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Immune System
The Immune System
The function of the immune system is to
fight infection through the production of
cells that inactivate foreign substances or
cells
 This process is called immunity
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First Line of Defense
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The function of the first line of defense is to
keep pathogens out of the body.
This role is carried out by skin, mucus, sweat,
and tears.
Your body’s most important non-specific defense
is the skin
Mucus, saliva, and tears contain lysozyme.
Lysozyme breaks down the cell wall of many
bacteria.
Second line of defense
If pathogens do enter your body, they
may replicate rapidly and release toxins.
 When this happens, the inflammatory
response is activated,
 The inflammatory response is a nonspecific response to tissue damage caused
by injury or infection.
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The Inflammatory Response
When pathogen are detected, the immune
system produces millions of white blood
cells – lymphocytes, which fight the
infection
 Blood vessels near the wound expand to
allow more white blood cells to enter the
tissues.
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Fever
The immune system also releases
chemicals that increase the core
temperature of the body.
 A fever is advantageous because many
pathogens can only survive within a
narrow temperature range.
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Interferons
When viruses enter cells, sometimes the
cell will produce a chemical called
interferon – because it interferes with viral
replication.
 This gives the specific immune response
more time respond.
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Specific Defenses
A substance that gets past the nonspecific defenses, will trigger an immune
response.
 A substance that triggers an immune
response is called an antigen.
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Specific Immune Defences
The cells of the immune system that recognize
specific antigens are two types of lymphocytes
(white blood cells)
 B lymphocytes (B cells) and T lymphocytes (T
cells)
 B cells provide immunity in the body fluids
(humoral immunity)
 T cells provide a defense against abnormal cells
and pathogens in side cells. (cell-mediated
immunity).
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Humoral Immunity
When a pathogen invades the body, its
antigens are recognized by a small fraction
of the body’s B cells.
 These B cells grow and divide rapidly
producing plasma and memory cells
 Plasma cells release antibodies.
 Memory cells remain in the body long
after the antibodies have neutralized the
infection.
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Antibody
Cell-Mediated Immunity
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The body’s primary defense against its
own cells when they have become
cancerous or infected by a virus is called
cell-medicated immunity.
Cell-Mediated Immunity
During cell-mediated immunity, T cells divide
and differenciate into killer T cells, helper T cells,
suppressor T cells, and memory T cells.
 Killer T cells track-down and destroy the
bacteria, fungi, protozoan, or foreign tissue that
cantains the antigen.
 Helper T cells make memory T cells for future
attack by same pathogen.
 Suppressor T cells release chemicals that
shutdown killer T cells.
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The very end……