The Lymphatic System and Immunity

The Lymphatic System and Immunity
Innate immunity Adaptive immunity Aging and the immune system Copyright © 2015 John Wiley & Sons, Inc. All rights reserved.

Lymphatic System Immunity or resistance is the ability to use our body’s defenses to ward off damage or disease. The two types of immunity are (1) innate and (2) adaptive. Innate (nonspecific) immunity refers to defenses that are present at birth. They are always present and available to provide rapid responses to protect us against disease. Adaptive (specific) immunity refers to defenses that involve specific recognition of a microbe once it has breached the innate immunity defenses. Adaptive immunity is based on a specific response to a specific microbe; that is, it adapts or adjusts to handle a specific microbe. Copyright © 2015 John Wiley & Sons, Inc. All rights reserved.

Lymphatic System Adaptive immunity involves lymphocytes (a type of white blood cell) called T lymphocytes (T cells) and B lymphocytes (B cells). The body system responsible for adaptive immunity (and some aspects of innate immunity) is the lymphatic system. The lymphatic system consists of lymph, lymphatic vessels, a number of structures and organs containing lymphatic tissue, and red bone marrow. Lymphatic tissue is a specialized form of reticular connective tissue that contains large numbers of lymphocytes. Copyright © 2015 John Wiley & Sons, Inc. All rights reserved.

Lymphatic System Most components of blood plasma filter out of blood capillary walls to form interstitial fluid, the fluid that bathes the cells of body tissues. After interstitial fluid passes into lymphatic vessels, it is called lymph. Both fluids are chemically similar to blood plasma. The lymphatic system has 3 primary functions: Drains excess interstitial fluid. Transports dietary lipids. Carries out immune responses. Copyright © 2015 John Wiley & Sons, Inc. All rights reserved.

Components of the Lymphatic System
Copyright © 2015 John Wiley & Sons, Inc. All rights reserved.

Lymphatic System Lymphatic vessels begin as lymphatic capillaries in tissue spaces between cells. The lymphatic capillaries merge to form larger lymphatic vessels, which ultimately drain into the thoracic duct or right lymphatic duct. Ultimately, the thoracic duct empties its lymph into the left internal jugular and left subclavian veins, and the right lymphatic duct empties its lymph into the right internal jugular and right subclavian veins. Thus, lymph drains back into the blood. Located at intervals along lymphatic vessels are lymph nodes, masses of B cells and T cells surrounded by a capsule. Lymph flows through lymph nodes. Copyright © 2015 John Wiley & Sons, Inc. All rights reserved.

Lymphatic Capillaries

Lymphatic System The same two pumps that aid return of venous blood to the heart maintain the flow of lymph: Respiratory pump. Skeletal muscle pump. Primary lymphatic organs are the sites where stem cells divide and develop into mature B cells and T cells. They include the red bone marrow (in flat bones and the ends of the long bones of adults) and the thymus. Stem cells in red bone marrow give rise to mature B cells and to immature T cells that migrate to the thymus, where they mature into functional T cells. Copyright © 2015 John Wiley & Sons, Inc. All rights reserved.

Lymphatic System The secondary lymphatic organs and tissues are the sites where most immune responses occur. They include lymph nodes, the spleen, and lymphatic nodules. Thymus is a two-lobed organ located posterior to the sternum, medial to the lungs, and superior to the heart. It contains large numbers of T cells and macrophages. Lymph nodes are located along lymphatic vessels and are heavily concentrated near the mammary glands and in the axillae and groin. They contain B cells that develop into plasma cells, T cells, dendritic cells, and macrophages. Lymph enters nodes through afferent lymphatic vessels and exits through efferent lymphatic vessels. Copyright © 2015 John Wiley & Sons, Inc. All rights reserved.

Structure of a Lymph Node

Lymphatic System The spleen is the largest single mass of lymphatic tissue in the body. It lies between the stomach and diaphragm and is covered by a capsule of dense connective tissue. It contains two types of tissue, white pulp (lymphatic tissue where B and T cells carry out immune responses) and red pulp (blood-filled sinuses where worn-out blood cells and platelets are removed). Lymphatic nodules are egg-shaped masses of lymphatic tissue that are not surrounded by a capsule. They are plentiful in the connective tissue of mucous membranes lining the gastrointestinal, urinary, and reproductive tracts and the respiratory airways. Copyright © 2015 John Wiley & Sons, Inc. All rights reserved.

Innate Immunity Innate (nonspecific) immunity includes the external physical and chemical barriers provided by the skin and mucous membranes. It also includes various internal defenses, such as antimicrobial substances, natural killer cells, phagocytes, inflammation, and fever. The skin and mucous membranes of the body are the first line of defense against pathogens. These structures provide both physical and chemical barriers. Any pathogens that get past the surface barriers encounter a second line of defense consisting of internal antimicrobial substances, phagocytes, natural killer cells, inflammation, and fever. Copyright © 2015 John Wiley & Sons, Inc. All rights reserved.

