CHAPTER 24
The Immune System
Pathogens
• Disease causing agents
such as bacteria,
viruses, fungi,
protozoans, and other
parasites. ( NOT all
microorganisms are
pathogens)
Transmission of disease
• Pathogens can be
transmitted to a host from
reservoirs in four main
ways: by direct contact, by
an object, through the air,
or by an intermediate
organism called a vector.
Immune System
• Bodies primary defense against pathogens
• Three cooperative lines of defense have evolved to
counter these threats.
– Two of these are nonspecific - that is, they do not
distinguish one infectious agent from another.
1st line: Physical Barriers
• non-specific defense
• external barriers
– skin & mucus membranes
– excretions
•
•
•
•
•
sweat
stomach acid
tears
mucus
saliva
– “lick your wounds”
Lining of
trachea:
ciliated cells &
mucus secreting
cells
2nd: Generalist, broad range patrols
• Patrolling white blood cells
– attack invaders that get through the skin
• recognize invader by reading antigen
– surface name tag
– phagocyte cells
• macrophages
• “big eaters”
Macrophage “eating”
bacteria
Lymph system
Production of white blood cells
& traps “foreign” invaders
lymph vessels
(intertwined amongst blood vessels)
2nd “circulatory” system
lymph node
The lymphatic system becomes a crucial
battleground during infection
• a network of lymphatic
vessels and organs
– It returns tissue fluid to the
circulatory system
– It fights infections
• Lymph nodes are key sites
for fighting infection
– They are packed with
lymphocytes and
macrophages
Phagocytes
• Macrophages wander in
the interstitial fluid
– They “eat” any bacteria
and virus-infected cells
they encounter
Phagocytes
macrophage
bacteria
white blood cells that eat
macrophage
yeast
Antimicrobial Proteins
• Interferons: acts in warning other cells of a
viral invasion
• Complement: help attract phagocytes to
foreign cells and help destroy foreign cells
Natural Killer cells
• A type of white blood cell that destroy the
body's own infected cells, may attack cells that
form tumors
The inflammatory response mobilizes
nonspecific defense forces
• Tissue damage triggers the inflammatory response (redness,
swelling, warmth, pus) injured cells release chemical signals
• histamines
– increases blood flow
– brings more white blood cells to fight bacteria
– brings more red blood cells & clotting factors to repair
• The inflammatory response can
– disinfect tissues
– limit further infection
Fever
• When a local response is not enough
– full body response to infection
– raises body temperature
– higher temperature helps in defense
• slows growth of germs
• helps macrophages
• speeds up repair of tissues
SPECIFIC IMMUNITY~ 3rd line of
defense
• IMMUNE RESPONSE
a recognition system that distinguishes “self”
from “non-self”
• responds to foreign molecules called antigens
• Stimulates the body to make antibodies:
specific defensive proteins which help to
counter antigens in various ways
How are invaders recognized?
• Antigens
– chemical name tags on the surface of
every cell
• “self” vs. “invader”
one of your
own cells
antigens say:
“I belong here”
disease-causing
virus
disease-causing
bacteria
antigens say:
“I am an invader”
antigens say:
“I am an invader”
Immunity=protection afforded to an organism
by previous exposure to an antigen
•
1.
