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Chapter 30Lymph

Transport and Immunity

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The Lymphatic System Functions in Transport and Immunity

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30.1 Lymphatic vessels transport lymph

Lymphatic system is closely associated with the cardiovascular system

Has four main functions that contribute to homeostasis Lymphatic capillaries absorb excess tissue fluid and return it to

the bloodstream In the small intestines, lymphatic capillaries called lacteals

absorb fats in the form of lipoproteins and transport them to the bloodstream

The lymphatic system is responsible for the production, maintenance, and distribution of lymphocytes

The lymphatic system helps defend the body against pathogens Lymphatic vessels form a one-way system that begins

with lymphatic capillaries Lymphatic capillaries take up excess tissue fluid, lymph

Lymph also contains defense molecules, antibodies, which are produced by lymphocytes

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Figure 30.1 The vessels and organs of the lymphatic system

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30.2 Lymphatic organs defend the body

Red bone marrow - site of stem cells capable of producing lymphocytes Become mature B cells, a major type of lymphocyte, in the bone marrow

Thymus gland - located in thoracic cavity between trachea and sternum T cells, the other major type of lymphocyte, migrate from the bone marrow

through the bloodstream to thymus, where they mature Lymph nodes - small, ovoid structures occurring along lymphatic vessels

Located at body nodes, such as groin and armpits Have many open spaces called sinuses

Spleen - located in upper left side of abdominal cavity posterior to stomach Most of the spleen is red pulp that filters the blood Red pulp consists of blood vessels and sinuses, where macrophages remove

old and defective blood cells Patches of lymphatic tissue in the body:

Tonsils, in pharynx; Peyer patches located in intestine; and appendix

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Figure 30.2 The lymphatic organs

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The Body’s First Line of Defense Against Disease Is Nonspecific and Innate

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30.3 Barriers to entry, complement proteins, and certain blood cells are first responders

Barriers to entry such as the skin Nonchemical, mechanical barriers, such as the skin

and the mucous membranes Protective proteins

Complement proteins are composed of a number of blood plasma proteins that “complement” certain immune responses and help destroy pathogens in three ways

Bind to mast cells and trigger histamine release to create enhanced inflammation

Bind to the surface of pathogens already coated with antibodies Form a membrane attack complex that produces holes in the

surface of some bacteria and viruses Interferons are cytokines - soluble proteins that affect the

behavior of other cells Inflammatory response

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Phagocytes and Natural Killer Cells

Neutrophils are cells that are able to leave the bloodstream and engulf bacteria in connective tissues

Eosinophils are phagocytic, but they are better known for mounting an attack against animal parasites The two most powerful of the phagocytic white blood

cells are macrophages and macrophage - derived dendritic cells

Natural killer (NK) cells are large, granular lymphocytes that kill virus-infected cells and cancer cells by cell-to-cell contact

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Figure 30.3A Overview of nonspecific defenses

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Figure 30.3B Action of the complement system against a bacterium

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APPLYING THE CONCEPTS—HOW BIOLOGY IMPACTS OUR LIVES

30.4 A fever can be beneficial

Several hypotheses have been proposed as to the benefits of a fever Perhaps a fever is the body’s way of informing us

that something is wrong At times, a fever may directly participate in

overcoming an illness Example: a fever can contribute to the host’s defense by

providing an unfavorable environment for the invader

A fever may stimulate immunity A fever has been shown to limit the growth of tumor cells

more severely than that of normal body cells

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30.5 The inflammatory response is a localized response to invasion

Inflammatory response - a series of events that occur whenever tissue is damaged An inflamed area has four outward signs:

redness, heat, swelling, and pain

Steps in the inflammatory response Chemical mediators, such as histamine, cause the capillaries to

dilate and become more permeable Migration of phagocytes, namely neutrophils and monocytes,

also occurs during the inflammatory response Macrophages also release colony-stimulating factors, cytokines

that pass by way of the blood to the red bone marrow, where they stimulate the production and release of white blood cells

A blood clot can form to seal a break in a blood vessel

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Figure 30.5A Inflammatory response

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Figure 30.5B A macrophage engulfing bacteria

