LESSON 3: LYMPHATIC SYSTEM AND BODY DEFENSES
3rd QUARTER | ANATOMY AND PHYSIOLOGY 2
OUTLINE
I.
Lymphatic System
II. Body Defenses
III. Developmental Aspect of Lymphatic System
and Body Defenses
IV. Interrelation among other organ systems
•
Figure 11.1 shows the
one way system of
lymphatic vessels where
lymph flows only towards
the heart (see pink arrow)
LYMPHATIC SYSTEM
•
•
Consists of two semi-independent parts:
1. Lymphatic Vessels
2. Lymphoid Tissues and Organs
Lymphatic System Functions
§ Transports
escaped
fluids
from
the
cardiovascular system back to the blood
§ Plays essential roles in body defense and
resistance to disease
•
LYMPHATIC VESSELS
•
•
•
Lymph consists of excess tissue fluid and plasma
proteins carried by lymphatic vessels
If fluids are not picked up, edema occurs as fluid
accumulates in tissues
Lymphatic vessels (lymphatics) pick up excess fluid
(lymph) and return it to the blood
Figure 11.1 shows the
relationship between the
blood
vessels
and
lymphatic vessels. As
pointed by the pink arrow,
the tissue fluid that goes
out of the capillaries will
become lymph and will
enter
the
lymph
capillaries
Figure 11.2 shows how
edema looks like which is
a consequence of failure
to pick up fluids that
accumulates in tissues.
Edema can also be a
consequence of high
blood pressure
A.G. RODRIGUEZ & D. TAN
Lymphatic Vessels (lymphatics)
§ Form a one-way system
§ Lymph flows only toward the heart.
Lymphatic Capillaries
§ Weave between tissue cells and blood
capillaries
§ Walls overlap to form flaplike minivalves
§ Fluid leaks into lymph capillaries
§ Capillaries are anchored to connective tissue by
filaments
§ Higher pressure on the inside closes minivalves
§ Fluid is forced along the vessel
Figure 11.3a shows how the lymphatic capillaries (green vessels in the
photo above) weaves itself to the blood capillaries. Figure 11.3b shows
the flaplike minivalve of the lymphatic capillary as well as the filaments
that it uses to anchor to connective tissues.
•
Lymphatic collecting vessels
§ Collect lymph from lymph capillaries
§ Carry lymph to and away from lymph nodes
§ Return fluid to circulatory veins near the heart
o Right lymphatic duct drains the lymph
from the right arm and the right side of the
head and thorax
o Thoracic duct drains lymph from rest of
body.
PAGE 1 OF 10
LYMPHATIC NODES
•
•
Figure 11.1 highlights the
location of the lymphatic
collecting vessels.
•
•
•
•
Lymph nodes filter lymph before it is returned to the
blood
Harmful materials that are filtered:
§ Bacteria
§ Viruses
§ Cancer cells
§ Cell debris
Defense cells within lymph nodes
§ Macrophages – engulf and destroy bacteria,
viruses, and other foreign substances in lymph
§ Lymphocytes – respond to foreign substances
in lymph
Most lymph nodes are kidney-shaped, less than 1
inch long, and buried in connective tissue
§ Surrounded by a capsule
§ Divided into compartments by trabeculae
Cortex (outer part)
§ Contains follicles - collections of lymphocytes
§ Germinal centers enlarge when antibodies are
released by plasma cells
Medulla (inner part)
§ Contains phagocytic macrophages
Figure 11.4 highlights the different regions of the body that is drained
by the right lymphatic and thoracic duct.
LYMPHATIC VESSELS (continuation)
•
•
Lymphatic vessels are similar to veins of the
cardiovascular system
§ Thin-walled
§ Larger vessels have valves
§ Low-pressure, pumpless system
Lymph transport is aided by:
§ Milking action of skeletal muscles (similar to
how skeletal muscles can open valves of veins
when it is “squeezed” by the muscles)
§ Pressure changes in thorax during breathing
§ Smooth muscle in walls of lymphatics
Figure 11.5 shows the parts of the lymphatic nodes. Highlighted are the
cortex and the follicle cells and germinal center in it and the medulla.
•
Flow of lymph through nodes
1. Lymph enters the convex side through afferent
lymphatic vessels.
2. Lymph flows through a number of sinuses inside
the node
3. Lymph exits through efferent lymphatic vessels.
Because there are fewer efferent than afferent
vessels, flow is slowed.
