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The Immune System
• Defense mechanisms keep us healthy
– Physical and chemical barriers i.e. skin, stomach
acids
• Prevent many harmful substances from entering
body and kill many that successfully entered
– Nonspecific mechanisms i.e. WBC which engulf
harmful organisms (phagocytosis)
• Help body to respond to tissue damage
– Specific defense mechanisms i.e. immune
responses
• Recognize and kill particular microorganisms and
abnormal cells
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• mechanisms work simultaneously to protect us.
– wide variety of cells, proteins, chemicals and
organs are involved including lymphatic
system, immune system, and circulatory
system.
• Some microorganisms cause cell death and
disease. called pathogens.
– invade or poison living cells.
• Release enzymes or toxins that damage cells
• cause cell rupture, or invade cells and use raw
materials within cell to duplicate themselves and
starve or kill healthy cell.
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• Eukaryotes (most organisms except
bacteria)
– Defining feature of eukaryotic cells is
membrane bound nucleus.
• Nucleus contains chromosomes and
associated proteins.
• Have well organized internal structures
called organelles.
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• Prokaryotes (bacteria)
– Single celled
– No nucleus or membrane bound organelles
– DNA contained in 1 chromosome
– Outer surface covered by a rigid cell wall that
surrounds the plasma membrane and gives
bacteria their shape (spheres, rods, spiral)
– Use of variety of resources to get materials for
energy, growth and reproduction
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Viruses
• Extremely small infectious agents
– Structurally, consists of only a small piece of
RNA or DNA, which contains the virus’
genetic material, surrounded by a protein coat
– Has no organelles of its own so can’t grow or
reproduce on its own; forces living cell to
make more copies of the virus.
• Viruses can only reproduce when they make
contact with a living cell. Take over living cell
and use cell’s organelles to reproduce
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• Modes of entry into living cells:
– Taken into cell cytoplasm by endocytosis. Once
inside, protein coat dissolves and viral genetic
material is released and incorporated into cell’s
genetic material
– Merge their outer coat with cell membrane and
release genetic contents into cell’s cytoplasm
– Attach to outer surface of cell membrane and
inject their genetic material into cell
• Once inside the cell, the virus’ genetic material
causes cell to begin producing copies of virus
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Prions
• infectious proteins that cause normal brain cell proteins
to misfold and build more prions.
– (Word “prion” comes from the first 2 letters of protein and last 3
letters of infection)
– prions accumulate in brain cells until cells malfunction
or stop working. Infected cells die and burst, releasing
prions to infect other brain cells.
• Gradual build up of prions causes debilitating
neurological symptoms and progressive
degeneration.
• No known cure available; prions resist cooking, freezing,
drying
• Disease called Mad Cow disease in animals or
Creutzfeldt-Jakob disease in humans. Both fatal
neurological disorders.
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Determination of Health Risk
Factors Which Determine the Danger from a
Pathogen
• Transmissibility: how easily it is passed from
person to person
• Mode of transmission: how it is transmitted
– respiratory, fecal, oral, body fluids
• Virulence: how damaging the resulting disease
is
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lymphatic system movie
• http://daphne.palomar.edu/ccarpenter/
scroll down to “useful and interesting anatomy-related links and about
¾ way down is link
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Lymphatic System
The lymphatic system consists of :
• Lymphatic vessels
• Lymphoid tissues and organs throughout the
body
– Lymphatic vessels transport back to the blood
any fluids which have escaped from the
circulatory system and moved into the interstitial
fluid.
• Once interstitial fluid enters a lymphatic vessel, its
name changes to lymph
– Lymphatic tissues contain phagocytic cells and
lymphocytes which are essential to the body’s
defense mechanism and its resistance to
diseases.
• Lymph nodes-clean lymph as it passes through
them
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Lymphatic System
Functions:
—Protection against disease and injury
—Filtration of foreign material to defend against infection and
injury
—Maintenance of blood volume in cardiovascular
system
—Capillaries are not watertight and some fluid leaks out into
the tissues
—Removes excess tissue fluid & returns it to the circulatory
system
—Transport of fats and fat-soluble material
absorbed from the digestive system
—Lymph activates the immune system.
—Lymphocytes monitor the lymphatic stream for the presence
of antigens and mount an attack against them.
