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Which sites on antibodies are specifically referred to as paratopes?
What are the large molecules that antibodies bind to called?
What is the primary function of antibodies in the immune response?
Which class of antibodies would most likely respond first to an infection?
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Which of the following best describes the relationship between a plasma cell and the naïve B cell it originated from?
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What do antibodies typically defend against?
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In the context of immune response, which two mechanisms are typically involved in a successful defense against pathogens?
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Which characteristic is NOT associated with the different classes of antibodies?
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What role does mucin play in the body's defenses?
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How does lysozyme contribute to the body's defense?
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Which of the following is a function of defensins?
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What is the primary mechanism by which cilia help in the respiratory tract?
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What initiates the activation of internal innate defenses?
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Which leukocytes are primarily involved in phagocytosis during innate immunity?
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Which of the following describes the nature of internal innate defenses?
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What is dermcidin's role in the immune response?
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What are the two types of adaptive immunity?
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What is the role of effector cells in the immune response?
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What triggers the activation of naïve lymphocytes?
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What is clonal selection in adaptive immunity?
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What are memory cells responsible for in the immune response?
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Which statement is true regarding lymphocyte specificity?
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What is the primary function of activated complement in the immune system?
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How do T lymphocytes and B lymphocytes contribute to adaptive immunity?
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What is the primary immune response?
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What is the role of memory cells in the adaptive immune response?
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How do T-cell receptors recognize antigens?
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What is the function of Class I MHC proteins?
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Which cells typically express Class II MHC proteins?
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What is cell-mediated immunity primarily effective against?
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What distinguishes secondary immune responses from primary responses?
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Which of the following statements is true regarding antigen presentation?
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What is the primary role of cytotoxic T (TC) cells in the immune response?
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Where does the activation of naive T cells primarily occur?
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What must occur for a helper T (TH) cell to become activated?
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How do regulatory T (TReg) cells contribute to immune function?
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What role do cytokines play in the activity of TC cells after activation?
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What triggers the apoptosis of abnormal body cells by TC effector cells?
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What is necessary for the complete activation of TC cells?
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What characterizes the interaction between TH cells and antigen-presenting cells (APCs)?
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What is the role of hydrolytic enzymes in phagolysosomes?
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How do macrophages contribute to the immune response aside from phagocytosis?
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Which cell type is primarily responsible for releasing histamine during the inflammatory response?
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What is the primary function of interferons in the immune system?
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What outcome occurs as a result of degranulation by neutrophils?
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What is the purpose of membrane attack complexes (MACs) in the immune response?
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How do naïve lymphocytes respond upon encountering an antigen?
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What is the role of effector cells in the adaptive immune response?
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What defines clonal selection in the context of adaptive immunity?
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Which statement accurately describes how lymphocytes achieve specificity for antigens?
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Study Notes
External Innate Defenses
- Mucin is a protein that dissolves in water to form mucus, which traps pathogens in the respiratory, digestive, and urogenital tracts.
- Lysozyme is an enzyme that kills bacteria by disrupting bacterial cell walls and is secreted into saliva, tears, and respiratory mucus.
- Defensins are peptides produced by epithelial cells and immune cells that destroy pathogens (bacteria, viruses, fungi).
- Dermcidin is a peptide found in sweat that kills bacteria and fungi.
- Cilia on cells of the upper respiratory tract sweep mucus and trapped pathogens upward toward the mouth, where they can be swallowed and destroyed by gastric juice.
- Tears and saliva wash pathogens from the eyes and oral cavity.
- Urine flow helps remove pathogens from the lower urinary tract.
Internal Innate Defenses
- Pathogens that evade external defenses are met by internal defenses.
- Internal defenses are not specific to pathogens but respond to a broad range of microorganisms and harmful substances.
- Pattern recognition receptors (PRRs) on body cells bind to pathogen-associated molecular patterns (PAMPs) present on microorganisms and viruses.
- Binding of PAMPs to PRRs activates internal innate defenses.
Internal Innate Defenses: Leukocytes
- Macrophages (derived from monocytes) and neutrophils both engage in phagocytosis, engulfing and destroying pathogens.
Adaptive Immunity
- Adaptive immunity is specific to particular pathogens and relies on cell-mediated immunity and humoral immunity.
- Pathogens possess distinct antigens, which are molecules that trigger an immune response by being recognized as foreign.
- T lymphocytes (T cells) and B lymphocytes (B cells) have surface receptors that bind to specific antigens.
- Each lymphocyte possesses numerous antigen receptors with the same specificity, allowing it to recognize and respond to only one specific antigen.
- Naïve lymphocytes are mature lymphocytes that have not encountered antigens.
- Activation of naïve lymphocytes is required for them to fight an invader.
- This activation happens only to lymphocytes with receptors that bind the invader's antigen.
- Clonal selection occurs when an activated lymphocyte proliferates to form a large number of identical cells.
- This process ensures that only cells capable of responding to a specific antigen are replicated.
Adaptive Immunity: Primary and Secondary Immune Responses
- Effector cells immediately combat the pathogen that stimulated clone production.
- Memory cells are long-lived cells held in reserve for future responses.
- The initial response to a new pathogen is a primary immune response.
