2. Germ Theory of
Disease
• “Microorganisms cause infectious
disease”
• Louis Pasteur and Robert Koch did several
experiments to identify disease causing
agents.
• Determined that each disease is caused
by a “specific” microorganism

3. Agents of Disease
• The following types of
organisms can cause
disease:
1. Viruses
2. Bacteria
3. Protists (malaria)
4. Worms
5. Fungi
• Pathogen is anything
that causes disease.

4. Koch’s Postulates
• In order to identify what organism causes a specific
disease, certain rules are followed.
• Koch Postulates:
1) pathogen must be found in subject with disease
but never in a healthy subject
2) pathogen can be isolated from sick person and
grown in lab
3) pathogens injected into healthy person will
cause the individual to become infected with the
same disease
4) injected pathogens can be isolated from newly
infected individual and are identical to original
pathogens

5. Koch’s Experiment- Germ
Theory
• Koch’s postulates are very important because
they are the basic steps for identifying, curing,
and preventing specific diseases.

7. What is a system?
• A group of tissues (organs) work together
to do a task.
• Ex) digestive system, circulatory system,
immune system…
• Function of the immune system is to
protect body from invasion by pathogens.

8. Overview of Body’s
Defenses
Non-Specific Defenses Specific Defenses
First Line of Defense Second Line of
Defense
Immune Response
Skin and Mucous Inflammatory
Response
Non-Specific
WBC (phagocytes)
Specific (diverse)
Antigens/Antibodies
Lots WBC
Memory

9. Non-Specific Defense
• Similar to “walls of a fort” protect by keeping
pathogens out of body
• Body does NOT distinguish one pathogen from
another
• Your body has several non-specific defenses…
1) External- skin and mucous membranes
(1st
line defense)
2) Internal- Inflammatory response
(2nd
line defense)

10. “Skin”
• Physical barrier
• Chemical barrier-
secretes oil and
sweat (lowers pH
skin), tears (contain
enzyme called
lysozyme), and saliva
• Sheds constantly
(1 million cells per
hour)

11. “Mucous Membranes”
• Skin contains natural
openings (nose, mouth,
trachea, esophagus)
• These areas are lined by
mucous membranes
• Secrete mucus traps
foreign objects
• Areas lined with cilia
• Any pathogens make it
past, may be killed by
stomach acids.

12. “Small Scale
Infections”
• The first line of defense has been broken… second line of defense
is triggered to attack any invaders present
• Inflammatory response
• Body’s attempt to destroy pathogens that enter the body when
the skin is injured
• Triggers series of reactions …
1.) Chemical called histamine is released from white blood
cells called basophils
2) Blood vessels in area of injury swell
3) Tissue at injury site swells
4) Temperature in area of injury rises = redness
5) White blood cells called phagocytes move from the vessels
into the injured tissue eat pathogen and damaged skin cells
6) Platelets clot blood and seal infected area

14. “What if pathogens get
in?”
• White blood cells take over and specifically identify and
eliminate the pathogen.
• White blood cells = “soldiers”
• Immune Response

15. Organs of the Immune
System
White blood cells
called leukocytes
Made thymus and
bone marrow
Stored tonsils,
spleen, and lymph
nodes.

16. How does your body
know
there is an invader?
• All pathogens have “distinct” antigens.
• Antigens are marker proteins- trigger immune
response
• Your body must recognize antigens in order to
identify and defeat the pathogen.
• Normal cells also have antigens.
Antigen

18. Antibodies
• Your white blood cells produce antibodies in
response to specific antigens.
• These are specific to each pathogen.
• All pathogens are unique, your immune system
has to prepare a specific defense against each
invader.
• If you makes/have the antibodies it can kill the
pathogen and you can fight the infection.
• B-cells (type of white blood cell) make the
antibodies!

19. Building “Immunity”
• What happens if a pathogen makes it
past the first lines of defense and avoids
the inflammation response?
• Your body must “actively” fight the
disease.
• This takes time.
• This requires a special group of white
blood cells  lymphocytes.

