18.1 Overview of Specific Adaptive Immunity
3 min read•june 18, 2024
is our body's sophisticated defense system against pathogens. It remembers previous encounters, allowing for faster and stronger responses to repeat invaders. This system's key players are B and , which work together to create targeted responses.
are the triggers for , while are the weapons. These Y-shaped come in different classes, each with unique functions. From neutralizing toxins to activating other immune components, play crucial roles in defending our bodies.
Key Concepts in Adaptive Immunity
Key concepts of adaptive immunity
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- enables the adaptive immune system to respond more rapidly and effectively to previously encountered pathogens
- B and T cells are long-lived cells that persist after an infection has resolved (measles, chickenpox)
- is the initial adaptive immune response to a specific antigen characterized by lag, logarithmic, and plateau phases generating effector and memory cells (first exposure to a vaccine)
- is the subsequent adaptive immune response to the same antigen that is faster, stronger, and more specific than the due to memory cells with a shorter lag phase and higher antibody titers (booster shots)
- allows the adaptive immune system to recognize and respond to specific as each lymphocyte bears receptors specific for a particular antigen enabling targeted responses to different pathogens (influenza strains)
- ensures that only lymphocytes with receptors specific to the antigen proliferate and differentiate into effector cells
Humoral vs cellular immunity
- is mediated by and antibodies
- differentiate into that secrete antigen-specific antibodies (, )
- Antibodies neutralize pathogens, facilitate phagocytosis, and activate the system
- Effective against extracellular pathogens (bacteria) and toxins (tetanus)
- is mediated by
- directly kill infected or abnormal cells (virus-infected cells, tumor cells)
- secrete to regulate and coordinate immune responses (IL-2, IFN-γ)
- Effective against intracellular pathogens (viruses, intracellular bacteria) and abnormal cells (cancer)
- T cells recognize antigens presented by the on cell surfaces
Antigens and Antibodies
Antigens and immune recognition
- Antigens are substances that can elicit an adaptive immune response typically proteins, polysaccharides, lipids, or nucleic acids recognized by antigen-specific receptors on B and (bacterial cell wall components, viral proteins)
- are specific regions on an antigen recognized by antibodies or T cell receptors with a single antigen having multiple determining the precision of the immune response (linear vs conformational epitopes)
- are small molecules that can elicit an immune response when conjugated to a larger but are not immunogenic on their own due to their small size (penicillin, nickel)
Antibody structure and function
- Antibody structure consists of Y-shaped proteins composed of four polypeptide chains: two and two
- Variable regions at the tips of the Y confer antigen
- Constant regions determine the antibody's effector functions and class ()
- Antibody functions include:
- : Binding to pathogens or toxins to prevent their entry into cells
- : Coating pathogens to facilitate phagocytosis by immune cells
- : Triggering the to enhance immune responses
- Antibody classes (isotypes) have distinct characteristics and functions:
- IgM: First antibody produced during a primary response; pentameric structure (agglutination)
- IgG: Main antibody in serum; monomeric structure; crosses the placenta providing passive immunity to the fetus
- : Predominant antibody in secretions (, , milk); dimeric structure (mucosal immunity)
- : Involved in allergic reactions and defense against parasites; binds to and basophils (anaphylaxis)
- : Antigen receptor on naive B cells; role in B cell activation and differentiation
Immune System Regulation and Maturation
- mechanisms prevent the immune system from attacking the body's own tissues
- The is the interface between an antigen-presenting cell and a T cell, crucial for T cell activation
- is the process by which B cells produce antibodies with increased affinity for the antigen over the course of an immune response
Key Terms to Review (99)
Activation of cytotoxic T cells: Activation of cytotoxic T cells involves the recognition of antigens presented by infected or abnormal cells, followed by the proliferation and differentiation into effector cells capable of inducing apoptosis in target cells.
Adaptive immunity: Adaptive immunity is a specialized immune response that develops over time, involving the activation and clonal expansion of lymphocytes. It provides long-lasting protection and memory against specific pathogens.
