Chapter 14 - The Lymphatic System and Immunity

C h a p t e r 14 The Lymphoid System and Immunity Anatomical barriers and defense mechanisms constitute nonspecific defense, and lymphocytes provide specific defense Overview of the Lymphoid System Pathogens Microscopic organisms that cause disease: Viruses Bacteria Fungi Parasites Each attacks in a specific way Overview of the Lymphoid System The Lymphoid System Protects us against disease Lymphoid system cells respond to: Environmental pathogens Toxins Abnormal body cells, such as cancers Overview of the Lymphoid System Specific Defenses Lymphocytes: Part of the immune response Identify, attack, and develop immunity: to a specific pathogen Overview of the Lymphoid System The Immune System Immunity: The ability to resist infection and disease All body cells and tissues involved in production of immunity: Not just lymphoid system Overview of the Lymphoid System Nonspecific Defenses Block or attack any potential infectious organism Cannot distinguish one attack from another Components of the Lymphoid System Lymphatic vessels (lymphatics) Carries lymph from peripheral tissues to the venous system Fluid (Lymph) A fluid similar to plasma but does not have plasma proteins Lymphocytes, phagocytes, and other immune system cells Lymphoid tissues and lymphoid organs Components of the Lymphoid System Figure 14-1 Functions of the Lymphoid System To produce, maintain, and distribute lymphocytes Return fluid and solutes to the blood Distribute hormones, nutrients, and waste products from their tissues of origin to the general circulation Lymphatic Vessels Are vessels that carry lymph Lymphoid system begins with the smallest vessels: Lymphatic capillaries (terminal lymphatics): differ from blood capillaries in four ways: start as pockets rather than tubes have larger diameters have thinner walls are flat or irregular in section Lymphatic Vessels Figure 14-2a Lymphatic Vessels Figure 14-2b Lymphatic Vessels Major Lymph-Collecting Vessels The base of the thoracic duct: Expands into cisterna chyli Cisterna chyli receives lymph from: Right and left lumbar trunks Intestinal trunk Lymphatic Vessels The Inferior Segment of Thoracic Duct Collects lymph from: Left bronchiomediastinal trunk Left subclavian trunk Left jugular trunk Empties into left subclavian vein Lymphatic Vessels The Right Lymphatic Duct Collects lymph from: Right jugular trunk Right subclavian trunk Right bronchiomediastinal trunk Empties into right subclavian vein The Lymphatic Ducts and the Venous System Figure 14-3 Lymphocytes Three Classes of Circulating Lymphocytes T cells: Thymus dependent B cells: Bone marrow derived NK cells: Natural killer cells Lymphocytes T Cells Make up 80% of circulating lymphocytes Three Main Types of T Cells Cytotoxic T cells : directly attack foreign cells or body cells infected by viruses Helper T cells: stimulate T & B cells Suppressor T cells: inhibit T & B cells Lymphocytes B Cells Make up 10% to 15% of circulating lymphocytes Differentiate (change) into plasma cells Plasma cells: Produce and secrete antibodies (immunoglobulin proteins) Antibody-mediated immunity: A chain of events that destroys the target compound or organism Lymphocytes Natural Killer (NK) Cells Also called large granular lymphocytes Make up 5% to 10% of circulating lymphocytes Responsible for immunological surveillance Attack foreign cells, virus-infected cells, and cancer cells Figure 14-4 The Origins of Lymphocytes T Cells and B Cells Migrate throughout the body: To defend peripheral tissues Retain their ability to divide: Is essential to immune system function The Origins of Lymphocytes Differentiation B cells differentiate: With exposure to hormone called cytokine (interleukin-7) T cells differentiate: With exposure to several thymic hormones Lymphoid Nodules Areolar tissue (loose connective tissue) with densely packed lymphocytes Germinal center contains dividing lymphocytes They are not surrounded by a fibrous capsule, and their size can increase or decrease depending on the number of lymphocytes The Tonsils Figure 14-5 Lymphoid Nodules Distribution of Lymphoid Nodules Respiratory tract (tonsils) they guard the entrance to the digestive and respiratory track Along digestive (Peyer’s patch) and urinary tracts If a pathogen becomes established in the nodule an inflammatory response occurs (tonsillitis, appendicitis) Lymphoid Organs Lymph nodes Thymus Spleen Are separated from surrounding tissues by a fibrous connective tissue capsule Lymphoid