Class 20 Immune System Biology Notes PDF

Class 20 Immune System Unit 4  Chapter 23 The Immune System Prepared by Wendi A. Roscoe, Fanshawe College Copyright...

Class 20 Immune System Unit 4  Chapter 23 The Immune System Prepared by Wendi A. Roscoe, Fanshawe College Copyright © 2020 Nelson Education Ltd. 2 23.1 Overview of the Immune System: Functions Drains excess interstitial fluid from interstitial space into lymphatic vessels, then returns it to bloodstream Transports dietary fats and fat-soluble vitamins from small intestine to bloodstream Recognizes and kills infectious organisms, including bacteria, viruses, fungi, and parasites Recognizes and tolerates our own cells, as well as non-harmful foreign molecules such as food and environmental substances Produces immunological memory cells that prevent infection from the same organism in the future Copyright © 2020 Nelson Education Ltd. 3 23.1 Overview of the Immune System Copyright © 2020 Nelson Education Ltd. 4 23.2 Anatomy of the Lymphatic System Copyright © 2020 Nelson Education Ltd. 5 23.2 Anatomy of the Lymphatic System Fluid accumulates in the interstitial fluid and can cause edema (swelling). Causes of fluid buildup Increased capillary hydrostatic pressure Kidneys not functioning properly Valve failure—high pressure in veins Lack of skeletal muscle contraction (e.g., patients who are bedridden) Medications Decreased plasma proteins Blocked lymphatic vessels Copyright © 2020 Nelson Education Ltd. 6 23.2 Anatomy of the Lymphatic System Copyright © 2020 Nelson Education Ltd. 7 23.2 Anatomy of the Lymphatic System Bone marrow contains hematopoietic stem cells that differentiate into red and white blood cells and platelets. B cells undergo a maturation process. Thymus contains thymocytes (immature T cells) that undergo a maturation process to eliminate any cells that recognize “self” antigens. Mature B and T cells that are “tolerant” of self-antigens migrate to the lymph nodes and react only to specific infections that match their specific receptors. Copyright © 2020 Nelson Education Ltd. 8 23.2 Anatomy of the Lymphatic System Lymph nodes contain immune cells that recognize and fight infections, some toxins, and dead cells carried in the lymph. Lymph nodes are located in larger numbers in areas where microorganisms can enter the body, such as the ears, mouth, lungs, urogenital region, and digestive tract, as well as near mammary glands. Copyright © 2020 Nelson Education Ltd. 9 23.2 Anatomy of the Lymphatic System Copyright © 2020 Nelson Education Ltd. 10 23.2 Anatomy of the Lymphatic System Spleen Red pulp contains macrophages, red blood cells, and platelets. It is the location of the breakdown of old red blood cells. White pulp contains lymphocytes, macrophages, and dendritic cells involved in the adaptive immune response. Lymphatic nodules Similar to lymph nodes except not surrounded by a capsule Examples: tonsils, adenoids, Peyer’s patches located around small intestines, gut-associated lymphoid tissue (GALT) Copyright © 2020 Nelson Education Ltd. 11 23.2 Anatomy of the Lymphatic System Copyright © 2020 Nelson Education Ltd. 12 23.3 Innate Immune Response First line of defence Skin provides protection from foreign invaders in several ways. The skin and mucus provide a physical barrier. Mucous membranes are found in the digestive system and respiratory system. There are specialized immune cells throughout the layers of the skin; some detect invasion and some destroy invaders. When a foreign pathogen (bacteria, virus, fungus, or parasite) enters the body, the immune system detects foreign proteins on the surface of the pathogen; these are called antigens. Note: Antigens can also be peptides, lipoproteins, glycoproteins, or carbohydrates. Copyright © 2020 Nelson Education Ltd. 13 23.3 Innate Immune Response The skin provides chemical defences as well as physical defences. Oil glands (sebaceous) make the skin surface very acidic. Sweat contains the enzyme lysozyme, which attacks and digests the cell walls of many bacteria (not normal flora). Lysozyme is also present in tears. Copyright © 2020 Nelson Education Ltd. 14 23.3 Innate Immune Response The linings of the digestive and respiratory tracts provide potential routes of entry for microbes. They also have the following mechanisms to prevent infection: Lysozyme is present in saliva. Hydrochloric acid and digestive enzymes provide protection