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Lymph: WBCs, fat cells, and protein-containing
fluid transported by lymphatic vessels;
Lymphatic vessels have:
– Walls consisting of 3 thin layers
– One way valves to prevent backflow of lymph
(lymph flows only toward the heart)
– Skeletal muscle contraction and pressure
changes in the chest during breathing keep
the lymph flowing
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– Lymph capillaries have wide spaces between
its cells.
• Can take up substances, including proteins,
bacteria and cancer cells, that are too large to
enter a blood capillary.
• These substances use the lymphatic vessels to
travel throughout the body.
– Lymphatic capillaries are typically located
throughout the blood capillary beds
• Easy to pick up the fluid that has leaked from the
circulatory system into the tissue spaces.
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– As blood circulates through the body, nutrients,
wastes and gasses are exchanged between the blood
and the interstitial fluid.
– Fluid which remains in the tissue spaces becomes
part of the interstitial fluid (approximately 3 liters).
– This fluid and any plasma proteins that escape from
the blood stream are carried back to the blood.
– As the fluid pressure in the tissue spaces increases,
little flaps in the lymphatic capillaries are forced open,
the excess fluid enters the lymphatic capillaries and is
returned into the circulatory system
• Ensures that there is sufficient blood volume for
circulatory system to function properly.
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Located at intervals along the lymphatic vessels are
organs called lymph nodes.
• Lymph nodes are the principal lymphatic organ in the
body.
– Nodes filter and remove microorganisms, cellular debris, and
abnormal cells from the lymph before returning the cleansed
fluid to the cardiovascular system.
– This prevents microorganisms from being spread into the blood
and sent to other parts of the body
• Lymph nodes cluster along the lymphatic
vessels and most are buried in connective
tissue so we can’t see them.
• Large clusters of nodes occur near body surfaces
in the inguinal (groin), axillary and cervical
regions.
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• Lymphatic capillaries merge to form small
vessels  larger and larger vessels  trunks
 2 major lymphatic ducts
– the right lymphatic duct and the thoracic
duct
– right lymphatic duct drains the right arm and
the right side of the head and chest and
drains into the right subclavian vein;
-- thoracic duct is larger and drains lymph from
rest of the body and drains into left
subclavian vein
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Other important lymphatic system structures:
– Spleen, thymus gland, tonsils and adenoids
Spleen---Largest lymphatic organ
• Is a site for production of lymphocytes, usually in
response to invading pathogens, and RBC
• Contains macrophages that
– filter blood and trap bloodborne antigens;
– scavenge and break down microorganisms,
foreign matter, and old or damaged RBC and
platelets
– Saves hemoglobin (iron) from the RBC
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Spleen:
• Cleans and stores blood;
– blood is used in case of severe blood loss
(hemorrhage) or a fall in blood pressure or
whenever extra oxygen carrying capacity is
needed.
• Immune surveillance and response
• Helps fight infection
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• If the spleen is removed, the lymph glands, liver
and bone marrow take over most of its functions.
– In children under 12, the spleen can regenerate if a
small part of it is left in the body
• Main distinction between spleen and lymph
nodes is which fluid they clean
– Spleen cleans the blood
– Lymph nodes clean the lymph
• Together they keep the circulating body fluids
clean of damaged cells and microorganisms.
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Some Diseases Can Cause Spleen to Enlarge:
• an enlarged spleen more likely to rupture and bleed if
injured
– Tuberculosis, Mononucleosis, leukemia
• A swollen spleen can be felt as a lump in upper left
abdomen
• A strong blow to abdomen can rupture spleen and cause
severe internal bleeding.
– splenectomy to prevent hemorrhage
– can live without a spleen because functions are
shared by lymph glands, liver, red bone marrow
– are more vulnerable to infection if have had
splenectomy
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Thymus
• Gland contains lymphocytes and epithelial cells
• Secretes 2 hormones, thymosin and
thymopoietin, that stimulate T lymphocytes
(T cells) to mature and work against specific
pathogens which invade body
• Gland is largest and most active during
childhood and begins to shrink after
adolescence since defense mechanisms are
usually well established by then.
