Transcript Chapter 29
Chapter 29 Viral mysteries video • http://www.youtube.com/watch?v=TVLo2CtB 3GA&feature=related 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? 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. 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? What is a viruses? • A virus is 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. 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. 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. The Immune System • Some viruses cause more damage than others. The severity of any illness typically depends on how quickly the immune system responds 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. 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? The Immune System • Immunity is the resistance to a given pathogen conferred by the activity of the immune system. 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. 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 The Immune System • Innate immunity includes 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. The Immune System • Adaptive immunity includes 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. 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. 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. Inborn Defenses • When pathogens manage to overcome chemical defenses, they begin to replicate. • Inflammatory response is an innate defense that is activated by local tissue damage. 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 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. Inborn Defenses • Phagocytes include macrophages that 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. Inborn Defenses • Natural killer cells are a type of white blood cell that acts during the innate immune response to find and destroy virally infected cells and tumor cells. Inborn Defenses • Virus-infected cells can produce interferon proteins that help protect adjacent cells from becoming infected. • Send out SOS Inborn Defenses • Complement proteins help destroy pathogens by coating or puncturing them. • Flag for destruction by phagocytes 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 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&fe ature=related • Infected cells die, weakening the respiratory tract. 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? 1918 • 50 million deaths • 525 million infected • Why did some survive? 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. Immunological Memory • The cells of the adaptive immune system are the B and T lymphocytes, which are produced in the bone marrow. Immunological Memory • Some immature lymphocytes in bone marrow become B cells, which produce antibodies during the adaptive immune response. 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. 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. 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. 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 antibody specific to that particular antigen. • An antibody is a protein that binds to antigens and either neutralizes them or flags other cells to destroy pathogens. Immunological Memory • Cell-mediated immunity is a type of adaptive immunity that rids the body of altered (infected or foreign) cells. 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 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 Autoimmune Diseases • An autoimmune disease results from a misdirected immune response in which the immune system mistakenly attacks healthy cells. • Multiple sclerosis, lupus, rheumatoid arthritis 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. 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. 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. 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. Building a Line of Defense • Vaccines work 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. Antigenic Drift and Antigenic Shift • Mutation and gene exchange are two mechanisms by which viruses can change. Antigenic Drift and Antigenic Shift • Antigenic drift is 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. Antigenic Drift and Antigenic Shift • Antigenic shift refers 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.