Immunity and cell structure Flashcards
What are the two main immune defence mechanisms?
1) cell mediated response (T cells)
2) humoral response (T cells then mainly involves B cells)
Every pathogen will have specific NON-SELF molecules (usually proteins) that can…
help our cells to identify them (and distinguish them due to varying tertiary structures)
What do protein molecules on foreign material help our cells to identify?
- pathogens eg. HIV
- cells from other organisms of the same species
- toxins produced by pathogens
- abnormal body cells such as cancer cells
Explain what happens to the immune system during an organ transplant?
recognises the tissue/organ as non-self so attempts to destroy it
What can be done to prevent rejection in organ transplants?
administer immunosuppressive drugs
transplant from relatives who are genetically similar
Briefly explain the time lag between the body’s expose to a pathogen and its immune response to bring the pathogen under control.
- millions of lymphocytes in blood
- one lymphocyte has a surface protein that is complimentary to the surface protein on the antigen
- correct lymphocyte undergoes clonal selection and expansion
- time lag = time for clonal selection and expansion
Why is infection in the fetus are?
protected by the placenta
What happens to lymphocytes that show an immune response to slef natigens/
undergo programmed cell death (apoptosis) before they can differentiate into mature lymphocytes
sm random in the textbook
X
Name two type of white blood cell
phagocytes
lymphocytes
Explain phagocytosis
- chemical products of pathogens or dead/damaged/abnormal cells act as attractants causing phagocytes to move towards the pathogen
- phagocyte engulfs pathogen to form a vesicle called a phagosome
- lysosomes inside phagocyte move towards phagosome and fuse with it
- enzymes within the lysosomes called lysozymes destroy the ingested pathogen (eg. hydrolysis of cell wall)
- soluble, useful products from breakdown of pathogen are absorbed into the phagocyte’s cytoplasm
Define antigen
foreign protein that stimulate immune response and production of antibodies
What type of immune response is phagocytosis?
non-specific
Specific immune response (disadv, adv)
slower at first
can provide long term immunity
Define B cell
cells associated with humoral immunity that mature in the bone marrow and secrete antibodies
Define T cell
cells associated with cell-mediated immunity that are originally stem cells in the bone marrow and then migrate to the thymus gland to mature
What do T cells usually only respond to?
antigen present on a cell surface rather than antigens floating in the blood
Define antigen presenting cell
also called an ‘accessory cell’
cells that present foreign antigens from other foreign cells on their own cell surface membrane
Explain 4 ways T cells distinguish invader cells form normal cells.
(phagocytes, virus, transplant, cancer)
1) phagocytes have engulfed and hydrolysed a pathogen to present some of its (pathogen’s) antigens on its own cell surface membrane
2) body cells invaded by a virus present some of the viral antigens on its own cell surface membrane
3) transplanted cells have different antigens on their cell surface membrane
4) cancer cells present antigens on their cell surface membranes
Define cell mediated immunity
an immune response that does not involve antibody production.
A response where T cells respond to specific antigens on a cell, in turn activating other immune cells and the release of cytokines.
Response of T cells to infection by pathogen:
1) Phagocytes take up pathogen
2) Phagocyte become APC (places antigens from pathogens on its cell surface membrane)
3) T helper cell binds to these specific antigens on the APC to produce activated T helper cell which undergoes clonal expansion by rapid mitosis.
4) Active T helper cell:
- develop into memory cells
- binds to and activates cytotoxic T cell producing activated cytotoxic T cells and cytotoxic memory cells
- B cell becomes APC and active B cell binds to active T cell which caused it clonal expansion that produces memory B cells and plasma cells (these secrete antibdodies)
- stimulate phagocytes to engulf pathogens (phagocytosis)
Explain how cytotoxic T cells kill infected cells?
they produce perforin (a protein) that makes holes in cell surface membrane which then becomes freely permeable so the cell dies
Cytotoxic are most effective against killing viruses which are inside body cells as it prevents the virus from multiplying and infecting more cells
Which cells are involved in humoral immunity?
B cells
Explain what happens in a humoral response when a B cell responds to an antigen?
Millions of different types of B cells in the blood
One B cell has a ANTIBODY specific to the antigen on the pathogen where it’s shape is exactly complimentary
The antigen enters the B cell by endocytosis and gets presented on the surface. (APC)
T helper cells bind to the processed antigens and stimulate the B cell to divide by mitosis to form clones of identical B cells that all produce exactly the same antibody.
This is clonal selection and clonal expansion.
Define monoclonal antibody
Antibodies produced by clones of the same (B) cell
After B cell clones have been made what two types of cell do they differentiate into?
