cells in immunity
Name two types of phagocyte.
macrophages and neutrophils
What is APC?
antigen presenting cells.
The cell ingest antigens and display them on their surface, allowing T-lymphocytes to bind to the antigen and stimulate immune response.
Define autoimmune disease.
Autoimune disease: caused by the immune system producing antibodies against self antigens as it fails to distinguish between self and non self antigens.
Describe the structure of an antibody.
Antibodies have 2 identical binding sites formed by both light and heavy chains. The sequence of amino acids in this region make the specific 3-D shape which binds to just one type of antigen. R group interactions with the antigen gives it the specific shape.
Is most vaccination active or passive immunisation?
Active.
Where do lymphocytes originated? (State the specific site for different lymphocytes)
B-lymphocytes: bone marrow
T-lymphocytes: thymus gland
Describe the clonal expansion of B-lymphocytes.
▪ When mature, each B cell produces one type of antibody molecule.
▪ Part of the antibody molecules form a glycoprotein receptor that combines specifically with one type of antigen.
▪ Once combined, the B cell will undergo mitosis repeatedly to form clone cells.
▪ As only the B cells with antibodies complementary to antigens divide like this, it is known as clonal selection followed by clonal expansion.
What is myasthenia gravis (MG)?
The autoimmune disease that targets the neuromuscular junctions between motor neurones and skeletal muscle cells.
Describe the diagnosis with monoclonal antibodies.
▪ Radioactive chemicals are attached to each antibody that binds to fibrin. Radioactivity emitted by these antibodies can be detected by gamma rays camera, thus finding the position of a clot.
▪ The same method can be used to locate cancer cells and identify the exact strain of a virus or bacterium during an infection.
How to make vaccines?
Use antigenic materials, which could be a live, dead or attenuated micro-organism, or perhaps a harmless form of a toxic (toxoid) or simply surface antigens.
Name two molecules released by phagocytes, which distroy bacteria and virus respectively.
Lysozyme: enzyme that disrupts the cell walls of gram-positive bacteria by digesting the peptidoglycan. It is found in human tears, saliva and lysosomes.
Interferons: proteins produced by virus-infected body cells in response to the virus. Interferons trigger the production of a second protein that inhibits viral replication by binding to mRNA coded by the virus.
Explain the role of memory cells in long-term immunity.
for long-term immunity ;
B and T memory cells remain in the body for, a long time / a lifetime ;
memory cells for secondary (immune) response ;
secondary response is faster / more effective (than primary immune response) ;
(so) higher concentration antibodies / quicker production antibodies ;
Idea of more (specific) memory cells in the body than (specific) lymphocytes before primary response ;
increase chance that pathogen encountered more rapidly (to mount a response) ;
Treatment for MG.
▪ Drug that inhibits acetylcholinerase, increasing the concentration of ACh in synapses so its action in stimulating muscle fibres to contract lasts for longer.
▪ Surgical removal of the thymus gland as it is the site of maturation of the helper T cells that stimulate B cells to produce antibodies to the ACh receptors.
Outline the hybridoma method for the production of monoclonal antibodies.
▪ A mouse is injected with relevant antigen, stimulating immune response.
▪ Plasma cells specific to antigen are extracted from the spleen and fused with cancerous cells forming hybridoma cells.
▪ Hybridoma cells that produce the required antibody are cloned.
What is antigenic variation?
Viruses are constantly mutating and changing - the reason we cannot create a vaccine against the common cold or influenza is because it mutates very frequently and the vaccine will not be effective eg in AIDS/HIV. These mutations are known as antigenic drift (minor changes in antigen structure still recognised by memory cells) or shift (major changes not recognised). Plasmodium parasites are eukaroytic in nature and have far more genes and thus antigens on their cell surfaces.
Describe how macrophage/neutrophil engulf and destroy pathogens.
neutrophil recoginize the bacteria, bacteria attach to neutrophil by the recognition of antibody marked on pathogen and receptor protein on neutrophil cell membrane;
endocytosis happens, neutrophil cell membrane engulfs the pathogen;
digestive enzymes are secreted into the phagocytic vacule;
bacteria are, killed / destroyed / broken down / digested e.g. carbohydrase / lysozyme / protease / nuclease ;
or killed by, hydrogen peroxide / H2O2 / free radicals ;
murein / peptidoglycan, polysaccharide(s), polypeptides, nucleic acids, lipids are broken down
glycosidic, peptide, ester, phosphodiester bonds are broken down
Describe how could T lymphocytes destruct tumor cells in the body.