Organs Lymph Nodes Are small oval lymphoid organs covered by a fibrous capsule They filter and purify the lymph before it reaches the venous system At least 99% of the antigens are removed stimulating B & T cells Lymphoid Organs Lymph Nodes Afferent lymphatic vessels: Carry lymph: from peripheral tissues to lymph node Efferent lymphatic vessels: Leave lymph node at hilum Carry lymph to venous circulation The Structure of a Lymph Node Figure 14-6 Lymphoid Organs The Thymus A pink gland located in the mediastinum posterior to the sternum involved in T cell maturation It secretes hormones called thymosins which stimulate lymphocyte stem cell division and T cell maturations Atrophies after puberty: Diminishing effectiveness of immune system Divisions of the Thymus Thymus is divided into two thymic lobes Septa divide lobes into smaller lobules The Thymus Figure 14-7a The Thymus Figure 14-7b The Thymus Figure 14-7c Lymphoid Organs Three Functions of the Spleen Filters Blood Removing abnormal blood cells and other blood components by phagocytosis Storage of iron recycled from red blood cells Initiation of immune responses by B cells and T cells: In response to antigens in circulating blood Lymphoid Organs Structure of the Spleen Located between the stomach and diaphragm it is usually deep red color Inside fibrous capsule: Red pulp: contains many red blood cells White pulp: resembles lymphoid nodules The Spleen Figure 14-8a The Spleen Figure 14-8b The Spleen Figure 14-8c Roles of the Lymphoid System in Body Defenses Body defenses provide resistance to fight infection, illness, and disease Two categories of defenses Nonspecific defenses Specific defenses Nonspecific and specific defenses operate together to provide resistance to infection and disease Each nonspecific defense responds in a characteristic way regardless of the potential threat Nonspecific Defenses Seven major categories of nonspecific defenses Physical barriers Phagocytes Immunological surveillance Interferons Complement Inflammatory response Fever Nonspecific Defenses Physical Barriers Keep hazardous materials outside the body Phagocytes Attack and remove dangerous microorganisms, the first line of cellular defense removing microorganisms before lymphocytes become aware of their presence There are 2 general classes: microphages and macrophages Microphages are the neutrophils and eosinophils neutrophils these will leave the blood enter the peripheral tissue that has been injured Eosinophils are less abundant and target foreign compounds or pathogens that have been coated with antibodies Nonspecific Defenses Immunological Surveillance Constantly monitors normal tissues: With natural killer cells (NK cells), they recognize antigens formed on abnormal cells not found on the membrane of normal cells NK cells are much less selective about their target than other lymphocytes, they secrete a protein called perforins which kill the abnormal cell by creating large pores in the cell membrane There respond more rapidly than T & B cells upon contact with an abnormal If cancer cells avoid detection… a process called immunological escape it can multiply and spread without NK cell interference Nonspecific Defenses Interferons Chemical messengers released by activated lymphocytes, macrophages and cells infected with a virus that trigger production of antiviral proteins in normal cells Antiviral proteins: Do not kill viruses Block replication in cell, and activate macrophages and NK cells Nonspecific Defenses Complement (C) Proteins Form the complement system, there are 11 proteins which interact with one another in a chain reaction Complement action of antibodies Complement activation is known to: 1) attract phagocytes 2) stimulate phagocytosis 3) destroy cell membranes 4) promote inflammation Nonspecific Defenses Inflammation Triggers a complex inflammatory response within a localized tissue: swelling, redness, heat, and pain. Produced by any stimulus that kills cells or damages loose connective tissue: mast cells within the affected tissue plays a pivotal role What does inflammation do? Temporary repair and prevent access of additional pathogens Slow the spread of pathogens Mobilize defenses and aid in regeneration Nonspecific Defenses Fever A high body temperature greater than 37.2’C (99’F): The hypothalamus acts as the bodies thermostat, pyrogens increase the set point resulting in a rise in body temp Increases body metabolism Accelerates defenses (phagocytosis and enzymatic reactions) Inhibits some