Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings PowerPoint Lectures for Biology, Seventh Edition Neil Campbell and Jane Reece Lectures by Chris Romero Chapter 43 The Immune System
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Overview: Reconnaissance, Recognition, and Response Two major kinds of defense have evolved – 1) Innate Immunity Present before any exposure to pathogens and is effective from the time of birth Involves nonspecific responses to pathogens Consists of external barriers plus internal cellular and chemical defenses – 2) Acquired Immunity/Adaptive Immunity Develops after exposure to agents such as microbes, toxins, or other foreign substances involves a very specific response to pathogens lymphocytes produce antibodies; others destroy infected cells, cancer cells, or foreign tissue
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LE 43-2 Invading microbes (pathogens) External defenses Skin Mucous membranes Secretions INNATE IMMUNITY Rapid responses to a broad range of microbes ACQUIRED IMMUNITY Slower responses to specific microbes Internal defenses Phagocytic cells Inflammatory response Humoral response (antibodies) Antimicrobial proteins Natural killer cells Cell-mediated response (cytotoxic lymphocytes)
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Innate immunity: External Defenses External Defenses – Skin and mucous membranes are physical barriers – In the trachea, ciliated epithelial cells sweep particles out – Secretions from the skin Create pH between 3 and 5 (too acidic for microbes) Lysozyme, which digests bacterial cell walls
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Innate Immunity: Internal Defenses A) Phagocytic Cells: engulf prey, form a vacuole that fuses with a lysosome – Macrophages migrate through the body and are found in organs of the lymphatic system B) Antimicrobial Proteins: attack microbes directly or impede their reproduction C) Inflammatory Response: histamine and other chemicals released from injured cells promote vasodilation – allow more fluid, phagocytes, and antimicrobial proteins to enter tissues D) Natural Killer Cells: attack virus-infected body cells and cancer cells, triggering apoptosis
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Inflammatory Respose
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Acquired Immunity: Lymphocytes at Work Antigen: a foreign molecule that is recognized by lymphocytes and elicits a response from them A lymphocyte recognizes and binds to a small portion of the antigen called an epitope Two main types of lymphocytes circulate in the blood of vertebrates: – B lymphocytes (B cells): bind to specific, intact antigens – T lymphocytes (T cells): bind to antigen fragments that are bound to cell-surface proteins called MHC molecules (“Major Histocompatibility Complex”)
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings MHC Molecules Infected cells produce MHC molecules, which bind to antigen fragments and are transported to the cell surface, a process called antigen presentation A nearby T cell can then detect the antigen fragment displayed on the cell’s surface Class I MHC molecules are found on almost all nucleated cells of the body – They display peptide antigens to cytotoxic T cells Class II MHC molecules are located mainly on dendritic cells, macrophages, and B cells – They display antigens to helper T cells
LE 43-9 Antigen- presenting cell Antigen fragment Class II MHC molecule T cell receptor Helper T cell Antigen fragment Class I MHC molecule T cell receptor Cytotoxic T cell Infected cell Microbe
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Lymphocyte Development Lymphocytes arise from stem cells in bone marrow
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings PowerPoint Lectures for Biology, Seventh Edition Neil Campbell and Jane Reece Lectures by Chris Romero The Immune System: Acquired Immune Response Chapter 43
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Humoral and Cell-Mediated Immunity Humoral Responses: involve activation and selection of B cells, resulting in production of secreted antibodies Cell-Mediated Responses: involve activation and selection of cytotoxic T cells
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Helper T Cells Activated helper T cells secrete cytokines that stimulate other lymphocytes
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Cytotoxic T Cells The activated cytotoxic T cell secretes proteins that destroy the infected target cell
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Antibody Classes The five major classes of antibodies, or immunoglobulins, differ in distribution and function
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Antibody-Mediated Disposal of Antigens The binding of antibodies to antigens is also the basis of antigen- disposal mechanisms Microbes are eliminated by phagocytosis and complement- mediated lysis
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Active and Passive Immunization Active Immunity: develops naturally in response to an infection – It can also develop following immunization, also called vaccination – In immunization, a nonpathogenic form of a microbe or part of a microbe elicits an immune response to an immunological memory Passive Immunity: provides immediate, short-term protection – It is conferred naturally when IgG crosses the placenta from mother to fetus or when IgA passes from mother to infant in breast milk – It can be conferred artificially by injecting antibodies into a nonimmune person
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Blood Groups and Transfusions Antigens on red blood cells determine whether a person has type A, B, AB, or O blood Antibodies to nonself blood types exist in the body A red blood cell antigen called the Rh factor creates difficulties when an Rh-negative mother carries successive Rh-positive fetuses
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Allergies Allergies are exaggerated (hypersensitive) responses to antigens called allergens In localized allergies such as hay fever, IgE antibodies produced after first exposure to an allergen attach to receptors on mast cells The next time the allergen enters the body, it binds to mast cell–associated IgE molecules Mast cells release histamine and other mediators that cause typical allergy symptoms
LE IgE Allergen Granule Mast cell Histamine
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Autoimmune Diseases Autoimmune Diseases: immune system loses tolerance for self and turns against certain molecules of the body – Rheumatoid Arthritis is an autoimmune disease leading to damage and inflammation of joints Other examples of autoimmune diseases: – Systemic lupus erythematosus – Multiple sclerosis – Insulin-dependent diabetes
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Immunodeficiency Diseases Inborn/Primary: results from hereditary or congenital defects – Innate, acquired, or both defense may be impaired Acquired/Secondary: results from exposure to chemical and biological agents – Range from temporary states to chronic diseases – i.e.: AIDS
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Acquired Immunodeficiency Syndrome AIDS arises from loss of helper T cells, thus it impairs both the humoral and cell-mediated immune responses The loss of helper T cells results from infection by the human immunodeficiency virus (HIV)