Immune responses (copy)

What is a pathogen

Disease causing agent

What is the immune system

Organs and processes of the body that provides resistance to pathogens,foreign cells,abnormal body cells (damaged/infected or cancerous),toxins

What is a phagocyte

White blood cells which engulf pathogens or cells that are infected damaged or dying

Describe phagocytosis (6 marks)

• Pathogen releases chemoattractants which the phagocyte is attracted to

• Pathogen is engulfed in a vesicle called a phagosome

• Phagosome membrane fuses with the membrane of the lysosome

• Lysosome contains hydrolytic enzymes called lysozymes which are released into phagosome

• Lysozymes are enzymes which hydrolyse the molecules the pathogen is made of

• Soluble products (sugars,amino acids) are absorbed into the cytoplasm of the phagosome

• Antigens are presented on its cell surface membrane and phagocyte becomes an APC

What is an APC

Protein on the cell surface membrane that can trigger an immune response

What can T cells recognise

APC,cancer,damaged or infected cells,foreign cells

Describe the cell mediated response

• Specific helper T cells have receptors which are complementary to the specific antigen and it binds to the APC which becomes activated

• Activation causes T cell to divide by mitosis to produce genetically identical T cells (clónale selection) AND secrete chemicals

• The chemicals-stimulate B cells, stimulate cytotoxic T cells, stimulate and attracts phagocytes, forms memory T cells

• Cytotoxic T cells kill APC (more specific in another flashcard)

Explain the role of cytotoxic T cells in the cell mediated response

T killer cells can be activated by binding to APC and the chemicles secreted by TH cells.

TC produces TOXINS which make APC membrane permeable,creates holes which toxins get in destroying organelles eso KILLS APC

Explain the role of memory T cells in the cell mediated response

Formed from T helper cells they have the same complementary receptor to the specific antigen and live in the body for longer so the next time antigen is encountered there is a faster immune response

Where are B lymphocytes made

Mature In the bone marrow and is responsible for humoral response

What is an antibody

A protein produced by B plasma cells which binds to the specific complementary antigen

Describe the structure of an antibody

• Protein with a quaternary structure has 4 polypeptide chains,2 heavy and 2 light

• Heavy and light chains are held by disulphide bonds

• The variable regions form 2 antigen binding sites,they have a specific tiertiary structure making it complementary to ONE specific antigen

• Rest of antibody is constant

Explain why the specificity of an antibody depends on its variable regions (2)

• Has a specific tiertiary structure

• Which is complementary to one antigen

What is agglutination

Clumping together of antigen bearing cells in the presence of their complementary antibody .These are antigen-antibody complexes

What are the uses of antibodies

• Agglutination

• Attracts phagocyte

• Makes phagocytosis more efficient because of agglutination

• Toxin neutralisation-antibodies bind toxins so they cannot affect their target

• viral neutralisation

Describe the humoral response

• A specific B cell encounters an antigen,B cell has protein receptors on its cell surface membrane which are complementary to the specific shape of the pathogens antigen

• B cell engulfs the pagocyte amd presents its antigens on its own cell surface membrane becoming an APC

• TH cells with complementary receptors to the specific antigen bind to the antigen on the B cell,releases chemicals and activates them

• The B cells divide by mitosis through clonal selection and form B plasma and B memory cells

• B plasma -produce monoclonal antibodies which are specific to the pathogens antigen

• B memory-faster secondary immune response as it has the same complementary receptor

Describe and explain the primary response

• Less antibodies produced more slowly

• Time taken for antigen to bind to complementary receptor on specific B cell

• Time taken for specific B cell to become activated by TH cell

• Time taken for specific B cell to divide by mitosis to produce plasma cells

• Plasma cells produce specific antibodies

Describe and explain the secondary response

• More antibodies produced more quickly

• Primary response causes many clones of long living specific B memory cells.