in the digestive tract. Sticky mucus traps most microorganisms in the respiratory tract, and cilia continually move mucus up toward the throat. Resident bacteria—normal flora in the digestive tract—help prevent infections. Copyright © 2020 Nelson Education Ltd. 15 23.3 Innate Immune Response Second line of defence When a pathogen crosses the boundaries of the skin or mucous membranes, an infection occurs; then, cellular and chemical defences come into play. Cells that kill invading microbes Proteins that kill invading microbes The inflammatory response The temperature response Copyright © 2020 Nelson Education Ltd. 16 23.3 Innate Immune Response Copyright © 2020 Nelson Education Ltd. 17 23.3 Innate Immune Response Copyright © 2020 Nelson Education Ltd. 18 23.3 Innate Immune Response Copyright © 2020 Nelson Education Ltd. 19 23.3 Innate Immune Response Interferons are produced in cells infected by viruses or bacterial toxins. Once interferons are formed in the infected cell, the cell secretes them to the surrounding area. The neighbouring (uninfected) cells are warned by the interferons and, therefore, produce proteins that inhibit viral replication if they are infected. Interferons activate natural killer cells in infected areas. They can activate p53. (Do you recall what this is?) They are partly responsible for making you feel unwell when you are sick. Copyright © 2020 Nelson Education Ltd. 20 23.3 Innate Immune Response Copyright © 2020 Nelson Education Ltd. 21 23.3 Innate Immune Response The complement system consists of approximately 20 different proteins that circulate freely in the plasma (made in liver) in an inactive state until they encounter either a fungal or bacterial cell wall. They activate to form a membrane attack complex that forms a pore opening in the foreign cell’s membrane, causing water to rush in and burst the cell. The complement system is also triggered by antibodies. It facilitates phagocytosis. Copyright © 2020 Nelson Education Ltd. 22 23.3 Innate Immune Response Copyright © 2020 Nelson Education Ltd. 23 23.3 Innate Immune Response Copyright © 2020 Nelson Education Ltd. 24 23.3 Innate Immune Response 1. Mast cells and basophils release histamine and prostaglandins in damaged tissues. 2. These chemicals cause vasodilation and make capillaries more permeable in order to allow white blood cells to enter the tissue (the reason for redness and swelling). Prostaglandins activate pain sensors (and cause aching when sick). 3. Neutrophils and macrophages kill microbes and engulf dead cells. Pus is a mixture of dead cells and white blood cells. What are the symptoms of inflammation? Redness, pain, swelling, heat Copyright © 2020 Nelson Education Ltd. 25 23.3 Innate Immune Response When macrophages attack, they send a signal to the hypothalamus to raise body temperature, causing fever. Some pathogens can secrete toxins that act as pyrogens, triggering the brain to increase body temperature. A fever curbs microbial growth but can be dangerous if the body temperature is too high because it begins to inactivate the body’s cellular enzymes. A fever up to 39°C is beneficial. A fever of 40°C should be treated with an antipyretic. A fever over 42°C can be fatal. Copyright © 2020 Nelson Education Ltd. 26 23.3 Innate Immune Response Copyright © 2020 Nelson Education Ltd. 27 23.4 Adaptive Immune Response Cells involved in adaptive immune response B cells Plasma cells Helper T cells Cytotoxic T cells Regulatory T cells Copyright © 2020 Nelson Education Ltd. 28 23.4 Adaptive Immune Response: Antigen Recognition Monocytes are in constant circulation in the bloodstream. When monocytes encounter a pathogen, they differentiate into macrophages. Macrophages have a very long lifespan (months to years), whereas neutrophils only live for a few hours. Macrophages recognize pathogens by pathogen-associated molecular patterns (PAMPs), which are not found on human cells. Macrophages phagocytose and digest microbes, and then display the digested microbe proteins on their cell surfaces to alert other immune cells. This is called antigen presentation. Copyright © 2020 Nelson Education Ltd. 29 23.4 Adaptive Immune Response: MHC The MHC I protein is found on all cells in the body and allows the immune system to recognize one’s own cells. Antigen-presenting immune cells (macrophages and dendritic cells) have MHCI and MHC II surface proteins, which are