CELL RECOGNITION AND THE IMMUNE SYSTEM
Why are booster vaccines often given?
To make sure that memory cells are produced.
What are the four main stages in the immune response?
1 - Phagocytes engulf pathogens. 2 - Phagocytes activate T-cells. 3 - T-cells activate B-cells, which divide into plasma cells. 4 - Plasma cells make more antibodies to a specific antigen.
"What is an antigen?" 2 marks.
1 - a protein on the surface of a pathogen/cell/toxin 2 - that stimulates an immune response/antibody production
"What is a vaccine?" 2 marks.
1 - contains antigens, which may be free or attached to a dead or attenuated (weakened) pathogen 2 - leads to formation of specific memory B cells
"What are monoclonal antibodies?" 1 mark.
1 - identical antibodies against one specific antigen produced by a single clone of plasma cells
Describe the secondary immune response. (3 steps)
1) If the same pathogen enters the body again, the immune system will produce a quicker, stronger immune response, which is called the secondary response. 2) Clonal selection happens faster as memory B-cells are activated and divide into plasma cells that produce the right antibody to the antigen. Memory T-cells are activated and divide into the correct type of T-cells to kill the cell carrying the antigen. 3) The secondary response often gets rid of the pathogen before you begin to show any symptoms, as you are immune to the pathogen.
What is a phagocyte?
A type of white blood cell that carries out phagocytosis, which is the engulfment of pathogens. They are found in the blood and in tissues, and are the first cells to respond to an immune system trigger inside the body.
What is a T-lymphocyte?
A type of white blood cell that has receptor proteins on its surface that bind to complementary antigens presented to it by phagocytes, which activates the T-cell.
What is a B-lymphocyte?
A type of white blood cell that is covered in antibodies, which are 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.
What are pathogens?
Organisms that cause disease.
Explain the second stage in the immune response. (1 step)
PHAGOCYTES ACTIVATE T-CELLS 1) The receptor proteins on the surface of the T-cell bind to complementary antigens on the surface of the phagocytes, which activates the T-cell (whether it be a helper T-cell or a cytotoxic T-cell).
What is passive immunity?
The type of immunity you get from being given antibodies made by a different organism, so your immune system doesn't produce any antibodies of its own.
Explain the first stage in the immune response. (5 steps)
PHAGOCYTES ENGULF PATHOGENS 1) A phagocyte recognises the foreign antigens on a pathogen. 2) The cytoplasm of the phagocyte moves round the pathogen, engulfing it. 3) The pathogen is now contained in a phagocytic vacuole in the cytoplasm of the phagocyte. 4) A lysosome fuses with the phagocytic vacuole and the lysozymes break down the pathogen. 5) The phagocyte then presents the pathogen's antigens on its surface to activate other immune system cells.
What does the humoral response involve?
B-cells, clonal selection and the production of monoclonal antibodies.
Give examples of the different types of T-lymphocytes.
Helper T-cells release chemical signals that activate and stimulate phagocytes, and activate B-cells. Cytotoxic T-cells destroy abnormal and foreign cells.
What are the disadvantages of taking a vaccine orally?
It could be broken down by enzymes in the gut, or the molecules of the vaccine may be too large to be absorbed into the blood.
"Describe and explain how a secondary immune response differs to a primary immune response" 4 marks.
1 - a secondary immune response is a faster and stronger response than the primary response 2 - this is because memory cells are produced during the primary response, which are able to recognise the foreign antigen when it is encountered again 3 - during the second infection, memory B-cells can quickly divide to form plasma cells, which secrete the correct antibody to the antigen 4 - memory T-cells quickly divide into the right type of T-cells to kill the cell carrying the antigen
"Explain why a child who has had mumps will not suffer from mumps a second time." 2 marks.
1 - after the first infection, memory cells are made 2 - secondary response means antibodies are produced very quickly and in large numbers, so virus is destroyed before symptoms can occur
"Describe the function of antibodies." 2 marks.
1 - antibodies bind pathogens together in agglutination 2 - this allows phagocytes to engulf many pathogens at once
"Describe the response of B lymphocytes to a foreign antigen." 5 marks.
1 - antigen is presented to B-cell in lymph nodes 2 - cell with complementary receptors are activated 3 - also activated by helper T-cell 4 - forms clones of plasma cells that secrete specific antibodies 5 - memory B cells retain immunological memory of original antigen
"Describe the response of T lymphocytes to a foreign antigen." 5 marks.
