2. Immune System
The function of the immune system is to fight infection through the production of cells that inactivate foreign substances or cells. This process is called immunity.

3. Innate immunity: against foreign bodies, injury and pathogens
Innate immunity: against foreign bodies, injury and pathogens. Is a fast response to any pathogen (not specific or specialized), meant to be a general defense to act quickly and destroy any pathogens within a few hours.
Adaptive Immunity: against specific pathogens or changed/damaged body cells. Occurs about 4-7 days after infection if the innate immune response fails. Slower response than innate system, but targets specific pathogens more accurately.

4. Nonspecific Defence:
The first line of defence: prevent pathogens from entering the body. This is carried out by skin, sweat, saliva, mucus and tears. Some are physical barriers and others are chemical barriers.
Physical barriers:
The most important of these defences is the skin. Normally bacteria cannot get through layers of dead skin cells on the surface. When the skin is broken, pathogens have free access to the body where they multiply and grow causing inflammation, redness and pain.
Nose and throat contain mucus and cilia which prevent pathogens from entering the lungs
Chemical barriers:
Sweat and oil glands produce acidic environments that kills bacteria
Saliva, tears and mucus contain the enzyme lysozyme, which breaks down cell walls of bacteria.
Recall from digestive system: stomach acid and enzymes destroy many pathogens which make it to the stomach.

5. Second line of defence: when pathogens enter the body, they can multiply quickly releasing toxins into the tissues. When this happens, the body activates its inflammatory response, which is a reaction to tissue damage caused by injury or infection.

6. Injured body cells, and a special WBC called a basophil from bone marrow, release chemicals called histamines, which begin an inflammatory response
Histamine increases capillary dilation, and make them permeable to some proteins and some WBC
Blood vessels near the wound expand to allow more white blood cells in.
The immune system also raises the internal body temperature (fever) At elevated temperatures, the growth of pathogens is slowed or stopped.
The high temperature also increases heart rate so white blood cells get to the infected site faster.
Result of inflammatory response: increase temperature, increased white blood cell count, redness, prevents infection from spreading, and damaged tissues area cleaned.
When pathogens are detected, the immune system produces millions of white blood cells.
Most of these white blood cells are phagocytes which engulf or swallow bacteria cells. After they do this, they will often "show off" the antigen that was present on the pathogen so that it can be recognized by other cells

8. Types of WBC: Macrophages, neutrophils, eosinophils, lymphocytes
Macrophages are found in tissues and wait to engulf pathogens when they are present.
Neutrophils and eosinophils from bone marrow are attracted to the site if unsuccessful. They are both phagocytic cells
If a pathogen is still present, monocytes (immature macrophages from lymph tissue) which travel in the circulatory system will pass through capillaries at the infected site and develop into macrophages where needed

9. Natural killer cells – a type of lymphocyte made in lymph tissue and bone marrow - recognizes cells that have been infected by a virus, bacteria, or have become tumorous (by detecting changes to the surface of the cell). It destroys these cells. (here, the cells that are being destroyed are the body's OWN cells, but they have become infected or damaged)
Other types of lymphocytes (B and T cells) are part of SPECIFIC DEFENSE, and act to destroy and remember specific types of pathogens and infected cells

12. Specific Defences:
Third line of defence: the Immune System!!! (adaptive immunity)
If a pathogen makes it past the nonspecific responses, the immune system reacts with specific responses, called the immune response.
This response is triggered by an antigen which can be a virus, bacteria or other pathogen.
The white blood cells associated with the immune response are lymphocytes.
There are two types of lymphocytes in the immune response: B cells and T cells.
There are 2 kinds of adaptive immunity:
Humoral immunity: B cells (bone marrow derived) provide immunity against antigens and pathogens in the body fluids. B-cells are found circulating in blood, waiting to become activated
Cell-mediated immunity: T cells (mature in the thymus) provide a defence against abnormal cells or pathogens inside living cells.

