Chapter 15 The Lymphatic System and Immunity

Chapter 15 The Lymphatic System and Immunity

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The Lymphatic System • Lymph—fluid in tissue spaces that carries protein molecules and other substances back to the blood

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The Lymphatic System • Lymphedema—swelling (edema) of tissues caused by blockage of lymphatic vessels – Elephantiasis—severe lymphedema of limbs resulting from parasite infestation of lymphatic vessels

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The Lymphatic System • Thymus – Plays central role in immunity – Produces T lymphocytes or T cells – Secretes hormone called thymosin – Atrophies in adults

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The Lymphatic System • Tonsils – Three around openings of mouth and throat • Palatine tonsils (“the tonsils”) • Pharyngeal tonsils (adenoids) • Lingual tonsils

– Subject to chronic infection – Enlargement of pharyngeal tonsils may impair breathing

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The Lymphatic System • Spleen – Largest lymphoid organ in body – Located in upper left quadrant of abdomen – Often injured by trauma to abdomen – Surgical removal called splenectomy – Functions include phagocytosis of bacteria and old RBCs; acts as a blood reservoir – Splenomegaly—enlargement of the spleen 15 Mosby items and derived items © 2010, 2006, 2002, 1997, 1992 by Mosby, Inc., an affiliate of Elsevier Inc.

The Immune System • Protects body from pathogens, foreign tissue, and cancer cells • Nonspecific immunity – Skin—barrier to bacteria and other harmful agents

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The Immune System • Nonspecific immunity – Tears and mucus—wash eyes and trap bacteria – Inflammation attracts immune cells to site of injury, increases local blood flow, increases vascular permeability; promotes movement of WBCs to site of injury or infection 17 Mosby items and derived items © 2010, 2006, 2002, 1997, 1992 by Mosby, Inc., an affiliate of Elsevier Inc.

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Humoral immunity

Active

Passive

Naturally acquired

Artificially acquired

Naturally acquired

Artificially acquired

Infection; contact with pathogen

Vaccine; dead or attenuated pathogens

Antibodies pass from mother to fetus via placenta; or to infant in her milk

Injection of immune serum (gamma globulin)

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Figure 21.13

The Immune System • Specific immunity—ability to recognize, respond, and remember antigen • Inborn immunity—inherited immunity to certain diseases from time of birth

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Antibody A

Antigenbinding sites

Antigenic determinants

Antigen

Antibody B Antibody C

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Figure 21.7

Adaptive defenses

Humoral immunity Antigen

Antigen-antibody complex

Antibody

Inactivates by Neutralization (masks dangerous parts of bacterial exotoxins; viruses)

Agglutination (cell-bound antigens)

Enhances Phagocytosis

Fixes and activates Precipitation (soluble antigens)

Enhances

Complement

Leads to

Inflammation

Cell lysis

Chemotaxis

Histamine release Mosby items and derived items © 2010, 2006, 2002, 1997, 1992 by Mosby, Inc., an affiliate of Elsevier Inc.

Figure 21.15

Immune System Cells • Phagocytes – Ingest and destroy foreign cells or other harmful substances via phagocytosis – Macrophages and DCs act as antigenpresenting cells (APCs) by displaying ingested antigens on their outer surface to trigger specific immune cells

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Adaptive defenses

Immature lymphocytes

Red bone marrow: site of lymphocyte origin

Humoral immunity Cellular immunity

Primary lymphoid organs: site of development of immunocompetence as B or T cells Secondary lymphoid organs: site of antigen encounter, and activation to become effector and memory B or T cells

Red bone marrow

1 Lymphocytes destined to become T cells

migrate (in blood) to the thymus and develop immunocompetence there. B cells develop immunocompetence in red bone marrow. Thymus Bone marrow

2 Immunocompetent but still naive Lymph nodes, spleen, and other lymphoid tissues

lymphocytes leave the thymus and bone marrow. They “seed” the lymph nodes, spleen, and other lymphoid tissues where they encounter their antigen. 3 Antigen-activated immunocompetent

lymphocytes (effector cells and memory cells) circulate continuously in the bloodstream and lymph and throughout the lymphoid organs of the body.