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Tonsils
• Lymphocytes in tonsils gather and filter out
many of the microorganisms that enter throat
in food or air
• Tonsillitis and tonsillectomy:
– Tonsils in the back of the throat are largest
and most often infected
– If infection is serious, tonsillectomy
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Adenoids
• Also known as pharyngeal tonsils; are at back of
nasal passages
• Tend to enlarge during early childhood, begin to
shrink after 5 years of age, and disappear by
puberty
• If keep enlarging and block airflow from nose to
the throat
– Causes mouth breathing, a nasal voice, and
snoring
– Remove surgicallyadenoidectomy
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Lines of Defense
The lymphatic system works with other body
systems to protect us against pathogens and
cellular changes
Remember the defense mechanisms which we
spoke about earlier:
– Physical and chemical barriers
– Non-specific defense mechanisms
– Specific defense mechanisms
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Non-Specific Defense Systems
First Line of Defense
• Physical and chemical barriers
– Physical barriers: prevent pathogens from entering
the body
– Chemical defenses produce substances that slow the
growth or kill pathogens
• The intact skin and mucous membranes are our
most important barrier and first line of defense.
• Structure: dead layer, inhospitable to microorganisms
• Constant replacement and repair: many adhering
microorganisms removed
• Acidic pH (5–6): too acidic for many
microorganisms; this inhibits their growth
• Sweat glands produce antibiotic fluid (dermicidin)
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• Other: tears, saliva (saliva and tears secrete lysozyme,
an enzyme which kills bacteria), earwax, digestive
acids, hair, mucus (mucus is sticky and traps
pathogens), vomiting, urination, defecation,
resident bacteria (normal flora), mucous
membranes (line all body cavities open to the exterior)
• Most “successful” pathogens enter the body
where we don’t have skin and they can take
advantage of moist surfaces in direct contact
with living cells.
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Nonspecific Defenses: Second Line
Antimicrobial proteins, phagocytes and other cells
inhibit the spread of invaders throughout the body.
– These defenses don’t target specific pathogens;
they occur in response to any body threat
• They work to actively seek out pathogens
which have penetrated our physical and
chemical barriers and are killing or damaging
cells and then attack the invaders
– Respond to tissue damage by removing debris
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Nonspecific Defenses
Phagocytosis: by neutrophils, macrophages (chief
phagocyte), and eosinophils
• Neutrophils (most abundant WBC) are the
first WBC at the infection site.
– Antimicrobial chemicals (defensins) are produced
and pierce the pathogen’s cell membrane
– They engulf, digest and destroy bacteria in the
blood and tissue fluids
• Remember that some WBC can filter through
the walls of blood vessels into tissue spaces
(they are attracted by substances released by
injured cells at the infection site)
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– Monocytes leave the blood vessels, enter the tissue
fluids, and develop into macrophages which engulf
and digest large numbers of pathogens and anything
foreign to the body and help to activate T cells.
• Macrophages also cleanup by scavenging old
blood cells, dead tissue fragments and other
cellular debris.
– They also release chemicals that stimulate the
production of more WBC.
– Eosinophils surround large invaders and
bombard them with digestive enzymes as well as
surround and digest some foreign proteins.
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• When the body is actively fighting an infection,
many WBC die.
• We also have tissue fluid, dead phagocytes,
dead pathogens and cellular debris at the
infection site.
– These produce pus.
• If the pus becomes trapped and can’t drain,
body forms an abscess.
– walls off pus by forming a connective tissue “jail cell”
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Inflammatory response / Inflammation:
• Triggered by any type of tissue injury
– Ultimate goal of inflammation is to clear the injured
area of pathogens, dead tissue cells, and other debris
so that the tissue can be repaired
• Visible Signs: redness, warmth, swelling, pain, and
sometimes, impairment of function
– we rest the injured part to decrease the flow of inflammatory
material from the injured area
– Tissue damage leads to release of chemicals from
damaged cells. The chemicals stimulate MAST
CELLS, connective tissue cells specialized to release
histamine. Histamine causes blood vessels to dilate
so more blood flows into the area which causes the
redness, warmth/heat, swelling.
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– Local capillaries also release fluid containing clotting
factors and antibodies. This fluid goes into the tissue
spaces, causing swelling and then pain from pressure
on local nerve endings.
• Swelling helps to dilute harmful substances and
brings complement proteins and clotting factors.
• Complement system or complement proteins
– Group of plasma proteins that circulate, in an inactive
state, in the blood and assist other defense
mechanisms; they enhance or “complement” the
effectiveness of all the lines of defense
– When presence of an infection activates a
complement protein, the protein activates another and
each protein keeps activating others.
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Some complement protein cells:
– form large protein complexes that create holes in (lyse)
bacterial cell walls.
• Fluids and salts enter and the bacterium swells and bursts.
