Immunology: Animal Defense Systems

1. 31 Immunology: Animal Defense Systems

2. Chapter 31 Immunology: Animal Defense Systems • Key Concepts • 31.1 Animals Use Innate and Adaptive Mechanisms to Defend Themselves against Pathogens • 31.2 Innate Defenses Are Nonspecific • 31.3 The Adaptive Immune Response Is Specific

3. Chapter 31 Immunology: Animal Defense Systems • Key Concepts • 31.4 The Adaptive Humoral Immune Response Involves Specific Antibodies • 31.5 The Adaptive Cellular Immune Response Involves T Cells and Their Receptors

4. Chapter 31 Opening Question How can a person survive an infection and be resistant to further infection?

5. Concept 31.1Animals Use Innate and Adaptive Mechanisms to Defend Themselves against Pathogens • Animals have various means of defense against pathogens—agents that cause disease. • Two general types of defense mechanisms can provide immunity—the ability to avoid disease when invaded by a pathogen.

6. Concept 31.1Animals Use Innate and Adaptive Mechanisms to Defend Themselves against Pathogens • Innate immunity—nonspecific, used against many organisms: • Includes barriers, such as skin and molecules toxic to invaders, as first line of defense. • Second line of innate defenses includes phagocytic cells, which ingest foreign cells and other particles. • These defenses may be present all the time or activated rapidly.

7. Concept 31.1Animals Use Innate and Adaptive Mechanisms to Defend Themselves against Pathogens • Adaptive immunity is specific: • Distinguishes between substances produced by self and nonself. • Involves antibody proteins and others that bind to and destroy pathogens. • Slow to develop and long-lasting, found only in vertebrate animals.

8. Table 31.1 Innate and Adaptive Immune Responses to an Infection

9. Concept 31.1Animals Use Innate and Adaptive Mechanisms to Defend Themselves against Pathogens • Mammals have both kinds of defense systems—they work together as a coordinated system. • The main factors in immunity are specific cells and proteins. • These are produced in the blood and lymphoid tissues and circulate throughout the body

10. Concept 31.1Animals Use Innate and Adaptive Mechanisms to Defend Themselves against Pathogens • White blood cells, or leukocytes, are suspended in the blood plasma. • Two kinds: • Phagocytes (such as macrophages) are large cells that engulf pathogens and other substances by phagocytosis. • Lymphocytes, which include B cells and T cells, are involved in adaptive immunity

11. Figure 31.1 White Blood Cells

12. Concept 31.1Animals Use Innate and Adaptive Mechanisms to Defend Themselves against Pathogens • Cell–cell interactions in the mammalian defense system involve four key protein types: • Antibodies—proteins that bind specifically to substances identified by the immune system • Antibodies are produced by B cells.

13. Concept 31.1Animals Use Innate and Adaptive Mechanisms to Defend Themselves against Pathogens • Major histocompatibility complex (MHC) proteins are found in two classes: • MHC I proteins are found on most cell surfaces • MHC II proteins are found on most immune system cells • MHC proteins are important self-identifying labels.

14. Concept 31.1Animals Use Innate and Adaptive Mechanisms to Defend Themselves against Pathogens • T cell receptors are integral membrane proteins on T cells, recognize and bind nonself molecules on other cells • Cytokines are soluble signaling proteins that bind to a cell’s surface receptors and alter that cell’s behavior

15. Concept 31.2 Innate Defenses Are Nonspecific • Nonspecific defenses are general mechanisms—the first line of defense. • They are genetically programmed and “ready to go.” • In mammals, they include physical barriers as well as cellular and chemical defenses.

16. Concept 31.2 Innate Defenses Are Nonspecific • Skin is a primary nonspecific defense. The physical barrier of the skin as well as the saltiness of the skin make it hard for bacteria to penetrate. • Normal flora—the bacteria and fungi that usually live on body surfaces They are part of the defense system because they compete with pathogens for nutrients and space.

17. Figure 31.2 Innate Immunity

18. Concept 31.2 Innate Defenses Are Nonspecific • Mucus is secreted by mucous membranes. Mucus traps microorganisms so cilia can remove them. • Cilia continuously move the mucus plus debris up towards nose and mouth. • Lysozyme, an enzyme that attacks bacterial cell walls, is found in tears, nasal mucus, and saliva.

