Chapter 22 Review: The Lymphatic System and Immunity

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1 Chapter 22 Review: The Lymphatic System and Immunity Components of the Lymphatic System Lymph Clear, pale yellow fluid basically the same as interstitial fluid but in a different location Lymphatic vessels transport the lymph Lymphatic tissues Red bone marrow stem cells develop into lymphocytes and RBCs Movement of lymph plasma filters through capillary walls interstitial fluid drains into lymph capillaries bloodstream A one-way system Uses the same 2 pumps that aid venous return Milking action of skeletal muscle contractions Valves in lymphatic vessels prevent backflow Important function to return plasma proteins to blood stream Lymphatic tissues and organs Primary lymphatic organs Sites where stem cells become immunocompetent (able to mount an immune response) Red bone marrow Thymus Secondary lymphatic organs Sites where most immune responses occur Lymph nodes Spleen Lymphatic nodules Not surrounded by a connective tissue capsule Overview - immune defenses Nonspecific Immunity External barriers Internal defenses

Nonspecific Defenses: external barriers Nonspecific internal defenses Generic and rapid response to pathogens Antimicrobial proteins Interferons Complement system Lymphocytes Macrophages, neutrophils

2 Nonspecific Defenses: external barriers Nonspecific internal defenses Generic and rapid response to pathogens Antimicrobial proteins Interferons Complement system Lymphocytes Macrophages, neutrophils (phagocytic) Natural killer cells Inflammation Fever The action of interferon NK cells A virus-infected cell produces interferon molecules that bind to receptors on healthy cells Interferon stimulates them to make antiviral proteins Target NK A major component of the innate immune system Kill cells that are missing "self" (MHC) markers Release small proteins called perforin and granzyme that cause the target cell to die by apoptosis Specific immune mechanisms Specific defenses Antibody-mediated immunity Cell-mediated immunity An elaborately coordinated response to infection Two properties Specificity for particular foreign molecules (antigens) Memory for previously encountered antigens

3 Antibody-mediated immunity The body contains millions of B cells, each able to respond to a specific antigen Directed against extracellular pathogens (bacteria, viruses, toxins) Steps in antibody-mediated immunity Image: Max Planck Institute of Neurobiology Antigen detection B cell activation and clonal selection Activated B cells form Plasma cells that secrete antibodies Memory cells Antibodies enter the circulation and neutralize the antigen Antibodies Antibodies enhance phagocytosis Y-shaped proteins that bind antigens The variable (V) regions at the end of each arm of the Y form the antigen binding site Each site binds to one antigen in a highly specific lock-and-key manner Figure Antibodies agglutinate and precipitate antigens Antibodies inactivate viruses

Cell-mediated immunity Specific defenses Antibody-mediated immunity Cell-mediated immunity T cells Mature in the thymus Differentiate into helper T cells cytotoxic T cells memory T cells Directed

4 Cell-mediated immunity Specific defenses Antibody-mediated immunity Cell-mediated immunity T cells Mature in the thymus Differentiate into helper T cells cytotoxic T cells memory T cells Directed against intracellular pathogens, some cancer cells and tissue transplants Helper T cells: antigen recognition and activation T cells must be presented with processed antigens A macrophage engulfs a microbe and breaks it into fragments (1) MHC self-proteins bind the foreign antigens (2) and display them on the cell s surface (3) Macrophages are specialists at antigen presentation Receptors on helper T cells recognize and bind to the MHCantigen complex (4) This activates the T cell Roles of activated helper T cells Proliferation Releases cytokines Cytokines Cytotoxic T cells kill infected cells Small protein hormones that help control the immune response needed for many normal cell functions Examples of cytokines (see Table 22.2 in Tortora) Interleukins (IL-1, IL-2, IL-4, IL-5) Tumor necrosis factor (TNF) Interferons How do cytotoxic T cells identify infected cells? Membrane receptors on T C cell bind selfnonself complexes on infected cells The binding activates the T C cell Figure 24.14

Cytotoxic T cells kill infected cells The activated T C cell produces a protein called perforin that makes holes in the infected cell s plasma membrane Other proteins enter the infected cell and

5 Cytotoxic T cells kill infected cells The activated T C cell produces a protein called perforin that makes holes in the infected cell s plasma membrane Other proteins enter the infected cell and trigger a process called programmed cell death (apoptosis) Figure Cytotoxic T cells kill infected cells Two mechanisms for killing infected target cells Perforins punch holes in target cells and lyse the cell Granzymes trigger apoptosis After killing the target cell, a cytotoxic T cell can detach and attack another infected target cell displaying the same antigen LE 24-UNp542B Lymphocytes (Immune system contains millions of different kinds) B cells Antigen receptors recognize one specific kind of antigen T cells Cell-mediated immunity Surface marker CD8 protein CD4 protein Ab-mediated immune response Secrete antibodies, which mark invaders Cell-mediated immune response Attack infected cells Help activate B cells Cell mediated immunity 2:50 How does the body respond to a bacterial infection? The first responders Phagocytes Inflammation External barriers Skin, mucous membranes, secretions Specific responses B cells produce antibodies to epitopes on bacteria Helper T cells How does the body respond to a viral infection? The common cold Complement Cytotoxic T cells attack invading pathogens

6 The common cold A contagious viral disease of the upper respiratory track Primarily caused by rhinoviruses The most common infectious disease in humans Cold viruses live only in the nose The major entry point for the virus is the nose First line of defense external barriers mucous membranes of the nose From the nose, the virus is transported to the back of the nasopharynx Cold viruses attach to cells lining the nasopharynx How a cold virus infection occurs The virus attaches to a receptor (ICAM-1) located on the surface of nasal cells. After attaching to the receptor, the virus is taken into the cell, where it starts an infection How a viral infection occurs Virus binds to the plasma membrane The virus is taken into the cell where it starts an infection Viral RNA is integrated into the cell genome The infected cell manufactures new virus. The infected cell eventually ruptures and dies, releasing newly made virus Nonspecific defenses Cold symptoms are due mainly to the body's response to the infection. When a nasal cell is infected by a cold virus, the immune system responds by activating the inflammatory response The immune system releases histamine and other inflammatory mediators that cause dilation of blood vessels and mucus secretion. The production of interferon is an important host defense mechanism. A virus-infected cell produces interferon, a hormone that stimulates healthy cells to make antiviral proteins Specific immune responses The host's immune system effectively deals with the infection. Antibody-mediated response: the body begins producing specific antibodies that bind to the virus and prevent it from infecting cells.

Cell-mediated immune response Infected host cells display viral antigens on the cell surface If a cytotoxic T cell recognizes a viral fragment there, it will destroy the host cell the virus-specific

7 Cell-mediated immune response Infected host cells display viral antigens on the cell surface If a cytotoxic T cell recognizes a viral fragment there, it will destroy the host cell the virus-specific T-cells proliferate. Macrophages destroy the virus through phagocytosis and destroy infected cells to prevent further viral replication. How does the body respond to a viral infection? The first responders macrophages Inflammation Interferon External barriers Skin, mucous membranes, secretions Rhinovirus Specific responses B cells produce antibodies to epitopes on virus Helper T cells Cytotoxic T cells attack virus-infected cells

The Immune System. 2 Types of Defense Mechanisms. Lines of Defense. Line of Defense. Lines of Defense

The Immune System. 2 Types of Defense Mechanisms. Lines of Defense. Line of Defense. Lines of Defense The Immune System 2 Types of Defense Mechanisms Immune System the system that fights infection by producing cells to inactivate foreign substances to avoid infection and disease. Immunity the body s ability