important for “presenting” antigens to lymphocytes, which then activate the lymphocytes (B cells and T cells). Copyright © 2020 Nelson Education Ltd. 30 23.4 Adaptive Immune Response Copyright © 2020 Nelson Education Ltd. 31 23.4 Adaptive Immune Response Lymphocytes are white blood cells that are critical to the specific immune response. T cells Originate in the bone marrow but migrate to the thymus gland for maturation during embryonic development Recognize microorganisms and viruses by the specific antigens on their surfaces B cells Complete their maturation in the bone marrow and, when an antigen is encountered, differentiate into plasma cells and secrete antibodies Coat the antigen and mark the cell bearing that antigen for destruction Copyright © 2020 Nelson Education Ltd. 32 23.4 Adaptive Immune Response The T cell response is also called the cell-mediated response. CD4+ helper T cells secrete cytokines to activate B cells, cytotoxic T cells, NK cells, and macrophages. CD8+ cytotoxic T cells destroy virus-infected cells, cancer cells, and transplant tissue cells with perforin. Suppressor or regulatory T cells inhibit B cells and T cells. Cytotoxic T cells generally fight intracellular infections by killing the infected cells. Copyright © 2020 Nelson Education Ltd. 33 23.4 Adaptive Immune Response Copyright © 2020 Nelson Education Ltd. 34 23.4 Adaptive Immune Response: Helper T Cells Copyright © 2020 Nelson Education Ltd. 35 23.4 Adaptive Immune Response: Cell-Mediated When macrophages process the foreign antigens to trigger the cell- mediated response the activated helper T cells secrete interleukin-2 (IL-2); IL-2 stimulates the proliferation of cytotoxic T cells, which destroy infected body cells (perforin); cytotoxic T cells kill cells that are infected and are displaying antigen on MHC I; and activated cells continue to proliferate and clone themselves until the viral infection is killed. Copyright © 2020 Nelson Education Ltd. 36 23.4 Adaptive Immune Response: Cell-Mediated Copyright © 2020 Nelson Education Ltd. 37 23.4 Adaptive Immune Response Helper T cells differentiate into subtypes of helper T cells. TH1 cells increase activation of cytotoxic T cells in the case of viral infection. TH2 cells increase activation of B cells in the case of a bacterial infection. Some helper T cells will become memory cells. Some helper T cells can become regulatory T cells, also called TH17, that slow down the immune response and prevent reactions against any self-antigens. Some become tolerant (TH0) and do not react to antigens—specifically, with high exposure to an antigen, such as food, normal flora bacteria, and harmless environmental molecules. Copyright © 2020 Nelson Education Ltd. 38 23.4 Adaptive Immune Response: Humoral B cells differentiate into plasma cells when activated by an infectious organism, then secrete antibodies (specific for that infection). The B cell response is also called the humoral immune response. B cells and antibodies fight any extracellular infection (bacteria, viruses outside of cells, parasites, fungi, and toxins produced by bacteria). Copyright © 2020 Nelson Education Ltd. 39 23.4 Adaptive Immune Response: Humoral Activated B cells can bind to free, unprocessed antigens, and antigen particles enter the B cell by endocytosis. Antigens are then processed and placed on the surface complexed with MHC II proteins. (Recall that B cells are also antigen-presenting cells.) Helper T cells that are able to recognize the specific antigen bind to the antigen-MHC II protein complex and release interleukin-2 (IL-2), which furthers the immune response. Copyright © 2020 Nelson Education Ltd. 40 23.4 Adaptive Immune Response: Humoral Copyright © 2020 Nelson Education Ltd. 41 23.4 Adaptive Immune Response: Humoral Copyright © 2020 Nelson Education Ltd. 42 23.4 Adaptive Immune Response: Humoral Copyright © 2020 Nelson Education Ltd. 43 23.4 Adaptive Immune Response: Memory Cells As a result of the first infection, a large clone of lymphocytes that can recognize a pathogen remains (B cell and T cell memory cells). The secondary immune response is a more effective response when the pathogen is encountered again. Most of the time, you will not even know that your immune system is fighting a pathogen that it already recognizes. Copyright © 2020 Nelson Education Ltd. 44 23.4 Adaptive Immune Response Copyright © 2020 Nelson Education Ltd. 45