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The Body’s Second Line of Defense Against Disease Is

Specific to the Pathogen

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30.6 The second line of defense targets specific antigens

Immunity is complete when a foreign substance is unable to cause an infection First - specific defense requires that the body be able

to recognize a particular molecule, an antigen Other antigens are termed self-antigens because the body

itself produces them

Second - after recognizing antigens, the immune system can respond to them

Third - the immune system can remember antigens it has met before

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30.7 Specific immunity can be active or passive

Active Immunity Develops naturally after a person is infected with a

pathogen Vaccine contains antigens that cause body to

develop antibodies specific to these antigens Passive Immunity

Occurs when an individual is given prepared antibodies (immunoglobulins) to combat a disease Since these antibodies are not produced by the individual’s

plasma cells, passive immunity is short-lived Even though passive immunity does not last, it is sometimes

used to prevent illness in a patient who has been unexpectedly exposed to an infectious disease

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Figure 30.7A  Vaccines immunize children against diseases

Figure 30.7B Breastfeeding provides infants with antibodies

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30.8 Lymphocytes are directly responsible for specific defenses

Specific defenses primarily depend on two types of lymphocytes - B cells and T cells Capable of recognizing antigens because they have specific

antigen receptors B cells have B cell receptors (BCR) T cells have T cell receptors (TCR)

B cells are responsible for antibody-mediated immunity Once a B cell combines with an antigen, it gives rise to plasma

cells, which produce specific antibodies T cells are responsible for cell-mediated immunity

T cells do not recognize an antigen until it is presented to them by an antigen-presenting cell (APC)

Cells differentiate into either helper T cells, which release cytokines, or cytotoxic T cells, which attack and kill virus-infected cells

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Figure 30.8 Overview of specific defenses

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30.9 Antibody-mediated immunity involves B cells

Clonal selection model describes what happens when a B cell receptor (BCR) combines with an antigen Antigen “selects” the B cell that will clone

Cytokines secreted by helper T cells stimulate B cells to clone Defense by B cells is called antibody-mediated immunity because most

members of a clone become plasma cells that produce specific antibodies

Immunization involves the use of vaccines to bring about clonal expansion, not only of B cells, but also of T cells

Antibodies also known as immunoglobulin (Ig) Most typical antibody, called IgG, is a Y-shaped

molecule with two arms IgG has constant regions, where the sequence

of amino acids is set, and variable regions, where the sequence of amino acids varies between IgGs

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Figure 30.9A Clonal selection model as it applies to B cells

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Figure 30.9B Antibody titers

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30.10 Cell-mediated immunity involves several types of T cells

T cells develop into T cell receptors (TCR) When a T cell leaves the thymus, it has a unique TCR, just as B

cells have a BCR T cells are unable to recognize an antigen alone

Antigen must be displayed by antigen-presenting cell (APC) APC breaks the pathogen apart in a lysosome

Piece of the pathogen is then displayed in an MHC (major histocompatibility complex) protein

Types of T Cells Cytotoxic T cells have storage vacuoles containing perforins and

storage vacuoles containing enzymes called granzymes Helper T cells play a critical role in coordinating nonspecific

defenses and specific defenses, including both cell-mediated immunity and antibody-mediated immunity

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Figure 30.10A Clonal selection model as it applies to T cells

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Figure 30.10B Cell-mediated immunity

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Cytokines and Cancer Therapy

Cytokine simply means a soluble protein that acts as a signaling molecule Cytokines stimulate white blood cells, they have been studied as

a possible adjunct therapy for cancer Cytokines called interleukins are produced by white

blood cells, and they act to stimulate other white blood cells When cancer cells carry an altered protein on their cell surface,

they should be attacked and destroyed by cytotoxic T cells Tumor necrosis factor (TNF) is a cytokine produced by

macrophages that has the ability to promote the inflammatory response and to cause the death of cancer cells TNF stimulates the body’s immune cells to fight cancer