(Normal cells have proteins to inactivate the complement.)
– bind to bacterial cell membranes and mark them for
destruction by phagocytes.
– stimulate mast cells to release histamine or help get
additional phagocytes to infection site.
– dispose of cellular debris
– begin tissue repair process
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Second Line of Defense
Natural killer (NK) cells: lymphocytes which destroy tumor
cells and virus infected cells by releasing chemicals
that break down their targets’ cell membranes.
– (NK cells are non-specific killers; they do NOT target
specific enemies).
– They police the body via the blood and lymph and
identify invading cells by markers on the plasma
membranes (the lack of “self” cell surface receptors).
– After an attack from NK cells, the “bad” cell
membranes develop holes and the nucleus
disintegrates.
– NK cells also secrete substances that help the
inflammatory response.
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• Interferons: interfere with virus spread
– When a cell becomes virus infected, it will ultimately
succumb to the virus, but it will try to help protect
other normal cells by releasing a group of proteins
called interferons.
• Viruses lack the cellular machinery to make ATP or proteins.
In order to survive, the viruses alter the host’s cell’s
“machinery” so it will make more viruses.
– Interferons diffuse to healthy cells, bind to their cell
membranes, and stimulate the still healthy cell to
produce proteins that prevent the virus from making
the proteins it needs to survive. This makes it harder
for the virus to establish itself.
• Interferons also activate macrophages and mobilize
natural killer cells.
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• Video on viruses
• http://www.npr.org/blogs/krulwich/2011/06/
01/114075029/flu-attack-how-a-virusinvades-your-body
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• Fever: increases host cell defenses and
metabolic activity
– When macrophages attack they release pyrogens into the
bloodstream and cause a fever
– The higher temperature helps our body fight infection and
makes the virus uncomfortable due to the heat.
• Fever increases the metabolic rate and thus speeds up
the defense mechanisms and tissue repair processes
• An extremely high fever can be dangerous because it
can affect the shape of the chemical bonds that give
proteins their shape and allow them to function.
• Inflammation is localized response to infection; fever is
systemic response to invading microorganisms
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immune response:
• http://www.cancerresearch.org/Resources.aspx?id=586
•
http://highered.mcgrawhill.com/olcweb/cgi/pluginpop.cgi?it=swf::535::535::/sites
/dl/free/0072437316/120110/micro33.swf::Interaction of
Antigen Presenting Cells and T-helper Cells
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Third Line: Specific Defense Mechanisms
• Immune response—targets specific enemies,
• takes more time to mobilize than non-specific defenses
– Has 3 important characteristics:
• Recognizes and targets specific pathogens or
foreign substances
• Has “memory”—stores information from past
exposures so responds more quickly next time
pathogen attacks
• Is systemic; protects entire body (resulting
immunity is not limited to infection site)
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• Key to this specific defense is the body’s ability to
distinguish between self and non-self.
– Defends the body by directly attacking cells
– indirectly by releasing mobilizing chemicals and
protective antibodies (proteins that bind with and
neutralize specific antigens)
– Genes determine which foreign substances our
immune system will be able to recognize and resist
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Has 2 separate but overlapping branches
1. Humoral immunity: provided by antibodies present in
the body’s “humors” or fluids—blood, lymph
--antibodies (produced by B lymphocytes) circulate in the
blood and lymph and bind to bacteria, bacterial toxins, and
free viruses. They inactivate these microorganisms and
mark them for destruction by phagocytes or complement.
2.
Cell mediated immunity: T lymphocytes and other
cells protect the body and defend it attacking the
infected cells.
– act directly to kill the foreign cells or
– indirectly  release chemical mediators that
stimulate the inflammatory response or activate
other lymphocytes or macrophages
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• Antigens (antibody generating)
• Any substance that mobilizes immune system
and causes an immune response.
• Each antigen has a unique shape so
immune system can recognize it.
–Antigens are usually a large protein or
polysaccharide molecule
–The immune system responds by
making antibodies to attack and kill
antigen.
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Major histocompatibility complex (MHC)
proteins
– self-markers or self-antigens--surface protein which our
immune system uses to recognize that cells belong to
you.
– They signal immune system to not react
• Some small molecules don’t cause an immune
response, however if they link up with body’s
proteins, immune system may think they are
foreign and start an attack, causing
hypersensitivities i.e. allergies, medicine
reactions, poison ivy reaction, etc.--AUTOIMMUNE
• Transplant reactions
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• Lymphocytes are the main fighter of the immune
system and protect the body against antigens.