Figure 11.1 shows the
relationship of the lymph
nodes to the lymphatic
vessels in terms of
location.
Figure 11.5 shows the flow of lymph from the afferent lymphatic vessels
to the efferent lymphatic vessels.
A.G. RODRIGUEZ & D. TAN
PAGE 2 OF 10
OTHER LYMPHOID ORGANS
•
Several other lymphoid organs contribute to
lymphatic function (in addition to the lymph nodes)
§ Spleen
§ Thymus
§ Tonsils
§ Peyer’s patches
§ Appendix
BODY DEFENSES
Innate (nonspecific) defense system
• Mechanisms protect against a variety of invaders
• Responds immediately to protect body from foreign
materials
Adaptive (specific) defense system
• Fights invaders that get past the innate system
• Specific defense is required for each type of
invader
• The highly specific resistance to disease is
immunity
INNATE (NONSPECIFIC) BODY DEFENSES
•
Figure 11.6 shows the location of other lymphoid organs in the body.
•
Innate body defenses are mechanical barriers to
pathogens
(harmful
or
disease-causing
microorganisms) and include:
§ Body surface coverings
o Intact skin
o Mucous membranes
§ Specialized human cells
§ Chemicals produced by the body
Table 12.1 provides a more detailed summary
Spleen
• Located on the left side of the abdomen
• Filters and cleans blood of bacteria, viruses, debris
• Provides a site for lymphocyte proliferation and
immune surveillance
• Destroys worn-out blood cells
• Forms blood cells in the fetus (this function will later
on be passed to the bone marrow)
• Acts as a blood reservoir.
Thymus
• Found overlying the heart
• Functions at peak levels only during youth
• Produces T-lymphocytes
Tonsils
• Small masses of lymphoid tissue deep to the
mucosa surrounding the pharynx (throat)
• Trap and remove bacteria and other foreign
pathogens
• Tonsillitis results when the tonsils become
congested with bacteria
Peyer’s Patches
• Found in the wall of the small intestine
• Similar lymphoid follicles are found in the appendix
• Macrophages capture and destroy bacteria in the
intestine
Mucosa-associated lymphoid tissue (MALT)
• Includes:
§ Peyer’s patches
§ Tonsils
§ Appendix
• Acts as a sentinel (indicator of the presence of a
disease) to protect respiratory and digestive tracts
A.G. RODRIGUEZ & D. TAN
PAGE 3 OF 10
1st
Surface membrane barriers
• Surface membrane barriers, such as the skin and
mucous membranes, provide the first line of
defense against the invasion of microorganisms.
o Protective secretions produced by these
membranes.
§ Acidic skin secretions inhibit bacterial
growth
§ Sebum is toxic to bacteria
§ Mucus traps microorganisms
§ Gastric juices are acidic and kill
pathogens
§ Saliva and tears contain lysozyme
(enzyme that destroys bacteria).
Cells and chemicals: Internal defenses 2nd
• Cells and chemicals provide a second line of
defense.
§ Natural killer cells and phagocytes
§ Inflammatory response
§ Chemicals that kill pathogens
§ Fever
Natural Killers (NK) Cells
• Lyse (burst) and kill cancer cells, virus-infected
cells
• Release chemicals called perforin and granzymes
to degrade target cell contents
Inflammatory Response
• Triggered when body tissues are injured
• Four most common indicators (cardinal signs) of
acute inflammation.
1. Redness
2. Heat
3. Pain
4. Swelling (edema)
• Damaged cells release inflammatory chemicals
§ Histamine
§ Kinin
• These chemicals cause:
§ Blood vessels to dilate
§ Capillaries to become leaky
§ Phagocytes and white blood cells to move into
the area (called positive chemotaxis)
•
Process of the inflammatory response
1. Neutrophils migrate to the area of
inflammation by rolling along the vessel wall
(following the scent of chemicals from
inflammation)
2. Neutrophils squeeze through the capillary
walls by diapedesis (passage of blood
vessels through the intact walls of the
capillaries) to sites of inflammation
3. Neutrophils gather in the precise site of
tissue injury (positive chemotaxis) and
consume any foreign material present
Figure 11.8 shows the process
of inflammatory response
through phagocytes such as
neutrophils
Phagocytes
• Cells such as neutrophils and macrophages engulf
foreign material by phagocytosis
• The phagocytic vesicle is fused with a lysosome,
and enzymes digest the cell’s contents
Figure 11.9 shows a
scanning electron micrograph
of phagocytosis by a
macrophage as it ingests a
bacillus-shaped
bacteria
(encircled)
Figure 11.7 is a flowchart that
shows
the
cascade
of
inflammatory events after an
injury.