1 - antigen is presented to T-cell in lymph nodes 2 - T cell with specific receptor complementary to antigen is activated 3 - produces clones 4 - helper T cells activate B cells 5 - cytotoxic T cells destroy pathogen
"Describe the role of phagocytes in the destruction of pathogens." 3 marks.
1 - engulf pathogen which becomes enclosed in phagosome 2 - lysosome fuses with phagosome 3 - lysozyme enzymes digest pathogen
"How do antibodies lead to the destruction of bacterial cells?" 3 marks.
1 - form antigen-antibody complexes 2 - causes agglutination of bacterial cells/pathogen 3 - leading to phagocytosis of pathogen/bacterial cells
"What is an antibody?" 2 marks.
1 - protein secreted by plasma cell 2 - with receptor the right shape to bind to a specific antigen
"What is meant by herd immunity?" 2 marks.
1 - when most members of a population are vaccinated 2 - it is difficult for an infected person to pass the infection onto another individual
Describe the 4 main differences between active and passive immunity.
1) Active requires exposure to the antigen, passive doesn't. 2) With active immunity, it takes a while for protection to develop, but with passive immunity, protection is immediate. 3) In active immunity, memory cells are produced, which doesn't happen in passive immunity. 4) Protection is long term in active immunity as the antibody is produced after activation of memory cells in response to the complementary antigen being present in the body, but in passive immunity, protection is short term as the antibodies given get broken down.
Describe and explain antigenic variation and its effects and issues. (6 steps)
1) Antigens on the surface of pathogens activate the primary response. 2) When you're 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) Some pathogens can change their surface antigens, and this antigen variability is called antigenic variation. Different antigens are formed to due changes in the genes of a pathogen. 4) This means that when you're infected for a second time, the 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. 5) This primary response takes time to get rid of the infection, which is why you get ill again. 6) Antigenic variation also makes it difficult to develop vaccines against some pathogens for the same reason, e.g. for HIV and the influenza virus.
Describe the two 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 ca be injected with antibodies against the tetanus toxin, collected from blood donations.
Describe the two 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.
Describe the difficulty surrounding the influenza virus vaccine. (5 steps)
1) The influenza vaccine changes every year as the antigens on the surface of the influenza virus change regularly, forming new strains of the virus. 2) Memory cells produced from vaccination wth one strain of the flue will not recognise other strains with different antigens as 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 programme of vaccination using the most suitable vaccine.
Describe the primary immune response. (5 steps)
1) When an antigen enters the body for the first time, it activates the immune system, which 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 to the antigen. 3) Eventually, the body will produce enough of the right antibody to overcome the infection, but during this time, the infected person will show symptoms of the disease. 4) After being exposed to an antigen, both T and B-cells produce memory cells, which remain in the body for a long time. Memory T-cells remember the specific antigen and will recognise it a second time round, and memory B-cells record the specific antibodies needed to bind to the antigen. 5) The person is now immune as their immune system has the ability to respond quickly to a second infection.
Explain the fourth stage in the immune response. (4 steps)
PLASMA CELLS MAKE MORE ANTIBODIES TO A SPECIFIC ANTIGEN 1) Plasma cells are clones of the B-cell, so they secrete loads of antibodies that are specific to the antigen, which are called monoclonal antibodies. 2) The monoclonal antibodies bind to the antigens on the surface of the pathogen to form lots of antigen-antibody complexes. 3) The antibodies have two binding sites each, so they can bind to two pathogens at the same time, so the pathogens become clumped together in a process called agglutination. 4) Phagocytes then bind to the antibodies and phagocytose many pathogens at once, which leads to the destruction of pathogens carrying this antigen in the body.
Explain the third stage in the immune response. (3 steps)
T-CELLS ACTIVATE B-CELLS, WHICH DIVIDE INTO PLASMA CELLS 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. 3) The activated B-cell divides into plasma cells in a process called clonal selection.
What does the cellular response involve?
The T-cells and other immune system cells that they interact with, e.g. phagocytes.
What is active immunity?
The type of immunity you get when your immune system makes its own antibodies after being stimulated by an antigen.
How do vaccinations prevent a person from developing certain diseases?
The vaccine produces a primary response, so memory cells are made, which means when the person encounters the real pathogen, antibodies are made very quickly and in large numbers before symptoms can occur.
Describe the structure of antibodies.
They are proteins and so 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 antibody has a variable region with a unique tertiary structure due to the different amino acid sequences, that is complementary to one specific antigen. All antibodies have the same constant region.
How are antigens used by the immune system?
They are used by the immune system to identify pathogens, abnormal body cells, toxins, and cells from other individuals of the same species, e.g. organ transplants.