Biology 212 Anatomy & Physiology I Body Defenses

Body Defenses: Homeostasis: Protects body against foreign organisms, toxins, chemicals, damaged cells & tissues, etc. Two forms: - Nonspecific defenses - Specific defenses

Nonspecific Body Defenses - First line defenses Epithelial Barriers: Skin, cornea, mucous membranes Phagocytes: Macrophages, neutrophils, eosinophils Antimicrobial chemicals: Acids - stomach, vagina, urethra Lysozyme: polysaccharide, binds to & destroys bacterial cell walls Complement: proteins, bind to bacteria & parasites - directly lyse them - mark them for phagocytes Interferons: proteins, prevent viruses from infecting cells & mark virus-infected cells for phagocytes

Nonspecific Body Defenses - Second lines of defense after foreign material enters tissues Fever

Nonspecific Body Defenses - Second lines of defense after foreign material enters tissues Fever Inflammation: Inflammatory chemicals from damaged tissues Vasodilation Pain Increased capillary permeability Swelling Increased oxygen Attraction of leukocytes: macrophages lymphocytes neutrophils eosinophils basophils

Nonspecific Body Defenses - Second lines of defense after foreign material enters tissues Fever Inflammation

Specific or Immune Defenses - Specific: Provides defense against specific molecules (antigens) recognized as "non-self" - Adaptive: Defenses can be targeted against new antigens - Systematic: Defenses are distributed through entire body, not limited to site of infection - Memory: Mounts stronger and faster defense against previously encountered antigens The immune system must also develop Self-Tolerance: It must not respond to the body’s own cells & molecules

Terminology Pathogen: Any organism (e.g. bacterium, virus, parasite) against which the immune system responds Antigen: Any molecule against which the immune system responds: May be isolated molecule May be part of larger structure (e.g. protein within a cell membrane) Antibody: A specific protein, also called immunoglobulin, which binds to an antigen. Produced by lymphocytes Antigenic Determinant or Epitope: The specific part of an antigen which an antibody recognizes and binds to

Specific or Immune Defenses Two inter-related components: - Cell-mediated immunity Macrophages and T-lymphocytes Lymphocytes directly attack invading or damaged cells - Humoral immunity Antibodies produced by plasma cells (B-lymphocytes) (with some help from T-lymphocytes) Antibodies attach to invading cells or isolated antigens

Naturally Artificially Acquired Acquired Immunity Naturally Artificially Acquired Acquired Active Passive Active Passive Antigens enter Antibodies pass Antigens Injection of the body from mother to injected into preformed naturally by fetus through body through antibodies or infection or placenta; or vaccination serum which contact with from mother to with dead contains pathogen infant in milk or weakened antibodies Body produces pathogens antibodies and Body produces immune cells antibodies and immune cells

Cells of the Immune System: 1. Macrophages: 2. Lymphocytes and the cells into which they mature 3. Other Antigen Presenting Cells

Cells of the Immune System: 1. Macrophages: Engulf and destroy pathogens, damaged cells, etc. Present antigens to lymphocytes Secrete Activation Factors

Cells of the Immune System: 1. Macrophages: Engulf and destroy pathogens, damaged cells, etc. Present antigens to lymphocytes Secrete Activation Factors 2. Lymphocytes and the cells into which they mature B - lymphocytes Plasma cells Memory cells T - lymphocytes Cytotoxic (killer) cells Helper cells Regulatory/Suppressor cells

Cells of the Immune System: 1. Macrophages: Engulf and destroy pathogens, damaged cells, etc. Present antigens to lymphocytes Secrete Activation Factors 2. Lymphocytes and the cells into which they mature B - lymphocytes Plasma cells Memory cells T - lymphocytes Cytotoxic (killer) cells Helper cells Regulatory/Suppressor cells Other Antigen Presenting Cells: Reticular cells Dendritic cells

Macrophages in Immunity

Lymphocytes in Immunity Two types: Both originate in bone marrow T – Lymphocytes: Become immunocompetent in thymus Responsible for cell-mediated immunity B – Lymphocytes: Become immunocompetent in bone marrow & regions of digestive system Responsible for humoral immunity Both reproduce themselves during immune response

Humoral Immune Response Effective against both isolated antigens and cells. Begins when immunocompetent B-lymphocyte recognizes & binds to a specific antigen, becoming activated.

Antibodies from plasma cells have three actions: Neutralize the antigen by changing its shape Cause antigens or pathogens to agglutinate or precipitate Mark the antigen or pathogen to be phagocytosed Antibody binding onto an antigen or pathogen also stimulates nonspecific defenses such as inflammation or fever.

Cell-mediated Immune Response Effective against invading cells or damaged cells Begins when macrophage or infected cell presents antigen to immunocompetent T-lymphocytes, activating them When cytotoxic T-lymphocyte activated, it binds to target cell & releases molecules which directly damage it, e.g. perforin, lymphotoxins, tumor necrosis factor, oxygen-free-radicals

Cell-mediated Immune Response Effective against invading cells or damaged cells Begins when macrophage or infected cell presents antigen to immunocompetent T-lymphocytes, activating them When helper T-lymphocyte activated, it secretes chemicals which activate macrophages and stimulate proliferation of both B- and cytotoxic T-lymphocytes

Cell-mediated Immune Response Third type, regulatory or suppressor T-lymphocytes, secrete chemicals which suppress the activities of both T- & B-lymphocytes. Necessary to “wind down” immune response after antigen or invading/damaged cell destroyed Minimizes risk of cross-reactivity and damage to “self” cells (autoimmune diseases) Help convert activated T- & B-lymphocytes to memory cells