viruses and bacteria Nonspecific Defenses Nonspecific Defenses Figure 14-9 Figure 14-10 Immunity (specific defenses) responds to specific threats and is either cell mediated or antibody mediated Specific resistance is due to coordinated activities of T & B cells T cells provide a defense against abnormal cells and pathogens inside living cells “cell-mediated immunity” (or cellular immunity) B cells provide a defense against antigens and pathogens in body fluids “antibody-mediated immunity (or humoral immunity) Types of Immunity Active Immunity : appears after exposure to an antigen as a consequence of the immune response Naturally acquired: Through environmental exposure to pathogens Begins to develop after birth and is continually enhanced as new pathogens are encountered Induced: Through vaccines containing pathogens (antigen) This is the idea of vaccinations(immunizations) to prevent disease A vaccine contains either dead or inactive pathogens or antigens from that pathogen Types of Immunity Passive Immunity : is produced by the transfer of antibodies to an individual from some other source Naturally acquired: Antibodies acquired from the mother protect her baby against infection during gestation or in early infancy (through breast milk) Induced: By an injection of antibodies to fight infection or prevent disease after exposure to the pathogen An example would be rabies, antibodies that attach the rabies virus are injected into a person recently bitten by a rabid animal Types of Immunity Figure 14-11 Properties of Immunity Specificity Each T or B cell responds only to a specific antigen and ignores all others The cell membrane of each T & B cells have receptors that recognize only one antigen Versatility The body produces many types of lymphocytes: Each fights a different type of antigen Active lymphocyte clones itself to fight specific antigen Memory Some active lymphocytes (memory cells): Stay in circulation Provide immunity against new exposure, a second exposure results in a stronger and longer lasting response Tolerance Immune system ignores “normal” (self) antigens An Overview of the Immune Response Figure 14-12 T cells play a role in the initiation and control of the immune response Before an immune response can occur T cells must be activated by exposure to an antigen T cells recognize antigens when those antigens are bound to membrane receptors (glycoproteins) of other cells The structure of these antigen binding membrane receptors (glycoproteins) is genetically determined and differs among individuals The membrane receptors (glycoproteins) are called major histocompatibility complex (MHC) protein which are grouped into 2 classes Class 1 MHC ? when an antigen is bound it tells the immune system “hey I’m an abnormal cell…kill me” Class 2 MHC ? when an antigen is bound it tells the immune system “hey this antigen is dangerous…get rid of it” Antigen Presentation MHC Proteins The membrane glycoproteins that bind to antigens Genetically coded in chromosome 6: The major histocompatibility complex (MHC) Differs among individuals Antigen Presentation Two Classes of MHC Proteins Class I: Found in membranes of all nucleated cells The infected cell can use this marker to alert the body that they have been infected and to kill it Class II: Found in membranes of antigen-presenting cells (APCs) Found in lymphocytes and phagocytes After APC engulf and break down a pathogen fragments of the foreign antigen are displayed on their cell surface bound to class 2 MHC proteins T cells that contact this APC’s membrane become activated initiating an immune response The T cell has specific receptors that recognize either class 1 or 2 MHC proteins and also have binding sites that detect specific bound antigens, T cell activation occurs when the MHC protein contains the specific antigen the T cell is programmed to detect Antigen Presentation Class I MHC Proteins Pick up small peptides in cell and carry them to the surface: T cells ignore normal peptides Abnormal peptides or viral proteins activate T cells to destroy cell Antigen Presentation Class II MHC Proteins Antigenic fragments: From antigenic processing of pathogens Bind to Class II proteins Inserted in plasma membrane to stimulate T cells Antigen Presentation Antigen-Presenting Cells (APCs) Responsible for activating T cells against foreign cells and proteins Phagocytic APCs Free and fixed macrophages: In connective tissues Kupffer cells: Of the liver Microglia: In the CNS T Cell Activation Cytotoxic