1. Chapter 22
The Immune System
Part C

2. Two Intrinsic Defense Systems Innate (nonspecific) system
Immunity:
Two Intrinsic Defense Systems
Innate (nonspecific) system
responds quickly
Adaptive (specific) defense system
Takes longer to react than the innate system

3. Innate (nonspecific) Defense System
Innate system consists of two components:
First line of defense:
Includes external body barriers
Second line of defense:
Includes internal defenses:

4. Innate Nonspecific Defenses

5. Innate (nonspecific) Defense System: Surface Barriers
Make up the first line of defense
Include:
Skin (keratin in the skin):
Physical barrier to most microorganisms & their toxins
Resists weak acids & bases
Mucosae:
Similar mechanical barriers
Line all body cavities open to the exterior

6. Chemical Barriers Epithelial membranes produce protective chemicals:
Skin acidity (pH of 3 to 5) inhibits bacterial growth
Sebum contains chemicals toxic to bacteria
Stomach mucosae secrete:
Concentrated HCl
Protein-digesting enzymes

7. Chemical Barriers, cont’d.
Saliva & lacrimal fluid contain lysozyme
Mucus traps microrganisms & particles entering:
The digestive system
The respiratory system

8. Internal Defenses: Cells and Chemicals
Called upon when 1st line of defense is penetrated
Nonspecific cellular & chemical devices:
Phagocytes
Natural killer (NK) cells
Antimicrobial proteins (in blood and tissue fluid)
Inflammatory response (other cells involved)
Fever

9. Phagocytes Macrophages: Chief phagocytic cells Include two types:
Free macrophages:
Regional wanderers
Searching for invaders & cellular debris
Ex. alveolar macrophages
Fixed macrophages:
Confined to a particular organ,
Ex. Kupffer cells (liver)
Microglia (brain)
Figure 21.2a

10. Phagocytes (Macrophages)
Figure 21.2a

11. Phagocytes, cont’d Neutrophils: Eosinophils: Most abundent WBCs
Become phagocytic on encountering infectious material
Eosinophils:
Weakly phagocytic
Important in defending against parasitic worms

12. Mechanism of Phagocytosis
Microbes adhere to the phagocyte
Pseudopods form & engulf the particle (antigen) into a phagosome
Phagosomes fuse with a lysosome (phagolysosome)
Proteolytic enzymes of phagolysosome digest invaders
Indigestible & residual material is removed by exocytosis
Some organisms escape phagocytosis unrecognized

13. Microbe adheres to phagocyte.1
Microbe adheres to phagocyte. 2
Phagocyte forms pseudopods that
eventually engulf the particle.
Phagocytic vesicle
containing antigen
(phagosome).
Lysosome 3
Phagocytic vesicle is
fused with a lysosome.
Phagolysosome 4
Microbe in fused vesicle
is killed and digested by
lysosomal enzymes within
the phagolysosome, leaving
a residual body.
Acid
hydrolase
enzymes
Residual body 5
Indigestible and
residual material
is removed by
exocytosis.
(b)
Figure 21.2b

14. Natural Killer (NK) Cells
Large granular lymphocytes (Small distinct group)
Police the blood & lymph
Nonphagocytic and nonspecific
Can lyse and eliminate cancer and virus-infected cells
Kill by:
Releasing perforins & other cytolytic chemicals
Enhance inflammatory response by:
Secreting potent chemicals

15. Inflammation: Tissue Response to Injury
Triggered whenever body tissues are injured by:
Physical trauma
Intense heat
Chemical irritants
Infectiuos agents:
Viruses
Bacteria
Fungi

16. Inflammation Response
The four major signs of acute inflammation are:
Redness
Heat
Swelling
Pain
Beneficial effects:
Prevents local spread of damaging agents
Disposes off cell debris and pathogens
Sets the stage for repair processes

17. Inflammation Response
Released chemicals cause:
Dilatation of local small blood vessels
Vessel dilatation leads to:
Increased blood flow
Hyperemia (blood congestion)
Hyperemia accounts for:
Redness, &
Heat of inflamed area

18. Inflammatory Response: Vascular Permeability
Chemicals liberated also cause:
Increased perrmeability of local capillaries
Fluid seeps thru capillaries into tissue spaces causing:
Edema (local swelling)
Seeped fluid contains:
Clotting factors
Proteins
Antibodies

19. Inflammatory Response: Edema
Contributes to the sensation of pain
Helps dilute harmful substances
Brings in large quantities of
Oxygen, and
Nutrients needed for repair
Allows entry of:
Clotting proteins, which prevent the spread of bacteria

20. Inflammatory Response: Phagocytic Mobilization
Four main phases:
Leukocytosis:
Injured cells release leukocytosis-inducing factors
Bone marrow responds by releasing neutrophils
Margination:
Neutrophils cling to the walls of capillaries in injured area
Diapedesis:
Neutrophils squeeze thru capillaries & begin phagocytosis
Chemotaxis:
Inflammatory chemicals attract more neutrophils to injury site

21. Innate defenses
Internal defenses 4
Positive
chemotaxis
Inflammatory
chemicals diffusing
from the inflamed
site act as chemotactic
agents 1
Neutrophils enter blood
from bone marrow 3
Diapedesis 2
Margination
Endothelium
Basement membrane
Capillary wall
Figure 21.4

22. Antimicrobial Proteins
The most important antimicrobial proteins are:
Interferon
Complement proteins
Enhance the innate defenses by:
Directly attacking microorganisms
Hindering microorganism reproductive ability

23. Virus-invaded host cell activates synthesis of IFN
Interferon (IFN)
Virus-invaded host cell activates synthesis of IFN
Interferon molecules:
Leave the infected cell
Enter neighboring cells
Interferon stimulates neighboring cells to:
Activate genes to produce antiviral proteins
Antiviral proteins:
Nonspecifically block viral reproduction in neighboring cells

24. Interferon (IFN)
Figure 21.5

25. Interferon Family Interferon Family: They include:
A number of related proteins
With slightly different physiological effects
They include:
Gamma () interferon: secreted by lymphocytes
Alpha () interferon: secreted by most other WBCs
Beta () interferon: secreted by fibroblasts

26. Interferon Family, cont’d.
In addition to the antiviral effect, interferons also:
Activate macrophages
Mobilize NKs
FDA-approved alpha IFN is used:
As an antiviral drug against hepatitis C virus
To treat genital warts caused by the herpes virus

27. At least 20 proteins that circulate in the blood
Complement
At least 20 proteins that circulate in the blood
Present in an inactive form in blood
Provides a major mechanism for destroying foreign substances in the body
Enhances the effectiveness of both:
Nonspecific defenses
Specific defenses

28. Fever Abnormally high body temperature
Occurs in response to invading microorganisms
Body temperature is regulated by:
A cluster of neurons in the hypothalamus
Referred to as the body’s thermostat
The thermostat is reset upwards in response to pyrogens
Pyrogens are chemicals secreted:
By leukocytes and macrophages
In response to exposure to bacteria & other foreign substances

29. High fever is dangerous because it:
Fever (cont’d.)
High fever is dangerous because it:
Denatures enzymes
Shuts down metabolism
Moderate fever can be beneficial, as it:
Stimulates the liver & spleen to sequester iron and zinc (needed by microorganisms)
Increases metabolic rate speeding up tissue repair