1. Foundations in Microbiology Seventh Edition Chapter 15 Adaptive, Specific Immunity and Immunization Lecture PowerPoint to accompany Talaro Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

2. 2 15.1 Specific Immunity – Adaptive Line of Defense Third line of defense – acquired Dual System of B and T lymphocytes –Immunocompetence Antigen – Molecules that stimulate a response by T and B cells Two features that characterize specific immunity: –Specificity – antibodies produced, function only against the antigen that they were produced in response to –Memory – lymphocytes are programmed to “recall” their first encounter with an antigen and respond rapidly to subsequent encounters

3. 3 Classifying Immunities Active immunity – results when a person is challenged with antigen that stimulates production of antibodies; creates memory, takes time, and is lasting Passive immunity – preformed antibodies are donated to an individual; does not create memory, acts immediately, and is short term Natural immunity – acquired as part of normal life experiences Artificial immunity – acquired through a medical procedure such as a vaccine

4. 4 Natural active immunity – acquired upon infection and recovery Natural passive immunity – acquired by a child through placenta and breast milk Artificial active immunity – acquired through inoculation with a selected Ag Artificial passive immunity – administration of a preparation containing specific antibodies

5. 5 Figure 15.1

6. 6 Overview of Specific Immune Responses Separate but related activities of the specific immune response: Development and differentiation of the immune system Lymphocytes and antigen processing The cooperation between lymphocytes during antigen presentation B lymphocytes and the production and actions of antibodies T lymphocyte responses

7. 7 Figure 15.2 (I)

8. 8 Figure 15.2 (II-V)

9. 9 15.2 Development of the Immune Response System Cell receptors or markers confer specificity and identity of a cell Major functions of receptors are: 1. To perceive and attach to nonself or foreign molecules 2. To promote the recognition of self molecules 3. To receive and transmit chemical messages among other cells of the system 4. To aid in cellular development

10. 10 Major Histocompatibility Complex (MHC) Receptors found on all cells except RBCs Also known as human leukocyte antigen (HLA) Plays a role in recognition of self by the immune system and in rejection of foreign tissue

11. 11 Functions of MHC Genes for MHC clustered in a multigene complex: –Class I – markers that display unique characteristics of self molecules and regulation of immune reactions Required for T lymphocytes –Class II – regulatory receptors found on macrophages, dendritic cells, and B cells Involved in presenting antigen to T-cells

12. 12 Figure 15.3

13. 13 Lymphocyte Receptors Lymphocyte’s role in surveillance and recognition is a function of their receptors B-cell receptors – bind free antigens T-cell receptors – bind processed antigens together with the MHC molecules on the cells that present antigens to them

14. 14 Clonal Selection Theory Lymphocytes use 500 genes to produce a tremendous variety of specific receptors Undifferentiated lymphocytes undergo a continuous series of divisions and genetic changes that generate millions of different cell types Each cell has a particular/unique receptor specificity

15. 15 In the bone marrow, lymphocytic stem cells differentiate into either T or B cells B cells stay in the bone marrow T cells migrate to the thymus Both T and B cells migrate to secondary lymphoid tissue

16. 16 Figure 15.4

17. 17 Lymphocyte specificity is preprogrammed, existing in the genetic makeup before an antigen has ever entered the system Each genetically different type of lymphocyte (clone) expresses a single specificity First introduction of each type of antigen into the immune system selects a genetically distinct lymphocyte Causes it to expand into a clone of cells that can react to that antigen

18. 18 Figure 15.5

19. 19 Specific B-Cell Receptor: Immunoglobulin Receptor genes of B cells govern immunoglobulin (Ig) synthesis Large glycoproteins that serve as specific receptors of B cells Composed of 4 polypeptide chains: –2 identical heavy chains (H) –2 identical light chains (L) Y shaped arrangement – ends of the forks formed by light and heavy chains contain a wide range of variable antigen binding sites Variable regions Constant regions

20. 20 Figure 15.6 (a)

21. 21 Development of Receptors Immunoglobulin genes lie on 3 different chromosomes Undifferentiated lymphocyte has 150 different genes for the variable region of light chains and 250 for the variable region and diversity region of the heavy chain During development, recombination causes only the selected V and D genes to be active in the mature cell Once synthesized, immunoglobulin is transported to cell membrane and inserted there to act as a receptor

22. 22 Figure 15.6 (b)

23. 23 T-Cell Receptors for Antigen Formed by genetic recombination, with variable and constant regions 2 parallel polypeptide chains Small, not secreted

24. 24 Figure 15.7 Proposed structure of the T-cell receptor

25. 25 15.3 Lymphocyte Responses and Antigens B-cell maturation –Directed by bone marrow sites that harbor stromal cells, which nurture the lymphocyte stem cells and provide hormonal signals –Millions of distinct B cells develop and “home” to specific sites in the lymph nodes, spleen, and GALT –Come into contact with antigens throughout life –Have immunoglobulin as surface receptors for antigens

