Chapter 29

1. Chapter 29 Viral mysteries

2. video • http://www.youtube.com/watch?v=TVLo2CtB3GA&feature=related

3. Influenza “FLU” • Fall of 1918, deadly illness around world • Disease so deadly so people died one day after getting sick/ • Most died struggling to clear their airways of blood-tinged froth. • Why did the disease move so quickly over the globe?

4. Influenza “FLU” • Flu killed more people in a year than Black Death or Black Plague (bacteria) • Killed 1/3 of European population in 1300’s • Used in 1940, WWII by Japanese • Killed more people in 24 weeks than AIDS has killed in 24 years. • Pandemic-epidemic of infectious diseases that spreads across a large region • At least 50 million people around the world die before the flu pandemic was over.

5. Viruses • Cause of the flu was a virus. Same virus that causes flu in people every year. • Most recover but still some die • Flu pandemic of 1918 was a mystery for many years. Why??? • Today we understand more about what made the flu so deadly. Still 36, 000 people die from complications each year • Mostly deaths among young children and elderly. Why?

6. What is a viruses? • A virusis an infectious particle consisting of nucleic acid surrounded by a protein shell. • Viruses are considered to be nonliving because even though all viruses have genes, they are not made of cells.

7. Viruses • In order for a virus to reproduce, it must infect a host cell in order to use the host cell’s machinery to replicate and make more viruses. • Viruses eventually destroy the host cell.

8. Viruses • Unlike cells, which rely on DNA as their hereditary material, viruses can store their genetic information in the form of either DNA or RNA. • RNA viruses are influenza virus, colds, measles, mumps, AIDS, and polio • DNA viruses include hepatitis B, chicken pox, and herpes. • Each type of virus has a characteristic shape, with a distinctive protein shell.

9. The Immune System • Some viruses cause more damage than others. The severity of any illness typically depends on how quickly theimmune systemresponds and how well the infected tissue can repair itself. • The immune system is a system of cells and tissues that acts to defend the body against foreign cells and infectious agents.

10. Virus • Cold virus • Normal recover completely. Lung cells divide to replace damaged ones • Polio virus • Attacks nerve cells. • May cause permanent damage to motor skills • People who survive will likely never contract the disease again – bodies become immune to the infection. • Today children are vaccinated against polio- disease is nonexistent in Western World. • Flu virus of 1918 • What did the autopsies how was the cause of so many people dying?

11. The Immune System • Immunityis the resistance to a given pathogen conferred by the activity of the immune system.

12. The Immune System • The body’s immune system defends the body from different kinds of pathogens– foreign particles such as viruses, bacteria, and parasites that cause an immune response.

13. The Immune System • The human immune system has two primary lines of defense that coordinate to protect us from pathogens and other harmful substances. • Innate and adaptive immunity

14. The Immune System • Innate immunityincludes nonspecific defenses, such as physical and chemical barriers and phagocytic cells, that are present from birth and are always active. • We are born with these defense mechanisms and they are always active. • Remember they are nonspecific and do not specifically recognize foreign invaders.

15. The Immune System • Adaptive immunityincludes the coordinated actions of specialized white blood cells called lymphocytes. • The adaptive response is highly diverse: it learns to respond to specific pathogens and substances. • Important to response to many types of pathogens. • Adaptive immunity confers long-lasting immunity against specific pathogens.

16. Inborn Defenses • The innate immune system starts defending at sites where the body is exposed to the outside world, and it is always present and active.

17. Inborn Defenses • Physical barriers • Enzymes in saliva, nasal hairs, mucus lines the throat • When pathogens do successfully breach physical barriers, the body tries to flush them out with more fluid – chemicals, like histamine • A molecule released by damaged tissue and during allergic reactions are released and trigger runny noses, watery eyes, coughs, and sneezes to expel the invaders.

18. Inborn Defenses • When pathogens manage to overcome chemical defenses, they begin to replicate. • Inflammatory responseis an innate defense that is activated by local tissue damage.

19. Inborn Defenses • Damaged tissues and certain bacterial and viral infections release chemicals that cause blood vessels to swell and leak fluid into surrounding tissues • Attracting various types of white blood cells to the inflamed site. • The fluid at inflamed sites also contain clotting proteins that stop the bleeding and prevent pathogens from spreading to neighboring tissues. • Swelling, pain, and redness

20. Inborn Defenses • Several different types of white blood cells contribute to our innate defenses. Phagocytes are a type of white blood cell that engulfs and ingests damaged cells and pathogens.

21. Inborn Defenses • Phagocytes include macrophagesthat reside in tissues, and neutrophils that are found in the bloodstream. • Phagocytes release killing enzymes and then bind and engulf invaders. • They can also activate the adaptive immunity.

22. Inborn Defenses • Natural killer cellsare a type of white blood cell that acts during the innate immune response to find and destroy virally infected cells and tumor cells.