• They come from the red bone marrow and mature into
immunocompetent cells, either T cells (T lymphocytes)
or B cells (B lymphocytes).
• They are named for where they mature
– T cells mature in the thymus gland; B cells mature in bone
marrow
– Both recognize and target antigen bearing cells differently.
Activated T cells manage the immune response and some
of them directly attack and destroy infected cells .
B cells produce plasma cells which secrete antibodies into
the blood and body fluids.
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The immune system’s response depends on
– the ability of its cells to recognize antigens,
– bind to them
– communicate with one another so that the whole
system mounts a response specific to the antigens.
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B cells
are responsible for antibody-mediated immunity.
• Antibodies are proteins that bind with and neutralize
specific antigens.
– are released into the lymph, blood, and tissue fluid so
they can circulate throughout the body.
– Antibodies immobilize antigens until they can be
destroyed by phagocytes or other means.
• B cells mature in bone marrow.
–Mature cells have surface receptors that allow them to
recognize specific antigens.
– travel in the blood to the lymph nodes, spleen and
tonsils and remain inactive until they meet a foreign
cell with the specific antigen to which they respond.
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• The foreign cell stimulates the B cell to grow and
multiply. The resulting group of identical cells is
called a clone.
• Clone cells are also called plasma cells; they
secrete their antibodies into the lymph and the
blood plasma. (Plasma cells live for 4-5 days.)
• Antibodies also produced by the B cells and
circulate in our blood.
– When the antibodies meets the correct antigen, they
bind to them and create an antigen-antibody
complex.
– This complex marks the antigen and the cell carrying
it for destruction.
• Macrophages and activated B cells engulf foreign
particles and digest them.
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• Some of the clone cells become memory cells.
– remain inactive in our body until the same antigen
reappears.
– Memory cells store information about the
pathogen;
• if we have a second exposure, the immune
response is faster because the memory cells react
immediately.
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Antibodies:
– Neutralize non-self antigens by inactivating
them and tagging them for destruction
– Their “Y” shape allows them to “lock” into a
cell and attack its contents.
– Five classes of antibodies: IgG, IgM, IgA, IgD,
IgE
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Immunoglobulins
Antibodies are also called immunoglobulins;
–
are the gamma globulin part of blood proteins.
– are proteins secreted by activated B cells or plasma cells
in response to an antigen and bind specifically with an
antigen.
– Will latch onto intact bacteria and foreign molecules in the
extracellular environment (body secretions, tissue fluid), as
well as in blood and lymph.
Five major classes: (MADGE is a mneumonic)
• IgG-75%
• IgM-5-10%
• IgA-15%
• IgD-<1%
• IgE-0.1%
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T cells
• Circulate continuously throughout the body
• responsible for cell-mediated immunity which
depends upon the actions of several types of T
cells. (They attack pathogens which enter into the
healthy cell and damage it.)
– T cells don’t produce antibodies; they directly
attack foreign cells that carry antigens or they
release proteins that boost other aspects of
the immune response.
– T cells can identify and kill infected human
cells before the cells have a chance to
release new pathogens into the blood.
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– T cells are “designed” for cell to cell
interactions and most of their attacks on
antigens target body cells infected by viruses
and bacteria, abnormal or cancerous body
cells and cells of transplanted foreign tissues.
– More T cells are mobilized when
macrophages and activated B cells act as
antigen-presenting cells (APCs) which
engulf foreign particles, partially digest them
and display fragments of the antigen on their
surface.
• serves as an alarm to other immune cells that
there is invader in body.
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Types of T Cells
• Helper T cells (CD4 cell) : secrete a class of signaling
molecules called cytokines which help recruit other
immune cells to fight off intruders.
– Lymphokines**, a protein that enhances
inflammation and the immune response by stimulating
the actions of T cells and macrophages
– Interleukins** promote development of other immune
cells.
– Without helper T cells, there will be no immune
response because they direct or help complete the
activation of all other immune cells.
– Are actually hormones
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• Cytotoxic T cells (also known as Killer T cells) are the
only cells that directly attack and kill abnormal and
foreign cells.
• Memory T cells: reactivate on re-exposure and
stimulate the immune response.
• Suppressor or Regulatory T cells suppress other
immune cells after an antigen has been neutralized.
