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Chapter: 18 Immune System
• The human body has structures and
processes that resist the continuous threat
of invasion by pathogens.
• Immunity is based on recognition of self
and destruction of foreign material.
I.
Defense against infectious disease
A. Primary defense is to keep pathogens out
1. Pathogen: any living organism or virus that is
capable of causing a disease
a) Include viruses, bacteria, protozoa, fungi,
and worms
b) Exposure to majority of pathogens does not
result in disease since we are well defended
2. Antibiotics: chemicals that can kill
bacteria
B. Skin and mucous membranes from a primary defense
1. Prevent pathogens from having the chance to
cause disease: stay away from sources of infection
a) Quarantine: isolate people who have
highly transmittable diseases
b) Not possible to avoid all sources of
infection
2. Skin: first line of defense with two layers
a) Dermis: underneath layer that is alive with sweat
glands, capillaries, sensory receptors, and dermal
cells (give structure and strength to skin)
b) Epidermis: top layer made up of mainly
dead cells that are constantly being replaced as the
underlying dermal cells die and move upwards
i) Forms a good barrier against most
pathogens as long as it stays intact
ii) Important to keep skin clean and cover cuts
3. Pathogens can enter the body that are not covered
by skin
a) Entry points are lined with tissue cells that
form a mucous membrane that produce and
secrete a lining of sticky mucus
b) Mucous: traps pathogens to prevent them
from reaching cells that they could infect
c) Cilia: hair like extensions capable of wavelike movement that are on mucous membrane
tissue that can move pathogens up and out
(trachea) Skin
National Institute of Health: bacteria outnumber their human hosts
by 10 to 1 cells. Bacteria account for 2% of body mass of an adult
C. Blood clotting minimizes the chances of infection and
blood loss
1. Small blood vessels are broken, blood escapes
and the damaged vessels are often in the skin,
creating a way for pathogens to enter the body
2. Body has evolved a set of responses to create a
clot that seals the damaged blood vessel
Blood Clotting
Break in Capillary Wall
Clumping of Platelets
Clot Forms
Blood vessels injured.
Platelets clump at the site
and release thromboplastin.
Thromboplastin converts
prothrombin into thrombin..
Thrombin converts
fibrinogen into fibrin, which
causes a clot. The clot
prevents further loss of
blood..
3. Plasma proteins: circulate in the blood plasma
and some are involved in clotting
a) Prothrombin and fibrinogen: remain
inactive until events of bleeding
4. Platelets: form in the bone marrow and one cell
breaks into fragments without a nucleus and live for
8-10 days
5. Blood clotting process
a) Damage cells of blood vessel releases
chemicals that stimulate platelets to stick to the
damaged area
b) Damaged tissue and platelets release clotting
factors that convert prothrombin in thrombin
i) Thrombin: active enzyme that catalyzes
the conversion of soluble fibrinogen into
insoluble fibrin
ii) Fibrin: fibrous protein that forms a meshlike network that helps to stabilize the platelet
plug
c) Cellular debris becomes trapped in the fibrin mesh to
form a stable clot
d) Clot prevents further blood loss and entry of pathogens
Animation link Blood clotting Clot
6. Hemophilia: inherited (X chromosome)blood-clotting disorder
a) Lack the ability to produce one of the chemicals needed
for normal clotting
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b) Signs and symptoms of hemophilia: vary depending on
your level of clotting factors. If your clotting-factor level is
mildly reduced, you may bleed only after surgery or
trauma. If your deficiency is severe, you may experience
spontaneous bleeding.
