Cell recognition and the immune system Flashcards
Non-specific response meaning + examples
The response is immediate and the same for all pathogens
eg physical barrier or phagocytosis
Specific response meaning + examples
The response is slower and specific to each pathogen
eg cell-mediated response (T cell) or humoral response (B cell)
Antigen WHAT IS IT ???????
Molecules of which that, when recognised as non-self/foreign by the immune system, can stimulate an immune response and lead to the production of antibodies.
Often proteins on the surface of cells. Proteins have a specific tertiary structure/shape, allowing different proteins to act as specific antigens.
What do antigens allow the immune system to identify, since they are specific?
Pathogens eg viruses, fungi and bacteria
Cells from other organisms of the same species eg organ transplants or blood transfusions
Abnormal body cells eg cancerous cells/tumours
Toxins released from bacteria
Lymphocytes what are they and stuff
White blood cells that fight infection
If they have antigens (on their cell surface membrane) that are complementary to the body’s own (self) cells, they are suppressed or die
Where are lymphocytes produced in an adult?
In an adult, lymphocytes are produced in the bone marrow.
Any lymphocytes that show an immune response to self antigens undergo a programmed death (apoptosis) before they can differentiate into mature lymphocytes.
Where are lymphocytes produced in a foetus?
Due to the protection of the placenta, infection is rare. Therefore, lymphocytes will only come into contact with self-cells.
Some of the lymphocytes will have receptors that match exactly those of the self cells. These will die or be suppressed.
Phagocyte what is it and examples
A white blood cell that can carry out phagocytosis
eg the macrophage and the neutrophil
Process of phagocytosis (non-specific immune response)
Phagocyte is attracted to pathogen due to the chemical products it produces
Phagocyte eg macrophage recognises foreign antigens on the pathogen and binds to the antigen.
Phagocyte engulfs pathogen by surrounding it with its cell surface membrane/cytoplasm
Pathogen contained in a vesicle called a phagosome in the cytoplasm of the phagocyte.
Lysosome fuses with the phagosome and releases lysozymes (hydrolytic enzymes) into the phagosome
These hydrolyse/digest the pathogen. Digestible materials are absorbed into the cytoplasm of the phagocyte, indigestible materials are excreted.
Phagocyte becomes antigen-presenting (displays foreign antigens on their surface) and stimulates specific immune response.
T-lymphocytes where do they mature and what are they associated with
T-lymphocytes mature in the thymus gland
They are associated with cell-mediated immunity; immunity involving body cells
T-lymphocytes what do they respond to
T-lymphocytes only respond to antigens that are presented on a body cell (rather than to antigens within the body fluids)
This is called cell-mediated immunity
Receptors on each T-cell respond to a single antigen
The cellular response (T-lymphocytes and foreign antigens eg infected cells, cells of the same species)
T-lymphocyte recognises antigen-presenting cells after phagocytosis (foreign antigens)
Specific T-helper cell with receptor complimentary to specific antigen binds to it, triggers activation and dividing rapidly by mitosis to form T-cell clones
T-cell clones what do they do
Stimulates B-cells for the humoral response
Stimulates cytotoxic T-cells to kill infected cells by producing perforin
Stimulates phagocytes to engulf pathogens by phagocytosis
Develops into memory cells that enable a rapid response to future infections by the same pathogen.
The action of T-cells is most effective against viruses because they replicate inside cells
Cytotoxin T-cells
Cytotoxin T-cells kill abnormal cells by producing a protein called perforin in the cell surface membrane
Cell membrane becomes freely permeable to all substances and the cell dies as a result
The humoral response (the response of B lymphocytes to a foreign antigen e.g. in blood/tissues)
Clonal selection:
- Specific B cell binds to antigen presenting cell and is stimulated by helper T cells
- Divides rapidly by mitosis to form clones (clonal expansion)
Some become B plasma cells for the primary immune response – secrete large amounts of monoclonal antibody into blood
Some become B memory cells for the secondary immune response
Antigen variability is often an explanation for why…
New vaccines against a disease need to be developed more frequently e.g. influenza
Vaccines against a disease may be hard to develop or can’t be developed in the first place e.g. HIV
May experience a disease more than once e.g. common cold