Germ Theory of
• “Microorganisms cause infectious
• Louis Pasteur and Robert Koch did several
experiments to identify disease causing
• Determined that each disease is caused
by a “specific” microorganism
Agents of Disease
• The following types of
organisms can cause
3. Protists (malaria)
• Pathogen is anything
that causes disease.
• 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
4) injected pathogens can be isolated from newly
infected individual and are identical to original
Koch’s Experiment- Germ
• Koch’s postulates are very important because
they are the basic steps for identifying, curing,
and preventing specific diseases.
What is a system?
• A group of tissues (organs) work together
to do a task.
• Ex) digestive system, circulatory system,
• Function of the immune system is to
protect body from invasion by pathogens.
Overview of Body’s
Non-Specific Defenses Specific Defenses
First Line of Defense Second Line of
Skin and Mucous Inflammatory
• Similar to “walls of a fort” protect by keeping
pathogens out of body
• Body does NOT distinguish one pathogen from
• Your body has several non-specific defenses…
1) External- skin and mucous membranes
2) Internal- Inflammatory response
• Physical barrier
• Chemical barrier-
secretes oil and
sweat (lowers pH
skin), tears (contain
lysozyme), and saliva
• Sheds constantly
(1 million cells per
• Skin contains natural
openings (nose, mouth,
• These areas are lined by
• Secrete mucus traps
• Areas lined with cilia
• Any pathogens make it
past, may be killed by
• 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
“What if pathogens get
• White blood cells take over and specifically identify and
eliminate the pathogen.
• White blood cells = “soldiers”
• Immune Response
Organs of the Immune
White blood cells
Made thymus and
spleen, and lymph
How does your body
there is an invader?
• All pathogens have “distinct” antigens.
• Antigens are marker proteins- trigger immune
• Your body must recognize antigens in order to
identify and defeat the pathogen.
• Normal cells also have antigens.
• 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
• 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
• What happens if a pathogen makes it
past the first lines of defense and avoids
the inflammation response?
• Your body must “actively” fight the
• This takes time.
• This requires a special group of white
blood cells lymphocytes.
• Many types of WBC
work together during
the immune response to
fight the infection.
• 3 major classes of
1) B-cells (plasma cells)
-Helper T cells
-Killer T cells
-Suppressor T cells
3) Memory cells
Step #1 “Invader
• 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.
• Helper T cells release interleukin 2 – signals
help other leukocytes (other T-cells and B-cells)
Step #2 “Cloning
• B cells make antibodies - lock onto
antigens.“Marked for death.”
• Killer T cells kill infected body cells.
Step #3 “The Attack Phase”
Step #3 “The Attack
• Macrophages clean up- eating pathogens,
damaged body cells, etc.
• Suppressor T cells “call off the troops” stopping
the immune response.
Step #4 “Memory
• Memory cells “remember” the attack and
recognize a pathogen if it re-enters body.
• Primary vs. secondary immune response
Active vs. Passive
• 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
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
If the key fits the lock = bad!!!
Blood Transfusions and the Immune
• Blood cells have marker proteins or
Organ Transplants and the
• Foreign organs also have marker
• If recognized as “foreign” = REJECTION.
• Doctors must “match” a new organs
marker proteins to the patients.
• Drugs can help suppress the immune
What if the immune
• 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
• Person’s immune system attacks various
organs or cells of the body (skin, joints,
kidneys, heart, and lungs) causing
• Lupus is a multi-system disease because
it can affect many different tissues and
organs in the body.
• 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
• Immune system
around nerve cells
• Symptoms: loss ability to walk and move,
loss bladder control, paralysis and death
What if the immune
• Sometimes the immune system collapses
• Ex) HIV
• Virus invades macrophages and helper T
• Without these WBC immune response
will not work
• Body becomes overwhelmed with
pathogens (HIV AIDS)
What if the immune
• Sometimes the immune
thinking something is a
pathogen when it is NOT
• Allergy- immune system
response to a non-
• Ex) pollen, food, insect
bite, dust, etc.
Steps – Allergic
• 1) Pollen inhaled
• 2) cells of nasal
passage called mast
cells release chemical-
• 3) nearby capillaries
swell- increases fluid
*Allergies are treated
with medication that
(chemical that blocks
Immune System and
• Major function of immune system is to
patrol for cancer cells
• Called Immunological Surveillance
• Killer-T cells can identify, attack, and
destroy cancer cells