Adaptive Immunity: Adaptive immunity is the specialized, antigen-specific immune response that develops over time to combat specific pathogens more effectively. It involves the activation and proliferation of lymphocytes, particularly T cells and B cells, to recognize and neutralize or destroy foreign invaders.
Affinity maturation: Affinity maturation is the process by which B cells produce antibodies with increased binding affinity for their specific antigen during an immune response. It occurs primarily in the germinal centers of lymph nodes.
Affinity Maturation: Affinity maturation is a process that occurs during the adaptive immune response, where B cells undergo somatic hypermutation and clonal selection to produce antibodies with increased binding affinity for their target antigen. This process helps to refine and optimize the humoral immune response over time.
Aggregation: Aggregation in immunology refers to the clumping together of particles, such as cells or pathogens, often facilitated by antibodies. This process is crucial for enhancing the immune system's ability to target and eliminate foreign invaders.
Anti-AChR antibodies: Anti-AChR antibodies are autoantibodies directed against acetylcholine receptors on the neuromuscular junction. They play a crucial role in the pathogenesis of myasthenia gravis by impairing neuromuscular transmission.
Anti-parasitic defenses: Anti-parasitic defenses are specialized adaptive immune responses that protect the host from parasitic infections. These defenses involve both cellular and humoral components of the immune system to identify and eliminate parasites.
Antibodies: Antibodies are specialized proteins produced by B cells that recognize and neutralize specific antigens. They play a crucial role in the adaptive immune response by identifying and binding to foreign pathogens.
Antibodies: Antibodies are specialized proteins produced by the immune system to recognize and neutralize foreign substances, such as bacteria, viruses, and other pathogens. They play a crucial role in the body's specific adaptive immune response, as well as in vaccine effectiveness and the development of hypersensitivities and immunodeficiencies.
Antibody-dependent cell-mediated cytotoxicity (ADCC): Antibody-dependent cell-mediated cytotoxicity (ADCC) is an immune response where effector cells recognize and kill target cells that are coated with antibodies. It involves the interaction between the Fc region of antibodies and Fc receptors on effector cells, leading to the destruction of the target cell.
Antigen binding: Antigen binding is the specific interaction between an antigen and an antibody or a receptor on a lymphocyte. This interaction is crucial for the immune system to recognize and neutralize pathogens.
Antigenic: Describes substances that can provoke an immune response in the body by interacting with specific antibodies or T-cell receptors. These substances are typically foreign molecules such as pathogens, toxins, or other foreign particles.
Antigens: Antigens are molecules or molecular structures that can be recognized by the immune system, specifically by antibodies, B cells, or T cells. They trigger an immune response when detected in the body.
Antigens: Antigens are any substances that can induce an immune response and bind to specific antibodies or receptors on immune cells. They are a crucial component of the adaptive immune system, playing a central role in vaccine development and fluorescent antibody techniques.
B cells: B cells are a type of white blood cell that plays a crucial role in the adaptive immune system by producing antibodies. They originate in the bone marrow and are responsible for humoral immunity.
B lymphocytes: B lymphocytes, also known as B cells, are a type of white blood cell crucial for the adaptive immune response. They produce antibodies to neutralize pathogens and remember past infections for faster responses in the future.
B Lymphocytes: B lymphocytes, also known as B cells, are a type of white blood cell that play a crucial role in the adaptive immune response. They are responsible for the production of antibodies, which help neutralize and eliminate foreign pathogens and toxins from the body.
Bone marrow: Bone marrow is a spongy tissue found inside certain bones, such as the hip and thigh bones. It is crucial for the production of blood cells, including those vital for the immune system.
Breast milk: Breast milk is a nutrient-rich fluid produced by the mammary glands of mammals to feed their young. It contains antibodies and immune cells that provide passive immunity to infants.
C-reactive protein: C-reactive protein (CRP) is a substance produced by the liver in response to inflammation. It is commonly used as a biomarker to assess levels of systemic inflammation in the body.
C1 complex: The C1 complex is a key component of the classical pathway of the complement system, which is part of the immune response. It consists of three subcomponents: C1q, C1r, and C1s.
