Innate Immunity Chapter 15

1. Innate ImmunityChapter 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 PLAY

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. 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 PLAY

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 15.17.1

29. Events in Inflammation Figure 15.17.2

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