1. Microbiology: A Systems Approach, 2nd ed.
Chapter 14: Host Defenses I- Overview and Nonspecific Defenses

2. 14.1 Defense Mechanisms of the Host in Perspective
Figure 14.1

3. Barriers at the Portal of Entry: A First Line of Defense
Figure 14.2

4. Figure 14.3

5. Nonspecific Chemical Defenses
Sebaceous secretions and specialized glands- antimicrobial
Lysozyme in tears
Lactic acid and electrolyte concentrations of sweat
Skin’s acidic pH and fatty acid content
HCl in the stomach
Digestive juices and bile in the intestine
Semen- antimicrobial chemical
Acidic pH in the vagina

6. Genetic Differences in Susceptibility
Some hosts are genetically immune to the diseases of other hosts
Particularly true of viruses

7. 14.2 The Second and Third Lines of Defense: An Overview
Immunology: the study of all features of the body’s second and third lines of defense
Healthy functioning immune system is responsible for:
Surveillance of the body
Recognition of foreign material
Destruction of entities deemed to be foreign

8. Figure 14.4

9. Self and Nonself
White blood cells must distinguish self from nonself cells
Evaluates cells by examining markers on their surfaces

10. 14.3 Systems Involved in Immune Defenses
Body compartments
Intracellular
Extracellular
Lymphatic
Cerebrospinal
Circulatory
Physically separated but have numerous connections

11. Body Compartments that Participate in Immune Function
Reticuloendothelial system (RES)
Spaces containing extracellular fluid (ECF)
Bloodstream
Lymphatic system

12. The Communicating Body Compartments
Figure 14.5

13. Immune Functions of the Reticuloendothelial System
Provides a passageway within and between tissues and organs
Coexists with the mononuclear phagocyte system

14. Figure 14.6

15. Origin, Composition, and Functions of the Blood
Circulatory system
Circulatory system proper
Lymphatic system

16. Figure 14.7

17. Fundamental Characteristics of Plasma
Hundreds of different chemicals
Main component is water (92%)
Proteins such as albumin and globulins, immunochemicals, fibrinogen and other clotting factors, hormones, nutrients, dissolved gases, and waste products

18. A Survey of Blood Cells Hematopoesis: production of blood cells
Relatively short life
Primary precursor of new blood cells: pluripotential stem cells in the marrow
Red blood cells (erythrocytes)
White blood cells (leukocytes)
Platelets (thrombocytes)
Differentiation

19. Figure 14.8

20. (a)
Figure 14.9
(b)

21. Leukocytes
Granulocytes
Agranulocytes

22. Granulocytes Neutrophils Eosinophils Basophils Phagocytosis
Attack and destroy large eukaryotic pathogens
Also involved in inflammation and allergic reactions
Basophils
Parallel eosinophils in many actions

23. Agranulocytes
Monocytes
Lymphocytes

24. Monocytes
Discharged by bone marrow into bloodstream, live as phagocytes for a few days, then differentiate into macrophages
Responsible for
Many specific and nonspecific phagocytic and killing functions
Processing foreign molecules and presenting them to lymphocytes
Secreting biologically active compounds that assist, mediate, attract, and inhibit immune cells and reactions
Dendritic cells

25. Lymphocytes
Key cells in the third line of defense and the specific immune response
When stimulated by antigens, transform into activated cells that neutralize and destroy that foreign substance
B cells
Humoral immunity: protective molecules carried in the fluids of the body
Produce specialized plasma cells which produce antibodies
T cells
Cell-mediated immunity: T cells modulate immune functions and kill foreign cells

26. Erythrocyte and Platelet Lines
Erythrocytes
Develop from stem cells in the bone marrow
Lose their nucleus just prior to entering circulation
Transport oxygen and carbon dioxide to and from the tissues
Platelets
Formed elements in circulating blood
Not whole cells
Function primarily in hemostasis and in releasing chemicals for blood clotting and inflammation

27. Components and Functions of the Lymphatic System
Lymphatic system: compartmentalized network of vessels, cells, and specialized accessory organs
Transports lymph through a system of vessels and lymph nodes
Major functions
Provide an auxiliary route for the return of extracellular fluid to the circulatory system proper
Act as a drain-off system for the inflammatory response
Render surveillance, recognition, and protection against foreign materials

28. Figure 14.10

29. Lymphatic Fluid
Lymph
Plasmalike liquid formed when certain blood components move out of blood vessels into the extracellular spaces and diffuse or migrate into the lymphatic capillaries
Composition parallels that of plasma, but without red blood cells

30. Lymphatic Vessels Along the lines of blood vessels
Similar to thin-walled veins
High numbers in hands, feet, and around the areola of the breast
Flow of lymph is in one direction only- from extremities toward the heart
Lymph is moved through the contraction of skeletal muscles through which the lymphatic ducts wend their way

31. Lymphoid Organs and Tissues
Lymph nodes
Thymus
Spleen
Gut-associated lymphoid tissue (GALT)
Tonsils
Loose connective tissue framework that houses aggregations of lymphocytes

