Immune Responses Overview
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Questions and Answers

Which type of T cells recognizes peptide antigens associated with class I MHC molecules?

  • Memory T cells
  • Regulatory T cells
  • CD8 + T cells (correct)
  • CD4 + T cells
  • What is the maximum length of peptides that can bind to class II MHC molecules?

  • 30 amino acids or more (correct)
  • 6 amino acids
  • 16 amino acids
  • 12 amino acids
  • What enhances the expression of MHC gene products?

  • Cytokines such as IFN-γ (correct)
  • Protein degradation
  • Antigen presentation
  • T cell activation
  • What role do molecules produced during innate immune responses play in adaptive immunity?

    <p>They stimulate adaptive immunity and influence responses. (C)</p> Signup and view all the answers

    What do polymorphic MHC residues form to determine the binding specificities for peptides?

    <p>Pockets that interact with anchor residues (D)</p> Signup and view all the answers

    Where are class I MHC molecules expressed?

    <p>On all nucleated cells (D)</p> Signup and view all the answers

    What is the function of IL-10 in the immune response?

    <p>To inhibit activation of macrophages and DCs. (C)</p> Signup and view all the answers

    Which component primarily delivers peptides to the endoplasmic reticulum for class I MHC binding?

    <p>TAP (transporter associated with antigen processing) (A)</p> Signup and view all the answers

    Which of the following distinguishes between different antibody isotypes?

    <p>The heavy chain C regions. (A)</p> Signup and view all the answers

    What is one characteristic of antibody molecules?

    <p>They have a symmetric core structure. (C)</p> Signup and view all the answers

    What is the initial step in the antigen processing pathway?

    <p>Proteolytic degradation of proteins into peptides (D)</p> Signup and view all the answers

    How do complement fragments generated by the alternative pathway function?

    <p>They provide second signals for B cell activation. (C)</p> Signup and view all the answers

    Which cells primarily express class II MHC molecules?

    <p>Specialized antigen presenting cells (APCs) (A)</p> Signup and view all the answers

    What is the significance of hypervariable regions in antibodies?

    <p>They determine antigen specificity. (C)</p> Signup and view all the answers

    What is the role of autophagy gene products in inflammatory responses?

    <p>They inhibit the secretion of inflammatory cytokines. (B)</p> Signup and view all the answers

    What defines the antigen-combining site of an antibody?

    <p>The N-terminal domains of both heavy and light chains. (B)</p> Signup and view all the answers

    What is the primary outcome of complement activation on microbial surfaces?

    <p>It generates membrane pores that kill bacteria. (A)</p> Signup and view all the answers

    Which pathways initiate the activation of the complement system in innate immunity?

    <p>Alternative and lectin pathways. (D)</p> Signup and view all the answers

    What role do cytokines such as IL-1 and TNF play in innate immune responses?

    <p>They stimulate chemokine production and increase neutrophil production. (D)</p> Signup and view all the answers

    Which of the following best describes the function of PAMPs and DAMPs in the immune response?

    <p>They induce effector mechanisms of innate immunity. (D)</p> Signup and view all the answers

    How do phagocytes generally eliminate microbes?

    <p>By producing reactive oxygen species, nitric oxide, and enzymes. (D)</p> Signup and view all the answers

    Which cytokine is primarily involved in systemic effects like fever and acute-phase protein synthesis?

    <p>IL-6 (D)</p> Signup and view all the answers

    What best describes the role of macrophages in tissue repair during an immune response?

    <p>They produce cytokines that stimulate inflammation and promote repair. (D)</p> Signup and view all the answers

    What distinguishes microbial surfaces from normal host cells in terms of complement activation?

    <p>Normal host cells do not lack regulatory proteins that inhibit complement. (B)</p> Signup and view all the answers

    What is the role of mast cells and basophils during an allergic response?

    <p>They synthesize and secrete lipid mediators and cytokines. (C)</p> Signup and view all the answers

    Which of the following is NOT a manifestation of immediate hypersensitivity?

    <p>Chronic inflammation (C)</p> Signup and view all the answers

    What is the most severe form of immediate hypersensitivity?

    <p>Anaphylactic shock (B)</p> Signup and view all the answers

    What triggers the late-phase reaction in immediate hypersensitivity?

    <p>Neutrophil infiltration (A), Eosinophil infiltration (C)</p> Signup and view all the answers

    What type of allergic reactions can food allergens cause?

    <p>Diarrhea and vomiting (A)</p> Signup and view all the answers

    What is the main goal of desensitization immunotherapy?

