Topic cell: cell recognition and the immune system Flashcards
State what would happen if a non-self cell is detected:
An immune response is triggered
State what can be identified by different surface molecules
Pathogens
Cells from other organisms of the same species
Abnormal body cells (e.g. cancer cells)
Toxins
Describe how self-cells are recognised
Lymphocytes are made when you are a foetus. When you are a foetus in the womb you are unlikely to be exposed to any cells other than self-cells. The lymphocytes complementary to the antigens on self-cells will die or production will be suppressed. This is to prevent your lymphocytes from attacking your own cells.
The only remaining lymphocytes are complementary to pathogens and non-self cells. The same process occurs after birth in the bone marrow. Any new lymphocytes made in the bone marrow which are complementary in shape to antigens on self-cells will be destroyed
When this process doesn’t work and lymphocytes which attack self-cells are produced, this causes the symptoms of autoimmune diseases.
Define Antigen -
Antigens are molecules that generate an immune response by lymphocyte cells when detected in the body. They are usually proteins and are located on the surface of cells.
Define antigen variability
Pathogenic DNA can mutate frequently. If a mutation occurs in the gene which codes for the antigen, then the shape of the antigen will change.
What impact does antigen variability have on disease prevention?
Any previous immunity to this pathogen (either naturally through prior infection or artificially through vaccination) is no longer effective, as all the memory cells in the blood will have a memory of the old antigen shape.
Which blood cells are responsible for the non-specific and specific responses?
Non-specific - phagocytes
Specific - lymphocytes
describe phagocytosis:
Phagocytes are in the blood and tissues and any chemicals or debris released by pathogens or abnormal cells attract the phagocytes and they will move towards these cells.
There are many receptor binding points on the surface of phagocytes. They will attach to chemicals or antigens on the pathogen via these receptors.
The phagocyte changes shape to move around and engulf the pathogen. Once engulfed, the pathogen is contained within a phagosome vesicle.
A lysosome within the phagocyte will fuse with the phagosome and release its contents.
The lysozyme enzyme is released into the phagosome. This is a lytic enzyme which hydrolyses the pathogen.
This destroys the pathogen.
The soluble products are absorbed and used by the phagocyte
Describe T cells
Lymphocytes are white blood cells involved in the specific immune response. All lymphocytes are made in the bone marrow but T cells mature in the thymus.
The cell-mediated response is the response involving T cells and body cells
Antigen-Presenting Cells (APC) are any cell that presents a non-self antigen on their surface. Name four examples.
Infected body cells presenting viral antigens on their surface
A macrophage which has engulfed and destroyed a pathogen presenting the antigens on their surface
Cells of a transplanted organ will have different shaped antigens on their surface compared to your self-cell antigens
Cancer cells will have abnormal-shaped self-cell antigens.
Describe the cell-mediated response ( 4 marks)
1.Once a pathogen has been engulfed and destroyed by a phagocyte, the antigens are presented on the cell surface. This is now called an antigen-presenting cell (APC).
2.Helper T cells have receptors on their surface which can attach to the antigens on APC.
3.Once attached, this activates the helper T cells to divide by mitosis to replicate and make large numbers of clones.
4.Cloned helper T cells differentiate into different cells.
What do helper T cells stimulate?
- Activate B lymphocytes
- Phagocytosis
- Cytotoxic T cells
describe and explain the role of cytotoxic cells
Cytotoxic T cells destroy abnormal or infected cells. They release a protein, perforin, which embeds in the cell surface membrane and makes a pore (a hole) so that any substances can enter or leave the cell and this causes cell death.
This is most common in viral infections because viruses infect body cells. Body cells are sacrificed to prevent viral replication.
Define what an antibody is:
Quaternary structure proteins are made up of four polypeptide chains. Each different antibody has a different shaped binding site, which is the variable region. The shape of the antigen-binding site is unique to the shape of a particular antigen.
Draw and label an antibody:
Describe agglutination and explain its importance (2
marks):
Antibodies are flexible and can bind to multiple antigens to clump them together. This is agglutination. This makes it easier for phagocytes to locate and destroy the pathogens.
Describe what happens when antigens in the blood collide
with a complementary antibody on a B cell:
Antigens in the blood collide with their complementary antibody on a B cell. The B cell takes in the antigen by endocytosis and then presents it on its cell surface membrane.
Describe the process of clonal selection (3
marks):
When a B cell collides with a helper T cell receptor, this activates the B cell to go through clonal expansion and differentiation (clonal selection).
B cells undergo mitosis to make large numbers of cells, which differentiate into plasma cells or memory B cells.
Plasma cells make antibodies whereas B memory cells can divide rapidly into plasma cells when re-infected with the same pathogen to make large numbers of antibodies rapidly.
Memory B cells can live for decades in your body, whereas plasma cells are short-lived. Describe what happens when a memory B cell binds with
an antigen it has previously encountered.
Memory B cells do not make antibodies, rather they will divide by mitosis and make plasma cells rapidly if they collide with an antigen they have previously encountered.
This results in large numbers of antibodies being produced so rapidly that the pathogen is destroyed before any symptoms can occur.
This is active immunity.
explain the primary and secondary immune responses.
The primary response occurs the first time you are exposed to a pathogen. You produce fewer antibodies and at a slower pace, as there are no memory B cells for that shape antigen.
If you are exposed to the same antigen again, the secondary response, then you produce large numbers of antibodies very rapidly.
This is because if the antigen collides with the memory B cells it will trigger clonal expansion and rapid production of plasma cells to make that antibody.
Contrast passive and active immunity (3 marks)
1.Passive immunity is when antibodies are introduced into the body whereas active is when antigens are introduced
- Passive immunity does not provide long-term immunity whereas active does.
3.Active immunity results in you making your own antibodies, whereas passive does not.
Define:
Natural active immunity
Following infection and the creation of the body’s own antibodies and memory cells
Define: Artificial active immunity
Following the introduction of a weakened version of the pathogen or antigens via a vaccine.
explain how a vaccine works.
Small amounts of weakened or dead pathogens or antigens are introduced orally or by injection.
Exposure to the antigens activates the B cells to go through clonal expansion and differentiation (clonal selection).
B cells undergo mitosis to make large numbers of cells, which differentiate into memory cells or plasma cells.
Plasma cells make antibodies
B memory cells divide rapidly into plasma cells when re- infected with the same pathogen to make large numbers of antibodies rapidly.