23. Inborn Defenses • Virus-infected cells can produce interferon proteins that help protect adjacent cells from becoming infected. • Send out SOS

24. Inborn Defenses • Complement proteinshelp destroy pathogens by coating or puncturing them. • Flag for destruction by phagocytes

25. Inflammation Overdrive • Our innate defenses are sufficient to fight off many types of infection, but the inflammatory response can go into overdrive and destroy the very tissue it is trying to save. • Influenza virus evades the body’s physical barriers and takes up residence in the upper respiratory tract: nose, mouth, throat • Particle quickly move to other parts of the body

26. Viruses hijack’s host cell • Viruses uses the cells machinery to replicate their own genetic material. • 10 hr after a virus invades a cell, new viral particles are being releases. • 1,000 to 10,000 viral particles ready to invade other cells. • http://www.youtube.com/watch?v=Rpj0emEGShQ&feature=related • Infected cells die, weakening the respiratory tract.

28. 1918 Flu • 1997, Researcher’s found a flu victim buried in permafrost outside of Alaska • 2008 a scientists isolated the flu virus for the pandemic of 1918 • Virus had genes to allow it to penetrate the lungs more effectively • It lead to a massive inflammatory response. • Balance between define and destruction is delicate. • Immune system can destroy the organ it is trying to save. • What killed so many people of 1918?

30. 1918 • 50 million deaths • 525 million infected • Why did some survive?

31. Immunological Memory • Whereas the innate immune system is always ready to fight, the adaptive immune system must be primed over time. • With repeated exposure to infectious agents, our bodies develop a memory of every infectious agent that gets past our innate defenses. • Should we confront the same pathogen twice, immunological memory helps our bodies fight off infection before it can take hold.

32. Immunological Memory • The cells of the adaptive immune system are the B and T lymphocytes, which are produced in the bone marrow.

33. Immunological Memory • Some immature lymphocytes in bone marrow become B cells, which produce antibodies during the adaptive immune response.

34. Immunological Memory • Other lymphocytes migrate from the bone marrow to the thymus, a gland in the chest, where they become T cells. T cells can destroy infected cells or stimulate B cells to produce antibodies, depending on the type of T cell.

35. Immunological Memory • Both B cells and T cells eventually make their way to the lymph nodes and other organs of the lymphatic system, where they lie in wait for pathogens. • With these two types of immune cells, the adaptive immune system mounts a dual defense.

36. Immunological Memory • In humoral immunity, specialized T cells called helper T cells and B cells work together to recognize bacterial and viral antigens. • Humoral immunity acts by releasing antibodies that bind to antigens on free-floating pathogens • An antigen is a specific molecule (or part of a molecule) to which specific antibodies can bind, and against which an adaptive response is mounted.

37. Immunological Memory • When a helper T cell recognizes a particular antigen, it can activate a corresponding B cell. • That B cell will divide repeatedly to create an army of plasma cells – cells that secrete many copies of an antibodyspecific to that particular antigen. • An antibody is a protein that binds to antigens and either neutralizes them or flags other cells to destroy pathogens.

38. Immunological Memory • Cell-mediated immunityis a type of adaptive immunity that rids the body of altered (infected or foreign) cells.

39. Immunological Memory • In cell-mediated immunity, cytotoxic T cells recognize infected or foreign cells because these cells display foreign antigens on their surfaces. • The cytotoxic T cells bind to antigens on the altered cells and release cytotoxic chemicals that cause the altered cells to self-destruct. • Bind to and destroy infected cells in body tissues

40. Allergies • When the immune system attacks antigens from outside the body, such as those in the environment (like dust or certain types of food), an allergy is the result. • Common • Running nose, watery eyes, sneezing

41. Autoimmune Diseases • An autoimmune diseaseresults from a misdirected immune response in which the immune system mistakenly attacks healthy cells. • Multiple sclerosis, lupus, rheumatoid arthritis

42. Building a Line of Defense • First-time exposure to a pathogen will almost certainly cause illness because the adaptive response takes 7-10 days to develop.

43. Building a Line of Defense • Over time an exposed individual will recover as T and B cells are activated and antibody levels increase. This initial slow response is the primary response.

44. Building a Line of Defense • Some B and T cells become memory cells– a long-lived B or T cell that is produced during the primary response and that is rapidly activated in the secondary response. • These memory cells remain in the bloodstream and “remember” the infection.

45. Building a Line of Defense • The next time the same pathogen is encountered, memory B and T cells become active, dividing rapidly and producing very high levels of antibodies. • They fight the specific pathogen so quickly that the illness usually doesn’t occur a second time. This rapid reaction is called the secondary reaction.

46. Building a Line of Defense • Vaccineswork due to the secondary response. • The source of all vaccines is the pathogen itself. Dead, weakened, live • The goal of a vaccine is to create a primary response in the body that’s strong enough to create memory cells, yet weak enough not to cause disease symptoms. • If the pathogen is subsequently encountered naturally, the secondary response is prepared.

47. Antigenic Drift and Antigenic Shift • Mutation and gene exchange are two mechanisms by which viruses can change.

48. Antigenic Drift and Antigenic Shift • Antigenic driftis the gradual accumulation of mutations that causes small changes in the antigens on the virus surface. Antigenic drift explains why there can be different types, or strains, of a virus circulating at the same time.

49. Antigenic Drift and Antigenic Shift • Antigenic shiftrefers to changes in antigens that occur when viruses exchange genetic material with other strains. • This does not simply create a small change in viral gene sequence: it introduces an entirely new allele, and therefore an entirely new antigenic protein. • Antigenic shift is responsible for widespread pandemics.