1. The Body’s Defense against Foreign Agents

2. How our immune system works
Our body’s immune system works to protect us from foreign agents trying to enter our bodies.
Immunity is the body’s capability to repel foreign substances, pathogens and cancer cells.
Our immune system puts up three lines of defense against invaders.
Each line of defense is designed to pick up where the previous line may have failed.

3. _____________

4. 1st Line of Defense
This line of defense is referred to as NONSPECIFIC IMMUNITY. This means that it will put up a battle to protect us from any pathogen (invader).
The first line of defense includes:
Skin - provides a physical barrier preventing pathogens from entering

5. Mucous membranes – line the respiratory, urinary, reproductive and gastrointestinal tracts. Trap invaders in sticky mucous and expel it from the body by the wave-like motion of the cilia as well as coughing and sneezing.
Tears, mucous and saliva wash bacteria away.

6. 2nd Line of Defense
If pathogens make it through the first line of defense, they must combat the second line.
This response is also NONSPECIFIC so it will react to any invader.

7. The second line of defense includes:
The Inflammatory Response – results in pain, redness, heat and swelling.
It can be initiated by damage to the body’s tissues due to physical agents or microbial infection.
The functions of the inflammatory response are to destroy the cause of infection and remove it from the body.
If that fails, to contain the infection to a small area to limit its effects.
It also helps to replace or repair tissues that were damaged by the infection.

8. Macrophages – These cells engulf and destroy foreign material through phagocytosis.

9. 3rd Line of Defense
If the invader makes it past the first two lines of defense, the immune system identifies the invader (pathogen) and prepares a specific response.
This response is known as the immune response and is considered to be SPECIFIC IMMUNITY. This means that the response targets specific pathogens.

10. Specialized cells of the immune system produce specific proteins called antibodies to fight specific antigens.
B Cells – produce antibodies that bind to a specific antigen so that it can be removed from the body.
This is called an ANTIBODY MEDIATED RESPONSE.
The antibody and antigen fit together like a lock and key. This means that the antibody produced to fight the antigen, will bind to that specific antigen only.
T Cells – do not produce antibodies. They attack cells directly.
This is called a CELL MEDIATED RESPONSE.
When the T cell binds to antigens on the infected cell, it causes it to burst.

12. Specific Immunity - The Immune Response
When an antigen (a foreign substance in the body) enters your body for the first time, your immune system produces antibodies (proteins that attach themselves to specific foreign substances) against it.
This is called the primary response and it can take a few days to occur. That’s why you may still get sick.

13. If the same antigen were to enter your body a second time, the correct antibodies are produced very quickly and in much larger amounts.
This is called the secondary response. It is usually fast enough to overpower an invader so the body does not suffer from the same disease again.

14. When B cells are activated to produce antibodies against an antigen and T cells are activated to attack invaders directly, they also produce memory cells.
Memory B cells and Memory T cells can live for a lifetime. These cells produce a secondary immune response if the same antigen or invader appears in the body again.

15. Types of Immunity There are two types of immunity: a) Active Immunity
The body produces its own antibodies and T cells to attack particular antigens.
This can result from having the disease or illness before – your body still has the memory cells to quickly produce antibodies or T cells…..you have built up an “immunity” to that particular pathogen.

16. This can also result if you have received a vaccination for a particular disease. A vaccination consists of dead or weakened bacteria or viruses which can still act as an antigen. Because the cell is weakened or dead it can no longer cause the disease. The immune system responds to it by producing antibodies or T cells. The memory cells will remain in your body for a long period of time giving you immunity to that disease.

17. b) Passive Immunity
A person is given antibodies from the blood of either another person or animal. This is also called “borrowed immunity”.
It is temporary. It usually does not last for more than a month because the body destroys the borrowed antibodies.
It is very fast acting.
Eg. Maternal Immunity – antibodies from the mother enter the baby’s blood before birth and provide the infant with passive immunity for the first few months of a child’s life. Antibodies are also present in the mother’s milk.

18. Allergies
Allergies are hypersensitivities to substances such as pollen, food or animal hair that ordinarily would do no harm to the body.
Immediate Allergic Response – can occur within seconds of contact with the antigen. The response is caused by the release of histamine by cells which brings about the allergic symptoms.
Anaphylactic shock – an immediate allergic response that occurs because the allergen has entered the blood stream. Characterized by a sudden and life threatening drop in blood pressure.
Delayed Allergic Response – initiated by memory T cells at the site of allergen contact in the body.