5.Cell recognition and the immune system Flashcards
Each type of cell have specific molecules on its surface (most importantly proteins) which enable the immune system to identify…
- pathogens
- cells from other organisms of the same species
- toxins
- abnormal body cells (eg. cancer cells)
How do lymphocytes recognise cells belonging to the body (in the fetus)
- in the fetus millions of lymphocytes are present each capable of recognising a different chemical shape
- these lymphocytes are constantly colliding with other cells are infection is rare
- this means lymphocytes are exclusively colliding with the body’s own cells
- lymphocytes that have receptors fitting with the bodies own cells die or are supressed
- only lymphocytes that might fit foreign material are left
How do lymphocytes recognise cells belonging to the body (in adults)
- lymphocytes are produced in the bone marrow and initially only encounter self-antigens
- any lymphocytes that show an immune response to self-antigens undergo programmed cell death before they can differentiate into mature lymphocytes
- no clones of these anti-self lymphocytes will appear in the blood leaving only lymphocytes that might fit foreign material are left
Name the two kinds of white blood cells
- phagocytes
- lymphocytes
What is phagocytosis
A mechanism by which cells engulf particles to form a vesicle or a vacuole
Describe the steps of phagocytosis
- chemical products of a pathogen or a dead damaged or abnormal cell attract phagocytes to move towards it
- phagocytes have several receptors on their cell surface membrane that recognise and attach to chemicals on the surface of the pathogen
- the engulf the pathogen to form a vesicles known as a phagosome
- lysosomes move towards the vesicle and fuse with it
- enzymes called lysozymes present in the lysosome destroy the bacteria by hydrolysis
- the soluble products from the breakdown of the pathogen are absorbed into the cytoplasm of the phagocyte
What is an antigen
A molecule that is recognised by the immune system as foreign triggering the production of an antibody as part of the body’s defence system
Is phagocytosis specific or non specific
Non specific
Name two types of lymphocyte
- b lymphocytes
- t lymphocytes
What type of immunity are B lymphocytes associated with
Humoral immunity
What type of immunity are T lymphocytes associated with
Cell-mediated immunity
How can T lymphocytes distinguish invader cells from normal cells
- phagocytes that have engulfed and hydrolysed a pathogen present pathogens antigens on their own cell surface membrane
- body cells invaded by a virus present some viral antigens on their own cell surface membrane
- transplanted cells from same species have different antigens on their cell surface membrane
- cancer cells are different from normal body cells and present antigens on their cell surface membranes
What are cells that display foreign antigen on their surface called
Antigen-presenting cells
T lymphocytes only respond to what
Antigens presented on a body cell rather than to antigens within the body fluids
Describe the first stages in the response of T lymphocytes to infection by a pathogen (cell-mediated response)
- pathogens invade body cells or are engulfed by phagocytes
- cell or phagocyte places antigens from the pathogen on its cell-surface membrane
- receptors on a specific helper T cell fit exactly on these antigens
- this attachment activates the T cell to divide rapidly by mitosis and form a clone of genetically identical cells
After the first stages of the cell mediated response what do the clones of the T cells do
- develop into memory cells (that enable a rapid response to future infections by the same pathogens)
- stimulate phagocytes to engulf pathogens by phagocytosis
- stimulate B cells to divide and secrete their antibody
- activate cytotoxic T cells
Why is it called humoral response
Because it involves antibodies
Every antigen has a B cell that is
Complementary
Clones of B cells produced develop into one of two types of cells
- plasma cells
- memory cells
What are plasma cells
Secrete antibodies usually into blood plasma. Only last for a few days. Antibodies lead to the destruction of the antigen.
Define an antibody
A protein produced by lymphocytes in response to the presence of a specific antigen, which it then destroys
What is the primary response
The production of antibodies and memory cells
What are memory cells
Responsible for the secondary immune response. Last for decades. When they encounter the same antigen they divide rapidly and develop into plasma cells and more memory cells. The plasma cells produce antibodies needed to destroy the pathogen.