• Specific B memory cell quickly form specific B plasma cells

• Plasma cells produce more antibodies more quickly

• Pago gen is quickly destroyed before it produces any symptoms

What is a monoclonal antibody

Antibodies that have the same tiertiary structure and are all specific to only one antigen,this he because they come from the same clone B plasma cells

What uses do monoclonal antibodies have in medical treatment

• Monoclonal antibodies carry drugs bound to the antibody to specific antigen presenting cells

• Monoclonal antibodies themselves can bind to specific antigen presenting cells destroys APC by phagocytosis ans agglutination

How are monoclonal antibodies used in medical diagnosis

• Monoclonal antibodies will bind to a specific substance this will confirm its presence (ELISA test)

Describe antigenic variability

• Pathogen DNA mutates and shape of the antigen will change ,any previous immunity to pathogen is no longer effective.This is because receptor and antibodies from B-memory cells are not complementary to the mutated antigens therefore there is a slow primary immune response and the person experiences symptoms

Describe conserved antigens

• The antigens are conserved from one generation to the next.secondary immune response is recognised by complementary receptors on memory B cells secondary immune response is faster and destroys the pathogen before symptoms are felt

What is a vaccine

• Contains an antigen or several antigens from a pathogen that stimulate an immune response resulting in the formation of memory cells,can contain dead or weakened forms of the pathogen

• Results in T cell activation,B cell activation,B plasma cell production,antibodies production,B memory cell production

What is immunity

The ability of an organism to resist a particular infection or toxin by the action of the specific immune response

What is herd immunity

When enough individuals are immune to prevent the spread of a pathogen because of lack of susceptible hosts

Describe the ELISA test

• The test well has the antibody complementary to the patients antigen OR the antigen complementary to specific patients antibodies

• Blood which contains antigen/antibodies is added to well

• If present they will bind

• Antibodies binding site has a specific tertiary structure and is complementary to the antigen

• Plate is washed and enzyme linked antibody is added to the test well and it binds to the patients protein (antigen or antibody)

• Plate is washed again and a colourless substrate is added it binds to the enzyme and there is a colour change

Why is the plate washed

1st time washed to remove blood so no substances contaminate and bind to the enzyme linked antibody so prevents a false positive test resukt

2nd time removed unbound antibodies so it does not bind to the substrate so there is no colour change no false positive test result

Describe the lateral flow test

• Sample added (protein of interest-antigen/hormone/antibody)

• Protein /antigen binds to the first unbound labelled antibody.

• Then the antibody-antigen complexes flow down the stent strip

• The bound antibodies in the test line bind to the antigen of the antigen antibody complexes if present,so the coloured beads collect and line is seen(positive test result)

• The first unbound labelled antibody binds to the bound antibody of the control line,the coloured beads collect showing the unbound antibodies moved and the test is working

What organelles do HIV have

• Lipid envelope

• Enzyme reverse transcriptase-turn vRNA into vDNA

• Attachmeant proteins

• Single stranded RNA

• Protein capsid

  
  

Describe how HIV replicates and destroys TH cells

• HIV is non living and therefore cannot undergo cell division

• The viruses attachment proteins bind to the CD4 receptor proteins on the surface of the T helper cells

• The viruses lipid envelope fuses with the cell membrane of the Th cell

• Protein capsid breaks down

• RNA and enzymes (reverse transcriptase) of the virus are now released into the cytoplasm of the host cell

• Reverse transcriptase enables viral RNA to act as a template to form DNA

• The viral DNA is incorporated into the cell DNA (infection)

• The viral DNA can now be transcribed into mRNA

• Viral mRNA passes through the nuclear pore and attaches to a ribosome

• Viral mRNA is translated into viral proteins that can be assembled into new HIV

• HIV particles bud off the Th cell so that the TH cell membrane firms the lipid envelope of the virus

Why do antibiotics not work on viruses

viruses do not have the same organelles and enzymes as a bacteria so the antibiotics cannot bind and target parts of the virus