1. Immune System Part II: The Innate Immune System1

2. Devastation Caused by Pathogens
Influenza epidemic Killed 22 million people in 18 months.
Three million people will die from malaria this year.
Since 1980, over 619,000 people have died from AIDS in the U.S.
Ever seen Contagion?
Emphasize
Influenza epidemic of killed 22 million people in 18 months. With 25 million American infected, the Red Cross often worked around the clock.
Three million people will die from malaria this year alone.
AIDS has killed 619,000 people in the U.S from the beginning of the epidemic in Worldwide approximately 1.8 million died from AIDS in 2011.
The immune system is a defense system to fight against invading pathogens. 2

3. Overview of the Immune System
Parts of the Immune System
Innate Immunity
Barrier Defenses
Cellular Response
Chemical Response
Adaptive Immunity
Cell Mediated Response
Humoral Response
Emphasize the following
Innate immunity is referred to as nonspecific immunity in the AP Biology Curriculum Framework (see 2.D.4.a). There are two parts to innate immunity including both chemical responses and cellular responses.
-Rapid response
-Cells involved have cell receptors that recognize PAMPS or signature molecules shared by pathogens
-Response involves a variety of phagocytes
-Response can also produce chemical response which includes complementary proteins, antimicrobial proteins
-Response can also include inflammatory response
Emphasize that this is an ancient response that seems to have its origin in cells before plants and animals diverged.
Adaptive Immunity was called specific immunity, and then later it was called by acquired immunity. It is referred to as the “specific immune response” in the AP Biology Curriculum Framework (see 2.D.4.b) It involves two responses, cell mediated response and humoral response. It also requires cells involved in innate immunity to activate adaptive immunity.
-Cell mediated response attacks infected cells
-Humoral response includes the production of antibodies that interacts with the pathogen itself.
-Much slower response
-Recognition of traits specific to particular pathogen, using a vast array of different cells (B cell and T cell lymphocytes) and receptors. 3 3

4. Innate Immunity (Nonspecific Immunity)
First Line of Defense
Innate Immunity (Nonspecific Immunity)
Innate Immunity-Activated immediately upon exposure to pathogen and is the same response for each exposure.
First line of Defense: Integument System-
Skin and mucous membranes provide a physical barrier to entry of pathogens. Skin contains keratin, a structural protein that helps form that barrier. Mucus helps trap pathogens.
Skin's fatty acids and secretion from tears, sweat and oil glands are toxic to bacteria.
Natural bacterial fauna can outcompete many pathogen.
Your are born with your Innate Immunity and it does not require exposure to the disease to activate it. First line of defense-This defense works to keep the pathogen out of the body.
Integumentary System-
Skin & mucous membranes line entire body (mucous membranes line every opening into the body) - skin contains keratin which is a structural protein that helps form a physical barrier to the entry of pathogens; Mucous membranes produce mucus that helps trap foreign particles. The numerous cell layers in both help provide a barrier, as well.
Skin's fatty acids and secretion from sweat and oil glands are toxic to bacteria. Some of the secretions contain lysozyme which can break down cell walls of many bacterial cells. Also the secretions keep the pH of the skin ranges from 3-5 which is too acidic for many bacteria.
Mucous membranes secrete mucous that traps and allows for the removal of invading pathogen
The skin also has a natural fauna of bacteria that can outcompete most pathogens. 4 4

5. Body Passages and Innate Immunity
Trachea lined with ciliated cells and cells that secrete mucus.
Esophagus leads to stomach with a pH of 1-2 (acidic) which kills most pathogens
Urinary tract has lower pH (again acidic) and is flushed with urine.
Tear ducts with lysozymes.
Reproductive tract also has a lower pH (acidic once more).
Body passages-
Trachea has mucus produced by the respiratory system. This mucus traps particles and the cilia sweep it out of the tube (to the back of the throat where it is swallowed into the stomach and destroyed by the acid). The orange cells produce mucus that that traps microorganisms that enter. The yellow cells are ciliated which beat in unison to expel mucus and trapped microorganisms upward to pharynx.
Esophagus leads to stomach with pH of 1-2 which kills most invading pathogens. No matter how hard you wash an apple, you still swallow thousands of microorganisms.
All openings into the body are lined with mucous producing membranes. SO anything that enters the human body has to either cross the skin or a mucous membrane.
The lower pH of the urinary and reproductive tract help prevent the entry of pathogens. 5 5