19. Concept 31.2 Innate Defenses Are Nonspecific • Mucous membranes produce defensins, peptides with hydrophobic domains that are toxic to many pathogens. • Defensins insert themselves into the plasma membrane of the pathogen and make it permeable. • Harsh conditions in the internal environment, such as extreme acidity, can also kill pathogens.

20. In-Text Art, Ch. 31, p. 623 (1)

21. Concept 31.2 Innate Defenses Are Nonspecific • Pathogens that do penetrate surfaces encounter more complex nonspecific second defenses: • Activation of defensive cells • Secretion of defensive proteins—complement and interferon proteins • Pathogenic cells, viruses, or fragments of invaders can be recognized by phagocytes, which then ingest them by phagocytosis.

22. Concept 31.2 Innate Defenses Are Nonspecific • Natural killer cells—a type of lymphocyte that can detect virus-infected cells and some tumor cells: • Can initiate apoptosis in these cells • Can interact with the specific defense mechanisms and lyse cells labeled by antibodies

23. Concept 31.2 Innate Defenses Are Nonspecific • Vertebrate blood has antimicrobial proteins that make up the complement system. • Proteins act in a cascade—each protein activates the next. • Provide three types of defense: • Attach to microbes and mark them for phagocytes to engulf • Activate inflammation response and attract phagocytes to site of infection • Lyse invading cells

24. Concept 31.2 Innate Defenses Are Nonspecific • Interferons are signaling molecules produced by cells infected by a pathogen. • Interferons increase resistance of neighboring cells to the pathogen by: • Binding to receptors on noninfected cell membranes—stimulate a signaling pathway that inhibits viral reproduction • Stimulating cells to hydrolyze pathogen’s proteins to peptides

25. Concept 31.2 Innate Defenses Are Nonspecific • Inflammation is a coordinated response to injury—it isolates damage, recruits cells against pathogens, and promotes healing. • Mast cells are cells adhering to skin and organ linings; release chemical signals: • Tumor necrosis factor—cytokine that kills target cells and activates immune cells

26. Concept 31.2 Innate Defenses Are Nonspecific • Prostaglandins—initiate inflammation in nearby tissues, dilate blood vessels and interact with nerve endings, increasing sensitivity to pain • Histamine—amino acid derivative that increases permeability of blood vessels so white blood cells can act on tissues

27. Concept 31.2 Innate Defenses Are Nonspecific • Symptoms of inflammation: Redness, swelling, heat, pain, result from dilation of blood vessels in the area. • Phagocytes enter the area and engulf pathogens and dead cells. • Cytokines may signal the brain to produce fever—toxic to some pathogens. • Pus is a mixture of leaked fluid and dead cells. • Platelets appear near a wound to promote healing.

28. Concept 31.2 Innate Defenses Are Nonspecific • The inflammation response may be too strong: • In an allergic reaction, a nonself molecule that is normally harmless binds to mast cells, causing the release of histamine and subsequent inflammation. • In autoimmune diseases, the immune system fails to distinguish between self and nonself, and attacks tissues in the organism’s own body. • In sepsis, the inflammation due to a bacterial infection does not remain local.

29. Figure 31.3 Interactions of Cells and Chemical Signals Result in Inflammation

30. Concept 31.3 The Adaptive Immune Response Is Specific • Scientists discovered that a factor that develops in blood serum in response to a toxin is an example of adaptive immunity that is specific to the toxin. • Passive immunity is the development of immunity from antibodies received from another individual.

31. Figure 31.4 The Discovery of Specific Immunity (Part 1)

32. Figure 31.4 The Discovery of Specific Immunity (Part 2)

33. Concept 31.3 The Adaptive Immune Response Is Specific • Adaptive immunity has four key features: • Specific—focuses on antigens that are present • Diverse—responds to novel pathogens • Distinguishes selffrom nonself, prevents destruction of self cells • Has immunological memory, to respond to a later exposure to a pathogen

34. Concept 31.3 The Adaptive Immune Response Is Specific • Specificity—lymphocytes are crucial: • T cell receptors and antibodies bind to specific nonself molecules (antigens). • Specific sites on the antigens are called antigenic determinants, or epitopes.

