Transcript Chapter 36 - Immune System

#36 (pg. 722 – 736)
Chapter
Immune System
Guarding against disease
Ouch!
Specific defenses
• Specific defenses are those that give us
immunity to certain diseases.
• In specific defenses, the immune system
forms a chemical “memory” of the
invading microbe. If the microbe is
encountered again, the body reacts so
quickly that few or no symptoms are felt.
Major players
• The major players in the immune system
include:
• Macrophage (WBC – engulf antigens)
• T cells (helper, cytotoxic, memory) - wbc
• B cells (plasma, memory) - antibodies
• Antibodies
Some vocabulary:
• Antibody: a protein produced by the human
immune system to tag and destroy invasive
microbes.
• Antibiotic: various chemicals produced by
certain soil microbes that are toxic to many
bacteria. Some we use as medicines.
• Antigen: any protein that our immune system
recognizes as “not self.”
Antibodies
• Antibodies are
assembled out of
protein chains.
• There are many
different chains that the
immune system
assembles in different
ways to make different
antibodies.
Antigen recognition
• Cells of the immune system are “trained” to
recognize “self” proteins vs. “not self” proteins.
• If an antigen (“not self”) protein is encountered
by a macrophage, it will bring the protein to a
helper T-cell for identification.
•
If the helper T-cell recognizes the protein as
“not self,” it will launch an immune response.
Helper T cells
• Helper T-cells have receptors for
recognizing antigens. If they are
presented with an antigen, they release
cytokines to stimulate B-cell division.
• The helper T-cell is the key cell to signal
an immune response. If helper T-cells
are disabled, as they are in people with
AIDS, the immune system will not
respond.
B cells
• B-cells in general produce antibodies. Those
with antibodies that bind with the invader’s
antigen are stimulated to reproduce rapidly.
• B-cells differentiate into either plasma cells
or memory B-cells. Plasma cells rapidly
produce antibodies. Memory cells retain the
“memory” of the invader and remain ready
to divide rapidly if an invasion occurs again.
Clonal Selection
Role of antibodies
• Antibodies released into the blood
stream will bind to the antigens for which
they are specific.
• Antibodies may disable some microbes,
or cause them to stick together
(agglutinate). They “tag” microbes so
that the microbes are quickly recognized
by various white blood cells.
“Killer” T cells
• While B-cells divide and differentiate, so
do T-cells.
• Some T-cells become cytotoxic, or “killer”
T-cells. These T-cells seek out and
destroy any antigens in the system, and
destroy microbes “tagged” by antibodies.
• Some cytotoxic T-cells can recognize
and destroy cancer cells.
Calling a halt
• When the invader is destroyed, the
helper T-cell calls a halt to the immune
response.
• Memory T-cells are formed, which can
quickly divide and produce cytotoxic Tcells to quickly fight off the invader if it is
encountered again in the future.
Helping the immune system
• Medical science has created to systems
for augmenting the human immune
system:
• Antibiotics
• Vaccines
How antibiotics work
• Antibiotics help destroy bacteria (but not
viruses).
• Antibiotics work in one of several ways:
• Slowing bacteria reproduction.
• Interfering with bacterial cell wall
formation.
Antibiotic myths
• Antibiotics are not antibodies.
• Antibiotics do not weaken our immune system.
They help it by weakening bacteria.
• Humans do not become “immune” to antibiotics.
Bacteria that resist antibiotics and are not
completely destroyed may multiply, producing
more antibiotic-resistant bacteria.
Vaccine history
• Variolation: The deliberate inoculation of
people with secretions from smallpox (Variola)
sores. Used for centuries in Asia and Africa.
• Vaccination: Invented by Edward Jenner in
1796. Jenner knew that dairy maids who had
contracted cowpox never got smallpox. He
inoculated a boy with secretions from cowpox
sores, and showed the boy was immune to
smallpox. (From vacca, Latin for cow.)
How vaccines work
• Modern vaccines are created from killed
bacteria or viruses, or fragments of
proteins from these microbes.
• The proteins are recognized as antigens
by our immune systems. This causes a
mild immune response. Memory T-cells
and B-cells remain ready to fight off the
illness if it is encountered again.
Vaccine myths
• The flu vaccine does not give you the flu. Some
people get the vaccine too late, or catch a cold
and think they have the flu.
• Vaccines are not less effective than a “natural”
infection with the illness. The immunity is the
same, and a mild response to a vaccine is much
less risky than a full-blown infection of measles.
• Many myths exist about the safety of vaccines.
Vaccine risks are actually very slight.
But I caught a cold... again!
• Because there are over 100 different
known rhinoviruses, it’s possible to catch
colds again and again.
• In addition, cold viruses can mutate
quickly. No sooner do we have immunity
to one form than along comes another.
Echinacea?
• Echinacea is supposed to
“strengthen” the immune
system.
• Studies in petrie dishes
showed Echinacea
stimulated white blood
cells to produce more
virus-killing peroxides, but
controlled human trials
have found no significant
effects.
Evolution of the flu
• Flu viruses also mutate quickly.
• The same form of the flu may have the
ability to infect several different
vertebrate animals.
• Different forms may hybridize their
genetic material, causing new strains to
develop in a single generation.
New Flu
Allergies
• Allergies are an immune system reaction
to harmless antigens.
• Some, such as pollen, may get in
through the respiratory system.
Fragments of food proteins may get
through the digestive system.
• The next time these proteins are
encountered, the immune system attacks
them.
Achoo!
• Pollen is a harmless
protein, yet we can
become allergic to it.
• Most of the symptoms
are caused by
histamines released by
mast cells. That is why
antihistamines are used
to treat allergies.
Autoimmune disorders
• Autoimmune disorders occur when the
immune system fails to recognize a
protein as “self” and launches an attack.
• Multiple sclerosis, lupus, and rheumatoid
arthritis are examples. None of these can
be cured, but they can be controlled with
drugs.
Cancer
• Cancer occurs when the mechanisms that
control cell division fail, and body cells divide out
of control.
• Cytotoxic T-cells can recognize and destroy
these cells. But if division is too rapid, the T-cells
cannot keep up.
• Some cancer research involves assisting
cytotoxic T-cells in recognizing and destroying
cancer cells.
SCID
• Severe Combined Immune Deficiency is a
genetic condition in which one or more genes
for proteins crucial for the immune system are
defective. Children born with SCID have no
immune system.
• Gene therapy has been used to inject a good
copy of the defective gene into blood cells or
bone marrow cells. In several cases this has
been effective, though it is still experimental.
AIDS
• AIDS (Acquired Immune Deficiency Syndrome)
is caused by an infection by the HIV (Human
Immunodeficiency Virus), which attacks and
destroys T-helper cells. Because it attacks the
immune system directly, finding a vaccine has
been difficult.
• Some drugs can slow down HIV reproduction,
but no cure exists yet. Prevention is still the best
“cure.”