1. Foundations in Microbiology Sixth Edition
Lecture PowerPoint to accompany
Foundations in Microbiology Sixth Edition
Talaro
Chapter 14
Nonspecific Host Defenses
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

2. Defense Mechanisms of the Host
To protect the body against pathogens, the immune system relies on a multilevel network of physical barriers, immunologically active cells, and a variety of chemicals.
first line of defense – any barrier that blocks invasion at the portal of entry – nonspecific
second line of defense – protective cells and fluids; inflammation and phagocytosis – nonspecific
third line of defense – acquired with exposure to foreign substance; produces protective antibodies and creates memory cells – specific

3. Physical or Anatomical Barriers: First Line of Defense
Skin and mucous membranes of respiratory, urogenital, eyes and digestive tracts
outermost layer of skin is composed of epithelial cells compacted, cemented together and impregnated with keratin; few pathogens can penetrate if intact
flushing effect of sweat glands
damaged cells are rapidly replaced
mucous coat impedes attachment and entry of bacteria
blinking and tear production
stomach acid
nasal hair traps larger particles

4. Nonspecific Chemical Defenses
Sebaceous secretions
Lysozyme, an enzyme that hydrolyzes the cell wall of bacteria, in tears
High lactic acid and electrolyte concentration in sweat
Skin’s acidic pH
Hydrochloric acid in stomach
Digestive juices and bile of intestines
Semen contains antimicrobial chemical.
Vagina has acidic pH.

6. Genetic Defenses
Some hosts are genetically immune to the diseases of other hosts.
Some pathogens have great specificity.
Some genetic differences exist in susceptibility.

7. Structure and Function of the Organs of Defense and Immunity
The study of the body’s second and third lines of defense is called immunology.
Functions of a healthy functioning immune system:
Constant surveillance of the body
Recognition of foreign material
Destruction of entities deemed to be foreign

9. Immune System
Large, complex, and diffuse network of cells and fluids that penetrate into every organ and tissue
Four major subdivisions of immune system are:
Reticuloendothelial system (RES)
Extracellular fluid (ECF)
Bloodstream
Lymphatic system

11. Reticuloendothelial System (RES)
Network of connective tissue fibers that interconnects other cells and meshes with the connective tissue network surrounding organs
Inhabited by phagocytic cells – mononuclear phagocyte system – macrophages ready to attack and ingest microbes that passed the first line of defense

12. Origin, Composition, and Functions of the Blood
Whole blood consists of plasma and blood cells – red blood cells and white blood cells.
Serum is the liquid portion of the blood after a clot has formed-minus clotting factors.
Plasma – 92% water, metabolic proteins, globulins, clotting factors, hormones and all other chemicals and gases to support normal physiological functions

13. White Blood Cells
Neutrophils % - lobed nuclei with lavender granules; phagocytes
Eosinophils – 1-3% - orange granules and bilobed nucleus; destroy eucaryotic pathogens
Basophils, mast cells – 0.5% - constricted nuclei, dark blue granules; release potent chemical mediators
Lymphocytes – 20-35% - large nucleus B (humoral immunity) and T cells (cell-mediated immunity) involved in the specific immune response
Monocytes, macrophages – 3-7%- large nucleus; phagocytic

14. Lymphatic System
Provides an auxiliary route for return of extracellular fluid to the circulatory system
Acts as a drain-off system for the inflammatory response
Renders surveillance, recognition, and protection against foreign material

16. Lymphatic Fluid
Lymph is a plasma-like liquid carried by lymphatic circulation
Formed when blood components move out of blood vessels into extracellular spaces
Made up of water, dissolved salts, 2-5% proteins
Transports white blood cells, fats, cellular debris and infectious agents

17. Lymphatic Vessels
Lymphatic capillaries permeate all parts of the body except the CNS.
Thin walls easily permeated by extracellular fluid which is then moved through contraction of skeletal muscles
Functions to return lymph to circulation; flow is one-direction-toward the heart-eventually returning to blood stream

18. Lymphoid Organs and Tissues
Classified as primary and secondary
Primary lymphoid organs – sites of lymphocytic origin and maturation – thymus and bone marrow
Secondary lymphoid organs and tissues – circulatory-based locations such as spleen and lymph nodes; collections of cells distributed throughout body tissues – skin and mucous membranes – SALT, GALT, MALT

20. Lymphoid Organs
Thymus – high rate of growth and activity until puberty, then begins to shrink; site of T-cell maturation
Lymph nodes - small, encapsulated, bean-shaped organs stationed along lymphatic channels and large blood vessels of the thoracic and abdominal cavities
Spleen – structurally similar to lymph node; filters circulating blood to remove worn out RBCs and pathogens

21. Actions of the Second Line of Defense
Recognition
Inflammation
Phagocytosis
Interferon
Complement

22. Recognition
Protein receptors within cell membrane of macrophages, called Toll-like receptors
Detect foreign molecules and signal the macrophage to produce chemicals which:
stimulate an inflammatory response (nonspecific)
promote the activity of B and T cells (specific)

23. Inflammatory Response
Classic signs and symptoms characterized by:
Redness – increased circulation and vasodilation in injured tissue in response to chemical mediators and cytokines
Warmth – heat given off by the increased blood flow
Swelling – increased fluid escaping into the tissue as blood vessels dilate-edema; WBC’s, microbes, debris and fluid collect to form pus; helping prevent spread of infection
Pain – stimulation of nerve endings
Possible loss of function

24. Events in inflammation
Insert figure 14.13
Events in inflammation

25. Unique Characteristics of Leukocytes
Diapedesis – migration of cells out of blood vessels into the tissues
Chemotaxis – migration in response to specific chemicals at the site of injury or infection

27. Fever
Initiated by circulating pyrogens which reset the hypothalamus to increase body temperature; signals muscles to increase heat production and vasoconstriction
exogenous pyrogens – products of infectious agents
endogenous pyrogens – liberated by monocytes, neutrophils, and macrophages during phagcytosis; interleukin-1 (IL-1) and tumor necrosis factor (TNF)
Benefits of fever:
inhibits multiplication of temperature-sensitive microorganisms
impedes nutrition of bacteria by reducing the available iron
increases metabolism and stimulates immune reactions and protective physiological processes

28. Phagocytes and Phagocytosis
3 main types of phagocytes:
Neutrophils – general-purpose; react early to bacteria and other foreign materials, and to damaged tissue
Eosinophils – attracted to sites of parasitic infections and antigen-antibody reactions
Macrophages – derived from monocytes; scavenge and process foreign substances to prepare them for reactions with B and T lymphocytes

29. Phagocytosis General activities of phagocytes:
To survey tissue compartments and discover microbes, particulate matter and dead or injured cells
To ingest and eliminate these materials
To extract immunogenic information from foreign matter

31. Interferon
Small protein produced by certain white blood cells and tissue cells
alpha interferon- lymphocytes and macrophages
beta interferon – fibroblasts and epithelial cells
gamma interferon – T cells
Produced in response to viruses, RNA, immune products, and various antigens
Bind to cell surfaces and induce expression of antiviral proteins
Inhibit expression of cancer genes

33. Complement
Consists of 26 blood proteins that work in concert to destroy bacteria and viruses
Complement proteins are activated by cleavage.
Classical pathway – activated by the presence of antibody bound to microorganism
Alternative pathway – begins when complement proteins bind to normal cell wall and surface components of microorganisms