Release of kinins, histamines
and other chemicals cause
blood vessels to dilate,
capillaries to become leaky and
WBC’s to enter the area.
Figure 11.10 shows the
steps
involved
in
phagocytosis by a
microphage.
Dilation of blood vessels can
lead to increase blood flow,
capillaries becoming leaky can
lead to edema and clotting
proteins in the area while WBC’s
are for removal and damaged
tissues and pathogens. This will
all eventually cause healing.
A.G. RODRIGUEZ & D. TAN
PAGE 4 OF 10
Antimicrobial Proteins
• Enhance innate defenses by:
§ Attacking microorganisms directly
§ Hindering reproduction of microorganisms
•
Most important types:
§ Complement proteins
§ Interferon
•
Antimicrobial proteins: complement proteins
§ Complement refers to a group of at least 20
plasma proteins that circulate in the plasma
§ Complement is activated when these plasma
proteins encounter and attach to cells (known
as complement fixation)
§ Membrane attack complexes (MACs), one
result of complement fixation, produce holes
or pores in cells.
o Pores allow water to rush into the cell
o Cell bursts (lyses)
§ Activated
complement
enhances
the
inflammatory response
Figure 11.13 shows activated complement proteins forming a
membrane attack complex after complement fixation. This causes
formation of pores that allow water to rush into the cell causing cell
lysis
•
Antimicrobial proteins: interferons
§ Interferons are small proteins secreted by
virus-infected cells.
§ Interferons bind to membrane receptors on
healthy cell surfaces to interfere with the ability
of viruses to multiply.
Fever
• Abnormally high body temperature is a systemic
response to invasion by microorganisms
• Hypothalamus regulates body temperature at
37oC (98.6oF)
• The hypothalamus thermostat can be reset higher
by pyrogens (secreted by white blood cells)
• High temperatures inhibit the release of iron and
zinc (needed by bacteria) from the liver and spleen
• Fever also increases the speed of repair processes
A.G. RODRIGUEZ & D. TAN
ADAPTIVE DEFENSE SYSTEM
• Adaptive Body Defenses
Three aspects of Adaptive Defense
§ Antigen specific – the adaptive defense
system recognizes and acts against particular
foreign substances
§ Systemic—immunity is not restricted to the
initial infection site
§ Memory – the adaptive defense system
recognizes and mounts a stronger attack on
previously encountered pathogens
o Two arms of the Adaptive Defense System
§ Humoral immunity = antibody-mediated
immunity
² Provided by antibodies present in body fluids
§ Cellular immunity = cell-mediated immunity
² Targets virus-infected cells, cancer cells,
and cells of foreign grafts
1. Antigen
o Antigens are any substance capable of exciting the
immune system and provoking an immune
response for using words and different patterns of
development
o Examples of common nonself antigens (those
that are not found in the cells of your body; “Self”
antigens include the antigens A and B in our RBCs
that are used to determine blood type)
§ Nominalization – act of transforming verbs to
nouns as much as possible; instead of suggest
refuse, employ, you use suggestion, arrival,
employment
§ Foreign proteins provoke the strongest
response
§ Nucleic acids
§ Large carbohydrates
§ Some lipids
§ Pollen grains
§ Microorganisms (bacteria, fungi, viruses)
o Self-Antigens
§ Human cells have many protein and
carbohydrate molecules
§ Self-antigens do not trigger an immune
response in us
§ The presence of our cells in another person’s
body can trigger an immune response because
they are foreign
² Restricts donors for transplants
o Haptens, or incomplete antigens, are not
antigenic by themselves
§ Humoral immunity = antibody-mediated
immunity
§ When they link up with our own proteins, the
immune system may recognize the combination
as foreign and respond with an attack
§ Found in poison ivy, animal dander, detergents,
hair dyes, cosmetics
2. Cells of the Adaptive System
o Crucial Cells of the Adaptive System
§ Lymphocytes – respond to specific antigens
² B lymphocytes (B cells) produce
antibodies and oversee humoral immunity
² T lymphocytes (T cells) constitute the cell-
PAGE 5 OF 10
mediated arm of the adaptive defenses; do
not make antibodies
§ Antigen-presenting cells (APCs) — help the
lymphocytes but do not respond to specific
antigens
o Lymphocytes
§ Arise from hemocytoblasts of bone marrow
§ Whether a lymphocyte matures into a B cell or
T cell depends on where it becomes
immunocompetent (capability to respond to a
specific antigen by binding to it with antigenspecific receptors that appear on the
lymphocyte’s surface)
§ T cells develop immunocompetence in the
thymus and oversee cell-mediated immunity
² Identify foreign antigens
² Those that bind self-antigens are destroyed.
