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Chapter 43 The Immune System PowerPoint Lectures for Biology, Seventh Edition Neil Campbell and Jane Reece Lectures by Chris Romero Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Overview: Reconnaissance, Recognition, and Response • An animal must defend itself – From the many dangerous pathogens it may encounter in the environment • Two major kinds of defense have evolved that counter these threats – Innate immunity and acquired immunity Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Innate immunity – Is present before any exposure to pathogens and is effective from the time of birth – Involves nonspecific responses to pathogens Figure 43.1 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 3m • Acquired immunity, also called adaptive immunity – Develops only after exposure to inducing agents such as microbes, toxins, or other foreign substances – Involves a very specific response to pathogens Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • A summary of innate and acquired immunity INNATE IMMUNITY Rapid responses to a broad range of microbes External defenses Invading microbes (pathogens) Internal defenses Skin Phagocytic cells Mucous membranes Antimicrobial proteins Secretions Inflammatory response Figure 43.2 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings ACQUIRED IMMUNITY Slower responses to specific microbes Natural killer cells Humoral response (antibodies) Cell-mediated response (cytotoxic lymphocytes) • Concept 43.1: Innate immunity provides broad defenses against infection • A pathogen that successfully breaks through an animal’s external defenses – Soon encounters several innate cellular and chemical mechanisms that impede its attack on the body Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings External Defenses • Intact skin and mucous membranes – Form physical barriers that bar the entry of microorganisms and viruses • Certain cells of the mucous membranes produce mucus – A viscous fluid that traps microbes and other particles Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • In the trachea, ciliated epithelial cells – Sweep mucus and any entrapped microbes upward, preventing the microbes from entering the lungs 10m Figure 43.3 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Secretions of the skin and mucous membranes – Provide an environment that is often hostile to microbes • Secretions from the skin – Give the skin a pH between 3 and 5, which is acidic enough to prevent colonization of many microbes – Also include proteins such as lysozyme, an enzyme that digests the cell walls of many bacteria Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Internal Cellular and Chemical Defenses • Internal cellular defenses – Depend mainly on phagocytosis • Phagocytes, types of white blood cells – Ingest invading microorganisms – Initiate the inflammatory response – Most types of phagocytes are Neutrophils (60-70%), last only a few days Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Phagocytic Cells • Phagocytes attach to their prey via surface receptors – And engulf them, forming a vacuole that fuses with a lysosome 1 Pseudopodia surround microbes. Microbes 2 Microbes are engulfed into cell. MACROPHAGE 3 Vacuole containing microbes forms. Vacuole Lysosome containing enzymes 4 Vacuole and lysosome fuse. 5 Toxic compounds and lysosomal enzymes destroy microbes. Figure 43.4 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 6 Microbial debris is released by exocytosis. • Macrophages, a specific type of phagocyte – Can be found migrating through the body – Can be found in various organs of the lymphatic system Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • The lymphatic system – Plays an active role in defending the body from pathogens 1 Interstitial fluid bathing the tissues, along with the white blood cells in it, continually enters lymphatic capillaries. Interstitial fluid Adenoid Lymphatic capillary 2 Fluid inside the lymphatic capillaries, called lymph, flows through lymphatic vessels throughout the body. Tonsil 4 Lymphatic vessels return lymph to the blood via two large ducts that drain into veins near the shoulders. Lymph nodes Blood capillary Spleen Peyer’s patches (small intestine) Tissue cells Lymphatic vessel Appendix Lymphatic vessels Figure 43.5 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Lymph node Masses of lymphocytes and macrophages 3 Within lymph nodes, microbes and foreign particles present in the circulating lymph encounter macrophages, dendritic cells, and lymphocytes, which carry out various defensive actions. Antimicrobial Proteins • Numerous proteins function in innate defense – By attacking microbes directly of by impeding their reproduction • About 30 proteins make up the complement system – Which can cause lysis of invading cells and help trigger inflammation • Interferons (help control spread of infection) – Provide innate defense against viruses and help activate macrophages Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Inflammatory Response • In local inflammation, histamine and other chemicals released from injured cells – Promote changes in blood vessels that allow more fluid, more phagocytes, and antimicrobial proteins to enter the tissues – Systemic response: increases production of WBC in bone marrow, increases heat. – Septic shock: death by systemic response (high fever and low blood pressure) Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Major events in the local inflammatory response Blood clot Pin Pathogen Macrophage Chemical signals Phagocytic cells Capillary Blood clotting elements Phagocytosis Red blood cell 1 Chemical signals released by activated macrophages and mast cells at the injury site cause nearby capillaries to widen and become more permeable. 