1. Microbiology: A Systems Approach
PowerPoint to accompany
Microbiology: A Systems Approach
Cowan/Talaro
Chapter 15
Specific Immunity and Immunization
Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

2. Chapter 15 Topics - Thirdline of Defense - B cells - T cells
- Specific Immunities

3. Thirdline of Defense
Specific immunity is a complex interaction of immune cells (leukocytes) reacting against antigens
Specific
Self and nonself (foreign)
Antigens
Antibodies & specialized lymphocytes

4. Self and nonself Markers glycoproteins located on the cell surface
Eg. Major histocompatibility complex (MHC)

5. Markers Host cells proteins (ex. MHC) confer specificity and identity
Role – detection, recognition, and communication
Lymphocyte cells recognize the host cell markers as “self”
Lymphocyte cells recognize microbe markers as ‘nonself’

6. Major histocompatibility complex (MHC)
Self receptor
Glycoprotein
Found on all nucleated cells
In humans – Human leukocyte antigen (HLA) is equivalent to the MHC
Different Classes of MHC

7. Specific Acquired Immunities
Active
Passive
Natural
Artificial
Vaccines

8. Active Antigen activates B and T cells Memory cells
Long-term protection
Natural or artificial

9. Passive
Receive pre-formed antibodies from another individual or animal
No memory cells
No antibody production
Short-term protection
Natural or artificial

10. Natural
Immunity produced by normal biological experiences, no medical intervention
Natural active
Eg. Infection
Natural passive
Eg. Mother to child – across the placenta, via breast milk

11. Artificial
Immune protection through medical procedures or intervention
Artificial active
Eg. vaccination
Artificial passive
Eg. Injection of preformed antibodies (antiserum)
Immediate but short-lived protection

12. Summary of the different acquired immunities.
Fig Categories of acquired immunities

13. Duality of the Immune System
Humoral Immunity
B-lymphocytes produce antibodies
Antibodies in fluids ( blood, lymph, etc.)
Defense against
Bacteria
Toxins
Circulating viruses

14. Duality of the Immune System
Cell-Mediated Immunity
T-cells (lymphocytes)
Acts against foreign tissues or organisms
Regulates the activity of other immune system cells

15. Cell-Mediated Immunity
Defends against
Bacteria or viruses that are within the host cells
Fungi, protozoa and helminths
Transplanted tissue
cancer

16. Mature T and B cells migrate to the lymphoid tissue, where they encounter antigens.
Fig Major stages in the development of B and T cells.

17. Stages Dual lymphocyte development and differentiation
Presentation of antigens
Challenge of B and T lymphocytes by antigens
Production of antibodies by B cells (plasma cell)
T lymphocyte responses

18. An overview of the stages of lymphocyte development and function.
Fig Overview of the stages of lymphocyte development

19. Receptors Present on B and T cells
Immunoglobulin molecule
Light chain
Heavy chain
Variable region
Constant region
B cell receptors are secreted as antibodies

20. The structure of a receptor for B cells.
Fig Simplified structure of an immunoglobulin
molecule on the surface of B cells.

21. The structure of the receptor for T cells.
Fig Proposed structure of the T cell receptor for antigen.

22. Antigens
Foreign material
Size and shape are important

23. Antigens Microbial products Non-microbial products
Capsules, cell walls
Flagella
Fimbria
Bacterial toxins
Viral protein coats
Other surface molecules
Non-microbial products
Pollen
Egg white
Blood cell surface markers
Serum proteins from other individuals
Transplanted tissues

24. Foreign material Antigenic Proteins and polypeptides
enzymes, cell surface structures, hormones, exotoxins) – usu.
Glycoproteins - blood cell markers
Large Polysaccharides - capsules, LPS)
Not very Antigenic
Lipids & cell membranes
Nucleic acids (DNA)

25. Size and shape Size affects antigenicity Haptens
Too small – no immune recognition
Large – immune recognition
Proteins are better immunogens than polysaccharides because of their complex shape
Haptens
antigens that are too small to elicit an immune response

26. A hapten can complex with a larger carrier protein in order to stimulate an immune response.
Fig The hapten-carrier phenomenon.

27. Superantigen Bacterial toxins
T cell activation much greater than normal antigens
Large release of cytokines
Results in toxic shock syndrome and some autoimmune diseases

28. Examples of different antigens and their characteristics.
Fig Characteristics of antigens.

29. Antibody Product of B cell activation Structure
Immunoglobulin (Ig) family of proteins
Produced in response to an antigen
Structure
Highly specific for the antigen that stimulated the production of the antibody
Antigen –binding site on the antibody specifically binds the antigen
Has at least two antigen-binding sites

30. Antibody Structure 2 identical heavy chains 2 identical light chains
Linked by disulfide bridges
Variable region binds antigen
Constant region determines the class of the antibody
Fc – stem region binds complement or allow antibody to be attached to the surface of a cell.