26. 26 Lymphocyte Responses and Antigens T-cell maturation –Maturation is directed by the thymus gland and its hormones –Different classes of T-cell receptors termed CD - Cluster of differentiation CD4 and CD8 –Mature T cells migrate to lymphoid organs

27. 27

28. 28 Entrance and Processing of Antigens and Clonal Selection Antigen (Ag) is a substance that provokes an immune response in specific lymphocytes Property of behaving as an antigen is antigenicity –Foreignness, size, shape, and accessibility

29. 29 Characteristics of Antigens Perceived as foreign, not a normal constituent of the body Foreign cells and large complex molecules over 10,000 MW are most antigenic Antigenic determinant, epitope – small molecular group that is recognized by lymphocytes Antigen has many antigenic determinants

30. 30 Figure 15.8

31. 31 Haptens – small foreign molecules that consist only of a determinant group –Not antigenic unless attached to a larger carrier Carrier group contributes to the size of the complex and enhances the orientation of the antigen

32. 32 Figure 15.9 The hapten-carrier phenomenon

33. 33 Special Categories of Antigens Alloantigens – cell surface markers and molecules that occur in some members of the same species but not in others Superantigens – potent T cell stimulators; provoke an overwhelming response Allergen – antigen that evokes allergic reactions Autoantigens – molecules on self tissues for which tolerance is inadequate

34. 34 15.4 Cooperation in Immune Reactions to Antigens The basis for most immune responses is the encounter between antigens and white blood cells Lymph nodes and spleen concentrate the antigens and circulate them so they will come into contact with lymphocytes

35. 35 Antigen Processing and Presentation to Lymphocytes T-cell dependent antigens must be processed by phagocytes called antigen presenting cells (APC) APCs modify the antigen; then the Ag is moved to the APC surface and bound to MHC receptor Antigen presentation involves a direct collaboration among an APC, and a T helper cell –Interleukin-1 is secreted by APC to activate T H cells –Interleukin-2 is produced by T H to activate B and other T cells

36. 36 Figure 15.10

37. 37 15.5 B Cell Responses B-cell activation and antibody production –Once B cells process the Ag, interact with T H cells, and are stimulated by growth and differentiation factors, they enter the cell cycle in preparation for mitosis and clonal expansion –Divisions give rise to plasma cells that secrete antibodies and memory cells that can react to the same antigen later

38. 38 Figure 15.11

39. 39 Antibody Structure and Functions Immunoglobulins Large Y-shaped protein Consist of 4 polypeptide chains Contains 2 identical fragments (Fab) with ends that bind to specific antigen Fc binds to various cells and molecules of the immune system

40. 40 Figure 15.12

41. 41 Figure 15.13

42. 42 Antibody-Antigen Interactions Principle antibody activity is to unite with the Ag, to call attention to, or neutralize the Ag for which it was formed Opsonization – process of coating microorganisms or other particles with specific antibodies so they are more readily recognized by phagocytes Agglutination – Ab aggregation; cross-linking cells or particles into large clumps Neutralization – Abs fill the surface receptors on a virus or the active site on a microbial enzyme to prevent it from attaching –Antitoxins are a special type of Ab that neutralize bacterial exotoxins

43. 43 Figure 15.14

44. 44 Functions of the Fc Fragment Fc fragment binds to cells – macrophages, neutrophils, eosinophils, mast cells, basophils, and lymphocytes Certain antibodies have regions on the Fc portion for fixing complement –Binding of Fc may cause release of cytokines

45. 45 Classes of Immunoglobulins 5 classes of immunoglobulins (Ig): 1.IgG – monomer, produced by plasma cells (primary response) and memory cells (secondary), most prevalent 2.IgA – monomer circulates in blood, dimer in mucous and serous secretions 3.IgM – five monomers, first class synthesized following Ag encounter 4.IgD – monomer, serves as a receptor for antigen on B cells 5.IgE – Involved in allergic responses and parasitic worm infections

46. 46

47. 47 Antibodies in Serum If separated by electrophoresis, globulin separates into 4 bands: –Alpha-1 (α 1 ), alpha-2 (α 2 ), beta (β), and gamma (γ) Most are antibodies γ is composed primarily of IgG; β and α 2 are a mixture of IgG, IgA, and IgM

48. 48 Figure 15.15 Pattern of human serum after electrophoresis

49. 49 Primary and Secondary Responses to Antigens Primary response – after first exposure to an Ag immune system produces IgM and a gradual increase in Ab titer (concentration of antibodies) with the production of IgG Secondary response – after second contact with the same Ag, immune system produces a more rapid, stronger response due to memory cells –Anamnestic response