6. Second Line of Defense Phagocytes and the Chemicals Released
Second Line of Defense-Activation of phagocytes (leukocytes/white blood cells)
Made in the red bone marrow.
Found in connective tissue, tissue lining organs, lymph nodes and circulating in the blood.
Second Line of Defense-Activation of leukocytes which are phagocytes.
Terminology
Leukocytes-are white blood cells.
Two types:
Phagocytes- are white blood cells that phagocytize (engulf or “eat”) pathogens.
Lymphocytes-are white blood cells that are involved in the adaptive immune response. They are not phagocytes. T cells help activate B cells and kill infected body cells. B cells produce antibodies. Natural killer cells aid in disposing of infected cells.
Graphic 6

7. Neutrophils and Eosinophils
Neutrophils- are the first to arrive; numerous (1 billion made each day); survive only a few days. These are expendable cells.
That “parasitic worm” comment is bound to spark some discussion!
Neutrophils, which are produced in the bone marrow and circulate in the blood, are a type of white blood cell. Neutrophils, are abundant and make up about 50% to 75% of white blood cells. Neutrophils respond to infection and attack bacteria and other foreign invaders directly.
Eosinophils are a type of white blood cell produced in the bone marrow. They make up about 1 to 3% of the total number of white blood cells. Eosinophils can circulate in the blood and also are found outside blood vessels in other organs in the body. The gastrointestinal (GI) tract typically has the highest number of eosinophils relative to other organs.
Eosinophils- are weakly phagocytic cells that kill invaders that are clumped together. They also destroy parasitic worms. 7

8. Basophils and Mast Cells
Mast cells reside in connective tissue. Mast cells are present in most tissues characteristically surrounding blood vessels and nerves, and are especially prominent near the boundaries between the outside world and the internal milieu, such as the skin, mucosa of the lungs and digestive tract, as well as in the mouth, conjunctiva and nose.
Basophils circulate in the blood and like mast cells contain histamine.
What’s histamine, they ask…
Histamine triggers the inflammatory response. Histamine increases the permeability of the capillaries to white blood cells and some proteins, to allow them to engage pathogens in the infected tissues. Emphasize to students that their immune system is on “high alert” if they are in need to an “antihistamine” to combat flu-like symptoms!
Graphic
Basophils and mast cells are leukocytes in nearby connective tissue which produce histamines which are released when these cells are damaged. 8 8

9. Monocytes and Macrophages
Monocytes-are transformed into large macrophages involved in
phagocytosis and also important in the adaptive immune response as an antigen presenting cell.
Monocytes- When they arrive at the site of the infection, they are transform into large macrophages; very efficient and also involved in primary immune response. The second picture is a monocyte that has been transformed into a macrophage. This macrophage is engulfing bacterial cells and destroying them. Macrophages will put the degraded pathogen parts on its cell membrane and become an antigen presenting cell to activate the adaptive immune response.
Monocytes are a type of white blood cell and are part of the innate immune system of vertebrates including all mammals (humans included), birds, reptiles, and fish. Monocytes play multiple roles in immune function. Such roles include: (1) replenish resident macrophages and dendritic cells under normal states, and (2) in response to inflammation signals, monocytes can move quickly (approx. 8–12 hours) to sites of infection in the tissues and divide/differentiate into macrophages and dendritic cells to elicit an immune response. Half of them are stored in the spleen. 9 9