Unexplained and excessive bleeding from cuts or injuries, or
after surgery or dental work
Many large or deep bruises
Unusual bleeding after vaccinations
Pain, swelling or tightness in your joints
Blood in your urine or stool
Nosebleeds without a known cause
In infants, unexplained irritability Hemophilia site video
D. When pathogens get past skin and mucous membranes
1. Immune response: series of events when a pathogen
enters the body
a) Primary immune response: first encounter with
a particular pathogen
i) Takes a week or more to be successful and
symptoms of the disease with be experience as
the immune system works to eliminate the
pathogen
b) Secondary immune response: second or
third encounter with a particular pathogen
i) Quicker and more intense response so
symptoms are rarely experienced
ii) Immune to a disease: ability to
accomplish a secondary immune
response for a particular antigen
2. Role of phagocytic white blood cells
a) White blood cells (leucocytes): cells in
bloodstream that help us fight off pathogens and
provide us with immunity for pathogens that we
encounter more than once
b) Macrophage: type of leucocyte that is involved in
the early process of fighting off a pathogen
i) Large and change shape to surround an
invading cell through phagocytosis
ii) Can squeeze their way in and out of small
blood vessels and encounter invading cell outside
the bloodstream
c) Non-specific immunity: macrophage
recognizes the invading cell as either “self” or
“not-self” and engulfs a “not-self” cell and
lysosomes inside the macrophage digests the
cell inflammatory response
E. Antibodies produced by lymphocytes lead to specific
immunity
1. Antibodies: proteins that are produced by the body
in response to a specific type of pathogen
a) Each antibody is different because it
response to a different pathogen
b) Y-shaped protein
b) Pathogen: made up of cells with cell
membranes or is a virus made up of a capsid
(protein coat)
2. Antigen: proteins embedded on the outer surface of the
invader (bacteria) “not-self” proteins that trigger an
immune response
3. Antibody has a binding site where it attaches itself to an
antigen
a) Antigen is on the surface of the pathogen ,
so the antibody becomes attached to the
pathogen
4. Plasma cells (lymphocytes): leucocytes that produce
antibodies
a) Body has many different types of antibody
producing plasma cells
b)Each type of plasma cell produces one type of
antibody
c) Each cell only produces a small number of
antibodies in comparison with the large number of
pathogens during an infection
d) Evolution of the immune system has provided a way
for producing many of the same type of plasma cells
when needed
5. Steps of a typical primary immune response
a) Specific antigen is identified (cold virus)
b) Specific plasma cell is identified that can produce
an antibody that will bind to the antigen (proteins of
the capsid coat of the cold virus)
c) Specific plasma cell type clones itself (division
by mitosis) to increase rapidly the number of that
type of plasma cell
d) Newly formed army of plasm cells begins
antibody production
e) Newly released antibodies circulate in the
bloodstream and eventually find their antigen match
(proteins of the virus capsid)
f) Using various mechanisms the antibodies help
eliminate the pathogens
g) Memory cells: some of the cloned plasma cells
remain in the bloodstream and provide immunity
against a second infection by the same pathogen
h) Secondary immune response: Memory plasma
cells respond quickly if the same antigen is
encountered again
6. Vaccines: weakened or non-pathogenic forms of the
pathogens that cause a primary immune response within
your body Vaccine TED How vaccines work Small pox
a) Leads to the production of memory cells as the
actual disease would do
b) If you encounter the real pathogen later, then the
memory cells with imitate a quick secondary
response
c) Quick response stops any symptoms of the disease
F. What is HIV and how does it affect the human immune
system?
1. HIV: human immunodeficiency virus: targets the
lymphocytes cell types involved in the immune
response
a) Infected person will experience a severe
drop in lymphocytes and lose the ability to
produce adequate antibodies
b) Takes many years after the initial infection
before the person loses specific immune responses and it is
then called AIDS (acquired immune deficiency syndrome)