T killer cells/ cytotoxic T cells: destroy the cell to which they are bound. They search the body for cells that have become invaded by pathogens and are displaying the pathogen’s antigen on their plasma membranes. When T-killer cells recognise the antigens, they attach themselves to the surface of infected cells and secrete toxic substances that kill the cells and pathogens within them.
How does MG caused?
In MG: helper T cells that are specific for these cell surface receptors for ACh stimulate a clone of B cells to differentiate into plasma cells and secrete antibodies that bind to the receptor, blocking the transmission of impulses from motor neurones. Hence, muscle cells do not receive any stimulation, causing
muscle weakness.
Outline the use of monoclonal antibodies in the treatment of disease.
▪ Mabs from rats into humans trigger an immune response as they are non-self. This is overcome by altering genes that code for polypeptide chains of antibodies into human sequences and the type/position of sugar groups into human antibodies.
▪ Used in cancer therapy by marking cancerous cells for their destruction or binding to protein produced by T cells that reduces immune response.
▪ Controls over/inappropriate production of B cells, preventing leukaemia and autoimmune diseases.
Outline how this vaccine can give protection against certain bacteria?
vaccine contains (subunit B/ bacterial) antigen(s) ;
primary immune response occurs ;
correct ref to B-lymphocytes / formation of plasma cells ; secretion of, antibody / immunoglobulin (against cholera antigens)/ antitoxins ;
T-helper lymphocytes secrete cytokine ;
cytokine increases humoral response / stimulates T-killer cells / stimulates macrophages ;
memory cell production ;
secondary (immune) response /response on further infection, is faster ;
higher levels of antibodies produced (during further infection) ;
active artificial immunity (against cholera) ;
Describe and explain the significance of the increase in white blood cell count in humans with leukemias.
Leukemias: cancers of immature WBC, disrupting normal levels of RBC or platelets, causing anaemia and risk of excessive bleeding. Mature WBC decrease so that people become more susceptible to infections; they are said to be immunosuppressed.
If a male is infected by HIV, the number of helper T cell would decrease rapidly. How could the lower number of helper T affect his immunity?
1 low Th cells means increased risk of developing an infectious disease ;
2 low levels / less, cytokine, secreted ;
role of cytokine:
3 stimulates activity of macrophages / produces angry macrophages ;
4 stimulates, B-lymphocytes / plasma cells / humoral, response ;
5 (so lower concentrations / less / no), antibody, produced / secreted ;
6 stimulates, T-cytotoxic / T-killer, cells ;
7 (so) fewer infected cells killed ;
8 more time for pathogens to, reproduce / spread ;
9 fewer memory cells (to fight future infection) ;
There is no cure for MG. State the possible reason for that.
▪ Defective B cells are continuously produced
▪ They continue to release antibodies against receptors
▪ Even if all the B plasma cells are used up, memory cells of these defective B cells are still present
Suggest the advantages and disadvantages of artificial passive immunity. (3)
advantages
1 antibodies are provided to people immediately / no delay for plasma cells to secrete antibodies ;
2 antibodies, immediately neutralise toxins / prevent viruses entering cells ;
3 prevents disease (in the individual) / promotes quicker recovery ;
4 prevents spread of the pathogen through the population / prevents people dying ;
5 antibodies can be manufactured quickly in response to mutations that occur in virus
disadvantages
6 short-term / temporary (immunity) ;
7 no memory cells produced ;
8 can have infections of same pathogen again ;
9 allergic reaction / immune response, to the (non-human) antibodies given ;
10 ref. to cost qualified ; e.g. needs to be repeated / high cost of production of antibodies11 AVP – for advantage (A) or disadvantage (D) ;
A student was asked to explain why vaccination has successfully eradicated smallpox but not other diseases, such as measles, malaria and sickle cell anaemia. These are the statements made by the student.
1 The antigens of the virus causing smallpox did not change, unlike the antigens of the virus causing measles.
2 Sickle cell anaemia has many different types of mutation, unlike smallpox, so each would require a vaccine.
3 Unlike smallpox, malaria involves animals as part of the transmission cycle and this makes the cycle harder to break.
4 The vaccine against measles often causes a poor primary immune response so that booster vaccines are required, unlike the vaccine against smallpox.
Which statements are possible explanations?
A 1, 3 and 4
B 1 and 2
C 1 and 4 only
D 2 and 4
A