Chapter 5: Cell Recognition And Immune Response Flashcards
How can the body determine self and non-self cells?
Each cell has specific molecules on its surface which are of most types. They are mostly proteins with enormous variety and highly specific tertiary structure.
What are types of non self cells?
- pathogens
- cells from other organisms of the same species
- toxins produced by certain pathogens
- abnormal body cells
How could the immune system be destructive?
Cells in humans given by tissue or organ transplants could be killed
To minimise the effect, transplants are usually given by close relatives to minimise rejection
What do phagocytes do?
Phagocytes ingest and destroy pathogens by phagocytosis
How do phagocytes carry out the process of phagocytosis?
- The phagocyte is attracted to the pathogen by chemical products of the pathogen along a concentration gradient
- The phagocyte has several receptors on its cell surface membrane that attach to chemicals on the surface of the pathogen
- Lysosomes within the phagocyte migrate towards the phagosome formed by engulfing the bacterium
- The lysosomes release their lysozymes into the phagosome, where they hydrolyse the bacterium.
- The hydrolysis products of the bacterium are absorbed by the phagocyte
What is an antigen?
An antigen is any part of an organism or substance that is recognised as non self - proteins that are part of the cell membrane.
What are B lymphocytes?
They are made in the bone marrow. It is associated with humoral immunity involving antibodies that are present in body fluids.
What are T lymphocytes?
They are made in the thymus gland. They are associated with cell mediated immunity involving body cells.
What are cells that display foreign antigens on their surface called?
Antigen presenting cells
How do T lymphocytes respond to an infection by a pathogen?
- Phagocytes engulf pathogen and then present its antigens on its surface
- Receptors on the T helper cells are specific and fit exactly on to these antigens
- This activates the T cell to divide rapidly by mitosis to form clones with the same receptors
- The cloned cells turn into:
- memory cells for rapid response
- stimulate phagocytes to engulf pathogens
- stimulate B cells to divide and secrete their antibodies
- activate cytotoxic T cells
What is Immunity?
The body’s defences seem to be better prepared for a second infection of the same pathogen and can kill it before it causes harm
How do cytotoxic T cells kill infected cells?
They produce a protein called perforin which makes holes in the cell surface membrane of the pathogen. This makes the walls freely permeable to substances (allowing water in and bursting the cell)
Why are T cells most effective against viruses?
Viruses use body cells to replicate so by killing the body cells, the T cells prevent viruses from multiplying and infecting more cells
What is the humoral response?
It involves antibodies which are soluble in blood and tissue fluid in the body
What do B cells produce?
B cells produce antibodies and memory cells
The antibodies are specific to the antigen of the pathogen - they are complementary
How do B cells work?
- The antigen enters the B cell by endocytosis and get presented on the surface
- The T helper cells bind to the processed antigens and stimulate the B cell so it can replicate by mitosis to form clones (clonal selection)
- The cloned plasma cells secrete specific antibodies to destroy them
If a toxin is also released by a pathogen then B cells produce clones of another antibodies
What are plasma cells and what type of response do they provide?
They secrete antibodies into the blood which destroy the antigens. They only survive a few days
They are part of the primary immune response
What are memory cells and what response do they provide?
They circulate the body and its fluids so when the same antigen occurs again, they will divide rapidly and develop into plasma cells and more memory cells. They provide long term immunity and are part of the secondary immune response.
What is the secondary response?
The antibodies are produced at a faster rate
The antibodies stay in the blood for a longer time
More antibodies are produced
Therefore they pathogen may be killed without any symptoms being felt
What are antibodies made of and what are their structures?
Antibodies are made of polypeptide chains- two heavy and light chains. Each antibody has a specific binding site that fits the specific antigen to form an antigen-antibody complex. The binding site is different on different antibodies so it is called the variable region. The rest of the structure is called the constant region.
Binding site is specific due to specific 3D structure
What is agglutination?
Antibodies clump bacterial cells together so the phagocytes can locate and ingest them easily.
What are the two ways antibodies work?
- agglutination
- markers
How are antibodies markers?
They serve as markers that stimulate phagocytes to engulf bacterial cells to which they are attached
What are monoclonal antibodies?
An antibody specific to an antigen that has been isolated and cloned
What is direct monoclonal antibody therapy?
Antibodies specific to antigens on cancer cells are given to patient. They attach to the surface of their cancer cells and block chemical signals to inhibit uncontrolled growth
