Lesson 17
Immune System Overview
Core Components
Adenoids
Tonsils
Bone Marrow
Skin
Mucosa
Thymus
Spleen
Lymph Nodes
White Blood Cells
Learning Objectives
Describe the human body's innate defenses.
The innate defenses include physical barriers like skin and mucous membranes, internal defenses such as inflammation, phagocytic cells, and natural killer cells, as well as physiological responses like fever. These defenses respond quickly and non-specifically to pathogens.
Summarize the inflammatory response.
The inflammatory response is triggered by injury or infection and involves chemical alarm systems that lead to vasodilation and increased capillary permeability, resulting in redness, warmth, swelling, pain, and potential loss of function. Key players include neutrophils and monocytes that mature into macrophages to aid in recovery.
Describe the organs and tissues of the lymphatic system and their roles in immunity.
The lymphatic system includes the spleen, thymus, lymph nodes, and mucosa-associated lymphoid tissue (MALT). These structures serve as sites for the production and maturation of immune cells, filtering pathogens, and facilitating the activation of lymphocytes.
Distinguish between two parts of the adaptive immune response: humoral and cellular immunity, and identify the cell types involved in each.
Humoral immunity is mediated by B cells and involves the production of antibodies that target free pathogens, while cellular immunity involves T cells, specifically Helper T cells and Cytotoxic T cells, which target infected or cancerous cells directly.
Describe the structure and function of antibodies.
Antibodies, or immunoglobulins, are Y-shaped proteins produced by plasma cells. They consist of heavy and light chains and function to bind to specific antigens, marking them for destruction or neutralization by other immune components.
Explain what may happen when the immune system malfunctions.
When the immune system malfunctions, it can lead to autoimmune diseases, where the body attacks its own tissues, or inadequate immune responses, leading to increased susceptibility to infections or cancers. Examples include rheumatoid arthritis and multiple sclerosis.
Key Terms
Adaptive Immunity: A specific immune response that adapts to particular pathogens and retains memory for faster responses upon subsequent exposure.
Allergens: Substances that cause allergic reactions by triggering inappropriate responses from the immune system.
Allergy: An abnormal immune response to a substance (allergen) that is harmless to most individuals, leading to various symptoms.
Anaphylaxis: A severe, potentially life-threatening allergic reaction that requires immediate medical attention, characterized by difficulty breathing, swelling, and a drop in blood pressure.
Antibodies: Proteins produced by plasma cells that specifically bind to antigens to neutralize or eliminate them.
Antigen: Any substance that triggers an immune response, recognized as foreign by the immune system.
Antigen Presenting Cells (APC): Cells that capture, process, and present antigens to T cells, facilitating the activation of the adaptive immune response.
Antigen-Specific: A descriptor for immune responses that target a unique antigen, distinguishing them from nonspecific reactions.
Antihistamines: Medications that block the effects of histamine, used to relieve allergy symptoms.
Apoptosis: Programmed cell death, a process that eliminates damaged or unnecessary cells in a controlled manner.
Autoimmunity: A condition where the immune system mistakenly attacks the body’s own tissues, mistaking them for foreign invaders.
Autoimmune Disorders: Diseases resulting from the immune system's inappropriate response against its own cells, such as rheumatoid arthritis and lupus.
B Cells: A type of lymphocyte that matures in the bone marrow and produces antibodies as part of the humoral immune response.
Basophils: A type of white blood cell that releases histamines and contributes to inflammatory responses and allergic reactions.
Bone Stem Cells: Undifferentiated cells in the bone marrow that can develop into various types of blood cells, including immune cells.
Cell-Mediated Immunity: An immune response involving T cells that directly attack infected or cancerous cells.
Cytokines: Small proteins released by cells that have a specific effect on the interaction and communication between cells in the immune response.
Cytotoxic T Cells: A type of T cell that directly kills infected or cancerous cells.
Dendritic Cell: An antigen-presenting cell that captures, processes, and presents antigens to T cells, acting as a bridge between innate and adaptive immunity.
Eosinophil: A white blood cell involved in combating parasitic infections and allergic reactions.
Epitope: The specific part of an antigen that is recognized and bound by an antibody or T cell receptor.
Helper T Cells: A type of T cell that orchestrates the immune response by activating B cells and other immune cells.
Heavy Chains: The larger chains of antibodies that determine their class and biological properties.
Histamines: Chemicals released by mast cells and basophils during allergic reactions that cause inflammation and other symptoms.
Humoral Immunity: An aspect of the adaptive immune response involving the production of antibodies by B cells in response to antigens.
Human Leukocyte Antigens (HLAs): Molecules on cell surfaces that help the immune system distinguish self from non-self, important for organ transplant compatibility.
Immediate Hypersensitivity: An exaggerated immune response that occurs rapidly after exposure to an allergen, leading to allergic reactions.
