Lecture 10 Immune System Lecture 10 1. Introduction 2. Nonspecific External Defenses 3. Innate Immune Response 4. Acquired Immune Response 5. Antibiotics and Vaccines 1
The not-so-common cold A cold is an infection of the mucus membranes of the respiratory tract by a rhinovirus. Over 100 rhinoviruses have been identified, which is one reason why we don t become immune to the cold. Virus vs. Bacteria Colds and influenza are caused by viruses. Rhinovirus Viruses are non-living particles that contains genetic material, they hijack your cells to reproduce. Viruses cannot be killed with antibiotics. Influenza virus 2
Virus vs. Bacteria Bacteria are living organisms that have a metabolism, have DNA, and can reproduce on their own. E. coli Bacteria can be killed with antibiotics. Streptococcus Fungi, Protista, & Worms! 3
Immune System Viruses, bacteria, fungi, protists, and worms are everywhere. Some of them want to invade your body. How does your body defend itself against them? Viruses and Bacteria Immune System: Body Defenses 4
Defense Against Disease 1. Nonspecific External Barriers 2. Innate Immune System 3. Acquired (Adaptive) Immune System Nonspecific External Barriers 5
First Line of Defense Non-Specific External Defenses are designed to prevent infections by viruses and bacteria from entering the body. These include: Intact skin Saliva in Mouth Stomach Acid Small Intestine Bile Mucus and Cilia Cough Reflex The Skin Dead skin cells are constantly sloughed off, making it hard for invading bacteria to colonize. Sweat and oils contain antimicrobial chemicals, including some antibiotics. 6
Saliva Mucus and Cilia Mucus contains special enzymes that destroy bacterial cell walls. The normal flow of mucus washes bacteria and viruses off of mucus membranes. Cilia in the respiratory tract move mucus out of the lungs to keep bacteria and viruses out. 7
Cough Reflex Coughing ejects mucus and foreign matter from the lungs. Coughs may be voluntary, but more often in response to stimulation of receptors in the respiratory tract. Low ph. Stomach acid prevents bacterial and fungal growth. Stomach Acid When it is properly acidic, bacteria that are ingested along with food don t stand a chance. It acts as an acid buffer to protect the body from pathogens. 8
Innate Immune System Innate Immune System Innate Immune System (IIS) comprises the cells and mechanisms that defend the host from infection by other organisms. IIS provides immediate defense against infection. The cells of the innate system recognize and respond to pathogens in a generic way, but, IIS does not confer long-lasting or protective immunity to the host. 9
Ouch! 1. Inflammation Acute inflammatory response is the body s initial reaction to tissue damage. 1. Wound occurs! 2. Wounded cells secrete chemicals that stimulate release of histamine. 3. Histamine causes fluids to collect around an injury to dilute toxins. This causes swelling. 4. The temperature of the tissues may rise, which can kill temperature-sensitive microbes. 10
2. Phagocytes Phagocytes are several types of white blood cells (including macrophages and neutrophils) that seek and destroy invaders. Phagocytes are attracted by an inflammatory response of damaged cells. 3. Natural Killer Cells Are white blood cells that recognize and destroy virus-infected cells or those that have become cancerous 11
Fever Fever is a defense mechanism that can destroy many types of microbes. While high fevers can be dangerous, some doctors recommend letting low fevers run their course without taking aspirin or ibuprofen. Acquired (Adaptive) Immune System 12
Acquired Immune System AIS gives us immunity to certain diseases. In the AIR, the immune system forms a chemical memory of the invading microbe. If the microbe is encountered again, the body reacts so quickly that few or no symptoms are felt. Some Vocabulary: Antigen (Pathogen) - any substance that causes an immune system to produce antibodies against it (e.g. bacteria, virus, etc.). Antibody - a protein produced by the human immune system to tag and destroy invasive microbes. 13
Acquired Immune System Lymphocytes - Main players of the acquired immune system They are white blood cells that circulate in the bloodstream and lymphatic system Two different types: T Cells (T Lymphocytes) B Cells (B Lymphocytes) Acquired Immune System T Cells - 3 types: Helper T Cells - detect the invading pathogen and trigger production of killer T cells Killer T Cells - attack and kill invading pathogen and infected body cells Suppressor T Cells - slow down and halt the immune response when the threat has been handled 28 14
