Chapter 4- Immune System
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Form 4 Biology
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Immune system is group of organs, cells and chemicals working together to
defend the body against infections and diseases.
Immunology is the study of the physiological defense by which the body
destroys or neutralizes foreign matter, both living and non-living things.
Immune response is how the body recognizes and defends against harmful or
foreign substances such as antigen.
Antigen is a molecule that provokes a specific immune response.
Immunity is the body’s resistance against diseases and infections.
Antibody is a Y-shaped protein produced by the body’s immune system to
identify and neutralize harmful and foreign substances.
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Chapter 4- Immune System
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Functions of Immune System
1. Protection against infections.
2. Removal of debris and dead cells.
3. Destroy cancer cells.
4. Isolates or removes non-microbial
foreign substances.
Difference between Specific and Non-specific Immune Defense
Non-specific Immunity System
Specific Immune System
(Innate immunity)
(Adaptive or acquired immunity)
Present at birth
Develop after birth or through
vaccination
Does not involve specific recognition of
pathogens
Involves specific recognition of
pathogen
Faster response
Slower response
Has no memory (does not develop
memory)
Has memory (develops memory)
Inherited
Not inherited
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Chapter 4- Immune System
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Components of the
Function (role) of Defense
First Line of Defense
Skin
Sweat
Provides both physical and chemical barriers
against the invading pathogens


Sebum
Sebum inhibits and slows down the growth of
certain pathogenic bacteria on the skin.
Mucus and cilia
Filter, trap and remove microbes and other
inhaled particles from the body.
(in respiratory passages)

Saliva
Stomach acid (HCL) and
digestive enzymes
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Sweat contains the enzyme lysozyme which
digests bacterial cell wall.
Sweat lowers the pH of the skin which inhibits
the growth of many microorganisms on the skin.

Saliva contains the enzyme lysozyme which
kills bacteria by destroying bacterial cell wall.
Saliva washes microbes from the teeth and
mucous membranes of the mouth
Destroy pathogens in the swallowed food
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Chapter 4- Immune System
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
Tears

Urine
Blood clotting
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

Tears contain the enzyme lysozyme which kills
certain pathogens.
Tears wash away irritating substances and
microbes from the eyes.
Washes microbes from urethra
Low pH of urine slow down microbial growth in
the urinary system
Blood clotting prevents entry of pathogens by
sealing the wound rapidly.
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Chapter 4- Immune System
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Inflammation is a localized
nonspecific immune response to
an infection or injury.
Mast cells in body tissues
release chemical called histamine
which initiates the process of
inflammation.
Mechanisms (steps) of Inflammatory Response
1. Vasodilation (Dilation of local blood vessels).
2. Increased blood flow.
3. Increased permeability of blood capillaries.
4. Migration of phagocytes from the blood to the site of infection.
5. Killing and destroying pathogens through phagocytosis.
Characteristics or signs of the inflammatory response (Inflammation):
1. Redness
2. Warm (Heat / fever)
3. Swelling
4. Pain
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Chapter 4- Immune System
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Fever is an abnormally elevated body
temperature.
Macrophages release a chemical
called interleukin-1 which stimulates
the hypothalamus to increase body
temperature and cause fever.
Role of Fever in Immune Defense Mechanisms
1) Fever stimulates the process of phagocytosis.
2) Fever causes the liver and spleen to store iron (Reduces the
blood level of iron).
3) Fever speeds up tissue repair.
Phagocytosis is the process of engulfing and destroying pathogens by the phagocytes.
Phagocytes are white blood cells that engulf and destroy pathogens through phagocytosis.
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Mechanisms (Steps) of Phagocytosis
(1)
(2)
(3)
(4)
(5)
(6)
(7)
Chemotaxis
Attachment (adherence)
Endocytosis (Ingestion)
Vacuole formation
Killing and digestion
Formation of residual body
Exocytosis
Chemotaxis is the process of
attracting phagocytes to the site
of infection.
Histamine is the chemical which
attracts phagocytes to the site of
infection
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White Blood Cells in
Function (role) of Defense
Second Line of Defense
Neutrophils
Macrophages
(Monocytes mature into
macrophages)
Engulf and destroy pathogens through phagocytosis





Release chemical called histamine (cytokine)
which causes the inflammatory response.
Mast cells
Natural killer cells
(NK Cells or Killer cells)


Lyse and kill virus-infected body cells.
Lyse and kill cancer cells.

Release chemical called histamine which causes
inflammation.
They respond to allergic reactions.
Basophils

Eosinophils
Dendritic cells
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Engulf and destroy pathogens
Destroy cancer cells
Destroy worn out and dead cells
Release a chemical called interleukin-1
Present antigen of killed microbe to T-Cells
(T-helper cells) to initiate adaptive immune
response
Kill parasitic worms
They present the antigen of the killed pathogen to
T-lymphocytes (T-helper cells).
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Chapter 4- Immune System
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Note
Macrophages and dendritic cells are
known as antigen presenting cells
(APCs), because they present the
antigen of killed pathogen to the
lymphocytes for immune response.
Anti-microbial Proteins in
Second Line of Defense
Function (role) of Defense
Interferons
(Interferons are secreted by the virus
infected body cells)
Complement Proteins
(Complement system)
Interferons reduce the spread of virus in the body
Complement proteins make a hole on the
membrane of the pathogen to rush in water
and rupture.