- prevent the immune response from going haywire
and attacking healthy cells.
--may also help to control autoimmune reactions
As infection is brought under control, regulatory T
cells instruct the B cells, helper T cells, and killer T
cells to switch to “stand-by”;
• infection is winding down, they are not needed
now
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Immune Memory allows us to have immunity:
Development of Immunity:
Primary Immune Response
• The first exposure to an antigen generates a
primary immune response.
• This process involves recognition of the antigen
and production of B and T cells
• Characteristics: lag time of 3–6 days for antibody
production.
– Antibody concentrations rise and peak at 10–12 days
and then level off.
• During lag time, B cells specific to the antigen
multiply and develop into plasma cells.
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Secondary Immune Response
• B and T cells create a population of memory
cells which is the basis for immunity from
disease.
• Subsequent exposure to the pathogen creates
the secondary immune response.
– This response is faster, longer lasting and
more effective than the primary immune
response.
– Antibody levels remain much higher in the
body after a second exposure to the same
antigen.
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Memory cells recognize the pathogen, bind to
it, and produce T cells and plasma cells.
• within a few days antibody concentrations
rise rapidly.
– Memory cells live for a long time and
many retain their ability to generate a
secondary immune response over a
lifetime.
– Other memory cells need to be
reactivated by “booster” shots after a
certain time period.
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War Against Pathogens
• Active immunization and vaccines: give body dose of
antigen in advance so immune system will create
primary immune response. If we are re-exposed to
antigen, we have already developed antibodies and
memory cells so body can react quickly. Are effective
against viruses.
• Passive immunization involves giving prepared
antibodies (gamma globulin serum) for specific
pathogen. Effective against existing infections; can be
given if already exposed.
– Provides short term immunity (2-3 weeks which is
lifespan of prepared antibodies) because person’s
own B cells aren’t activated and memory cells don’t
develop.
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• Antibiotics: kill bacteria or inhibit growth;
effective only against bacteria (ineffective with
viruses); resistance a problem
• Monoclonal antibodies are produced in lab
from clones of hybrid cells; are pure
preparations of antibodies specific to one
antigen
– Typically used for screening tests i.e. pregnancy
tests, STDs, cancer, hepatitis and rabies
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Tissue Rejection
Goal of the immune system is to protect the body from
invasion by foreign cells. If tissue is not a match the
body will reject it.
• Transplants: 75% match essential
– Before transplant can be done, need match
between
• ABO and other blood group antigens
• Tissue match for MHC antigens
– After transplant, patient must take
immunosuppressive drugs to block any potential
immune response
• this can cause the person’s immune system to be
unable to protect the body against any foreign agents
and can cause death.
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Recent advances in transplant surgery have
made the outcome more successful:
1. improvements in immunosuppressive
drugs,
2. better techniques for tissue typing,
3. national sharing of information and
donor organs through organ bank
systems
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Inappropriate Immune Responses
• An allergy is an inappropriate response of the immune
system to an allergen (a substance that causes an
allergic reaction).
– hypersensitivity reaction; excessive inflammatory
response. The immune system causes tissue
damage as it fights off a perceived threat (pollen,
animal dander) that would otherwise be harmless.
– Localized: affect only the area exposed—warmth,
swelling and pain; also increases secretion of mucus
– Systemic: affect several organ systems; includes
constriction of smooth muscle in the lungs and
digestive system and dilation of blood vessels
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• Anaphylactic shock: severe systemic allergic
reaction. The allergen somehow enters the
blood and circulates rapidly throughout the body.
– Symptoms: difficulty breathing, severe
stomach cramps, swelling throughout the
body, circulatory collapse, life threatening fall
in blood pressure
– People with a history of strong allergic
reactions need to carry a prescription
emergency kit with an epinephrine filled
syringe
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Inappropriate Immune Responses:
Autoimmune Disorders
• Defective recognition of “self”the immune system
produces antibodies and cytotoxic T cells that attack its
own cells.
– Possible causes:
1. certain antigens are never exposed to the immune
system as it undergoes fetal development. These
antigens were never programmed into the system as
self so when tissue damage exposes them, the
mature system responds as if they were foreign
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To avoid potential auto-immune diseases,
developing T cells are exposed to as many selfproteins as possible and the body will destroy any
cells that display any reactivity to the body. This
ensures that the remaining T cells will react only to
non-self molecules.
