Transcript The Immune System

The Immune System
By the end of this class you should
understand:
• The nature and needs of different types of
pathogens
• The major components of our body’s defenses
against infection
• The difference between the two branches of
the immune system
• The process by which the body mounts an
immune response to infection
The Immune System
• The immune system is a vast and
complex network of cells that
protect us from infection by
pathogens
– A pathogen is anything that can
cause illness
• The immune system is often
described in military terms and
includes imagery of violence
– The essential function of the
immune system is to distinguish
self from nonself
• And to destroy the nonself
Pathogen
• A pathogen is anything that
creates (generates) illness
• The two most common pathogens
are bacteria and viruses
• Other pathogens include
protozoans, worms, flukes, fungi,
toxic chemicals, and inanimate
objects such as asbestos fibers
– Even a certain protein, called a prion,
can cause disease by converting your
own proteins to prions!
Bacteria
• Bacteria are free-living organisms
– Satisfy all criteria for being alive,
including having a metabolism and
reproducing
• Most bacteria are entirely harmless
– Die when exposed to oxygen, skin, or
other bacteria
• Our body has colonies of bacteria
that grow on our skin and in our guts
to keep harmful bacteria out
– These are called normal flora and
taking antibiotics can harm these
colonies and render you more
vulnerable to infection!
Virus
• A virus is not alive
• A virus consists of two parts:
a nucleic acid strand that
contains the information for
making more viruses, and a
delivery package of protein
• Viruses convert target cells
into factories for making
more viral protein and
DNA/RNA
Pathogenic Activity
• Every pathogen has its own reasons for
harming the human body
– Some bacteria invade cells to hide from the
immune system
– Many viruses destroy the cells they infect in the
process of making more viruses
– Some bacteria release toxins that harm our tissues
– Many pathogenic bacteria that invade the blood
do so to eat our glucose
Barrier Method
• Our body has a number of
pathogen barriers to prevent
pathogen entry
– Skin is impermeable to almost all
pathogens
– Mucus, saliva, tears and earwax all
contain pathogen-killing molecules
• Most infections begin either with
breaking the skin or
eating/inhaling pathogens that
infect the epithelium of the
throat or digestive tract
Lymphatic Circulation
• Much like the shoulder of the
roads that only police and
construction may drive on, our
blood has a parallel circulatory
system called lymph
• Lymph is blood plasma and white
blood cells, and also picks up
pathogens from the tissues
• Lymph filters through lymph
nodes which are packed with
white blood cells
Immune Tissue
• Immune tissue is tissue filled
with different kinds of white
blood cells
– Lymph nodes filter the lymph
– The spleen filters the blood
– Other organs (appendix,
tonsils, etc) filter other regions
• Note these organs can be
removed, they are not vestigial
but instead are redundant
Innate Immune System
• The innate immune system is one of the two
branches of the immune system
• It is always active
• It targets anything that doesn’t belong in the
body
• It is not sufficient to repel a major infection
– Often compared to police officers (vs. national
guard of the acquired immune system)
Innate Immune Components
• Natural Killer cells
– Destroy malformed cells such as cancer cells and cells
infected with certain viruses
• Phagocytes
– A number of types of cells perform phagocytosis,
which means “cell eating”
– The two major phagocytes are neutrophils and
macrophages
• Complement
– Blood proteins that are toxic to bacteria
Phagocytosis
• Phagocytosis is a threestep process:
1. Detect that something
is foreign (e.g. has
bacterial cell wall)
2. Engulf that thing into
a vesicle
3. Merge that vesicle
with a lysosome
(vesicle containing
lysis enzymes)
Neutrophils
• Neutrophils are the most
common white blood cell in
the body
• They perform phagocytosis
until they die
– Large numbers of dead
neutrophils form pus
• They live primarily in the
bloodstream
• They can access tissues when
the tissue is damaged and
undergoes inflammation
Inflammation
• When tissue is damaged,
histamines are released that
signal the local capillaries to
dilate, causing them to become
leaky
• Additional blood flows to the
larger capillaries
– Four signs of inflammation: calor
dolor rubor tumor
– Heat, pain, redness, swelling
– Aids healing and allows
neutrophils to enter tissues
Inflammation
• Neutrophils are drawn to the
inflammation by the
histamines
• Complement proteins can
also leak into the tissues and
attach to bacteria
• Macrophages are large
phagocytes that live in tissues
– Macrophages can also perform
antigen presentation
Antigen Presentation
• An antigen is a molecule from a
pathogen that the immune
system can respond to
• Antigen presentation is how the
acquired immune system is
activated
• When a macrophage ingests a
pathogen it extracts markers
from the pathogen and places
them in a molecule called MHC2
Antigen Presentation
• A macrophage can migrate
through the lymph to lymph
nodes and present its MHC2
molecules to Helper T Cells
– T cells are trained in a gland called
the thymus
– Helper T Cells are also sometimes
called CD4+ cells because they
express the CD4 receptor
• A Helper T Cell that recognizes
the antigen will “activate” by
cloning itself and releasing signal
molecules
Helper T Cell activity
• Helper T Cells are in control of the
other two types of lymphocytes:
Killer T Cells and B Cells
• Helper T Cells are crucial for this
activation
– The HIV which causes AIDS infects
Helper T Cells, preventing the
acquired immune system from
activating
• Depending on the type of
infection, one or both of the other
lymphocytes will be stimulated
Killer T Cells
• Killer T Cells are also known as
cytotoxic T cells or CD8+ cells
• Killer T cells bind to MHC1
molecules found on all cells
with a nucleus in the body
– MHC1 is an antigen presenting
molecule that collects antigens
from inside the cell
• Any cell infected with hidden
bacteria or viruses are
revealed by the MHC1 and the
cell is killed by the Killer T Cell
B Cells
• B Cells, when stimulated by
the antigen presentation and
Helper T Cell signals, clone
themselves and begin
producing massive amounts
of antibodies
– Antibodies stick to the antigen
in the blood and tissues and
cause them to stick together
– Antibodies are also found in
saliva, tears, etc
Flow of Information
Memory Cells
• When T and B cells are
activated and make
thousands of clones,
some of them become
memory cells
• Memory cells live for
decades, constantly
searching for the same
antigen that activated
them in the first place
– This is why you normally
only get a disease once
Vaccination
• It was noticed in the 19th
century that milk maids never
got smallpox because they
often got cowpox
– Cowpox and smallpox share the
same antigens
• Giving doses of cowpox made
it so the subject would not get
smallpox and became immune
– This was derided as
“encowment”, which in french is
vaccination
Protip:
• VACCINES DO NOT CAUSE AUTISM
• There was a time when vaccines were packaged with
an antiseptic called thimerosal, which is a mercurycontaining compound
– They are no longer packaged as such
• The original study linking vaccines and autism was
discredited, and many scientists have repeated the
experiment but found no statistically significant
difference
• Autism is a developmental disorder and more
prevalent in males, it cannot be caused by an injection
at six months of age
Thanks for coming!
• Wednesday: Chapter 13!