Carrier molecule: A carrier molecule is a molecule that binds to an antigen and helps to present it to immune cells, enhancing the immune response. These molecules play a crucial role in the adaptive immune system.
Cellular immunity: Cellular immunity is a type of immune response that involves the activation of T-cells to fight pathogens, especially intracellular pathogens like viruses. It does not involve antibodies but relies on direct cell-mediated mechanisms to eliminate infected cells.
Cellular Immunity: Cellular immunity refers to the immune response mediated by T lymphocytes, which directly attack and eliminate foreign or infected cells. It is a crucial component of the adaptive immune system that provides protection against intracellular pathogens, such as viruses and some bacteria, as well as abnormal cells like cancer cells.
Classical pathway: The classical pathway is a mechanism of the complement system that is activated by antibodies bound to antigens, leading to a cascade of immune responses. It plays a crucial role in both innate and adaptive immunity.
Clonal Selection: Clonal selection is a fundamental principle in immunology that describes how the adaptive immune system generates a diverse repertoire of antigen-specific lymphocytes and selectively expands those that recognize and bind to foreign pathogens. It is a crucial mechanism that underpins the specific adaptive immune response.
Complement: The complement system is a group of proteins in the blood that aids antibodies and phagocytic cells in clearing pathogens from an organism. It plays a crucial role in both innate and adaptive immunity.
Complement Activation: Complement activation refers to the cascade of enzymatic reactions that are initiated upon the recognition of foreign or altered self-molecules, leading to the formation of a membrane attack complex that can lyse target cells. This process is a crucial part of the innate immune response and helps bridge the gap between innate and adaptive immunity.
Complement cascade: The complement cascade is a series of protein activations in the blood that enhances immune responses by promoting inflammation, phagocytosis, and cell lysis. It is a crucial part of the innate immune system and complements the actions of antibodies in adaptive immunity.
Constant region: The constant region is the part of an antibody's structure that remains the same among different antibodies of the same class. It is responsible for mediating interactions with immune cells and effector functions.
Cytokines: Cytokines are small proteins released by cells, especially those of the immune system, that have a specific effect on interactions and communications between cells. They play crucial roles in regulating immune responses and inflammation.
Cytokines: Cytokines are a diverse group of small proteins secreted by various cells, primarily immune cells, that act as signaling molecules to coordinate and regulate immune responses, inflammation, and other physiological processes. They play a crucial role in cellular defenses, pathogen recognition, inflammation, adaptive immunity, and various immune-related disorders and conditions.
Cytotoxic T Cells: Cytotoxic T cells, also known as CD8+ T cells, are a specialized subset of T lymphocytes that play a crucial role in the adaptive immune response by directly killing infected or cancerous cells. They are a key component of cellular immunity, responsible for the destruction of target cells that display foreign or abnormal antigens on their surface.
Cytotoxic T lymphocytes: Cytotoxic T lymphocytes (CTLs) are a subset of T cells that directly kill infected or cancerous cells. They recognize antigens presented by MHC class I molecules on target cells.
Disulfide bonds: Disulfide bonds are covalent bonds that form between the sulfur atoms of two cysteine amino acids, stabilizing protein structures. In adaptive immunity, these bonds play a crucial role in maintaining the integrity of antibodies.
DNA ligase: DNA ligase is an enzyme that facilitates the joining of DNA strands by catalyzing the formation of a phosphodiester bond. It is essential in DNA replication and repair processes.
Eosinophils: Eosinophils are a type of white blood cell that plays a critical role in the immune system, particularly in combating parasitic infections and mediating allergic reactions. They are part of the body's innate nonspecific host defenses as well as involved in certain adaptive immune responses.
Epitopes: Epitopes are specific regions on an antigen that are recognized and bound by antibodies or T-cell receptors. They play a crucial role in the specificity of the immune response.
Epitopes: Epitopes, also known as antigenic determinants, are the specific regions on the surface of an antigen that are recognized and bound by antibodies or T cell receptors. These unique molecular structures on the surface of pathogens or foreign substances are crucial for the activation of the adaptive immune response.
