Immunity Flashcards
What does HIV stand for
Human immunodeficiency virus
Why is HIV known as a retrovirus
it possess RNA and reverse transcriptase which can make DNA from RNA- a reaction that is the reverse of that carried out by transcriptase
What is the difference between HIV and AIDS
-HIV is a virus while AIDS describes the condition caused by infection with HIV
Describe how HIV is replicated
-attachment proteins attach to receptor on t-helper cell
-RNA enters cell
-reverse transcriptase converts RNA to DNA
-HIV DNA inserts into host DNA
-uses human enzymes (transcription and translation) to make copies of RNA and proteins
-Viral protein assembled and released
Symptoms of HIV
-low number of T-helper cells
-less antibodies which causes infection more
What does HIV cause
AIDS
How is HIV diagnosed
measure T helper cell count in blood
Pathogen
Microorganism that causes disease (bacteria, virus and fungi)
Immunity
When the bodies defence mechanisms overwhelm a pathogen and destroy it.
What are the 2 types of defence mechanisms
-General, immediate defences (skin, phagocytosis
-Specific responses (T-cells, B-cells)
Antigens
part of an organism that is identified as non-self that triggers an immune response
What are 4 materials that the body can recognise as non-self
-Pathogens
-Cells from other organisms
-Toxins
-Abnormal body cells (cancer)
Phagocytosis
-Pathogen secretes chemicals and phagocyte detects them
-Pathogen binds to a receptor
-membrane binds to the pathogen in a vesicle as a phagosome
-Phagosome binds to the lysosome turning into a phagolysosome
-Lysozymes hydrolyse pathogen
-waste material leaves via exocytosis
Describe how phagocytosis of a virus leads to presentation of its antigens
-phagosome fuses with lysosome
-Destroyed by lysozymes
-antigen is displayed on the cell membrane
Describe how presentation of a virus antigen leads to the secretion of an antibody against the antigen
- Helper t-cells bind to the antigen
-stimulates a specific B cell - B cell clones
-Forms plasma cells that release antibodies
Describe how HIV is replicated once inside helper T cells
-RNA converted into DNA using reverse transcriptase
-DNA inserted into nucleus
-DNA transcribed to HIV mRNA
-HIV mRNA translated into viral protein
Describe how a phagocyte destroys a pathogen present in the blood
-Engulfs
-forming vesicle and fusing with lysosome
-Enzymes hydrolyse
Give two cells other than a pathogen that can stimulate an immune response
-abnormal body cells (cancer)
-Cells from other organisms
What is the role of the disulfide bridge in forming the quaternary structure of an antibody?
Joins two different polypeptides
Explain how HIV affects the production of antibodies when AIDS develops in a person
- less antibodies produced
- because HIV destroys T helper cells
-Fewer B cells activated
What response do T cells produce
Cell mediated
What response do B cells produce
Humoral
What is the cell mediated response
-pathogen invade body cells
-phagocyte places antigen on cell surface
-receptor on T helper fits antigen
-activates rapid mitosis of T cells
-Stimulates: memory cells to develop, phagocytes, B cells and cytotoxic cells
What is a cytotoxic T cell
Kill abnormal cells and body cells by producing perforin that makes hole in the cell surface membrane
-Useful against viral infections
What is the humoral response
- B cells produces from the cell mediated response
-Clonal selection
-B cells differentiate into Plasma cells and memory cells
-Plasma cells secrete antibodies
Describe how B-lymphocytes respond when they are stimulated by antigens.