10. Dendritic Cells King of the Immune System
Dendritic cells (DC) are found in skin, nasal passages, intestines, spleen and throat Population numbers are smaller than other phagocytes.
Emphasize that these cells are also made in the bone marrow. They were not discovered until 1970’s and their function not fully appreciated until recently.
Facts about dendritic cells (DC)
When mature, DC have extensions like the dendrites found on certain neurons
Act like macrophages and do phagocytosis and will put antigens (parts of pathogens) on their surface to become an antigen presenting cell.
Found in tissue where pathogens are most likely to make an entrance into the body and in the skin.
Smaller than macrophages
Once activated, the DC undergoes a dramatic change and makes its way to the lymph nodes to activate B cell and T cell lymphocytes.
Also DC have been found to aid in preventing autoimmune diseases like diabetes, and arthritis.
DCs were discovered by Dr. Ralph Steinman and Dr. Zanville Cohn (Steinman also coined the name dendritic cells) in Steinman continued investigating DCs to determine their function. Macrophages were thought to be the connection between innate immunity and adaptive immunity (This was Dr. Steinman’s discovery). The dendritic cells, however, are as important as macrophages in becoming antigen presenting cells. In 2011, Dr. Steinman was awarded the Nobel Prize in Physiology or Medicine for his contribution to immunology. Dr. Steinman died three days prior to the announcement. Since the Nobel Prize is not awarded posthumously, it presented a problem. The committee decided that as the decision to award the prize "was made in good faith", it would remain unchanged.
Graphic and 10

11. Dendritic Cells
Dendritic cells are important in adaptive immunity as an antigen presenting cell
The cell on the right a an immature dendritic cell and the one on the left has been activated.
Graphic 11

12. Phagocytes and TLR Receptors
Phagocytes have Toll-like-receptors (TLR) which recognize signature molecules.
The phagocyte engulfs the pathogens within a vesicle and deactivates or kills the pathogen.
Phagocytes can eat themselves to death.
In general, phagocytes in mammals have the ability to distinguish pathogens because they contain receptor sites called Toll-like receptors (TLR). TLR recognizes certain molecules that are common to pathogens but not mammals.
The TLR receptor is unique and will attach only to signal molecules. The signal molecules or signature molecules for a group of pathogens are also called pathogen-associated molecular patterns (PAMPs).
For example, only one receptor might be needed for bacteria because bacteria have cell walls made of murein or muramic acid. If a bacterium with the cell wall made of murein attaches to the receptor, it is recognized as a foreign object.
Once the PAMP is attached to the receptor, then a signal transduction pathway is activated resulting in a response that would aid in eliminating the pathogen. Most often phagocytosis occurs and the pathogen is taken into the cell enveloped in a small vacuole. It is fused with a lysosome where enzymes from the lysosome kill or deactivate the pathogen. It also can activate the inflammatory response.
For example:
TLR4 receptor for a lipopolysaccharide found in gram-negative bacteria
TLR5 receptor for protein flagellin found in bacteria
TLR3 receptor DS RNA found in certain RNA viruses
TLR9 receptor for unmethylated DNA found in DNA viruses and bacteria
The microbial peptides put holes in the pathogen membrane, coat the cell wall. This is important because only small number of cells is needed to fight a vast number of pathogens. This information was also found on the evolution of cells. This is a core process.
Remind the students that is also an example of cell communication.
Pus are the remains of phagocytes that literally devoured so many pathogens that they have busted open. 12

13. Natural Killer Cell (not a phagocyte)
Natural killer cells can detect infected cells and cancerous cells due to changes in plasma proteins of the cells.
They secrete chemicals into the infected cells and kill them or puncture the infected cell’s membrane.
Natural killer cells are leukocytes that roam the body contacting cells looking for infected cells by viruses and/or cancer cells. Eukaryotic cells are transformed when infected by viruses and cancer cells are also transformed by changes. These changes include changes in the surface proteins. Natural killer cell (in the foreground) is killing a cancer cell by punching holes in the plasma membrane. Water will rush in and lyse the cell. 13 13

14. Natural Killer Cells Animation
Scroll over the bottom of the image to activate the video controls and then press play. 14

15. Phagocytes and Chemical Response
Phagocytes can also activate chemical responses like the inflammatory response and the production of antimicrobial peptides. 15

16. Chemical Responses
Kinins or chemokines (microbial peptides) are released by certain phagocytes.
These molecules increase circulation and capillary permeability.
Attract leukocytes to site of injury
Affect nerve cells making area tender
Leukocytes follow an increased concentration gradient of chemokines to site of the infection, as shown in the graphic.
Graphic- 16 16

