Adaptive Immunity Lecture
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Questions and Answers

Which of the following properly describes the function of antigen presenting cells (APCs)?

  • APCs release cytokines to directly kill foreign cells.
  • APCs produce antibodies to neutralize pathogens.
  • APCs phagocytose antigens and display them using Major Histocompatibility Complex. (correct)
  • APCs are synonymous with T cells.

    • What role do helper T cells play in cell-mediated immunity?

  • They are responsible for clonal selection and expansion of B cells.
  • They suppress the immune response.
  • They produce cytokines that enhance the activity of other immune cells. (correct)
  • They kill infected host cells directly.

    • Which statement about cytotoxic T cells is accurate?

  • They function by binding to antigens for clonal selection.
  • They regulate the production of antibodies.
  • They primarily produce interleukin-10.
  • They can utilize the perforin/granzyme system to eliminate cells. (correct)

    • What happens to the antigen after it is phagocytosed by an APC?

    <p>It is digested into particles for presentation.</p> Signup and view all the answers

    What is the normal range for T cell counts in healthy individuals?

    <p>600 – 1200 cells/μl</p> Signup and view all the answers

    Why do B lymphocytes utilize B cell receptors (BCR)?

    <p>To bind directly to antigens and recognize specific epitopes.</p> Signup and view all the answers

    What is the primary function of regulatory T cells (Tregs) in the immune system?

    <p>To suppress the immune response and maintain tolerance.</p> Signup and view all the answers

    In which process do antigen fragments get displayed on the surface of an APC?

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

    How does the perforin/granzyme system function in immunity?

    <p>It allows cytotoxic T cells to enter infected cells and induce apoptosis.</p> Signup and view all the answers

    What characterizes the immune response of adaptive immunity compared to innate immunity?

    <p>High specificity for antigens</p> Signup and view all the answers

    Which type of lymphocyte is primarily responsible for producing antibodies?

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

    What is the significance of memory cells in adaptive immunity?

    <p>They enable a quicker response upon re-exposure to the same antigen.</p> Signup and view all the answers

    What does the term 'clonal selection' refer to in the context of adaptive immunity?

    <p>The activation of specific lymphocytes that recognize a particular antigen.</p> Signup and view all the answers

    Which of the following is NOT a feature of adaptive immunity?

    <p>Immediate response</p> Signup and view all the answers

    During which process do T cells become activated?

    <p>Binding with antigens directly</p> Signup and view all the answers

    Which statement best describes the function of effector cells in the adaptive immune response?

    <p>They eliminate pathogens and participate in the immune response.</p> Signup and view all the answers

    What is the role of antigen presentation in adaptive immunity?

    <p>To display antigens for T cell recognition.</p> Signup and view all the answers

    Which of the following processes occurs first in the adaptive immune system?

    <p>Clonal selection of lymphocytes</p> Signup and view all the answers

    In which organ do T lymphocytes mature?

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

    Which statement accurately describes the structure of antibodies?

    <p>Antibodies are Y-shaped molecules made up of four polypeptide chains including both variable and constant regions.</p> Signup and view all the answers

    What role does the fragment crystallizable (Fc) portion of an antibody play?

    <p>It mediates physiological effects by binding to Fc receptors on cells.</p> Signup and view all the answers

    Which immunoglobulin is known for its ability to cross the placenta?

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

    How many antigen-binding sites does a typical antibody possess?

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

    What distinguishes IgA from other immunoglobulin classes?

    <p>It is the only antibody found in bodily secretions as a dimer.</p> Signup and view all the answers

    Which type of immunoglobulin accounts for 70-75% of circulating immunoglobulins?

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

    Which statement is true regarding the heavy chains in antibodies?

    <p>The type of heavy chain determines the isotype of the immunoglobulin.</p> Signup and view all the answers

    What is a characteristic feature of IgM?

    <p>It typically exists as a pentamer.</p> Signup and view all the answers

    Which immunoglobulin class is least understood and characterized by its minor presence in serum?

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

    What is the composition of the antigen-binding sites (Fab) in an antibody?

