Cell Recognition and the Immune System
Get a hint
The human body's two types of defences to protect itself from pathogens - ANSWER: -
Non-specific
> General and immediate defences
- Specific
> Less rapid but longer-lasting
Non-specific - ANSWER: - Skin forming a barrier to prevents pathogens from entering
- Phagocytosis - to kill any pathogens
Specific - ANSWER: Involves lymphocytes (a type of white blood cell) and takes two
forms:
1) Cell-mediated responses involving T-lymphocytes
2) Humoral responses involving B-lymphocytes
How are all lymphocytes able to distinguish between the body's own cells and
molecules (self) and those that are foreign (non-self)? - ANSWER: 1. All types of cells,
self or non-self, have specific molecules on its surface that identify it
2. There is a variety of types of these molecules, but it is the proteins (glycoproteins)
that are the most important:
- Proteins have a huge variety and a highly specific tertiary structure
- It is this variety that distinguishes once cell from another
What do protein molecules on lymphocyte surfaces allow the immune system to
identify? - ANSWER: o Pathogens (e.g. HIV)
o Non-self material (e.g. cells form other organisms of the same species)
o Toxins (e.g. those produced by certain pathogens, like the bacterium that causes
cholera)
o Abnormal body cells (e.g. Cancer cells)
What is the first stage to removing the threat foreign cells pose? - ANSWER: Identifying
them
How can the immune response be an issue for organ transplantation and what is done
to overcome this issue? - ANSWER: - The immune system will recognise tissue or
organ transplants as non-self and therefore tries to destroy the transplant
- To minimise tissue rejection, donor tissues for transplants are normally matched as
closely as possible to those of the recipient
- Best matches are often from relatives
, - In addition, immunosuppressant drugs are often administered to reduce the level of
the immune response
We lymphocytes produced in response to an infection? - ANSWER: No - they already
exist
Why is there a high probability that when a pathogen enters the body a lymphocyte will
'recognise' the pathogen? - ANSWER: Given there are ten million different types of
lymphocyte, one of these lymphocytes will have a protein on its surface that is
complementary to one of the proteins of the pathogen
What explains the lag time between the body's exposure to a pathogen and the body's
defences bringing it under control? - ANSWER: Clonal selection
Clonal selection - ANSWER: 1. As there are so many different types of lymphocytes,
there are very few of each type
2. When an infection occurs, the one type already present that has the complementary
proteins to that of the pathogen is stimulated to divide to build up its numbers to a level
where it can be effectively destroyed
How do lymphocytes recognised own body cells? - ANSWER: 1. In the foetus, the
lymphocytes are constantly colliding with other cells
2. Infections in the foetus are rare as it is protected from the outside world by the mother
and the placenta
3. So therefore, lymphocytes collide almost exclusively with the body's own material
(self)
4. Some of the body's lymphocytes will have receptors that exactly fit those of the
body's own cells
5. These lymphocytes either die or are suppressed
6. The only remaining lymphocytes are those that might fit foreign material (non-self),
and therefore only respond to foreign material
In adults where are lymphocytes produced? - ANSWER: In the bone marrow
What happens to any lymphocytes that show an immune response to self-antigens? -
ANSWER: They undergo apoptosis (programmed cell death) before they differentiate
into mature lymphocytes
> No clones of these anti-self lymphocytes will appear in the blood, leaving only those
that might respond to non-self antigens
If a pathogen is to infect the body what must it first do? - ANSWER: Gain entry
What is the body's first line of defence against pathogens? - ANSWER: Creating a
physical or chemical barrier
Get a hint
The human body's two types of defences to protect itself from pathogens - ANSWER: -
Non-specific
> General and immediate defences
- Specific
> Less rapid but longer-lasting
Non-specific - ANSWER: - Skin forming a barrier to prevents pathogens from entering
- Phagocytosis - to kill any pathogens
Specific - ANSWER: Involves lymphocytes (a type of white blood cell) and takes two
forms:
1) Cell-mediated responses involving T-lymphocytes
2) Humoral responses involving B-lymphocytes
How are all lymphocytes able to distinguish between the body's own cells and
molecules (self) and those that are foreign (non-self)? - ANSWER: 1. All types of cells,
self or non-self, have specific molecules on its surface that identify it
2. There is a variety of types of these molecules, but it is the proteins (glycoproteins)
that are the most important:
- Proteins have a huge variety and a highly specific tertiary structure
- It is this variety that distinguishes once cell from another
What do protein molecules on lymphocyte surfaces allow the immune system to
identify? - ANSWER: o Pathogens (e.g. HIV)
o Non-self material (e.g. cells form other organisms of the same species)
o Toxins (e.g. those produced by certain pathogens, like the bacterium that causes
cholera)
o Abnormal body cells (e.g. Cancer cells)
What is the first stage to removing the threat foreign cells pose? - ANSWER: Identifying
them
How can the immune response be an issue for organ transplantation and what is done
to overcome this issue? - ANSWER: - The immune system will recognise tissue or
organ transplants as non-self and therefore tries to destroy the transplant
- To minimise tissue rejection, donor tissues for transplants are normally matched as
closely as possible to those of the recipient
- Best matches are often from relatives
, - In addition, immunosuppressant drugs are often administered to reduce the level of
the immune response
We lymphocytes produced in response to an infection? - ANSWER: No - they already
exist
Why is there a high probability that when a pathogen enters the body a lymphocyte will
'recognise' the pathogen? - ANSWER: Given there are ten million different types of
lymphocyte, one of these lymphocytes will have a protein on its surface that is
complementary to one of the proteins of the pathogen
What explains the lag time between the body's exposure to a pathogen and the body's
defences bringing it under control? - ANSWER: Clonal selection
Clonal selection - ANSWER: 1. As there are so many different types of lymphocytes,
there are very few of each type
2. When an infection occurs, the one type already present that has the complementary
proteins to that of the pathogen is stimulated to divide to build up its numbers to a level
where it can be effectively destroyed
How do lymphocytes recognised own body cells? - ANSWER: 1. In the foetus, the
lymphocytes are constantly colliding with other cells
2. Infections in the foetus are rare as it is protected from the outside world by the mother
and the placenta
3. So therefore, lymphocytes collide almost exclusively with the body's own material
(self)
4. Some of the body's lymphocytes will have receptors that exactly fit those of the
body's own cells
5. These lymphocytes either die or are suppressed
6. The only remaining lymphocytes are those that might fit foreign material (non-self),
and therefore only respond to foreign material
In adults where are lymphocytes produced? - ANSWER: In the bone marrow
What happens to any lymphocytes that show an immune response to self-antigens? -
ANSWER: They undergo apoptosis (programmed cell death) before they differentiate
into mature lymphocytes
> No clones of these anti-self lymphocytes will appear in the blood, leaving only those
that might respond to non-self antigens
If a pathogen is to infect the body what must it first do? - ANSWER: Gain entry
What is the body's first line of defence against pathogens? - ANSWER: Creating a
physical or chemical barrier