Helper T Cells The Helper T-Cell is the key cell to signal an immune response. If helper T-cells are disabled, the immune system will not respond. AIDS Helper T-Cells are disabled B Cells - a type of lymphocyte (white blood cell) that monitor the blood and tissue fluids for antigens. Following the body s first exposure to a pathogen, the B Cells have a memory of the pathogen When they encounter a specific invading pathogen again, they produce antibodies - proteins that bind to specific invader (antigen) Killer T-Cells recognize the antibodies and will kill the pathogen that is tagged with them. 30 15
Antibodies Antibodies released into the blood stream will bind to the antigens (pathogens) that they are specific for. Antibodies may disable some microbes, or cause them to stick together (agglutinate). They tag microbes so that the microbes are quickly recognized by the Killer t-cells. Let s put it all together 1. Antigen invades body for the first time you get sick 2. T-helper cells recognize threat and trigger the T-killer cells 3. B-cells produce antibodies that mark the antigen so that the t-killer cells know which cells to attack. 4. Once the t-killer cells have the upper hand, the t-suppressor cells go into action and begin shutting down the immune response. 5. Your immune system now has a memory of the antigen/pathogen. If the pathogen ever invades again, your immune system is ready to defend your body against it. When/if it does invade, you never know it 16
Immunity After surviving infection by a pathogen, a person often acquires immunity to future infections by the same pathogen B and T cells become memory cells when exposed to an infectious agent, allowing recognition and quick action to destroy the invader before the illness begins 33 Human Assist Antibiotics and Vaccines 17
Helping the immune system Medical science has created to systems for augmenting the human immune system: Antibiotics Vaccines How antibiotics work Antibiotics help destroy bacteria (but not viruses). Antibiotics work in one of several ways: Slowing bacteria reproduction. Interfering with bacterial cell wall formation. 18
Antibiotic myths Antibiotics are not antibodies. Antibiotics do not weaken our immune system. They help it by weakening bacteria. Humans do not become immune to antibiotics. Bacteria that resist antibiotics and are not completely destroyed may multiply, producing more antibioticresistant bacteria. How vaccines work Modern vaccines are created from killed bacteria or viruses, or fragments of proteins from these microbes. The proteins are recognized as antigens by our immune systems. This causes a mild immune response. Memory T-cells and B-cells remain ready to fight off the illness if it is encountered again. 19
How vaccines work Vaccine myths The flu vaccine does not give you the flu. Some people get the vaccine too late, or catch a cold and think they have the flu. Vaccines are not less effective than a natural infection with the illness. The immunity is the same, and a mild response to a vaccine is much less risky than a full-blown infection of measles. There is NO link between vaccines and autism. 20
Vitamin C for colds? Vitamin C is necessary for many body functions. Absorption of Vitamin C increases during illness. It also has a very slight antihistamine effect. Vitamin C won t cure a cold, but may support some aspects of immune response. Some studies have shown that moderate use of zinc lozenges slightly decreases the duration and severity of colds. However, too much zinc can suppress the immune system, and can reach toxic levels. Zinc nasal sprays can destroy olfactory receptors. Zinc for colds? 21
Vitamin D for colds? New research suggests that Vitamin D plays a role in immune response, and may be critical for fighting off viruses. Vitamin D is fat-soluble and can accumulate to toxic levels. A blood test can determine if a person needs to take Vitamin D. Echinacea for colds? Echinacea is supposed to strengthen the immune system. Studies in petri dishes showed Echinacea stimulated white blood cells to produce more virus-killing peroxides, but controlled human trials have not had consistent results. 22