    <p>Formed from the variable regions of the heavy and light chains.</p> Signup and view all the answers

    Study Notes

    Adaptive Immunity Lecture

    • Adaptive immunity is slower than innate immunity but develops throughout a lifetime
    • It is highly specific to antigens
    • It has a memory function, meaning it adapts and improves after initial exposure to an antigen and responds more rapidly on subsequent exposure

    Adaptive Immunity: The Three Rs

    • Recognize: Each cell has a specific receptor for an antigen. Cells from the innate immune system assist with recognition. Recognition is followed by clonal selection
    • Respond: This involves cytokine secretion, antibody production, and direct cell killing.
    • Remember: Memory cells are created for a faster and stronger response on subsequent exposure to the same antigen

    Cells Involved in Adaptive Immunity

    • Lymphocytes: Include B Lymphocytes and T Lymphocytes
    • B Lymphocytes: Produce antibodies. B cells mature in the bone marrow.
    • T Lymphocytes: Involved in cell-mediated immunity. T-cells mature in the thymus.

    Clonal Selection

    • Each lymphocyte has receptors for a single antigen
    • The repertoire of lymphocytes is incredibly diverse
    • Few lymphocytes are specific to any one antigen
    • Each of these lymphocytes is highly specific
    • When an antigen binds to a lymphocyte, the lymphocyte becomes activated, and it begins to rapidly replicate, forming a clone
    • This clone differentiates into effector cells and memory cells

    Antigen Presentation

    • Antigen presenting cells (APCs) introduce antigens to T cells. APCs include phagocytes such as dendritic cells, macrophages, and neutrophils.
    • APCs use the Major Histocompatibility Complex (MHC) to display digested antigen fragments on their surface.
    • The antigen is phagocytosed by an APC
    • Fragments of the antigen are transported to the surface of the APC.
    • The antigen is displayed on the MHC Class II molecule for recognition by T cells

    T Cell Types

    • Helper T cells: Produce cytokines to enhance the activity of B cells, macrophages and other T cells
    • Cytotoxic T cells: Kill foreign cells or infected host cells, using perforin/granzyme which are proteins
    • Regulatory T cells: Suppress the immune response, produce the anti-inflammatory cytokine interleukin (IL)-10

    B Cells and Antibodies (Humoral Immunity)

    • B cell receptors (BCRs) are antibodies that bind antigens directly
    • BCRs recognize specific epitopes (antigenic determinants) on an antigen
    • Following clonal selection and expansion, B cells produce antibodies with the same specificity as their BCR

    Antibody Structure

    • Antibodies (immunoglobulins) have two identical heavy chains and two identical light chains, arranged in a Y shape
    • Each antibody has two antigen-binding sites (Fab regions)
    • The stem of the antibody (Fc region) binds to Fc receptors on cells to mediate the physiological effects of antibodies

    Antibody Isotypes

    • The five classes of antibodies are: IgG, IgM, IgA, IgD, and IgE
    • Each has different functions and characteristics
    • IgG is the most abundant in the blood
    • IgM is the first antibody produced in an immune response
    • IgA is found in secretions
    • IgD is found on the surface of B cells
    • IgE is involved in allergic responses

    Antibody Function

    • Antibodies have various functions, including neutralization of antigens/toxins, opsonization (marking pathogens for phagocytosis), antibody-dependent cellular cytotoxicity (ADCC) (targets pathogens for destruction by other cells), complement activation, and inflammation

    Primary vs. Secondary Antibody Response

    • Primary response is a slower response to an initial encounter with an antigen (5-10 days), with lower antibody titres (amounts of antibody present) and mainly IgM type
    • Secondary response to subsequent encounter is much faster (1-3 days), with higher antibody titres and mainly IgG type
    • Antibody response to second encounter is often more specific (affinity maturation)

    Immunologic Memory

    • A critical aspect of adaptive immunity
    • On a second exposure to the same antigen, the immune response is faster, more extensive, and more effective at eliminating the pathogen compared to the initial response because of memory cells

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    Description

    Explore the intricacies of adaptive immunity, including its slower response time compared to innate immunity and its ability to develop a memory function. Understand the roles of lymphocytes, the three Rs (Recognize, Respond, Remember), and the specifics of B and T lymphocyte functions in immune responses.

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