Immunology: Superantigens Overview
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Questions and Answers

Which type of cell is classified as a professional antigen-presenting cell?

  • Epithelial cells
  • Endothelial cells
  • Dendritic cells (correct)
  • Fibroblasts

    • What is the role of MHC class I molecules in antigen presentation?

  • They present peptides to CD4+ T cells.
  • They activate macrophages directly.
  • They present lipid antigens to B cells.
  • They present peptides to CD8+ T cells. (correct)

    • Which type of antigen-presenting cell requires activation through phagocytosis?

  • B cells
  • Macrophages (correct)
  • Dendritic cells
  • Epithelial cells

    • What characterizes nonprofessional antigen-presenting cells?

    <p>They can present antigens for limited times during inflammation.</p> Signup and view all the answers

    In which pathway are intravesicular pathogens processed?

    <p>Vesicular (endocytic) pathway</p> Signup and view all the answers

    Which cells present antigens in association with MHC class II molecules?

    <p>Professional antigen-presenting cells</p> Signup and view all the answers

    What type of cells do CD1 molecules present lipid antigens to?

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

    What is the main function of professional antigen-presenting cells?

    <p>To present antigens and activate T cells.</p> Signup and view all the answers

    What is the role of superantigens in T cell activation?

    <p>They polyclonally activate a large fraction of T cells.</p> Signup and view all the answers

    Which of the following is an example of a superantigen?

    <p>Staphylococcal enterotoxins</p> Signup and view all the answers

    What distinguishes endogenous antigens from exogenous antigens?

    <p>Endogenous antigens are processed within the cell's cytoplasm.</p> Signup and view all the answers

    Which T cell type recognizes antigens presented by MHC class I molecules?

    <p>CD8+ T cells</p> Signup and view all the answers

    What is a characteristic feature of T-independent antigens?

    <p>They exhibit a polymeric structure with repeated antigenic determinants.</p> Signup and view all the answers

    What is the main function of antigen processing?

    <p>To digest proteins into peptides for MHC display.</p> Signup and view all the answers

    Which statement accurately describes the size of antigenic determinants recognized by B cells?

    <p>They typically consist of 4-8 residues.</p> Signup and view all the answers

    How do CD4+ T cells recognize antigens?

    <p>In the context of MHC class II molecules.</p> Signup and view all the answers

    What is a potential consequence of the polyclonal activation of B cells by T-independent antigens?

    <p>B cells can activate clones specific to other antigens.</p> Signup and view all the answers

    Which molecules serve as co-receptors for T cells?

    <p>CD4 and CD8 molecules</p> Signup and view all the answers

    How are T-dependent antigens primarily characterized?

    <p>They have few copies of many different antigenic determinants.</p> Signup and view all the answers

    What is a consequence of the hyperactivation of the immune system due to superantigens?

    <p>Excess release of cytokines by T cells.</p> Signup and view all the answers

    How do superantigens differ from conventional T-dependent antigens?

    <p>They activate nearly all T cells in the population.</p> Signup and view all the answers

    What is a primary requirement for T cells to recognize processed antigenic determinants?

    <p>MHC presentation of processed antigens.</p> Signup and view all the answers

    Which of the following compositions do T cell-recognized antigenic determinants mainly have?

    <p>Proteins and some lipids.</p> Signup and view all the answers

    In terms of antigen processing, what is essential for epitope presentation to T cells?

    <p>Loading of processed peptides onto MHC molecules.</p> Signup and view all the answers

    Study Notes

    Superantigens

    • Superantigens can activate up to 25% of T cells, significantly more than conventional antigens.
    • Examples:
      • Staphylococcal enterotoxins: Cause food poisoning.
      • Staphylococcal toxic shock toxin: Linked to toxic shock syndrome.
      • Staphylococcal exfoliating toxins: Responsible for scalded skin syndrome.
      • Streptococcal pyrogenic exotoxins: Associated with shock.
    • Diseases caused by superantigens result from hyperactivation of the immune system and cytokine release by T cells.

    Antigen Processing and Presentation

    • Antigen Processing: Digests proteins into peptides for display with MHC class I or II molecules on cell membranes.
    • Endogenous Antigens: Processed within the cell's cytoplasm.
    • Exogenous Antigens: Internalized via phagocytosis or endocytosis and processed in the endocytic pathway.
    • T cells recognize antigens as short peptides presented by MHC class-I (for CD8+ T cells) or MHC class-II (for CD4+ T cells).

    T Cell Recognition

    • CD4+ T cells interact with MHC class-II; CD8+ T cells interact with MHC class-I, determined by co-receptors.
    • CD4 molecule binds to the β2 domain of MHC class-II.

    T-independent and T-dependent Antigens

    • T-independent Antigens:

      • Directly stimulate B cells, commonly polysaccharides.
      • Characterized by repeated polymeric structures.
      • Induce polyclonal activation of B cells and are resistant to degradation.

    • T-dependent Antigens:

      • Require T cell assistance for antibody production, typically proteins.
      • Feature a few copies of numerous antigenic determinants.

    Antigenic Determinants

    • Recognized by B cells:

      • Composed of proteins, polysaccharides, nucleic acids with both linear and conformational determinants.
      • Typically sized 4-8 residues, with a focus on immunodominant epitopes.

    • Recognized by T cells:

      • Mainly proteins (some lipids), processed and presented via MHC.
      • Typically sized 8-15 residues and limited to those that can bind to MHC.

    Antigen-Presenting Cells (APCs)

    • Only cells presenting peptides with MHC class II to CD4 T cells are classified as APCs; those presenting MHC class I are target cells.
    • Types of APCs:
      • Professional APCs:
        • Dendritic cells: Most effective APCs, high MHC class II and co-stimulatory molecule expression.
        • Macrophages: Require activation via phagocytosis for MHC class II expression.
        • B cells: Constitutively express MHC class II but need activation for co-stimulatory expression.
      • Nonprofessional APCs: Can act as APCs temporarily during inflammation (e.g., epithelial and endothelial cells).

    Pathways of Antigen Processing

    • Two distinct processing pathways:
      • Cytosolic (Endogenous) Pathway: For pathogens replicating in the cytosol, presenting to CD8+ T cells via MHC class I.
      • Vesicular (Endocytic) Pathway: For intravesicular pathogens, presenting to CD4+ T cells via MHC class II.

    CD1 Molecules

    • Group 1 CD1 molecules present lipid antigens to a diverse range of T cells, aiding adaptive immunity against various microbial lipid antigens.

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    Antigens PDF

    Description

    Explore the fascinating world of superantigens and their role in T cell activation. This quiz covers various examples of superantigens, including those from Staphylococcus and Streptococcus bacteria, and their implications in diseases such as food poisoning and toxic shock syndrome.

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