Cells: Immunity Flashcards
Define Infection
The entry of any living organism into the body
What is a pathogen?
A harmful microorganism that causes disease
What is the immune system?
A group of cells, tissues, organs and mechanisms that defend an organism against pathogens and other foreign substances.
What are the two types of defence mechanisms?
Non-specific
Specific
What is a Non-specific response and what are some examples?
The response is immediate and the same for all pathogens.
-Physical and chemical barriers e.g skin and lysosomes in tears
-Phagocytosis
What is a Specific response and what are some examples?
Response is slower and specific to each pathogen.
-Cell mediated response by T-lymphocytes
-Humoral response by B-lymphocytes
Explain the process of Phagocytosis
- Pathogens that have invaded the body release chemicals called chemoattractants.
- Phagocytes are attracted to the chemicals, and respond the the chemical stimuli, chemotaxis, and move towards the pathogens.
- The phagocytes have receptors that recourse chemicals.
- The phagocyte begins to engulf the pathogen, forming a phagosome.
- Lysosomes in the phagocyte move towards the phagosome and fuse with it, forming a phagocytic vesicle.
- Lysosomes release lysozymes into vesicle where they destroy the pathogens cell wall.
- Soluble products from the pathogen are absorbed into the phagocytes cytoplasm.
Define Antigen
Markers that allow cell to cell recognition and can either be self or non-self
What are the two types of T-lymphocytes?
T helper cells
Cytotoxic T cells
Describe how T helper cells work
(cellular response)
- Pathogen invades body cells
- Phagocyte places antigens from the pathogen on its cell surface membrane.
- Receptors on specific T helper cells fit exactly onto these antigens.
- Attachment activates the T cell to divide rapidly by mitosis and form a clone of genetically identical cells.
- The cloned T cells differentiate:
-Develop memory cells to respond to future infections
-Stimulate phagocytes to engulf pathogens
-Stimulate B cells to divide and secrete their antibody
-Become Cytotoxic T cells
Explain how Cytotoxic T cells work
(Cellular response)
They kill abnormal and body cells infected by pathogens by producing a protein call Perforin that makes holes in the membrane.
This makes the cell freely permeable to everything, so the cell dies.
Where are T-lymphocytes made and matured?
-Made in the bone marrow
-Mature in the thymus gland
What is an antigen-presenting cell?
A cell that presents antigens of other foreign cells on its own surface.
How do our cells distinguish between self and non-self?
Central tolerance:
-Lymphocytes will collide with the body’s own material (self).
-Some lymphocytes have receptors that will fit ‘self’, so they die.
-The remaining lymphocytes are those that may fit foreign material (non-self), so can stay.
-Any lymphocytes that do show an immune response to any self-antigens will undergo programmed death ‘apoptosis’, before they differentiate into mature lymphocytes. This is called clonal deletion.
> In adults, lymphocytes produced in bone marrow initially only encounter self-antigens.
What happens if clonal deletion does not work properly?
May result in an autoimmune disease where the body’s immune system destroys its own tissues, e.g type 1 diabetes.
Why might a transplant be rejected from one body to another?
One body has different genes and encode different proteins to another, so the marker molecules will be different and will be identified as ‘non-self’ and foreign in another persons body, so our immune system will attack (T cells) and possibly reject.
What are the various roles of T cells?
-T helper cells
-Cytotoxic cells
-Simulation of phagocytes
-Simulation of B cells
-Memory cells
Define what Phagocytosis is
Pathogens engulfed by phagocytes
Where are B Lymphocytes made and mature?
-Produced by haematopoietic stem cells in the bone marrow
-Mature in the bone marrow
What is the role of B Lymphocytes?
-Produce antibodies which are released into body fluids, so responsible for hummoral immunity
-Memory of immune system
-They do not directly attach to pathogens
Describe the process B lymphocytes go through to fight infection
- Surface antigen of an invading pathogen are taken up by B cells
- B cells process the antigens and presents them on its surface
- Helper T cells attach to the processed antigens on the B cell, activating the B cell
- B cell is now activated so goes through mitosis to give a clone of plasma cells
- Cloned plasma cells produce and secrete the specific antibody that exactly fits the antigen on the pathogens surface
- Antibody attaches to antigen on the pathogen and destroys them.
- Some B cells develop into memory cells to respond to future infections by dividing rapidly and producing the antibodies (secondary immune response).
What is a Plasma Cell?
They secrete antibodies into the blood plasma, but can only survive a few days.
Are antibodies proteins?
Yes
Briefly describe the structure of an antibody
-A quaternary structure
-4 polypeptide chains
-Pairs of long, heavy and short, light, joined by disulphide bridges
What 2 regions are there on an antigen and describe where they are?
Variable region: top section ( v shape)
Constant region: bottom section ( ll )
these don’t vary between antibody types
What is at the end of every variable region?
An antigen binding site to form an antigen-antibody complex
What is ‘agglutination’?
(bacterial cells) clumps together so easier for phagocytes to locate, serves as markers.
What are antibodies produced in the natural immune system called?
