3.2 Cells and the Immune system Flashcards
This covers: The Immune system, Immunity and Vaccines, Antibodies in medicine, Interpreting Vaccine and Antibody Data, HIV and Viruses
Define antigens.
Antigens are molecules (usually proteins) that can generate an immune response when detected by the body.
Extra Info: Usually found on surface of cells and used by immune system to identify pathogens.
What are the 4 main stages in an 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 specific to antigen.
What are specific and non-specific mechanisms involved in immunity?
Non-specific:
They DO NOT distinguish between one type of pathogen/antigen and another but respond to all in the same way.
Specific: They do distinguish between different pathogens/antigens. These responses are slower but give long lasting immunity.
What’s an antigen?
Antigens are large molecules recognised as non-self by the immune system which stimulates an immune response including antibody generation.
Give details of how phagocytosis works. There are about 6 main points to cover.
In blood, white blood cells that carry out phagocytosis are called phagocytes - this is a non-specific response.
• Chemical products of pathogens are dead, damaged or abnormal cells act as attractants causing a phagocyte to move towards the pathogen.
• Phagocyte have several receptors on CSM - recognise and attach to chemicals on the surface of the pathogen.
• Engulf pathogen –> Forms vesicles –> Called Phagosome.
• Lysosomes move towards the vesicle and fuse with it.
• Digestive, hydrolytic enzymes called lysozyme in lysosome destroy ingested bacteria - hydrolysis of cell wall. Process same as that for digestion of food into intestine, names hydrolysis of large insoluble molecules into smaller soluble ones.
What does phagocyte do after phagocytosis?
Presents the antigens on the plasma membrane
What are the specific immune responses?
Specific immune response depends on type of white blood cell called a lymphocyte.
What are the 2 types of lymphocytes called? Give some info on them
T lymphocytes and B lymphocytes. They’re formed in the bone marrow and develop and mature in different places. Have millions of different types of B and T lymphs. Each type recognises one.
What’s cell mediated immunity?
This is an immune response that doesn’t involve antibodies. But rather involves the activation of phagocytes, antigen-specific cytotoxic T-lymphocytes, and the release of various cytokines in response to an antigen.
How do T - Lymphocytes work?
T lymphocytes can distinguish invades cells from normal cells because:
- Phagocytes that have engulfed and hydrolysed a pathogen present some of pathogens antigens on own CSM.
- Body cells –> invaded by virus–> Present viral antigens on CSM
- Transplanted cells from same species –> different antigens on CSM
- Cancer cells different from normal cells –> present antigens on the CSM.
What are APCs (antigen presenting cell) and how are they used?
Present antigens of other cells on it’s own CSM as T-lymphs only respond to antigens on OWN body cells - This is called cell-mediated immunity/ cellular response (because it’s on its own cells). There’s a vast number of T-lymphs - each responds to different antigens.
What are the different stages of the response of T-lymphocytes? i.e. describe a cellular response.
1) Pathogens invade body cells/taken in by phagocytes.
2) Phagocyte places antigens from pathogen on its very own CSM
3) Receptors on T-helper cells fit exactly onto the antigen.
4) Attachment activates T cells to divide rapidly –> form clone of genetically identical cells.
5) Cloned T cells:
- Develop into memory cells–> enable rapid response to future infection by the same pathogen.
- Stimulate phagocytes to engulf pathogens by phagocytosis.
- Stimulates B cells to divide and secrete antibody.
- Activate cytotoxic t cells.
What happens after T cell activates?
Mitotic division starts to occur to form clones that are genetically identical cells. The cloned cells then:
- Activate T killer cells.
- Form T memory cells
- stimulate to divide to form plasma cells and secrete antibodies
- stimulate phagocytes to engulf pathogens
How do T killer cells work?
- T killer cells get activated
- activated when detects something that is non-self, may be infected.
- Release perforin
- makes holes in the CSM
- Freely permeable to substances and eventually dies from water loss
What does humoral immunity involve? Why is it called humoral immunity?
Humoral immunity involves antibodies which are soluble in the blood tissue fluid of the body and tissue fluid can also be called humour hence the name humoral immunity.
How do B cells/B lymphocytes function? I.e. What happens when a non-self ANTIGEN enters the blood and meets a b cell?
- There’s only one B cell complementary to the antigen.
- The B cell binds to foreign antigens & processes them.
- Helper T cells (activated earlier) bind to these processed antigens and ACTIVATE B cells.
- The activated B cell divides by mitosis –> Forms clones of B cells that are genetically identical.
- Cytokines released by Th cause some B cells to form plasma cells –> This is called clonal selection. These produce/secrete antibodies (specific in shape to a foreign antigen), MONOCLONAL antibodies.
- The antibody binds to the non-self antigens and destroys them (primary immune response)
- Some B cells develop into memory B cells. These are responsible for primary immune response giving long-lasting immunity.
What are monoclonal antibodies?
Many different B cells from clones, each of which produces ONE specific antibody, these antibodies are referred to as MONOCLONAL ANTIBODIES.
What are plasma cells and what do they do?
Plasma cells are basically B and T lymphocytes that have differentiated to become plasma cells. The function of plasma cells is to produce antibodies that are complementary to an antigen.
What are the 3 main organelles found in plasma cells?
- 80s ribosomes
- mitochondria - release energy for ATP for protein synthesis.
- Golgi apparatus - modify proteins chemically.
What’s an antibody?
An antibody is a protein that B cell secretes in response to a non-self antigen.
Describe the structure of an antibody.
- An antibody is a y shaped molecule
- Made up of 4 polypeptide chains, two long or two heavy chains and two short or light chains held together by disulfide bridges/bands.
- Variable regions are different on different antibodies and bind to non-self antigens.
- The variable region is a sequence of amino acids that form a specific 3D shape - bind to a single type of antigen with a complementary molecular shape.
- Y shape has linked a hinge, allows arms to flex so variable region can change mold to fit more precisely around antigen.
What is the purpose of an antibody and how does it work to kill foreign pathogens?
Antibody’s variable region should be complementary in shape to a foreign antigen. Due to the complementary shape, able to form an antigen-antibody complex. The antibody is flexible and can bind to another antigen on another a pathogen - can, therefore, cause agglutination. Agglutination makes it easier for phagocyte to consume pathogen.
Other than causing agglutination, what else can antibodies do?
Antibodies are able to neutralise toxins.
Neutralising toxins can prevent symptoms.
Define antigen, antibody agglutination and neutralisation.
Antigen - A large molecule that is recognised as non-self by the immune system and stimulates an immune response including the production of antibody.
Antibody - (immunoglobulin) is a protein that a B lymphocyte cell secretes in response to a non-self antigen. Every antibody is a y-shaped molecule, made of 4 polypeptide chains.
Agglutination - stick the pathogens by binding antigens and clumping them together.
Neutralisation - neutralise toxins/stop pathogens from entering cells.
