Cell Recognition and Immune Systems Flashcards
What are the two types of defence mechanisms?
Non specific
Specific
What are types of non specific defence mechanisms?
Physical barrier
Phagocytosis
What are types of specific defence mechanisms?
Cell mediated response -
T lymphocytes
Humoral response -
B lymphocytes
What are some physical barriers?
Skin Eyelashes Eyelids Ear wax Mucus Epithelial cells Scabs
What are antigens?
A protein that causes an immune response
What makes it so antigens can be recognised?
Highly specific tertiary structure with a variety of 3D structure
What can the immune system detect that isn’t part of the body’s self molecules?
Pathogens
Transplant organs
Toxins
Cancer cells
What is phagocytosis? Generally
Where a phagocyte engulfs a pathogen
What is the process of phagocytosis?
The phagocyte is attracted to the pathogen from it’s chemical products
Receptors bind to the surface of the pathogen
The phagocyte invaginates around the virus which engulfs it
The lysosomes move towards the pathogen and eventually forms a phagosome
The lysosomes release hydrolytic enzymes which breaks down the pathogen
Waste products will be discharged eventually
How is the phagocyte attracted to the pathogen?
It moves along a concentration gradient in response to the chemical products it creates
Why does the phagocyte invaginate? What is it?
The action of being turned inside out or folded back on itself creating a cavity or pocket indentation
It does this to prevent its membrane damaging permanently
What are some properties of B lymphocytes?
Matures in bone marrow
Used in humoral immunity
Produces antibodies
Responds to viruses, bacteria and foreign material
What are some properties of T lymphocytes?
Matures in Thymus gland
Used in cell-mediated immunity
Responds to foreign material, cancer and transplant organs
How do T-cells start to deal with a pathogen?
A phagocyte/macrophage will have engulfed the pathogen and displayed it’s antigen on it’s surface
The antigen is displayed to many different T-cells in the lymph nodes until the right one is found
What happens after the right T-cell has been found for the antigen?
Clonal selection: stimulated T cell divides many times via mitosis
Then differentiation will occur into either:
Killer T-cells
Helper T-cells
What do Killer T-cells do?
They bind to cells presenting the complementary antigen
The Killer T-cell releases cytotoxins to kill the cell
Producing a protein called perforin that makes holes in the cell membrane
The holes and mis-shape leads to the cell dying
What do Helper T-cells do?
They secrete chemicals that stimulates:
Phagocytic cells
B-cells to produce antibodies
Activates Killer T-cells
They also can become memory cells
How do B-cells deal with antigens?
A variety of B-cells with different shaped receptors are presented to the antigens
Clonal selection: the cell with the right shaped receptor to the antigen is stimulated to divide by mitosis
Either
Plasma cells or memory cells are produced
What do plasma cells produce?
They secrete up to 2000 antibodies into the circulation every second
But they can only survive for a few days
This is the primary immune response
What do memory cells do?
They circulate in the blood and tissue fluid in readiness for future infection
This is the secondary immune response
What is the structure of an antibody?
Y shaped molecule made from 4 polypeptide chains
It has a heavy chain and a smaller light chain on each side of the Y
The variable region is half the light chain
The constant region is the heavy chain and the second half of the light chain
At the top it has complementary binding antigen sites
What does the variable region of an antibody do?
Binds to specific antigens
What does the constant region of an antibody do?
Binds to receptors on B-cells
What are antibodies?
Proteins with specific binding sites for antigens - synthesised by B-cells
How do antibodies work?
They bind with a complementary antigen forming antigen-antibody complexes
This prepares the antigen for destruction as it makes it easier for a phagocyte to locate them
They serve as a marker causing agglutination (clumping) of antigens
Why does one pathogen cause a polyclonal response?
Each pathogen may have many different shaped antigens on it’s surface therefore it takes many different antibodies to neutralise the pathogen
What are monoclonal antibodies?
Produced by a single clone of cells consisting of identical antibody molecules
What can monoclonal antibodies be used for?
Diagnosing - using the Elisa test
Targeting specific antigens - cancer treatment
Pregnancy testing
How are monoclonal antibodies produced?