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APPLYING THE CONCEPTS—HOW BIOLOGY IMPACTS OUR LIVES

30.11 Monoclonal antibodies have many uses

Every plasma cell derived from a single B cell secretes antibodies against a specific antigen Called monoclonal antibodies because all of them are the

same type Research Uses for Monoclonal Antibodies

Monoclonal antibodies are useful because of their extreme specificity for a particular molecule

Medical Uses for Monoclonal Antibodies Can be used to make quick and certain diagnoses of various

conditions Used to signify pregnancy by detecting a particular hormone in the

urine of a woman after she becomes pregnant Monoclonal antibodies can be used not only to diagnose infections

and illnesses but also to fight them Monoclonal antibodies have shown promise as potential drugs to

fight disease

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Figure 30.11 Production of monoclonal antibodies

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Abnormal Immune Responses Can Have Health Consequences

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30.12 Tissue rejection makes transplanting organs difficult

Certain organs could be transplanted easily from one person to another if the body did not reject them Rejection occurs because antibodies and cytotoxic T cells bring

about the destruction of foreign tissues in the body It is best if the transplanted organ has the same type of

MHC antigens as those of the recipient Cytotoxic T cells recognize foreign MHC antigens Well-known immunosuppressive drugs act by inhibiting the

production of certain cytokines that stimulate cytotoxic T cells Xenotransplantation, the transplantation of animal

tissues and organs into human beings, is another way to solve the problem of rejection Genetic engineering can make pig organs less antigenic by

removing the MHC antigens

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30.13 Autoimmune disorders are long-term illnesses

Autoimmune disorders - failure of the immune system to distinguish between foreign antigens and the self-antigens Chronic inflammation occurs, and cytotoxic T cells or antibodies

mistakenly attack the body’s own cells

Rheumatoid arthritis causes recurring inflammation in synovial joints Complement proteins, T cells, and B cells all participate in deterioration

of the joints, which eventually become immobile

Systemic lupus erythematosus (lupus) is characterized by presence of antibodies to the nuclei of body’s cells Affects multiple tissues and organs, and is poorly understood

Exact events that trigger an autoimmune disorder are not known Some autoimmune disorders set in following a noticeable infection Most autoimmune disorders probably start after an undetected

inflammatory response

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Figure 30.13A Rheumatoid arthritis

Figure 30.13B Systemic lupus; a butterfly-shaped rash appears on face

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APPLYING THE CONCEPTS—HOW BIOLOGY IMPACTS OUR LIVES

30.14 Allergic reactions can be debilitating and even fatal

Allergies are hypersensitivities to substances, such as pollen, food, or animal hair, that ordinarily would do no harm to the body Response to antigens, called allergens, usually includes some tissue

damage An immediate allergic response can occur within seconds of contact

with the antigen The response is caused by antibodies known as IgE When an allergen attaches to the IgE antibodies and the antibodies attach to

their receptors on mast cells, the mast cells release histamine that bring about allergic symptoms

Asthma, the airways leading to the lungs constrict, resulting in difficult breathing accompanied by wheezing

Anaphylactic shock - an immediate allergic response that occurs because the allergen has entered the bloodstream Characterized by a sudden and life-threatening drop in blood pressure

Delayed allergic response is initiated by memory T cells at the site of allergen contact in the body Allergic response is regulated by cytokines secreted by both T cells and

macrophages

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Figure 30.14

An allergic reaction

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Connecting the Concepts:Chapter 30

The defense mechanisms of humans have been extensively studied, but little is known about these mechanisms in other animals Body has the skin and mucous membranes that act as barriers to

prevent pathogens from entering the blood and lymph Nonspecific defense mechanisms, such as the complement system and

phagocytosis by white blood cells, come into play Then, specific defense mechanisms, which are dependent on the

activities of B cells and T cells, bring infection to an end The cardiovascular and lymphatic systems are intimately connected

in that tissue fluid becomes lymph in lymphatic vessels, and is derived, in part, from the water and small molecules that leave the bloodstream

Blood is refreshed because the digestive, respiratory, and urinary systems make exchanges with the external environment The food we eat is digested into nutrients that enter the blood; gas

exchange in the lungs permits the removal of carbon dioxide from blood and the entrance of oxygen into blood; and the kidneys remove and excrete metabolic wastes taken from the blood