35. Concept 31.3 The Adaptive Immune Response Is Specific • An antigenic determinant is a specific portion of a large molecule. • A single antigenic molecule can have multiple, different antigenic determinants. • The host responds to an antigen’s presence with highly specific defenses using T cell receptors and antibodies.

36. Concept 31.3 The Adaptive Immune Response Is Specific • Diversity: • The immune system must respond to a wide variety of pathogens by activating specific lymphocytes from a pool. • Diversity is generated primarily by DNA changes—chromosomal rearrangements and other mutations. • The adaptive immune system is “predeveloped”—all of the machinery available to respond to an immense diversity of antigens is already there, even before the antigens are encountered.

37. Concept 31.3 The Adaptive Immune Response Is Specific • Antigen binding “selects” a particular B or T cell for proliferation. • A particular lymphocyte is selected via binding and activation, and then it proliferates to generate a clone—called clonal selection for this mechanism of producing an immune response.

38. Figure 31.5 Clonal Selection in B Cells

39. Concept 31.3 The Adaptive Immune Response Is Specific • Normally, the body is tolerant of its own molecules; develops during early B and T cell differentiation. • Clonal deletion—Any immature B and T cells that show the potential to mount an immune response to self antigens undergo apoptosis.

40. Concept 31.3 The Adaptive Immune Response Is Specific • A failure of clonal deletion—autoimmunity. • In diseases such as systemic lupus erythematosis (SLE) or Hashimoto’s thyroiditis, immune cells mount a response against normal tissues.

41. Concept 31.3 The Adaptive Immune Response Is Specific • Immunological memory—the immune system “remembers” a pathogen after the first encounter. • Primary immune response—when antigen is first encountered, “naïve” lymphocytes proliferate to produce two types of cells— effector and memory cells.

42. Concept 31.3 The Adaptive Immune Response Is Specific • Effector cells carry out the attack. Effector B cells (plasma cells) secrete antibodies. Effector T cells secrete cytokines and other molecules. • Memory cells arelong-lived cells that can divide on short notice to produce effector and more memory cells. • Memory B and T cells may survive for decades.

43. Concept 31.3 The Adaptive Immune Response Is Specific • Secondary immune response—when antigen is encountered again, memory cells proliferate and launch an army of plasma cells and effector T cells. • Vaccinations trigger a primary immune response to prepare the body for a quicker, secondary response, if it encounters the pathogen again.

44. Concept 31.3 The Adaptive Immune Response Is Specific • The adaptive immune response involves three phases: • Recognition phase—the organism discriminates between self and nonself to detect a pathogen. • Activation phase—the recognition event leads to a mobilization of cells and molecules to fight the invader. • Effector phase—the mobilized cells and molecules destroy the invader.

45. Figure 31.6 The Adaptive Immune System (Part 1)

46. Figure 31.6 The Adaptive Immune System (Part 2)

47. Concept 31.3 The Adaptive Immune Response Is Specific • The three phases can occur in either of two types of response: the humoral immune response and the cellular immune response. • Humoral immune response involves B cells that make antibodies. • Cytotoxic T (TC) cells are the workhorses of the cellular immune response.

48. Concept 31.3 The Adaptive Immune Response Is Specific • A key event is the exposure or presentation of the antigen to the immune system. • In humoral immunity, this occurs when an antigen binds to a B cell that has an antibody specific to that antigen. • In cellular immunity, an antigen is inserted into the membrane of an antigen-presenting cell. • The antigen is recognized by a T-helper (TH) cell,with a specific T cell receptor protein.

49. Concept 31.3 The Adaptive Immune Response Is Specific • Antigen binding readies a B cell for division. • Antigen fragments bind to the MHC complex and are presented on the B cell surface. • A specific TH cell binds and stimulates the B cell to divide and form a clone. • In the cellular immune response, TH cell binding to the antigen-presenting cell causes cytokine release. • Cytokines stimulate TC cells with the same T cell receptor to divide.

50. Concept 31.3 The Adaptive Immune Response Is Specific • The result of activation is the formation of two clones of cells: • A clone of B cells that can produce antibodies specific for the antigen • A clone of TC cells that express a T cell receptor that can bind to any cell expressing the antigen on its surface