Transcript Document 638631

Unit 4 - Immunology and Public Health
CfE Higher Human Biology
22. Specific Cellular Defences
Learning Intentions
I can describe clonal selection theory.
I can state that lymphocytes have a single type of membrane receptor specific for one antigen.
Antigen binding leads to repeated lymphocyte division resulting in a clonal population of lymphocytes
I can describe the structure of T- and B-lymphocytes
I can state that Lymphocytes respond specifically to antigens on foreign cells, cells infected by
pathogens and toxins released by pathogens.
I can state that T-lymphocytes have specific surface proteins that allow them to distinguish between
the surface molecules of the body’s own cells and cells with foreign molecules on their surface.
I can state that immune system regulation failure leads to T-lymphocyte immune response to selfantigens (auto immune disease).
I can state that allergy is a hypersensitive B- lymphocyte response to an antigen that is normally
harmless.
I can state that one group of T-lymphocytes destroy infected cells by inducing apoptosis. Another
group of T-lymphocytes secrete cytokines that activate B lymphocytes and phagocytes. When
pathogens infect tissue, some phagocytes capture the pathogen and display fragments of its antigens
on their surface. These antigen presenting cells activate the production of a clone of T-lymphocytes
that move to the site of infection under the direction of cytokines.
I can state that each B-lymphocyte clone produces a specific antibody molecule that will recognise a
specific antigen surface molecule on a pathogen or a toxin. Antigen-antibody complexes may inactivate
a pathogen or toxin or render it more susceptible to phagocytosis. In other cases the antigenantibody complex stimulates a response which results in cell lysis. B-lymphocytes activated by antigen
presenting cells and T-lymphocytes produce a clone of B-lymphocytes that secrete antibodies into the
lymph and blood where they make their way to the infected area.
I can describe immunological memory.
I can state that some T- and B-lymphocytes produced in response to antigens by clonal selection
survive long-term as memory cells. A secondary exposure to the same antigen rapidly gives rise to a
new clone of lymphocytes producing a rapid and greater immunological response
Immune surveillance the Third
Line of Defence
There are a wide range of different immune cells (white
blood cells) which are constantly patrolling the body,
looking for signs of infection or damage.
They can summon other immune cells by releasing cytokines
and they may also carry out a response themselves. this
results in large numbers of phagocytes(non-specific) and
T cells(specific) collecting at the damaged/infected site.
White blood cells can also squeeze through the capillary
wall to get access to surrounding tissues.
Specific Immune Response of
Lymphocytes
Lymphocytes are made
in the bone marrow
from stem cells.
Some leave and mature
in the thymus gland;
T-lymphocytes (T
cells) and others
remain and mature in
the bone marrow, Blymphocytes (B
cells)
Clonal selection theory
Each lymphocyte produces only one type of antigen
receptor.
However, due to the huge number present, they are
able to cover every possible antigen.
Very quickly after being made, any lymphocytes with
antigen receptors for self-antigens are destroyed.
The remainder patrol the body until they are
activated by binding to a non-self antigen, causing
them to clone themselves many times making a
large clonal population.
A non-self antigen could include viruses, bacteria,
bacterial toxins, cancer cells and molecules on the
surface of transplanted cells.
Clonal
Selection
Theory
Confusing self and non-self
Antigens are protein molecules (in plasma membrane) present on
the surface of all cells. As we saw previously, our immune system
should be able to read the surface antigens of a cell and tell if it is
self or non-self.
However, sometimes it can fail to recognise our own cells and attack
them – autoimmunity e.g.
• Rheumatoid arthritis - the immune system attacks and erodes the
cartilage at a joint-the cartilage is replaced by fibrous tissue which
joins the two bones together making the joint immovable
• Multiple Sclerosis - the immune system attacks the myelin sheath
around the nerve cells so that they can no longer transmit nerve
impulses efficiently and the person suffers major disabilities.
• Type 1 diabetes
• Any lymphocyte ( during maturation of B cells and T cells) with an
antigen receptor that would fit a body cell surface protein is
weeded out and destroyed by apoptosis.
Our immune system can also over react to harmless substances to give
allergies.
ABO blood group system
•
Four types of blood group exist in humans and they are A,B, AB and O.
•
The surface antigens on the red blood cells (RBCs)of an individual
determine their blood group.
•
There are 2 antigens, A and B.
•
When Individuals possess one antigen they are either group A (has A
antigens) or B (has B antigens); with both antigens they are group AB;
and with neither they are group O.
•
The antibodies in the blood plasma of an individual are determined by
their blood group and are the ones opposite to their blood group.
•
Individuals with group A have anti-B antibodies; those with group B
have anti-A antibodies; those with group AB have neither anti-A nor
anti-B; and those with group O have both anti-A and anti-B antibodies.
Blood Groups
•
Knowledge of an individuals blood group is essential for blood
transfusions. Antibodies in the plasma of the recipient would attack
foreign antigens of an unsuitable donor.
•
If a person with group A blood (with A antigens on the surface of blood
cells) were to be given a transfusion of group B blood (with B antigens)
then anti-B antibodies( from group A person) would combine with the B
antigens on the surface of the donated red blood cells and this would
result in clumping (agglutination) of the blood which gets all lumpy. This
can block small blood vessels and lead to major problems, maybe even
death.
•
Certain combinations of blood groups are compatible. For example a
person with blood group B can receive blood of type O without risk of
agglutination because group B blood has anti A antibodies and O has no
antigens on the surface
Blood group B person can also receive blood from group B.
•
ABO Blood Group System
• If a person of group A was given a transfusion of
group B then anti B antibodies (from group A person)
would combine with he B antigens on the donated
blood and clumping would result.
