IMMUNE SYSTEM
Biology 2201
The ability of the body to fight infection by
producing antibodies or cells that deactivate
foreign substances.
Immune System
 The system in the body responsible for maintaining
homeostasis by recognizing harmful from no harmful
organisms and produces an appropriate response
 Pathogen: virus, bacteria or other microorganism that causes
disease
 Antigen: Toxin produced by a foreign invader
 Antibody
 Y shaped protein molecule created by plasma cells during
specific immune response.
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Function is to attach to and deactivate antigens/pathogens present in
the bloodstream during a specific immune response
Parts of the Immune System
 Blood( white blood cells in particular)
 Lymph nodes
 Spleen
 Bone marrow(to produce more WBC’s
There are 2 types of diseases:
 Noninfectious - often called functional diseases, whereby
an organ does not work properly anymore. (e.g. cancer,
heart disease)
 Infectious - caused by a disease-producing organism called a
pathogen. (e.g. measles, colds, flu, malaria, etc.)
The body’s defenses against pathogens
include:
1. Non-specific Defenses
2. Specific Defenses
Body’s Lines of Defense
 First Line
 Second Line –non specific Immune response
 Third Line- specific immune response
1. Non-specific Defenses
 These are your first line of defense against pathogens. They
guard against all foreign organisms and not just any one
specific organism.
 The major forms of non-specific defenses come into action as
follows:
(A) Physical and Chemical Barriers
 skin
 membrane linings
 sweat
 saliva
 stomach acid
 urine
 tears
 mucus
(B) Inflammatory Response – 2nd line Defenses
 It is a reaction that causes redness, swelling, pain, and warmth in the area of
infection. Cells damaged by the infection release chemicals, that causes an
increase in blood flow to the infected area.
 These are defenses that the body uses no matter what the invader may be.
These defenses are:
 A. Phagocytosis- done by macrophages
 B. Natural Killers cells- the killer cells kill infected cells
 Inflammation- cuts off the infected area from the rest of the body
 Fever-raising temperature kills invading microorganisms
 This results in WBCs called phagocytes being transported to the site of the
infection. The phagocytes ingest the pathogens and damaged tissue,
resulting in the formation of puss. This usually kills the pathogen.
Sometimes the infection gets to the lymphatic system and causes the lymph
nodes to swell.
If the infection is serious, it results in the formation of
more phagocytes. If this does not finish the infection,
chemicals are released that increase the body
temperature. This is called a fever. A fever serves two
major purposes:
(i) it kills microorganisms that cannot survive the
higher temperature
(ii) it slows down microorganisms, giving the WBCs
a chance to destroy them
* If the pathogen is a virus, another defense
system occurs. It is called interferon. It is a
substance produced by cells infected by a
virus. It causes non-infected cells to produce
an enzyme that blocks reproduction of the
virus.
2. Specific Defenses – 3rd line
Defenses
 If the pathogen gets past the non-specific defenses, it will
encounter the specific defenses. It is at this stage that the
immune system comes into play.
 These are defenses that the body uses for specific invaders.
These defenses include
 The production of antibodies
 The killing of specifically infected body cells and microbes
 It provides the body with the ability to fight infection through
the production of antibodies or cells that inactivate foreign
substances or cells.
• The immune system includes all parts of the
body that are involved in the recognition and
destruction of foreign materials.
• The basis of immunity lies in the body’s ability
to distinguish between its own substances (itself)
and foreign substances (non-self).
• Any foreign substance that triggers a specific
defense response is called an antigen.
• Antigens are usually protein, but can be
carbohydrates, lipids or nucleic acids. These are
carried on the surface of bacteria, viruses, and
other pathogens that may enter the body.
• The response to an antigen is called an
immune response.
The Mechanism of specific
Immune response
 When you become infected with a pathogen the following
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series of events occurs.
Step 1: The pathogen is attacked by macrophages and they
engulf the organism /particle
Step 2: the macrophage displays a form of the antigen on its
surface
Step 3: helper T cells recognize the antigen on the surface of
the macrophage and it begins two forms of response. One is
called cellular immunity and the other is Humoral or
blood Immunity
Note: suppressor T cells release substances that slow
down the immune response and eventually stop it.
Cellular And Humoral or Blood
immunity
 Cellular Immunity
 Humoral or Blood
 Helper T- cells activates a
Cytotoxic T- cell
 Cytotoxic T- cell divides Tcells into Cytotoxic T- cells
and memory T-cells
 Killer T- cells kill infected
cells
 Memory T-cells remain
ready for a second invasion
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immunity
Helper T -cell activates a Bcell
B- cell divides into plasma
and memory B- cells
Plasma cells create antibodies
Antibodies attach to and
deactivate pathogens found
in blood
Memory B -cells remain
ready for a second invasion
Types of Immunity
1. Active Immunity
 The body produces its own antibodies or killer T cells to
attack a specific antigen.
