Lecture 22: The Lymphatic System and Immunity

Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings

Fundamentals of

Anatomy & PhysiologyF

rederic H. M

artiniLecture 22: The Lymphatic System and Immunity

Lecturer: Dr. Barjis

Room P307

Phone: (718) 260-5285

E-Mail: [email protected]

Learning Objectives

• Describe the structure and function of lymphatic cells, tissues and organs

• List the body’s nonspecific defenses and describe the components and mechanisms of each

• Define specific resistance and distinguish between cell-mediated immunity and antibody mediated immunity

Learning Objectives

• Discuss the role of the T cell, B cell and antibodies in specific immunity

• Describe the origin, development, activation and regulation of normal resistance to disease

• Discuss the effects of stress and aging on the immune system

• The lymphatic system

• Contains cells, tissues, and organs responsible for defending the body

• Lymphocytes resist infection and disease by responding to

• Invading pathogens such as bacteria or viruses

• Abnormal body cells such as cancer cells

• Foreign proteins such as toxins

lymphatic system

The Components of the Lymphatic System

• Lymph

• Lymphatic vessels

• Lymphoid tissues and organs

• Lymphocytes and supporting phagocytic cells

The lymphatic system consists of

• Primary function is production, maintenance, and distribution of lymphocytes

• Lymphocytes must:

• Detect where problems exist

• Be able to reach the site of injury or infection

• Return of fluid and solutes from peripheral tissue to blood

• Distribution of hormones, nutrients, and waste product from their tissue of origin to general circulation.

Functions of lymphatic system

• Lymphatic capillaries

• Small lymphatic vessels

• Major lymph-collecting vessels

Lymphatic vessels include

Lymphatic Capillaries

• Superficial and deep lymphatics

• Thoracic duct

• Cisterna chyli

• Right lymphatic duct

Major lymph-collecting vessels

The Relationship between the Lymphatic Ducts and the Venous System

• Most of the lymph returns to the venous circulation by Thoracic duct

The Relationship between the Lymphatic Ducts and the Venous System

• Account for 20-30 % of circulating WBC, but body contain 10 to the power of 12 lymphocytes

• There are tree classes of lymphocytes

• T (thymus dependent) cells

• B (bone marrow-derived) cells

• NK (natural killer) cells

Lymphocytes

Lymphocytes

• Cytotoxic T cells (TC) – attack foreign cells

• Helper T cells (TH) – activate other T cells and B cells

• Suppressor T cells (TS) – inhibit the activation of T and B cells

• TH and TS cells regulates immune response

Major types of T cells

Lymphocytes

• Active B cell differentiates into

• Memory B Cell or

• Plasma B cell

• Plasma B cells synthesize and release antibody

Major types of B cells

• Lymphocyte production and maturation involves bone marrow, thymus, and peripheral lymphoid tissue

• B cells and NK cells mature in bone marrow

• T cells mature in the thymus

Lymphocyte production (lymphopoiesis)

The Derivation and Distribution of Lymphocytes

• Connective tissue dominated by lymphocytes

• Lymphoid nodules

• Lymphocytes are packed densely

• Found in the respiratory, digestive, and urinary tracts

• MALT (mucosa-associated lymphoid tissue)

• Collection of lymphoid tissues linked with the digestive system

Lymphoid tissue

Lymphoid Nodules

• Lymph nodes – function in the purification of lymph

Lymphoid organs

Lymphoid organs include: lymphoid nodes, thymus and spleen

• Located behind sternum in anterior mediastinum

• Reaches its maximum size just before puberty

• Consists two lobes• Divided into of lobules, each with a cortex and

medulla

• Lymphocytes in cortex are dividing, when mature migrate to modula and after 3 weeks enter the blood

• Secretes thymic hormones: thymosins, thymopoietins, and thymulin• stimulate stem cell division and T-cell

differentiation

The Thymus

The Thymus

• Largest mass of lymphoid tissue

• Cellular components form pulp

• Red pulp contains RBC

• White pulp similar to lymphoid nodules

• Spleen functions include

• Removal of abnormal blood cells and other blood components

• Storage of iron

• Initiation of the specific immune response

The Spleen

The Spleen

• Nonspecific defenses

• Do not distinguish one type of pathogen (e.g. bacteria) from another type

• There are 7 types of non specific defenses

• Specific defenses

• Protect against one particular threats

• Specific defense depend upon the activation of lymphocytes

Lymphatic system and body defenses

• Keep hazardous organisms outside the body

• Includes hair, epithelia, secretions of integumentary and digestive systems

Nonspecific Defenses

Physical barriers

• Remove cellular debris and respond to invasion by foreign pathogens


Phagocytes

• Constant monitoring of normal tissue by NK cells

• NK cells

• Recognize cell surface markers on foreign cells

• Destroy cells with foreign antigens

• Activation of NK cells:• Recognition of unusual surface proteins

• Rotation of the Golgi toward the target cell and production of perforins

• Release of perforins by exocytosis

• Interaction of perforins causing cell lysis


Immunological surveillance


Immunological Surveillance)

How Natural Killer Cells Kill Cellular Targets


• Interferons are small proteins that act as chemical messengers that coordinate defense

• Interferons are released by virally infected cells and activated lymphocyytes

• Interferons bind to the surface of abnormal cells and trigger the production of antiviral proteins that prevents virus proliferation.