13. Humoral Immunity:
Involves finding and destroying pathogens that are circulating in the body. When a pathogen enters the body, it is recognized by the body’s B cells by the antigens on the surface of the pathogen. (It recognizes that these cells do not belong in the body). These cells are activated. They divide and multiply producing large numbers of plasma cells and memory B cells.
Plasma cells release antibodies. These antibodies can cause the pathogens to lyse or clump together. (remember antigens and antibodies in blood!!)
Antibodies are proteins that recognize and bind to antigens. These clumped/dead cells are then engulfed by macrophages to remove them.
Once the pathogen is gone, the memory B cells remain and remember the pathogen. They are now capable of producing antibodies specific to that pathogen. This greatly reduce the chances of getting the same disease more than once - as the pathogen will immediately be recognized the second time and eliminated quickly by the memory B cells.
Should the same disease enter the body again, the memory B cells can rapidly form new plasma cells to produce the specific antibodies to destroy the pathogen

15. Cell Mediated Immunity:
Cell Mediated Immunity is the body’s defence against its own cells which have become cancerous or infected.
It relies on T-cells which come into direct contact with antigens (not just releasing antibodies) and works to attack bacteria, virus, fungi, and infected body cells
T cells divide into 4 types

16. Killer T cells (cytotoxic T cells) – track down infected or cancerous cells that need to be destroyed. A cell that is infected with a virus will display the antigens from the virus on its plasma membrane, and will wait for a Killer T-cell to come by and destroy it. The killer T-cells will attach to the antigens of the infected cell, and then secrete proteins which destroy the membrane of the cell. The remaining dead cells is removed by phagocytes. This is very similar to natural killer cells, however cytotoxic T cells only recognize one specific type of pathogen, and therefore only search for cells that are infected with that pathogen. (Only has one target)
Helper T cells – raise the alarm and coordinate other cells. Activate cells that can destroy pathogens, but don’t kill pathogens themselves. Produce memory T cells by dividing rapidly once a pathogen is detected. Assist B-cells in recognizing antigens of pathogens, by taking the antigen to the B-cell to be recognized. (Train the B-Cells and activates them)
HIV/AIDS – attacks these cells – which means other T and B cells can’t do their job as well
Suppressor T cells – release substances to shut down the killer T cells when disease is stopped - a hyperactive immune system can begin to attack itself by releasing too many chemicals and/or antibodies. It may also lose the ability to recognize itself from its not-self (autoimmune diseases). (Tell immune system to ‘stand down’)
Memory T cells – remember the pathogen and will cause a secondary response if the disease returns

18. TRANSPLANTS - Killer T cells are useful in fighting diseases but can make organ transplants difficult.
The body may recognize the organs as being foreign and the immune system will try to attack it.
This is known as organ rejection.
You need to find a donor with nearly identical cell markers.
Recipients may need drugs to suppress immune responses for the rest of their lives.

19. How can you build immunity?
New particles take longer to identify, and a person remains ill until a new antibody can be crafted
Old particles are quickly recognized, and a person may never become ill from that invader again. This person is now immune.

20. What is immunity?
Resistance to a disease causing organism or harmful substance
Two types:
Active Immunity
Passive Immunity

21. Acquired Immunity:
Active Immunity – You produce the antibodies. Your body has been exposed to the antigen in the past either through:
a. Exposure to antigen – any exposure to a disease creates memory cells. You fought it, you won, you remember it.
b. Vaccination - a vaccine contains a small culture of the disease. It is introduced to the body to build up an immune response. Planned exposure to a form of the antigen that has been killed or weakened – You detected it, eliminated it, and remember it

22. Vaccine
Antigens are deliberately introduced into the immune system to produce immunity
Because the bacteria has been killed or weakened, minimal symptoms occur
Have eradicated or severely limited several diseases from the face of the Earth, such as polio and smallpox

23. How long does active immunity last?
It depends on the antigen
Some disease-causing bacteria multiply into new forms that our body doesn’t recognize, requiring annual vaccinations, like the flu shot
Booster shot - reminds the immune system of the antigen
Others last for a lifetime, such as chicken pox

24. 2. Passive Immunity –
a. During development – antibodies are passed from mother to fetus
b. Breast feeding – antibodies passed from mother to child
c. Certain vaccinations – antibodies produced in other animals are injected into the body (ie: against malaria, rabies, tetanus)