immunity

antigens are proteins, polysaccharides or glycoproteins on the surface of cells which allow the recognition of foreign cells as non-self cells. they are found on the cell surface.

immunoglobulin proteins produced in response to the antigen during the immune response

non- specific defense mechanisms are quick and work on a variety of pathogens and always work in the same way. they are physical barriers to infection. e.g phagocytosis or barriers to entry like our skin specific defense mechanisms are specific to the pathogen, so work slower than non-specific defense mechanisms. e.g. lymphocytes, B lymphocytes and T lymphocytes

• the pathogen is recognised as foreign due to non-self antigen being identified • the pathogen then attaches to the phagocyte by antibody and surface receptors • the pathogen is then engulfed by the ohagocyte by endocytosis- the infolding of the plasma membrane to form a phagosome • the phagosome is a membrane bound vesicle containing the pathogen • lysosomes containing lysin and hydroltic enzymes fuse to the phagosome • the pathogen is then digested by hydrolysis of the cell wall and harmless products are excreted or used by the phagocyte the phagocyte can ten display antigenic components on the plasma membrane ( antigen presentation) which can trigger the immune response as these antigens trigger T cells

T lymphocytes respond to an organisms own cells that have been invaded by foreign material e.g viruses or cancer or transplanted material which is genetically different

T cells have receptor proteins on their surfaces which can bind to complementary antigens which are presented on the surface of phagocytes. this activates the T cell

helper T cells release chemical signals that activate and stimulate phagocytes and cytotoxic T cells. they also activate B cells

cytotoxic T cells kill abnormal and foreign cells

B cells are a type of white blood cell which are involved in the humoral response

they divide into plasma cells which secrete antibodies which are specific to the antigens on the foreign pathogen.

• the foreign cell in the body has specific antigens on the cell surface • the B lymphocyte has antibodies on its surface which are specific to one antigen. when the B cell meets an antigen which is complementary to the antibodies on its surface, it binds to it • this along with the substances released from helper T cells activates the B cell. this is called clonal selection. • the activated B cell divides into plasma cells. the plasma cells secrete large quantities of this specific antibody which circulate in the blood • the antibodies are specific to the antigen, so attach due to their complementary shapes, forming an antigen-antibody complex

cellular- the T cells and the other immune system cells they interact with e.g phagocytes humoral- B cells, clonal selection and the production of monoclonal antibodies

main cells involved: B lymphocytes where do cells develop: bone marrow and also mature in the bone marrow antibodies: yes- produced by plasma cells how are pathogens identified: antigen presenting cells (APCs) or antigens in the blood how are pathogens killed: antibodies how do they divide once theyre stimulated: mitosis- they divide into memory and plasma cells

main cells involved: T lymphocytes where do cells develop: produced in bone marrow and mature in the thymus antibodies: no how are pathogens identified: antigen presenting cells, antigens on the pathogens cell surface membrane how are pathogens killed: theyre digested by phagocytosis or theyre killed by cytotoxic T cells how do cells divide once theyre stimulated: mitosis- they divide into helper T cells and cytotoxic T cells

• when an antigen enters the body for the first time, it activates the immune system- the primary response • the primary response is slow because there arent many B cells that can make the antibody which is complementary to the antigen. therefore the person will show symptoms to the infection • after being exposed to the antigen, both T and B cells produce memory cells which will stay in the body for a long time • memory T cells remember the specific antigen and will recognie it if the person becomes infected a second time • memory B cells remember the specific antibodies needed to bind to the antigen • the person is now immune and has the ability to respond quickly to a second infection

• if the same pathogen enters the body again, the immune system will produce a quicker, stronger immune response • clonal selection happens faster- memory B cells are activated and divide into plasma cells to produce the correct antibody. memory T cells divide into active T cells to kil the cell carrying the antigen • the secondary response often gets rid of the pathogen before you show any symptoms since you are immune.`

plasma cells are identical to the B lymphocyte they’ve been produced from. therefore the antibodies they secrete are specific to the one antigen- these are monoclonal antibodies. an antibody has two binding sites so can bind to two pathogens at the same time. this means that pathogen become clumped together- this is called agglutination. phagocytes then bind to the antibodies and can phagocytose many pathogens at once, so can destroy the cells carrying the foreign antigen

antibodies are proteins which are made up of chains of amino acids. the specificity of an antibody depends on its variable regions which form the antigen binding sites. each antibidy has a different shaped binding site due to the different tertiary structures of the proteins. this is complementaty to one antigen. all antibodies have the same constant region

antibodies are made up of 4 polypeptide chains the heavy chain: the longer pair of chains the light chain: the shorter pair of chains constant region: the rest of the antibody which binds to receptors of other cells variable region: the binding site has a different shape on all antibodies, based on the antigen they are specific to, therefore the variable region changes in shape antigen binding site: complementary to the specific antigen receptor binding site: constant region binds to receptors of other cells disulphide bridge: act as a hinge to give flexibility fot th variable region to adapt to the antigen

vaccines help to avoid infction from diseases they contain antigens which cause your body to produce memory cell against a particular pathogen without it causing disease so you become immune without experiencing symptoms. antigens in vaccines may be free or attached to a dead or attenuated/weakened pathogen booster vaccines may be taken at a later date to ensure memory cells have been produced

vaccines protect individuals who have them because they give them immunity to a particular disease and also reduce the occurence of the disease therefore those who are not/choose not to be vaccinated are also protected because there are less people to catch the disease from

vaccines can be injected or taken orally but if you take them orally, theres a chance the vaccine will be broken down by enzymes in the gut, or the molecules may be too large to be absorbed into the blood stream

• animal rights issues- all vaccines are tested on animals before human use. animal based substances may also be used to produce the vaccine which some people may not agree with. • some people may choose to not be vaccinated due to the risk of side effects but are still protected due to herd immunity which some people think is unfair • if there was a new epidemic, there would be a rush to get vaccinated which could cause arguments over who should be prioritised to recienve the vaccine first.

antigens on the surface of pathogens activate the primary immune response. when yore infected for a second time by the same pathogen (which has the same antigens) the activate the secondary response so you dont get ill however, pathogens such as influenza and HIV show antigenic variation, meaning the surface antigens change often due to changes in the genes of the pathogen this means when youre infected for the second time, your body does not recognise the antigen, even though it is the same pathogen. therefore the primary response is triggered again and you will show symptoms for the infection antigenic variation therefore makes it difficult to produce vaccines for pathogens such as HIV and influenza