Self-tolerance is important part of
lymphocyte “education”
§ B cells develop immunocompetence in bone
marrow and provide humoral immunity
§ Immunocompetent T and B lymphocytes
migrate to the lymph nodes and spleen, where
encounters with antigens occur
§ Differentiation from naïve cells into mature
lymphocytes is complete when they bind with
recognized antigens
§ Mature lymphocytes (especially T cells)
circulate continuously throughout the body
o Antigen-presenting Cells (APCs)
§ Lymphocytes – respond to specific antigens
§ Engulf antigens and then present fragments of
them on their own surfaces, where they can be
recognized by T cells
§ Major types of cells behaving as APCs
² Dendritic Cells
² Macrophages
² B lymphocytes
§ When they present antigens, dendritic cells and
macrophages activate T cells, which release
chemicals
3. Humoral (antibody-mediated) immune response
o B lymphocytes with specific receptors bind to a
specific antigen
o The binding event sensitizes, or activates, the
lymphocyte to undergo clonal selection
o A large number of clones is produced (primary
humoral response)
o Most of the B cell clone members (descendants)
become plasma cells
§ Produce antibodies to destroy antigens
§ Activity lasts for 4 or 5 days
§ Plasma cells begin to die
o Some B cells become long-lived memory cells
capable of mounting a rapid attack against the
same antigen in subsequent meetings (secondary
humoral response)
§ These cells provide immunological memory
A.G. RODRIGUEZ & D. TAN
o Active Immunity
§ Occurs when B cells encounter antigens and
produce antibodies
§ Active immunity can be:
² Naturally acquired during bacterial and viral
infections
² Artificially acquired from vaccines
o Passive Immunity
§ Occurs when antibodies are obtained from
someone else
² Naturally acquired from a mother to her
fetus or in the breast milk
² Artificially acquired from immune serum or
gamma globulin (donated antibodies)
§ Immunological memory does not occur
§ Protection is short-lived (2–3 weeks)
§ Monoclonal Antibodies
² B lymphocytes (B cells) produce
antibodies and oversee humoral immunity
² Antibodies prepared for clinical testing for
diagnostic services
² Produced from descendants of a single cell
line
² Exhibit specificity for only one antigen
² Examples of uses for monoclonal antibodies
Ä Cancer Treatment
Ä Diagnosis of Pregnancy
Ä Treatment after exposure to hepatitis and
rabies
PAGE 6 OF 10
2. IgA—found mainly in secretions, such as
mucus or tears
3. IgD—important in activation of B cell
4. IgG—can cross the placental barrier and
fix complement; most abundant antibody in
plasma
5. IgE—involved in allergies
o Antibodies (immunoglobulins, lgs)
§ Occurs when antibodies are obtained from
someone else
§ Constitute gamma globulin part of blood
proteins
§ Soluble proteins secreted by activated B cells
(plasma cells)
§ Formed in response to a huge number of
antigens
o Antibody Structure
§ Four polypeptide chains, two heavy and two
light, linked by disulfide bonds to form a T- or Yshaped molecule
§ Each polypeptide chain has a variable (V)
region and a constant (C) region
² Variable regions form antigen-binding sites,
one on each arm of the T or Y
² Constant regions determine the type of
antibody formed (antibody class)
o Antibody Classes
§ Antibodies of each class have slightly different
roles and differ structurally and functionally
§ Five
major
immunoglobulin
classes
(MADGE)
1. IgM—can fix complement (refers to a grp
of at least 20 plasma proteins that circulate
in the plasma)
A.G. RODRIGUEZ & D. TAN
o Antibody Function
§ Antibodies inactivate antigens in a number
of ways
² Complement fixation: chief antibody
ammunition used against cellular antigens
² Neutralization: antibodies bind to specific
sites on bacterial exotoxins or on viruses that
can cause cell injury
² Agglutination: antibody-antigen reaction
that causes clumping of cells
² Precipitation: cross-linking reaction in
which antigen-antibody complex settles out
of solution
4. Cellular (cell-mediated) Immune Response