17. Complement Proteins and the Killer Instinct
2. Complement proteins (approx. 30 proteins) work by a number of different methods.
These proteins create pores in invading bacteria, causing water to rush in.
Complement proteins got their name because their activity was said to complement the activity of the antibody. This system, however, works without the activation of antibodies. It is evident that this mechanism evolved much earlier in the innate system than the evolution of the adaptive system. 17 17

18. Complement Proteins
Scroll across the bottom of the image to activate the video controls and press Play. 18

19. Complement Proteins
Scroll across the bottom of the image to activate the video controls and press Play. 19

20. Complement Proteins Forming Pores
This shows how complement proteins actually form pores in a bacterium.
Graphic 20 20

21. Complement Proteins and Opsonizaton
Complement proteins along with antibodies will coat a bacterium. Phagocytes recognize both the complement proteins and the antibody. Phagocytes will engulf the pathogen and destroy it.
Opsonization (literally means “to make tasty”)
Emphasize that the phagocyte has receptor sites for both the antibody and the complement protein complex.
Graphic 21 21

22. Interferons
The transduction pathway activates antiviral genes to produce proteins that will protect the cell against viral infection. IMPORTANT: Interferon will not protect the infected cell but interferon protects neighboring cells from viral infection.
Interferon is used as a treatment for chronic viral hepatitis C and viral hepatitis B.
The term interferon comes from the action of the substance interfering with viral reproduction.
Graphic
3. Interferons are proteins made by virus-infected cells. They are secreted and transported to neighboring cells to prevent viral infection from the infected cell. 22 22

23. Histamine Release and Inflammatory Response
4. Histamine is released by mast cells and basophil cells which are attracted to an injury site. When the skin is penetrated, cells are ruptured releasing chemical signals to attract the mast and basophil cells. These cells release histamine.
This illustrates the inflammatory response that is most important. Explain the diagram and make sure that all the students understand the parts each cell is contributing to this process. 23 23

24. Inflammatory Response
Increases capillary permeability. The area becomes swollen, red, temperature increases from the increased blood flow.
Phagocytes leave the capillary bed because they are attracted histamine and other signals.
Phagocytes clean up pathogens and cell debris.
The four classic signs of inflammation are heat, redness, swelling and pain. Ask students to use the diagram to explain how/why each of these symptoms result, as well as the benefits of inflammation.
When the skin is penetrated, cells are ruptured. The ruptured cells release chemical signals to attract mast and basophil cells to the site. The mast and basophils then cells release histamine.
Histamine increases capillary permeability. The area becomes swollen as fluids leave the capillary beds to the injured area. Nerve endings become tender.
Phagocytes come to the injured area via the circulatory system. The phagocytes (first to arrive are neutrophils and then sometime later macrophages) leave the capillary beds to the injured area.
They clean up pathogens and cellular debris.
Some phagocytes die in cleaning up the site forming pus. 24 24

25. Homeostasis and Inflammatory Response
Inflammation continues as long as the triggers (pathogens) are present.
When phagocytes complete their job by removing the pathogens, macrophages begin to secrete substances that-
Suppress inflammation
Promote tissue repair
If the stimulus persists, then the inflammation continues. Continued inflammation is called chronic inflammation and is not normal. Chronic inflammation causes diseases such as asthma, Crohn’s disease, rheumatoid arthritis, atherosclerosis, diabetes and cancer.
Graphic 25 25

26. Fever Inflammatory response is often accompanied by fever.
Some cytokines stimulate the brain to make prostaglandins. These prostaglandins stimulate the hypothalamus to a new temperature set point. The signals the hypothalamus sends out then:
Constrict blood vessels in the skin
Contract skeletal muscles
Increase heart rate and respiration
Is fever good or bad?
Fever increases circulation and also increases enzyme activity and metabolism. Another benefit of fever is that some pathogens reproduce slower at a higher temperature.
If the temperature is too high, the body responds by sweating and opening up blood vessels in the skin. Temperatures above 105o F can cause serious damage to the brain.
Also point out that not all people are “average”. Ask students what the “average” human body temperature is. They should respond 98.6F or 37 C. HOWEVER it is not uncommon for someone’s healthy body temperature to be 97F which means a fever of 99 F is indeed troublesome for that individual! 26 26