20. “The Soldiers”
• Many types of WBC
work together during
the immune response to
fight the infection.
• Macrophages
• Lymphocytes

21. “The Soldiers”
• 3 major classes of
lymphocytes:
1) B-cells (plasma cells)
2) T-cells
-Helper T cells
-Killer T cells
-Suppressor T cells
3) Memory cells

22. Step #1 “Invader
Identification”
• Macrophages identify pathogen, eat it, display
antigens, signal helper T cells (interleukin-1).
• Body temperature will increase (interleukin-1) in
attempt to slow down pathogen.

23. • Helper T cells release interleukin 2 – signals
help other leukocytes (other T-cells and B-cells)

24. Step #2 “Cloning
Phase”
• B cells make antibodies - lock onto
antigens.“Marked for death.”
Antibodies
Antigen

25. • Killer T cells kill infected body cells.
Step #3 “The Attack Phase”

26. Step #3 “The Attack
Phase”
• Macrophages clean up- eating pathogens,
damaged body cells, etc.
• Suppressor T cells “call off the troops” stopping
the immune response.

27. Step #4 “Memory
Phase”
• Memory cells “remember” the attack and
recognize a pathogen if it re-enters body.
• Primary vs. secondary immune response

28. Active vs. Passive
Immunity
• Active = your body must fight off the
disease to build up antibodies. Ex.)
Fighting an infection or Vaccination
• Passive = receiving antibodies from an
outside source. Ex.) Breast feeding

29. Other Topics – Related
to Immune System
•It is the job of the immune system to
distinguish between the body’s own
molecules and foreign molecules
•Antigens – “marker proteins”
•Blood Transfusions and Organ Transplants

30. If the key fits the lock = bad!!!
Blood Transfusions and the Immune
System
• Blood cells have marker proteins or
“antigens”

31. Organ Transplants and the
Immune System
• Foreign organs also have marker
proteins.
• If recognized as “foreign” = REJECTION.
• Doctors must “match” a new organs
marker proteins to the patients.
• Drugs can help suppress the immune
response (immunosuppresants).

32. What if the immune
system fails?
• Sometimes the immune system loses the
ability to distinguish itself from non-self.
• Results in autoimmune disease
• Body attacks own tissues
• Ex) lupus, multiple sclerosis, arthritis

33. LUPUS
• Person’s immune system attacks various
organs or cells of the body (skin, joints,
kidneys, heart, and lungs) causing
damage
• Lupus is a multi-system disease because
it can affect many different tissues and
organs in the body.

34. LUPUS
Symptoms:
• Fatigue
• Low-grade fever, rarely exceeding 102°F
• Muscle pain and joint pain or swelling
• Skin rash (face, back, arms) and hair loss
• Kidney problems and weight loss

36. Multiple
Sclerosis
• Immune system
attacks mylein
around nerve cells
• Symptoms: loss ability to walk and move,
loss bladder control, paralysis and death

37. What if the immune
system fails?
• Sometimes the immune system collapses
• Ex) HIV
• Virus invades macrophages and helper T
cells
• Without these WBC immune response
will not work
• Body becomes overwhelmed with
pathogens (HIV  AIDS)

38. What if the immune
system fails?
• Sometimes the immune
system overreacts
thinking something is a
pathogen when it is NOT
• Allergy- immune system
response to a non-
pathogenic antigen
• Ex) pollen, food, insect
bite, dust, etc.

39. Steps – Allergic
Reaction
• 1) Pollen inhaled
• 2) cells of nasal
passage called mast
cells release chemical-
histamine
• 3) nearby capillaries
swell- increases fluid
*Allergies are treated
with medication that
contains
antihistamines
(chemical that blocks
histamine)

40. Immune System and
Cancer
• Major function of immune system is to
patrol for cancer cells
• Called Immunological Surveillance
• Killer-T cells can identify, attack, and
destroy cancer cells