Questions and Answers
What is one of the major functions of the immune system?
Which component is primarily responsible for recognizing foreign entities?
What distinguishes primary lymphoid organs from secondary lymphoid organs?
Which of the following is NOT a characteristic of the adaptive immune system?
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What is a common disorder associated with the immune system?
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What is a primary function of the immune system's innate immunity?
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How does adaptive immunity differ from innate immunity?
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Which of the following describes a characteristic of innate immunity?
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What occurs when the immune system cannot destroy a foreign entity?
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Which statement regarding the cellular and molecular effectors of innate immunity is true?
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What is the primary role of the NADPH oxidase complex in phagocytes?
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Which component most effectively kills Gram-positive bacteria?
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What unique strategy do neutrophils utilize when surrounded by bacteria?
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How do lysozyme and lactoferrin differ in their mechanisms of action?
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What is one of the significant effects of the low pH found in lysosomes?
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What is the primary role of defensins in innate immunity?
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Which typically triggers the acute inflammatory process?
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What defines a pattern-recognition receptor in innate immunity?
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What is the first line of defense in innate immunity?
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Which of the following is a characteristic mechanism of phagocytosis in innate immunity?
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What is the primary factor required to stabilize the C3 convertase in the alternative pathway?
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Which statement about the production of antibodies is true?
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How does the C5 convertase typically form in relation to the C3 convertase?
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What role does the Membrane Attack Complex (MAC) play in the immune response?
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What triggers the secretion of mannose-binding lectin by the liver?
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What is the primary function of the C3 convertase in the complement system?
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Which pathway of complement activation involves the binding of MBL to mannose on the pathogen's surface?
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What role does C5b play in the membrane attack complex (MAC)?
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Which complement component is recognized as an important opsonin facilitating phagocytosis?
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How does the alternative pathway of the complement system initiate its response?
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Study Notes
Overview of Immunology
- Immunology encompasses protection against pathogens, foreign cells, and tissue repair.
- It includes a diverse array of cells and unique lymphatic tissues, alongside various molecular signals.
- Disorders related to immunology include allergies, autoimmune diseases, and inflammatory states.
Major Functions of the Immune System
- Recognition: Identifies foreign entities and damaged tissues.
- Destruction: Eliminates pathogens through disruption of cell membranes and enzymatic degradation.
- Communication: Facilitates interaction between recognizing and destroying entities.
- Memory and Specificity: Exhibits primary and secondary immune responses with memory for faster, more effective reactions.
Types of Immunity
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Innate Immunity:
- First line of defense, responding within hours to days.
- Less specific, with fixed responses that do not adapt.
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Adaptive Immunity:
- Activated when innate defenses fail, taking days to weeks.
- Highly specific, capable of generating memory and adapting through clonal selection.
Clonal Selection Theory
- Each lymphocyte carries a unique receptor, which is crucial for activation.
- Activated lymphocytes proliferate into clones with identical receptors.
- Self-reactive lymphocytes are eliminated early in development.
Components of the Immune System
- Lymphocytes: Include B cells (mature in bone marrow) and T cells (mature in the thymus).
- Granulocytes: Include neutrophils (short-lived phagocytes), eosinophils (defense against parasites), and basophils and mast cells (involved in allergic responses).
- Natural Killer Cells: Part of innate immunity, targeting infected or cancerous cells without specific receptors.
Lymphoid Organs
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Primary Lymphoid Organs:
- Bone marrow and thymus are sites for lymphocyte maturation.
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Secondary Lymphoid Organs:
- Sites for the initiation of adaptive responses.
- Includes lymph nodes (filter lymph), spleen (filters blood and produces antibodies), and mucosal-associated lymphoid tissue (MALT) for antigen collection.
Specific Mechanisms
- B Cell Receptors: Secrete antibodies upon activation; recognize various antigens (proteins, lipids, nucleic acids).
- T Cell Receptors: Recognize antigens through interaction with presenting cells; essential for helper and cytotoxic functions.
- Antigen Presentation: T cells require close interaction with presenting cells for activation.
Memory in Adaptive Immunity
- Enhanced response upon re-exposure to antigens leads to faster, larger, and qualitatively different secondary responses.
- Memory is a result of the initial activation and expansion of specific lymphocyte clones.
Morphological Characteristics of Leukocytes
- Microscopic Appearance: Distinct shapes and structures can identify different leukocyte types.
- Location: Found in circulation and concentrated in lymphatic tissues.
Summary
- The immune system is a complex network of cells and organs that work together to protect the body against a vast range of pathogens and maintain tissue homeostasis through recognition, response, memory, and repair mechanisms.
Innate Immunity Overview
- Innate immunity provides immediate defense against pathogens, acting within minutes to hours of infection.
- Mechanisms of innate immunity distinguish between host cells and pathogens effectively.
- Only when innate defenses are compromised, adaptive immunity comes into play.
Barriers of Innate Immunity
- Major barriers include physical, chemical, and cellular defenses:
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Chemical Barriers
- Lysozyme: Present in secretions like tears and saliva, hydrolyzes peptidoglycan in bacterial cell walls.
- Defensins: Cationic peptides effective against Gram-positive/negative bacteria and some viruses; they destabilize membranes, degrade proteins, and inhibit viral binding and assembly.
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Chemical Barriers
Phagocytosis and Microbe Destruction
- Phagocytosis: Process where phagocytes engulf and destroy pathogens through mechanisms, primarily in macrophages and neutrophils.
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Microbe Killing Mechanisms:
- Phagosomes merge with lysosomes and release reactive oxygen species (ROS) and hydrolytic enzymes.