Memory B cells
Plasma cells
Memory B cells
- responsible for secondary immune response
- provide long term immunity
- live a lot longer than plasma cells
- do NOT produce antibodies directly
- when the memory B cells encounter the same antigen again they divide rapidly into plasma cells and more memory cells
- the plasma cells can then produce the antibody specific to the antigen whilst the new memory cells circuits in the blood ready for future infection by the same pathogen.
Explain the primary B cell immune response vs the secondary B cell immune response.
Primary immune response:
Millions of B cells in blood, only one has specific antibody to the antigen, bonds and is complimentary. B cell takes up the antigen by endocytosis and presents it on its cell surface membrane. T helper cell binds to processed antigens on the B cell (now an APC) and stimulate it to divide rapidly into plasma cells and memory cells.
Memory cells circulate for next time (what do they do next time?)
Secondary:
Memory cells encounter same antigen and divide rapidly to produce plasma cells (that produce the correct antibody) and more memory cells.
So faster response because memory cell bind to antigen? And immediately stimulate correct plasma cells with correct antibodies?
What do memory cells mean happens in the secondary immune response?
An increased quantity of the correct antibodies is secreted at a faster rate that the primary immune response
Summarise the role of B cells in humoral immunity. (6)
1) the surface antigens of the invading pathogen are taken up by a B cell
2) the B cell processes the antigen and presents it on its cell surface membrane
3) T helper cells bind to the processed antigens on the B cell and activate the B cell
4) this stimulate sin to divide rapidly by mitosis to produce clones (clonal selection and expansion) which are either memory B cells or plasma cells.
5) the plasma cells secrete the antibody specific to the antigen on the pathogen’s cell surface and kill the pathogen
6) the memory B cells circuit in the blood so next time the same pathogen invades they can divide rapidly into more memory B cells and plasma cells (which secrete the correct specific antibody)
Define antibody
Proteins with binding sites specific to a particular antigen that are serve test by plasma cells which have differentiated form B cells
Describe the structure of an antibody
- 4 polypeptide chains
- 2 heavy chains
- 2 light chains
- TWO antigen binding sites
- one receptor binding site
- forms antigen-antibody complexes
- binding site is different on each antibody - ‘variable region’
- ## rest of antibody is the same - ‘constant region’
What to talk about when reference antibody binding sites?
- specific tertiary structure of the protein
How do antibodies assist destruction of a pathogen?
- could cause AGGLUTINATION of bacterial cells… clumps of bacterial cells form making them easier for phagocytes to identify them
- stimulates phagocytes to engulf the bacterial cells the antibodies are attached to
How does agglutination work?
Each antibody binds to two pathogenic cells causing them to clump together
Explain direct monoclonal antibody therapy in cancer treatment.
- monoclonal antibodies that are specific to antigens on cancer cells are produced
- these antibodies are given to a patient; they bind to the antigens on the cancer cells
- by binding they block chemical signals that stimulate uncontrolled growth
Example of a monoclonal antibody used in cancer treatment?
Herceptin
Breast cancer monoclonal antibody
Advantage of direct monoclonal antibody therapy?
Since antibodies are not toxic and they are highly specific, they lead to fewer side effects that other forms of therapy
Explain indirect monoclonal antibody therapy in cancer treatment
- involves attaching a radioactive or cytotoxic drug to the monoclonal antibody
- when the antibody binds to the antigen on the cancer cell it kills them
Advantages of indirect monoclonal antibody therapy?
- can be used in small doses (why?)
- using in small does is cheaper and means less side effects
Name four disease that monoclonal antibodies are used in diagnosis for?
Influenza
Hepatitis
Chlamydia
Certain cancers
How are monoclonal antibodies used in identification of tumors?
They bind to specific antigens on cancer cells causing them to clump together which makes it easier to identify a cancerous tumor that can then be treated or removed
How can monoclonal antibodies be used to diagnose prostrate cancer?
XXX
Men with prostate cancer produce more prostate specific antigen (PSA) leading to unusually high levels in the blood
Using a monoclonal antibody which interacts with this antigen means you can obtain a measure of how much PSA is in the blood (depending on how much monoclonal antibody binds?/clumping?)
Above normal level of PSA suggests disease so gives early warning
How are monoclonal antibodies used in pregnancy testing?
Used for early detection of pregnancy
Placenta produces human chorionic gonadatrophin (hCG) that is found in mother’s urine.
Monoclonal antibodies linked to colored particles; if they bind to the hCG present in urine,
hCG-antibody-colour complex moves along strip until it is trapped by a different type of antibody which creates a colored line.