Lymphocytes are type of white blood cells that carry out specific immune
response.
The two types of lymphocytes that play a role in adaptive immunity are:
1. T- lymphocytes (T-cells) – mature in thymus gland
2. B-lymphocytes (B-cells) – mature in the bone marrow.

T and B lymphocytes are stored and activated in the lymph nodes.

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Chapter 4- Immune System
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Types of T-cells and their Role
Types of T-lymphocytes (T-cells)
Inducer T cells
Helper T cells
Cytotoxic T cells (Killer T cells)
Suppressor T cells (Regulatory T
cells)
Memory T cells
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Role/ function
Oversee the development of T-cells in the
thymus gland.
(Cause the thymus gland to maturate more Tlymphocytes.
 Initiate the immune response.
 Secrete chemical called interleukin-1
(Lymphokines or cytokines), which
stimulate Cytotoxic T-cells,
macrophages and B-lymphocytes to
carry out immune response.
 Stimulate B-cells to divide and secrete
antibodies.
Lyse body cells that have been infected by
virus.
(Kill virus-infected cells, foreign cells and
cancer cells)
Terminate the immune response
(Deactivate the immune response once the
pathogen has been defeated)
(Inhibit the activation of T and B cells)
Remain in the blood and provide long term
protection.
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Chapter 4- Immune System
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Types of B-cells and their Role
Types of B-lymphocytes (B-cells)
Plasma cells
Memory cells


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Role/ function
Plasma cells secrete antibodies.
Remain in the blood and provide long term
protection.
The immune response to the first invasion of a pathogen is called primary
response.
The immune response to the second invasion of the same pathogen is called
secondary response.
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Primary Response
Secondary response
Slower response
Faster response
Slow production of antibodies
Fast production of antibodies
Fewer antibodies are produces
More antibodies are produced
Secondary response is faster than the primary response, because there are
many memory cells in the body and more antibodies are produced quickly.

Antibody, also known as immunoglobulin (Ig) is a Y—shaped globular
protein produced by the plasma cells of B-lymphocytes to identify and
neutralize harmful and foreign substances in the body.
o Antibodies are found in blood plasma, tissue fluid, tears, and mucus and
also in breast milk.

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Functions of the Antibody
1- Opsonization - they label or mark antigens (pathogen) for the
phagocytes to destroy them.
2- Neutralization of toxins - they neutralize the toxins released by the
pathogen.
3- Agglutination - antibodies cause sticking together of pathogens, so
they are easier for phagocytes to ingest.
4- Some antibodies activate the complement proteins which form a hole
in the membrane of the pathogens causing them to burst.
5- Antibodies bind to the surface of the virus and prevent them infecting
or entering host cells.
6- Antibodies prevent pathogens from sticking to the body tissues.
o An antibody consists of four polypeptide chains;
1. Two heavy chains (a long polypeptide) – heavy chains are identical
2. Two light chains (a short polypeptide) – light chains are identical
o The four chains in an antibody molecule are held together by disulphide (—S—
S—) bonds, forming a Y-shaped molecule.
o An antibody is also made up of a constant region and variable region.
o The region of the antibody that has a constant structure is called constant
region.
o The binding site of the antigen of the antibody is called the variable region and
is different in different antibodies.
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Chapter 4- Immune System
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Chapter 4- Immune System
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Active Immunity
o Active immunity is the immunity gained when an antigen or pathogen
enters the body.
o Active immunity involves the production of antibodies by the body’s
immune system.
o Active immunity is a long lived immunity.
o There are two types of active immunity:
1. Natural active immunity
2. Artificial active immunity
o Natural active immunity is the immunity gained naturally during an
infection or after the body encounters a pathogen.
o Artificial active immunity is the immunity gained through vaccination.
o Immunization is the process by which a person becomes protected
against a disease through vaccination.
o Immunization is an artificial active immunity, because it is an immunity
gained through vaccination.
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Chapter 4- Immune System
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Passive Immunity
o Passive immunity is the immunity developed from antibodies provided
from outside the body.
o Passive immunity is short lived immunity against a pathogen.
o The two types of passive immunity are:
1. Natural passive immunity
2. Artificial passive immunity
o Natural passive immunity is the immunity gained from antibodies of
mother across placenta or breast milk (colostrums).
o
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Artificial passive immunity is the immunity gained when antibodies or
antitoxins from external source are received through injection, e.g.
antivenin.
Immunity
Example
Natural Active
Direct contact with pathogen
Natural Passive
Antibodies from mother, e.g. across placenta,
breast milk (or colostrums).
Artificial Active
Vaccination
Artificial Passive
Injection of antibodies or antitoxins
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