Lesson # 11

1. Immunity-2 Lesson # 11 Objectives: Chapter 22 1- To distinguish between cellular immunity and humoral immunity.2- Identify the two forms of active immunity and the two forms of passive immunity. 3- List the four general properties of immunity. 4- Identify the four major types of T cells. 5- Describe the mechanism of antigen presentation. 6- Describe the activation of CD8 and CD4 cells. 7- Describe the structure of the antibodies and the different types of antibodies. 8- Distinguish between primary and secondary immune responses.

2. The Lymphoid System and Body Defenses 1- Nonspecific Defenses They do not distinguish one type of threat from another. The response is the same, regardless of the type of invading agent. The protection provided is called nonspecific resistance. • 1- Physical Barriers • 5- Complement • 2- Phagocytes • 6- Inflammatory Response • 3- Immunological Surveillance • 7- Fever • 4- Interferons 2- Specific Defenses They protect against a specific threat, and are ineffective against a different threat. The protection provided by the specific defenses is called Immunityor specific resistance. The Immunity or specific resistance depends on the activity of specific lymphocytes.

3. Forms of Immunity o Specific Defenses Innate Innate It is present at birth and it is not related to previous exposure to a particular antigens. At birth, the human being has specific immunity against some diseases that can affect other species. Adaptive Immunity Adaptive Immunity is not present at birth. It is developed in response to an antigen exposure (active immunity), or may be received from another source (passive immunity). The immune system of a person is activated by the exposure to antigens . Active Immunity The person receives antibodies produced in other person or an animal. Passive Immunity

4. The immune system of a person is activated by the exposure to antigens . Active Immunity Naturally Acquired Active Immunity. The exposure to antigens begins after birth and continues in a natural way during the whole life. Artificially induced active immunity. The exposure to antigens is produced artificially under controlled conditions (immunization or vaccination). The person receives antibodies produced in other person or an animal. Passive Immunity Naturally Acquired Passive Immunity. When a baby receives antibodies from the mother, either during gestation (by crossing the placenta), or in early infancy (through breast milk). Artificially Induced Passive Immunity. When a person receives antibodies produced in other person or animal to treat a disease (ex: antibodies against rabies virus or snake venom).

5. Forms of Immunity Adaptive Immunity Innate Immunity Genetically determined. No prior exposure or antibody production Produced by antigen exposure or antibodies from another source Active Immunity Passive Immunity Produced by transfer of antibodies from another source Produced in response to antigen exposure Naturally Acquired Active Immunity Induced Active Immunity Naturally Acquired Passive Immunity Induced Passive Immunity • It is the production of one’s own antibodies or T cells as a result of infection or natural exposure to antigen • It is the production of one’s own antibodies or active T cells as a result of vaccination to prevent disease • Conferred by transfer of maternal antibodies across the placenta or in breast milk • Conferred by administration of antibodies from another person or animal • It is temporary.

6. Properties of Immunity • 1- Specificity, 2- Versatility, 3- Memory, 4- Tolerance • 1- Specificity • Each T or B cell is activated by specific antigens and responds only to this specific antigen and ignores all others.

7. 2- Versatility • The body produces many types of lymphocytes and each fights a different type of antigen. Active lymphocyte clones (reproduces) itself to fight specific antigen. Clones of activated B cells Activation

8. 3- Memory • Activated lymphocytes produce one group of cells that remains inactive (as memory cells) until it meets the same antigen and then produces a faster, stronger and longer-lasting response. Clones of activated B cells Activation Clones of memory B cells

9. 4- Tolerance • The immune system ignores “normal” antigens (self- antigens).

10. Antibody-mediated Immunity and Cell-mediated Immunity Y Y Antigens Antigens Y Y Y Y Antibody-mediated Immunity or Humoral Immunity Antibodies Activated Cytotoxic T lymphocyte Cytotoxic T lymphocyte Cell-mediated Immunity or Cellular Immunity • 1-Perforin and granzymes that kill cells. • 2- Interferons that inhibit viral replication.

11. Cellular Immunity Antigen Presentation Adaptive Defenses Antigen presentationtriggers specificdefenses, or animmune response. T lymphocytes recognize antigens that are bound to glycoproteins in plasma membrane of other cells. Some phagocytic cells can engulf and breakdown pathogens to create antigens to be presented to the T cells. Those cells are called antigen presenting cells.

