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) 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

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 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

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

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

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

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

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

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

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

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

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

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

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

Humoral Immune Response Figure 12.13

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

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: 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 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