1. Innate Immunity Chapter 15

2. First Line of Defense
Structures, chemicals, processes that work to prevent pathogens entering the body…Barriers to Entry
Nonspecific defenses
Includes the skin and mucous membranes of the respiratory, digestive, urinary, and reproductive systems
Animation:
Host Defenses
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3. Skin – Physical Components of Defense
Epidermis
Outer layer composed of multiple layers of tightly packed cells
Few pathogens can penetrate these layers
Shedding of dead skin cells removes attached microorganisms
Epidermal dendritic cells (Langerhans cells)
These are able to phagocytize pathogens
Dermis
Contains protein fibers …collagen
Give skin strength and pliability to resist abrasions that could introduce microorganisms

4. Skin – Chemical Components of Defense
Perspiration secreted by sweat glands
Salt – inhibits growth of pathogen by drawing water from their cells
Antimicrobial peptides – sweat glands secret dermicidins
Lysozyme – destroys cell wall of bacteria
Sebum secreted by sebaceous (oil) glands
Helps keep skin pliable and less likely to break or tear
Lowers the pH of the skin to a level inhibitory to many bacteria

5. Mucous Membranes
Line all body cavities open to the outside environment
Epithelium
Thin, outer covering of the mucous membranes
Unlike surface epidermal cells, epithelial cells are living
Tightly packed to prevent entry of pathogens
Continual shedding of cells carries attached microorganisms away

6. Microbial Antagonism
Normal microbiota help protect the body by competing with potential pathogens
Various activities of the normal microbiota make it hard for pathogens to compete
Consumption of nutrients makes them unavailable to pathogens
Create an environment unfavorable to other microorganisms by changing pH

7. Other First-Line Defenses
Many body organs secrete chemicals with antimicrobial properties
Example: lacrimal glands that bathe the eye

8. More First Line Defenses

9. Second Line of Defense
Operates when pathogens succeed in penetrating the skin or mucous membranes
Nonspecific defense
Composed of cells, antimicrobial chemicals, and processes but no physical barriers
Many of these components are contained or originate in the blood

10. Blood
Composed of cells and portions of cells within a fluid called plasma
Plasma is mostly water containing electrolytes, dissolved gases, nutrients, and proteins
When the clotting factors (a group of plasma proteins) are removed from plasma, the remaining fluid is called serum
Other plasma proteins include complement proteins and antibodies
The cells and cell fragments in plasma are called formed elements

11. Formed Elements Three types of formed elements
Erythrocytes – carry oxygen and carbon dioxide in the blood
Platelets – involved in blood clotting
Leukocytes – involved in defending the body against invaders
Two groups
Granulocytes
Agranulocytes

12. Granulocytes
Contain large granules that stain different colors based on the dye used
Basophils – stain blue with the basic dye methylene blue
Eosinophils – stain red/orange with the acidic dye eosin
Neutrophils – stain lilac with a mixture of acidic and basic dyes
Neutrophils and eosinophils can phagocytize pathogens
White blood cells are capable of diapedesis

13. Agranulocytes Cytoplasm appears uniform under a light microscope
Two types
lymphocytes – most involved in adaptive immunity
monocytes – leave the blood and mature into macrophages

14. Phagocytic cells of the second line of defense
Macrophages
Phagocytic cells of the second line of defense
Wandering macrophages leave the blood via diapedesis and phagocytize throughout the body
Fixed macrophages do not move throughout the body and often phagocytize within a specific organ
Include alveolar macrophages (lungs), microglia (central nervous system), Küpffer cells (liver)
All macrophages, plus monocytes attached to endothelial cells, constitute the mononuclear phagocytic system

15. Lab Analysis of Leukocytes
The differential white blood cell count (the diff) can signal signs of disease
Increased eosinophils can indicate allergies or parasitic worm infection
Bacterial diseases often show increase in leukocytes and in neutrophils
Viral infections may show increase in lymphocytes

17. Components of the Second Line of Defense
Phagocytosis
Extracellular killing by leukocytes
Nonspecific chemical defenses
Inflammation
Fever

18. Phagocytosis Cells capable of phagocytosis are called phagocytes
Animation:
Phagocytosis
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19. Extracellular Killing by Leukocytes
Three Cell types that kill extracellularly
Eosinophils
Mainly attack parasitic helminths (worms) by attaching to their surface
Secrete toxins that weaken or kill the helminth
Natural killer lymphocytes (NK cells)
Secrete toxins onto the surface of virally infected cells and tumors
Neutrophils
Produce chemicals that kill nearby invaders

20. Nonspecific Chemical Defenses
Some chemicals augment phagocytosis
Some attack pathogens directly
Some enhance other features of innate immunity
Nonspecific chemical defenses includes
Lysozyme
Complement
Interferon
Defensins

21. Complement System
Set of serum proteins designated numerically according to the order of their discovery
Complement activation results in lysis of the foreign cell
Complement can be activated in several ways
Classical pathway
Complement named for the events of this originally discovered pathway…the various complement proteins act nonspecifically to “complement” the action of antibodies
Alternate pathway
Activation occurs independent of antibodies

22. Complement – Two Pathways
Figure 15.10

23. Inactivation of Complement
Body’s own cells withstand complement cascade
Membrane-bound proteins on many cells bind with and break down activated complement proteins
Animation:
The Complement System
PLAY

24. Interferons
Protein molecules released by host cells to nonspecifically inhibit the spread of viral infections

25. Inflammation
Nonspecific response to tissue damage resulting from various causes
Characterized by redness, heat, swelling, and pain
Two types
Acute
Chronic
Animation:
Inflammation
PLAY

26. Acute vs. Chronic Inflammation
Acute inflammation
Develops quickly and is short lived
Is usually beneficial
Important in the second line of defense
Dilation and increased permeability of the blood vessels
Migration of phagocytes
Tissue repair
Chronic inflammation
Develops slowly and lasts a long time
Can cause damage to tissues

27. Increased Vascular Permeability during Inflammation

28. Events in Inflammation
Figure

29. Events in Inflammation
Figure

30. Fever A body temperature over 37C
Results when chemicals called pyrogens trigger the hypothalamus to increase the body’s core temperature
Various types of pyrogens
Bacterial toxins
Cytoplasmic contents of bacteria released by lysis
Antibody-antigen complexes
These signal for the production of interleukin-I (IL-1)

31. Fever Production
IL-1 production causes the hypothalamus to secrete prostaglandin which resets the hypothalamic “thermostat”
Communication with the brain initiates muscle contractions, increased metabolic activity, and constriction of blood vessels which raises the body’s temperature
Chills associated with fever are due to the reduced blood flow of constricted vessels
Decrease in IL-1 production results in the body’s temperature returning to normal

32. Benefits of Fever Enhances the effects of interferons
Inhibits growth of some microorganisms
May enhance the performance of phagocytes, cells of specific immunity, and the process of tissue repair

33. A Summary of Some Nonspecific Components of the First and Second Lines of Defense
Table 15.5