2. Antibodies produced against a foreign antigen cross
react with the person’s own tissues
There are currently no cures for these disorders.
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Some Autoimmune conditions:
• Multiple Sclerosis- a disorder of the CNS which causes
damage to the myelin sheath, so nerve impulses are
slowed down or stopped.
• Diabetes Mellitis
• Glomerulonephritis: severe decrease in kidney function
• Systemic Lupus erythematosus (SLE or lupus): body
attacks its own connective tissue with inflammation and
subsequent pain
• Rheumatoid arthritis: inflammed synovial membrane
which causes damage to the joints, tissues, and bones; B
cells produce antibodies against a protein in the cartilage of
synovial joints.
• Myasthenia Gravis: impairs communication between
nerves and skeletal muscles
– Drooping upper eyelids, difficulty swallowing and talking
and generalized muscle weakness
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Immune Deficiency: general term for an improperly
functioning immune system
• AIDS (acquired immune deficiency syndrome)
(Syndrome is a term for a group of symptoms that occur together)
• Characterized by severe weight loss, night sweats, swollen lymph
nodes, frequent infections
• Disease Progression:
– You become infected with HIV-the human
immunodeficiency virus
– HIV targets cells and attaches to CD4 receptors of T
helper cells. It infects by entering the cell and using
the cell’s machinery to reproduce itself
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• Belongs to a class of virus called Retrovirus.
This virus attaches to the CD4 receptor of a
helper T cell.
– fuses the retrovirus with the cell’s membrane and
releases the viral RNA and enzymes into the cell.
– forces the host cell to make viral DNA which is
then inserted into cell’s DNA.
– Now cell makes more of viral RNA and its
proteins. Because T cell produces so many new
viral cells, it uses up its energy, cell ruptures and
releases more viral copies.
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• Transmission: This is a fragile virus that can’t
survive dry conditions. It cannot be transmitted by
air, casual contact, doorknobs or toilet seats.
– It can be transmitted in body fluids (i.e. blood,
sexual contact, semen, breast milk, vaginal
secretions), or contaminated hypodermic
needles; pregnant mothers can pass it on to the
fetus or the newborn.
– It is not known to be transmitted by contact with
urine, feces, saliva**, perspiration, tears** or
nasal secretions. **=possibly transmitted here
– Generally not transmitted blood transfusions now
because of more extensive screening of donated
blood.
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• AIDS progression falls into 3 phases:
– Phase I: lasts from a few weeks to a few
years after initial exposure
• flu-like symptoms: swollen lymph nodes,
chills, fever, fatigue, body aches.
• Virus is multiplying, antibodies are made
but are ineffective for complete virus
removal because virus particles remain
inside the cells so antibodies can’t reach
them.
• Person is said to be HIV+; does not yet
have AIDS
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– Phase II: from six months to 10 years after
initial exposure (generally it takes about 10
years to progress to this phase)
• opportunistic infections generally present
because more of the helper T cells are
killed. 5% may not progress to next phase
– In Phase I and II infected people may be
unaware that they have HIV and can
unsuspectingly pass it on to other people.
– Phase III: helper T cells below 200 cells/mm,
opportunistic infections and cancers present,
now person is said to have clinical AIDS;
untreated AIDS is nearly always fatal.
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• By destroying so many of the helper T cells, the
AIDS virus prevents our B cells from becoming
activated to produce antibodies. This is why
people with AIDS die of infections or cancers a
healthy immune system can combat.
AIDS Pandemic
• More than 36 million infected with HIV worldwide
• Most infections in sub-Saharan Africa
• Increasing spread in Asia and India
• Most often spread by heterosexual contact
outside United States
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New AIDS Treatments
• Enzyme inhibitors: AZT, ddI, d4T, 3TC (inhibit
enzymes virus needs in order to reproduce)
• Protease inhibitors: ritonavir, saquinavir
(protease is a required enzyme for viral protein
assembly)
• Early treatment may delay or prevent clinical
AIDS
• Vaccine: virus mutates rapidly preventing
effective vaccine production at this time
• The reason AIDS is so devastating is that the
virus that causes AIDS destroys helper T cells
and weakens the body’s ability to mount a cell
mediated immune response.
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Safer Sex
• Abstinence
• Reduce number of sexual partners
• Choose sexual partners with low-risk behavior
• Avoid high-risk sexual practices
• Use latex or polyurethane condoms or barriers
• GET TESTED
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