• People with blood group O can donate blood to people
with blood groups A, B, AB and O i.e. O is the
universal donator (O has neither antigen A nor
antigen B present and clumping will not happen).
• People with group AB can receive blood from A, B, AB
and O because neither anti A nor anti B antibodies
are present
• It is the incompatibility between the donor’s cells
and the recipients plasma which results in
agglutination.
ABO blood group system
Agglutination of red blood
cells
Rhesus D-antigen
• Humans have the ABO system of antigens on
their red blood cells.
• most people have a further antigen on the
surface of their red blood cells called antigen
D and those who possess it are said to be
Rhesus positive (Rh+).
• Those who lack antigen D and who react to its
presence by forming anti-D antibodies are
said to be Rhesus negative (Rh-).
• Transfusion of Rh+ red blood cells to a Rhperson must be avoided because the
recipient’s immune system would respond and
produce anti- D antibodies which would
remain leaving the person sensitised.
• Any subsequent transfusion of Rh+ red blood
cells would be liable to cause the sensitised
Rh- person to suffer severe agglutination
which could be fatal.
• Antigen D is genetically determined by a
dominant allele (D); lack of antigen D by a
recessive allele (d).
• So Rh+ individuals have genotype DD or Dd;
Rh- individuals have genotype dd
• If a Rh- woman (dd) marries a Rh+ man (DD) each child
will be Rh+ (Dd).
• If a Rh- woman (dd) marries a Rh+ man (Dd) there is a
50% chance that each of their children will be Rh+ (Dd).
Inheritance of Rhesus D antigen
Woman x
dd
Rh-
man
DD
Rh+
all Dd (Rh+)
woman x man
dd
Dd
RhRh+
Dd and dd
Rh+ and Rh-
• If a Rh- mother has a Rh+ foetus (with antigen D) then
the baby has antigen D on its blood cells which are foreign
to the mothers immune system.
• Mothers and baby’s blood are not in direct contact and
the immune system is unaware of this in the first
pregnancy and nothing happens.
• During birth a small amount of foetal blood can mix with
the mothers blood and the mothers immune system
responds by producing anti-D antibodies (sensitised) and in
subsequent pregnancies if the foetus is Rh+ antibodies
against antigen D cross the placenta and attack and destroy
foetal red blood cells (haemolytic disease of the new
born).
• It can be treated by giving the baby blood transfusions and
it can be prevented by injecting the mother with anti-D
immunoglobulins soon after the birth of each Rh+ babythese antibodies destroy any antigens from the foetus
before the mothers immune system can respond to them.
Auto immunity
When the immune system no
longer tolerates it’s own
antigens, the T-lymphocytes
attack the cells.
In rheumatoid arthritis,
cytokines cause
inflammation which will
attack the bone and
cartilage in joints, causing
them to be replaced with
fibrous tissue which leaves
the joint less mobile than
before.
Allergy
An allergy is an exaggerated response by the body to environmental
antigens that normally would be considered to be harmless.
B-lymphocytes sometimes over-react to harmless substances like dust,
pollen and feathers etc. or even medicines such as penicillin.
The B-lymphocytes release antibodies which cause mast cells to release
histamine. Histamine produces the symptoms typical of hay fever like a
blocked, runny nose to try and get rid of the foreign body. Symptoms
are reduced by taking antihistamine drugs.
Some allergies are so severe that they can trigger anaphylactic shock
where the histamine causes such a huge drop in blood pressure it can be
life threatening.
Questions
1) What are the two types of lymphocytes?
2) Where do T lymphocytes mature?
3) Why are cytokines released at the site of
infection?
4) What is the name of the proteins found on
cell surfaces that illicit an immune response?
5) Describe clonal selection.
6) a) What is autoimmunity?
b) Give a condition linked to autoimmunity.
Answers Q1-6
1)
2)
3)
4)
5)
•
•
•
6)
What are the two types of lymphocytes?
– B and T lymphocytes
Where do T lymphocytes mature?
– Thymus gland
Why are cytokines released at the site of infection?
- to summon other immune cells to the site of the infection
What is the name of the proteins found on cell surfaces that illicit an immune
response?
- Antigen
Describe clonal selection. –
Immature lymphocytes with ‘self’ markers destroyed
Remaining lymphocytes patrol body until activated by binding ‘non-self’ antigen
Activated lymphocytes copied ( cloned) and mount attack
a) What is autoimmunity?
- The immune system recognises ‘self’ as ‘non- self’ and attacks tissues
b) Give a condition linked to autoimmunity.
– MS, Rheumatoid arthritis , type 1 diabetes
Rheumatoid Arthritis
1. What is rheumatoid arthritis? Describe in
detail.
2. Who is more likely to suffer from this
condition and in which age group does onset
most frequently occur.
3. Which chemical messengers are thought to
play a key role in the progression of this
condition?
4. Explain this .
5. What treatment is available?
6. Draw a diagram from page 318 to illustrate
the effect of this condition on a joint-colour.
Hay fever.
1. Which particle causes hay fever?
2. Why does this reaction take place?
3. Describe the process involved to result
in hay fever-draw out figure 22.9 to
answer this question.
4. What are the symptoms?
5. What is the treatment?
Allergic Asthma.
1. What is anaphylactic shock?
2. Give an example of something that may
cause this.
3. Name the cells that release large
amounts of histamine.
4. What effect does histamine have?
5. What should people do who are
hypersensitive to these allergens?
6. Give another name for epinephrine.
Allergic Asthma.
1. What is asthma?
2. What are its effects? Draw figure
22.11 to help explain your answer.
3. Give examples of things that can cause
an attack of this kind.
4. Who are more likely to be affected in
the UK?
5. What can sufferers do to try to
control their condition?
6. Do you know any asthmatics?