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Transcript
Specific Defense Mechanisms – The Immune System The Specific Defense System 3rd Line of Defense Antigen specific – recognizes and acts against particular foreign substances Systemic – not restricted to the initial infection site Has memory – recognizes and mounts a stronger attack on previously encountered pathogens Types of Immunity 1. Humoral immunity Antibody-mediated immunity Cells produce antibodies for defense found in the fluid (serum) 2. Cellular immunity Cell-mediated immunity Lymphocytes target virus infected cells, cancer cells, foreign grafts. Antigens (Nonself) Any substance capable of exciting the immune system and provoking an immune response Examples of common antigens - Foreign proteins - Nucleic acids - Large carbohydrates - Some lipids - Pollen grains - Microorganisms Self-Antigens Human cells have many surface proteins Our immune cells do not attack our own proteins Our cells in another person’s body can trigger an immune response because they are foreign - Restricts donors for transplants Allergies Many small molecules (called haptens or incomplete antigens) are not antigenic, but link up with our own proteins The immune system may recognize and respond to a protein-hapten combination The immune response is harmful rather than protective because it attacks our own cells Cells of the Immune System Lymphocytes Originate from hemocytoblasts in the red bone marrow B lymphocytes become immunocompetent in the bone marrow T lymphocytes become immunocompetent in the thymus Macrophages Arise from monocytes Become widely distributed in lymphoid organs Activation of Lymphocytes Humoral (Antibody-Mediated) Immune Response B cells w/ specific receptors bind to specific antigen Binding activates the B-cell to undergo clonal selection Many clones are produced (1° humoral response) Most B cells become plasma cells - Produce antibodies to destroy antigens - Activity lasts for four or five days Some B cells become memory cells (2° humoral response) Stem Cells Immature B Bone Marrow Formed in bone marrow, become immunocompetent (appearance of Cells cell surface antibodies), then migrates to lymph nodes. Activated B Cells Plasma Cells Secretes Antibodies Memory When comes in contact with specific antigen they undergo repeated mitosis and form clones. Remembers subsequent Cells exposure, then can change to plasma cells rapidly. Humoral Immune Response Secondary Response Memory cells are long-lived A second exposure causes a rapid response The secondary response is stronger, faster & longer lasting Active Immunity When your own immune system encounters antigens and produces antibodies Active immunity can be naturally or artificially acquired Passive Immunity Antibodies are obtained from someone else - mother to fetus (placenta or milk) - Injection of immune serum or gamma globulin Immunological memory does not occur Protection provided by “borrowed antibodies” Monoclonal Antibodies Antibodies prepared for clinical testing or diagnostic services Produced from descendents of a single cell line Examples of uses for monoclonal antibodies - Diagnosis of pregnancy - Treatment after exposure to hepatitis and rabies Antibodies (Immunoglobulins) (Igs) Soluble proteins secreted by B cells (plasma cells) Carried in blood plasma Capable of binding specifically to an antigen Antibody Structure Four amino acid chains linked by disulfide bonds Two identical amino acid chains are linked to form a heavy chain The other two identical chains are light chains Specific antigenbinding sites are present Antibody Classes Antibodies of each class have slightly different roles Five major immunoglobulin classes IgM – can fix complement IgA – found mainly in mucus IgD – important in activation of B cell IgG – can cross the placental barrier IgE – involved in allergies Antibody Function Antibodies inactivate antigens in a number of ways Complement fixation Neutralization Agglutination Precipitation Antibody Function Cellular (Cell-Mediated) Immune Response •Development of T Cells »Stem cells from the bone marrow seed the thymus gland, and shortly before and after birth they develop into T cells (lymphocytes). »They leave the thymus and take up residence in lymph nodes. »They have specific antibody molecules that fit one specific antigen embedded in its plasma membrane. »The second stage of development occurs when the T cell comes in contact with its specific antigen…(antigen presentation by macrophage). Cellular (Cell-Mediated) Immune Response »…when this happens the T cell changes into a sensitized T cell. »Produces cell-mediated immunity (resistance to disease organisms resulting from the action of cells). »After antigen binding, clones form as with B cells, but different classes of cells are produced T Cell Clones • Cytotoxic T cells • Specialize in killing infected cells • Insert a toxic chemical (perforin) PRESS TO PLAY CYTOTOXIC T CELLS ANIMATION • Helper T cells • Recruit other cells to fight the invaders • Interact directly with B cells PRESS TO PLAY HELPER T CELLS ANIMATION T Cell Clones • Suppressor T cells • Release chemicals to suppress the activity of T and B cells • Stop the immune response to prevent uncontrolled activity • A few members of each clone are memory cells Summary of the Immune Response Figure 12.19 Organ Transplants and Rejection • Major types of grafts • Autografts – tissue transplanted from one site to another on the same person • Isografts – tissue grafts from an identical person (identical twin) • Allografts – tissue taken from an unrelated person • Xenografts – tissue taken from a different animal species Organ Transplants and Rejection • Autografts and isografts are ideal donors • Xenografts are never successful • Allografts are more successful with a closer tissue match Disorders of Immunity: Allergies (Hypersensitivity) • Abnormal, vigorous immune responses • Types of allergies • Immediate hypersensitivity • Triggered by release of histamine from IgE binding to mast cells • Reactions begin within seconds of contact with allergen • Anaphylactic shock – dangerous, systemic response Allergy Mechanisms Figure 12.20 Disorders of Immunity: Allergies (Hypersensitivity) • Types of allergies (continued) • Delayed hypersensitivity • Triggered by the release of lymphokines (not histamine) from activated helper T cells • Symptoms usually appear 1–3 days after contact with antigen • Common example: allergic contact dermatitis (poison ivy) Disorders of Immunity: Immunodeficiencies • Production or function of immune cells or complement is abnormal • May be congenital (SCID) or acquired (AIDS) • AIDS cripples the immune system by interfering with the activity of helper T cells • Read 394-395 Disorders of Immunity: Autoimmune Diseases • The immune system does not distinguish between self and nonself • The body produces antibodies and sensitized T lymphocytes that attack its own tissues Disorders of Immunity: Autoimmune Diseases • Examples of autoimmune diseases • Multiple sclerosis – white matter of brain and spinal cord are destroyed • Myasthenia gravis – impairs communication between nerves and skeletal muscles by destroying Ach receptors on muscles. • Juvenile diabetes – destroys pancreatic beta cells that produce insulin • Rheumatoid arthritis – destroys synovial membranes in and near joints Disorders of Immunity: Autoimmune Diseases • Examples of autoimmune diseases (continued) • Systemic lupus erythematosus (SLE) – attacks connective tissue in general. Affects kidney, heart, lung and skin • Glomerulonephritis – impairment of renal function Self Tolerance Breakdown • Inefficient lymphocyte programming • Appearance of self-proteins in the circulation that have not been exposed to the immune system • Eggs • Sperm • Eye lens Self Tolerance Breakdown • Cross-reaction of antibodies produced against foreign antigens with self-antigens • Rheumatic fever Developmental Aspects of the Lymphatic System and Body Defenses • Except for thymus and spleen, the lymphoid organs are poorly developed before birth • A newborn has no functioning lymphocytes at birth; only passive immunity from the mother • If lymphatics are removed or lost, severe edema results, but vessels grow back in time