32. Lymph Nodes Small, encapsulated, bean-shaped organs
Usually found in clusters along lymphatic channels and large blood vessels of the thoracic and abdominal cavities
Major aggregations: axillary nodes, inguinal nodes, cervical nodes

33. Spleen
Similar to a lymph node except it filters blood instead of lymph
Filters pathogens from the blood

34. The Thymus: Site of T-Cell Maturation
Thymus originates in the embryo
High rates of activity and growth until puberty
Shrinks gradually through adulthood
Thymic hormones help thymocytes develop specificity to be released as mature T cells

35. Figure 14.11

36. Miscellaneous Lymphoid Tissue
Bundles of lymphocytes lie at many sites on or just beneath the mucosa of the gastrointestinal and respiratory tracts
Tonsils
Breasts of pregnant and lactating women
GALT in the intestinal tract
Appendix
Lacteals
Peyer’s patches
Mucosal-associated lymphoid tissue (MALT)
Skin-associated lymphoid tissue (SALT)
Bronchial-associated lymphoid tissue (BALT)

37. 14.2 The Second Line of Defense
Inflammation
Phagocytosis
Interferon
Complement

38. The Inflammatory Response: A Complex Concert of Reactions to Injury
Reaction to any traumatic event in the tissues
Classic signs and symptoms
Rubor (redness)
Calor (warmth)
Tumor (swelling)
Dolor (pain)
Fifth symptom has been added: loss of function

39. Figure 14.12

40. Chief Functions of Inflammation
Mobilize and attract immune components to the site of the injury
Set in motion mechanisms to repair tissue damage and localize and clear away harmful substances
Destroy microbes and block their further invasion

41. The Stages of Inflammation
Figure 14.13

42. Vascular Changes: Early Inflammatory Events
Controlled by nervous stimulation, chemical mediators, and cytokines released by blood cells, tissue cells, and platelets in the injured area
Vasoactive mediators affect the endothelial cells and smooth muscle cells of blood vessels
Chemotactic factors (chemokines) affect white blood cells
Cause fever, stimulate lymphocytes, prevent virus spread, and cause allergic symptoms
Arterioles constricted at first but quickly vasodilation takes place

43. Edema: Leakage of Vascular Fluid into Tissues
Exudates: the fluid that escapes through gaps in the walls of postcapillary venules
Accumulation of exudates causes edema
Contains plasma proteins, blood cells, and cellular debris
May be clear (serous) or may contain red blood cells or pus
Diapedesis: how WBCs leave the blood vessels and into tissue spaces
Chemotaxis: the tendency of WBCs to migrate in response to a specific chemical stimulus

44. Benefits of Edema and Chemotaxis
Dilutes toxic substances
Fibrin clot can trap microbes and prevent further spreading
Phagocytosis occurs immediately

45. Figure 14.14

46. Late Reactions of Inflammation
Long-lived inflammation attracts a collection of monocytes, lymphocytes, and macrophages to the reaction site
Macrophages clear pus, cellular debris, dead neutrophils, and damaged tissue
B lymphocytes produce antibodies
T lymphocytes kill intruders directly
Late in the process the tissue is repaired or replaced by connective tissue (scar)

47. Fever: An Adjunct to Inflammation
An abnormally elevated body temperature
FUO: fevers of unknown origin
Initiation of fever
Pyrogen sets the hypothalamic “thermostat” to a higher setting
Muscles increase heat production
Peripheral arterioles decrease heat loss through vasoconstriction
Pyrogens can be exogenous or endogenous

48. Benefits of Fever
Inhibits multiplication of temperature-sensitive microorganisms
Impedes the nutrition of bacteria by reducing the availability of iron
Increases metabolism and stimulates immune reactions and naturally protective physiological processes

49. Phagocytosis: Cornerstone of Inflammation and Specific Immunity
General activities of phagocytes
Survey the tissue compartments and discover microbes, particulate matter, and injured or dead cells
Ingest and eliminate these materials
Extract immunogenic information (antigens) from foreign matter
Three main types
Neutrophils
Monocytes
Macrophages

50. Figure 14.15

51. Figure 14.16

52. Mechanisms of Phagocytic Recognition, Engulfment, and Killing
Figure 14.17

53. Interferon: Antiviral Cytokines and Immune Stimulants
Interferon (IFN): involved against viruses, other microbes, in immune regulation and intercommunication
Three major types
Interferon alpha
Interferon beta
Interferon gamma
All three classes produced in response to viruses, RNA, immune products, and various antigens
Bind to cell surfaces and induce changes in genetic expression
Can inhibit the expression of cancer genes and have tumor suppressor effects

54. Figure 14.18

55. Complement: A Versatile Backup System
At least 26 blood proteins that work in concert to destroy bacteria and certain viruses
Cascade reaction
Three different pathways that all yield similar end results
Classical pathway
Lectin pathway
Alternative pathway

57. Complement Cascade Initiation Amplification and cascade Polymerization
Membrane attack

58. Classical Pathway
Figure 14.19