Download File

 Our
body’s immune system works to protect
us from foreign agents trying to enter our
bodies.
 Immunity is the body’s capability to repel
foreign substances, pathogens and cancer
cells.
 Our immune system puts up three lines of
defense against invaders.
 Each line of defense is designed to pick up
where the previous line may have failed.
_____________
st
1


Line of Defense
This line of defense is referred to as NONSPECIFIC
IMMUNITY. This means that it will put up a battle to
protect us from any pathogen (invader).
The first line of defense includes:
 Skin - provides a physical barrier preventing
pathogens from entering
Mucous membranes –
line the respiratory,
urinary, reproductive
and gastrointestinal
tracts. Trap invaders
in sticky mucous and
expel it from the body
by the wave-like
motion of the cilia as
well as coughing and
sneezing.
 Tears, mucous and
saliva wash bacteria
away.

nd
2


Line of Defense
If pathogens make it through the first line of defense,
they must combat the second line.
This response is also NONSPECIFIC so it will react to
any invader.

The second line of defense includes:
 The Inflammatory Response – results in
pain, redness, heat and swelling.
 It can be initiated by damage to the body’s
tissues due to physical agents or microbial
infection.
 The functions of the inflammatory response
are to destroy the cause of infection and
remove it from the body.
 If that fails, to contain the infection to a
small area to limit its effects.
 It also helps to replace or repair tissues
that were damaged by the infection.
 Macrophages
– These cells engulf
and destroy foreign material through
phagocytosis.
rd
3
Line of Defense
If the invader makes it past the first
two lines of defense, the immune
system identifies the invader
(pathogen) and prepares a specific
response.
 This response is known as the immune
response and is considered to be
SPECIFIC IMMUNITY. This means that
the response targets specific
pathogens.



Specialized cells of the immune system
produce specific proteins called antibodies to
fight specific antigens.
 B Cells – produce antibodies that bind to a
specific antigen so that it can be removed
from the body.
 This is called an ANTIBODY MEDIATED
RESPONSE.
 The antibody and antigen fit together like
a lock and key. This means that the
antibody produced to fight the antigen,
will bind to that specific antigen only.
 T Cells – do not produce antibodies. They
attack cells directly.
 This is called a CELL MEDIATED RESPONSE.
 When the T cell binds to antigens on the
infected cell, it causes it to burst.
 When
an antigen (a foreign substance in the
body) enters your body for the first time,
your immune system produces antibodies
(proteins that attach themselves to specific
foreign substances) against it.
 This is called the primary response and it
can take a few days to occur. That’s why you
may still get sick.
 If
the same antigen were to enter your body
a second time, the correct antibodies are
produced very quickly and in much larger
amounts.
 This is called the secondary response. It is
usually fast enough to overpower an invader
so the body does not suffer from the same
disease again.
 When
B cells are
activated to
produce antibodies
against an antigen
and T cells are
activated to attack
invaders directly,
they also produce
memory cells.
 Memory B cells and
Memory T cells can
live for a lifetime.
These cells produce
a secondary immune
response if the
same antigen or
invader appears in
the body again.
There are two types of immunity:
a) Active Immunity
 The body produces its own antibodies and T
cells to attack particular antigens.
 This can result from having the disease or
illness before – your body still has the
memory cells to quickly produce antibodies
or T cells…..you have built up an “immunity”
to that particular pathogen.

 This
can also result if you have received a
vaccination for a particular disease. A
vaccination consists of dead or weakened
bacteria or viruses which can still act as an
antigen. Because the cell is weakened or
dead it can no longer cause the disease. The
immune system responds to it by producing
antibodies or T cells. The memory cells will
remain in your body for a long period of time
giving you immunity to that disease.
b) Passive Immunity
 A person is given antibodies from the blood of
either another person or animal. This is also
called “borrowed immunity”.
 It is temporary. It usually does not last for more
than a month because the body destroys the
borrowed antibodies.
 It is very fast acting.
 Eg. Maternal Immunity – antibodies from the
mother enter the baby’s blood before birth and
provide the infant with passive immunity for the
first few months of a child’s life. Antibodies are
also present in the mother’s milk.





Allergies are hypersensitivities to substances such as
pollen, food or animal hair that ordinarily would do
no harm to the body.
Immediate Allergic Response – can occur within
seconds of contact with the antigen. The response is
caused by the release of histamine by cells which
brings about the allergic symptoms.
Anaphylactic shock – an immediate allergic response
that occurs because the allergen has entered the
blood stream. Characterized by a sudden and life
threatening drop in blood pressure.
Delayed Allergic Response – initiated by memory T
cells at the site of allergen contact in the body.