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Immune System
A Boo Boo lets in germs
Like…Bacteria
Or a virus
A germ is still a germ….
Pathogen=agent that causes disease
2. Antigen= foreign particle that triggers an
immune response
- often they are proteins on
the surface of viruses and
bacteria
1.
Your Body’s Defenses Against
Disease
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Nonspecific Defenses: Attack all
pathogens and antigens the same way
Specific Defenses: Immune Response –
Attack pathogens that get past the
nonspecific defenses
Nonspecific Defenses
This means that the identity of
the pathogen/antigen is not
important. The response is the
same if a bacteria, virus, splinter
or bullet invades the body.
Nonspecific Defenses
First Line Defenses
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Skin: Forms a physical barrier to pathogens
-oils and sweat make skin acidic – inhibits
the growth of pathogens
-lysozyme-enzyme found in sweat and tears
digests bacterial cell walls
Mucus Membranes-layers of tissue which
secrete mucus
- found in body openings and the respiratory
system
- mucus traps pathogens
Nonspecific Defenses
Second
Line Defenses
 Inflammatory Response
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Damaged cells release histamines – chemical cry for help
- histamines cause blood vessels to dilate (open) bringing
blood to the area.
- the dilated blood vessels become leaky releasing fluid and
white blood cells in the infected area
- causes swelling and redness in the damaged area
- pus – fluid and dead cells forms
White Blood cells
- Macrophages – “Big Eaters” engulf and kill pathogens
- Neutrophils-engulf bactera and release chemicals that
kill the bacteria and themselves.
- Natural Killer Cells – recognize and kill virus infected
cells and tumors
Textbook page 925
Histamines are released
Blood vessels dilate
and leak
Macrophage
Nonspecific Defenses
Second Line Defenses (continued)
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Temperature Response - Fever –
-Body temp increases in response to infection
-pathogenic bacteria don’t grow well at higher temp

Proteins
- Complement Proteins: kill pathogens by punching a
hole in the cell membrane
- Intrerferon:
a protein released by cells infected by viruses
-causes nearby cells to release an enzyme preventing the virus
from reproducing
Fevers help eliminate pathogens
Specific Defenses

Third Line of Defense
Specific Defenses
- identity of pathogen/
antigen must be known
- the specific immune
response is tailored to
the specific pathogen
Specific Defenses
Macrophage Links Nonspecific to Specific
When a macrophage engulfs a pathogen, it
displays the viral antigen on its surface
The antigen is joined to a MHC
(Major Histocompatibility Complex)
The MHC is a protein on the surface of
all vertebrate cells
The anitgen must be bound to the MHC for the Helper T Cell to recognize it
Specific Defenses
Helper T Cells
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Receptor proteins on helper T cells (TH) bind to
viral antigens displayed on the macrophage
causes macrophage to
release Interleukin1
Interleukin1 activates
the helper T cells (TH)
Specific Defenses
Helper T Cells
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continued
Activated helper T cells (TH) release proteins called
cytokines which activate cytotoxic T cells (TC) and B cells
The activated (TC) and B cells begin to divide
Specific Defenses
Cell Mediated Response

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Receptor proteins on the
cytotoxic T cells (TC) bind to
viral antigens displayed by
infected cells
Cytotoxic T cells (TC) punch a
hole in the cell’s membrane
Your body produces many
cytotoxic T cells (TC)
- each specific to a particular antigen
Specific Defenses
Antibody Mediated Response
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B cells divide and develop into
plasma cells
Plasma cells release large numbers
of antibodies
Antibodies bind to antigens on
pathogens
Antibodies cause pathogens to clump
holding them until macrophages
can engulf them
Antibodies are specific to a particular pathogen-your
body produces the antibodies in response to infection
The Specific Defense has two
phases

Primary Immune
Response:
-Occurs when the body
has never encountered a
pathogen /antigen
before.
-Immune system goes
through all of the steps
-After the threat has
passed, MEMORY Cells
are made.

Secondary Immune
Response:
The next time the
pathogeninvades
MEMORY Cells identify
the invader and a
massive volume of
antibodies are released,
destroying the invader
before you feel ill.
You are immune!
Vaccines
Polio
1952 60,000 cases
in the US
3000 fatalities
1955 Salk vaccine
1979 eliminated in US
How do vaccines work?
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Vaccines are made up of weakened viral
particles.
The weakened particles stimulate a small
number of antibodies and memory cells to
be produced. Primary Immune Response
When a the pathogen attacks, the
antibody production is larger.
Secondary Immune Response
Immune Response
Vocabulary
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Pathogen B cells T cells
Macrophages
Nonspecific Defense
Vaccines
Primary Immune Response
Secondary Immune Response