V] THE HEALTHY IMMUNE SYSTEM

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V THE HEALTHY IMMUNE SYSTEM
A. Non-specific Mechanical Defenses
1a. In order to cause a disease, microorganisms
must first enter the enchanted forest in some
way.
b. The skin protects us from surface pathogens.
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2a. Tears, saliva and mucus help wash away
pathogens
b. and contain mild bactericidal
(bacteria-killing) chemicals.
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c. If pathogens enter through the air way they
are trapped in a layer of mucus.
d. They may be removed through the continuous,
wave- like motion of cilia, moving dirty mucus up
to where it can be swallowed, coughed or
sneezed.
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B. Non-specific Innate Immune Responses
1a. several types of leukocytes (white blood
cells) that attack and eliminate anything they
recognize asforeign.
b. macrophages will engulf or eat the invading
cells
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c. neutrophils will surround invading cells
release lysozymes that destroy the invader
themselves
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2. inflammation causes more fluid in an area
which allows the entry of other immune cells and
chemicals into the infected area and helps
contain the infection
3. fever raises body temperature over 40oC which
is less favorable to viral replication
4. interferon (a chemical released by a
virus-infected cell), signals neighboring cells
to produce antiviral substances
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5. complement (a cascade of 20 anti-infective
proteins) released when the first protein in the
cascade contacts the cell wall of certain
bacteria and fungi
a. the complement may surround and smother an
invader
b. the complement may puncture the cell
membrane of the invader
c. the complement may tag the invader and
attract a macrophage
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C. Specific Immune Responses
1. Cell-mediated immunity by T-Cells
a. They are called T cells because they
mature in the thymus, high in the chest behind
the breastbone.
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b. The process starts when a macrophage engulfs
the invader and processes an antigen a specific
surface component of the pathogen, usually a
protein.
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c. The macrophage displays the antigen
fragments combined with a Major
Histocompatibility Complex MHC protein on the
macrophage cell surface.
MHC protein
processed antigen
antigen
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d. A receptor on a circulating, resting helper
T cell recognizes the antigen-protein complex
binds to it.
T-cell receptor
Helper-T-cell
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e. The binding process causes the helper T cell
to activate the cytotoxic T cell or Killer T
cell so that it can attack and destroy the
diseased cell. The killer T cell does NOT attack
the pathogen.
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f. The helper T cell also releases lymphokines
which attract other T cells and B cells
g. The body also releases suppressor T cells
that will calm the body and shut off the immune
response.
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MHC protein
MHC protein__
Killer-T-cell
Activated helper-T-cell
Infected cell
Activated killer-T-cell
Cell dies
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MHC protein
MHC protein__
helper-T-cell
Activated helper-T-cell
Infected cell
Activated killer-T-cell
Cell dies
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2. Humoral response B cells
a. B-cells are lymphocytes that grow to
maturity in the bone marrow
b. B-cells produce antibodies that circulate
in the blood and lymph streams and attach to
foreign antigens to mark them for destruction
by other immune cells.
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c. Antibodies are proteins with the same basic
Y shape but with a special region that is highly
specific to target a given antigen.
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d. The variety of antibodies is very large.
Different antibodies are destined for different
purposes.
i Some coat the foreign invaders to make them
attractive to the circulating scavenger cells,
phagocytes, that will engulf an unwelcome
microbe.
ii Some antibodies combine with antigens and
activate a cascade of nine proteins, known as
complement, that have been circulating in
inactive form in the blood. Complement helps
destroy foreign invaders and remove them from
the body.
iii Still other types of antibodies block
viruses from entering cells.
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e. The final group of B cells are the B memory
cells that retain the information about the
geometry of an antigen so that on a subsequent
exposure, the body will recognize the invader
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f. Activation of B cells to make antibody
The B cell uses one of its receptors to bind to
its matching antigen, which the B cell engulfs.
antigen
B-cell
MHC protein
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The B cell then displays a piece of the antigen,
bound to a MHC protein, on its cell surface.
MHC protein
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This whole complex then binds to an activated
helper T cell.
activated helper-T-cell
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This binding process stimulates the
transformation of the B cell into an
antibody-secreting plasmacell.
plasma cell
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Remember some key points
A. Non-specific defenses
1. Mechanical barriers
skin, tears, mucous
2. Innate
macrophages, neutrophils, fever, inflammation,
interferon, complement
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B. Specific responses
1. T -cells
macrophages, antigens, helper-T-cells,
killer-T-cells, suppressor-T-cells
2. B-cells
macrophages, antigens, helper-T-cells, B-cells, B
memory-cells
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D. PROBLEMS IN THE IMMUNE SYSTEM
1. ALLERGIES
a. a foreign protein is recognized as an invader
and the body responds to its presence
b. basophil cells WBC release histamine
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c. histamine makes capillaries more permeable
to allow WBC to leave find invaders
d. as an indirect result tissues swell this
may be annoying or even life threatening
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2. AUTOIMMUNE DISEASES
a. the self / non-self system breaks down
self antigens are treated as non-self
b. this is usually the result of an injury to
specific cells and does not affect all self
proteins
c. or it is possible that a few killer T cells
attack your cells and suppressor T cells fail to
control them
d. either way, when the suppressor T cells do
not control self attacks ? autoimmune disease
e. eg. type I diabetes your own killer T
cells attack your beta cells in the Islets of
Langerhans multiple sclerosis you attack your
own myelin sheath cells
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3. Leptin effect on immune system
a. Fat cells secrete leptin
b. Leptin suppresses the B-cell response
c. People with more body fat secrete more leptin
d. Therefore, people with more body fat have
a suppressed immune system
e. These people will heal more slowly after
surgery
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F. PASSIVE ACTIVE IMMUNITY
1. Passive immunity
a. direct passage of antibodies into a person
b. placenta passes antibodies into baby from
the mother
c. colostrum passes transfer factor protein
that helps T cells B cells recognize pathogens
d. a tetanus shot is a shot of antibodies
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2. Active Immunity
a. this is when something is injected into the
body to trigger a T cell and B cell response
b. what is injected?
- coat of a pathogen
-dead pathogens
- similar pathogens eg. cowpox for smallpox
- antigens of the pathogen
c. problem what if the pathogen changes its
antigen?