The Immune System: Structure and Function PDF

The Immune System: Structure and 8/27/24, 6:12 PM Platform | Study Fetch Function (00:00 - 00:12) Introduction to the topic of the immune system (00:12 - 00:23) Overview of the immune system as the body's natural defense...

The Immune System: Structure and 8/27/24, 6:12 PM Platform | Study Fetch Function (00:00 - 00:12) Introduction to the topic of the immune system (00:12 - 00:23) Overview of the immune system as the body's natural defense system Will discuss innate and adaptive immunity (00:23 - 00:34) Lesson overview: Innate immunity Adaptive immunity Innate Immunity (00:34 - 00:46) Innate immunity refers to a non-specific defense mechanism against foreign invaders Has multiple different facets (00:46 - 00:58) Barriers Body's first line of defense are outer barriers: Skin Cilia in respiratory epithelium Stomach acid Symbiotic bacteria (00:58 - 01:10) Skin has sebaceous glands that secrete sebum, which has antimicrobial properties Skin is 3 layers thick to provide a barrier (01:10 - 01:21) Cilia in respiratory epithelium help sweep up mucus and particulates Mucus is then swallowed and interacts with stomach acid (01:21 - 01:36) Stomach acid has a low pH that kills many bacteria If stomach acid is reduced (e.g., with proton pump inhibitors), it can lead to increased risk of intestinal infections (01:36 - 02:02) Symbiotic bacteria in the gut outcompete potential pathogens for resources Limited resources (food, space, etc.) in the GI tract mean symbiotic bacteria can prevent infection https://www.studyfetch.com/platform/studyset/66cd116dd279f5220d947c66/material/66ce2cc6f069b6d6b89c5eb3/document?go=note 1/9  (02:02 - 02:28) 8/27/24, 6:12 PM Platform | Study Fetch Inflammatory Response Mast cells release histamine, making capillary walls more permeable Chemoattractants are released, causing immune cells to leave capillaries and enter the area (02:28 - 02:42) Signs of inflammation: Redness Heat Swelling Pain (02:42 - 03:11) Inflammatory response process: 1. Mast cells release histamine 2. Capillary walls become more permeable 3. Chemoattractants released 4. Immune cells leave capillaries and enter the area Adaptive Immunity (03:11 - 03:29) Adaptive immunity is a specific defense mechanism Will discuss this in more detail in the next part of the lesson Inflammatory Response and Immune Cells (00:03:29 - 00:03:59) Increased heat, pain, and redness are signs of an inflammatory response Leukocytes (white blood cells) are the main immune cells: Neutrophils, lymphocytes, monocytes, eosinophils, and basophils Neutrophils phagocytose pathogens and release a respiratory burst to kill them (00:03:59 - 00:04:18) Natural killer cells are part of the innate immune system and are always ready to attack infected cells using perforin and granzymes They don't need to be activated like other lymphocytes (00:04:18 - 00:04:36) Cells present peptides from within the cell on MHC (major histocompatibility complex) molecules Some viruses or infections can stop this presentation to avoid detection https://www.studyfetch.com/platform/studyset/66cd116dd279f5220d947c66/material/66ce2cc6f069b6d6b89c5eb3/document?go=note 2/9  (00:04:36 - 00:04:47) 8/27/24, 6:12 PM Platform | Study Fetch If cells downregulate MHC presentation, natural killer cells will recognize them as abnormal and kill them (00:05:03 - 00:05:14) Monocytes become macrophages when they leave the vasculature Macrophages consume pathogens, dead cells, and other debris (00:05:14 - 00:05:26) Eosinophils contain granules with enzymes that attack parasites (00:05:26 - 00:05:46) Basophils contain granules with histamine, which increases capillary permeability, and heparin, which prevents blood clots (00:05:46 - 00:06:17) Extravasation is the process where leukocytes leave the vasculature and migrate towards the site of infection or injury Leukocytes respond to chemical attractants and interact with factors on the endothelial cell wall to squeeze between the cells (00:06:17 - 00:06:45) Leukocytes follow the chemical signals to the site of damage Monocytes differentiate into macrophages to consume pathogens Eosinophils and neutrophils release chemicals to kill external threats (00:06:45 - 00:07:02) Mnemonic for relative white blood cell counts: Neutrophils, Lymphocytes, Monocytes, Eosinophils, Basophils (NLMEB) Neutrophils are the most common (40-60%) (00:07:02 - 00:07:24) When people have abnormal white blood cell counts, it can indicate an underlying condition Extravasation and Leukocyte Migration Key Points: Leukocytes leave the vasculature through a process called extravasation They respond to chemical attractants released at the site of infection/injury Leukocytes interact with factors on the endothelial cell wall to squeeze between the cells They then follow the chemical signals to the site of damage Steps of Extravasation: 1. Leukocytes in the blood respond to chemical attractants 2. Leukocytes bind to adhesion factors on the endothelial cell wall 3. Leukocytes squeeze between the endothelial cells and leave the vasculature 4. Leukocytes follow the chemical signals to the site of infection/injury White Blood Cell Types and Functions Leukocyte Types: https://www.studyfetch.com/platform/studyset/66cd116dd279f5220d947c66/material/66ce2cc6f069b6d6b89c5eb3/document?go=note 3/9  Neutrophils 8/27/24, 6:12 PM Platform | Study Fetch Phagocytose pathogens Release respiratory burst to kill pathogens Lymphocytes Include natural killer cells that attack infected cells Monocytes/Macrophages Consume pathogens, dead cells, and debris Eosinophils Contain granules with enzymes that attack parasites Basophils Contain granules with histamine and heparin Relative White Blood Cell Counts (NLMEB): 1. Neutrophils (40-60%) 2. Lymphocytes 3. Monocytes 4. Eosinophils 5. Basophils MHC Presentation and Natural Killer Cells Key Points: Cells present peptides from within the cell on MHC molecules Some pathogens can stop this MHC presentation to avoid detection If MHC presentation is downregulated, natural killer cells will recognize the cell as abnormal and kill it Natural Killer Cells: Part of the innate immune system Always ready to attack infected or abnormal cells Use perforin and granzymes to kill target cells Don't need to be activated like other lymphocytes Inflammatory Response Signs of Inflammation: Increased heat Pain Redness Purpose of Inflammation: Allows the body to recognize and respond to injury or infection Recruits immune cells to the site of damage https://www.studyfetch.com/platform/studyset/66cd116dd279f5220d947c66/material/66ce2cc6f069b6d6b89c5eb3/document?go=note 4/9  Key Inflammatory Mediators: 8/27/24, 6:12 PM Platform | Study Fetch Chemical attractants that draw leukocytes to the site Factors that allow leukocytes to extravasate and migrate Innate Immunity: Neutrophils and Dendritic Cells (00:07:24 - 00:07:35) Neutrophils can indicate a blood infection by their increased count Neutrophils help identify bacterial infections in the blood Dendritic Cells (00:07:35 - 00:07:47) Dendritic cells act as a messenger between the innate and adaptive immune systems They reside in various tissues throughout the body Dendritic cells pick up foreign material from their environment and use those fragments to teach the immune system about invaders The Complement System (00:07:47 - 00:08:20) The complement system is a group of 30 proteins that work together to enhance the immune response It is activated through a cascade of protein interactions The three pathways that activate the complement system are: Classical complement pathway Alternative complement pathway Lectin pathway Complement System Functions (00:08:20 - 00:08:47) The complement system will assemble the membrane attack complex (MAC) to punch holes in the membranes of infected cells This helps kill infected cells in the body Mnemonic for complement system functions: Histamine release Immune complex clearance Generates cytokines Helps optimize phagocytosis Creates the membrane attack complex https://www.studyfetch.com/platform/studyset/66cd116dd279f5220d947c66/material/66ce2cc6f069b6d6b89c5eb3/document?go=note 5/9  Adaptive Immunity 8/27/24, 6:12 PM Platform | Study Fetch (00:09:22 - 00:10:52) Major Histocompatibility Complex (MHC) MHC class I is found on all nucleated cells and displays self-peptides This allows the immune system to recognize "self" cells It also displays any abnormal peptides expressed within the cell MHC class II is found on antigen presenting cells (like dendritic cells) Antigen presenting cells take up proteins from their environment, process them, and display the peptides on MHC class II Lymphocytes: B Cells and T Cells Lymphocytes are the immune cells involved in adaptive immunity Antibodies recognize specific epitopes (parts of proteins) on pathogens The epitope is the specific part of a protein that an antibody binds to "Antibodies are proteins that recognize a specific part of a specific protein. Those proteins are typically found on the surface of bacteria or cells and those are going to be called epitopes." MHC