 Ex.You have a throat infection and you have built up antibodies
against a clod virus
 You were given a vaccination for polio so your body built up
antibodies to the polio antigen
 Active immunity is long lasting. It develops in two ways:
 (i) when a person had the disease
 (ii) by vaccination of a weakened or milder form of the
pathogen
 Vaccination: an injection of a weakened strain of an infectious
microbe that causes the body to produce antibodies without
harming the body
2. Passive Immunity
 This is borrowed immunity. The person is given antibodies
from another person or animal who has been infected by the
antigen.
 Ex. Maternal immunity: a mother gives antibodies to her child
while breast feeding. This protects the baby against infection
until the baby is ale to produce its own antibodies
 It is only temporary - lasting only 30 days, but faster acting
then the active immunity response.
Immune System and Transplants
 The immune response can result in problems with organ
transplants. The body recognizes transplanted organs as
foreign to the body, and tries to fight them as if they were a
pathogen.
 The result would be the destruction of the transplanted
organ. This is controlled in two ways:
(i) Donor and recipient are closely matched.
(ii) Recipient is given drugs to suppress the
immune system.
An immune response can involve two
categories of reactions:
 B cell reactions
 T cell reactions
1. Antigen enters body
2. Macrophage ingests antigen and displays form of antigen on cell membrane
3. T cell recognizes antigen
3. B cell recognizes antigen
4. Helper T cell recognizes
antigen displayed by macrophage
5. T cell stimulated to divide by
helper T cell to form killer T cells
and memory T cells
5. B cell stimulated to divide by
helper T cell to form plasma cells
and memory B cells
6. Killer T cells bind to virusinfected cells
6. Plasma cells produce
antibodies that bind to antigen
7. If antigen enters body again,
memory T cells divide to produce
new killer T cells
7. If antigen enters body again,
memory B cells divide to produce
new plasma cells
Types of Immunity Responses
1. Primary Immune Response
 This occurs when an antigen enters the body for the first time.
 It takes 5 days for the body to recognize the antigen and start
production of antibodies.
 It takes another 10 to 15 days for the antibodies to build up.
2. Secondary Immune Response
 This occurs if an antigen that has entered the body before, enters a
second time.
 There is a shorter response time of only 1 to 2 days for
antibody production.
 Memory B cells – easily recognize the antigens and produce
mass quantities of antibodies in a very short period of time
 Memory T- cells- quickly recognize infected cells and kill
them quickly
Autoimmune Diseases
 Autoimmune diseases are disease where the immune system
begins to attack itself.
 ex/; Rheumatoid Arthritis- crippling disease of the joints
 Lupus-disease of blood and organs
 Multiple sclerosis-disease of the nervous system
Causes” unknown
Cures/ Treatments no cures. Usually treated with drugs
Allergies and Allergic reaction
 Allergy- an exaggerated response by the immune system to
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an allergen
Allergen: a normally harmless substance that causes an
allergic reaction. Ex. Dust pollen mould food insect stings
Types of allergic reactions there are twp types of allergic
reactions
Immediate-occurs within seconds and abnormally lasts for
about 30 mins
Delayed-takes longer to react and can last for a much longer
time
Mechanism of an allergic Reaction
 During an allergic reaction antibodies cause histamines to be
released from certain cells
 Histamines
 Chemical released into the blood stream that cause
 Swelling inflammation of tissues
 Release of fluids(runny nose and eyes
 Muscle spasms(some cases
 Anaphylaxis or anaphylactic shock:
 This is the sudden and severe allergic reaction to a substance that can
cause death
 Treatments for allergies
 Avoidance of material-especially food
 Epinephrine-epi pen
 Contains a hormone called epinephrine that helps restore
normal blood pressure during anaphylactic shock
 Antihistamines
 Drugs such as Benadryl , Sudafed and Actified contain chemical called
antihistamines that help reduce the amount of histamine in the blood. This
reduces the allergic reaction
AIDS
Acquired Immune Deficiency Syndrome
 The cause of AIDS is a virus called the human
immunodeficiency virus - HIV.
 The virus attacks the helper T cells of the immune system.
 The virus enters the T cell and remains within the cells for
months or even years without producing symptoms.
The virus has a number of disturbing
properties:
 (1) It is able to mutate giving it the ability to produce different
strains. (HIV-1;1981, HIV-2; 1985)
 (2) It causes change in the cell membrane of the T cell causing
them to fuse together. This allows the virus to pass from cell to
cell without entering the bloodstream and becoming exposed to
antibodies present in the blood.
• When HIV becomes active, the individual
develops AIDS. The virus reproduces, spreads,
and destroys helper T cells. The T cells become a
HIV factory.
• Some possible triggers for HIV activation are:
(i) other co-infections
(ii) contain a gene like a ticking time bomb
The decrease in helper T cells weakens the
immune system. The body loses its ability to
fight disease and becomes susceptible to
opportunistic infections and malignancies.
Spread of AIDS
 1. Sexually transmitted
 2. Blood-to-blood contact
 3. Mother to fetus during pregnancy or at the time of birth
 * In rare cases through breast milk
Prevention of AIDS
 1. Abstinence from sexual activity
 2. Use of a latex condom, plus spermicidal nonoxynol-9
 3. Avoid sharing of needles during of intravenous drug use