2 Fluid, antimicrobial proteins, and clotting elements move from the blood to the site. Clotting begins. Figure 43.6 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 3 Chemokines released by various kinds of cells attract more phagocytic cells from the blood to the injury site. 4 Neutrophils and macrophages phagocytose pathogens and cell debris at the site, and the tissue heals. Natural Killer Cells • Natural killer (NK) cells – Patrol the body and attack virus-infected body cells and cancer cells – Trigger apoptosis in the cells they attack Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Concept 43.2: In acquired immunity, lymphocytes provide specific defenses against infection • Acquired immunity – Is the body’s second major kind of defense – Involves the activity of lymphocytes Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • An antigen is any foreign molecule – That is specifically recognized by lymphocytes and elicits a response from them • A lymphocyte actually recognizes and binds – To just a small, accessible portion of the antigen called an epitope Antigenbinding sites Antibody A Antigen Antibody B Antibody C Figure 43.7 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Epitopes (antigenic determinants) Antigen Recognition by Lymphocytes • The vertebrate body is populated by two main types of lymphocytes – B lymphocytes (B cells) and T lymphocytes (T cells) – Which circulate through the blood • The plasma membranes of both B cells and T cells – Have about 100,000 antigen receptor that all recognize the same epitope Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings B Cell Receptors for Antigens • B cell receptors – Bind to specific, intact antigens – Are often called membrane antibodies or membrane immunoglobulins Antigenbinding site Antigenbinding site Disulfide bridge Variable regions Light chain Constant regions C C Transmembrane region Plasma membrane Heavy chains B cell Figure 43.8a Cytoplasm of B cell (a) A B cell receptor consists of two identical heavy chains and two identical light chains linked by several disulfide bridges. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings T Cell Receptors for Antigens and the Role of the MHC • Each T cell receptor – Consists of two different polypeptide chains AntigenBinding site Variable regions Constant regions V V C C Transmembrane region Plasma membrane a chain b chain Disulfide bridge Cytoplasm of T cell Figure 43.8b (b) A T cell receptor consists of one a chain and one b chain linked by a disulfide bridge. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings T cell • T cells bind to small fragments of antigens – That are bound to normal cell-surface proteins called MHC molecules • MHC molecules – Are encoded by a family of genes called the major histocompatibility complex Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Infected cells produce MHC molecules – Which bind to antigen fragments and then are transported to the cell surface in a process called antigen presentation • A nearby T cell – Can then detect the antigen fragment displayed on the cell’s surface • Depending on their source – Peptide antigens are handled by different classes of MHC molecules Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Class I MHC molecules, found on almost all nucleated cells of the body – Display peptide antigens to cytotoxic T cells Infected cell Antigen fragment 1 1 A fragment of foreign protein (antigen) inside the cell associates with an MHC molecule and is transported to the cell surface. Class I MHC molecule 2 T cell receptor Figure 43.9a (a) Cytotoxic T cell Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 2 The combination of MHC molecule and antigen is recognized by a T cell, alerting it to the infection. • Class II MHC molecules, located mainly on dendritic cells, macrophages, and B cells – Display antigens to helper T cells Microbe 1 A fragment of foreign protein (antigen) inside the cell associates with an MHC molecule and is transported to the cell surface. Antigenpresenting cell Antigen fragment 1 Class II MHC molecule 2 2 The combination of MHC molecule and antigen is recognized by a T cell, alerting it to the infection. Figure 43.9b Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings (b) T cell receptor Helper T cell • Lymphocytes – Arise from stem cells in the bone marrow • Newly formed lymphocytes are all alike Bone marrow Lymphoid stem cell – But they later develop into B cells or T cells, depending on where they continue their maturation Thymus T cell B cell Blood, lymph, and lymphoid tissues (lymph nodes, spleen, and others) Figure 43.10 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Generation of Lymphocyte Diversity by Gene Rearrangement • Early in development, random, permanent gene rearrangement – Forms functional genes encoding the B or T cell antigen receptor chain – A person has about one million B cells and about ten million T cells Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Immunoglobulin gene rearrangement V4–V39 DNA of undifferentiated B cell V2 V1 V40 V3 J1 J2 J3 J4 J5 Intron C 1 Deletion of DNA between a V segment and J segment and joining of the segments DNA of differentiated B cell