    <p>To prevent Th2 cell responses and IgE production for specific allergens. (B)</p> Signup and view all the answers

    How does genetic susceptibility impact allergic diseases?

    <p>It interacts with environmental factors to promote atopy. (B)</p> Signup and view all the answers

    Which type of receptor-targeted therapy is approved for some allergic diseases?

    <p>Monoclonal antibodies against IgE (D)</p> Signup and view all the answers

    What characterizes the earliest B cell precursors known as pro-B cells?

    <p>Ig genes are in the germline configuration. (D)</p> Signup and view all the answers

    At which stage does V-D-J recombination complete at the Ig heavy chain locus?

    <p>Pro-B to pre-B cell transition (D)</p> Signup and view all the answers

    What does the pre-B cell receptor consist of?

    <p>Surrogate and light chains with signaling molecules. (A)</p> Signup and view all the answers

    What process occurs as immature B cells differentiate to prevent self-reactivity?

    <p>Receptor editing may be induced. (D)</p> Signup and view all the answers

    What is the significance of allelic exclusion during B cell maturation?

    <p>It prevents rearrangement on the other heavy chain allele. (A)</p> Signup and view all the answers

    What is the primary type of immunoglobulin expressed on the surface of immature B cells?

    <p>IgM (C)</p> Signup and view all the answers

    What occurs during the early stages of T cell maturation in the thymus?

    <p>Thymocytes rearrange their TCR genes. (D)</p> Signup and view all the answers

    Which of the following describes the pre-T stage of thymocytes?

    <p>They remain double-negative while completing TCR β chain recombination. (C)</p> Signup and view all the answers

    What is the primary role of class I MHC molecules in the immune response?

    <p>To present peptides from intracellular proteins to CD8 + T cells (C)</p> Signup and view all the answers

    Which process allows dendritic cells to present antigens from virus-infected cells to CD8 + T cells?

    <p>Cross-presentation (C)</p> Signup and view all the answers

    What happens to the invariant chain (Ii) associated with class II MHC molecules during antigen processing?

    <p>It is proteolytically cleaved, allowing peptide binding (B)</p> Signup and view all the answers

    How do class II MHC molecules primarily contribute to the activation of the immune response?

    <p>By binding peptides from extracellular proteins for CD4 + helper T cell recognition (B)</p> Signup and view all the answers

    Which component is involved in the removal of CLIP from the peptide-binding cleft of class II MHC molecules?

    <p>DM molecules (C)</p> Signup and view all the answers

    What does the presence of foreign protein antigens rely on in terms of immunogenicity?

    <p>Antigen-processing pathways generating peptides binding to self MHC molecules (A)</p> Signup and view all the answers

    Which statement accurately reflects the function of signaling receptors on the cell surface?

    <p>They initiate signaling that leads to altered gene expression in the nucleus. (C)</p> Signup and view all the answers

    What is the main pathway for presenting antigens derived from extracellular microbes?

    <p>Through class II MHC molecules to CD4 + helper T cells (D)</p> Signup and view all the answers

    Flashcards

    Complement System

    A group of proteins in the blood that work together to destroy pathogens. They are activated in a cascade, leading to the formation of fragments of C3 and C5, which promote inflammation and phagocytosis.

    MBL (Mannose-binding lectin)

    Proteins that are activated when they bind to specific molecules on microbial surfaces. They initiate the alternative and lectin pathways of complement activation.

    Phagocytosis

    The process by which microbes are engulfed and destroyed by phagocytes. This is a key function of innate immunity.

    Phagocytes

    Specialized immune cells that engulf and destroy pathogens. Examples include neutrophils and macrophages.

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    Neutrophil

    A type of immune cell that is abundant in the blood and is the first line of defense against infection.

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    Macrophage

    A type of immune cell that resides in tissues and is involved in both innate and adaptive immunity. They are effective phagocytes and also produce cytokines.

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    Cytokines

    Small signaling molecules that are produced by cells of the immune system. They help to regulate immune responses, such as inflammation.

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    TNF (Tumor necrosis factor)

    A type of cytokine that is produced by macrophages, DCs, and other innate immune cells. It induces inflammation and helps to recruit other immune cells to the site of infection.

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    What are antigen-presenting cells (APCs)?

    Immune system cells that recognize and engulf pathogens, triggering the adaptive immune response.

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    What are the roles of cytokines and costimulators in adaptive immunity?

    Cytokines secreted by APCs that activate and differentiate T cells into effector T cells, enhancing their function.

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    What role does the complement system play in adaptive immunity?

    Complement fragments, part of the innate immune system, that act as second signals for B cell activation and antibody production.