Polyclonal
Briefly describe the process of obtaining monoclonal antibodies
- Mouse exposed to non-self material (antigen)
- B cells in mouse produce a mixture of antibodies and they are extracted
- Mixed with tumour cells to readily divide
- Detergent is added to break down cell surface membranes to enable them to fuse together forming hybridoma cells
- These are separated and tested, cultured to form a clone
- Clone is grown on a large scale and extracted= monoclonal antibodies
What 3 ways can monoclonal antibodies be used to treat cancer?
-Block, prevents growth
-Flag, for our immune system
-Deliver, kills
What are 2 ways monoclonal antibodies are used in medical testing?
-Pregnancy testing
-Prostate cancer testing
How do monoclonal antibodies work on a pregnancy test?
-Placenta produces the hormone HCG, found in mothers urine
-Test strip contains monoclonal antibodies for HCG
-If pregnant, the monoclonal antibodies have an enzyme attached to it that binds to HCG, forming an antigen-antibody complex
-These move up the strip until they reach the immobilised mono anti
-These two bind, triggering an enzyme to interact with a dye that changes the colour of the test line
-Control line tests any excess antibodies
How are monoclonal antibodies used to test for prostate cancer?
-Men with this often produce a specific protein called prostate specific antigen (PSA), having unnaturally high levels of it in blood.
-Mono anti measure the amount this in blood sample
-A value outside of the normal PSA is not a diagnosis, but an early warning
What are some ethical issues of monoclonal antibodies?
-Use of mice, giving them cancer
-Deaths associated with the use
-Drugs present new dangers, side effects
Define Immunity
The ability of an organism to resist infection, provided by the memory cells.
What are the 2 types of immunity and their 2 sub sections?
Active and Passive
both can be natural or artificial
What is active immunity and describe the 2 ways it can be carried out?
The immune system has created its own antibodies.
Natural- caught a disease and made antibodies
Artificial- antibodies have been created in response to a vaccination of antigens
What is passive immunity and describe the 2 ways it can be carried out?
Antibodies are given to individuals from an outside source, so no direct contact with pathogen or antigen.
Natural- transferred from breast milk
Artificial- can be injected
These are only short-term and cannot be replaced, no memory cells
What is a vaccination and what does it do?
Contains one or more types of antigen from pathogen, and stimulates the production of memory cells.
Provides herd immunity
What may a vaccination contain?
- Isolated antigens (e.g cell surface proteins)
- Inactivated form of pathogen, killed by heat treatment
-Attenuated form of pathogen (less virulent) - Just the toxin from the pathogen
How much of the population has to be vaccinated for it to be effective herd immunity?
80%
What is ‘antigenic variability’?
Pathogens may mutate frequently so antigens change, so we can vaccinate against everything.
What is HIV?
Human Immunodeficiency virus
What is AIDS?
Acquired immune deficiency syndrome
What group does HIV belong to?
Retrovirus
How does HIV replicate?
- HIV enters the bloodstream and circulates
- A protein (GP20) on HIV binds to a protein called CD4, which occurs on lots of different cells, frequently binding to T helper cells.
- The protein capsid fuses with the cell surface membrane, and the RNA and enzymes of HIV enter the t helper cell.
- HIV reverse transcriptase converts the viruses RNA to DNA
- Newly made DNA is moved into the t helper cells nucleus where it is inserted into cells DNA
- HIV DNA in nucleus creates mRNA using the new cells enzymes; this mRNA contains instructions for making new viral proteins, and the RNA goes into the new HIV
- mRNA passes out of nucleus and uses cells protein synthesis mechanisms to produce HIV particles.
- HIV particles breakaway from T helper cells with a piece of their cell surface membrane surrounding them forming their lipid envelope.
How does HIV cause the symptom of AIDS?
-Attacks t helper cells, so now has a low level in blood
-Without these, B cells cannot be stimulated for antibodies and cytotoxic T cells to kill.
-The body’s immune response is too low and you are more susceptible to other infections
-Contracted diseases can cause death
Why are antibiotics ineffective against AIDS?
-Viruses rely on a host cell to carry out their metabolic activities, so the antibiotics have no mechanisms or structures to disrupt.
-They have a protein coat where antibodies don’t have a site to work.
What does the ELISA test do?
Uses antibodies to detect proteins e.g HIV
Describe the process of the ELISA test
- Apply sample (HIV antigens) to slide, where they will attach to the bottom
- Wash the surface several times to remove any unattached antigens.
- Add antibody specific to antigen we are trying to detect (in blood sample) and leave to bind together.
- Wash to remove any excess antibody.
- Add the 2nd antibody to bind to the 1st, which has an enzyme attached to it- then wash
- Add a colourless substrate to enzyme, where the enzyme will act on it and change it to a coloured product.
- The amount of antigen present is relative to the intensity of the colour.
What are the first and second antibodies called that binds in the ELISA test?
Primary and Secondary antibodies
How can HIV transfer?
-Sex
-Blood donation
-Sharing needles
-Mother to child across placenta
-Through breast milk
