Download Chapter 15 The Lymphatic System and Immunity

Chapter 15
The Lymphatic System
and Immunity
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The Lymphatic System
• Lymph—fluid in tissue spaces that
carries protein molecules and other
substances back to the blood
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The Lymphatic System
• Lymphedema—swelling (edema) of
tissues caused by blockage of lymphatic
vessels
– Elephantiasis—severe lymphedema of
limbs resulting from parasite infestation of
lymphatic vessels
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The Lymphatic System
• Thymus
– Plays central role in immunity
– Produces T lymphocytes or T cells
– Secretes hormone called thymosin
– Atrophies in adults
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The Lymphatic System
• Tonsils
– Three around openings of mouth and throat
• Palatine tonsils (“the tonsils”)
• Pharyngeal tonsils (adenoids)
• Lingual tonsils
– Subject to chronic infection
– Enlargement of pharyngeal tonsils may impair
breathing
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The Lymphatic System
• Spleen
– Largest lymphoid organ in body
– Located in upper left quadrant of abdomen
– Often injured by trauma to abdomen
– Surgical removal called splenectomy
– Functions include phagocytosis of bacteria
and old RBCs; acts as a blood reservoir
– Splenomegaly—enlargement of the spleen
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The Immune System
• Protects body from pathogens, foreign
tissue, and cancer cells
• Nonspecific immunity
– Skin—barrier to bacteria and other harmful
agents
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The Immune System
• Nonspecific immunity
– Tears and mucus—wash eyes and trap
bacteria
– Inflammation attracts immune cells to site
of injury, increases local blood flow,
increases vascular permeability; promotes
movement of WBCs to site of injury or
infection
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Humoral
immunity
Active
Passive
Naturally
acquired
Artificially
acquired
Naturally
acquired
Artificially
acquired
Infection;
contact
with
pathogen
Vaccine;
dead or
attenuated
pathogens
Antibodies
pass from
mother to
fetus via
placenta;
or to infant
in her milk
Injection of
immune
serum
(gamma
globulin)
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Figure 21.13
The Immune System
• Specific immunity—ability to recognize,
respond, and remember antigen
• Inborn immunity—inherited immunity to
certain diseases from time of birth
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Antibody A
Antigenbinding
sites
Antigenic determinants
Antigen
Antibody B
Antibody C
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Figure 21.7
Adaptive defenses
Humoral immunity
Antigen
Antigen-antibody
complex
Antibody
Inactivates by
Neutralization
(masks dangerous
parts of bacterial
exotoxins; viruses)
Agglutination
(cell-bound antigens)
Enhances
Phagocytosis
Fixes and activates
Precipitation
(soluble antigens)
Enhances
Complement
Leads to
Inflammation
Cell lysis
Chemotaxis
Histamine
release
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Figure 21.15
Immune System Cells
• Phagocytes
– Ingest and destroy foreign cells or other
harmful substances via phagocytosis
– Macrophages and DCs act as antigenpresenting cells (APCs) by displaying
ingested antigens on their outer surface to
trigger specific immune cells
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Adaptive defenses
Immature
lymphocytes
Red bone marrow: site of lymphocyte origin
Humoral immunity
Cellular immunity
Primary lymphoid organs: site of
development of immunocompetence as B or
T cells
Secondary lymphoid organs: site of
antigen encounter, and activation to become
effector and memory B or T cells
Red
bone marrow
1 Lymphocytes destined to become T cells
migrate (in blood) to the thymus and develop
immunocompetence there. B cells develop
immunocompetence in red bone marrow.
Thymus
Bone marrow
2 Immunocompetent but still naive
Lymph nodes,
spleen, and other
lymphoid tissues
lymphocytes leave the thymus and bone
marrow. They “seed” the lymph nodes,
spleen, and other lymphoid tissues where
they encounter their antigen.
3 Antigen-activated immunocompetent
lymphocytes (effector cells and memory
cells) circulate continuously in the
bloodstream and lymph and throughout
the lymphoid organs of the body.
