Download 11.1 Immunity Notes - Twanow

How do your body systems protect you
from infection and disease?
11.1 Defense Against Infectious Disease
Learning Targets: Describe blood clotting,
challenge and response, clonal selection,
and memory cells. Explain the principle of
vaccination.
Nonspecific Defenses:
• External defenses – skin
and mucus membranes
– Act as a barrier, trap
foreign materials
– Low pH (such as in
stomach) and secretions
(ex. lysozyme in tears) kill
some pathogens
• Internal defenses –
phagocytic cells
(white blood cells that
eat invaders)
– Phagocytes or
macrophages may
circulate or stay in
one tissue – they
catch microbes with
long pseudopodia,
and engulf pathogens
• Blood Clotting
– Use the video clip
to put the steps in
the correct order
• Blood Clotting
– Initiated by
chemical signals
released by
damaged cells
– Platelets adhere to
the damaged area
and begin to plug
the opening
• Blood Clotting
– Tissues and
platelets release
chemicals that
convert prothrombin
to thrombin
– Thrombin converts
fibrinogen into fibrin
which creates a
supportive mesh to
stabilize the clot
Why are the defenses above called
nonspecific?
• These defenses respond to microbes or
“invaders” in general, not specific to any
bacteria, virus, or fungus.
Lymphatic System – circulates fluid and
white blood cells back to blood
• Organs of the lymphatic system include
the lymph nodes and spleen, which trap
“invaders”
Lymphatic System – circulates fluid and white
blood cells back to blood
• The lymphatic system also includes the bone
marrow and thymus, where lymphocytes mature
Why does the doctor feel your lymph nodes
during a regular checkup?
• Lymph nodes swell when the body is
fighting disease, as the white blood cells in
lymph nodes multiply to catch diseasecausing invaders (pathogens)
Specific Defenses:
• Involve lymphocytes (other specialized white
blood cells) responding to antigens
• Lymphocytes include B cells and T cells
– Antigens = “antibody generators,” (ex. bacteria,
viruses, fungi, cancer) - anything that causes B cells to
produce antibodies
– Antibodies are proteins that bind antigens to help the
immune system destroy them
• Each B cell and T cell has membrane receptors
for one specific antigen
• In your blood cells, a type of recombination
leads to millions of unique B cells and T cells so
your body can respond to millions of different
antigens
• Challenge and Response
– A pathogen challenges the immune system and is
eaten by a phagocyte
– Parts of the pathogen (antigens) are presented
on the surface of the cell
– A helper T cell with receptors that match that
antigen is activated to start the immune response
• Clonal Selection
– Helper T cells and B cells
that match the specific
antigen (invader) are cloned
– Activated B cells divide and
produce plasma cells and
memory cells
– Plasma cells produce
antibodies that attach to and
mark antigens
– Memory cells activate the
immune system quickly next
time the antigen appears
Why are the defenses above called specific?
• Each lymphocyte (B cell or T cell)
recognizes one specific antigen, so
responds to one specific pathogen
(bacteria, virus, fungus, etc). Each B cell
and T cell has unique receptors on its
membranes to recognize an antigen.
Immune Response
• Primary response – first exposure to an antigen
– Response is 10-17 days while your body goes
through clonal selection
– You may get sick in the “lag time” while your body
multiplies B and T effector cells to combat the
disease-causing antigen
• Secondary response – subsequent exposures to
an antigen
– Response is 2-7 days; your body makes more
effectors cells than in a primary response, and
antibodies/cells have a higher affinity for the antigen
– You won’t get sick because your body remembers
how to fight effectively
How is the difference between primary and
secondary response related to vaccines?
• We use vaccines – a dead or non-pathogenic
version of a disease-causing microbe – to
expose our bodies to the antigen. Our bodies go
through a primary response and create memory
cells. If we are exposed to the disease-causing
pathogen, our bodies respond quickly
(secondary response) and we don’t get sick.
• Active vs. Passive Immunity
Immunity due to
antibodies acquired from
another organism through
the placenta, colostrum, or
injection
Immunity due to
antibodies produced by
the organism itself after
challenge and response
to a pathogen
• Polyclonal vs Monoclonal Antibodies
Many B cells are
activated and divide in
response to various
antigens on the surface
or one pathogen. Many
types of antibodies are
produced.
A specific B cell is
isolated in laboratory
culture to divide and
produce one type of
antibody.
• Monoclonal
antibody
production
• Monoclonal antibody
production
– A lab animal is injected
with an antigen
– The activated B cells are
removed from the spleen
– The B cells are fused with
tumor cells
(=hybridomas)
– These hybrids are tested
for antibody production
– The desired cells are
cultured to produce the
antibody
• Monoclonal antibody uses
– Pregnancy tests – antibodies to
hcg (pregnancy hormone) are
fused to an enzyme that changes
color if antibodies bind the
hormone
– Cancer treatment – how do you
think antibodies could be used to
fight cancer cells?
• Monoclonal antibody uses
– Pregnancy tests – antibodies to
hcg (pregnancy hormone) are
fused to an enzyme that changes
color if antibodies bind the
hormone
– Cancer treatment – antibodies
could potentially target cancer cell
markers and carry toxins to tumors
Self-Recognition
• Your immune system must recognize your
own cells so it won’t attack them
• MHC (major histocompatibility complex)
molecules are important self markers
– MHC molecules bind antigens inside white blood cells
and present them on the surface to activate immune
responses
Self-Recognition
– MHC genes affect which antigens your MHC
molecules bind, so which antigens your
immune system can respond to
– Summarize the dirty T-shirt study and its evolutionary
explanation.