Interferons (cytokines)

Nonspecific Defenses• There are 11 plasma complement proteins

(C)

• They are activated by:• Classical pathway

• In Classical pathway compliment binds to Ab molecule,

• Alternative pathway• In alternative pathway compliment binds to bacterial

cell

• Both pathways trigger:• Chain of reaction and result attraction of

phagocytes,

• Stimulation of phagocitic activity,

• Promotion of inflammation and

• Result puncture of bacterial cell

Complement system


• Localized tissue response to injury producing

• Swelling

• Redness

• Heat

• Pain

• Effects of inflammation include

• Temporary repair of injury

• Slowing the spread of pathogens

Inflammation


Inflammatory Response


• Maintenance of a body temperature above 37.2oC (99oF)

• High temperature may inhibit some viruses and bacterial activities.

• It increases metabolism (1°C increase in temperature would increase metabolism by 10%)

• Pyrogens reset the hypothalamic thermostat and raise body temperature

• Pyrogen secretion is stimulated by Ag, macrophages

Fever

Specific Defenses

• Act on specific Ag only

• T-Cells are responsible for cell mediated immunity (cellular immunity) – defense against abnormal cells and pathogens inside cells

• B-cells provide Ab-mediated immunity (also called humoral immunity) – defense against Ags and pathogens in body fluid

Specific Defenses

• Innate immunity

• Genetically determined

• Present at birth

• Acquired immunity

• Not present at birth

• Achieved by exposure to antigen

• Acquired immunity can be

• Active immunity

• Passive immunity

Forms of immunity

Types of Immunity

Properties/characteristics of immunity

• Specificity – activated by and responds to a specific antigen

• Versatility – is ready to confront any antigen at any time

• Memory – “remembers” any antigen it has encountered

• Tolerance – responds to foreign substances but ignores normal tissues

The immune system response

• Antigen triggers an immune response

• Activates T cells and B cells

• T cells are activated after phagocytes exposed to antigen

• T cells attack the antigen and stimulate B cells

• Activated B cells mature and produce antibody

• Antibody attacks antigen

T cell activation

• T cells recognize Ag-glycoprotein complex in cell membrane

• Glycoproteins are synthesized in the region called Major Histocompatibility Complex (MHC)- so they are known as MHC proteins

• Each individual have different MHC proteins

• There are 2 classes of MHC proteins:

• MHC class I

• MHC class II

MHC classes• Class I – found on all nucleated cells

• They are synthesized, and transported to membrane by vesicles of golgi apparatus

• As they are formed, they pick up small peptides from the cytoplasm and take them to membrane

• If the peptides that are picked up by MHC proteins are self (belong to the body), T-cells will ignore them,

• If the peptides that are picked up by the MHC proteins are none self (do not belong to the body i.e. if they are antigens) then T-cell becomes activated anddestroy the abnormal cell.

Antigens and MHC Proteins

MHC classes

• Class II – found on antigen presenting cells and lymphocytes

• Phagocitic cells engulf pathogen

• Once the pathogen is inside the phagocitic cell, lysosome action breaks down the pathogen into fragments (Ag)

• Endoplasmic reticulum produces MHC II proteins

• Ag fragments will bound to MHC ll proteins and will be presented on the cell membrane

• MHC II and Antigen complex on the surface of membrane will activate T cells

Antigens and MHC Proteins

B cells and Antibody Mediated Response

• B cells produce specific Ab

• There are millions of B-cells - each with specific Ab on its membrane

• When B- cells are activated they can produce up to 100 million Ab per hour

Antibodies structure

• Antibodies are Y-shaped proteins consisting of:

• Two parallel polypeptide chains

• Heavy chains and light chains

• Constant region and variable region

• Antigen binding site

Antibody Structure

Antibody Structure

Actions of antibodies include:

• Neutralization

• Agglutination and precipitation

• Activation of complement

• Attraction of phagocytes

• Opsinization

• Stimulation of inflammation

• Prevention of adhesion

Classes of Antibodies (immunoglobins)

• IgG – resistance against many viruses, bacteria and bacterial toxins

• IgE – accelerates local inflammation and responsible for allergic reaction

• IgD – found on the surface of B cells

• IgM – first type secreted after antigen arrives

• IgA – primarily found in glandular sec

Primary and secondary antibody response

• Primary response

• Takes about two weeks to develop

• Produced by plasma cells

• Secondary response

• Rapid increase in IgG

• Maximum antibody titer app

Aging and the Immune Response

• Immune system becomes less effective

• Increased susceptibility to infection

• Immune surveillance declines

With age

• The structure and function of lymphatic cells, tissues and organs

• The body’s nonspecific defenses and the components and mechanisms of each

• Specific resistance, cell-mediated immunity and antibody mediated immunity

• The role of the T cell, B cell and antibodies in specific immunity

• The origin, development, activation and regulation of normal resistance to disease

• The effects of stress and aging on the immune system

You should now be familiar with:

Documents

Lecture 22: The Lymphatic System and Immunity