3.2.4 Cell recognition and the immune system Flashcards
What are causes of disease?
Life style - smoking, alcohol, no exercise.
Genetic defect - caused by a mutation in the DNA coding for a protein.
Infection - caused by a pathogen : a microbe (bacteria, fungus, virus or protocista) that causes illness.
How do pathogens cause disease?
Damage host tissues by breaking cell membranes or preventing DNA, RNA and protein synthesis.
Produce toxins e.g. cholera toxin.
What role does lymphatic vessels have in the immune system? + what do they contain?
They contain lymphatic fluid that circulates and removes waste and harmful substances from the body.
What role do lymph nodes have in the immune system? + what do they contain?
They are filters that remove harmful substances.
They contain white blood cells called lymphocytes.
Outline the 1st line of defence
Skin creates a barrier to infection.
Outline the 2nd line of defence
White blood cells (leukocytes) respond non-specifically.
Outline the 3rd line of defence
Specific responses from lymphocytes.
Antigen definition
- A cell-surface molecule which stimulate immune response (Any part of an organism or substance that the immune system recognises as foreign).
- Usually (glyco)protein, sometimes (glyco)lipid or polysaccharide.
- immune system recognises as “self” or “non-self” = enables identification of cells from other organisms of same species, pathogens, toxins & abnormal body cells.
What are the 2 types of the defence mechanism?
Non-specific & specific
What is the non specific defence mechanism and give examples
The response is immediate & always the same e.g. physical barrier, phagocytosis.
What is the specific defence mechanism and give examples
The response is slower & different for each pathogen e.g. cell mediated T-lymphocytes, humoral B-lymphocytes.
What are the physical barriers to infection (1ST LINE DEFENCE)?
- Tears contain lysosome.
- Stomach acid & enzymes.
- Cilia & mucus lining respiratory surfaces.
- Epithelial layer of the skin.
- Platelets - damaged skin (blood clots)
What are the 5 key steps of phagocytosis? How does phagocytosis destroy pathogens? (2ND LINE OF DEFENCE)
1.The phagocyte is attracted to the pathogen by chemicals produced by pathogens (chemotaxis).
2. The phagocyte engulfs pathogen via endocytosis to form a phagosome.
3. Lysosomes migrate towards the phagosome formed by engulfing the pathogen (phagolysosome).
4. The lysosomes release their lytic enzymes into the phagosome, where the pathogen is broken down.
5. The breakdown products of the pathogen are absorbed by the phagocyte are presented on their cell membrane.
What is humoral immunity? (3RD LINE OF DEFENCE) + what does it involve?
Humoral immunity involves B-lymophocytes (B-cells). These are a type of white blood cell and are made and developed in the bone marrow. They are found in bodily fluids e.g. blood, lymph and plasma. They also respond to foreign bacteria & viruses.
Outline the process of Humoral Immunity (B-cells)
- Once phagocytes have engulfed and digested an invading pathogen, some of the antigens from the pathogen are displayed on its surface. This is called ANTIGEN PRESENTATION.
- T helper cells attach to the presented antigens and stimulate B-cells to divide by mitosis.
- The cloned B-cells develop and differentiate into Plasma and Memory cells.
Outline the primary immune response in humoral immunity (PLASMA CELLS)
These are plasma cells which secrete antibodies directly and destroy the pathogen and any toxins. They only live a few days & secrete 2000 antibodies per second.
Outline the secondary immune response in humoral immunity (MEMORY CELLS)
These are memory cells which do not secrete antibodies, they circulate in the blood & tissue fluid and divide rapidly into more plasma cells & memory cells when they encounter the same pathogen again.
Is the quantity of antibodies in the blood lower during the primary or secondary response over time?
Primary response.
What is cell mediated immunity? (3RD LINE OF DEFENCE) + what does it involve?
Cell mediated immunity involves T-lymphocytes (T-cells). These are made in the bone marrow and mature in the thymus. They respond to the body’s own cells altered by cancer, cells infected with viruses & to transplanted tissues.
Outline the process of Cell Mediated Immunity (T-cells)
What is the Cellular Immune Response?
Non-self antigens entering lymph nodes from cancer cells or transplanted organs sensitise T-cells within the lymph nodes. The sensitised T-cells divide rapidly by mitosis to generate large numbers of cloned (identical) T-cells.
