Chapter 35: Immune System &
Disease
Ms. Luaces
Honors Biology
Pathogens
35.1 Infectious Disease
• Pasteur & Koch came up with
the germ theory of disease:
infectious diseases occur when
microorganisms cause
physiological changes that
disrupt normal body function
– Can be caused by viruses,
bacteria, fungi, protists and
parasites
– Except for parasites, all others
known as pathogens
35.1 Infectious Disease
• Koch’s Postulates:
– 1. Pathogen must always be
found in sick body but not
healthy body
– 2. Pathogen can be isolated &
grown in lab
– 3. If pathogen infects healthy
host, should produce sickness
– 4. Pathogen can be isolated from
new host & looks identical
35.1 Infectious Disease
• What’s the different between a symbiont
and pathogen?
– Symbionts are either harmless or beneficial
– Pathogens destroy host cells, release
poisons, block blood flow, and take up hosts
nutrients
35.1 Infectious Disease
• Diseases spread through coughing,
sneezing, physical contact, exchange of
body fluids, contaminated
water/food/animals
35.1 Infectious Disease
• Natural selection favors pathogens with
adaptations that help them spread from
host to host
– Coughing, sneezing, body-to-body contact,
sexual activity, drug usage, poor sanitation
– Best way to avoid infection is to constantly
wash your hands!
35.1 Infectious Disease
• Those pathogens that thrive in both
human and animal hosts are known as
zoonosis
– West Nile virus, Mad cow disease, Lyme
disease, Ebola
– Carriers of the disease who don’t get sick
are known as vectors
Let’s Practice!
• Pg. 475 – 476
• Q&A
• Work with a buddy – one sheet of paper
for both of you!
35.2Nonspecific Defenses
• Include skin, tears and other secretions,
inflammatory response, interferon's and
fever
– First line of defense: skin, which is the most
widespread defense
35.2Nonspecific Defenses
• Pathogens can enter through the mouth,
nose or eyes which are protected by
saliva, mucus and tears
– Contains lysozyme which breaks down
bacterial cell walls
– Stomach secretions (acid) also protect
35.2Nonspecific Defenses
• Second line of defense includes
inflammatory response, interferon's, and
fever
35.2Nonspecific Defenses
• Inflammatory response causes areas to
become red and painful because of
histamines (release by mast cells to
increase flow of blood and fluids to the
area)
– White blood cells (phagocytes) will then
engulf and destroy bacteria
35.2Nonspecific Defenses
• Interferon's inhibit synthesis of viral
proteins
– Aka “interfere” with viral growth, slowing
down the production of new viruses
35.2Nonspecific Defenses
• Fever increases body temperature to
slow down or stop the growth of some
pathogens
– Sometimes also speeds up several parts of
the immune response
35.2 Specific Defenses
• Specific defenses distinguish between
“self” and “other” and inactivate / kill
any foreign substance or cell that enters
the body
– Nonspecific = general threat
– Specific = particular pathogen
35.2 Specific Defenses
• Recognizes specific chemical markers on
own cells – own secret password
– If the marker is not recognized, will attack
and remember it for later as “non-self” so
that it can kill it quickly if it enters the body
again: immune response
35.2 Specific Defenses
• Antigens are any foreign substances that
can stimulate an immune response
– Found on the outer surface (the “flag”)
– Immune responds by increasing # of cells to
attack or produce proteins called antibodies
35.2 Specific Defenses
• Antibodies tag antigens for destruction
by immune cells (the “alert!!”)
• The shape of each antibody allows it to
bind to only one antigen – very specific
35.2 Specific Defenses
• Main working cells of the immune system
are
– B lymphocyte cells: grow and mature in red
bone marrow; have antibodies on them;
attack in body fluids
– T lymphocyte cells: grow in red bone
marrow but mature in thymus; have to be
presented with antigen to attack
35.3 Fighting Infectious Disease
• Vaccination: injecting a weakened form
of a pathogen, or of a similar but less
dangerous pathogen, to produce
immunity
– Jenner
35.3 Fighting Infectious Disease
• Vaccination stimulates the immune
system with an antigen. The immune
system produces memory B cells and T
cells that quicken and strengthen the
body’s response to repeated infection
35.3 Fighting Infectious Disease
• 2 types of immunity:
– Active: natural / deliberate exposure to
antigen
– Passive: antibodies are produced by other
individual or animal and passed through
pregnancy, breast milk, or injection (only
gives TEMPORARY immunity)
35.3 Fighting Infectious Disease
• 1900 – 30% deaths related to infectious
diseases
• 2005 - <5% deaths “ “
• How? Public health has prevented disease
by monitoring & regulating food and water,
providing vaccinations, and promoting
healthy behaviors
35.3 Fighting Infectious Disease
• Antibiotics can kill bacteria (but CANNOT
kill viruses) and some antiviral
medications can slow down viral activity
– Alexander Fleming – discovered first
antibiotic, penicillin
35.3 Fighting Infectious Disease
• We had mostly wiped out polio in the
U.S. & eliminated smallpox globally, but
now it’s back! Why?
– Human / animal interaction
– Misuse of medications leads to resistance by
pathogens