- Subsequent responses to the same pathogen are secondary immune responses.
- Memory cells are responsible for immunological memory, making subsequent responses faster and more effective.
Antigen Presentation
- Lymphocyte activation requires recognition and binding of foreign antigens to B-cell and T-cell receptors.
- B-cell receptors can bind unaltered, isolated antigens.
- T-cell receptors recognize antigens only when they are presented on the surface of cells in association with major histocompatibility complex (MHC) proteins.
- This process is called antigen presentation.
- There are two classes of MHC proteins: MHC I and MHC II.
- MHC I proteins are present on all nucleated cells, while MHC II proteins are found only on antigen-presenting cells (APCs), which include dendritic cells, macrophages, and B cells.
- MHC I molecules display fragments of antigens produced within the cell presenting them.
- MHC II proteins display fragments of foreign antigens taken into APCs via phagocytosis.
Cell-Mediated Immunity
- Cell-mediated immunity defends against intracellular pathogens, cancer cells, and foreign cells through the activity of various T cells.
- Cytotoxic T (TC) cells (CD8+ cells) are effector cells that directly destroy infected or abnormal cells.
- T cell activation requires interactions between naïve T cells and APCs.
- Helper T (TH) cells (CD4+ cells) become activated when presented with a foreign antigen in association with MHC II on an APC.
- Activated TH cells replicate to form a clone of effector cells.
- TH cells stimulate APCs to present co-stimulatory molecules to TC cells, completing TC cell activation.
- Activated TC cells are stimulated by cytokines (secreted by TH cells) to divide and form a clone of effector and memory cells.
- TC effector cells release cytotoxins to induce apoptosis in cells displaying the targeted antigen.
- Regulatory T (TReg) cells suppress the immune response, preventing overactive responses that could damage healthy tissues.
Phagocytosis
- Phagocytes (immune cells) engulf pathogens or other materials and enclose them in vesicles called phagosomes.
- Hydrogen ions are pumped into phagosomes, acidifying them.
- Acidified phagosomes fuse with lysosomes, forming phagolysosomes.
- Phagolysosomes contain hydrolytic enzymes that digest and destroy the engulfed material.
Other Immune Cell Functions
- Macrophages activate lymphocytes involved in adaptive immunity.
- Neutrophils undergo degranulation, releasing defensive substances like antimicrobial molecules (defensins) and cytokines.
- Natural killer (NK) cells induce virus-infected and cancer cells to undergo apoptosis.
- Mast cells, basophils, and eosinophils participate in inflammatory responses, defense against parasites, and allergic reactions.
- Mast cells release histamine, leading to vasodilation and increased capillary permeability.
Antimicrobial Proteins
- Interferons are proteins produced by virus-infected cells that interfere with viral replication and regulate leukocyte activity.
- Complement is a system of over 30 proteins that enhance phagocyte efficiency, regulate inflammation, and form membrane attack complexes (MACs) that lyse pathogens.
Adaptive Immunity
- Adaptive immunity is specific and targets particular pathogens.
- Pathogens possess distinct antigens, molecules that trigger an immune response by being recognized as foreign.
- Adaptive immunity relies on lymphocytes: T lymphocytes (T cells) and B lymphocytes (B cells).
- T and B cells have surface receptors that bind to specific antigens.
- Naïve lymphocytes are mature lymphocytes that haven't encountered their specific antigens.
- Upon activation, naïve lymphocytes proliferate to form a clone of identical cells. This process is called clonal selection.
- Clones differentiate into effector cells that combat pathogens and memory cells that are held in reserve.
Cell-Mediated Immunity
- Cytotoxic T (TC) cells destroy infected or abnormal body cells.
- Helper T (TH) cells become activated when presented with a foreign antigen in association with MHC II on an antigen-presenting cell (APC).
- Activated TH cells replicate and form a clone of effector cells.
- TH cells stimulate APCs to present co-stimulatory molecules to TC cells, completing their activation.
- Activated TC cells release cytotoxins to induce apoptosis in cells displaying the targeted antigen.
- Regulatory T (TReg) cells suppress overactive immune responses.
Humoral Immunity
- Humoral immunity involves B cells and antibodies.
- Antibodies are secreted by activated B cells.
- Humoral immunity is also known as antibody-mediated immunity.
- B cell antigen receptors have the same structure as antibodies but are anchored to the B cell membrane.
- Some antigens activate B cells directly, while most require TH cell participation.
- B cells act as APCs, presenting antigens to TH cells, leading to their activation.
- Activated B cells differentiate into plasma cells, which secrete antibodies.
- Antibodies facilitate innate immunity by activating complement and acting as opsonins.
Autoimmunity
- The immune system normally distinguishes between self-antigens and foreign antigens.
- Autoreactive lymphocytes are eliminated or inactivated during development.
- Autoimmunity occurs when the immune system attacks self-antigens, resulting in autoantibodies and autoreactive TC cells.
- Autoimmune diseases can lead to the destruction of healthy cells.
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Description
This quiz covers the mechanisms of external and internal innate defenses in the human body. Learn about proteins, enzymes, and peptides like mucin, lysozyme, and defensins that play crucial roles in pathogen defense. Test your knowledge on how these defenses work together to protect against infections.