Fab antigen-binding sites: Fab antigen-binding sites are regions on an antibody that bind to antigens with high specificity. These sites are located on the variable regions of the antibody's light and heavy chains.
Fab region: The Fab region (Fragment, antigen-binding) is the part of an antibody that binds to antigens. It contains the variable regions of both the heavy and light chains of the antibody.
Fc receptors: Fc receptors are proteins found on the surface of certain immune cells that bind to the Fc region of antibodies. They play a crucial role in the immune response by mediating various functions such as phagocytosis and antibody-dependent cellular cytotoxicity.
Fc region: The Fc region is the tail part of an antibody that interacts with cell surface receptors and complement proteins. It plays a crucial role in modulating immune responses.
Flagellum: A flagellum is a whip-like structure that enables many microorganisms to move. It plays a crucial role in the motility of bacteria, aiding in their ability to locate nutrients and evade immune responses.
Granzymes: Granzymes are serine proteases released by cytotoxic T cells and natural killer (NK) cells. These enzymes induce apoptosis in target cells, thereby playing a crucial role in immune defense.
Haptens: Haptens are small molecules that, when combined with larger carrier proteins, can elicit an immune response. Alone, they are not immunogenic and cannot trigger a specific adaptive immune response.
Haptens: Haptens are small molecules that are unable to elicit an immune response on their own but can trigger an immune reaction when bound to a larger carrier molecule. They are crucial in the context of specific adaptive immunity, as they can induce an antibody response when presented to the immune system.
Heavy chains: Heavy chains are the larger polypeptide subunits of an antibody molecule, essential for determining its class and function. They form the backbone of the antibody structure and contribute to antigen binding.
Helper T cells: Helper T cells are a type of T lymphocyte that play a central role in the adaptive immune response by activating other immune cells. They are essential for initiating and regulating both cellular and humoral immunity.
Helper T Cells: Helper T cells are a subtype of T lymphocytes that play a crucial role in coordinating and regulating the adaptive immune response. They act as the orchestrators of the immune system, providing essential signals and support to other immune cells to mount an effective defense against pathogens and foreign invaders.
Hematopoietic stem cell: Hematopoietic stem cells are multipotent stem cells that give rise to all blood cell types, including myeloid and lymphoid lineages. They play a crucial role in the body's ability to regenerate and maintain the blood and immune systems.
Humoral immunity: Humoral immunity is a component of the adaptive immune system that involves the production of antibodies by B cells. These antibodies circulate in the blood and lymphatic system to neutralize pathogens.
Humoral Immunity: Humoral immunity refers to the antibody-mediated immune response, which involves the production of antibodies by B lymphocytes to neutralize and eliminate extracellular pathogens and toxins. It is a crucial component of the adaptive immune system that provides long-lasting protection against specific antigens encountered by the body.
Hyperpigmentation: Hyperpigmentation is the darkening of an area of skin caused by increased melanin production. It can be triggered by various factors, including autoimmune disorders.
IgA: IgA, or immunoglobulin A, is a type of antibody that plays a crucial role in the body's adaptive immune response. It is the predominant antibody found in mucosal areas, such as the respiratory, digestive, and urogenital tracts, where it helps protect these surfaces from invading pathogens.
IgD: IgD is an immunoglobulin isotype that is primarily expressed on the surface of mature, naïve B cells. It serves as an antigen receptor, playing a crucial role in the activation and differentiation of B cells as part of the adaptive immune response.
IgE: IgE is a class of antibody that plays a crucial role in the body's immune response, particularly in the context of allergic reactions and hypersensitivity. This antibody is primarily responsible for the immediate, or type I, hypersensitivity reactions that occur when the body is exposed to specific allergens.
IgG: IgG, or Immunoglobulin G, is the most abundant type of antibody found in the human body. It plays a crucial role in the adaptive immune response, contributing to pathogen recognition, phagocytosis, and the regulation of humoral immunity.
IgM: IgM is the largest antibody isotype found in the human body. It is the first antibody produced during an initial immune response and plays a crucial role in the early stages of the adaptive immune system's defense against pathogens.