What do the cloned T-cells do?
They mature and differentiate into cells that do different jobs.
What are two of the cells T-cells mature and differentiate into? + function of each
- TC Cells (Cytotoxic T-Cells) kill virus infected cells or cancerous cells by making holes in their membranes.
- TH Cells (Helper T-cells) stimulate B-lymphocytes to divide.
5 quick questions -
1. An enzyme found in white blood cells that digests pathogens.
2. Type of acid found in the stomach.
3. Type of immunity where antibodies are made.
4. Name of the white blood cells that produce antibodies.
5. Name of the blood cells that engulf pathogens.
- = Lysosomes.
- = Hydrochloric acid.
- = Active.
- = B-cells - Plasma cells.
- = Phagocytes.
What is immunity?
It is when an antigen is recognised by a type of white blood cell known as a phagocyte. It is the ability of our body to protect itself from a disease that we have already experienced. There are two interlinked types of immunity; cell mediated immunity and humoral immunity.
What is antigenic variability?
Some pathogens can change their surface antigens = the antigens on their cells keep changing making them unrecognisable to existing memory cells. These pathogens have over 100 strains e.g. the flu virus.
What causes antigen variability?
- Random genetic mutation changes DNA base sequence.
- Results in different sequence of codons on mRNA.
- Different primary structure of antigen = H-bonds, ionic bonds & disulfide bridges form in different places in tertiary structure.
- Different shape of antigen.
Explain how antigen variability affects the incidence of disease
Memory cells no longer complementary to antigen (memory cells produced during the primary response from the first infection will not recognise the different antigens) = individual not immune = can catch the disease more than once.
This means that the immune system has to carry out the primary response again against these new antigens.
Many varieties of a pathogen = difficult to develop vaccine containing all antigen type.
What are 2 examples of pathogens that show antigenic variation?
HIV & influenza virus
How does antigenic variation affect the production of vaccines to help prevent people from catching an influenza?
The flue is a virus which changes every year. This is because many new strains of the virus are formed by antigenic variation.
Memory cells produced from vaccination with one strain of the flu will not recognise other strains with different antigens. These strains are immunologically distinct.
Every year a new vaccination has to be made as there are many different strains of the virus circulating in the population.
A new vaccine which is developed along with others is chosen every year. The most effective one is chosen.
A program of vaccination is then implemented.
What are polyclonal antibodies?
These are antibodies which are proteins produced by B-lymphocytes on exposure to foreign material. They are specific to each antigen.
What is an antibody?
Proteins secreted by plasma cells.
Quaternary structure: 2 ‘light chains’ held together by disulfide bridges, 2 longer ‘heavy chains’.
Binding sites on variable region of light chains have specific tertiary structure complementary to an antigen. These variable regions can be changed by the amino acid sequence changing depending on which pathogen they come across.
The rest of the molecule is known as the constant region.
What are monoclonal antibodies?
These are antibodies produced from a single group of genetically identical B-cells (plasma cells). This means that they are all identical in structure.
Why are monoclonal antibodies useful?
- They are used to separate a chemical from a mixture.
- They are used in immunoassays to eliminate the quantity of a substance in a mixture e.g drug & pregnancy testing, AIDS testing.
What does cancer treatment involve?
It involves delivering cytotoxic drugs to cancer cells. Cancer cells have antigens on their surface that are not found on healthy cells.
During transplant surgery what can monoclonal antibodies be used to do?
They can be used to block T-cells that will cause rejection of a transplanted organ.
Outline how monoclonal antibodies made (7 steps)
- Inject foreign material into a mouse.
- B-cells of mouse make polyclonal antibodies.
- Extract B-cells from the spleen.
- Mix B-cells with cells from a cancer tumour in vitro.
- The detergent breaks the cell surface membranes of both cells and allows them to fuse.
- The fused cells are separated using a microscope and cultured to form a group (clone) of cells.
- Each cell is tested, only producing the required antibody are grown on a large scale.
What are the two responses the Immune Response can split into?
Cellular response or Humoral response.
What is the cellular response in the immune response?
The T-cells and other immune system cells that they interact with, e.g. phagocytes, from the cellular response.
What is the humoral response in the immune response?
