Activation of Th Cells
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Questions and Answers

Which characteristic of adaptive immunity allows it to respond specifically to millions of antigens?

  • Memory
  • Diversity (correct)
  • Specificity
  • Self and non-self discrimination

    • What is the primary limitation of passive immunity?

  • It provides lifelong immunity.
  • It is short-lasting. (correct)
  • It takes a long time to develop.
  • It requires previous exposure to pathogens.

    • How does active immunity primarily differ from passive immunity?

  • Active immunity leads to immunologic memory. (correct)
  • Active immunity provides antibodies without exposure to an antigen.
  • Active immunity occurs naturally, while passive immunity is always artificially acquired.
  • Active immunity is short-lasting.

    • Which form of immunity can be acquired through breast milk?

    <p>Naturally passive immunity</p> Signup and view all the answers

    What type of antibody is transmitted from mother to fetus through the placenta providing passive immunity?

    <p>IgG</p> Signup and view all the answers

    Which characteristic of adaptive immunity allows it to distinguish between 'self' and 'non-self'?

    <p>Self and non-self discrimination</p> Signup and view all the answers

    Which molecule on Th cells interacts with B7 on antigen-presenting cells (APCs) for activation?

    <p>CD28</p> Signup and view all the answers

    What is the role of IL-1 secreted by macrophages and other APCs?

    <p>It helps in the activation of Th cells.</p> Signup and view all the answers

    Which statement correctly describes the first signal for the activation of Tc cells?

    <p>Ag epitopes associated with MHC I on the surface of target cells.</p> Signup and view all the answers

    What is the function of IL-2 in Tc cell activation?

    <p>It provides a second signal for Tc cell activation.</p> Signup and view all the answers

    Which type of cell-mediated immunity is associated with Tc cell activity?

    <p>Cell-mediated immunity</p> Signup and view all the answers

    Which cytokine is involved in activating macrophages and NK cells during Th cell differentiation?

    <p>INF-gamma</p> Signup and view all the answers

    What is the primary function of the humoral immune response?

    <p>Eliminating extracellular microbes and their toxins</p> Signup and view all the answers

    Which cells are primarily involved in the process of opsonization?

    <p>Phagocytes</p> Signup and view all the answers

    Which type of immunity is responsible for resistance to tumors?

    <p>Cell mediated immune response</p> Signup and view all the answers

    Which of the following can be considered an antigen-presenting cell (APC)?

    <p>Langerhans cells</p> Signup and view all the answers

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

    <p>Present antigens to Th cells</p> Signup and view all the answers

    What triggers the activation of Th cells?

    <p>Presentation of antigens by APCs with MHC class II</p> Signup and view all the answers

    Which of the following is NOT a condition where cell mediated immunity plays a role?

    <p>Elimination of extracellular bacteria</p> Signup and view all the answers

    Which molecules are involved in the first signal for specific B-cell activation?

    <p>TCR on Th and Ag epitopes associated with MHC II on B cell</p> Signup and view all the answers

    What is the role of Tc cells in the cell mediated immune response?

    <p>Expression of cytotoxins</p> Signup and view all the answers

    What role do cytokines IL 2, 4, & 5 play in B-cell activation?

    <p>They help B cells proliferate into plasma cells and memory cells</p> Signup and view all the answers

    What is the second signal required for T-dependent B-cell activation?

    <p>Interaction between CD40 on B cell and CD40L on Th cells</p> Signup and view all the answers

    What occurs during the contraction phase of the immune response?

    <p>Restoration of homeostasis through the elimination of expanded lymphocyte clones</p> Signup and view all the answers

    Which cells regulate the response during the contraction phase?

    <p>Treg cells</p> Signup and view all the answers

    Which cell types are primarily involved in innate immunity?

    <p>Phagocytes and natural killer cells</p> Signup and view all the answers

    What characteristic does adaptive immunity possess that innate immunity lacks?

    <p>Very large diversity</p> Signup and view all the answers

    What is a defining feature of superantigens?

    <p>They cause systemic toxicity by activating multiple clones of T helper cells</p> Signup and view all the answers

    Which of the following diseases are associated with superantigens?

    <p>Rabies and toxic shock syndrome</p> Signup and view all the answers

    What is the specificity target for innate immunity?

    <p>For shared structures by microbes (PAMPs)</p> Signup and view all the answers

    Which characteristic is shared by both innate and adaptive immunity?

    <p>Non reactivity to self</p> Signup and view all the answers

    What is the role of antigen-presenting cells (APCs) in the adaptive immune response?

    <p>They engulf and process antigens to present them to T cells.</p> Signup and view all the answers

    How are cytotoxic T cells (Tc) activated?

    <p>By activation through Helper T cells (Th).</p> Signup and view all the answers

    Which cells differentiate into plasma cells in the adaptive immune response?

    <p>B cells</p> Signup and view all the answers

    What is the primary function of plasma cells?

    <p>To secrete antibodies that neutralize the antigen.</p> Signup and view all the answers

    Which cells are directly involved in killing infected cells?

    <p>Cytotoxic T cells</p> Signup and view all the answers

    What is the significance of memory cells in the adaptive immune response?

