Download File - Mr. Shanks` Class

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.
2a. Tears, saliva and mucus help wash away pathogens
b. and contain mild bactericidal (bacteria-killing) chemicals.
c. If pathogens enter through the air way they are
trapped in a layer of mucus.
d. They may be removed through the continuous, wavelike motion of cilia, moving dirty mucus up to where
it can be swallowed, coughed or sneezed.
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
c. neutrophils will surround invading cells & release
lysozymes that destroy the invader & themselves
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
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
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.
b. The process starts when a macrophage engulfs the
invader and processes an antigen [a specific
surface component of the pathogen, usually a
protein].
antigen
pathogen
c. The macrophage displays the antigen fragments
combined with a Major Histocompatibility Complex
[MHC] protein on the macrophage cell surface.
MHC protein
antigen
processed
antigen
d. A receptor on a circulating, resting helper T cell
recognizes the antigen-protein complex & binds to it.
T-cell receptor
Helper-T-cell
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.
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.
MHC protein__
MHC protein
Killer-T-cell
Activated helper-T-cell
Infected cell
Activated
killer-T-cell
Cell dies
MHC protein__
MHC protein
helper-T-cell
Activated helper-T-cell
Infected cell
Activated
killer-T-cell
Cell dies
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.
c. Antibodies are proteins with the same basic Y shape
but with a special region that is highly specific to
target a given antigen.
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.
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
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
The B cell then displays a piece of the antigen, bound to
a MHC protein, on its cell surface.
MHC protein
This whole complex then binds to an activated
helper T cell.
activated
helper-T-cell
This binding process stimulates the transformation of the
B cell into an antibody-secreting plasmacell.
plasma cell
Remember some key points
A. Non-specific defenses
1. Mechanical barriers:
skin, tears, mucous
2. Innate
macrophages, neutrophils, fever, inflammation,
interferon, complement
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
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
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
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
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
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
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?
-dead pathogens
- coat of a pathogen
- similar pathogens eg. cowpox for smallpox
- antigens of the pathogen
c. problem – what if the pathogen changes its antigen?