1. THE IMMUNE SYSTEM Biology Unit 71

2. Immunity
Immunity
The ability of the body to fight infection and/or foreign invaders by either:
a) producing antibodies or
b) destroying the invaders
Immune System
The system in the body responsible for maintaining homeostasis by recognizing harmful from nonharmful organisms and producing an appropriate response. 2

3. Foreign Invaders Called Pathogens
Viruses, bacteria or parasite that causes disease or immune response.
Toxins (poisons) that pathogens produce may cause harm to an organism as well.
PATHOGENS = BAD!

4. Parts of the Immune System
Blood - White Blood Cells in particular
Lymph nodes-stores T and B cells and traps antigens/pathogens
Thymus Gland – Produces T Lymphocytes (white blood cells)
Bone Marrow – Produces B Lymphocytes (white blood cells)
Lymphocytes = leukocytes = white blood cells

5. The Body’s THREE lines of Defense
First Line of Defense – The Skin
Provides Physical and Chemical barriers
Physical – hard to penetrate (go through)
Chemical – tears, sweat (washes away pathogens)

6. Second Line of Defense – non-specific (can kill ANY pathogen)
These are defenses the body uses no matter what the invader may be. These defenses include:
Phagocytosis – done by macrophages
Natural Killer Cells
Inflammation - caused by release of histamine (a chemical that fights invaders) from leukocytes
Fever – caused by histamines. The fever (high temp) kills invaders by denaturing (breaking down) their proteins.

7. Phagocytosis: a process where the cell “eats” a pathogen
Macrophage: a large cell that “eats” a pathogen
Inflammation: swelling
PHAG = “EAT”
CYTE = CELL
MACRO = LARGE

8. Third Line of Defense
This is a specific response to a specific pathogen/antigen.
PATHOGEN ANTIGEN ARE THE SAME THING! GEN = “BAD”
The response involves the creation of antibodies.

9. Phagocytes Produced throughout life by the bone marrow.
Scavengers – remove dead cells and microorganisms.
MICROORGANISMS OR MICROBES ARE VERY SMALL, ONE-CELLED ORGANISMS.
A SCAVENGER EATS DEAD ORGANISMS. 9

10. White Blood Cells
B-cells mature in bone marrow then concentrate in lymph nodes and spleen- Produce antibodies
T-cells mature in thymus
B and T cells mature then circulate in the blood and lymph
Circulation ensures they come into contact with pathogens and each other 10

11. B -cells
Some activated B cells become memory cells with antibodies on them. The antibodies have a shape that matches the antigen (pathogen) and “captures” it.
Memory cells divide rapidly as soon as the antigen is reintroduced.
When the pathogen/antigen infects again, it is destroyed before any symptoms show. 11

12. 12

13. T- cells After activation the cell divides to form:
T-helper cells containing chemicals that a) help B cells divide and
b) stimulate macrophages
Cytotoxic T cells (killer T cells)
-Kill body cells and antibodies that have captured the antigen
Memory T cells
-remain in body so they can “remember” the antigen/pathogen 13

14. The Immune Response Explained
Pathogen/antigen infects the body. (a foreign invader is entering!)
Macrophage eats antigen and displays portion on its surface.
Helper T- Cell recognizes antigen on the surface of the macrophage and sends a chemical signal to the body.
B-cells produce antibodies with receptors.
Killer T-cells eat B-cells along with the antibodies.

15. The Immune Response Explained
6. Suppressor T-cells recognize that the infection has been taken care of, and they send signals to stop the attacks.
7. Memory T and Memory B cells remain in the body for the next time that invader tries to attack!

16. Active and Passive Immunity
Active immunity: occurs whenever antibodies are created.
Natural active immunity - acquired due to infection (the body “remembers” the antigen/pathogen because it has created its own antibodies
Artificial active immunity – vaccination
A vaccine will cause the body to create antibodies. 16

17. Active and Passive Immunity
Natural passive immunity
A mother’s antibodies pass across the placenta to the fetus and remain for several months.
Colostrum (the first breast milk) contains lots of antibodies which remain on the surface of the baby’s gut wall and pass into the blood. 17

18. Vaccines A preparation containing an antigen/pathogen in the form of:
1) Whole live microorganism
2) Dead microorganism
3) Harmless microorganism
4) Toxoid (harmless form of toxin)
5) Preparation of harmless antigens 18

19. Vaccines Why aren’t they always effective?
Natural infections persist within the body for a long time so the immune system has time to develop an effective response, vaccinations from dead pathogens do not do this.
Less effective vaccines need booster injections to stimulate secondary responses 19

20. Allergies When the immune system responds to harmless substances
Allergens – antigenic substances which do no real harm
Allergens include house dust, animal skin, pollen, house dust mite and its feces 20

21. Autoimmune Diseases A. Autoimmune Diseases
- Occur when the immune system no longer recognizes the cells of your own body… the immune system attacks healthy body cells.
Examples include:
Diabetes Mellitus
Systemic Lupus Erythmatosus
Multiple Sclerosis
Rheumatoid Arthritis
Autoimmune diseases are more frequent in women than in men due to hormonal differences
These diseases are treated with drugs that suppress the immune system as well as with antibodies that attack lymphocytes

22. Autoimmune Diseases Diabetes Mellitus (Type I or Juvenile Onset)
-The immune system destroys the Insulin producing Beta cells of the pancreas.
Multiple Sclerosis
-occurs when the body attacks the myelin sheath of neurons.
-effects include the loss of motor control, feeling or even paralysis of the affected areas.
-MS generally attacks the neurons of the optic nerves, the brain and the spinal cord.

23. Autoimmune Diseases Rheumatoid Arthritis
The body’s own antibodies attack and destroy tissue at the joints
The condition is chronic, with episodes of pain and swelling
No cure, but patients may have joints removed and replaced by artificial ones

24. Immune System Diseases
The body's immune system does not work properly.
Severe Combined Immune Deficiency (SCID)
HIV/AIDS

25. Immune System Diseases
HIV/AIDS (Human Immunodeficiency Virus)
Attacks and kills Helper T Cells. Without these cells, circulating antibodies drop in number and the body is left more vulnerable to other invading microorganisms.

26. Organ Transplants Organ Transplants and Rejection
If the body receives tissue from another person or animal the body will recognize this tissue as foreign
An immune response will be started against the new tissue
If the immune system isn’t repressed, the new tissue will be rejected
This is why organ donors are closely matched to their recipients