The Bodys Defenses 2010 Pearson Education Inc Importance

Importance of Vaccine • A vaccine is a harmless derivative or variant of a disease-causing microbe. • Vaccinations against HIV, the virus that causes AIDS, have not been successful. © 2010 Pearson Education, Inc.

• The immune system is the body’s defense against disease. • Our bodies

• Three lines of defense protect us from invaders of varying types: – External barriers – Innate defenses, which are – Already present – React regardless of whether or not an invader has been previously encountered – Adaptive defenses, activated by exposure to specific invaders © 2010 Pearson Education, Inc.

THE BODY’S DEFENSES Innate Defenses (operate without previous exposure to pathogen) Internal innate defenses External innate defenses • Skin • Secretions • Mucous membranes • Mucus-producing cells • Antibodies Phagocytic cell Colorized SEM Cilia Phagocytic cells Adaptive Defenses (activated by exposure to specific pathogens) • • • Natural killer cells Defensive proteins Inflammatory response • Lymphocytes B cell The Lymphatic System (involved in internal innate defenses and adaptive defenses) T cell Lymph node Figure 24. 1

External Innate Defenses • The body has physical barriers including: – A tough outer skin layer generally impenetrable to viruses and bacteria – Mucous membranes covered with sticky mucus – Secretions (such as tears, sweat, and saliva) with antimicrobial chemicals – Strong stomach acids that kill most pathogens ingested with food © 2010 Pearson Education, Inc.

Internal Innate Defenses • To fight pathogens within the body, an animal’s immune system must: – Detect foreign particles and cells – Distinguish nonself from self • This second line of defense includes: – White blood cells – Defensive proteins © 2010 Pearson Education, Inc.

INTERNAL INNATE DEFENSES White Blood Cells Phagocytic cells (engulf foreign cells or substances) Natural killer cells (destroy infected body cells and cancerous cells) Defensive Proteins Interferons (protect body cells against viral infection) Complement proteins (cause invading microbial cells to lyse) Figure 24. 2

• Two important types of white blood cells are involved in internal innate defense: – Phagocytic cells engulf: – Foreign molecules and cells – Debris from dead cells – Natural killer (NK) cells: – Recognize virus-infected cells – Release chemicals that kill diseased cells © 2010 Pearson Education, Inc.

• The defensive proteins that aid in internal innate defenses work indirectly and directly. – Interferons indirectly help healthy cells resist damage. – Complement proteins attack pathogens directly. © 2010 Pearson Education, Inc.

Infected cell releases Interferon molecules. Virus Interferon molecules bind to healthy cell. Interferon molecules Antiviral proteins Virus-infected cell Healthy cell The binding stimulates production of antiviral proteins. Figure 24. 3 -3

The Inflammatory Response • Another example of an internal innate defense is the inflammatory response, a coordinated set of nonspecific defenses in response to injury or infection. © 2010 Pearson Education, Inc.

• Damaged cells release chemicals that: – Increase blood flow to the damaged area – Turn the wound red and warm • Anti-inflammatory drugs, such as aspirin and ibuprofen: – Dampen the normal inflammatory response – Reduce swelling and fever © 2010 Pearson Education, Inc.

Skin surface Blood clot Swelling Splinter Bacteria Chemical signals White blood cell Phagocytic cells and fluid move into area Blood vessel Tissue injury; release of chemical signals such as histamine Dilation and increased leakiness of local blood vessels; migration of phagocytic cells to the area Phagocytic cells engulf bacteria and cell debris; tissue heals Figure 24. 4 -3

The Lymphatic System • The lymphatic system consists of: – A branching network of vessels – Numerous lymph nodes – Several other organs • Lymphatic vessels carry lymph, a fluid that is similar to interstitial fluid surrounding body cells. © 2010 Pearson Education, Inc.

Tonsil Lymph nodes Lymphatic vessels entering veins Appendix Thymus Lymphatic vessels Spleen Figure 24. 5

• The lymphatic system: – Returns tissue fluid to the circulatory system –

ADAPTIVE DEFENSES • Adaptive defenses: – Are third line of defense – Are activated after exposure to specific pathogens – Depend upon lymphocytes that: – Recognize and – Respond to specific invading pathogens © 2010 Pearson Education, Inc.