divide by mitosis / form clones;
produce plasma cells;
(plasma cells) make antibodies;
(plasma cells) produce memory cells;
Agglutination
Group of antibodies clump together the pathogens making them easier to locate and stimulate phagocytosis
Monoclonal antibodies
Antibodies produced from a single clone of B cells
Active immunity
Produced by stimulating the production of antibodies by the individuals own immune system through exposure to antigen or pathogen
What are the 2 types of active immunity
Natural and artificial
Natural active immunity
results from an individual becoming infected under normal circumstances and the body producing its own antibodies and memory cells
artificial active immunity
following the introduction of a weakened version of the pathogen or antigen via vaccine
Passive immunity
Produced by the introduction of antibodies from an outside source, no memory cells are formed so immunity isn’t lasting
example of passive immunity
antibodies passed on to a foetus through the placenta
-through breast milk to a baby
vaccination
a small amount of weakened or dead antibody or pathogen is introduced in the mouth or by injection
What does the introduction of a vaccination do
-exposure to antigen stimulates B cells to go through clonal expansion and differentiation
-B cells undergo mitosis to make large numbers of cells which differentiate into plasma cells and memory cells
-B memory cells can rapidly divide into plasma cells upon reinfection with the same pathogen to make large numbers of antibodies
Describe the features of an effective vaccination programme
- suitable vaccine, economically available to most of the vulnerable population
- few side effects to prevent people from refusing the vaccine
- means to produce, store and transport the vaccine
- means of effectively administering vaccine
- possible to vaccinate majority of vulnerable population - herd immunity
Herd immunity
Once a large enough percentage of a population is vaccinated this will protect the unvaccinated individuals as it’s hard for the pathogen to spread
why is herd immunity important
because it’s never possible to vaccinate everyone in a large population such as babies and young children because their immune systems aren’t fully functional
Explain why vaccination rarely eliminates a disease
- vaccination does not cause immunity in some individuals
- individuals develop disease immediately after vaccination before immunity is reached
- pathogen mutates so vaccines no longer cause effective immunity - antigenic variability
- many varieties of a pathogen so impossible to develop vaccine to all
- some people may be against vaccination for religious, ethical or medical reasons
Antigenic variability
If a pathogen has a high mutation rate and the genes of the pathogen change leading to the antigen on the cell surface being different the antibodies produced will no longer be effective
Discuss the ethical issues associated with vaccination programmes
- use of animals in development of vaccines
- side effects that may cause long term harm
- whom should vaccines be tested on?
- should vaccination be compulsory
- should vaccination continue when disease incidence is low
How can lymphocytes distinguish between self and non self cells
The proteins that make up the cells are different as they have variety and a highly specific tertiary structure
What is the structure of an antibody
-4 polypeptide chains
-1 pair light/ 1 pair heavy
every antibody has a specific binding site to form antigen antibody complex (variable region)
What ways can monoclonal antibodies be used in medical treatment
-monoclonal antibody therapy for cancer by attaching to receptors to stop the rapid uncontrolled growth
-Medical diagnosis- by looking at the levels of antigens produced in things such as cancer
-pregnancy tests- Measured the hcg production
Direct monoclonal antibody therapy
-cancer can be treated by monoclonal antibodies which are designed with a binding site that’s complimentary to the antigen
-while the antibodies are bound to the cancer antigen, this prevents chemical binding to the cancer cells which enable uncontrolled cell division
-which prevents growth
Indirect monoclonal antibody therapy
-antibodies have drugs attached to them that are complementary to the cancer cell
-drugs are therefore delivered directly to the cancer cells and kill them which reduces side effects from chemotherapy and radiotherapy
The Elisa test- pregnancy test
-first mobile antibody, complimentary to the antigen being tested for has a coloured dye attached
-a second antibody complimentary in shape to the antigen is immobilised in the test
-A third antibody is immobilised an is complimentary in shape to the first antibody
The elisa test
-Add the test sample from a patient to the base of the beaker.
-Wash to remove any unbound test sample.
-Add an antibody complementary in shape to the antigen you are testing the presence of in the test sample.
-Wash to remove any unbound antibody.
-Add a second antibody the is complementary in shape to the first antibody, and binds to the first. The second antibody has an enzyme attached to it.
-The substrate for the enzyme, which is colourless, is added. This substrate produces coloured products in the presence of the enzyme.
What does the presence of colour in the elisa test indicate
the presence of the antigen in the test sample and the intensity of the colour indicates the quantity
What are ethical issues linked with the use of monoclonal antibodies
-The production of monoclonal antibodies involves the induction of tumour cells into mice
-There have been deaths associated wit the use of monoclonal antibodies when been used for treatment
-When testing for new drugs healthy volunteers have suffered multiple organ failures probably due to the production of T cells overproducing chemicals
Why are antibiotics ineffective against viruses
There are no metabolic processes or cell structures to disrupt. Viruses have a protein coat rather than a cell wall and so don’t have sites for antibiotics to work. when viruses are within an organisms own cells antibiotics cannot reach them.