B-cells, cloned selection and the production of monoclonal antibodies form the humoral response.
What are the two types of response which are needed to remove a pathogen from the body?
The cellular response and the humoral response.
Which cells do T-cells activate?
B-cells.
What coats pathogens to make it easier for phagocytes to engulf them?
Antibodies.
What is the primary immune response?
When an antigen enters the body for the first time it activates the immune system.
Why is the primary response slow?
Because there are no B-cells that can make the antibody which is needed to bind to it.
While the body is producing the correct amount of the right antibody to overcome the infection, what will the infected person show?
Symptoms.
After being exposed to an antigen, what happens?
(primary response)
T-cells and B-cells produce memory cells. These memory cells retain in the body for a long time.
What do memory T-cells remember?
(primary response)
They remember the specific antigen and will recognise it a second time round.
What do memory B-cells record?
(primary response)
They record the specific antibodies needed to bind to the antigen.
What is the secondary immune response?
The secondary immune response is when the same pathogen enters the body again. This time round, the immune system will produce a quicker, stronger immune response.
What selection happens faster in the secondary immune response?
Clonal.
What happens in the secondary immune response?
Memory B-cells are activated and divide into plasma cells that produce the right antibody to the antigen.
Memory T-cells are activated and divide into the correct type of T-cells to kill the cell carrying the antigen.
What does the secondary response often prevent and how?
Symptoms of the infection as it often gets rid of the pathogen before you are able to show any. This is because you are immune to the pathogen.
What do vaccines contain?
Antigens. These antigens cause your body to produce memory cells against a particular pathogen, without the pathogen causing disease.
You become immune without getting any symptoms.
Why are people which are not vaccinated also less likely to catch the disease?
They are less likely to catch the disease as there are fewer people to catch it from.
What is herd immunity?
When people who are not vaccinated are also less likely to catch the disease as there are fewer people to catch it from.
Do vaccines always contain antigens?
Yes and these may be free or attached to a dead or attenuated (weakened) pathogen.
What are the two ways vaccines can be taken?
By injection or orally.
What are disadvantages of taking a vaccine orally?
It could be broken down by enzymes in the gut or the molecules of the vaccines may be to large to be absorbed into the blood.
Why are booster vaccines sometimes given later on?
To ensure that memory cells are produced.
What activates the primary immune response?
Antigens on the surface of pathogens.
What are the two types of Immunity?
Passive & Active.
Active immunity is where …
… your immune system makes its own antibodies after being stimulated by an antigen.
How many types of active immunity are there and what are they?
There are 2 including, natural and artificial.
What is natural active immunity?
This is when you become immune after catching a disease.
What is artificial active immunity?
This is when you become immune after you’ve been given a vaccination containing a harmless done of antigen.
Passive immunity is the …
… type of immunity you get from being given antibodies made by a different organism - your immune system doesn’t produce any antibodies of its own.
How many types of passive immunity are there and what are they?
There are 2 including, natural and artificial.
4 factors of active immunity which are differences to passive immunity:
- Requires exposure to antigen.
- It takes a while for protection to develop.
- Memory cells are produced.
- Protection is long-term because the antibody is produced (after activation of memory cells) in response to complementary antigen being present in the body.
What is artificial passive immunity?
This is when you become immune after being injected with antibodies from someone else. E.g. If you contract tetanus you can be injected with antibodies against the tetanus toxin, collected from blood donations.
What is natural passive immunity?
This is when a baby becomes immune due to the antibodies it receives from its mother, through the placenta and in breast milk.
4 factors of passive immunity which are differences to active immunity:
- Doesn’t require exposure to antigen.
- Protection is immediate.
- Memory cells aren’t produced.
- Protection is short-term because the antibodies given are broken down.
Example: Targeting drugs to a particular cell type – Cancer cells
1) Different cells in the body have different surface antigens.
2) Cancer cells have antigens called tumour markers that are not found on normal body cells.
3) Monoclonal antibodies can be made that will bind to the tumour markers.
4) You can also attach anti-cancer drugs to the antibodies.
5) When the antibodies come into contact with the cancer cells they will bind to the tumour markers.
6) This means the drug will only accumulate in the body where there are cancer cells.
7) So, the side effects of an antibody-based drug are lower than other drugs because they accumulate near specific cells.
