Transcript Adaptive Defense System

Adaptive Defense System
Third Line of Defense
• Immune response - response to a
threat that targets specific antigens
• 2 types of immunity:
– Humoral immunity = antibody-mediated
• Provided by antibodies present in body fluids
– Cellular immunity = cell-mediated
• Targets virus-infected cells, cancer cells, and
cells of foreign grafts
• Antigens (nonself)
– Any substance capable of exciting the immune
system and provoking an immune response
– Examples:
• Foreign proteins (strongest)
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Nucleic acids
Large carbohydrates
Some lipids
Pollen grains
Microorganisms
restricts donors
for transplants
• Self-antigens
– Your immune cells do not attack your own cell
surface proteins
• Allergies
– Many small molecules (= haptens or incomplete
antigens) are not antigenic by themselves
– BUT link up with our own proteins to trigger
immune system
• harmful rather than protective because it attacks our
own cells
• Cells of the adaptive defense system:
– Lymphocytes respond to specific antigens
• What type of cell a hemocytoblast turns into
depends on where it becomes immunocompetent
– capable of responding to specific antigen by
binding to it
– B lymphocytes (B cells) – in bone marrow
– T lymphocytes (T cells) – in thymus
– Macrophages help lymphocytes
• Arise from monocytes
• In lymphoid organs
• Secrete cytokines (= proteins important in the
immune response)
Lymphocyte Differentiation and
Activation
Lymphocytes destined to become T cells
migrate from bone marrow to the thymus
and develop immunocompetence there.
B cells develop immuno-competence in
the bone marrow.
Bone marrow
Circulation
in blood
Immature
lymphocytes
Thymus
Immunocompetent,
but still naive,
lymphocytes
migrate via blood
Mature
immunocompetent
B and T cells
recirculate in
blood and lymph
After leaving the thymus or bone marrow
as naive immunocompetent cells,
lymphocytes “seed” the infected
connective tissues (especially lymphoid
tissue in the lymph nodes), where the
antigen challenge occurs and the
lymphocytes become fully activated.
Bone marrow
Activated (mature) lymphocytes circulate
continuously in the bloodstream and
lymph, and throughout the lymphoid
organs of the body.
Lymph nodes
and other
lymphoid tissues
KEY:
Site of lymphocyte origin
and
Sites of development of
immunocompetence as B
or T cells; primary lymphoid organs
Figure 12.11
Site of antigen challenge and final
differentiation to mature B and T cells
Lymphocytes destined to become T cells
migrate from bone marrow to the thymus
and develop immunocompetence there.
Bone marrow
Circulation
in blood
Immature
lymphocytes
Thymus
KEY:
Site of lymphocyte origin
and
Sites of development of
immunocompetence as B
or T cells; primary lymphoid organs
Site of antigen challenge and final
differentiation to mature B and T cells
Figure 12.11, step 1a
Lymphocytes destined to become T cells
migrate from bone marrow to the thymus
and develop immunocompetence there.
B cells develop immuno-competence in
the bone marrow.
Bone marrow
Circulation
in blood
Thymus
Immature
lymphocytes
Bone marrow
KEY:
Site of lymphocyte origin
and
Sites of development of
immunocompetence as B
or T cells; primary lymphoid organs
Site of antigen challenge and final
differentiation to mature B and T cells
Figure 12.11, step 1b
Lymphocytes destined to become T cells
migrate from bone marrow to the thymus
and develop immunocompetence there.
B cells develop immuno-competence in
the bone marrow.
Bone marrow
Circulation
in blood
Immature
lymphocytes
Thymus
Immunocompetent,
but still naive,
lymphocytes
migrate via blood
After leaving the thymus or bone marrow
as naive immunocompetent cells,
lymphocytes “seed” the infected
connective tissues (especially lymphoid
tissue in the lymph nodes), where the
antigen challenge occurs and the
lymphocytes become fully activated.
Bone marrow
Lymph nodes
and other
lymphoid tissues
KEY:
Site of lymphocyte origin
and
Sites of development of
immunocompetence as B
or T cells; primary lymphoid organs
Site of antigen challenge and final
differentiation to mature B and T cells
Figure 12.11, step 2
Lymphocytes destined to become T cells
migrate from bone marrow to the thymus
and develop immunocompetence there.
B cells develop immuno-competence in
the bone marrow.
Bone marrow
Circulation
in blood
Immature
lymphocytes
Thymus
Immunocompetent,
but still naive,
lymphocytes
migrate via blood
Mature
immunocompetent
B and T cells
recirculate in
blood and lymph
After leaving the thymus or bone marrow
as naive immunocompetent cells,
lymphocytes “seed” the infected
connective tissues (especially lymphoid
tissue in the lymph nodes), where the
antigen challenge occurs and the
lymphocytes become fully activated.
Bone marrow
Activated (mature) lymphocytes circulate
continuously in the bloodstream and
lymph, and throughout the lymphoid
organs of the body.