50. 50 Figure 15.16

51. 51 Monoclonal Antibodies Originate from a single clone and have a single specificity for antigen Pure preparation of antibody Single specificity antibodies formed by fusing a mouse B cell with a cancer cell Used in diagnosis of disease, identification of microbes and therapy

52. 52 Insight 15.2

53. 53 Insight 15.2

54. 54 15.6 T Cells & Cell-Mediated Immunity Cell-mediated immunity requires the direct involvement of T lymphocytes T cells act directly against Ag and foreign cells when presented in association with an MHC carrier T cells secrete cytokines that act on other cells Sensitized T cells proliferate into long-lasting memory T cells

55. 55

56. 56 Types of T Cells 1.T helper cells (CD4 or T H ) most prevalent type of T cell; regulate immune reaction to antigens, including other T and B cells; also involved in activating macrophages and increasing phagocytosis; differentiate into T helper 1 (T H 1) cells or T helper 2 (T H 2) cells 2.Cytotoxic T cells (CD8 or T C ) destroy foreign or abnormal cells by secreting perforins that lyse cells 3.Natural killer cells – lack specificity; circulate through the spleen, blood, and lungs

57. 57 Figure 15.17

58. 58 T Cells and Superantigens Reaction has drastic consequences Superantigens are a form of a virulence factor Provoke overwhelming immune responses by large numbers of T cells –Release of cytokines –Blood vessel damage –Toxic shock –Multiorgan damage

59. 59 15.7 Immunization: Manipulating Immunity Passive immunity – immune serum globulin (ISG), gamma globulin, contains immunoglobulin extracted from pooled blood; immunotherapy Treatment of choice in preventing measles and hepatitis A and in replacing antibodies in immunodeficient patients Sera produced in horses are available for diphtheria, botulism, and spider and snake bites Acts immediately; protection lasts 2-3 months

60. 60 Vaccination Artificial active immunity – deliberately exposing a person to material that is antigenic but not pathogenic Principle is to stimulate a primary and secondary anamnestic response to prepare the immune system for future exposure to a virulent pathogen Response to a future exposure will be immediate, powerful, and sustained

61. 61 Vaccine Preparation Most vaccines are prepared from: 1.Killed whole cells or inactivated viruses 2.Live, attenuated cells or viruses 3.Antigenic molecules derived from bacterial cells or viruses 4.Genetically engineered microbes or microbial agents

62. 62

63. 63 Killed or Inactivated Vaccines Cultivate the desired strain, treat it with formalin or some other agent that kills the agent but does not destroy its antigenicity Often require a larger dose and more boosters to be effective

64. 64 Live Attenuated Cells or Viruses Process that substantially lessens or negates the virulence of viruses or bacteria – eliminates virulence factors Advantages of live preparations are: –Organisms can multiply and produce infection (but not disease) like the natural organism –They confer long-lasting protection –Usually require fewer doses and boosters Disadvantages include: –Require special storage, can be transmitted to other people, can conceivably mutate back to virulent strain

65. 65 Antigenic Molecules Acellular or subcellular vaccines (subunit – if a virus) Exact antigenic determinants can be used when known: –Capsules – pneumococcus, meningococcus –Surface protein – anthrax, hepatitis B –Exotoxins – diphtheria, tetanus Antigen can be taken from cultures, produced by genetic engineering, or synthesized

66. 66 Figure 15.19

67. 67 Genetically Engineered Vaccines Insert genes for pathogen’s antigen into plasmid vector, and clone them in an appropriate host –Stimulated the clone host to synthesize and secrete a protein product (antigen), harvest and purify the protein – hepatitis “Trojan horse” vaccine – genetic material from a pathogen is inserted into a live carrier nonpathogen; the recombinant expresses the foreign genes –Experimental vaccines for AIDS, herpes simplex 2, leprosy, tuberculosis

68. 68 Genetically Engineered Vaccines DNA vaccines – create recombination by inserting microbial DNA into plasmid vector Human cells will pick up the plasmid and express the microbial DNA as proteins causing B and T cells to respond, be sensitized, and form memory cells –Experimental vaccines for Lyme disease, hepatitis C, herpes simplex, influenza, tuberculosis, malaria

69. 69 Figure 15.20

70. 70 Route of Administration and Side Effects Most administered by injection; few oral, nasal Some vaccines require adjuvant to enhance immunogenicity and prolong retention of antigen Stringent requirements for development of vaccines More benefit than risk Possible side effects include local reaction at injection site, fever, allergies; rarely back-mutation to a virulent strain, neurological effects

71. 71 Herd Immunity Immune individuals will not harbor it, reducing the occurrence of pathogens – herd immunity Less likely that a nonimmunized person will encounter the pathogen