Immune System

1. Chapter 21
Immune System
“If you’re not with us, you’re against us.”

2. Immunity
ability to provide resistance to disease
Adaptive Defenses
-- develop slowly
-- are directed
against specific
pathogens
Innate Defenses
--are present at
birth
--provide immediate
but generalized
protection
** defense mechanisms work together to fight off invaders
Pathogen: harmful or disease causing microorganism

3. Defending the Castle
• Our bodies, like a castle, is a fortress.
Both have three lines of defense:
• First: A Moat, Drawbridge and Walls. The first line
of defense in our bodies are also barriers
• Second: Foot Soldiers. If there is a breach in the
barriers troops are waiting inside the castle ready
to go after any invader. In our bodies the second
line of defense are nonspecific internal defenses
that attack any foreign invader.
• Third: Elite Fighting Force. These agents are
trained to identify and target specific invaders. Our
third line of defense are adaptive defenses
directed by B Cells and T Cells.

4. Lines of Defense
CIA agent
FBI agent

5. Innate Immunity: First Line of Defense
Surface Barriers
- Skin (keratin)
- Mucous
membranes
(including nasal
hairs and cilia)
Protective Chemicals: associated with
epithelial cells
– Acid: skin, stomach, vagina
– Enzymes: lysozymes (saliva,
respiratory mucus, tears); stomach
enzymes
– Mucin: dissolved in water forms
mucus (digestive and respiratory
passages)
– Defensins: antimicrobial peptides
(skin and mucosa)
– Other: sebum (skin) and dermacidin
(sweat) are bacteriotoxins
Both barriers are made of epithelial
tissue. Mucous membranes line the
surfaces of any internal part of your
body that has exposure to the outside
environment. Your respiratory,
gastrointestinal and urogenital tracts.
Remember talking about goblet cells
making sticky mucous to trap debris
and pathogens and that lovely cilia to
sweep it out of your body.

6. – Phagocytes: monocytes (become macrophages)
and neutrophils
– Natural Killer Cells: lyse cancer and virus-infected
body cells
– Inflammation
– Antimicrobial Proteins
• Interferons: interfere with viral replication
• Complement system:
– enhances phagocytosis and inflammation
– Membrane Attack Complex (MAC)
– Fever
Innate Immunity: Second Line of Defense
The important thing here is to understand these mechanisms are non-specific.
These mechanisms go after anything that is foreign. They do not know exactly which type
pathogen they are going after. Example: they can’t tell a bacteria that causes strep throat
from one that causes meningitis. They just know to kill bacteria or viruses.

7. Phagocytosis You are not responsible for
all these steps. Just
understand that
phagocytes engulf cells
and debris and lyse them.
The “waste” is exocytosed
back into the body where it
is recycled or excreted.
Neutrophil phagocytosis of bacteria
https://www.youtube.com/watch?v=Z_mXDvZQ6dU
Macrophage eats bacterial colony
https://www.youtube.com/watch?v=ilS3FzuN-uQ

8. Natural Killer Cells
• Defensive Cells: recognize generalized cell
abnormalities
• Lysis: cancer cells, and virus-infected cells
(no memory cells produced)
Natural killer cells destroying cancer cells
https://www.youtube.com/watch?v=Va1jaBGwoT8

9. Inflammation
• Triggers:
–physical trauma, intense heat, irritating
chemicals, infection
• Benefits:
–prevents spread of damaging agents
–disposes of cellular debris and pathogens
–alerts the adaptive immune system
–sets the stage for repair
Watch inflammation in action:
https://www.youtube.com/watch?v=fcAAnj4czzo

10. Inflammatory Chemicals
• released by:
– injured or stressed tissues or immune cells
• cause:
– vasodilation of local arterioles
– increased capillary permeability (leakiness)
– phagocyte mobilization
• include:
– histamines
– complement
– prostaglandins
– kinins

11. Chemotaxic agents
Injured Tissues
Release
Phagocytosis of
pathogens and
debris
Neutrophils and
monocytes arrive at
the injured area
Increased capillary
permeability (leakiness)
Clotting
proteins
wall off area
Arterioles dilate:
increases blood
flow to area
Inflammatory agents
Heat Redness Pain
Swelling
Locally increased
temperature causes
increased metabolic
rate
Temporary
impairment of
function
Healing
This is a great view of how
each part of the
inflammatory process works
These are the signs of an inflammatory response

12. COMPLEMENT SYSTEM
• 20 plasma proteins
– activated in a cascade
• Leads to:
– opsonization: enhances phagocytosis (to make tasty)
– enhanced inflammatory responses
– production of Membrane Attack Complexes (MAC):
proteins form pores in the pathogen’s cell membrane
causing them to lyse
Insertion of MAC
and cell lysis
Your book gets very complicated about this.
This is the level I expect you to understand.
Don’t worry about the actual cascade.
Watch insertion of a MAC (don’t worry about the details):
https://www.youtube.com/watch?v=rBNzS5x_ok0
Just watch
the first 3
minutes.
https://ww
w.youtube.
com/watch
?v=2-
57bqFSJ1E

13. Fever
WBC/Macrophages
Pyrogens
send
message to
hypothalamus
induces
1) Increases
metabolic rate
aids in healing
2) Liver and spleen
bind iron and zinc 
starve pathogens of
nutrients
secrete

14. A review from your friends at Crash Course
https://www.youtube.com/watch?v=GIJK3dwCWCw