MHC Classes: Structure and Function
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Questions and Answers

What type of T cells do MHC-class I molecules bind to?

  • CD4 T cells
  • Regulatory T cells
  • CD8 T cells (correct)
  • Natural Killer cells

    • What is the length of the antigen epitopes that can be bound by MHC-I molecules?

  • 8-11 amino acids (correct)
  • 5-7 amino acids
  • 16-20 amino acids
  • 12-15 amino acids

    • What cells do MHC-class I molecules present on?

  • Monocytes, macrophages, and dendritic cells
  • Lymphocytes, macrophages, and dendritic cells
  • Eosinophils, basophils, and neutrophils
  • Lymphocytes, neutrophils, basophils, eosinophils, and platelets (correct)

    • What is the function of MHC-class I molecules?

    <p>To present antigens to CD8 T cells and help kill infected cells</p> Signup and view all the answers

    What is unique about the peptide-binding cleft in class I molecules?

    <p>It is blocked at both ends</p> Signup and view all the answers

    What type of cells do MHC-class II molecules bind to?

    <p>CD4 T cells</p> Signup and view all the answers

    What is the main function of CD8 T cells?

    <p>To directly kill infected cells</p> Signup and view all the answers

    What is the MHC Class I binding region located in CD8 T cells?

    <p>α3 region</p> Signup and view all the answers

    What is the main mechanism of action of cytotoxic granules in CD8 T cells?

    <p>Creating pores in the lipid bilayer of the antigen</p> Signup and view all the answers

    What is the function of TNF-α and IFN-γ in CD8 T cells?

    <p>To secrete cytokines to kill infected cells</p> Signup and view all the answers

    What is the structure of the CD8 molecule?

    <p>A disulfide-linked dimer of two different chains</p> Signup and view all the answers

    What is the function of Fas molecules in CD8 T cells?

    <p>To induce apoptotic cell death</p> Signup and view all the answers

    What is the main region of the CD4 molecule that binds to MHC?

    <p>D1 domain</p> Signup and view all the answers

    What is the main function of CD8 T cells in immune defense?

    <p>To defend against intracellular pathogens</p> Signup and view all the answers

    What is the primary function of antigen-presenting cells?

    <p>To process and present antigens to T cells</p> Signup and view all the answers

    What is the main difference between CD4 and CD8 T cells?

    <p>CD4 cells are helper cells, while CD8 cells are cytotoxic</p> Signup and view all the answers

    What is the role of CD28 on T cells?

    <p>To interact with antigen-presenting cells</p> Signup and view all the answers

    What is the function of MHC molecules on antigen-presenting cells?

    <p>To process and present antigens to T cells</p> Signup and view all the answers

    Where do immature T cells migrate to mature?

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

    What is the type of immunity mediated by T cells?

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

    Which cells can recognize and respond to antigens without antigen presentation?

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

    What is the primary function of CD45 on T cells?

    <p>To facilitate signaling in immune cells</p> Signup and view all the answers

    Which cells can process and present antigens to T cells?

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

    What is the primary function of MHC molecules?

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

    What is the function of the constant regions in T cell receptors?

    <p>To determine the functionality of the T cells</p> Signup and view all the answers

    What type of bond connects the α and β chains of the T cell receptor?

    <p>Disulfide bond</p> Signup and view all the answers

    What is the function of the CD4 molecule?

    <p>To activate other immune cells for antigen killing</p> Signup and view all the answers

    What is the difference between CD4 and CD8 T cell receptors?

    <p>CD4 recognizes antigen bound to MHC-class II molecules, while CD8 recognizes antigen bound to MHC-class I molecules</p> Signup and view all the answers

    What is the function of CD8 T cells?

    <p>To kill the antigen by direct interaction</p> Signup and view all the answers

    What is the structure of the CD4 molecule?

    <p>It has four domains, D1, D2, D3, D4</p> Signup and view all the answers

    What is the function of the stalk segment in the T cell receptor?