Immunogens: Immunogens are substances that provoke an immune response by stimulating the production of antibodies or sensitizing T cells. They are typically foreign molecules like proteins, polysaccharides, or nucleic acids.
Immunological Synapse: The immunological synapse is a specialized cell-cell junction that forms between an antigen-presenting cell (APC) and a T cell during the initiation of an adaptive immune response. It serves as a platform for the efficient exchange of information and signals between the two cells, enabling the T cell to become activated and mount an appropriate immune response.
Isotype: An isotype refers to the different classes of antibodies (IgA, IgD, IgE, IgG, and IgM) found in all individuals of a species. These classes are determined by the constant region of the heavy chain in the antibody structure.
J chain: The J chain is a protein component that plays a critical role in the polymerization of immunoglobulins IgM and IgA. It facilitates the formation of pentameric IgM and dimeric IgA, enhancing their immune functions.
Light chains: Light chains are the smaller polypeptide subunits of antibodies, forming part of the antibody's antigen-binding site. They pair with heavy chains to create functional immunoglobulin molecules.
Macrophages: Macrophages are large phagocytic cells derived from monocytes that play a crucial role in both innate and adaptive immunity. They engulf and digest pathogens, dead cells, and cellular debris.
Major Histocompatibility Complex (MHC): The major histocompatibility complex (MHC) is a group of genes that encode cell surface proteins responsible for the regulation of the immune system. These proteins play a crucial role in the recognition of self versus non-self, allowing the immune system to distinguish the body's own cells from foreign invaders, such as pathogens or transplanted tissues.
Mast cells: Mast cells are a type of white blood cell that plays a critical role in the immune system by releasing histamine and other chemicals during inflammatory and allergic responses. They are primarily found in connective tissues, including the skin, lungs, and digestive tract.
Membrane attack complex (MAC): The membrane attack complex (MAC) is a structure formed on the surface of pathogen cell membranes by the complement system, leading to cell lysis and death. It is a critical component in the immune system's defense against bacterial infections.
Memory: Memory in adaptive immunity refers to the immune system's ability to recognize and respond more effectively to pathogens that it has encountered previously. This is a crucial aspect of the body's specific defense mechanisms.
Memory: Memory is the ability of the immune system to recognize and respond more quickly and effectively to pathogens that have been encountered before. It is a fundamental component of the adaptive immune response, allowing the body to mount a stronger and more targeted defense against recurring threats.
Mucus: Mucus is a viscous secretion produced by mucous membranes that serves as a protective barrier and trap for pathogens. It plays a critical role in the immune responses of the respiratory, digestive, and other systems.
Neutralization: Neutralization is a chemical reaction where an acid and a base react to form a salt and water. It is a key process in the immune system's adaptive response, where antibodies neutralize foreign pathogens by binding to them and preventing them from infecting host cells.
NK cells: Natural Killer (NK) cells are a type of lymphocyte that play a crucial role in the innate immune system by targeting and destroying virally infected cells and tumor cells. They do not require prior sensitization to specific antigens.
Opsonization: Opsonization is the process by which pathogens are marked for ingestion and destruction by phagocytes. This marking involves the coating of antigens with opsonins, such as antibodies or complement proteins.
Opsonization: Opsonization is the process by which certain molecules, known as opsonins, bind to the surface of a pathogen or foreign particle, making it more susceptible to phagocytosis by immune cells such as macrophages and neutrophils. This process enhances the recognition and engulfment of the target by phagocytes, improving the efficiency of the immune response.
Perforin: Perforin is a protein released by cytotoxic T cells and natural killer (NK) cells that forms pores in the membranes of target cells, leading to cell lysis. It plays a critical role in the immune system's ability to eliminate infected or cancerous cells.
Phagocytes: Phagocytes are immune cells that engulf and digest pathogens, cellular debris, and foreign particles. They play a crucial role in both innate and adaptive immunity.
Placental barrier: The placental barrier is a selective membrane in the placenta that regulates the exchange of substances between maternal and fetal blood. It acts as a protective filter to prevent harmful pathogens and toxins from reaching the fetus while allowing essential nutrients and gases to pass through.