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Adaptive defenses

Humoral immunity

Primary response (initial encounter with antigen)

Activated B cells

Proliferation to form a clone

Plasma cells (effector B cells)

Memory B cell— primed to respond to same antigen

Secreted antibody molecules Secondary response (can be years later)

Antigen Antigen binding to a receptor on a specific B lymphocyte (B lymphocytes with non-complementary receptors remain inactive)

Clone of cells identical to ancestral cells

Subsequent challenge by same antigen results in more rapid response

Plasma cells Secreted antibody molecules Copyright © 2010 Pearson Education, Inc.

Memory B cells

Secondary immune response to antigen A is faster and larger; primary immune response to antigen B is similar to that for antigen A.

Primary immune response to antigen A occurs after a delay.

Antibodies to B

Antibodies to A

First exposure to antigen A

Second exposure to antigen A; first exposure to antigen B Time (days)

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TH cell help in humoral immunity Activated helper T cell

1 TH cell binds with the

Helper T cell CD4 protein

self-nonself complexes of a B cell that has encountered its antigen and is displaying it on MHC II on its surface.

MHC II protein of B cell displaying processed antigen

2 TH cell releases

T cell receptor (TCR)

IL- 4 and other cytokines B cell (being activated) (a)

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interleukins as co-stimulatory signals to complete B cell activation.

TH cell help in cell-mediated immunity CD4 protein

Helper T cell

Class II MHC protein APC (dendritic cell)

1 Previously

activated TH cell binds dendritic cell. 2 TH cell stimulates

IL-2

dendritic cell to express co-stimulatory molecules (not shown) needed to activate CD8 cell. 3 Dendritic cell can

Class I MHC protein (b) Copyright © 2010 Pearson Education, Inc.

CD8 protein

CD8 T cell

now activate CD8 cell with the help of interleukin 2 secreted by TH cell.

Immune System Cells – Development of B cells • Second stage—inactive B cell develops into activated B cell – Initiated by inactive B cell’s contact with antigens, which bind to its surface antibodies, plus signal chemicals from T cells – Activated B cell, by dividing repeatedly, forms two clones of cells—plasma (effector) cells and memory cells – Plasma cells secrete antibodies into blood; memory cells are stored in lymph nodes – If subsequent exposure to antigen that activated B cell occurs, memory cells become plasma cells and secrete antibodies 33 Mosby items and derived items © 2010, 2006, 2002, 1997, 1992 by Mosby, Inc., an affiliate of Elsevier Inc.

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Immune System Cells – Functions of T cells—cell-mediated immunity • Cytotoxic T cells—kill infected or tumor cells by releasing a substance that poisons infected or tumor cells • Helper T cells—produce chemicals that help activate B cells • Regulatory T cells—release chemicals to suppress immune responses

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Hypersensitivity of the Immune System • Inappropriate or excessive immune response • Allergy—hypersensitivity to harmless environmental antigens (allergens) – Immediate allergic responses usually involve humoral immunity – Delayed allergic responses usually involve cell-mediated immunity 37 Mosby items and derived items © 2010, 2006, 2002, 1997, 1992 by Mosby, Inc., an affiliate of Elsevier Inc.

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Hypersensitivity of the Immune System • A healthy immune system works efficiently to fight off disease. In someone with an autoimmune disorder, the immune system wrongly identifies healthy tissues as foreign and tries to destroy them. • There are over 80 known types of disorders, affecting different areas of the body – from joints and muscles to skin and blood and organs. Among the most common autoimmune conditions are type 1 diabetes, multiple sclerosis, Crohn's disease, rheumatoid arthritis and psoriasis. There is no cure, but medication and a healthy lifestyle can help manage these conditions while researchers continue to look for new treatment approaches. 40 Mosby items and derived items © 2010, 2006, 2002, 1997, 1992 by Mosby, Inc., an affiliate of Elsevier Inc.

Hypersensitivity of the Immune System • Isoimmunity—excessive reaction to antigens from another human – May occur between mother and fetus during pregnancy – May occur in tissue transplants (causing rejection syndrome)

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Immune System Deficiency • Congenital immune deficiency or immunodeficiency (rare) – Results from improper lymphocyte development before birth – Severe combined immune deficiency (SCID)—caused by disruption of stem cell development

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Immune System Deficiency • Acquired immune deficiency – Develops after birth – Acquired immunodeficiency syndrome (AIDS)—caused by HIV infection of T cells

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