Immunizations: The process of inducing immunity through vaccination, exposing the immune system to a harmless form of an antigen.
Immunoglobulins: Another term for antibodies that are produced in response to antigens.
Immunology: The branch of medical science that deals with the immune system and its responses to pathogens.
Inflammation: A localized physical condition characterized by redness, swelling, heat, and pain, as a response to injury or infection.
Innate Immunity: The body's first line of defense against pathogens, consisting of physical barriers and immune cells that respond quickly and nonspecifically.
Leukocytes: White blood cells that are essential components of the immune system, involved in protecting the body against infections.
Light Chains: The smaller chains of antibodies that pair with heavy chains to form the complete antibody structure.
Lymphocytes: A subset of leukocytes that are crucial for the adaptive immune response; includes B cells and T cells.
Lymphoid Organs: Organs such as the thymus, spleen, and lymph nodes that play critical roles in the immune response and lymphocyte maturation.
Macrophages: Large phagocytic cells that engulf and digest pathogens and also function as antigen-presenting cells.
Major Histocompatibility Complex (MHC) Class I and II: Molecules on cell surfaces that present antigens to T cells; Class I presents to cytotoxic T cells, while Class II presents to helper T cells.
Mast Cells: Cells located in tissues that release histamines and other chemicals when activated, playing a key role in allergic reactions.
Memory B Cells: Long-lived B cells that remain after an infection has been cleared, enabling faster and more effective responses upon re-exposure to the same antigen.
Memory T Cells: Long-lived T cells that remember past infections and provide rapid responses upon re-exposure.
Microbiome: The collection of microorganisms residing in a specific environment of the body, which can influence immune responses.
Monocytes: Large white blood cells that differentiate into macrophages and dendritic cells when they migrate into tissues.
Mucosa-associated Lymphoid Tissue (MALT): Lymphoid tissue associated with mucosal surfaces, playing a role in immune responses to mucosal pathogens.
Mucous Membranes: Protective tissues that serve as a barrier against pathogens at various entry points in the body.
Natural Killer Cells: A type of lymphocyte that can recognize and kill virally infected cells or tumor cells without prior sensitization.
Neutrophils: The most abundant type of white blood cell, important for the early stages of inflammation and fighting infections through phagocytosis.
Naive B Cell: An immature B cell that has not yet encountered its specific antigen.
Naive Cytotoxic T Cell: An immature cytotoxic T cell that has not yet encountered its specific antigen.
Pathogen: Any harmful microorganism capable of causing disease, such as bacteria, viruses, fungi, or parasites.
Perforins: Proteins released by cytotoxic T cells that create pores in target cell membranes, leading to cell death.
Phagocyte: A type of immune cell that engulfs and digests pathogens and debris.
Phagocytosis: The process by which phagocytes engulf and digest pathogens and cellular debris.
Plasma B Cells: Activated B cells that are fully differentiated and produce large quantities of antibodies.
Primary Response: The initial immune response following the first exposure to an antigen, characterized by slower production of antibodies.
Secondary Response: A faster and more robust immune response upon re-exposure to the same antigen, due to memory cells.
Suppressor T Cells: A type of T cell that regulates or suppresses the immune response to maintain homeostasis and prevent autoimmunity.
T Cell Receptor: A molecule on T cells that recognizes and binds to specific antigens presented by MHC molecules.
T Cells: A type of lymphocyte that plays a central role in cell-mediated immunity and modulates the immune response.
Thymus Gland: An organ where T cells mature and differentiate, essential for the adaptive immune response.
Vaccination: The process of administering a vaccine to induce an immune response without causing disease, providing immunity against specific pathogens.
Vertebrate Immune System
Overview of Immune System
Innate Immune System
Recognition of traits shared by broad ranges of pathogens using a small set of receptors.
Non-specific and relies on shared traits of pathogens.
Relatively rapid response.
Adaptive Immune System
Recognition of traits specific to particular pathogens using a vast array of receptors.
Slower response but rapid secondary response.
Characteristics of the Immune Systems
Innate Immunity: Offers primary defense and primes for adaptive immunity.
Barrier Defenses: Skin, hair, cilia, mucus membranes.
Internal Defenses: Digestive enzymes, stomach acid, phagocytotic cells, natural killer cells, antimicrobial proteins, inflammatory response.
Adaptive Immunity:
Humoral Response: Antibodies defend against infections in body fluids.
Cell-mediated Response: Cytotoxic cells defend against infections in body cells.
Cells of the Immune System (Leukocytes)
Helper T Cell
Recognizes foreign peptides on antigen-presenting cells and induces cytokine release that activates B cells or macrophages.
Cytotoxic T Cell
Specifically recognizes and kills altered-self cells, including virally infected or tumor cells.
B Cell
Binds specific soluble antigens with its membrane-bound antibody; serves as an antigen-presenting cell to Helper T cells; differentiates into plasma and memory B cells upon activation.