V1 V3 J5 Intron V2 C 2 Transcription of resulting permanently rearranged, functional gene pre-mRNA V3 J5 Intron 3 mRNA Cap V 3 J5 C RNA processing (removal of intron; addition of cap and poly (A) tail) C Poly (A) 4 Translation Light-chain polypeptide Figure 43.11 V C Variable Constant region region Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings B cell receptor B cell Testing and Removal of Self-Reactive Lymphocytes • As B and T cells are maturing in the bone and thymus – Their antigen receptors are tested for possible self-reactivity • Lymphocytes bearing receptors for antigens already present in the body – Are destroyed by apoptosis or rendered nonfunctional – Failure to self-tolerance leads to autoimmune disease Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Clonal Selection of Lymphocytes • In a primary immune response – Binding of antigen to a mature lymphocyte induces the lymphocyte’s proliferation and differentiation, a process called clonal selection – If lymphocytes are selected by antigenreceptor, then it multiplies with effector cells and memory cells Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Clonal selection of B cells – Generates a clone of short-lived activated effector cells and a clone of long-lived memory cells Antigen molecules B cells that differ in antigen specificity Antigen receptor Antigen molecules bind to the antigen receptors of only one of the three B cells shown. The selected B cell proliferates, forming a clone of identical cells bearing receptors for the selecting antigen. Some proliferating cells develop into long-lived memory cells that can respond rapidly upon subsequent exposure to the same antigen. Antibody molecules Clone of memory cells Figure 43.12 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Clone of plasma cells Some proliferating cells develop into short-lived plasma cells that secrete antibodies specific for the antigen. • In the secondary immune response – Memory cells facilitate a faster, more efficient response 1 Day 1: First 2 Primary exposure to response to antigen A antigen A produces antibodies to A 3 Day 28: Second exposure to antigen A; first exposure to antigen B 4 Secondary response to antigen A produces antibodies to A; primary response to antigen B produces antibodies to B Antibody concentration (arbitrary units) 104 103 102 Antibodies to A Antibodies to B 101 100 Figure 43.13 0 7 14 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 21 28 35 Time (days) 42 49 56 • Concept 43.3: Humoral and cell-mediated immunity defend against different types of threats • Acquired immunity includes two branches – The humoral immune response involves the activation and clonal selection of B cells, resulting in the production of secreted antibodies – The cell-mediated immune response involves the activation and clonal selection of cytotoxic T cells Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • The roles of the major participants in the acquired immune response Cell-mediated immune response Humoral immune response First exposure to antigen Intact antigens Antigens engulfed and displayed by dendritic cells Antigens displayed by infected cells Activate Activate Activate B cell Gives rise to Plasma cells Figure 43.14 Memory B cells Helper T cell Gives rise to Active and memory helper T cells Secrete antibodies that defend against pathogens and toxins in extracellular fluid Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Secreted cytokines activate Cytotoxic T cell Gives rise to Memory cytotoxic T cells Active cytotoxic T cells Defend against infected cells, cancer cells, and transplanted tissues Helper T Cells: A Response to Nearly All Antigens • Helper T cells produce CD4, a surface protein – That enhances their binding to class II MHC molecule–antigen complexes on antigenpresenting cells • Activation of the helper T cell then occurs • Activated helper T cells – Secrete several different cytokines that stimulate other lymphocytes Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • The role of helper T cells in acquired immunity 1 After a dendritic cell engulfs and degrades a bacterium, it displays bacterial antigen fragments (peptides) complexed with a class II MHC molecule on the cell surface. A specific helper T cell binds to the displayed complex via its TCR with the aid of CD4. This interaction promotes secretion of cytokines by the dendritic cell. Cytotoxic T cell Dendritic cell Bacterium Peptide antigen Class II MHC molecule Helper T cell Cell-mediated immunity (attack on infected cells) TCR 2 3 1 CD4 Dendritic cell Cytokines 2 Proliferation of the T cell, stimulated by cytokines from both the dendritic cell and the T cell itself, gives rise to a clone of activated helper T cells (not shown), all with receptors for the same MHC–antigen complex. Figure 43.15 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings B cell 3 The cells in this clone secrete other cytokines that help activate B cells and cytotoxic T cells. Humoral immunity (secretion of antibodies by plasma cells) Cytotoxic T Cells: A Response to Infected Cells and Cancer Cells • Cytotoxic T cells make CD8 – A surface protein that greatly enhances the interaction between a target cell and a cytotoxic T cell Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Cytotoxic T cells – Bind to infected cells, cancer cells, and transplanted tissues • Binding to a class I MHC complex on an infected body cell – Activates a cytotoxic T cell and differentiates it into an active