Adaptive Immunity Host Defenses - PDF

Adaptive Immunity: Highly Specific Host Defenses Learning Objectives Main features of adaptive immune system Types of lymphocytes and their functions Development of tolerance Antigen presentation Antibody production and structural diversity Immune diso...

Adaptive Immunity: Highly Specific Host Defenses Learning Objectives Main features of adaptive immune system Types of lymphocytes and their functions Development of tolerance Antigen presentation Antibody production and structural diversity Immune disorders © 2018 Pearson Education, Inc.  26.4 Leukocyte Production and Diversity Lymphocytes are specialized leukocytes involved exclusively in adaptive immune response Two types of lymphocytes B cells: originate and mature in bone marrow. Produce antibodies. Protect against extracellular antigens. Confer antibody- mediated (humoral) immunity. T cells: originate in bone marrow, but mature in thymus. Defend against intracellular © 2018 Pearson Education, Inc. pathogens. Cell-mediated (cellular) immunity.  27.1 Specificity Specificity of antigen–antibody reaction is dependent on lymphocyte cell receptors interacting with individual pathogen © 2018 Pearson Education, Inc.  27.1 Memory Memory: Subsequent exposures to the same antigen result in rapid production of large quantities of antigen-reactive T cells or antibodies © 2018 Pearson Education, Inc. © 2018 Pearson Education, Inc. Figure 27.1c  27.1 Tolerance Tolerance: the acquired inability to make an adaptive immune response to one’s own antigens Discrimination between foreign and host antigens Failure to develop tolerance may result in reactions against self, called autoimmunity © 2018 Pearson Education, Inc.  27.2 Immunogens and Classes of Immunity Antibodies do not interact with an entire antigen, but only with a distinct portion of the molecule called an antigenic determinant or epitope. May include sugars, amino acids, and other organic molecules © 2018 Pearson Education, Inc.  27.2 Immunogens and Classes of Immunity Figure © 2018 Pearson Education, Inc. 27.5  27.3 Antibody Production by B Cells Antibodies, or immunoglobulins (Igs) soluble proteins or cell surface antigen receptors on B cells bind to toxins or viruses to neutralize them bind to foreign cells and make them easier to engulf by phagocytes (opsonization) © 2018 Pearson Education, Inc.  27.3 Antibody Production and Structural Diversity Immunoglobulin structure and function Antibodies or immunoglobulins (Igs) are protein molecules that interact specifically with antigenic determinants found in serum, milk, and mucosal secretions five major classes (IgG, IgA, IgM, IgD, and IgE) The heavy chains of a given antibody define its class based on amino acid sequence All five classes have different structural characteristics, expression patterns, and functional roles IgG is the most abundant antibody circulating in the body © 2018 Pearson Education, Inc.  Four polypeptide chains (two heavy and two light chains) Antigen-binding site results from interaction between heavy and light chains. Light chain Heavy chain © 2018 Pearson Education, Inc.  27.3 Antibody Production and Structural Diversity Other immunoglobulin classes and their functions IgM is usually an aggregate of five immunoglobulin molecules attached by at least one J (joining) chain © 2018 Pearson Education, Inc.  Dimers of IgA are present in body fluids such as saliva, tears, breast milk, colostrum, and mucosal secretions. © 2018 Pearson Education, Inc. Figure 27.9d  27.7 T Cell Receptors, TCRs TCRs of a given T cell bind only to MHC molecules having foreign antigens embedded in the MHC structure T cells do not interact with a foreign antigen unless it is presented in the context of an MHC protein TCRs bind both self MHC and foreign peptides TCRs and MHCs bind directly to peptide antigen © 2018 Pearson Education, Inc.  Dendritic cells and macrophages CD4 Helper CD8 Cytotoxic T cells T cells © 2018 Pearson Education, Inc. Figure 27.17  III. The Major Histocompatibility Complex (MHC) MHC Class I MHC Class II 1. Found on all nucleated cells 1. Found on professional antigen-presenting cells, such as dendritic cells, 2. Present internal macrophages, and B cells (endogenous/intracellular) antigen to CD8+ T cells. 2. Present the exogenous or Cytoplasmic antigen can extracellular antigen to CD4+ originate from intracellular T cells (helper T cells) after bacteria, viruses, or cancer cells internalization 3. The cell is then targeted for 3. Activate Helper T cells to destruction by cytotoxic T cells secrete cytokines that promote antibody secretion 4. Protects from intracellular 4. Protects from extracellular bacteria, viruses, or cancer cells bacteria and toxins © 2018 Pearson Education, Inc.  27.8 Cytotoxic T Cells Directly kill cells that display surface foreign antigens Contact between Tc cells and target cell is required for cell death On contact, granules in T cell migrate to contact site Degranulation occurs and causes pores (perforin) in target cell membrane Also contain granzymes that cause apoptosis © 2018 Pearson Education, Inc.  27.8 Helper T Cells Th1 subset activates macrophages Secrete cytokines (including gamma interferon and others) Activated macrophages kill intracellular bacteria Th2 subset - B cell activation and antibody production © 2018 Pearson Education, Inc.  V. Immune Disorders and Deficiencies 27.9 Allergy, Hypersensitivity, and Autoimmunity 27.10 Superantigens and Immunodeficiency © 2018 Pearson Education, Inc.  27.9 Allergy and Hypersensitivity Hypersensitivity - Inappropriate immune response that results in host damage Hypersensitivity diseases are categorized according to antigens and effector mechanisms involved © 2018 Pearson Education, Inc.  Allergy: antibody-mediated immediate hypersensitivity (type I hypersensitivity) © 2018 Pearson Education, Inc. Figure 27.24  27.9 Delayed-type, type IV hypersensitivity Cell-mediated hypersensitivity characterized by tissue damage due to inflammatory responses produced by Th1 inflammatory cells Symptoms appear several hours following secondary exposure to eliciting antigens Typical antigens include microbes. Ex. Tuberculin test for Mycobacterium tuberculosis © 2018 Pearson Education, Inc.  27.9 Autoimmunity Autoimmune diseases Occur when T and B cells are activated to produce immune reactions against self proteins Result in host tissue damage Some diseases are caused by autoantibodies (i.e., antibodies that interact with self antigens) Ex. Type 1 diabetes, rheumatoid arthritis © 2018 Pearson Education, Inc.  27.10 Superantigens Proteins that elicit a strong response because they activate T cells more than a normal immune response Produced by bacterial pathogens that interact with T cell receptors (TCRs) Superantigen-activated T cells may produce systemic diseases characterized by systemic inflammatory reactions © 2018 Pearson Education, Inc.  27.10 Immunodeficiency Active adaptive immunity is critical for infectious disease resistance. Deficiencies in B cells are prone to extracellular bacterial infections Deficiencies in T cells are prone to intracellular bacterial and viral infections, and cancers Severe combined immune deficiency syndrome (SCID) is a serious, congenital deficiency of both B and T cells Patients live a restricted life, limiting their exposure to pathogens (“Boy in the Bubble” syndrome) Acquired Immunodeficiency syndrome (AIDS) is caused by HIV infection that progresses and kills CD4+ T cells Patients are prone to opportunistic infections, and some types of cancer © 2018 Pearson Education, Inc.