• There are two types of lymphocytes: – B cells, which mature in the bone marrow, and – T cells, which mature in the thymus, a gland in the chest • B cells and T cells eventually make their way to: – Lymph nodes – Other lymphatic organs © 2010 Pearson Education, Inc.

Bone marrow Stem cell in bone marrow Immature lymphocytes in bone marrow Via blood to thymus B cell (matures in bone marrow) T cell (matures in thymus) Via blood Lymph nodes, spleen, and other lymphatic organs Figure 24. 6 -3

• Antigens: – Are molecules on the surfaces of viruses or foreign cells

Recognizing the Invaders • B and T cells develop antigen receptors on their surfaces. – All the antigen receptors on a particular cell recognize a single specific antigen. – The great diversity of B cells and T cells produces enough different antigen receptors to bind to just about every possible antigen. © 2010 Pearson Education, Inc.

• When a particular B cell binds to its particular antigen, it gives

Antigenbinding site Antigen-binding sites Computer model of an antibody Antibody Figure 24. 7

• Antibodies: – Are Y-shaped molecules – Have binding sites with tremendous variety – Enable the immune system to react to just about any kind of antigen – Combine with an antigen to form an antigen-antibody complex © 2010 Pearson Education, Inc.

• Monoclonal antibodies are: – Produced by cells descended from a single cell

Responding to the Invaders • B cells and T cells carry out a coordinated

Clonal Selection: Multiplying Lymphocytes • Clonal selection: – Generates B cells and T cells appropriate to the invading antigen – Is the mechanism that underlies the immune system’s specificity and memory of antigens © 2010 Pearson Education, Inc.

Antigens B cells that recognize different antigens Antigen receptor on cell surface Clone of identical cells Antibodies Clone of effector cells Clone of memory cells Figure 24. 9 -3

• Effector cells: – Are short-lived – Have an immediate effect against an

• The primary immune response: – Is the first response to exposure of

• Effector B cells: – Produce a peak amount of antibodies about two

Immunological Memory • Clonal selection also produces memory cells, which: – Are long-lived, lasting decades – Respond to subsequent exposures to a previously encountered antigen – Give rise to: – Effector cells – Even more memory cells © 2010 Pearson Education, Inc.

• In the secondary immune response, memory cells: – Bind to the antigen faster – Multiply more quickly • Thus, in adaptive defenses, but not innate defenses, exposure to a particular antigen enhances future responses to the same antigen. © 2010 Pearson Education, Inc.

Second exposure to antigen X, first exposure to antigen Y Secondary immune response to antigen X Antibody concentration First exposure to antigen X Primary immune response to antigen Y Antibodies to X 0 7 14 21 28 35 42 49 56 Time (days) © 2010 Pearson Education, Inc. Figure 24. UN 6

Vaccination • Vaccination confronts the immune system with a vaccine, which includes a harmless variant of a disease-causing microbe or one of its parts. • A vaccine stimulates the immune system to mount defenses against the actual pathogen possessing the same antigens. © 2010 Pearson Education, Inc.

• In the United States, vaccinations have virtually eliminated: – Polio – Mumps

Figure 24. 10 Colorized SEM

B Cells and the Humoral Immune Response • The humoral immune response is: –

T Cells and the Cell-Mediated Immune Response • The cell-mediated immune response: – Reacts to pathogens that have already entered body cells – Involves two main kinds of effector T cells: – Helper T cells – Cytotoxic T cells © 2010 Pearson Education, Inc.

• Helper T cells: – Stimulate the activity of cytotoxic T cells –

Phagocytic cell breaks microbe into antigen fragments. Microbe Phagocytic cell Antigen from microbe (nonself molecule) Self protein binds to antigen. Self protein displays antigen on surface. T cell receptor Colorized SEM Helper T cell Phagocytic cell (yellow) engulfing a foreign cell Receptor on helper T cell binds to the protein-antigen combination. Figure 24. 11

Clonal selection T cell receptor Phagocytic cell Activated helper T cell Cytotoxic T cell Cell-mediated immune response (attack on infected cells) Activates other T cells and B cells Self-nonself complex B cell Humoral immune response (secretion of antibodies) Figure 24. 12

Cytotoxic T Cells • Activated by helper T cells • Bind to infected cells and release proteins that trigger cell death Proteins Infected cell Cytotoxic T cell © 2010 Pearson Education, Inc. Figure 24. UN 5 b

• Cytotoxic T cells: – Are the only T cells that kill other body cells – Identify and find infected body cells – Synthesize and discharge proteins that: – Make holes in the infected cell’s plasma membrane or – Trigger a process that results in death of the infected cell Animation: Cytotoxic T Cells © 2010 Pearson Education, Inc.