Example: Targeting a particular substance for medical diagnosis – Pregnancy Testing
1) The application area contains antibodies for hCG bound to a coloured bead (blue).
2) When urine is applied to the application area any hCG will bind to the antibody on the beads, forming an antigen-antibody complex.
3) The urine moves up the stick to the test strip, carrying any beads with it.
4) The test strip contains antibodies to hCG that are stuck in place (immobilised).
5) If there is hCG present the test strip turns blue because the immobilised antibody binds to any hCG – concentrating the hCG-antibody complex with the blue beads attached. If no hCG is present, the beads will pass through the test area without binding to the anything, and so it won’t go blue.
What hormone do pregnancy tests detect?
+ where is it found?
They detect the hormone, human Chorionic Gonadotropin (hCG).
It is found in the urine of pregnant women.
What is an ELISA test?
It is a medical diagnostic test that uses antibodies.
What does ELISA stand for?
Enzyme-Linked ImmunoSorbent Assay.
What does an ELISA test allow you to see?
It allows you to see if a patient has any antibodies to a certain antigen or any antigen to a certain antibody.
What can an ELISA test be used to test for?
pathogenic infections, for allergies and for just about anything you can make an antibody for.
What is used in an ELISA test?
An antibody is used which has an enzyme attached to it. This enzyme can react with a substrate to produce a coloured product. This causes the solution in the reaction vessel to change colour.
What does it demonstrate if there is a colour change in an ELIZA test?
It demonstrates that the antigen or antibody of interest is present in the sample being tested. In some types of ELISA, the quantity of this antigen/antibody can be worked out from intensity of the colour change.
What does Direct ELISA use?
It uses ONE antibody that is complementary to the antigen you are testing for.
What does Indirect ELISA use?
It uses TWO different antibodies that are complementary to the antigen you are testing for.
Example: Using an ELISA as a HIV (Human Immunodeficiency Virus) Test
1) HIV antigen is bound to the bottom of a well in a well plate (a plastic tray with loads of little circular pits in it).
2) A sample of the patient’s blood plasma, which might several different antibodies, is added to the well. If there are any HIV-specific antibodies (i.e. antibodies against HIV) these will bind to the HIV antigen stuck to the bottom of the well. The well is then washed out to remove any unbound antibodies.
3) A secondary antibody, that has a specific enzyme attached to it, is added to the well. This secondary antibody can bind to the HIV-specific antibody (which is also called the primary antibody). The well is washed out again to remove any unbound secondary antibody. If there’s no primary antibody in the sample, all of the secondary antibody will be washed away.
4) A solution is added to the well. This solution contains a substrate, which is able to react with the enzyme attached to the secondary antibody and produce a coloured product. If the solution changes colour, it indicates that the patient has HIV-specific antibodies in their blood and is infected with HIV.
An indirect ELISA test can be used to see if a patient possesses antibodies to the … virus.
HIV
Why are the washing steps important in the ELISA test to test for HIV?
To make sure unbound antibodies aren’t left in the well which could affect the result.
What can the virus HIV cause?
AIDS.
What does AIDS stand for?
Acquired Immune Deficiency Syndrome.
What part of the body does HIV affect? and how does it affect it? and how does it affect someone?
The immune system.
It causes the immune system to deteriorate which causes it to eventually fail.
This makes someone with AIDS more vulnerable to other infections.
What cells does HIV infect and eventually kill? + what do these cells act as?
Helper T-cells.
These cells act as the host cells for the virus.
Role of helper T-cells
They send chemical signals that activate phagocytosis, cytotoxic T-cells and B-cells so they are hugely important cells in the immune response.
What does it mean if the body does not have enough helper T-cells?
It means the immune system is unable to carry out an effective response to infections because the immune system cells don’t work how they should.
What causes people infected with HIV to develop AIDS?
When the number of helper T-cells in their body reaches a critically low level.
HIV structure
- A core that contains the genetic material (RNA) and some proteins (including the enzyme reverse transcriptase, which is needed for virus replication).
- An outer coating of protein called a capsid.
- An extra outer layer called an envelope. This is made of a membrane stolen from the cell membrane of a previous host cell.
- Sticking out from the envelope are loads of copies of an attachment protein that help HIV attach to the helper T-cell.