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Adaptive defenses
Humoral immunity
Primary response
(initial encounter
with antigen)
Activated B cells
Proliferation to
form a clone
Plasma cells
(effector B cells)
Memory B cell—
primed to respond
to same antigen
Secreted
antibody
molecules
Secondary response
(can be years later)
Antigen
Antigen binding
to a receptor on a
specific B lymphocyte
(B lymphocytes with
non-complementary
receptors remain
inactive)
Clone of cells
identical to
ancestral cells
Subsequent
challenge by
same antigen
results in more
rapid response
Plasma
cells
Secreted
antibody
molecules
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Memory
B cells
Secondary immune response to
antigen A is faster and larger; primary
immune response to antigen B is
similar to that for antigen A.
Primary immune
response to antigen
A occurs after a delay.
Antibodies
to B
Antibodies
to A
First exposure
to antigen A
Second exposure to antigen A;
first exposure to antigen B
Time (days)
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TH cell help in humoral immunity
Activated helper
T cell
1 TH cell binds with the
Helper T cell
CD4 protein
self-nonself complexes of a
B cell that has encountered
its antigen and is displaying
it on MHC II on its surface.
MHC II protein
of B cell displaying
processed antigen
2 TH cell releases
T cell receptor (TCR)
IL- 4 and other
cytokines
B cell (being activated)
(a)
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interleukins as
co-stimulatory signals to
complete B cell activation.
TH cell help in cell-mediated immunity
CD4 protein
Helper T cell
Class II MHC
protein
APC (dendritic cell)
1 Previously
activated TH cell
binds dendritic cell.
2 TH cell stimulates
IL-2
dendritic cell to express
co-stimulatory
molecules (not shown)
needed to activate CD8
cell.
3 Dendritic cell can
Class I
MHC protein
(b)
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CD8
protein
CD8 T cell
now activate CD8 cell
with the help of
interleukin 2 secreted
by TH cell.
Immune System Cells
– Development of B cells
• Second stage—inactive B cell develops into activated B
cell
– Initiated by inactive B cell’s contact with antigens, which
bind to its surface antibodies, plus signal chemicals from T
cells
– Activated B cell, by dividing repeatedly, forms two clones
of cells—plasma (effector) cells and memory cells
– Plasma cells secrete antibodies into blood; memory cells
are stored in lymph nodes
– If subsequent exposure to antigen that activated B cell
occurs, memory cells become plasma cells and secrete
antibodies
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Immune System Cells
– Functions of T cells—cell-mediated immunity
• Cytotoxic T cells—kill infected or tumor cells by
releasing a substance that poisons infected or
tumor cells
• Helper T cells—produce chemicals that help
activate B cells
• Regulatory T cells—release chemicals to
suppress immune responses
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Hypersensitivity of
the Immune System
• Inappropriate or excessive immune
response
• Allergy—hypersensitivity to harmless
environmental antigens (allergens)
– Immediate allergic responses usually
involve humoral immunity
– Delayed allergic responses usually involve
cell-mediated immunity
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Hypersensitivity of
the Immune System
• A healthy immune system works efficiently to fight off
disease. In someone with an autoimmune disorder, the
immune system wrongly identifies healthy tissues as foreign
and tries to destroy them.
• There are over 80 known types of disorders, affecting
different areas of the body – from joints and muscles to skin
and blood and organs. Among the most common
autoimmune conditions are type 1 diabetes, multiple
sclerosis, Crohn's disease, rheumatoid arthritis and
psoriasis. There is no cure, but medication and a healthy
lifestyle can help manage these conditions while researchers
continue to look for new treatment approaches.
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Hypersensitivity of
the Immune System
• Isoimmunity—excessive reaction to
antigens from another human
– May occur between mother and fetus
during pregnancy
– May occur in tissue transplants (causing
rejection syndrome)
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Immune System Deficiency
• Congenital immune deficiency or
immunodeficiency (rare)
– Results from improper lymphocyte
development before birth
– Severe combined immune deficiency
(SCID)—caused by disruption of stem cell
development
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Immune System Deficiency
• Acquired immune deficiency
– Develops after birth
– Acquired immunodeficiency syndrome
(AIDS)—caused by HIV infection of T cells
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