killer Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • The activated cytotoxic T cell – Secretes proteins that destroy the infected target cell 2 1 A specific cytotoxic T cell binds to a class I MHC–antigen complex on a target cell via its TCR with the aid of CD8. This interaction, along with cytokines from helper T cells, leads to the activation of the cytotoxic cell. The activated T cell releases perforin molecules, which form pores in the target cell membrane, and proteolytic enzymes (granzymes), which enter the target cell by endocytosis. Cytotoxic T cell 3 The granzymes initiate apoptosis within the target cells, leading to fragmentation of the nucleus, release of small apoptotic bodies, and eventual cell death. The released cytotoxic T cell can attack other target cells. Released cytotoxic T cell Perforin Cancer cell Granzymes 1 TCR Class I MHC molecule Target cell 3 CD8 2 Apoptotic target cell Pore Peptide antigen Figure 43.16 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Cytotoxic T cell B Cells: A Response to Extracellular Pathogens • Activation of B cells – Is aided by cytokines and antigen binding to helper T cells – Pollen, toxins and bacteria activate B cells proliferation • The clonal selection of B cells – Generates antibody-secreting plasma cells, the effector cells of humoral immunity Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 1 After a macrophage engulfs and degrades 2 a bacterium, it displays a peptide antigen complexed with a class II MHC molecule. A helper T cell that recognizes the displayed complex is activated with the aid of cytokines secreted from the macrophage, forming a clone of activated helper T cells (not shown). A B cell that has taken up and degraded the same bacterium displays class II MHC–peptide antigen complexes. An activated helper T cell bearing receptors specific for the displayed antigen binds to the B cell. This interaction, with the aid of cytokines from the T cell, activates the B cell. 3 The activated B cell proliferates and differentiates into memory B cells and antibody-secreting plasma cells. The secreted antibodies are specific for the same bacterial antigen that initiated the response. Bacterium Macrophage Peptide antigen Class II MHC molecule B cell 2 3 1 TCR Clone of plasma cells Endoplasmic reticulum of plasma cell CD4 Cytokines Helper T cell Secreted antibody molecules Activated helper T cell Figure 43.17 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Clone of memory B cells Antibody Classes • The five major classes of antibodies, or immunoglobulins – Differ in their distributions and functions within the body – IgM, IgA, IgE, IgG, IgD Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • The five classes of immunoglobulins IgM (pentamer) First Ig class produced after initial exposure to antigen; then its concentration in the blood declines J chain IgG (monomer) Promotes neutralization and agglutination of antigens; very effective in complement activation (see Figure 43.19) Most abundant Ig class in blood; also present in tissue fluids Only Ig class that crosses placenta, thus conferring passive immunity on fetus Promotes opsonization, neutralization, and agglutination of antigens; less effective in complement activation than IgM (see Figure 43.19) Present in secretions such as tears, saliva, mucus, and breast milk IgA (dimer) Secretory component J chain Provides localized defense of mucous membranes by agglutination and neutralization of antigens (see Figure 43.19) Presence in breast milk confers passive immunity on nursing infant IgE (monomer) IgD (monomer) Figure 43.18 Transmembrane region Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Triggers release from mast cells and basophils of histamine and other chemicals that cause allergic reactions (see Figure 43.20) Present primarily on surface of naive B cells that have not been exposed to antigens Acts as antigen receptor in antigen-stimulated proliferation and differentiation of B cells (clonal selection) Antibody-Mediated Disposal of Antigens • The binding of antibodies to antigens – Is also the basis of several antigen disposal mechanisms – Leads to elimination of microbes by phagocytosis and complement-mediated lysis Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Antibody-mediated mechanisms of antigen disposal Binding of antibodies to antigens inactivates antigens by Viral neutralization (blocks binding to host) and opsonization (increases phagocytosis) Agglutination of antigen-bearing particles, such as microbes Precipitation of soluble antigens Complement proteins Bacteria Virus Activation of complement system and pore formation MAC Pore Soluble antigens Bacterium Figure 43.19 Foreign cell Enhances Leads to Phagocytosis Cell lysis Macrophage Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Active and Passive Immunization • Active immunity – Develops naturally in response to an infection – Can also develop following immunization, also called vaccination Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • In immunization – A nonpathogenic form of a microbe or part of a microbe elicits an immune response to an immunological memory for that microbe Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Passive immunity, which provides immediate, short-term protection – Is conferred naturally when IgG crosses the placenta from mother to fetus or when IgA passes from mother to infant in breast milk – Can be conferred artificially by injecting antibodies into a nonimmune person Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Concept 43.4: The immune system’s ability to distinguish self from nonself limits tissue transplantation • The immune system – Can wage war against cells from other individuals • Transplanted tissues – Are usually destroyed by the recipient’s immune system Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Blood Groups and Transfusions • Certain antigens on red blood cells – Determine whether a person has type A, B, AB, or O blood Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Antibodies to nonself blood types – Already exist in the body • Transfusion with incompatible blood – Leads to destruction of the transfused cells Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Recipient-donor combinations – Can be fatal or safe Table 43.1 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Another red blood cell antigen, the Rh factor – Creates difficulties when an Rh-negative mother carries successive Rh-positive fetuses Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Tissue and Organ Transplants • MHC molecules – Are responsible for stimulating the rejection of tissue grafts and organ transplants Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • The chances of successful transplantation are increased – If the donor and recipient MHC tissue types are well matched – If the recipient is given immunosuppressive drugs Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Lymphocytes in bone marrow transplants – May cause a graft versus host reaction in recipients Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Concept 43.5: Exaggerated, self-directed, or diminished immune responses can cause disease • If the delicate balance of the immune system is disrupted – The effects on the individual can range from minor to often fatal consequences Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Allergies • Allergies are exaggerated (hypersensitive) responses – To certain antigens called allergens Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • In localized allergies such as hay fever – IgE antibodies produced after first exposure to an allergen attach to receptors on mast cells Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • The next time the allergen enters the body – It binds to mast cell–associated IgE molecules • The mast cells then release histamine and other mediators – That cause vascular changes and typical symptoms Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • The allergic response IgE Allergen Histamine 1 3 2 Granule Mast cell 1 IgE antibodies produced in 2 On subsequent exposure to the 3 Degranulation of the cell, triggered by cross-linking of response to initial exposure same allergen, IgE molecules adjacent IgE molecules, to an allergen bind to attached to a mast cell recogreleases histamine and other receptors or mast cells. nize and bind the allergen. chemicals, leading to allergy symptoms. Figure 43.20 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • An acute allergic response sometimes leads to anaphylactic shock – A whole-body, life-threatening reaction that can occur within seconds of exposure to an allergen Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Autoimmune Diseases • In individuals with autoimmune diseases – The immune system loses tolerance for self and turns against certain molecules of the body Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Rheumatoid arthritis – Is an autoimmune disease that leads to damage and painful inflammation of the cartilage and bone of joints Figure 43.21 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Other examples of autoimmune diseases include – Systemic lupus erythematosus – Multiple sclerosis – Insulin-dependent diabetes Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Immunodeficiency Diseases • An inborn or primary immunodeficiency – Results from hereditary or congenital defects that prevent proper functioning of innate, humoral, and/or cell-mediated defenses Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • An acquired or secondary immunodeficiency – Results from exposure to various chemical and biological agents Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Inborn (Primary) Immunodeficiencies • In severe combined immunodeficiency (SCID) – Both the humoral and cell-mediated branches of acquired immunity fail to function Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Acquired (Secondary) Immunodeficiencies • Acquired immunodeficiencies – Range from temporary states to chronic diseases Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Stress and the Immune System • Growing evidence shows – That physical and emotional stress can harm immunity Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Acquired Immunodeficiency Syndrome (AIDS) • People with AIDS – Are highly susceptible to opportunistic infections and cancers that take advantage of an immune system in collapse Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Because AIDS arises from the loss of helper T cells – Both humoral and cell-mediated immune responses are impaired Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • The loss of helper T cells – Results from infection by the human immunodeficiency virus (HIV) Figure 43.22 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 1µm • The spread of HIV – Has become a worldwide problem • The best approach for slowing the spread of HIV – Is educating people about the practices that transmit the virus Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings