Immunology - A8 Flashcards
Define antigen
-foreign protein
-causes an immune response resulting in the production of specific antibody
Define self-antigen
-a molecule in the cell surface membrane if your own body cells
-allows your immune system to recognise the cell as self
Define pathogen
-micro-organisms which cause disease. All have antigens which are identified as foreign by immune system cells. Can cause an immune response
Define abnormal body cells
-cancerous or pathogen infected cells have abnormal antigens on their surface, which triggers an immune response. Can cause an immune response
Define toxins
molecules usually produced by a pathogen cells from other individuals of the same species. Can cause an immune response
How does the immune system protect against disease?
By identifying and killing invading pathogens and tumour cells. The immune system recognises anything foreign and can distinguish these from the organism’s own cells
Explain the process of phagocytosis.
1)phagocyte recognises foreign antigens on a pathogen
2)pathogen is engulfed by the phagocyte(phagocytosis)
3)pathogen is now in(the cytoplasm of the phagocyte in) a phagosome
4)lysosomes containing lysozymes fuse with the phagosome. lysozymes hydrolyse the pathogen
5)phagocyte then presents the pathogen and antigens on it’s cell surface membrane to active other immune cells
6)waste material is ejected from the cell by exocytosis
What is a phagocyte?
a type of white blood cell which engulfs pathogens
What is a t-cell?
A type of white blood cell which has receptor proteins on its surface that bind to complementary antigens presented by phagocytes- activates T-cell
What is a t-helper cell?
release chemical signals that activate and stimulate phagocytes and t-killer cells. they also activate b-cells which secrete antibodies
What are b-cells?
a type of wbc, covered in antibodies. Each b-cell has a different shaped antibody on it’s membrane, so different ones bind to different shaped antigens.
What are the two different types of defence mechanisms?
Specific and non-specific
What is a specific defence mechanism and give an example.
It has a slower response and is specific to each antigen.
Examples: cellular response(t-lymphocytes), humoral response(b-lymphocytes)
What is a non-specific defence mechanism? Give an example
It s an immediate response and is the same for all pathogens.
Examples: phagocytosis
What is a cellular response?
-T-helper cells with specific complementary receptors bind to the antigens being presented on the phagocyte
-this stimulates t-helper cells to undergo mitosis
-some stimulate into t-killer cells which go and destroy infected cells in the body
-t-helper cells with specific complementary receptors will bind to a specific b-cell causing clonal selection/expansion
What is a humoural response?
-t-helper cell with specific complementary receptors will bind to a specific b-cell causing clonal expansion via mitosis
-some b-cells differentiate into plasma cells which make antibodies(specific and complementary for the antigens presented on the phagocyte)
-some differentiate into b-memory cells that remain in the body(important in the secondary immune response)
Are antibodies proteins?
yes
What regions of each antibody are the same or different?
They all have the same constant regions.
Each antibody has a variable region with a unique tertiary structure, that’s complementary to one specific antigen.
Specificity depends on the variable regions which form the antigen binding sites(due to the tertiary structure)
What are the processes involved in the primary immune response?
phagocytosis, cellular response, humoral response
How is an antigen-antibody complex formed?
An antigen-antibody complex is formed by the binding of an antibody to it’s specific pathogen
How do antbodies destroy bacterial cells?
Antibodies bind to specific pathogen causing agglutination, which enhances phagocytosis
How can one antibody be specific to two things?
They have similar structures
What do T and B cells do after the primary response?
After the primary response, both T and B cells produce memory cells which remain in the body for a long time.
What do memory T-cells do?
Memory T-cells remember the specific antigen and will recognise it a second time round.
What do memory B-cells do?
Memory B-cells record the specific antibodies needed to bind the antigen.
What is the secondary immune response?
If reinfected with the same pathogen the immune system will produce more antibodies faster.(quicker and stronger immune response)
Why does clonal selection happen faster in a secondary immune response?
Memory B-cells are activated and divide into plasma cells that produce the right antibody to antigen
What happens when memory T-cells are activated in a secondary immune response?
Memory T-cells are activated and divide into the correct type of t-cell to kill the cell carrying the antigen.
Does a secondary immune response show symptoms?
Usually shows no or little symptoms
How do you know if memory cells are present?
The response is faster - faster production of antibodies
Why is the secondary immune response effective?
The secondary immune response is effective as most pathogens have the same antigens on their surface, and so are recognised by memory cells wen re-infection occurs.
What causes a change in tertiary structure of the antigens? What does this mean for the rest of the secondary response? What is this known as?
-Mutations in DNA change the tertiary structure of antigens(e.g. flu, HIV)
-memory cells cannot recognise pathogen(primary response has to occur)
-antibodies no longer complementary to antigens
-the individual will not be able to initiate a secondary response
-this is known as antigenic variability
What is active immunity?
The body comes into contact with antigens and produces plasma cells, antibodies and memory cells
What is passive immunity?
When you get given antibodies made by a different organism - your immune system doesn’t make it’s own antibodies
What are the differences between active and passive immnunity?
-Active: exposed to antigen, passive: no contact with antigen
- Active: plasma cells produce antibody, passive: antibodies received from an outside source(e.g. injection or mother’s milk)
-Active: takes time to work, passive: immediate
-Active: long term protection, passive: short term protection as antibodies broken down y body
-Active: memory cells made, passive: no memory cells made
What are vaccines?
Vaccines are when a weakened pathogen with antigens are injected into an organism to cause an immune response.
The pathogens are dead or weakened.
What is the definition of vaccinations?
The deliberate introduction of an antigen/weakened pathogen /attenuated pathogen to cause an immune response
Do vaccinations cause symptoms?
They intiate an immune response(primary) without the symptoms and produce memory cells
What happens if later infections occur after a vaccination?
If a later infection occurs, memory B-cells are able to produce antibodies to eliminate the pathogen before it causes disease.
What is herd immunity?
Most people are immune so do not become ill, so there is less chance of a non-immune person being exposed to the pathogen
What is a monoclonal antibody?
Antibodies with the same tertiary structure produced from cloned plasma cells
What are two uses of monoclonal antibodies?
They can be used for treating illnesses(anticancer drugs) and medical diagnosis(pregnancy testing)
How are monoclonal antibodies used in anti cancer drugs/ treating illnesses?
-cancer cells have different surface antigens than normal body cells ->tumour makers
-monoclonal antibodies can be produced which will be specific and complementary because of their tertiary structure and bind to the tumour makers in tumour cells
-if you attatch a drug to the monoclonal antibodies then the drug will only accumulate in the cancerous cells
-this decreases the side effects of the drug
How are monoclonal antibodies used in pregnancy testing/diagnosis(or drug testing)
-detect the hormone human chronic gonadotrop(hCG) found in the urine of pregnant women
1)application area contains antibodies that are complementary to hCG protein,bound to a colour bead
2)urine applied with hCG-hCG binds to the antibody with the coloured bead, forming an antigen-antibody complex
3)urine moves up the stick to the test strip, carrying beads with it.
4)test strip contains antibodies to hCG that are immobilised
5)if hCG is present the antibody bound hCG(with the coloured bead) will bind to one of the immobilised antibodies,causing a blue appearance in the test strip
What is an ELISA test?
Enzyme-linked immunosorbent assay tests allows you to see if a patient has any antibodies to a certain antigen or any antigen to a certain antibody.
What are the uses of ELISA tests?
Medical diagnosis-pathogenic jnfection(HIV) or allergies(nuts,lactose)
What does it mean if there is a colour change in an ELISA test?
Positive result.
Antibody or antigen is present in blood plasma
Are ELISA tests quantities or qualitative?
ELISA usually qualitative but sometimes quantitive depending on the intensity of the colour change.
What are the two types of ELISA test?
Direct and indirect
What is a direct ELISA test?
-uses a single antibody that is complementary for the antigen you’re testing for
1)antigens from patient sample are immobilised to the inside of a well in a well plate
2)antibody that is complementary to the antigen of interest is added,with an enzyme attatched.
3)if antigen is present, the detection antibody will bind.
4)well is washed to remove any unbound antibodies
5)substrate solution is added
6)if detection antibody is found,the enzyme converts substrate into coloured product = +ve result
What is an indirect ELISA test?
uses two different antibodies- used to detect pathogenic infection e.g. HIV
1)HIV antigen is immobilised in the well
2)sample of blood plasma added
3)if there are HIV-specific antibodies in plasma, these will bind to the antigens immobilised in the well
4)well is washed to remove any unbound antibodies
5)secondary antibody added which has an enzyme attached to it
6)secondary antibody can bind to HIV-specific antibody(primary antibody)
7)well washed out to remove any unbound secondary antibody(if no primary antibody bound, all secondary will be washed out as there is nothing to bind to)
8)substrate solution added to the well, if secondary antibody is present(enzyme bound), a coloured product will form= +ve result
What is HIV and AIDS?
-HIV(Human Immunodeficiency Virus)-virus that affects the human immune system
-leads to AIDS(Acquired Immune Deficiency Syndrome) - immune system deteriorates and eventually fails
-AIDS sufferers more vulnerable to infections such as pneumonia
How does HIV infect people?
-HIV infects and eventually kills helper T-cells, which act as the host for the virus
-think about how this effects the immune response
-people infected with HIV develop AIDS when helper T-cell numbers in their body reach a critically low level.
How is HIV transmitted?
HIV is spread from one infected person to another when bodily fluids mix: through sexual intercourse, when a blood transfusion is given from one infected person to a non-infected person, when an intravenous drug user shares a needle with an infected person, from a mother to an unborn baby across the placenta
What does initial infection of HIV look like?
-HIV replicates rapidly and the infected person may experience severe flu-like symptoms
-after this period, HIV replication drops to a lower level ->latency period(can last years)
-no/little symptoms during this period
What are the symptoms of AIDS?
-people with HIV are classed as having AIDS when symptoms of their failing immune system start to appear OR their T-cell count drops below a certain level
-time between infection with HIV and AIDS varies but average without treatment is 10 years
-initial symptoms - minor infections of mucus membranes(e.g. inside nose, ears, or genitals), and recurring respiratory infections
-as AIDS progresses, no. of immune cells decreases-> more susceptible to more serious infections inc. chronic diarrhoea, severe bacterial infection and TB
-late stages of AIDS(very low no. of immune system cells) - develop a range of serious infections: toxoplasmosis of the brain(parasite infection) and candidiasis of the respiratory system(fungal infection)
-it’s these serious infections that kill AIDS patients, not HIV itself
What is an opportunistic disease?
When the infected person starts to suffer from diseases that wouldn’t cause a problem to a healthy person. As a result, the person may die.
What is the survival time for someone with HIV/AIDS?
-varies a lot
-depends on other factors such as: existing infections, age, strain of HIV, access to healthcare
What are the structures within a virus(HIV)?
-attachment proteins that are complementary to receptors on the T-helper cell so HIV can bind(a type of glycoprotein)
-lipid envelope - made from the cell surface membrane of it’s host cell
-protein capsid- stores genetic material and enzymes
-RNA(*HIV’s genetic material) - codes for viral proteins
-reverse transcriptase(and other enzymes) which converts RNA into DNA
*present in all viruses
Describe the process of HIV replication.
1)attachment protein binds to a receptor molecule on the cell membrane of a host cell(T-helper cell)
2)capsid is released into the cell, where it uncoats and releases RNA into the cell’s cytoplasm
3)reverse transcriptase is used to make a complementary strand of DNA from the viral RNA template.
4)double stranded DNA is made and inserted into the human DNA(T-helper cells)
5)Host cell enzymes/ribosomes used to make viral proteins(e.g. capsid, RNA) from the viral DNA found within the human DNA
6)Viral proteins assembled into new viruses, which bud from the cell and go on to infect other cells
What does it mean if something is retrovirus?
RNA is converted back into DNA(it goes backwards). HIV is retroviral.
How do antibiotics kill bacteria?
Antibiotics kills bacteria by interfering with their metabolic reactions.
They target bacterial enzymes, ribosomes and cell walls
Why don’t antibiotic damage human cells?
As bacterial enzymes and ribosomes are different to humans’, the antibiotics only kill bacterial cells and don’t damage human cells
Why don’t antibiotics effect viruses?
-viruses aren’t affected by antibiotics because they don’t have bacterial enzymes, do not have metabolic processes to inhibit an d do not have a cell wall
-human viruses aren’t alive and so use human enzymes and ribosomes to replicate, so antibiotics can; inhibit them
-antiviral drugs target the few virus specific enzymes(enzymes that only viruses use) that exist.
How do you control HIV infections?
-no cure or vaccine for HIV but antiviral drug an be used to slow down the progression of HIV infections and AIDS in an infected person
-best way to control HIV is to reduce it’s spread
-sexual intercourse(barrier protection)
-infected body fluids(sharing needles)
-HIV+ mother to her foetus-> not all babies from HIV+ve mothers will be born with HIV->can reduce the risk by taking antiviral drugs during pregnancy
