The Immune System
Germ Theory
• Germ theory proposes that microorganisms cause diseases (not
spirits, as once believed).
– Proposed by Louis Pasteur
– Led to rapid advances in understanding disease
• Supported by Koch’s postulates.
– Disease-causing agents, or particles, are called pathogens.
There are different types of pathogens
• Bacteria are single-celled organisms:
– Cause illness by destroying cells, release
toxic chemicals
– Ex: Food poisoning, MRSA
• Viruses are genetic material surrounded
by a protein coat:
– Force host cells to make more viruses, small
– Ex: Flu, Cold, HIV
• Fungi can be multicellular or single-celled:
– Take nutrients from host cells by piercing healthy cells
– Occur in warm and damp places
– Ex: Athlete’s foot
• Protozoa are single-celled organisms.
– Use host cells to complete their life cycles
– Take nutrients from host cell
– Ex: Malaria
Review: Parasite
• Pathogens can be transferred by indirect or direct contact.
• Indirect contact does not require touching an infected
individual.
– Touching an infected
surface
– Breathing in infected
air
• Vectors :Carry a pathogen and transmit into
healthy cells
– Ex: Insects (ticks, mosquitoes, fleas), food
• Direct contact requires touching an infected individual.
– Includes:
• Kissing
• Sexual intercourse
• Hand shaking
tick
Many body systems protect you from
pathogens
• The immune system is the body system that fights off
infection and pathogens.
• Many other tissues and systems help the immune system.
– Skin is the (first) physical barrier to infection.
– Mucous membranes trap pathogens entering the body.
– The circulatory system transports immune cells.
Cells and proteins fight the body’s infections
• White blood cells attack infections
inside the body.
– Phagocytes engulf and destroy
pathogens.
– T cells destroy infected cells.
– B cells produce antibodies, which
deactivate the pathogen.
3 types of proteins fight off
invading pathogens
– Complement proteins weaken pathogen
membranes.
– Antibodies make pathogens ineffective.
– Interferons prevent viruses from infecting
healthy cells.
pathogens
antibody
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5
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Immunity prevents a person from getting
sick from a pathogen
• In all types of immunity, pathogens are
destroyed before you get sick.
– Passive immunity occurs without
an immune response.
• Mother’s milk
• Genetics
– Active immunity occurs after a
specific immune response.
• Having chicken pox
– Acquired Immunity occurs after
given a vaccine.
• Flu shot
Antibiotics and antiseptics cause pathogens to burst
• Antiseptics kill pathogens
outside of the body
– Do not target specific
pathogens
– Ex: Vinegar, Soap, Rubbing
Alcohol, Purel
• Antibiotics kill pathogens
inside the body.
– Target one specific bacterium
or fungus
– NOT effective against viruses
• Overuse and misuse of antibiotics can cause medicines to
become ineffective.
– Some bacteria in a population have genes that make them
immune to antibiotics.
– These bacteria spread the gene, making the antibiotics
useless.
A bacterium carries
genes for antibiotic
resistance on a plasmid.
A copy of the plasmid is transferred
through conjugation.
Resistance is quickly
spread through
many bacteria.
• Vaccines control pathogens and disease
– Injected with antibodies that have been exposed to the
pathogen.
• Gives instant but short- term protection.
– Given mild or dead version of the pathogen.
• Your body makes the antigens itself for long-term protection.
• Memory B cells stay for a long time, ready for another attack from
the same organism.
How a vaccination provides immunity
– Stimulates a specific
immune response
– Causes memory cells
to be produced
– Allows immune
system to respond
quickly to infection
– Has a fast response, a
person will not get
sick
1
memory B cells
Antigens in a vaccine
trigger an immune
response, and memory B
cells are made.
2
A memory B cell is
stimulated when the
real pathogen binds to
it.
3
The B cell quickly activates
and makes antibodies that
fight the pathogens before
you get sick.