2 types:
Active: long term, conferred
by actual encounter with
infection (naturally acquired)
or vaccination *(artificially
acquired)
* vaccine~ substance consisting of
weakened, dead, ,or parts of
pathogen or antigen that when
injected , stimulates the immune
system
Immunity
2. Passive: short term,
antibodies passed on,
not stimulated by
antigens,
acquired naturally by
placenta or breast milk
or artificially acquired
by a shot
Immune Response ~ 3rd line of defense
• Governed by 2 different parts of the immune
system
• 1. Humoral Immunity: results in the
production of antibodies
• 2. Cell-mediated Immunity: defensive
activities are carried out by specialized cells
circulating around the body
Lymphocytes ~type of white blood cell that carry
out the immune response
• Two kinds
– B cells secrete antibodies
that attack antigens
(humoral immunity)
– T cells attack cells
infected with pathogens
(cell-mediated immunity)
B lymphocyte
The initial immune response results in a type of
“memory”
• primary immune response produces memory cells
– These cells may confer lifelong immunity
When memory cells are activated by subsequent exposure to an antigen,
they mount a more rapid and massive secondary immune response
Humoral Immune Response
• Triggered by a specific antigen, a B cell
differentiates into a plasma cell
-The plasma cell secretes antibodies
Antibodies are the weapons of humoral
immunity
• An antibody molecule
has antigen-binding
sites specific to the
antigen
• Do not posses the
power to destroy
antigens directly, tag
and mark them for
destruction by a variety
of mechanisms
B cells & antibodies
• B cells
– white blood cells that attack
invaders in blood
– mature in Bone marrow
• Patrolling B cells
– make antibodies against invader immediately
• Memory B cells
– remembers invader
– can make antibodies quickly the next time
• protects you from getting disease more than once
Y
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Y Y
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memory
B cells
“reserves
Y
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Y Y
Y
Y
”
Y
10 to 17 days
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recognition
B cells
Y
release
antibodies
patrol blood
forever
Y
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Y
B cells
Y
Y
(foreign antigen)
Y
invader
Y
Y
B cells immune response
Y
What if the attacker gets past
the B cells in the blood &
infects some of your cells?
You need trained assassins to kill
off these infected cells!
T
2006-2007
Attack
of the
Killer T cells!
T cells
• T cells mature in Thymus
• Helper T cells
– sound the alarm for rest
of immune system
• Cytoxic or Killer T cells
– destroy infected body cells
• Memory T cells
– remembers invader & reacts against
it again quickly
Where’s that?
Cell-Mediated Immunity
• An antigen-presenting cell (APC) first displays a
foreign antigen and one of the body’s own self
proteins to a helper T cell
• The helper T cell’s receptors recognize the selfnonself complexes on the APC
- The interaction activates the helper T cells
– The helper T cell can then activate cytotoxic T cells with
the same receptors
– Helper T cells also stimulate the humoral responses
• Cytotoxic T cells( or Killer T cells) bind to infected
body cells and destroy them
Attack of the Killer T cells
• Killer T cells destroy infected body cells
– T cell binds to invaded cell
– secretes perforating protein
• punctures cell membrane of infected cell
• cell bursts
Killer T cell
vesicle
cell
membrane
Perforin
punctures
cell membrane
cell
membrane
invaded cell
Cytotoxic T cells (Killer T) may help prevent
cancer
– The surface molecules of
cancer cells are altered
by the disease
Immune response
invader
skin
invaders in body
invaders in blood
skin
invaders infect cells
macrophages
helper
T cells
B cells
Y
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Y
Y antibodies
Y
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Y
memory
T cells
Y
Y
Y antibodies
Y
Y
Y
Y
Y
Y
Y
memory
B cells
Y
patrolling
B cells
T cells
killer
T cells
The immune system depends on our
molecular fingerprints
– “Self” is signaled by major histocompatibility
complex (MHC), a group of proteins unique to
the individual that is present on the surface of
cells
• Can cause rejection of transplanted organs
DISORDERS OF THE IMMUNE SYSTEM
• Autoimmune diseases
– The system turns against
the body’s own
molecules
– Examples: Rheumatic
fever, Type I Diabetes,
Multiple Sclerosis,
Rheumatoid arthritis,
Lupus
Rheumatoid arthritis
DISORDERS OF THE IMMUNE SYSTEM
• Immunodeficiency
diseases
– Immune components
are lacking, and
infections recur
Ex: Acquired immune
deficiency syndrome
(AIDS)
SCIDS
HIV on a
lymphocyte
AIDS
– HIV (Human
Immunodeficiency
Virus) the virus that
causes AIDS
– HIV is transmitted
mainly
in blood and semen
– HIV kills helper Tcells and leads to
AIDS
DISORDERS OF THE IMMUNE SYSTEM
• Allergies are overreactions
to certain environmental
antigens called
allergens : Ex. Animal dander,
dust mites, pollen
release of histamine causes
symptoms
Antihistamines can relieve
symptoms
anaphylactic shock: life
threatening reaction to
injected or ingested
allergens.