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Immune System
Chapter 40-2
Immune System
 A series of defenses that guard your body against disease
 Function: to fight infection by producing cells that inactivate foreign
substances or cells
 This is called IMMUNITY
 Pathogen: disease causing agents such as bacteria, virus, and fungi
 Recognizes, attacks, destroys, & “remembers” each type of pathogen
that enters the body
 Produces specialized cells that inactivate the pathogen
Organs of the
Immune System
Nonspecific Defenses
 Do not discriminate between 1 threat and another (reacts
the same no matter what)
 Include physical & chemical barriers
 1st Line of Defense:
1. Most important – SKIN
2. mucus, saliva, tears, oil & sweat glands
 2nd Line of Defense: inflammatory response
Skin
 Very few pathogens can get across the layers of dead cells on the
surface
 When broken (cuts or wounds), pathogens enter very easily &
multiply
 Causes symptoms of INFECTION:
1. swelling
2. redness
3. pain
4. heat
Secretions of the Body
 Mucus, saliva and tears - all contain LYSOZYME – enzymes
that breaks down the cell walls of bacteria
 Oil & sweat glands produce an acidic environment on the skin
that kills many bacteria
 Mucus in mouth & nose help trap pathogens
 Stomach acids & digestive enzymes destroy many pathogens that
get in your stomach
Inflammatory Response

1.
2.
3.
4.
5.
6.
A nonspecific defense reaction to tissue damage caused by
injury or infection
Millions of white blood cells are produced – which fight the
infection
Blood vessels near the wound expand, allowing the WBCs to
travel faster to infected tissue
WBCs engulf & destroy bacteria
Area becomes swollen & painful
Body release chemicals to increase body temp. – fever –
slows or stops the growth of the pathogen
Fever also causes heart rate to increase which pushes WBCs
to infected tissue faster
White blood cell vs. Red blood cell
Interferons
 Proteins that help other cells resist viral infections
 Interfere with the growth of the virus
 Slows down the progress of the infection & gives the immune
system time to respond
Specific Defenses
 If a pathogen gets through the nonspecific defenses, the body
STARTS the IMMUNE RESPONSE
 ANTIGENS: substances that trigger this response – viruses,
bacteria
 Cells in the immune system can recognize these antigens are
called - lymphocytes
Lymphoctyes
 B Cells – provide immunity against antigens & pathogens in body
fluids
- this is called HUMORAL IMMUNITY
 T-cells – provide defense against abnormal cells & pathogens inside
living cells.
- this is called CELL-MEDIATED IMMUNITY
Humoral Immunity
 When a pathogen enters the body, it is recognized by a small
amount of B cells
 These B cells grow & divide rapidly – producing many
memory B cells & Plasma cells
Plasma cells
 Plasma cells release ANTIBODIES – recognize & bind to
antigens
 Antibodies attack the pathogen until it has taken it over
 Once infection is gone, the plasma cells die & stop producing
antibodies
Memory B Cells
 Remember every pathogen that enters the body
 Able to produce antibodies if exposed again
 Greatly reduces the chance of being infected again
Antibody Structure
 Shaped like a Y and has 2 binding sites to connect with
antigens
 The different shapes give antibodies the ability to recognize a
large variety of antigens
 Its estimated that a healthy adult can produce about 100
million different types of antibodies
Antigen-binding sites
Antigen
Antibody
Cell-Mediated Immunity
 The body’s primary defense against its own cells when they
have become cancerous or infected by viruses
 Also important in fighting infection by fungi & protists
 Viruses & other pathogens can not be destroyed by antibodies
alone
Process of cell mediated immunity
1.
2.
3.
4.
5.
T cells divide & change into Killer T cells, Helper T
cells, & Memory T cells
Killer T cells find & destroy the pathogen or foreign
tissue that contains the antigen
Helper T cells produce Memory T cells
Memory T cells remember the antigen in case of
future invasion
Once pathogen is taken over, Suppressor T cells shut
down Killer T cells
HIV – Human Immunodeficiency Virus
Acquired Immunity
 when immunity is taken from outside the body – not
naturally made
 Two types
 Active Immunity
 Passive Immunity
Active Immunity
 Vaccination – injection of a weakened form of a
pathogen to produce immunity
 More than 20 serious human diseases can be prevented
by vaccinations
 Modern vaccines stimulate the immune system to create
millions of plasma cells ready to produce specific types
of antibodies
 When the body reacts to the vaccines it is known as
Active Immunity
Passive Immunity
 When antibodies produced by other animals against a pathogen
are injected into the bloodstream
 Last only a short time
 Can develop naturally - passing from mother to child through
placenta or breast feeing
 or by deliberate exposure - vaccines for malaria or when
someone is bitten from snake or rodent