The Immune System

1. The Immune System Biology 2201 Unit Three Section Five

2. Introduction • The Immune System provides specific defenses giving the human body the ability to fight infection through the production of antibodies and cells that attack pathogens. • A Pathogen is any disease producing organism or virus which can produce toxins.

3. Toxins • Toxins are substance that interfere with the normal functioning of our body cells; (ex.) neurotoxins — attack nerve cells. • The immune system maintains good body homeostasis by recognizing and destroying harmful organisms or substances that may interfere with human health.

4. Examples • Some examples would be the following : • 1) Infectious Diseases : disorders spread by microorganisms or viruses that can be transmitted from one person to another. • 2) Venereal Diseases : spread by sexual contact — such as syphilis and gonorrhea (caused by bacteria) and the AIDS virus.

5. Historical Perspective • Robert Koch (1876) was a German doctor who discovered a way of identifying pathogens that caused a particular disease. Disease Transmission could be by bacteria and viruses. What Happens : • 1) Pathogens carried by the environment (air , water, etc.). • 2) Transmitted by direct bodily contact between an infected person and an uninfected person. • 3) Disease can be carried from one human to another by a third organism; (ex.) malaria.

6. Treatment could involve chemotherapy — use of chemicals such as antibiotics to treat disease. (ex). • An antibiotic can be a bacteria-killing substance produced in living things; such as penicillin (first discovered by Alexander Fleming in 1928). • Remember that an antibiotic can kill bacteria, but not a virus.

7. Immunity • Immunity is the ability of the body to resist a disease. The immune system is very active in the process of immunity and the body’s immune response.

8. Non-specific immunity • Where prior exposure is not necessary for it to be effective. • Non-specific immunity includes: • Physical barriers (1st line of defense) such as the skin, mucous membranes, sweat, saliva, gastric juices and tears. • Phagocytic cells (2nd line of defense) such as Macrophages, Neutrophils, and Monocytes.

9. Non-specific Defenses • Phagocytosis is the process by which a cell ingests bacteria to destroy them. Some ways the body counteracts pathogens are the following: • 1) Macrophages : phagocytic cells produced in bone marrow. They are found in the liver, spleen, brain and lungs and also circulate in the bloodstream and interstitial fluid. They protect body against a wide range of pathogens (disease causing agents); • 2) Neutrophils are leucocytes or WBC’s that engulf bacteria through phagocytosis. • 3) Monocytes are the WBC’s from which neutrophils and macrophages are derived. • 4) Natural killer cells are WBC’s that carry out phagocytosis on cancerous body cells or body cells infected by viruses.

11. Caption:-- Alveolar macrophage phagocytosis of E. coli on the outer surface of a blood vessel (lung pleural cavity). File Name:-- 8957BCategory:-- Medical Type of Image:-- SEMMagnification:-- x1,315--(Based on an image size of 1 inch in the narrow dimension)

12. Specific Immunity • The lymphocytes are specialized white blood cells (WBC’s) produced in bone marrow. • They are the primary structures of the specific immune system that protect the body against a wide variety of infections. • They are divided into two groups, depending on where they mature : • i) B lymphocytes (B cells) mature in bone marrow and • ii) T lymphocytes (T cells) mature in the thymus gland.

13. Immune Response • 1. An immune response is the reaction of the immune system to the presence of foreign cells or molecules. . • It causes the production of antibodies and specialized cells that bind to and inactivate foreign substances. • This immune response is an antigen / antibody reaction. An antigen is any substance that causes an immune response — (ex.) viruses , microorganisms ; (most antigens are proteins, but some can be CHO or nucleic acids). • An antibody is a protein in the blood that binds to and helps destroy foreign substances in the body; (it is a y-shaped molecule that attaches to an antigen).

14. 2. Complete Immune Response First-Line Defense — Physical and Chemical Barriers: • The body's first line of defense against pathogens involves several kinds of physical and chemical barriers. • These include skin, sweat, tear, saliva, membranes lining body passages, mucus, stomach acid, and urine. • Unbroken skin and the membranes lining the body passages are effective barriers to most pathogens. • Sweat, tears and saliva contain chemicals that kill or inhabit some bacteria. • Mucus that covers internal membranes entraps pathogens that are then washed away or destroyed by chemicals. • Stomach acid destroys many pathogens that may be present in food.

15. Second-Line Defense — Inflammatory Response : • If a pathogen gets past the first line on defense and starts and infection, parts of the second line of defense become activated. • This results in the inflammatory response, a reaction of the body that causes swelling, redness, warmth, and pain in the area of infection. Cells that are damaged from the infection release certain chemicals called histamines. • These chemicals causes blood vessels to dilate and become more permeable to fluid and leucocytes.