o Main difference between 2 arms of the adaptive
response
§ B cells secrete antibodies
§ T cells fight antigens directly
PAGE 7 OF 10
o Like B cells, immunocompetent T cells are
activated to form a clone by binding with a
recognized antigen
o Unlike B cells, T cells are unable to bind to free
antigens
§ Antigens must be presented by a macrophage,
and double recognition must occur
§ APC (Antigen presenting cells) engulfs and
presents the processed antigen in combination
with a protein from the APC
o Different classes of effector T cells
§ Helper T cells
² Recruit other cells to fight invaders
² Interact directly with B cells bound to an
antigen, prodding the B cells into clone
production
² Release cytokines, chemicals that act
directly to rid the body of antigens
§ Regulatory T cells
² Release chemicals to suppress the activity of
T and B cells
² Stop the immune response to prevent
uncontrolled activity
² A few members of each clone are memory
cells
§ Cytoxic (killer) T Cells
² Specialize in killing infected cells
² Insert a toxic chemical (perforin or
granzyme)
² The perforin enters the foreign cell’s plasma
membrane
² Pores now appear in the target cell’s
membrane
² Granzymes (protein-digesting enzymes)
enter and kill the foreign cell
² Cytotoxic T cell detaches and seeks other
targets
FUNCTION OF CELLS INVOLVED IN IMMUNITY
FUNCTION IN THE IMMUNE
ELEMENT
RESPONSE
Lymphocyte that resides in the
lymph nodes, spleen, or other
lymphoid tissues where it is induced
B Cell
to replicate by antigen-binding and
helper T cell interactions; its
progeny (clone members) form
plasma cells and memory cells.
Antibody-producing “machine” ;
produces huge numbers of the
Plasma Cell
same antibody (immunoglobulin);
specialized B cell clone descendant
A T cell that binds w a specific
antigen presented by an APC; it
stimulates the production of other
Helper T cell
immune cells (cytotoxic T cells and
B cells) to help fight the invader;
acts both directly and indirectly by
releasing cytokines
Activity enhanced by Helper t Cells;
its specialty is killing virus-invaded
Cytotoxic
T
body cells, as well as body cells that
Cell
have become cancerous; involved
in graft rejection
Slows or stops the activity of B and
T cells once the infection (or attack
Regulatory T
by foreign cells) has been
Cell
conquered. Thought to be important
in preventing autoimmune diseases
Descendant of an activated B cell or
T cell; generated during both
primary and secondary immune
responses; may exist in the body for
Memory Cell
years thereafter, enabling it to
respond quickly and efficiently to
subsequent infections or meetings
w the same antigen
Any of several cell types
(macrophage, dendritic cell, B cell)
that engulfs and digests antigens
that it encounters and presents
parts of them on its plasma
membrane for recognition by T cells
Antigenbearing receptors for the same
presenting Cell
antigen; this function, antigen
(APC)
presentation, is essential for normal
cell-mediated
responses.
Macrophages and dentritic cells
also release chemicals (cytokines)
that activate many other immune
cells.
o T cells must recognize nonself and self through the
process of antigen presentation
§ Nonself—the antigen fragment presented by
APC
§ Self—coupling with a specific glycoprotein on
the APC’s surface at the same time
FUNCTION OF CELLS INVOLVED IN IMMUNITY
FUNCTION IN THE IMMUNE
ELEMENT
RESPONSE
Protein produced by a B cell or its
Antibody
plasma-cell
offspring
and
(immunoglobulin)
released into body fluids (blood,
A.G. RODRIGUEZ & D. TAN
PAGE 8 OF 10
Cytokines
Tumor necrosis
factor (TNF)
Complement
Regulatory T Cell
Cytotoxins
lymph, saliva, mucus, etc.),
where it attaches to antigens,
causing
neutralization,
opsonization, precipitation, or
agglutination, which "marks" the
antigens for destruction by
phagocytes or complement.
Chemicals
released
by
sensitized T cells, macrophages,
and certain other cells
• Migration inhibiting factor
(MIF)—" inhibits" macrophage
migration and keeps them in
the local area.