Mouse is injected with an antigen
Isolate the immune cells - antibody forming cells
Fuse these with tumour cells creating hybridomas
The hybridomas’ are screened for production of desired antibody
They antibody producing hybridomas are cloned
Through clonal expansion you have monoclonal antibodies
What are some ethical issues with producing monoclonal antibodies?
You have to give the mouse cancer to get the tumour cells to make the hybridomas
Some patients have died
Drug trails on healthy humans could be fatal
Why are tumour cells used in the production of monoclonal antibodies?
They replicate very quickly
What happens at the primary response to an antigen?
B-cells need to find the complementary cells and they need to reproduce via mitosis after clonal selection
The B-cells will release plasma cells to release antibodies and deal with the exposure
What happens at the secondary response to an antigen?
After the first exposure memory cells were created and still some in the blood stream therefore they can reproduce much faster in order to flood the blood stream and get rid of the antigens more quickly
What is antigenic variability?
Antigens can alter to evade the hosts immune response allowing pathogens to cause re-infection
Resulting in antibodies previously produced as ineffective
What is artificial active immunity?
Vaccinations
What is an attenuated vaccine?
The pathogen is viable or live however altered to be harmless and less virulent
What is a vaccine containing dead microorganisms?
A vaccine consisting of pathogenic particles that have been cultured then killed
What are isolated antigens related to vaccines?
A pathogen’s antigen is separated and purified after being inactivated
It is combined with stabilisers before the final vaccine is produced
How do vaccinations prevent you from developing diseases?
The vaccines containing antigens of weak/dead pathogens are injected
Antibodies are created to deal with the antigens and memory cells are created
Upon second exposure the memory cells can recognise the pathogen and produce more antibodies much quicker
Why can’t we have one vaccine for all viruses?
The antigens on a virus are specific to one receptor of the antibody
Why can vaccinations not always eliminate disease?
Vaccination can fail to induce immunity in some individuals
Antigenic variability
Thousands of varieties of pathogens
Some pathogens hide within cells
What are the factors of a successful vaccination programme?
Large quantities of the vaccine available at a low cost i.e economically available
Few side effects
Vaccine can be produced, stored and transported hygienically
Trained medical staff available
All or most of the population must be vaccinated to produce herd immunity
What are the ethics of vaccines?
Using animal testing
Potential long term side effects
Who should the vaccines be tested on
In order to be effective most be vaccinated but should people get to choose
What is herd immunity?
Most of the population gets immunised and the spread of contagious disease is contained
It makes it difficult for a pathogen to travel
What does HIV stand for?
Human immunodeficiency virus
What are some properties of HIV?
Causes AIDs
Belongs to a group called retroviruses
What does HIV lead to? Examples?
Susceptible to other diseases i.e opportunistic infections
Sarcoma
Shingles
Pneumocystis
Affects the retina
What is HIV made up of?
RNA Reverse transcriptase Matrix Capsid Lipid membrane Attachment protein
How does HIV infect you?
It enters the body through blood or semen
A protein on HIV binds to CD4 (a receptor on T-cells) the protein capsid fuses with the cell surface membrane
It enters helper T-cells, releasing its RNA and reverse transcriptase
Reverse transcriptase copies viral RNA strand
Viral DNA is integrated into the host DNA and becomes active
Then mRNA leaves the nucleus using the cells protein synthesis to make HIV proteins
The new virus particles are released infecting other cells
Do you display signs of HIV?
Only some do
How is HIV spread?
Through fluids
Why are there very few drugs to treat viral diseases?
There are no metabolic mechanisms or cell structures for them to disrupt as they take over host cells
Viruses also have a protein coat therefore no sites for antibiotics to bind to
What is the ELIZA test?
Enzyme linked immunosorbent assay
Describe the ELIZA test?
Monoclonal antibodies are bound to a test tube
Antigens that fit bind to the antibodies (usually from the blood)
The test tube is washed out so only the antigens bound to antibodies remain
Enzyme antibody complex then binds to antigen antibody complex
A colourless substrate is added
From the presence of the enzyme it causes a colour change
Why is there no colour change in the ELIZA test is the result is negative?
If no antigens bind to the antibodies then no enzymes will bind
If no enzymes are present there will be no colour change
What is the positive ELIZA test for HIV?
Purple colour change