16. This increased blood flow and accumulation of fluid causes swelling and warmth in the affected area. • This attracts phagocytic macrophages that ingest and destroy large numbers of bacteria. • As the inflammatory response proceeds, the phagocytes ingest the pathogens and any damaged tissue. • Eventually pus, a mixture of phagocytes, dead cells, bacteria, and body fluid, collects in the wound. • The pus either drains or is absorbed by the body. Most of the time, the pathogen is destroyed, the inflammation dies down, and the wound heals.

17. Infected area (swelling, redness etc.) INFLAMMATION • Damaged cells (release certain chemicals called Histamines which cause increased blood flow to the damaged area by increasing the diameter of the capillaries) • Attracts Phagocytes (neutrophils and macrophages) — (WBC's that ingest large numbers of bacteria).

18. Third Line of Defense — The Immune Response : • This line of defense begins after the pathogen has been destroyed and the antigens from the pathogen protrude from a macrophage. • These antigens or foreign materials are easily detected as having genetic markers that differ from those of our own body. • After a macrophage displays an antigen on it's surface, helper T cells bind to the antigens on the surface of the antigen. • This triggers chemical messengers to be released to cause the T cells to multiply in number. • Some of the T cells can disrupt the reproductive cycle of the pathogen by destroying infected tissue cells.

19. The antibodies on B cells can bind to the antigens, thus helping to destroy the pathogens. • The T cells and the B cell antigen-antibody complex combine. • This union of T and B cells will activate the B cells. • Activated B cells will enlarge and divide producing memory B cells and plasma cells. • The plasma cells will produce the antibodies (at a rate of 2000 per second) to be released into the bloodstream to fight invading pathogens. • After the infection has been fought off, the memory T cells remain in the blood ready to fight off a new infection by the same pathogen. • If the same antigen is found again in the bloodstream, the response time will be much faster with higher levels of antibodies.

20. Acquired Immunity • Immunity can be acquired in two ways: naturally through infection or passive transfer, and artificially by medical treatments.

21. Passive Immunity • This type of immunity is acquired when a doctor gives you an injection or serum; (ie.) receive antibodies from another person. • This serum contains certain anti-bodies for fighting a particular disease and is obtained by taking a sample of blood from a person or animal who has recovered from the disease or has been immunized against it. • Instead of using the entire serum, the doctors use part of it that contains most of the anti-bodies.

22. Doctors can give this to people to protect them against such diseases as measles or viral hepatitis. • Passive immunity can also occur during pregnancy. • Antibodies from the mother can pass through the placental barrier and give the newborn short-term passive immunity to some diseases. • These antibodies are also present in breast milk and can prolong passive immunity.

23. Active Immunity • This type of immunity is acquired after a certain antigen enters the body through an infection or vaccination. • Memory B cells and T cells will react to a later attack by the same antigen much more quickly than the first time around because the cells store information about the antigen and know how to better destroy it. • The killer T cells' attack will be stronger and last longer the second time around.

24. Autoimmune Disorders • An autoimmune disease is a condition in which the body’s own T cells or antibodies attacking body tissues as foreign antigens. • The actual cause of this disease is unknown and there is a tendency for such diseases to be inherited. • MS (multiple sclerosis)is a condition which affects the myelin covering of nerve fibers. • Rheumatoid arthritisis a chronic autoimmune disease that affects the bone and tissue of joints in the body. • It is characterized by inflammation of the lining of the joints. What happens is that the body’s own immune system attacks the joints causing pain, stiffness and swelling to occur. • It is a crippling form of arthritis that can affect anyone but is most common in individuals between the ages of 25 and 50. • Treatment can involve drugs such as aspirin, NSAIDs (non-steroidal anti-inflammatory drugs and steroids. • More severe cases can involve using DMARDs (disease-modifying antirheumatic drugs) and corticosteroids.

25. An Allergic Reaction • Allergies are due to another type of immune malfunction. • It is an exaggerated response by the immune system to such allergens as pollen, mould or cat dander. • Allergic reactions to food or to inhaled allergens (as in asthma) are also possible. • An allergic reaction may be immediate or delayed with the immediate or acute reaction being the most common type. An immediate reaction can occur within 30 seconds and last up to 30 minutes. • What happens is that an allergen causes specialized antibodies to trigger certain cells to release histamines. • The histamines cause the permeability of blood vessels to increase, making the area red or swollen • It can also cause the release of cellular fluids, resulting in watery eyes and a runny nose. • This is your allergic reaction.