© 2010 Pearson Education, Inc. The Body’s Defenses  Innate Defenses  Adaptive Defenses  Immune Disorders

© 2010 Pearson Education, Inc. INNATE DEFENSES The immune system is the body’s defense against disease. Our bodies defend us against pathogens, disease-causing: –Viruses and –Microorganisms

© 2010 Pearson Education, Inc. 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

Mucus-producing cells Cilia External innate defenses Internal innate defenses Phagocytic cell The Lymphatic System (involved in internal innate defenses and adaptive defenses) Lymph node B cell T cell Innate Defenses (operate without previous exposure to pathogen) Adaptive Defenses (activated by exposure to specific pathogens) THE BODY’S DEFENSES Colorized SEM Skin Secretions Mucous membranes Natural killer cells Defensive proteins Inflammatory response Phagocytic cells Antibodies Lymphocytes Figure 24.1

© 2010 Pearson Education, Inc. 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

Phagocytic cells (engulf foreign cells or substances) Natural killer cells (destroy infected body cells and cancerous cells) White Blood Cells Interferons (protect body cells against viral infection) Defensive Proteins Complement proteins (cause invading microbial cells to lyse) INTERNAL INNATE DEFENSES Figure 24.2

Phagocytic cells (engulf foreign cells or substances) Natural killer cells (destroy infected body cells and cancerous cells) White Blood Cells Figure 24.2a

Interferons (protect body cells against viral infection) Defensive Proteins Complement proteins (cause invading microbial cells to lyse) Figure 24.2b

© 2010 Pearson Education, Inc. 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.

Interferon molecules Infected cell releases Interferon molecules. Virus Virus-infected cell Figure

Interferon molecules bind to healthy cell. Interferon molecules Infected cell releases Interferon molecules. Virus Virus-infected cellHealthy cell Figure

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

© 2010 Pearson Education, Inc. 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.

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

© 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. 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.

Lymphatic vessels Appendix Lymphatic vessels entering veins Lymph nodes Tonsil Thymus Spleen Figure 24.5

© 2010 Pearson Education, Inc. The lymphatic system: –Returns tissue fluid to the circulatory system –Helps to fight infections

© 2010 Pearson Education, Inc. ADAPTIVE DEFENSES Adaptive defenses: –Are the 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

EFFECTOR T CELLS Helper T Cells Recognize self-nonself complexes Activate other cells Proteins Cytotoxic T Cells activate Activated by helper T cells Bind to infected cells and release proteins that trigger cell death Infected cell Cytotoxic T cell Phagocytic cell Helper T cell Self-nonself complex Figure 24.UN5

Bone marrow B cell (matures in bone marrow) Stem cell in bone marrow Immature lymphocytes in bone marrow Via blood to thymus T cell (matures in thymus) Figure

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

© 2010 Pearson Education, Inc. Antigens: –Are molecules on the surfaces of viruses or foreign cells –Elicit a response from a lymphocyte

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 rise to other short-lived cells, which secrete a receptor-like molecule called an antibody.

Antigen- binding site Antigen Antigen-binding sites Computer model of an antibody Antibody Figure 24.7

© 2010 Pearson Education, Inc. 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 –Identical and specific for a single antigen

© 2010 Pearson Education, Inc. Responding to the Invaders B cells and T cells carry out a coordinated attack along with the innate defenses.

© 2010 Pearson Education, Inc. 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

B cells that recognize different antigens Antigens Antibodies Clone of identical cells Antigen receptor on cell surface Clone of memory cells Clone of effector cells Figure

© 2010 Pearson Education, Inc. 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. 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 –Smallpox

© 2010 Pearson Education, Inc. B Cells and the Humoral Immune Response The humoral immune response is: –The secretion of antibodies into the blood and lymph –Caused by effector B cells

© 2010 Pearson Education, Inc. 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 –Help activate B cells –Grow and divide to produce: –More activated helper T cells –Memory T cells

Phagocytic cell (yellow) engulfing a foreign cell Colorized SEM Receptor on helper T cell binds to the protein-antigen combination. Self protein displays antigen on surface. T cell receptor Helper T cell Antigen from microbe (nonself molecule) Self protein Phagocytic cell breaks microbe into antigen fragments. Microbe Self protein binds to antigen. Figure 24.11

© 2010 Pearson Education, Inc. 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

Foreign antigen Infected cell Activated cytotoxic T cell Cytotoxic T cell Infected cell Hole forming Other proteins Perforin protein Proteins Cytotoxic T cell binds to infected cell, becoming activated and producing perforin. 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

© 2010 Pearson Education, Inc. IMMUNE DISORDERS If the interplay of immune cells goes awry, problems can arise that range from mild irritations to deadly diseases.

© 2010 Pearson Education, Inc. 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.

Colorized SEM Effector B cell Ragweed pollen grains SENSITIZATION: INITIAL EXPOSURE TO ALLERGEN Allergen (pollen grain) enters bloodstream. B cells make antibodies. Figure

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

© 2010 Pearson Education, Inc. Anaphylactic shock: –Is an especially dangerous type of allergic reaction –Can be counteracted with injections of epinephrine

Figure 24.15

© 2010 Pearson Education, Inc. 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

Figure 24.16

© 2010 Pearson Education, Inc. 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. AIDS AIDS (acquired immunodeficiency syndrome): –Infects several million people each year –Has killed more than 30 million people worldwide

© 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 –Properly using condoms

Human helper T cell Colorized TEM HIV Figure 24.17

External INNATE DEFENSES Skin Mucous membranes Secretions Internal White blood cells Phagocytic cells Natural killer cells Interferons Complement proteins Defensive proteins The inflammatory response Involves chemical signals and phagocytic cells Figure 24.UN1