12. Antigen Presenting Cells (APC) They are specialized cells responsible for activating T cells against foreign cells (including bacteria) and foreign proteins. Antigen Presenting Cells (APCs) engulf invaders, process them, and present the antigens to the T lymphocytes. Antigenic fragments are displayed by plasma membrane. Phagocytic APCsengulf the extra- cellular pathogens. MHC protein Antigenic fragments are bound to MHC proteins. Lysosomal actionproduces antigenicfragments. The endoplasmicreticulum producesMHC proteins.

13. Antigen Recognition APCs have the antigens by binding them to specific proteins that are present in their cell membranes calledMajor Histocompatibility Complex (MHC). There are two types of MHC proteins: Class I MHC and Class II MHC. Class II MHC protein on the plasma membrane of the APC Displayed Antigenic fragment Displayed abnormal peptide Class I MHC protein on the plasma membrane of the APC Some Antigen Presenting Cells 1- Free and fixed macrophages in connective tissue. 2- Kupffer cells of liver. 4- Langerhan’s cells in skin. 3- Microglia in the CNS. 5- Dendritic cells in lymph nodes and spleen.

14. CD8 T Cells and CD4 T Cells • 1- Cytotoxic T cells (CD8) • They attack foreign cells and cells infected by viruses. They are responsible of cell-mediated immunity. (CD4) • 2- Regulatory T cells • They stimulate function of T cells and B cells. • They control the sensitivity of immune response. (CD8) • Inhibit function of T cells and B cells. • 3- Memory T cells (CD8 or CD4) • They respond to a previously encountered antigen. T lymphocytes have marker proteins in their membranes. • Helper T cells There are two groups of markers: CD8 and CD4 CD8 markers are found in Cytotoxic T cells and suppressor T cells. • Suppressor T cells CD4 markers are found in helper T cells.

15. Activation of CD8 T Cells • Cytotoxic T cells 2 1 • Cytotoxic T cells (CD8) recognize antigens bound to Class I MHC. 3 • When activated, cytotoxic T cells: • 1- Release perforin that destroy target cell membrane. • 2- Secret lymphotoxin that kills the target cell. • 3-Activate genes in the target cell that induce the cell to kill itself (apoptosis).

17. Activation of CD4 T Cells • Helper T cells • Helper T cells (CD4) recognize antigens bound to Class II MHC.

18. After activation, CD4 T cells secret cytokines that have the following effects: • 1- Stimulate T cell divisions, produce memory THcells and accelerate cytotoxic T cell maturation. • 2- Attract and stimulate macrophages. • 3- Attract and stimulate activity of cytotoxic T cells. • 4- Promote activation of B cells.

20. Some B lymphocytes differentiates into plasma cells, which are the cells responsible for antibody production

21. Antibody Structure Heavy chain Antigenbindingsite Antigenbinding site Disulfidebond Variablesegment Light chain Complementbinding site (classical pathway) Constantsegmentsof lightand heavychains Site of bindingto macrophages (Opsonization)

22. Classes of Antibodies IgG accounts for 80 % of all antibodies. They are responsible for resistance against many viruses, bacteria, and bacterial toxins. These antibodies can cross the placenta. IgE attaches to surfaces of basophils and mast cells. When a suitable antigen is bound by IgE, the cells release histamine and other chemical that accelerate inflammation. IgE is important also in allergic response . IgD can play a role in activation of B cells. It is the first antibody secreted after an antigen arrives. It has five valences. Agglutinins are IgM antibodies. IgA is found primary in glandular secretions as mucus, tears, saliva, and semen. These antibodies attack pathogens before they gain access to internal tissues.

24. Secretorypiece

25. Primary and Secondary Responses to Antigen Exposure The secondary or anamnestic response is produced by the reexposition to the same antigen. It is a greater response in a much sorter time. The primary immune response is the immune reaction brought about by the first exposure to an antigen. • It can take 2 weeks to develop and declines rapidly. It is produced by the effects of memory B cell activation. IgG rises very high and very quickly, and can remain elevated for extended time. • IgM is produced faster than IgG, but it less effective.