Infected cell Foreign antigen Perforin protein Activated cytotoxic T cell Infected cell Hole forming Proteins Other proteins Cytotoxic T cell binds to infected cell, becoming activated and producing perforin. Cytotoxic T cell Perforin makes holes in infected cell’s plasma membrane. Other proteins enter target cell through holes created by perforin. Infected cell is destroyed by lysis (bursting). Figure 24. 13 -4

IMMUNE DISORDERS • If the interplay of immune cells goes awry, problems can arise

Allergies • Allergies are sensitivities to harmless antigens in the environment. • Allergens are antigens that cause allergies. • The symptoms of an allergy result from a two-stage reaction sequence. © 2010 Pearson Education, Inc.

LATER EXPOSURES TO SAME ALLERGEN Colorized SEM SENSITIZATION: INITIAL EXPOSURE TO ALLERGEN Ragweed pollen grains Effector B cell Histamine Mast cell Allergen (pollen grain) enters bloodstream. B cells make antibodies. Antibodies attach to mast cell. Allergen binds to antibodies on mast cell. Histamine is released, causing allergy symptoms. Figure 24. 14 -5

• Anaphylactic shock: – Is an especially dangerous type of allergic reaction –

Figure 24. 15

Autoimmune Diseases • The immune system: – Normally reacts only against foreign (nonself) substances but – May attack: – Our own tissues – Tissues transplanted into our bodies © 2010 Pearson Education, Inc.

• Autoimmune diseases: – Occur when the immune system improperly attacks the body’s own molecules – May lead to serious diseases such as: – Lupus – Insulin-dependent diabetes – Multiple sclerosis – Rheumatoid arthritis © 2010 Pearson Education, Inc.

Figure 24. 16

Immunodeficiency Diseases • Immunodeficiency diseases: – Result when one or more of the components of the immune system are lacking – Leave affected people more susceptible to infections © 2010 Pearson Education, Inc.

• Immunodeficiencies may arise: – Through inborn conditions such as severe combined immunodeficiency (SCID) – From acquired illness such as Hodgkin’s disease, a type of cancer – From radiation or drug therapies used against many cancers © 2010 Pearson Education, Inc.

• HIV, the virus that causes AIDS: – Currently infects more than 33 million people worldwide – Attacks helper T cells – Cripples humoral and cell-mediated immunity • Lives can be saved by: – Reducing promiscuity © 2010 Pearson Education, Inc.

INNATE DEFENSES Internal External • Skin • Mucous • membranes Secretions White blood cells Defensive proteins • Phagocytic • cells Natural killer cells The inflammatory response • Involves chemical • Interferons signals and • Complement proteins phagocytic cells Figure 24. UN 1

LYMPHOCYTES (Immune system contains millions of different kinds. ) B cells (humoral immune response) • Secrete antibodies, which mark invaders T cells (cell-mediated immune response) • • Attack infected cells Help activate B cells Antigen receptors recognize one specific kind of antigen. Figure 24. UN 2

Antigen secretes B cell Antibody deactivates antigen or marks it for destruction. Antibody Figure 24. UN 3

Antigen receptor Antigen Lymphocyte Clonal selection Cells specific for this particular antigen Effector cells Memory cells Figure 24. UN 4

EFFECTOR T CELLS Helper T Cells • Recognize self-nonself complexes • Activate other cells activate Cytotoxic T Cells • Activated by helper T cells • Bind to infected cells and release proteins that trigger cell death Proteins Self-nonself complex Phagocytic cell Helper T cell Infected cell Cytotoxic T cell Figure 24. UN 5

Helper T Cells • Recognize self-nonself complexes • Activate other cells Self-nonself complex Phagocytic cell Helper T cell Figure 24. UN 5 a