Lymph nodes
and other
lymphoid tissues
KEY:
Site of lymphocyte origin
and
Sites of development of
immunocompetence as B
or T cells; primary lymphoid organs
Site of antigen challenge and final
differentiation to mature B and T cells
Figure 12.11, step 3
Humoral (Antibody-Mediated)
Immune Response
• primary humoral response: B lymphocytes
with specific receptors bind to a specific
antigen causes lymphocyte to make large
# of clones
– Most B cells become plasma cells
• Produce antibodies to destroy antigens
• Live 4 or 5 days
• secondary humoral response = Some B cells
become memory cells
• Live longer
– A second exposure causes a rapid response that
is stronger and longer lasting
Primary Response
(initial encounter
with antigen)
B lymphoblasts
Proliferation to
form a clone
Plasma
cells
Memory
B cell
Secreted
antibody
molecules
Secondary Response
(can be years later)
Antigen binding
to a receptor on a
specific B cell
(lymphocyte)
(B cells with
non-complementary
receptors remain
inactive)
Subsequent challenge
by same antigen
Clone of cells
identical to
ancestral cells
Plasma
cells
Secreted
antibody
molecules
Figure 12.12
Memory
B cells
Primary Response
(initial encounter
with antigen)
Antigen
Antigen binding
to a receptor on a
specific B cell
(lymphocyte)
(B cells with
non-complementary
receptors remain
inactive)
Figure 12.12, step 1
Antigen
Primary Response
(initial encounter
with antigen)
B lymphoblasts
Proliferation to
form a clone
Antigen binding
to a receptor on a
specific B cell
(lymphocyte)
(B cells with
non-complementary
receptors remain
inactive)
Figure 12.12, step 2
Antigen
Primary Response
(initial encounter
with antigen)
B lymphoblasts
Plasma
cells
Proliferation to
form a clone
Antigen binding
to a receptor on a
specific B cell
(lymphocyte)
(B cells with
non-complementary
receptors remain
inactive)
Memory
B cell
Secreted
antibody
molecules
Figure 12.12, step 3
Antigen
Primary Response
(initial encounter
with antigen)
B lymphoblasts
Proliferation to
form a clone
Plasma
cells
Memory
B cell
Secreted
antibody
molecules
Secondary Response
(can be years later)
Antigen binding
to a receptor on a
specific B cell
(lymphocyte)
(B cells with
non-complementary
receptors remain
inactive)
Subsequent challenge
by same antigen
Clone of cells
identical to
ancestral cells
Figure 12.12, step 4
Antigen
Primary Response
(initial encounter
with antigen)
B lymphoblasts
Proliferation to
form a clone
Plasma
cells
Memory
B cell
Secreted
antibody
molecules
Secondary Response
(can be years later)
Antigen binding
to a receptor on a
specific B cell
(lymphocyte)
(B cells with
non-complementary
receptors remain
inactive)
Subsequent challenge
by same antigen
Clone of cells
identical to
ancestral cells
Plasma
cells
Secreted
antibody
molecules
Figure 12.12, step 5
Memory
B cells
Humoral Immune Response
Figure 12.13
• Active Immunity
– Occurs when B cells encounter antigens and
produce antibodies
– Naturally acquired during bacterial and viral
infections
– Artificially acquired from vaccines
• Passive Immunity
– Occurs when antibodies are obtained from
someone else
• From a mother to her fetus (naturally acquired)
• From immune serums, like antivenom, or gamma
globulin that is given once exposed to hepatitis
(artificially acquired)
– Immunological memory does not occur
Types of Acquired Immunity
Figure 12.14
• Antibodies (Immunoglobulins or Igs)
– Soluble proteins secreted by B cells
– Carried in blood plasma
– Capable of binding specifically to an antigen
– Antibodies inactivate antigens in a number of
ways:
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•
•
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Complement fixation
Neutralization
Agglutination
Precipitation
Antibody Function
Figure 12.16
Cellular (Cell-Mediated) Immune
Response
• Antigens must be presented by macrophages to
a T cell
• T cells must recognize nonself and self antigens
(double recognition)
• After antigen binding, clones form:
– Cytotoxic (killer) T cells
• Specialize in killing infected cells by inserting a toxic
chemical, perforin
– Helper T cells
• Interact directly with B cells to recruit other cells to fight
the invaders
– Regulatory T cells
• Release chemicals to suppress T and B cells
• Stop the immune response to prevent uncontrolled activity
– A few members of each clone are memory cells
Figure 12.17
Figure 12.18
Organ Transplants and Rejection
• Major types of grafts
1. Autografts—tissue transplanted from one site
to another on the same person
2. Isografts—tissue from an identical twin
•
Autografts and isografts are most ideal donors
3. Allografts—tissue from an unrelated person
•
Most commonly used (from cadaver)
4. Xenografts—tissue from a different animal
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Whole organs are never successful but can use pig
heart valves in humans