Cell recognition and immunity Flashcards
What is an antigen
- Foreign molecule
- That stimulates an immune response leading to the production of an antibody
They are also soluble and are transported in bodily fluids
How are cells identified by the immune system
- Each type of cell has specfic molecules on its surface that identify it
- Often proteins have a specofic tertotary structure or glycoproteins or glycolipids
What is an example of a specifc and non specific response white blood cells?
Specific: Lymphocytes
Non Specific: Phagocytes
What does it mean by non specific response
Phagocytes will respond exactly the same no matter what the non self cell is being detcted
What types of cells and molecules can the immune system identify (4)
- Pathogens (diesease causing miceoorganisms) e.g. viruses bacteri aand fungi
- Cells from other organisms of the same species e.g. organ transplant (non self cells)
- Abnormal body cells e.g. cancer cells
- Toxins released by some bacteria
Describe phagocytosis of pathogens(5)
- Phagocyte attracted by chemicals/recognises foregin antigens on pathogen
- Phagocyte engulfs pathogen by surrounding it with its cell membrane
- Pathogen contained in vesicle called a phagosome in cytoplasm of Phagocyte
- Lysosome fuses with Phagosome and releases lysozomes
- Lysozomes hydrolyse pathogen
What does it mean by specific immune response
A response to an exact antigen on the surface of cells
They are slower in action
Provide long term immunity
Where are lymphocytes, Tcells and B cells made
- Lymphocytes are made in the bone marrow
- B cells are also made in the bone marrow and are matured there (B cells are associated with the humoral response)
- T cells are made in the thymus (T cells are associated with the Cell meidated response)
They are called T and B cells because of where they are made
What are Antigen Presenting Cells (APC) and give 4 examples of them
APCs are cells that present a non self antigen on thier surface
* Infected body cells- They present the viral antigens on thier surface
* Phagocytes- A phagocyte ,that has engulfed and destroyed a pathogen, will present the antigens on thier surface
* Transplanted cells- Have different shaped antigens on their surface compared to your self cells
* Cancer cells- Have abnormal shaped self cells
What is the cell mediated response
Just a basic definition
When the T cells involved only respond to antigens which are presented on cells and not antigens in fluids such as blood (humoral response)
Describe the response of T lymphocytes to a foreign antigen (Cell mediated response) (6)
- T lymphocytes recognise antigen presenting cells
- Specific helper T cells with complementary receptors (on cell surface) bind to an antigen on antigen presenting cell
- They activate and divide by mitosis to form clones which stimulate:
-Cytotoxic T cells–> destroy infected cells/tumour cells
-Specific B cells(humoral response)
-Phagocytes-Engluf pathogens by pahgocytosis
What do cytotoxic T cells do
- Destroy abnormal/infected cells
- They release a protein called perforin-Embeds in the cell surface membrane and makes a pore so that substances can enter and exit the cell—> leads to cell death
Where are cytotoxic T cells most commonly used in and what do they do to body cells
- Viral infections because viruses infect body cells
- They also sacrifce body cells to prevent viral replication
What type of cells are involved in the humoral response
B cells and Antibodies
How do B cells activate clonal selection
- B cells take in an antigen by endocytosis and then presents it on its cell surface membrane
- When the B cell collides with a helper T cell receptor, this actiavtes the B cell to go through clonal selection
What cells can B cells differentiate into and what do they do?
*Plasma cells-Make antibodies
*Memory B cell-Can rapidly divide into plasma cells upon secondary exposures to an infection to make large numbers of antibodies rapidly
What is the life span of Memory B cells and Plasma cells
Memory B cells- Can live for decades
Plasma cells- Short lived
How do memory B cells prevent symptoms from occuring when re-infected with a pathogen
- Memory B cells rapidly divide by mitosis forming plasma cells
- Large numbers of antibodies produced rapidly which destroys the pathogen
Describe the response of B lymphocytes to a foreign antigen (the humoral response) (6)
- Clonal selection
-Specific B lymphocyte with complemntary receptor (antobody on cell surface) binds to antigen
-So this is then stimulated by helper T cells (which releases cytokines)
-So divides (rapidly) by mitosis to form clones - Some differentiate into B plasma cells–> Secrete large amounts of (monoclonal) antibody
- Some differnetiate into B memory cells–> Remain in blood for secondary immune response
How do lymphocytes recognise cells belonging to the body
Lymphocytes in the fetus are constantly colliding with other cells
The ones with receptors that exactly fit the body’s own cells will either die or be suppressed
The only remaining lymphocytes are those that might fit foreign material(non self) and therefore only respond to foreign material
In adults, lymphocytes produced in the bone marrow initially only encounter self antigens
Any lymphocytes that shown an immune response to these self cells undergo apoptosis (programmed cell death) before they can differentiate into mature lymphocytes
Suggest a possible reason why a after a pathogen gains enter to the body it is often a number of days before the body’s immune system begins to control it
The lymphocytes that will finally control the pathogen need to build up their numbers and this takes time
it takes a number of days because of the amount of division needed