    <p>They can quickly respond to a second exposure of the same antigen.</p> Signup and view all the answers

    Which statement correctly describes the processing of super antigens?

    <p>Super antigens are not processed</p> Signup and view all the answers

    To which region of the T-cell receptor (TCR) do super antigens bind?

    <p>Variable region of β chain only of TCR</p> Signup and view all the answers

    What type of activation of T cells is caused by super antigens?

    <p>Non-specific activation</p> Signup and view all the answers

    What is a significant effect of cytokine release triggered by super antigens?

    <p>Very high harmful levels of cytokines released</p> Signup and view all the answers

    Which characteristic differentiates a classic antigen from a super antigen regarding TCR region binding?

    <p>Classic antigen binds to variable regions of both α and β chains of TCR</p> Signup and view all the answers

    Study Notes

    Characters of Adaptive Immunity

    • Adaptive immunity discriminates between "self" and "non-self" structures.
    • It is highly specific for the invading organism and can respond specifically to millions of antigens.
    • Adaptive immunity requires previous exposure to pathogens.
    • It has memory, meaning re-exposure to the same antigen results in a faster and stronger response, sometimes leading to lifelong immunity.

    Types of Adaptive Immunity

    Passive Immunity

    • Involves the transfer of readymade antibodies to an individual.
    • Provides rapid protection but is short-lasting.
    • Can be naturally acquired (e.g., from mother to fetus through the placenta or in breast milk) or artificially acquired (e.g., through injection of specific antibodies).

    Active Immunity

    • Involves the individual's active production of their own antibodies or sensitized lymphocytes specific to a foreign antigen.
    • Immunity develops slowly but lasts for a long time due to the development of immunologic memory.

    Mechanisms of Adaptive Immune Response (Active Immunity)

    Humoral (Antibody-Mediated) Immune Response (HI)

    • Directed mainly towards defense against extracellular microbes and their toxins, leading to their extracellular elimination or destruction via different cells (e.g., phagocytes and NK cells).

    Cell-Mediated Immune Response (CMI)

    • Responsible for a wide variety of protective mechanisms, including:
      • Resistance to viruses, protozoa, fungi, and intracellular bacteria (e.g., TB and Brucella).
      • Resistance to tumors.
    • However, CMI can also play a role in harmful conditions, such as:
      • Graft rejections.
      • Type IV hypersensitivity.
      • Autoimmune diseases.

    Stages of Specific CMI Immune Response

    Antigen Processing and Presentation

    • Antigen-presenting cells (APC) (e.g., macrophages) bind, ingest, and digest antigens into peptide fragments (Ag determinants or epitopes) and present them in association with MHC class II molecules on the cell surface to be recognized by TCR of Th cells.

    T Cells Activation

    • Th cells are activated in association with MHC and costimulatory molecules.
    • Activated Th cells secrete cytokines (e.g., IFN-γ), which activate macrophages and NK cells, increasing their killing effects against antigens.

    Activation of Tc Cells

    • Tc cells are activated in association with expression of cytotoxins (e.g., graft cells, tumor cells).

    Activation of Th Cells

    • Th cells are activated by two signals:
      • The first signal: Ag epitopes associated with MHC II on the surface of APC.
      • The second signal: Costimulatory molecules (e.g., CD28 on Th cells and B7 on APC).
    • Activated Th cells undergo proliferation and differentiation into effector cells, secreting cytokines (e.g., IFN-γ and IL-2) that activate macrophages and NK cells.

    Activation of Tc Cells

    • Tc cells are activated by two signals:
      • The first signal: Ag epitopes associated with MHC I on the surface of target cells.
      • The second signal: IL2 produced from activated Th cells.
    • Activated Tc cells undergo proliferation and secrete cytotoxins to kill target cells (e.g., graft cells, tumor cells, infected cells).

    Specific B Cells Activation (T-Dependent Activation)

    • Specific B cells (acting as APC) are activated by two signals:
      • The first signal: Interaction between TCR on Th and Ag epitopes associated with MHC II on the surface of B cells.
      • The second signal: Costimulatory molecules (e.g., CD40 on B cells and CD40L on Th cells).
    • Activated B cells differentiate into antibody-producing plasma cells and memory cells.

    Contraction Phase (Homeostasis)

    • Occurs when the effective immune response eliminates the microbe that initiates the response.
    • In this stage, expanded lymphocyte clones die, and homeostasis is restored.
    • This response is regulated by Treg cells.

    Memory Cells Formation

    • Some activated Th, Tc, and B cells become memory cells that can respond to exposure of the same antigen.

    Superantigens (SAgs)

    • Definition: Antigens capable of activating multiple clones of T helper cells.
    • Characteristics:
      • Bind to class II MHC molecules on APC and the TCR β chain on Th cells outside the peptide binding groove.
      • Activate Th cells even at very low concentrations.
      • Can cause lymphocyte exhaustion and systemic toxicity.
    • Examples: Staphylococcal enterotoxins and toxic shock syndrome toxins, Streptococcal pyrogenic exotoxin, and some viral superantigens (e.g., nucleoprotein of rabies virus).

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    Description

    Learn about the activation process of Th cells through two signals and the role of costimulatory molecules, macrophages, and cytokines in this process.

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