How do memory cells provide long term immunity
Increase the speed of the primary response meaning the infection can be destroyed before harmful symptoms appear
Describe the stages of the use of B cells in humoral immunity
- surface antigens of an invading pathogen are taken up by B cell
- the B cell processes the antigens and presents them on its surface
- helper T cells attach to the processed antigens thereby activating the T cell
- Some activated B cell begins to divide by mitosis to give clones of plasma cells
- These clones plasma cells produce and secrete the specific antibody that fits the antigen on the pathogens surface
- The antibody attaches to the antigen and destroys it
- Some activated B cells develop into memory cells
What are the differences between humoral and cell-mediated immunity
- humoral immunity secrete antibodies that defend against extracellular pathogens/ cell-mediated responses defend against infected cells, cancers and transplant tissues
- humoral involves antibodies, cell-mediated does not
- humoral is mediated by B cells, cell-mediated is mediated by T cells
What are antibodies produced by
(plasma) B cells
Describe the structure of an antibody
- made of 4 polypeptide chains
- one pair of chains are long (called heavy chains) and the other pair of chains are short (called light chains)
- the binding site is called the variable region (as it different on different antibodies)
- the rest of the body is known as the constant region which binds to receptors on cells such as B cells
What is formed when an antibodies binds to a antigen
Antigen-antibody complex
How do antibodies indirectly lead to the destruction of the antigen
- cause the aggulation of the bacteria cells, clumping them up making it easier for phagocytes to locate them as they are less spread out within the body
- they serve as markers that stimulate phagocytes to engulf the bacterial cells to which they are attached to
What is a monoclonal antibody
A antibody produced by a single clone of cells
How can monoclonal antibodies be used in cancer treatment
- monoclonal antibodies are produced that are specific to antigens on cancer cells
- antibodies are given to the patient and attach themselves to the receptor on their cancer cells
- this blocks the chemical signals that stimulate their uncontrolled growth
How can monoclonal antibodies be used in medical diagnosis
By using a monoclonal antibodies that interacts with a specific antigen of a disease it is possible to obtain a measure of the antigen which means the patient has the disease
Hoe can monolonal antibodies be used in pregnancy testing
- the placenta produces a hormone called hCG which is found in the mothers urine
- monoclonal antibodies are contained in the lateral flow assay and are coloured
- if hCG is present in the urine it binds to these antibodies as they are complementary
- the hCG-antibody-colour complex moves along the strip until it is trapped by another type of antibody on the display strip, creating a coloured line
What are some ethical issues raised by monoclonal antibodies
- production of them involves mice to produce antibodies and tumour cells, so is deliberately inducing cancer in mice
- there have been some deaths associated with the treatment
- testing their safety creates dangers, eg. TGN disaster
What is passive immunity
Immunity from the introduction of antibodies from another individual. They are not replaced when broken down and no memory cells are produced so there is no long lasting immunity
What is active immunity
Immunity from an individuals own immune system, from the production of antibodies from a plasma cell stimulated by an antigen
What are the two kinds of active immunity
- natural active
- artificial immunity
What is natural active immunity
Results from an individual becoming infected with a disease under normal circumstances, resulting in the production of antibodies and memory cells
What is artificial active immunity
Involves inducing an immune response in an individual, without them suffering the symptoms of the disease
What is vaccination
The introduction of a vaccine containing appropriate disease antigens into the body in order to induce immunity
What are features of a successful vaccination programme
- economically available
- few side effects
- means of producing, storing and transporting the vaccine
- means of administering the vaccine
- possible to vaccinated the vast majority of the vulnerable population to produce herd immunity
What is herd immunity
When a sufficiently large proportion of the population has been vaccinated to make it difficult for a pathogen to spread within that population.
Why is herd immunity important
As it is never possible to vaccinate everyone in a large population
Why might vaccination not eliminate a disease
- vaccination fails to induce immunity in certain individuals
- individual develops disease right after vaccination and therefore has not achieved immunity
- antigen variability may occur, mutations cause changes in antigen which isn’t recognised by the immune system
Name some ethical issues that arise due to vaccination
- uses animal testing
- some may cause long term side effects
- should vaccination be compulsory
What is the structure of HIV
- contain genetic material (RNA)
- reverse transcriptase
- capsid enclosing genetic material and enzymes
- lipid envelope surrounding everything
- attachment proteins on liquid envelope
Describe how HIV replicates
- HIV circulates the blood stream
- a protein on HIV binds to another protein on a cell
- the protein capsid fuses with the cell-surface membrane allowing the viris’ RNA and enzymes to enter the cell
- the HIV reverse transcriptase converts the RNA into DNA
- the DNA is moved into the cells nucleus where its inserted into its DNA
- mRNA is made from this DNA using the cells enzymes
- mRNA passes out the nucleus and uses the cells machinery to make HIV particles
- newly made HIV particles break away from the cell with a piece of its cell surface membrane which makes up their lipid envelope
How does HIV cause symptoms of AIDS
-HIV attacks T cells meaning the immune system cannot stimulate B cells to produce antibodies so diseases cannot be dealt with. Memory cells can also be attacked.
What does HIV particles attack
Helper T cells
What does an ELISA test do
It uses antibodies to detect the presence and quantity of a protein in a sample
Describe the steps in an ELISA test
- apply sample to a slide which antigens in the sample in the attach to
- wash to remove unattached antigens
- add the antibody that is specific to the antigen
- wash to remove excess antibodies
- add a second antibody that binds to the first antibody which has an enzyme attached to it
- add the colourless substrate on the enzyme
- the enzyme acts on the substrate changing it into a coloured product
- the amount of the antigen present is relative to the intensity of colour that develops
Why don’t antibiotics work on virus’
- antibiotics work by disrupting metabolic activities and cell structures
- there are no metabolic activities or cell structures for antibodies to disrupt as virus’ use other cells machinery for this.