T Cells Also called killer T cells Seek out and immediately destroy target cells Activated by exposure to antigen bound to Class 1 MHC proteins T Cell Activation Actions of Cytotoxic T Cells Release perforin: To destroy antigenic plasma membrane Secrete poisonous lymphotoxin: To destroy target cell by disrupting metabolism Secrete cytokines that activate genes in target cell: That cause cell to die “apoptosis” T Cells and Immunity Helper T Cells - are activated by exposure to antigens bound to Class 2 MHC proteins on antigen presenting cells Activated CD4 T cells divide into: Active helper T cells (TH cells): secrete cytokines Memory TH cells: remain in reserve When antigen appears a second time these cells will immediately differentiate into cytotoxic T cells and helper T cells enhancing the speed and effectiveness of the immune response T Cells and Immunity Memory TC Cells Produced with cytotoxic T cells Stay in circulation Immediately form cytotoxic T cells if same antigen appears again T Cells and Immunity Suppressor T Cells Secrete suppression factors Inhibit responses of T and B cells Act after initial immune response Limit immune reaction to single stimulus T Cell Activation Figure 14-13 B Cells respond to antigens by producing specific antibodies B Cells and Immunity B Cells Responsible for antibody-mediated immunity Attack antigens by producing specific antibodies Millions of populations, each with different antibody molecules If the corresponding antigen appears in the interstitial fluid they will be bound by that specific antibody on the surface of the B cell The antigen will be brought into the cell via endocytosis and will then be displayed on the surface of the cell via a Class 2 MHC… the B cell is now sensitized Once a helper T cell has become activated to the same antigen and is bound the MHC protein antigen complex of the sensitized B cell…the T cell releases cytokines The cytokines promote B cell activation, stimulating B cell division and B cell development into plasma cells The Sensitization and Activation of B Cells Figure 14-14 Antibody Structure Antibody Structure Two parallel pairs of polypeptide chains One pair of heavy chains One pair of light chains Each chain contains Constant segments (there are 5 types) Variable segments (this determines specificity) Antibody Structure Figure 14-12 Figure 22–22 Antibody Function Seven Functions of Antigen–Antibody Complexes Neutralization of antigen-binding sites Precipitation and agglutination: formation of immune complex Activation of complement Attraction of phagocytes Opsonization: increasing phagocyte efficiency Stimulation of inflammation Primary and Secondary Responses to Antigen Exposure First exposure Produces initial primary response Next exposure Triggers secondary response More extensive and prolonged Memory cells already primed Primary and Secondary Responses to Antigen Exposure The Primary Response Takes time to develop Antigens activate B cells Plasma cells differentiate Antibody titer (level) slowly rises Primary and Secondary Responses to Antigen Exposure The Primary Response Peak response: Can take 2 weeks to develop Declines rapidly IgM: Is produced faster than IgG Is less effective Primary and Secondary Responses to Antigen Exposure The Secondary Response Activates memory B cells: At lower antigen concentrations than original B cells Secretes antibodies in massive quantities Primary and Secondary Responses Figure 14-16 Hormones of the Immune System Six Groups of Hormonal Cytokines Interleukins – may be the most important chemical messenger in the immune system Interferons Tumor necrosis factors (TNFs) Chemicals that regulate phagocytic activities Colony-stimulating factors (CSFs) Miscellaneous cytokines Abnormal immune responses result in immune disorders Autoimmune Disorders A malfunction of system that recognizes and ignores “normal” antigens Activated B cells make autoantibodies against body cells Thyroiditis Rheumatoid arthritis Insulin-dependent diabetes mellitus (IDDM) Immunodeficiency Diseases Problems with embryological development of lymphoid tissues Can result in severe combined immunodeficiency disease (SCID) Viral infections such as HIV Can result in AIDS Immunosuppressive drugs or radiation treatments Can lead to complete immunological failure Allergies Inappropriate or excessive immune responses to antigens Allergens: Antigens that trigger allergic reactions Allergies Four Categories of Allergic Reactions Type I: Immediate hypersensitivity: hay