal selection
3) memory cells
4) the response is quicker
5) more T memory cells
whats a non-specific defensive mechanisms?
response is immediate and the same for all pathogens
1) primary methods e.g. skin - physical barrier
2) secondary methods e.g. phagocytosis
what a specific defence mechanisms?
response is slower and specific to each pathogen
1) cell - mediated response —> T lymphocytes
2) humoral response –> B lymphocytes
what are the first signs of an immune response?
- 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
how do vaccinations work to stop the spread of a disease?
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)
what is heard immunity
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
how can you take vaccinations and what are the disadvantages?
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
what is the use of a booster vaccines?
these can be given later on to make sure that memory cells are produced. this can be after several years
how does antigenic variation work?
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)
how could antigenic variation affect the production of vaccines to help prevent people from catching influenza?
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
what does it mean if your infected again for the second time but antigenic variation has taken place?
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
what is active immunity?
this is a type of immunity you get when your immune system makes its own antibodies after being stimulated by an antigen.
what are both types of active immunity?
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
what is passive immunity?
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.
what is both types of passive immunity?
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
what is the difference between active and passive immunity?
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
what is an attenuated microorganism?
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.
what are monoclonal antibodies?
antibodies produced from a single group of genetically identical B-cells (plasma cells). this means that they’re all identical in structure
why are monoclonal antibodies useful?
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
how can you use monoclonal antibodies for targeting drugs to a particular cell type - cancer cells?
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
how can you use monoclonal antibodies for targeting a particular - pregnancy testing
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
