1. The Immune System

2. Introduction Immune system
The body’s defenses against pathogens that produce disease
2 types of immunity
Nonspecific defenses (Innate defense)
Provide general protection against invasion by a wide range of pathogens
Present at birth–innate
2. Specific Defenses
Specific lymphocytes combat particular pathogens

3. Overview of the body’s defense
Three lines of defense protect us from pathogens

4. Nonspecific Defenses
A set of physical barriers and chemicals that prevent foreign invaders from getting inside our bodies

5. 1st Line of Defense External Barriers 1. PHYSICAL BARRIERS:
An outer layer of skin
Hair in the nostrils
Mucous membranes of the digestive and respiratory tracts

6. Cilia lining the upper
respiratory tract
propel trapped
particles up and out

7. Goblet cells secrete mucus, which coats the epithelial cells.
Mucus contains lysozyme, that breaks down bacterial cell walls.
Bacteria and other debris become trapped in the thick mucus.
Cilia sweep it up and out of the respiratory tract,
where it is expelled from the body by coughing, sneezing,
or even swallowing!

8. The Skin
Epidermis - outer layer of skin that provides a barrier against infection. Any microbes attached to outer layer of dead cells will be shed with those cells.
Dermis contains :
sweat glands
they produce salty perspiration to flush microbes and other contaminants out of the pores.  
Sweat also contains a special enzyme called lysozyme,. .

9. b. sebaceous glands that coat the skin with sebum, which is an oily substance that contains fatty acids that lower the pH of the skin surface to inhibit microbial growth

10. 2. Chemical defenses (barriers)
Sweat, saliva, and tears contain enzymes that kill bacteria.
Glands produce oils and acids
The acid pH of the stomach kills many bacteria

11. 3. Resident Bioflora
Beneficial microbes living on our skin and in our bodies that help block infection by disease-causing microbes

13. Where does all the dead skin go?
Dead skin cells can be found on our sheets, pillows, clothes, and even in the dust particles that form in our homes.
Dead skin cells are broken down by dust mites, which are microscopic parasites that live on our skin, hair, and eyelashes.

14. 2nd Line of Defense
Acts when an invader penetrates the body’s external barriers
Nonspecific – combats all invading microbes
Depend on white blood cells and defensive proteins.
White Blood Cells
(cells that fight infection)

15. 2nd Line of Defense Leukocytes – “Warriors of the immune system”
AKA white blood cells
Produced in the bone marrow
Include:
basophils, eosinophils, mast cells, neutrophils, monocytes, macrophages
Lymphocytes (specific immunity)

17. 2nd Line of Defense

18. 2nd Line of Defense
When the external barriers fail, a set of nonspecific internal defenses stands ready – the second line of protection
Antimicrobial proteins
Interferon
Complement
WBCs: phagocytic cells and natural killer cells
Inflammation
Fever

19. Antimicrobial proteins– Interferons (IFNs)
Protect body against viral infection
Cells infected by viruses produce interferon
IFNs stimulate healthy cells to produce proteins that inhibit viral reproduction

20. Antimicrobial proteins– the complement system
A group of ~20 proteins in blood plasma and cell Membranes
“Complement” proteins cause invading cells to lyse
Form a “membrane attack complex” that makes holes in some microbes
Causes the microbe to lyse
membrane
attack complex
fluids
fluids

21. The 2nd line of defense: WBCs
Phagocytes
Engulf microbes or other particles (by phagocytosis)
Phagocytes migrate to infected area by chemotaxis (attracted to chemicals released by invading microbes and host cells)

22. A Macrophage in action

23. White blood cells have specialized receptors on their surface that enable them to determine what is "self" and "non-self”
When "non-self" proteins are encountered, an immune response is mounted to destroy the foreign (non-self) substance.

25. Mononuclear Phagocytes
Cell Type
Location in Body
Function
Neutrophils
Circulate in body, few in tissue except during inflammation
Phagocytize and digest engulfed materials
Eosinophils
Mainly in blood except during inflammation and allergies
Participate in inflammatory reaction and immunity to some parasites
Basophils
Mast Cells
Basophils in circulation, mast cells present in most tissues
Release histamine and other inflammation causing chemicals
Mononuclear Phagocytes
(Monocytes)
In circulation. Differentiate into macrophages or dendritic cells when they migrate into tissue
Phagocytize and digest englulfed material
Macrophages
Present in virtually all tissues
Dendritic Cells
Initially in tissues but migrate to lymph nodes and other secondary organs
Gather antigen from tissues and present it to lymphocytes
Lymphocytes
In lymphoid organs and circulation
Participate in adaptive/specific immune response

26. Natural Killer (NK) cells
Destroy infected body cells and cancerous cells
NK cells bind to infected cells
Release perforins that penetrate the plasma membrane of infected cells causing them to lyse (similar effect as complement)

27. Chemical Messengers Cytokines – Include: Interleukin I and II
Histamine
Prostaglandins
Complement
Interferons

28. The 2nd line of defense: Inflammation
Occurs when tissue is damaged
Inflammation
an attempt to dispose of microbes
prevent their spread to other tissues
prepare the site for tissue repair
4 hallmark symptoms of the inflammatory response:
Redness
Pain
Swelling
Heat (warm to the touch)

29. What happens when you cut your finger?
Phagocytes engulf bacteria
Tissue heals

30. Steps in the Inflammatory Response
Tissue damage
Mast cells release Histamine
Histamine increases blood flow (by vasodilation) to damaged area (redness).
Causes capillaries to become leaky (swelling).
Damaged cells in area produce other chemicals that attract phagocytic cells to site.

31. Inflammatory Response
Prostaglandins produced – induces pain, and important in production of fever.
Chemicals released attract neutrophils which “stick” to capillary walls (margination), eventually “squeezing” through the leaky capillaries (extravasation).
Neutrophils and other phagocytes attracted to damaged site via cytokines.

32. 7. Ingest and destroy bacteria.
Platelets and clotting factors help to heal wound and confine infectious agents at wound site.
(McGraw Hill video)