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    What is the function of IL-10 in immune regulation?

    A key regulatory cytokine that inhibits the activation of macrophages and DCs, preventing excessive inflammation.

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    What are antibodies (immunoglobulins)?

    They are glycoproteins produced by B lymphocytes, consisting of two heavy chains and two light chains, forming the basic antibody structure.

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    What is the function of membrane-bound antibodies?

    Antibodies serve as receptors on B cells, triggering activation upon antigen binding.

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    What is the function of secreted antibodies?

    They neutralize microbes and toxins, and engage effector mechanisms to eliminate antigens, providing humoral immunity.

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    What are hypervariable regions in antibodies?

    These regions within the antibody molecule are highly variable, allowing for millions of different antibodies with distinct antigen specificities.

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    MHC Class I & II Presentation

    MHC molecules present peptides to T cells, with class I MHC presenting peptides to CD8+ T cells and class II MHC presenting to CD4+ T cells.

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    MHC Peptide Binding

    MHC molecules bind only one peptide at a time, but they can bind multiple peptides with similar structural features.

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    MHC Binding Specificity

    MHC molecules have specific pockets that interact with complementary residues on the peptide.

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    MHC Cleft Size

    The peptide-binding cleft of Class I MHC is smaller than Class II MHC, allowing Class I to bind shorter peptides and Class II to bind longer peptides.

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    MHC Expression

    Class I MHC is expressed on all nucleated cells, while Class II MHC is mainly expressed on antigen presenting cells (APCs).

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    Antigen Processing

    The process of converting native proteins into MHC-associated peptides for presentation to T cells.

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    Class I MHC Pathway

    For Class I MHC, proteins are degraded in the proteasome, generating peptides that are transported to the ER via TAP and bind to MHC.

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    MHC Surveillance

    Both extracellular and intracellular proteins can be sampled by antigen processing pathways, allowing for surveillance of both self and foreign proteins.

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    Cross-presentation

    A process where specialized antigen-presenting cells (APCs), primarily dendritic cells (DCs), engulf virus-infected or tumor cells, and transport their antigens into the cytosol for presentation by MHC class I molecules.

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    TAP-containing peptide-loading complex

    A protein complex within the endoplasmic reticulum (ER) that helps load peptides onto newly synthesized MHC class I molecules.

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    CLIP

    A small peptide remnant of the invariant chain (Ii) that initially occupies the peptide-binding cleft of MHC class II molecules. It must be removed by DM molecules before antigen peptides can bind.

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    DM

    A molecule that facilitates the exchange of CLIP with antigenic peptides in the MHC class II pathway. It is crucial for antigen presentation by MHC class II.

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    MHC molecules

    Molecules that act as 'signposts' on the cell surface, displaying fragments of proteins (peptides) from within the cell to T cells.

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    CD8+ cytotoxic T lymphocytes (CTLs)

    A class of T cells that recognizes antigens presented by MHC class I molecules and targets infected cells for destruction.

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    CD4+ helper T cells

    A class of T cells that recognizes antigens presented by MHC class II molecules and helps activate other immune cells to fight infections.

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    Immediate hypersensitivity

    A rapid immune response triggered by allergens that involves mast cells, basophils, and the release of histamine and other inflammatory mediators.

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    Anaphylactic shock

    A severe, life-threatening allergic reaction characterized by widespread vasodilation, vascular leakage, airway obstruction, and reduced blood volume.

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    Asthma

    Chronic inflammatory airway disease characterized by bronchial inflammation and episodes of reversible bronchoconstriction, often triggered by allergens.

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    Allergic rhinitis

    Inflammation of the nasal mucosa caused by allergens, often resulting in sneezing, runny nose, and itchy eyes.

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    Late-phase reaction

    A delayed immune response that occurs several hours after an initial exposure to an allergen. It is characterized by an influx of neutrophils and eosinophils.

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    Atopic susceptibility

    Inherited predisposition to develop allergic diseases, involving variations in specific genes that influence immune responses.

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    Desensitization immunotherapy

    Treatment involving controlled exposure to allergens with the aim of reducing the body's allergic response by potentially suppressing Th2 cell activity and decreasing allergen-specific IgE production.

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    Monoclonal antibodies for allergy treatment

    A type of medication used to manage allergic diseases that targets cytokines, their receptors, or IgE.

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    V(D)J Recombination

    The process where a cell's DNA is rearranged to create unique antibody or TCR genes, leading to a vast diversity of immune receptors.

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    Pro-B Cells

    Early B cell precursors that haven't undergone Ig gene rearrangement. They have the original, germline configuration of their Ig genes.

