The Immune Response


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The Immune Response

  1. 1. The Immune Response I. Specific immunity A. Occurs only in vertebrates Involves highly specific defense response B. Occurs When the host is exposed to Microorganism or its products Some tumor cells Certain macromolecules (Substances in the environment) C. Immune response Specific series of defensive actions that occurs throughout the body Lymphocytes recognize presence of foreign substances and act to eliminate them D. Three Characteristics of the immune system 1. Tolerance Distinguishes self from non-self Does not attack host macromolecules Attacks foreign macromolecules 2. Specificity Attacks foreign macromolecules with immune system cells that are specific for the particular foreign macromolecules 3.Memory Once immune system has recognized and reacted with a specific macromolecule it is able to react very quickly to subsequent exposure to the same macromolecule E. Immune system composed of two interdependent parts 1. Antibody mediated immunity - Humoral 2. Cell mediated immunity *Neither part functions without the other II. Humoral Immunity A. Antibody mediated immunity Neutralize foreign macromolecules by action of specific antibodies B. Antigen Any foreign macromolecules that induces the immune response Invading microorganisms contain a variety of antigens Common Antigens Proteins Nucleic Acids Polysaccharides Some lipids Lipopolysaccharides
  2. 2. C. Antigenic Determinants Epitopes Specific part of the antigen molecule that the antibody is directed against Projections from the surface of the antigen D. Common Antigenic Determinants Sugars Amino acid R groups Organic Acids Hydrocarbons E. Humoral Immune system Produces antibodies as a result of stimulation by antigens F. Antibodies Specific proteins that react with antigens Present in Blood Serum Other bodily fluids Proteins produced by the host Interfere with the normal functioning of the antigen Allow the host to destroy antigen G. Antibody structure Five classes of antibodies found in mammals All very similar Consist of four polypeptide chains Two identical light chains Two identical heavy chains Linked by disulfide bonds H. Antibody Molecule Antigen binding sites Chains folded to form two identical antigen binding sites on the surface of the antibody Interact with antigens in a lock and key fashion Antibody-Antigen combination I. Development of humoral immunity Specific sequence of events occurs when the host is exposed to an antigen Antigen localized in the cells of the reticuloendothelial system soon after it enters the body Liver Spleen Lymph nodes
  3. 3. J. Latent period Occurs immediately after first exposure Lasts several days No antibody can be detected in blood K. Primary response Initial production of a low level of antibody Antigen localized in cells of lympathic system soon after it enters the body Spleen Liver L. Antibody development Log phase Antibody level Rises logarithmically Plateau phase Antibody titer stabilizes No increase or decrease in the number of antibodies Decline phase Antibodies Combine with the antigen Removed from the circulation by phagocytes Booster response Booster response - Secondary response Rapid sudden increase in antibody level following a second or subsequent exposure to the same specific antigen Body mounts heightened response to same specific antigen Antibody level may be 10-1000 times greater than during the primary response M. Ability to form antibodies Vertebrates can produce between 10 and 100 million different kinds of specific antibodies Dependent on Age Nutrient state Hormonal balance Depressed by steroid hormones Exposure to radiation Certain viruses N. Development of T cells Some released into blood 70-80% of circulating lymphocytes are T cells Other T cells do not circulate
  4. 4. Found in Lymph nodes Spleen Cells predetermined to become T cells Leave the bone marrow Migrate to the thymus gland Complete their develop into T cells O. Lymphocytes Cells primarily responsible for the immune response Derived from stem cells in bone marrow Small mononuclear (single nucleus) leucocytes Non-phagocytic Immunologically competent (or precursors of such cells) 109 produced each day Migrate through the circulatory or lymphatic systems to lymphoid tissue Produce lymphocyte colonies P. Types of lymphocytes B lymphocytes or B cells T lymphocytes or T cells Q. B cell development Complete differentiation in Fetal liver Adult bone marrow B cell differentiation Distributed by the blood Make up 20-30% of the circulating lymphocytes R. Antibody production Requires interaction of three types of white blood cells Macrophage B lymphocyte T helper cell Macrophage, T cell, and B cell complex Macrophage (phagocyte) Ingests invading microorganisms B lymphocytes (B cells) Have specific antigenic receptors on their surface T helper cell Also have specific receptors on their surfaces which bind to specific antigen parts on the surface of the macrophage Produces chemical that stimulates the B cells to divide repeatedly Dividing B cells produce
  5. 5. Many plasma cells Memory B cells S. Complement system Combination of antigen and antibody has minimal effect until the complement system is activated Group on proteins in blood serum Effective against Gram negative bacteria Activated by the antibody-antigen comples Each protein has specific antibacterial function T. Complement fixation Complement proteins irreversibly changed during reaction with antigen-antibody complex Can’t be reused Basis of many medical diagnostic tests III. Cellular immune response A. General Involves T cells Does not involve B cells or antibodies B. T cells Become Immunologically competent As result of contact with specific antigens Competent T cells Release lymphokines Attack antigens directly Attract phagocytes Cause the inflammatory response C. Cellular Immune response Takes about 24 hours to develop after contact with the antigen D. T.B. skin test Relies on the cellular immune response Detects past or current infections with Mycobacterium tuberculosis Mycobacterium antigens injected subcutaneously into the forearm T.B. skin test-results No infection or no immunity  no reaction Immunity or active infection  positive reaction T.B. skin test-positive reaction Hard raised welt in the area of injection T cells activated by past encounters with Mycobacterium respond by producing lymphokines Lymphokins Attack Mycobacterium antigens directly Attract phagocytes to the area of the injection Cause the inflammatory response E. Killer Macrophages
  6. 6. Activated T cells produce lymphokines Act on developing macrophages killer macrophages Better able to kill invading foreign organisms Have large number of hydrolytic granules Kill bacteria that cause intracellular infections IV. Immunology and disease prevention A. Passive Immunity Organism is protected against by antibodies produced by another organism Short term immunity Antibodies prevent or cure disease for a short time Gradually lost Organism cannot produce more antibodies for itself Can be reinfected by the same pathogen B. Natural passive immunity Maternal antibodies transferred to fetus before birth Maternal antibodies protect the neonate Antibodies secreted into milk also protect baby C. Active immunity Occurs when organism is stimulated to develop its own antibodies Develops in response to infection or injection of specific antigen Individual is fundamentally changed Able to produce specific antibodies throughout life D. Vaccine Used to induce antibody formation Harmless product containing antigens from pathogens Organism itself Killed bacteria Viruses Attenuated strains