Plasma cells: Plasma cells are differentiated B lymphocytes that produce and secrete large quantities of antibodies. They play a critical role in the humoral immune response by targeting specific antigens.
Plasma Cells: Plasma cells are terminally differentiated B lymphocytes that are responsible for the production and secretion of antibodies, playing a crucial role in the humoral immune response. These specialized cells arise from activated B cells and are central to the adaptive immune system's ability to provide long-lasting protection against pathogens.
Poison ivy: Poison ivy is a plant that produces urushiol, an oily resin causing allergic reactions in most people. Contact with urushiol can lead to a rash characterized by itching, swelling, and redness.
Portal specificity: Portal specificity refers to the phenomenon where certain pathogens cause disease only when they enter the host through specific anatomical sites. This specificity is due to factors such as receptor availability, environmental conditions, and immune response at the entry site.
Primary response: The primary response is the body's initial immune reaction to a novel antigen. It involves the activation of naive B and T cells and takes longer to develop compared to subsequent exposures.
Primary Response: The primary response is the initial immune reaction that occurs when the body is exposed to a specific antigen for the first time. This response is characterized by the activation and proliferation of naive lymphocytes, leading to the production of antibodies and the establishment of immunological memory.
Proteins: Proteins are large, complex molecules composed of amino acids that perform a vast array of functions within living organisms. They are essential for the structure, function, and regulation of the body's tissues and organs.
Saliva: Saliva is a clear, watery fluid produced by salivary glands in the mouth. It contains enzymes, antibodies, and other substances that aid in digestion and provide immune defense.
Secondary response: The secondary response is the immune system's faster and more effective reaction to a pathogen upon subsequent exposures. It is mediated by memory cells that were generated during the primary response.
Secondary Response: The secondary response refers to the enhanced and accelerated immune response that occurs upon subsequent exposure to a specific antigen. This response is a hallmark of the adaptive immune system's ability to provide long-lasting protection against pathogens that have been encountered previously.
Self-Tolerance: Self-tolerance is the ability of the immune system to recognize and not mount an immune response against the body's own healthy cells and tissues. It is a crucial mechanism that prevents autoimmune diseases by ensuring the immune system does not attack the host's own cells.
Serum amyloid A: Serum Amyloid A (SAA) is an acute-phase protein produced primarily by the liver in response to inflammation. It plays a role in modulating the immune response and can act as a chemoattractant for immune cells.
Specificity: Specificity in immunology refers to the ability of the adaptive immune system to target specific antigens. This ensures that immune responses are directed against particular pathogens, minimizing collateral damage to host tissues.
Specificity: Specificity refers to the ability of a biological entity, such as an antibody or receptor, to recognize and bind to a particular target or antigen with a high degree of precision and selectivity. This term is crucial in understanding the adaptive immune response and the production of monoclonal and polyclonal antibodies.
T cells: T cells are a type of lymphocyte that play a central role in cell-mediated immunity. They are characterized by the presence of T-cell receptors (TCR) on their surface.
T lymphocytes: T lymphocytes, or T cells, are a type of white blood cell essential for the adaptive immune response. They originate in the bone marrow and mature in the thymus.
T Lymphocytes: T lymphocytes, also known as T cells, are a type of white blood cell that play a crucial role in the adaptive immune response. They are responsible for cell-mediated immunity, recognizing and destroying infected or cancerous cells, and regulating the overall immune function.
Tears: Tears are a liquid secretion produced by the lacrimal glands to lubricate the eyes and provide immune defense. They contain enzymes and antimicrobial proteins that protect against pathogens.
Urushiol: Urushiol is an oily organic allergen found in plants of the family Anacardiaceae, such as poison ivy, poison oak, and poison sumac. It triggers a type IV hypersensitivity reaction, leading to contact dermatitis.
Variable region: The variable region is the part of an antibody or T-cell receptor that varies between different antibodies or receptors and is responsible for binding to specific antigens. This variability allows the immune system to recognize a vast array of pathogens.