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    Pro-B to Pre-B Cell Transition

    The transition from pro-B to pre-B cells involves the completion of V-D-J recombination at the Ig heavy chain locus. This generates a mature mRNA, which is translated into the µ heavy chain protein.

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    Pre-B Cell Receptor

    A receptor formed by pairing the µ heavy chain with surrogate light chains. It helps signal for survival and proliferation, ensuring only productive clones survive.

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    B Cell Maturation in Bone Marrow

    The process where a B cell's genes are modified to remove self-reactive antibodies. If successful, the B cell differentiates into a mature B cell.

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    T Cell Maturation: Thymus Outer Cortex

    The process where thymocytes, the immature T cells, undergo TCR gene rearrangement and express CD3, TCR, CD4, and CD8 molecules. This occurs in the outer cortex of the thymus.

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    Pre-T Stage

    A stage where the thymocyte completes V-D-J recombination at the TCR β chain locus, resulting in the production of TCR β chain polypeptides.

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    Double-Positive T Cells

    Cells that express both CD4 & CD8 coreceptor molecules. These cells undergo further selection and differentiation in the thymus.

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    Study Notes

    Immune Responses

    • Protective immunity is mediated by innate and adaptive immunity
    • Innate immunity responds to shared microbial structures and host cell damage
    • Adaptive immunity is specific to different antigens with enhanced responses upon repeat exposure
    • Adaptive immunity features antigen specificity, diverse repertoire, memory, and discrimination between self and foreign antigens
    • Immunity can be active (via antigen response) or passive (via antibody/effector cell transfer)
    • Lymphocytes (B cells and T cells) are the key cells in adaptive immunity, each with unique antigen receptors
    • Adaptive immunity starts with antigen recognition by specific lymphocytes; antigen-presenting cells display antigens
    • Lymphocytes proliferate and differentiate into effector (antigen elimination) and memory cells (enhanced responses)
    • Humoral immunity (B cells and plasma cells) eliminates extracellular microbes via antibodies (neutralization, phagocytosis promotion)
    • Cell-mediated immunity (T cells) fights intracellular microbes via cytokines (like CD4+ helper T cells assisting macrophages and CD8+ cytotoxic T cells killing infected cells)

    Cells and Tissues of the Immune System

    • Immune system organization is key for effective innate and adaptive responses (rapid delivery of cells to infection sites, antigen location for lymphocytes)
    • Major effector cells include phagocytes (neutrophils, macrophages), mast cells, basophils, eosinophils, dendritic cells, innate lymphoid cells (ILCs), and natural killer (NK) cells, plus lymphocytes
    • Surface molecules, named via the CD nomenclature, are differentially expressed on immune cells
    • Neutrophils are abundant blood leukocytes, multilobed nucleus, cytoplasmic lysosomes. They are rapidly recruited for phagocytosis, microbial killing
    • Tissue resident macrophages act as sentinels detecting microbes and alerting the immune system and performing specialized functions in tissues
    • Monocytes are circulating phagocytes that mature to macrophages, clearing microbes, dead cells, and secreting cytokines/chemokines to recruit leukocytes and repair damage.
    • Dendritic cells (DCs) are bone marrow-derived antigen-presenting cells
    • Innate lymphoid cells (ILCs) are cytokine-producing, innate immune cells similar to CD4+/CD8+ T cell effector cells
    • B cells and T cells express diverse, specific antigen receptors, critical for adaptive immunity specificity/memory
    • B and T lymphocytes develop from a bone marrow precursor; B cells mature in marrow, T cells in the thymus before entering circulation and populating lymphoid organs
    • Naive B/T cells are mature but unstimulated lymphocytes
    • Effector B cells (plasma cells) secrete antibodies; effector T cells (including CD4+ helper and CD8+ cytotoxic T cells) have cytokine secretion or killing functions
    • Memory cells persist to rapidly respond to repeat exposure to an antigen

    Leukocyte Circulation and Migration into Tissues

    • Leukocyte migration from blood to tissues involves postcapillary venules, use of chemokines and adhesion molecules on leukocytes/endothelial cells
    • Selectins are carbohydrate-binding molecules mediating low-affinity leukocyte-endothelial cell interactions
    • Integrins are adhesion molecules for tight leukocyte-endothelial cell binding (LFA-1, VLA-4)
    • Chemokines are protein signals regulating leukocyte migration into tissues, and are bound to chemokine receptors, leading to leukocyte movement in chemotaxis along concentration gradients
    • Lymphocyte recirculation is critical for naive lymphocyte encounters with antigens in secondary lymphoid organs

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