2. How is HIV transmitted?
a) Person to person contact through unprotected sex
with an infected person
b) Using a hypodermic needle that had been used by
someone that is HIV-positive (HIV+)
c) Transmitted from HIV+ mother to her child
during pregnancy, labor, delivery, or breastfeeding
d) Blood transfusions: now tested for contamination
and not a risk
G. Use of antibiotics to combat bacterial infections
1. Bacteria: prokaryotic cells with a cell wall
2. Antibiotics: chemicals that selectively block
some of the biochemistry needed by bacteria while
having no effect on eukaryotic (human cells)
3. Many categories of antibiotics depending on the
biochemical pathway that is being targeted
a) May selectively block protein synthesis in
bacteria
b) May inhibit the production of a new wall way
which can block their ability to grow and divide
4. Antibiotics have no effect on viruses, since they use the
host cell to make new viruses
a) Any chemical used to inhibit this would hurt host
cell
b) Viruses don’t have a metabolism of their own
Virus
H. Bacterial resistance to antibiotics
1. Bacteria show genetic variation, reproduce
quickly, and populations can be very large
2. Genetic variants exist that are not affected by any
one antibiotic
3. Variants can reproduce and repopulate a colony
that are all resistant to the antibiotic and become a
new strain of bacteria
4. Long-term use and overuse of antibiotics has
now led to many species of bacteria that have
strains that are resistant to nearly all of the
antibiotics available
5. MRSA: type of staph infection caused by
Staphylococcus aureus that have developed
resistance to many types of antibiotics and is very
difficult to treat
Antibiotic resistance
II. Antibody Production
A. Blood type antigens: example of the differences in
plasma membrane proteins on red blood cells
1. Two blood types
a) ABO blood type: based on the presence or
absence of A and B protein
b) Rh blood type (rhesus: type of monkey
where it was discovered): based on the
presence or absence of Rh protein
2. ABO pattern
a) Type A: only A protein
b) Type B: only B protein
c) Type AB: both A and B proteins
d) Type O: neither A or B proteins
3. Rh patterns
a) Rh positive: has Rh protein
b) Rh negative: doesn’t have Rh protein
4. Immune system treats incompatible blood
like a virus or bacteria
5. Antibodies target the antigen proteins and
causes the blood to clump Blood types
B. Steps of mammalian immune response
1. B lymphocyte (plasma cell): synthesizing
and secreting a specific antibody that binds to
a specific antigen
a) Represent 1% of all the cells in blood
b) Cellular communication methods that
lead to cloning of the appropriate B-cell
type to combat a specific antigen when
needed
2. Large phagocytic leucocyte (macrophage): first
to encounter an antigen and it engulfs the not-self
antigen on a pathogen and digests it
3. Antigen presentation: pieces of the invader are
displayed on the cell membrane of the
macrophage
4. Helper T cells: leucocytes that can chemically
recognize the antigen being presented and they
become activated
5. Helper T-cells turn the immune response from
non-specific to antigen-specific and they
communicate with (activate) specific B-cell type
6. B-cell type: produce the needed antibody
7. Order of communication
a) Macrophage presents antigen
b) Helper T becomes activated
c) B lymphocyte becomes activated
8. Cell cloning: activated B-cell begins a series of cell
divisions by mitosis and all the cells produced the same
antibody
9. Two types of cloned cells
a) Plasma cells: secrete antibodies and fight
off the first infection
b) Memory cells: do no secrete
antibodies during the first infection,
but are long lived cells that remain
in blood waiting for the secondary
infection
C. True immunity
1. Primary infection: include the events of
antigen presentation, T-and B-cell activation
and B-cell cloning
a) Immune system helps to eradicate the
pathogen, but the steps take time
b) Pathogen produces symptoms
associated with the disease
2. Second infection of the same pathogen:
memory cells that were produced during the
primary infection are still circulating in the blood
a) Large number of memory cells respond to
the same pathogen very quickly
b) More antibodies are produced compared to
the primary infection
c) Usually the symptoms are not produced
D. Antibodies and how they help destroy pathogens
1. Antibodies: protein molecules produced by plasma
cell leucocytes in response to a specific pathogen
a) Antibodies have similar molecular structures
b) Y-shaped and share many of the same amino
acids sequences
i) Binding sites: ends of the forks of the Y
have two sequences of amino acids that are
unique to each type of antibody
ii) Two binding sites of each antibody are
identical to each other and are capable of binding