31. The complete structure of an IgG antibody.
Fig Working models of antibody structure.

32. V-region Variable (N-terminal of the heavy and light chains)
Binds to the antigen
Swiveling enables more efficient binding
Held together by disulfide bonds

33. Fc Constant (C-terminal of heavy chain) Binds to macrophages
Anchors Ig to lymphocyte
Held together by disulfide bonds
Responsible for class identification

34. Classes based on the Fc fragment Immunoglobulin (Ig) IgG IgA IgM IgD
IgE

35. IgG Monomer Primary response Memory cell response
Most prevalent in tissue fluid and blood

36. IgM Five monomers Held together by a J chain
First to be synthesized during primary immune response
Associated with complement fixation
Receptor for antigens on B cells
Circulates in the blood

37. IgA Monomer or dimer (secretory IgA)
Dimer – held together by a J chain
Secretory IgA (mucous and serous secretions)
Local immunity
Salivary glands, intestine, nasal membrane, breast, lung, genitourinary tract
Protection for newborns

38. IgD Monomer Small amounts in the serum
Receptor for antigens on B cells

39. IgE Allergies Parasite infections
Fc portion binds to mast cells and basophils
release chemical mediators that aid inflammation

40. The characteristics of the different immunoglobulin classes.
Table 15.2 Characteristics of the immunoglobulin classes.

41. B cells
Activation
Antibody
Antibody-antigen interaction
Response

42. Activation Clonal selection and binding of antigen
Instruction by chemical mediators
Transmission of signal to the nucleus
B cell changes into a plasma cells and begins mitosis
Clonal expansion and memory cell formation
Antibody production and secretion

43. Clonal selection The synthesis of varied receptor types Clone
approximately 500 genes undergo rearrangement
eventually one clone recognizes an antigen and expands (proliferates)
Clone
each mature lymphocyte possesses a single combination or receptor specificity
Expansion
a single cell is stimulated by antigen recognition
Clonal deletion
cells that recognize self are removed

44. The clonal selection theory of lymphocyte development and diversity.
Fig Overview of the clonal selection theory of lymphocyte
development and diversity.

45. The stages of B-cell activation and antibody synthesis.
Fig Events in B-cell activation and antibody synthesis.

46. Antibody-antigen interactions
Opsonization
Agglutination
Neutralization
Complement fixation

47. A complementary fit between an antibody and antigen involves hydrogen bonds and electrostatic attractions.
Fig Antigen-antibody binding

48. The different functions of antibodies.
Fig Summary of antibody functions

49. Agglutination Antibodies cross-link cells or particles into clumps
Renders microbes immobile
Enhances phagocytosis
Principle for certain immune tests (RBC typing)

50. Opsonization Microbes or particles coated with antibodies
Enables macrophages to recognize and phagocytize microbe

51. Neutralization Antibody binds to
The microbe or virus receptor
Antigenic site of a molecule (Eg. Exotoxin)
Prevents further binding of microbe or toxin

52. Complement fixation
Antibodies interaction with complement proteins (Eg. Classical pathway)
Lysis of microbial cell

53. Response
Primary
Secondary

54. Primary First exposure Latent period Synthesis of antibodies
Lack of antibodies synthesis
Synthesis of antibodies
Level of synthesis (titer)
IgM first
Followed by IgG, and some IgA and IgM

55. Secondary Re-exposure to the same immunogen (Anamnestic response)
Antibody synthesis, titer, and length of antibody persistence is rapid and amplified
Primarily due to memory cells

56. The stages of primary and secondary responses to antigens.
Fig Primary and secondary responses to antigens.

57. Apoptosis Programmed cell death
Genetic program that is turned on and stimulates the cell to digest itself
Debris is cleared away by macrophages without stimulating inflammation
The way the body gets rid of unneeded or worn out cells

58. T cell
Activation
Types

59. Activation Cell-mediated immunity Cytokines Antigen presenting cells
Interleukins – IL-1, IL-2
Gamma interferon
Tumor Necrosis Factor ( TNF)
Antigen presenting cells
Activated macrophages

60. Cell-mediated immunity
Direct involvement of T cells
Produce and react to cytokines
Activated simultaneously with B cell activation
Subset of T cells have unique CD receptors (CD4, CD8)

61. Antigen presenting cells (APC)
Macrophages and dendritic cells
Process and present antigen in association with MHC
T cell CD receptor recognize antigen/MHC

62. Transformation Activated T cells prepare for mitosis
Effectors cells or types (TH, TC) are produced
Memory cells are produced

63. Types
Helper T cells (TH)
Cytotoxic T cells (TC)

64. TH Regulate immune reactions to antigens by releasing cytokines
CD4 receptor
Type of cytokine will determine subset of TH
TH1 (activate other T cells, delayed type hypersensitivity)
TH2 (B cell differentiation)
Cytokines also activate macrophages
Most prevalent in the blood
Insert animation T helper cell dependent antigen

65. TC Binds and lyses cells (apoptosis) CD8 receptor
microbe, viral infected cells, foreign cells, cancer cells
CD8 receptor
Perforins – punch holes in the membrane
Granzymes – degrade proteins
Natural killer (NK) cells
related to TC
attack virus infected cells and cancer cells
Insert animation Cytotoxic T cell

66. An example of helper and cytotoxic T cell activation and differentiation.
Fig Overall scheme of T-cell activation and
differentiation into different types of T cells.

67. Characteristics of the different subsets of T cells.
Table 15.3 Characteristic of subsets of T cells.

68. Relationship between Cell-Mediated and Humoral Immunity
T- independent antigens
Can stimulate B-cells directly
Antibodies will be produced without the need for T-helper cells
T-dependent antigens
Most antigens are not sufficient to stimulate the B-cells directly
A T-helper cell has to recognize the antigen and assist the B-cell
Most antigens are T-dependent

69. An example of a cytotoxic T cell destroying a cancer cell.
Fig A cytotoxic T cell has mounted a successful
attack on a tumor cell.