Class Location Function Class I All nucleated cells Display self-peptides and abnormal peptides Class II Antigen presenting cells Display processed foreign peptides Adaptive Immunity: T Cells and B Cells Immature CD4 T Cells and CD8 T Cells (00:11:06 - 00:11:19) MHC class II molecules from antigen-presenting cells display peptides to immature CD4 T cells This interaction helps mature the CD4 T cells into helper T cells CD8 T Cells (00:11:19 - 00:11:31) MHC class I molecules are displayed to immature CD8 T cells This interaction helps mature the CD8 T cells into cytotoxic T cells https://www.studyfetch.com/platform/studyset/66cd116dd279f5220d947c66/material/66ce2cc6f069b6d6b89c5eb3/document?go=note 6/9 8/27/24, 6:12 PM Platform | Study Fetch Adaptive Immunity Lymphocytes (00:11:31 - 00:11:46) Adaptive immunity has two main types of lymphocytes: B cells and T cells T cells can be further divided into: Cytotoxic T cells (also called killer T cells) Helper T cells B Cells and Antibody Generation (00:11:46 - 00:12:09) B cells are responsible for generating antibodies B cells mature in the bone marrow, while T cells mature in the thymus Plasma cells are the mature B cells that produce antibodies CD8 Cytotoxic T Cells (00:12:22 - 00:12:34) CD8 T cells are cytotoxic and use cell-bound "antibodies" to identify and kill target cells CD4 Helper T Cells (00:12:34 - 00:12:47) CD4 T cells have a more regulatory, mediator role in modulating the immune response B Cell Clonal Selection (00:12:47 - 00:13:10) B cells undergo clonal selection based on how tightly their surface antibody binds to an antigen Tighter binding leads to B cell proliferation and clonal expansion Memory B Cells (00:13:10 - 00:13:21) Memory B cells store antigen information for decades without releasing antibodies They can quickly reactivate to produce antibodies upon re-exposure to the antigen Plasma Cells (00:13:21 - 00:13:43) Plasma cells are the mature B cells that actively produce and secrete antibodies Memory B cells can differentiate into plasma cells upon reactivation https://www.studyfetch.com/platform/studyset/66cd116dd279f5220d947c66/material/66ce2cc6f069b6d6b89c5eb3/document?go=note 7/9 8/27/24, 6:12 PM Platform | Study Fetch Antibody Structure (00:13:43 - 00:14:08) Antibodies are composed of heavy and light chains The variable regions at the ends bind to specific antigens The Immune System: Antibodies and T Cells (00:14:08 - 00:14:22) The constant region of an antibody helps with recognition by other cells The variable region of an antibody gives it specificity to a particular epitope or substrate (00:14:22 - 00:14:36) Different types of immunoglobulins (antibodies): IgM - the first to be produced, very large, does not cross the placental barrier IgA - passes to the newborn (00:14:36 - 00:14:50) IgE binds to allergens and triggers histamine release, causing anaphylactic shock IgD has an unknown function IgG can cross the placenta (00:14:50 - 00:15:03) IgG can also activate opsonization and complement (00:15:03 - 00:15:21)Mnemonic for Immunoglobulins: IgM - "IG most" (takes up the most space) IgA - "IGA" (a dimer) IgE - "IgE" (Eve has allergies) IgD - "IG don't" (unknown function) IgG - "IG go" (can cross the placenta) (00:15:21 - 00:15:33)B Cell Functions: Activate complement system Coat and neutralize antigens Tag antigens for removal (00:15:33 - 00:15:52)Mnemonic for B Cell Functions: "BC BG" (a high-end fashion company) "The fashion style is so trendy that even people compliment the coat tags" (00:16:05 - 00:16:20) T cells recognize and kill cells through their T cell receptor, which binds to antigen presented on MHC https://www.studyfetch.com/platform/studyset/66cd116dd279f5220d947c66/material/66ce2cc6f069b6d6b89c5eb3/document?go=note 8/9  (00:16:20 - 00:16:33) 8/27/24, 6:12 PM Platform | Study Fetch If MHC II presents the antigen, T cells will activate and become helper T cells If MHC I presents the antigen, T cells will activate and become cytotoxic T cells (00:16:33 - 00:16:49)Mnemonic for CD4/CD8 and MHC: CD8 x 1 = 8 (CD8 T cells recognize MHC I) CD4 x 2 = 8 (CD4 T cells recognize MHC II) (00:16:49 - 00:17:02) CD8 T cells recognize MHC I CD4 T cells recognize MHC II (00:17:02 - 00:17:20) Memory T cells persist in the body and respond quickly upon re-infection (00:17:20 - 00:17:30) You've mastered the immune system! Lots of different cell types and CDs to remember, but you've got this! https://www.studyfetch.com/platform/studyset/66cd116dd279f5220d947c66/material/66ce2cc6f069b6d6b89c5eb3/document?go=note 9/9