3.6 Flashcards
What is the Third Line of Defence
The third line of defence is a specific immune response which is brought about by
lymphocytes, a type of white blood cell which
comes from stem cells in the bone marrow.
How do lymphocytes work
• All lymphocytes have a single type
of membrane receptor on their
surface.
• Each lymphocyte has several
copies of one type of receptor.
These receptors are specific to an
antigen. Therefore, each
lymphocyte is only able to
become attached to one type of
antigen.
• The body possesses a huge
number of different lymphocytes.
What are antigens
A surface marker on any foreign molecule is
called an antigen. Antigens trigger an immune response
What are the 2 types of lymphocytes
T-lymphocytes and B-lymphocytes
What are B-lymphocytes
B Lymphocytes produce molecules
called antibodies.
Antibodies become bound to
antigens, inactivating the pathogen.
The resulting antigen-antibody
complex can then be destroyed by phagocytosis.
• B lymphocytes can sometimes
respond to antigens on
substances that are harmless to the body, e.g. pollen. This is called an allergic reaction.
What are T-lymphocytes
T lymphocytes are able to tell the
difference between self-antigens on
the body’s own cells and non-self-
antigens on pathogens or infected cells.
• If a T lymphocyte comes across a
pathogen with a non-self antigen, it
can cause the pathogen to die by a
process called apoptosis which is programmed cell death.
How do T Lymphocytes cause Apoptosis
T lymphocytes attach on to
antigens of infected
cells/pathogen and release
proteins. These proteins diffuse
into the infected cells causing
production of self-destructive
enzymes which cause cell death.
The remains of the cell are then
removed by phagocytosis.
What’s Autoimmunity
A failure in a regulation of the immune system
means that sometimes, T-Lymphocytes will
launch an attack on the body’s own cells.
• This is called autoimmunity and is the cause
of autoimmune diseases such as rheumatoid
arthritis and type 1 diabetes.
Primary and secondary response
Some of the cloned B and T lymphocytes
produced during an infection survive long-term
as memory cells.
• When a secondary exposure to the same antigen
occurs, these memory cells rapidly give rise to a
new clone of specific lymphocytes. These destroy
the invading pathogens before the individuals show symptoms
During the secondary response, antibody
production is greater and more rapid than during the primary response
the primary respon
Secondary response
Direct Attack on the Immune System
Some types of very successful pathogens have
often found a way of mounting a direct attack on
the immune system
• The human immunodeficiency virus (HIV) attacks
and destroys T lymphocytes. HIV causes
depletion of T lymphocytes which leads to the
development of AIDS (acquired immune
deficiency syndrome).
• Individuals with AIDS have a weakened immune
system and so are more vulnerable to
opportunistic infections.
