1. 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

2. Antigens (nonself) Self-antigens
Any substance capable of exciting the immune system and provoking an immune response
Examples:
Foreign proteins (strongest) restricts donors
for transplants
Nucleic acids
Large carbohydrates
Some lipids
Pollen grains
Microorganisms
Self-antigens
Your immune cells do not attack your own cell surface proteins

3. 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

4. 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)

5. Lymphocyte Differentiation and Activation
Site of lymphocyte origin
KEY:
Site of antigen challenge and final differentiation to mature B and T cells
Sites of development of immunocompetence as B or T cells; primary lymphoid organs
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.
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.
Activated (mature) lymphocytes circulate continuously in the bloodstream and lymph, and throughout the lymphoid organs of the body.
and
Bone marrow
Lymph nodes and other lymphoid tissues
Immature lymphocytes
Circulation in blood
Immunocompetent, but still naive, lymphocytes migrate via blood
Mature immunocompetent B and T cells recirculate in blood and lymph
Thymus
Figure 12.11

6. Figure 12.11, step 1a Site of lymphocyte origin KEY:
Site of antigen challenge and final differentiation to mature B and T cells
Sites of development of immunocompetence as B or T cells; primary lymphoid organs
Lymphocytes destined to become T cells migrate from bone marrow to the thymus
and develop immunocompetence there.
and
Bone marrow
Immature lymphocytes
Circulation in blood
Thymus
Figure 12.11, step 1a

7. Figure 12.11, step 1b Site of lymphocyte origin KEY:
Site of antigen challenge and final differentiation to mature B and T cells
Sites of development of immunocompetence as B or T cells; primary lymphoid organs
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.
and
Bone marrow
Immature lymphocytes
Circulation in blood
Thymus
Figure 12.11, step 1b

8. Figure 12.11, step 2 Site of lymphocyte origin KEY:
Site of antigen challenge and final differentiation to mature B and T cells
Sites of development of immunocompetence as B or T cells; primary lymphoid organs
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.
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.
and
Bone marrow
Lymph nodes and other lymphoid tissues
Immature lymphocytes
Circulation in blood
Immunocompetent, but still naive, lymphocytes migrate via blood
Thymus
Figure 12.11, step 2

9. Figure 12.11, step 3 Site of lymphocyte origin KEY:
Site of antigen challenge and final differentiation to mature B and T cells
Sites of development of immunocompetence as B or T cells; primary lymphoid organs
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.
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.
Activated (mature) lymphocytes circulate continuously in the bloodstream and lymph, and throughout the lymphoid organs of the body.
and
Bone marrow
Lymph nodes and other lymphoid tissues
Immature lymphocytes
Circulation in blood
Immunocompetent, but still naive, lymphocytes migrate via blood
Mature immunocompetent B and T cells recirculate in blood and lymph
Thymus
Figure 12.11, step 3

10. 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

11. Proliferation to form a clone
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)
Proliferation to form a clone
B lymphoblasts
Plasma cells
Secreted antibody molecules
Clone of cells identical to ancestral cells
Subsequent challenge by same antigen
Memory B cell
Memory B cells
Secondary Response (can be years later)
Figure 12.12

12. Primary Response (initial encounter with 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

13. Proliferation to form a clone
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)
Proliferation to form a clone
B lymphoblasts
Figure 12.12, step 2

14. Proliferation to form a clone
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)
Proliferation to form a clone
B lymphoblasts
Plasma cells
Secreted antibody molecules
Memory B cell
Figure 12.12, step 3

15. Proliferation to form a clone
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)
Proliferation to form a clone
B lymphoblasts
Plasma cells
Secreted antibody molecules
Clone of cells identical to ancestral cells
Subsequent challenge by same antigen
Memory B cell
Secondary Response (can be years later)
Figure 12.12, step 4

16. Proliferation to form a clone
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)
Proliferation to form a clone
B lymphoblasts
Plasma cells
Secreted antibody molecules
Clone of cells identical to ancestral cells
Subsequent challenge by same antigen
Memory B cell
Memory B cells
Secondary Response (can be years later)
Figure 12.12, step 5

17. Humoral Immune Response
Figure 12.13

18. Active Immunity Passive 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

19. Types of Acquired Immunity
Figure 12.14

20. 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:
Complement fixation
Neutralization
Agglutination
Precipitation

21. Antibody Function
Figure 12.16

22. 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

23. Figure 12.17

24. Figure 12.18

25. Organ Transplants and Rejection
Major types of grafts
Autografts—tissue transplanted from one site to another on the same person
Isografts—tissue from an identical twin
Autografts and isografts are most ideal donors
Allografts—tissue from an unrelated person
Most commonly used (from cadaver)
Xenografts—tissue from a different animal
Whole organs are never successful but can use pig heart valves in humans