5.4 B lymphocytes and humoral immunity Flashcards
What is humoral immunity
It involves antibodies, and antibodies are soluble in the blood and tissue fluid of the body
Its called humoral because an old fashioned word for body fluid is humour
How many different types of B cell are there and what do they do
. Possibly as many as 10 million, and each B cell starts to produce a specific antibody that responds to a specific antigen
Describe process of Clonal selection
. When antigen eg a protein on the surface of a pathogen, foreign cell, toxin, damaged or abnormal cell enters the blood or tissue fluid
There will be one B cell that has an antibody on its surface whose shape can exactly fit the antigen, so they are complimentary.
The antibody then attaches to the complimentary antigen , and the antigen enters the B cell by endocytosis and it gets presented on its surface
T helper cells bind to these processed antigens and stimulate the B cell to divide by mitosis to form a clone of identical B cells which all produce the antibody that is specific to the foreign antigen ,
This is called clonal selection and allows for the body to respond rapidly to any of a vast number of antigens
How is a pathogen different in practice compared to in clonal selection
Pathogens may have multiple types of proteins on its surface which all act as antigens
Some pathogens eg bacteria produce toxins which can act as an antigen
so therefore many different B cells make clones, each of which produces its own type of antibody which are referred to as monoclonal antibodies
In the B lymphocyte clones that produce cells, what two types of cell are produced
Plasma cells
Memory cells
What are plasma cells
What immune response are they part of, how long do they last
What do they do
Primary immune response
. Secrete antibodies usually in the blood plasma
. These plasma cells only survive for a few days but can produce 2000 antibodies each second during its brief lifespan
These antibodies lead to the destruction of the antigen
So plasma cells are therefore responsible for the immediate defence of the body against infection.
What are memory b cells, what immune response are they part of
How long do they last
Produced in the primary immune response but memory cells are responsible for the secondary immune response
Provide long term immunity against the original infection
. Memory cells live way longer than plasma cells, often for decades
. These do not produce antibodies directly, but circulate in the blood and tissue fluid
What happens when memory cells encounter the same pathogen again
When they encounter the same pathogen again they divide rapidly and develop into plasma cells and more memory cells.
The plasma cells produce the antibodies needed to destroy the pathogen while the new memory cells circulate in readiness for any future infection. The antibodies can be secreted faster than in the primary immune response so the infection is destroyed before it can cause any harm.
This is why the person is usually unaware they have ever been infected
Steps of B cells in humoral immunity
. The surface antigens of an invading pathogen are taken up by a B cell
. The B cell processes the antigens and presents them on its surface
. Helper T cells (which are activated in T lymphocytes) attach to the processed antigen on B cell which activate the B cell
. The B cell is now activated to divide by mitosis to give a clone of plasma cells
. The cloned plasma cells produce and secrete the specific antibodies that exactly fit onto the antigen on the pathogens surface
. The antibody attaches to the antigen on pathogen and destroy it
. Some B cells develop into memory cells which can respond to future infections by the same pathogen by dividing rapidly and turning into plasma cells that produce antibodies