    <p>To connect the domains to the transmembrane region</p> Signup and view all the answers

    What is the role of both CD4 and CD8 receptors?

    <p>Antigen binding and signal transmission for stimulating an immune response</p> Signup and view all the answers

    What is the primary function of macrophages in the condition described?

    <p>Eating blood cells</p> Signup and view all the answers

    What is the result of excessive inflammatory activation of macrophages?

    <p>Lymphocytes collecting in spleen and liver</p> Signup and view all the answers

    What is the name of the rare disease caused by excessive T cell activation?

    <p>Hemophagocytic lymphohistiocytosis (HLH)</p> Signup and view all the answers

    What percentage of HLH cases are familial?

    <p>25%</p> Signup and view all the answers

    What is the chance of a child having the disease if both parents are genetic carriers of HLH?

    <p>25%</p> Signup and view all the answers

    What is a common cause of acquired HLH?

    <p>Viral infections</p> Signup and view all the answers

    What is a common symptom of HLH?

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

    What is a possible symptom of HLH in young children and babies?

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

    Study Notes

    MHC Molecules and T Cell Receptors

    • There are two classes of MHC molecules: MHC-class I and MHC-class II, which differ in structure and expression pattern in cells.
    • MHC-class I molecules bind to CD8 T cell receptors (cytotoxic T cells), while MHC-class II molecules bind to CD4 T cell receptors (helper T cells).

    MHC-class I Molecules

    • MHC-class I molecules are designed to enable the body to recognize infected cells and destroy them with the help of cytotoxic CD8 T cells.
    • They are present on lymphocytes, neutrophils, basophils, eosinophils, and platelets.
    • MHC-class I molecules have a deep groove that can bind antigen epitopes of 8-11 amino acids long.
    • They display a part of the antigen peptides (the epitope) on the lymphocyte cell surface after the antigen-presenting cell processes or cleaves the antigen.

    T Lymphocytes (T cells)

    • T cells are born from hematopoietic stem cells found in the bone marrow.
    • Immature T cells migrate from the bone marrow to the thymus gland to mature.
    • After maturation, T cells express several receptors, including CD3, CD4, CD8, CD28, and CD45.
    • T cells do not recognize a soluble antigen in its free form; an antigen must be presented to the T cell receptor through antigen-presenting cells with the help of MHC molecules.

    Antigen-Presenting Cells

    • Antigen-presenting cells include macrophages, B cells, dendritic cells, neutrophils, basophils, eosinophils, and platelets.
    • They express MHC molecules on their surface.
    • The role of antigen-presenting cells is to cleave or process antigens into smaller fragments and present the epitopes on MHC molecules.

    CD4 and CD8 T Cell Receptors

    • CD4 T cells are called helper T cells and are responsible for activating other immune cells for antigen killing.
    • CD4 T cells recognize antigen that is bound to MHC-class II molecules of the antigen-presenting cell.
    • CD8 T cells are called cytotoxic T cells and are responsible for direct killing of the antigen through secretion of cytotoxic molecules.
    • CD8 T cells recognize antigen that is bound to MHC-class I molecules of the antigen-presenting cell.

    Structure of T Cell Receptors

    • T cell receptors consist of two chains, α and β, connected by a disulfide bond.
    • Each chain has carbohydrate side chains attached to each domain.
    • The α and β chains have a short cytoplasmic tail at the carboxyl-terminal end.
    • A short stalk segment connects the domains to the transmembrane region.

    Functions of CD8 T cells

    • CD8 T cells are important for immune defense against intracellular pathogens, including viruses, bacteria, and cancer cells.
    • When activated, CD8 T cells have three major mechanisms to kill infected cells: secretion of cytokines, production and release of cytotoxic granules, and apoptotic cell death through Fas molecules.

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    Description

    This quiz covers the basics of MHC class I and MHC class II molecules, including their structure, expression, and binding to T cell receptors. Learn about the differences between these two classes of MHC molecules.

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