fever, Type II: Cytotoxic reactions: transfusion of incompatible blood Type III: Immune complex disorders: phagocytes can not rapidly remove circulating antigen-antibody complex and can cause damage to blood vessels and kidney Type IV: Delayed hypersensitivity: rash due to poison ivy Allergies Type I Allergy Also called immediate hypersensitivity A rapid and severe response to the presence of an antigen Most commonly recognized type of allergy Includes allergic rhinitis (environmental allergies) Allergies Type I Allergy Sensitization leads to: Production of large quantities of IgE antibodies distributed throughout the body Second exposure leads to: Massive inflammation of affected tissues Allergies Type I Allergy Severity of reaction depends on: Individual sensitivity Locations involved Allergens (antigens that trigger reaction) in bloodstream may cause anaphylaxis Allergies Anaphylaxis Can be fatal Affects cells throughout the body Changes capillary permeability: Produces swelling (hives) on skin Smooth muscles of respiratory system contract: Make breathing difficult Peripheral vasodilatation: Can cause circulatory collapse (anaphylactic shock) The immune response diminishes with advancing age Immune System and Aging Four Effects of Aging on the Immune Response Thymic hormone production is greatly reduced T cells become less responsive to antigens Fewer T cells reduces responsiveness of B cells Immune surveillance against tumor cells declines For all body systems, the lymphoid system provides defenses against infection and returns tissue fluid to the circulation The Lymphoid System in Perspective Functional Relationships Between the Lymphoid System and Other Systems Copyright © 2010 Education, Inc. The Integumentary System provides physical barriers to pathogen entry; macrophages in dermis resist infection and present antigens to trigger immune response; mast cells trigger inflammation, mobilize cells of lymphoid system The Lymphoid System provides IgA antibodies for secretion onto integumentary surfaces The Integumentary System The Skeletal System The Skeletal System’s bone marrow produces and stores lymphocytes and other cells involved in the immune response The Lymphoid System assists in repair of bone after injuries; macrophages fuse to become osteoclasts The Nervous System The Nervous System’s microglia present antigens that stimulate specific defenses; glial cells secrete cytokines; innervation stimulates antigenpresenting cells The Lymphoid System’s cytokines affect hypothalamic production of CRH and TRH The Endocrine System The Endocrine System’s glucocorticoids have anti-inflammatory effects; thymosins stimulate development and maturation of lymphocytes; many hormones affect immune function The Lymphoid System’s thymus secretes thymosins; cytokines affect cells throughout the body The Cardiovascular System The Cardiovascular System distributes WBCs; carries antibodies that attack pathogens; clotting response helps restrict spread of pathogens; hemocytoblasts give rise to stem cells that produce WBCs The Lymphoid System fights infections of cardiovascular organs; returns tissue fluid to bloodstream The Muscular System The Muscular System protects superficial lymph nodes and lymphatic vessels in the abdominopelvic cavity; muscle contractions help propel lymph along lymphatic vessels The Lymphoid System assists in repair after injuries The Respiratory System The Respiratory System’s alveolar phagocytes present antigens and trigger specific defenses; provides oxygen and eliminates carbon dioxide for the lymphoid system The Lymphoid System’s tonsils protect against infection at entrance to respiratory tract The Digestive System The Digestive System provides nutrients required by lymphatic tissues; digestive acids and enzymes provide nonspecific defense against pathogens The Lymphoid System’s tonsils and intestinal lymphoid nodules defend against infection and toxins absorbed from the digestive tract; lymphatics carry absorbed lipids to venous system The Urinary System The Urinary System eliminates metabolic wastes generated by cellular activity; acid pH of urine provides nonspecific defense against urinary tract infection The Lymphoid System provides specific defenses against urinary tract infections The Reproductive System The Reproductive System’s secretions contain lysozymes and bactericides that provide nonspecific defense against reproductive tract infections The Lymphoid System provides IgA antibodies for secretion by epithelial glands