Natural Killer Cell (NK Cell)
Rapidly recognizes and kills virally infected or tumor cells by creating pores in the infected cell's membrane and secreting self-destruct signals.
Monocyte
Precursor of macrophages, located in blood.
Macrophage
A phagocytic tissue cell that serves as an antigen-presenting cell to Helper T cells.
Eosinophil
Important for the elimination of parasites and involved in chronic inflammatory diseases.
Neutrophils
A phagocytic cell that is found in blood in large numbers and attracted to tissues during inflammation.
Mast Cell
Located primarily under mucosal surfaces; releases mediators such as histamine that promote inflammation.
Basophil
A circulating cell that releases mediators like histamine promoting inflammation.
Dendritic Cell
Important antigen-presenting cell to naive Helper T cells; involved in innate and adaptive immunity by binding to pathogens and causing the release of cytokines.
Innate Immunity: Inflammatory Response
Chemical Alarm Systems: Activated by injury or infection.
Key Chemicals: Histamine, Prostaglandins; lead to:
Vasodilation
Increased capillary permeability
Resulting in swelling, pain, and potential loss of function.
Cell Recruitment: Involvement of Neutrophils and Monocytes that mature into macrophages.
Cytokine Release: Interleukin-1 signals hypothalamus, increasing body temperature.
Hallmarks: Redness, warmth, swelling (edema), pain, potential loss of function.
Functions: Chemicals released cause vasodilation and promote phagocytosis.
Characteristics of Adaptive Immunity
Specificity: Targeted immune responses.
Diversity: Vast repertoire of antigen receptors.
Memory: Secondary responses are faster and stronger.
Self vs. Non-self: Immune system avoids attacking host tissues.
Adaptive Immune Response
Humoral Immunity - B Cells
Maturation: Occurs in bone marrow.
Targets: Free pathogens using antibodies to combat infections.
Key Cell Types: B cells, Plasma cells, Memory B cells.
Cell-Mediated Immunity - T Cells
Maturation: Occurs in the thymus.
Targets: Infected cells, cancer cells, transplant tissues; induces apoptosis in those cells.
Key Cell Types: Helper T cells, Cytotoxic T cells, Memory cytotoxic T cells.
Antigen Presentation
APCs: Antigen-presenting cells become activated after encountering pathogens; present parts of the pathogen to lymphocytes in secondary lymphoid organs (lymph nodes, spleen, MALT).
Antigens and Antibodies
Antigen: Parts of cells recognized by white blood cells; serves as an ID card for pathogens.
Antibody: Protein produced by plasma cells that bind to antigens; known as immunoglobulin (Ig) and produced after stimulation by antigens.
Humoral Immunity and Antibody Production
Activation: B cell activated by helper T cell, clones itself, leading to the formation of memory B cells and plasma cells that produce antibodies (immunoglobulins).
Cell-Mediated Immunity
Cytotoxic T Cells
Clonal expansion leads to activation and cell-mediated response.
Mechanism: Apoptosis of infected cells enhanced through MHC interaction and secretion of proteins to destroy infected targets.
Immunological Memory
Primary Response: Slow response involving generation of plasma cells and T cells.
Secondary Response: Rapid response aided by memory cells leading to more efficient action.
Vaccines and Flu Shots
Purpose: Stimulate adaptive immunity artificially; involve altered pathogens or genetic material; do not cause disease.
Boosters: Sometimes required to strengthen memory cell response.
Flu Shot: Remixed annually based on flu virus mutations, illustrating the challenges in rapidly mutating viruses.
Benefits of Vaccination
Provides protection against contagious diseases, including those with high mortality rates.
Prevents spread to individuals unprotected (e.g., young infants, compromised immune systems).
Contributes to eventual disease eradication, exemplified by smallpox eradication.
HIV Infections and Immunosuppression
HIV Mechanism: Infects Helper T cells, leading to impairment of both humoral and cell-mediated responses resulting in AIDS.
Immune Evasion: HIV eludes immune responses due to antigenic variation and latent integration into host DNA.
Cytotoxic T Cells
Function as effector cells in response to infected cells; enhance interaction and elimination through MHC complex activation.
Malfunctions of Immune System
Includes Autoimmune diseases: immune system fails to distinguish self and attacks host tissue.
Examples: Rheumatoid arthritis, colitis, psoriasis, multiple sclerosis.
Cancer and Immunity
Impaired immune responses can increase cancer frequency.
Suggested Explanations:
Immune system roles in suppressing cancerous cells.
Increased inflammation may lead to enhanced cancer risk.
Antivenom Production
Process: Collect venom from milk snake and inject into horse to stimulate immune response, then collect plasma containing antibodies for antivenom.
Reacts specifically with venom (antigens) for neutralization of toxin effects.