How is the human body like a battlefield?
How does your body know when a substance is an
invader?
Your body can recognize
what is yours, & what is
not yours! It does this by
recognizing proteins on
the surface of your cells.
The Immune System
Why do we have an immune system?
1. Recognize “self” vs. “non-self”
2. Destroy “non-self”
Foreign Invaders (non-self)
• Antigen: any surface marker capable of triggering
an immune response
Antigens can be found on
bacterial cells, viruses, or any
non-self cell. They could even
be allergens or cancerous cells!
Antigens are displayed
on the surface of cell
membranes & viral
protein coats.
Your body knows
when an antigen is
not yours!
Fighting Foreign Invaders
• Antibodies: proteins in the body that recognize & attach
to pathogens (things that cause disease – bacteria, viruses,
etc.)
– Pathogens display antigens! Antibodies attach to antigens!
Once the body has been exposed
to a pathogen, it remembers!
This will reduce your chances of
another infection.
A. Antibody
B. Antigen
Antigen! Any pathogen (virus, bacteria, etc.)
displays antigens!
A patient gets a heart transplant. The new
heart displays:
A. Antibodies
B. Antigens
Antigen! Even if the heart is
made of human cells, the
patient’s body still recognizes it
as an invader. The patient’s
body could reject the new heart.
Which antigen will this antibody bind to?
A.
B.
C.
D.
Antigen A
Antigen B
Antigen C
None of the above
Antigen B! They match
like a lock & key or puzzle
pieces!
A
B
C
Anatomy of the Immune System
• Localized in several parts of the body:
– Immune cells develop in the bone marrow & thymus.
– Immune responses occur in the secondary organs.
Anatomy of the Immune System
• Spleen: filters & removes old
& damaged red blood cells
• Bone Marrow: tissue inside
bones that produces blood
cells
Anatomy of the Immune System
• Thymus: T-cells mature here
• Lymph Nodes: small organs that filter out dead cells,
antigens, etc. to present to white blood cells
Anatomy of the Immune System
• Lymphatic Vessels: collect fluid (lymph)
leaked from blood into the tissues &
return it to circulation
• Tonsils: 3 pairs of masses of lymphoid
tissue that help protect against bacteria
around the throat
Where are blood cells made in the body?
A.
B.
C.
D.
Spleen
Lymph Nodes
Bone Marrow
Appendix
Bone Marrow!
There are many
different types of
cells involved in the
immune system!
Defense Mechanisms
• Non-Specific: the body’s
attempt to destroy all types of
foreign invaders
– General, not targeted to a
specific pathogen
– Born with it
• Specific: immune response
specific for a certain pathogen
– Could be learned (your body
remembers!)
Antibody-Antigen binding represents which
type of defense?
A.
B.
C.
D.
Non-Specific
Specific
Neither
Both
Specific! Antibodies only bind
to 1 type of antigen. Once it
binds, your body will always
remember that antigen!
Which type of defense are baby’s born with?
A.
B.
C.
D.
Non-Specific
Specific
Neither
Both
Non-Specific! Specific immune responses are learned!
Some scientists believe that the reason baby’s have an
instinct to eat dirt is to build up their immune system.
Specific vs. Non-specific Defense
• Non-specific defenses will target any invader (general)!
– You are born with non-specific defenses.
• Specific defenses are learned! When a pathogen
invades your body, your immune system creates
antibodies that target that specific pathogen.
– If the pathogen tries to invade again in the future, your
body will be ready, because it remembers!
The 3 Lines of Defense Against Infection
• Before a pathogen triggers your immune system &
makes you sick, your body has other lines of defense
against infection!
1st Line of Defense – The Outer Layer of the Body
Non-Specific
• Goal: prevent organisms from gaining access to the
body
– Physical Barriers: skin & hair
– Chemical Barriers: sweat, tears, saliva, mucus (these
contain enzymes that break down cell walls of bacteria)
What if a pathogen breaks past the 1st line of
defense?
2nd Line of Defense – Cells/Proteins in our Blood Stream
Non-Specific
• Goal: recognize, neutralize, & destroy invaders
– Inflammation & Fever
– Increased blood flow to the area brings white blood cells
to fight infection
3rd Line of Defense – The Immune Response
Specific
• 2 types of cells are involved:
1. B Cells
2. T Cells
3rd Line of Defense – The Immune Response
Specific
• B Cells: provide immunity against antigens &
pathogens in the body by making antibodies
–
–
This is how vaccines work!
This is called humoral immunity.
1.
2.
3.
4.
B-Cell binds to an invading antigen.
T-Cell sends a signal the B-Cell.
B-Cell is activated to become a plasma cell.
Plasma cell releases antibodies specific to the antigen.
3rd Line of Defense – The Immune Response
• T Cells: provide defense against abnormal cells &
pathogens inside of living cells
–
Cell-mediated immunity
Steps of the Immune Response
1. Virus infects the body.
2. Macrophage eats the virus & displays viral antigens.
Macrophages are white
blood cells that engulf
pathogens.
This is a macrophage
engulfing bacterial cells!
Steps of the Immune Response
3. Macrophage activates helper T-Cells.
4. Helper T-Cells activate B-Cells & killer T-Cells.
Macrophages engulf
pathogens & display the
antigen proteins! This
signals the T-Cells.
Steps of the Immune Response
5. B-Cells will become memory cells & plasma cells;
they remember the antigen for the future!
6. Plasma cells make antibodies, which bind to the viral
antigens.
Steps of the Immune Response
7. Antibodies attach to the virus & infected body cells,
which signals their destruction.
8. Killer T-Cells DESTROY!
This is a killer T-Cell
attacking cancer cells!
You get a cut on your finger and it gets red and
swollen around the area.
A. First Line of Defense
B. Second Line of Defense
C. Third Line of Defense
Second Line of Defense!
If a person has B-Cells against a certain pathogen,
the person is:
A. Likely to develop the disease.
B. Less likely to develop the disease a second time.
C. Able to spread the disease to others with physical
contact.
D. Probably still sick with the disease.
This person is less likely to develop the disease a second time!
B-Cells are memory cells, meaning they remember pathogens
& prevent them from causing disease in the future!
How do vaccines work?
• Vaccines are composed of dead or weakened
pathogens (bacteria or viruses).
• When injected, the vaccine triggers an immune
response!
If you get the flu vaccine, your
body will begin to make
antibodies to fight the flu virus
so that you won’t get sick in the
future!
The polio vaccine contains weakened polio viruses. A
vaccinated individual becomes protected against polio,
because the weakened viruses:
A.
B.
C.
D.
Prevent further viral invasion.
Induce an inflammatory response.
Promote the production of antibodies.
Are too weak to cause illness.
The weakened viruses promote the
production of antibodies to prevent
further disease!