Innate Immunity Various body fluids contain four main types of antimicrobial substances that discourage microbial growth: interferons, complement system, iron-binding proteins, antimicrobial proteins (AMPs). When microbes penetrate the skin and mucous membranes or bypass the antimicrobial substances in blood, the next nonspecific defense consists of phagocytes and natural killer cells. Inflammation is a nonspecific defensive response of the body to tissue damage. Fever is an elevated body temperature that intensifies the effects of interferons, inhibits the growth of some microbes, and speeds up body reactions that aid repair. Copyright © 2015 John Wiley & Sons, Inc. All rights reserved.

Innate Immunity- Inflammation

Summary of Innate Defenses

Adaptive Immunity Adaptive (specific) immunity involves the production of specific types of cells or specific antibodies to destroy a particular antigen. An antigen is any substance (foods, microbes, drugs, pollen, etc.) that the immune system recognizes as foreign (nonself). Adaptive immunity involves lymphocytes called B cells and T cells. Both develop in primary lymphatic organs (red bone marrow and the thymus) from stem cells that originate in red bone marrow. There are two types of adaptive immunity: cell-mediated immunity (cytotoxic T cells directly attack invading antigens) and antibody-mediated immunity (B cells transform into plasma cells, then into antibodies). Copyright © 2015 John Wiley & Sons, Inc. All rights reserved.

Adaptive Immunity Clonal selection is the process by which a lymphocyte proliferates and differentiates in response to a specific antigen. The result of clonal selection is the formation of a clone of cells that can recognize the same specific antigen as the original lymphocyte. A lymphocyte that undergoes clonal selection gives rise to two major types of cells in the clone: effector cells and memory cells. The effector cells of a lymphocyte clone carry out immune responses that ultimately result in the destruction or inactivation of the antigen. Effector cells include active helper T cells, which are part of a helper T cell clone; active cytotoxic T cells, which are part of a cytotoxic T cell clone; and plasma cells, which are part of a B cell clone. Copyright © 2015 John Wiley & Sons, Inc. All rights reserved.

Adaptive Immunity The memory cells of a lymphocyte clone do not actively participate in the initial immune response. However, if the antigen reappears in the body in the future, the memory cells can quickly respond to the antigen by proliferating and differentiating into more effector cells and more memory cells. Memory cells include memory helper T cells, which are part of a helper T cell clone; memory cytotoxic T cells, which are part of a cytotoxic T cell clone; and memory B cells, which are part of a B cell clone. Copyright © 2015 John Wiley & Sons, Inc. All rights reserved.

Adaptive Immunity An antigen (meaning antibody generator) causes the body to produce specific antibodies and/or specific T cells that react with it. Antigens induce plasma cells to secrete antibodies, proteins that typically contain four polypeptide chains. The variable regions of an antibody are the antigen-binding sites, where the antibody can bind to a particular antigen. Antibodies belong to a group of plasma proteins called immunoglobulins. They are grouped in five different classes, each with specific functions: IgG, IgA, IgM, IgD, and IgE. Functionally, antibodies neutralize antigens, immobilize bacteria, agglutinate antigens, activate complement, and enhance phagocytosis. Copyright © 2015 John Wiley & Sons, Inc. All rights reserved.

Structure of an Antibody and Relationship from Antigen to Antibody

Classes of Immunoglobulins

Adaptive Immunity An antibody-mediated immune response begins with activation of a B cell by a specific antigen. B cells can respond to unprocessed antigens, but their response is more intense when they process the antigen. Interleukin-2 and other cytokines secreted by helper T cells provide costimulation for activation of B cells. Once activated, a B cell undergoes clonal selection, forming a clone of plasma cells and memory cells. Plasma cells are the effector cells of a B cell clone; they secrete antibodies. Copyright © 2015 John Wiley & Sons, Inc. All rights reserved.

Adaptive Immunity A hallmark of adaptive immune responses is memory for specific antigens that have triggered immune responses in the past. Immunological memory is due to the presence of long-lasting antibodies and very long-lived lymphocytes that arise during division and differentiation of antigen-stimulated B cells and T cells. Immunization against certain microbes is possible because memory B cells and memory T cells remain after a primary response to an antigen, providing immunological memory. The secondary response provides protection should the same microbe enter the body again. Copyright © 2015 John Wiley & Sons, Inc. All rights reserved.

Processing and Presenting of Antigen by Antigen-Presenting Cell

MHC – Major histocompatibility complex Small region of genome which encodes three classes of polymorphic molecules known as immune recognition unit. Products of the MHC gene complex are membrane bound receptors for antigens which, when bound, are displayed to T cells. If bound peptides are recognized by the T-cells, an immune response against these peptides is initiated. Copyright © 2015 John Wiley & Sons, Inc. All rights reserved.

Activation and Clonal Selection of Helper T Cell

Activation and Clonal Selection of a Cytotoxic T Cell

Action of a Cytotoxic T Cell

Activation and Clonal Selection of B Cells

Summary of Cell Functions in Adaptive Immune Responses

Secretion of Antibodies

Types of Adaptive Immunity

AGING AND THE IMMUNE SYSTEM

Aging and the Immune System
With advancing age, most people become more susceptible to all types of infections and malignancies. Their response to vaccines is decreased, and they tend to produce more autoantibodies (antibodies against their body’s own molecules). T cells and B cells are less responsive with age. Elderly individuals are encouraged to get influenza (flu) vaccinations each year. Copyright © 2015 John Wiley & Sons, Inc. All rights reserved.

The Lymphatic System and Immunity

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