to the same type of antigen
2. Antibodies help the immune response in several ways
a) Binding to the pathogen and marking it for
destruction by other cells
b) Use their two binding sites on two antigens
causing the antigens to stick together and clump the
pathogen so macrophages can find them for
destruction
E. Vaccinations confer immunity without resulting
in symptoms
1. Fundamental principle of immunity:
organisms can’t be immune to a pathogen
before being exposed to it at least once
2. Vaccine: composed of chemical
components of a pathogen after eliminating
the disease causing abilities of the pathogen
a) In 1796, Edward Jenner administered the first
vaccine by using cowpox pus to prevent infection of
smallpox
b) Vaccines act as the first exposure to the pathogen
since the leucocytes responsible for the primary
immune response still recognize the chemical
components from the vaccine as antigens and notself
c) On subsequent exposure to the real pathogen, the
secondary immune response is quicker and results in
higher antibody production and usually no obvious
symptoms are presented
3. World Health Organization began a campaign in
1967 to vaccinate the world against smallpox
and in 1977, the last case was reported in
Somalia
Vaccination are no longer given since there is
no one left to transmit the virus
F. Diseases that cross from one species to another
1. HIV/AIDS, SARS, Ebola, H1N1
2. Viral diseases that are serious and potentially
deadly symptoms have all originated in one
species and made the transition to infect another
species (humans)
3. Viral transition from one species to another
does not happen often in nature
a) Conditions and opportunity must be just
right
b) Protein match must occur for a virus to
recognize a cell as a host
c) Viral mutations allows the virus to enter a
new type of host
4. More common for diseases resulting from
bacteria and fungi to cross species barriers
a) Tuberculosis, salmonella, and ring worm
5. Billions of viruses, bacteria, and other
microbes on Earth, but only a very small
percentage of the total number of microbes is
pathogenic to any one species
G. Production of monoclonal antibodies
1. Polyclonal response: primary immune response by an
organism since the pathogen is being recognized as many
antigens
a) Virus capsid (protein coat) is made up of several
different proteins and each one can cause an immune
response
b) Several different kinds of plasma B cells undergo
clonal selection so different antibodies are produced
2. Monoclonal antibodies: pure antibodies all of the same
type (made by researchers using a unique procedure)
a) Infection of an antigen into a lab animal (mouse):
choice of the antigen is important since the
antibodies produce will only bind to a specific
antigen
b) Animals go through a primary immune response
c) Spleen of the animal is harvested in order to
obtain many blood cells
d) Some leucocytes cloned for the antigen will be
present
e) B cells are kept alive by fusing them with
cancerous (myeloma cells) and some form a hybrid
cell called hybridoma
f) Hybridoma cells produce antibodies and are very
long lived and are transferred to an environment
where only the hybridoma cells can survive
g) Surviving hybridoma cells are cultured in separate
containers
h) Container is tested for presence of a particular
antibody by doing an enzyme-linked immunosorbent
assay (ELISA)
i) ELISA identifies which containers hold a pure
colony of B cells that are producing the desired
antibody
j) Cells can be cultured for a very long time because
of the characteristics of the tumor cells
H. Use monoclonal antibodies to diagnose
pregnancy
1. Monoclonal antibodies can be used for a
wide variety of diagnostic purposes including
pregnancy
2. Embryo produces human chorionic
gonadotropin (HCG) hormone and only
pregnant women have this hormone in small
amounts in blood and urine
3. Hybridoma cells can be formed that produce
antibodies specific for HCG
4. Anti-HCG antibodies are chemically bonded to
an enzyme that catalyzes a color change when the
antibody encounters HCG molecules (Pregnancy
tests include a color indicator)
III. Allergies are the result of an immune response releasing
histamine
A. Allergic response: occurs when a nonpathogenic substance (allergen) is encountered by
certain leucocytes
1. Allergens can include harmless substances
like pollen, peanuts, egg whites, and bee
venom
2. First exposure to allergen produces a class
of antibodies called IgE
3. Ig E antibodies bind to the allergen during a
second exposure and trigger a response that leads to
the mast cell releasing large amounts of histamine
4. Histamine: chemical that causes the symptoms
characteristics of an allergy (congestion,
sneezing, itchy skin, red skin blotches, and other
more serious symptoms
Allergy animation