- Neutrophils can create neutrophil extracellular traps (NETs) to ensnare and kill bacteria, using chromatin and granule contents.
Pattern-Recognition Receptors (PRRs)
- Definition: PRRs identify and bind to pathogen-associated molecular patterns (PAMPs).
- Examples include Toll-like receptors (TLRs), Nod-like receptors (NLRs), and lectins.
- PRRs activate responses like phagocytosis and cytokine secretion, crucial for initiating immune responses.
Toll-Like Receptors (TLRs)
- Family of 10 membrane receptors specific to various pathogens.
- Common Ligands: Include lipopolysaccharides (LPS), RNA types, and flagellin.
- Cytokine Secretion: TLR activation releases inflammatory cytokines (e.g., IL-1β, IL-6, TNFα) and interferons (e.g., IFN-alpha/beta/lambda).
Consequences of TLR Signaling
- Gene mutations affecting TLR signaling, such as MyD88, highlight its functional importance in immunity.
- MyD88 deficiency results in frequent bacterial infections while sparing antiviral responses.
Nod-Like Receptors (NLRs)
- Intracellular receptors detecting intracellular degradation products of pathogens.
Chemokines
- Small molecules guiding leukocyte movement and adhesion during inflammation.
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Major Families:
- CXC: Attract neutrophils and have angiogenic properties.
- CC: Attract various leukocytes.
Leukocyte Migration
- Emigration and activation of leukocytes involve several steps:
- Stable Adhesion: Tight bonds form between leukocytes and endothelial cells.
- Diapedesis: Leukocytes transmigrate through the endothelium.
- Chemotaxis: Leukocytes follow chemokines to the infection site.
Inflammatory Mediators
- Various mediators enhance leukocyte migration and adhesion:
- Histamine and Thrombin: Promote rolling and selectin expression.
- TNF & IL-1: Induce ICAM expression on endothelial cells.
- Chemokines: Increase integrin affinity for tight adherence.
Chemotactic Agents
- Chemotactic agents (e.g., leukotriene B4, C5a) concentrate at damaged sites, guiding leukocyte migration to the infection.
Key Questions for Understanding
- Recognize how phagocytes distinguish targets like through opsonins.
- Understand the roles of lysosomes, free radicals, and antimicrobial peptides in pathogen destruction.
- Explore the significance of NETs beyond phagocytosis in host protection.
The Complement System
- A blood-borne molecular defense that enhances immunity from antibodies.
- Functions include aiding phagocytosis, destruction of microorganisms, and promoting inflammation.
- Activated through a tightly-controlled enzyme-triggered cascade at localized sites.
Pathways of Complement Activation
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Alternative Pathway
- C3 acts as a pattern-recognition receptor, binding to pathogens.
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Mannose-Binding-Lectin (MBL) Pathway
- Initiated by MBL binding to mannose on bacteria/viruses.
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Classical Pathway
- Activated when antibodies bind to pathogens, allowing C1q to bind to the Fc portion.
Complement Mechanism
- All pathways converge to produce stable C3 convertase, cleaving C3 into C3b and C3a.
- C3b aids in opsonization and progresses the complement cascade.
- C5 convertase formed when C3b binds to C3 convertase, cleaving C5 into C5a and C5b.
- C5b initiates cell lysis by assembling with C6, C7, C8, and C9 to form the Membrane Attack Complex (MAC), creating pores in microbial membranes.
Inflammatory Mediators
- C3a and C5a are potent inflammatory mediators, involved in promoting inflammation.
- Complement regulates inflammation to prevent damage to host tissues.
Role of DAMPs and PAMPs
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DAMPs (Danger-Associated Molecular Patterns)
- Signals released from damaged cells indicating cell stress or damage.
- Include substances like extracellular ATP and cholesterol crystals.
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PAMPs (Pathogen-Associated Molecular Patterns)
- Molecular patterns recognized by pattern recognition receptors (PRRs) to detect pathogens.
DAMP Detection
- NLRP3 receptors detect various DAMPs and PAMPs, forming inflammasomes that activate caspase-1.
- Caspase-1 converts pro-IL-1 to IL-1β, which is key in inflammatory responses.
Natural Killer (NK) Cells
- Specialized lymphoid-derived cells that detect and kill virally-infected or cancerous cells in a non-specific manner.
- Activated by type I interferons and IL-12.
- Use activating receptors (NKARs) to identify infected cells and inhibitory receptors (NKIRs) to avoid attacking healthy cells.
NK Cell Activation and Function
- Activation requires prior licensing, potentially by dendritic cells.
- Kill infected cells through receptor-mediated apoptosis and release of perforin and granzyme.
Complement-Related FAQs
- Complement deficiencies can lead to immunodeficiency and autoimmune diseases.
- C3 convertases and their activation differ among the pathways but align in function.
Acute Inflammation
- The process begins with pathogen detection and signaling, leading to cellular and histological changes.
- Involves various immune cells, cytokines, and tissue response, contrasting with chronic inflammation characterized by prolonged immune activity.
Summary Insights
- Complement pathways enhance immune responses against pathogens while maintaining control to avoid tissue damage.
- DAMPs and PAMPs play crucial roles in initiating inflammation and recruiting immune cells.
- NK cells integrate early antiviral responses and moderate adaptive immunity, serving as effective surveillance against abnormal cells.
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Description
This quiz covers the fundamental principles of immunology, including the major functions of the immune system and the types of immunity. It delves into concepts such as recognition, destruction, communication, and memory in immune responses. Learn about innate and adaptive immunity and their roles in protecting the body against pathogens.
