By: Diana Marzulli, Sony Abraham and

By: Diana Marzulli, Sony Abraham and
 The immune system is a complex, highly
developed system.
 The function of this system is to protect the
animal from intruders that could potentially harm
 Animals have two major forms of immunity:
innate immunity and acquired immunity
 Provides a broad defense against infection.
 An animal passes these defenses onto
 It is a non-specific defense: all antigens are
attacked equally.
 Divided into two parts: external defenses
and internal cellular and chemical defenses.
 Skin is the most important of the external
defenses. Normally, bacteria and viruses
cannot penetrate the skin. However, if
there is an opening in the skin (such as a
scratch or a cut) then the pathogens may
enter. That is where the other forms of
external defenses kick in.
 Pathogens are expelled from the lungs
by ciliary action. As the tiny hairs move
in an upward motion, coughing and
•Mucous membranes line the
genitourinary tracts. They stop
the entry of potentially harmful
•Certain cells produce microbes.
mucus: a fluid that traps
microbes and other particles.
•Bodily secretions cause an environment that is
hostel to microbes.
•The body produces lysosomes which destroy
susceptible bacteria as the enter the upper
 The microbes that do manage to break through the
external defenses are then attacked by the internal
 These defenses mainly rely on phagocytosis: the
ingestion of invading microorganisms by certain types
of white blood cells.
 These white blood cells, called phagocytes, attach to
the microbes via surface receptors found on
microorganisms but not normal body cells. The cell
then engulfs the microbes it has attached to and forms
a vacuole that fuses with a lysosome. The lysosome
then destroys the microbe through poisoning or
 Tissue damage by either physical injury or the entry of
pathogens leads to the release of chemical signals that
trigger an inflammatory response.
 Histamine is a chemical secreted during an
inflammatory response that dilates the capillaries,
causing more blood to flow to the area. This increased
blood supply causes the redness, heat, and associated
with inflammation.
 This increased blood flow delivers antimicrobial
proteins and other healing elements to the site.
 The body may also initiate a systemic response in
which a fever or increase in white blood cell count. The
most severe of systemic response is septic shock,
which often causes death.
 The key cells of acquired immunity that
provide specific defenses against infection.
 Activated by the cytokines excreted by the
 Any foreign molecule recognized by the
lymphocytes is known as an antigen. The
lymphocyte recognizes and then binds to
only a small region known as the epitope.
 There are two types of lymphocytes: B
lymphocytes (B Cells) and T lymphocytes (T
Cells). A single B or T cell contains about
100,000 antigen receptors which specific to
 B Cells are produced in the stem
cells of the bone marrow. They
produce antibodies (also known
as immunoglobulin) and oversee
humoral immunity. The recognize
and bind to intact antigens.
 T Cells are also produced in the
bone marrow, but migrate to the
thymus later. Unlike the B cells,
they do not produce antibodies
fragments of antigens bound to
MHC molecules.
 There are two types of T cells:
cytotic T cells and helper T cells.
Cytotic T cells eliminate infected
cells from the body as well as
 The humoral immune response involves both
the activation and clonal selection of B cells.
This results in the production and secretion of
antibodies that travel in the blood and the
 Cell-mediated immune response involves the
activation and clonal selection of T cells to
destroy target cells.
 The immune system has the ability to recognize the
body’s own cells from those of another individual. This
can lead to problems if a transplant is ever needed.
 Blood transfusions need to be done with either a donor
that matches the person’s exact blood type or with
blood that is type O (the universal donor).
 In order for a tissue or organ transplant to take place,
the recipient has to be matched with a donor that has
MHC molecules that closely resemble those of the
recipient. The recipient is also given medication that
suppresses immune responses. This can leave the
recipient more susceptible to disease during the
 Allergies are responses to a certain
type of antigen called an allergen.
During an allergy attack, histamines
are released and the usual reaction
takes place (sneezing, watery eyes,
diminish the symptoms. An attack can
sometimes lead to anaphylactic shock,
a severe drop in blood pressure upon
being exposed to an antigen. This can
cause death within a few minutes.
 Autoimmune diseases occur when the
immune system loses tolerance for
itself and turns on the body. Examples
of autoimmune diseases include
lupus, rheumatoid arthritis, and
multiple sclerosis)
 Immunodeficiency
•White blood cells attack any bacteria or viruses they
find in the lymph as it flows through the lymph nodes.
If cancer cells break away from a tumor, they often
become stuck in the nearest lymph nodes. This is why
doctors check the lymph nodes first when they are
working out how far a cancer has grown or spread.
•Filtering the blood is the job of the spleen. It filters
the blood to take out all the old red blood cells and
then destroys them. They are replaced by new red
blood cells that are made in the bone marrow. The
spleen also filters out bacteria, viruses and other
foreign particles found in the blood. White blood cells
in the spleen attack bacteria and viruses as they pass
•When people say "I'm not well,
my glands are up" they are
really saying they have swollen
lymph nodes because they
lymphatic system helps fight
infection in many ways such as
•Helping to make special white
blood cells (lymphocytes) that
produce antibodies
•Having other blood cells called
macrophages inside the lymph
nodes; which swallow up and
kill any foreign particles, for
example germs
•This function of the lymphatic
system is really part of the
Match the description on the top with the terms on the bottom by writing
the correct letter in each blank.
_____ 1. a disease that destroys the immune system
_____ 2. disease-causing bacteria
_____ 3. traps pathogens in respiratory system
_____ 4. contains weakened antigens
_____ 5. immunity occurring when your body makes its own antibodies
_____ 6. immunity occurring when antibodies are introduced from an
outside source
_____ 7. cells attacked by AIDS virus
Word Bank
a. active
b. passive
c. mucus
d. lymphocytes
e. pathogens
f. vaccine
1. Pathogens play a vital role protecting your body.
2. A virus is a preparation of a weakened or killed
pathogen which is used to create antibodies.
3. Neutrophils and lymphocytes can engulf foreign
bodies by the process called phagocytosis.
4. Serotonin is a chemical secreted during an
inflammatory response.
Autoimmune diseases occur when the immune
system loses tolerance for itself and turns on the
Matching Column:
4. F
5. A
True and False:
1. F
5. T
2. F
3. T
4. F
Campbell, N., Reece, J. (2005) A P Edition Biology 7th Ed.,
San Francisco Pearson Education