• Interleukin 2—stimulates T
cells and B cells to proliferate;
activates NK cells.
• Helper
factors—enhance
antibody formation by plasma
cells.
• Suppressor
factors—
suppress antibody formation
or T cell-mediated immune
responses
(interleukin-10
transforming growth factor and
others).
• Chemotactic factors—attract
leukocytes
(neutrophils,
eosinophils, and basophils)
into inflamed area.
• Gamma
interferon—
secreted by lymphocytes;
helps make tissue cells
resistant to viral infection;
activates macrophages and
NK cells; enhances maturation
of cytotoxic T cells.
Like perforin, causes cell killing;
attracts granulocytes; activates T
cells and macrophages.
Group of bloodborne proteins
activated after binding to
antibody-covered antigens; when
activated, complement causes
lysis of the microorganism and
enhances
inflammatory
response.
Substance capable of provoking
an immune response; typically a
large, complex molecule not
normally present in the body.
Perforin, granzymes—cell toxins
released by cytotoxic T cells and
NK cells
ORGAN TRANSPLANT AND REJECTIONS
• Major Types of Transplants, or Grafts
o Autografts—tissue transplanted from one site to
another on the same person
A.G. RODRIGUEZ & D. TAN
o Isografts—tissue grafts from a genetically identical
person (identical twin)
o Allografts—tissue taken from a person other than
an identical twin (most common type of graft)
o Xenografts—tissue taken from a different animal
species (never successful)
• Blood group and tissue matching is done to ensure
the best match possible
o 75% match is needed to attempt a graft
• Organ Transplant is followed by immunosuppressive
therapy to prevent rejection
DISORDERS OF IMMUNITY
• The most important disorders of the immune
system
o Allergies
§ Types of Allergies
² Immediate (acute) Hypersensitivity
Ä Seen in hives and anaphylaxis (allergic
reaction)
Ä Due to IgE antibodies and histamine
Ä Anaphylactic shock is systemic, acute
allergic response and is rare
² Delayed Hypersensitivity
Ä Reflects activity of T cells, macrophages,
and cytokines
Ä Symptoms usually appear 1–3 days after
contact with antigen
Ä Allergic contact dermatitis (poison ivy,
cosmetics)
o Autoimmune diseases
§ Occurs when the body’s self-tolerance breaks
down
§ The body produces auto-antibodies and
sensitized T lymphocytes that attack its own
tissues
§ Most forms of autoimmune disease result
from the:
² appearance of formerly hidden self-antigens
² changes in the structure of self-antigens, and
² antibodies formed against foreign antigens
PAGE 9 OF 10
that resemble self-antigens
§ Examples of autoimmune diseases
² Rheumatoid arthritis—destroys joints
² Myasthenia
gravis—impairs
communication between nerves and skeletal
muscles
² Multiple sclerosis—white matter of brain
and spinal cord is destroyed
² Graves’ disease—thyroid gland produces
excess thyroxine
² Type I diabetes mellitus—destroys
pancreatic beta cells, resulting in deficient
insulin production
² Systemic lupus erythematosus (SLE)—
affects kidney, heart, lung, and skin
² Glomerulonephritis—severe impairment of
kidney function due to acute inflammation
§ Immunodeficiencies
² May be congenital or acquired
Ä Severe combined immunodeficiency
disease (SCID) is a congenital disease
Ä AIDS (acquired immune deficiency
syndrome) is caused by a virus that
attacks and cripples the helper T cells
² Result from abnormalities in any immune
element
² Production or function of immune cells or
complement is abnormal
INTERRELATION AMONG OTHER ORGAN
SYSTEM
DEVELOPMENTAL ASPECT OF LYMPHATIC
SYSTEM AND BODY DEFENSES
• Lymphatic vessels form by budding off from veins
• Lymph nodes present by fifth week of development
• The thymus and the spleen are the first lymphoid
organs to appear in the embryo
• Other lymphoid organs are poorly developed before
birth
• The immune response develops around the time of
birth
• The ability of immunocompetent cells to recognize
foreign antigens is genetically determined
• Stress appears to interfere with normal immune
response
• Efficiency of immune response wanes in old age,
and infections, cancer, immunodeficiencies, and
autoimmune diseases become more prevalent
A.G. RODRIGUEZ & D. TAN
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