Antigen Presentation
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Antigen Presentation

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Questions and Answers

Which cell types can express HLA-2?

  • Erythrocytes and platelets
  • Smooth muscle cells and fibroblasts
  • Macrophages and dendritic cells (correct)
  • Neurons and astrocytes

    • Which type of antigen (intracellular or extracellular) corresponds to HLA-1 presentation?

  • Intracellular (correct)
  • Extracellular
  • Both intracellular and extracellular
  • None of the above

    • What is the process by which exogenous antigens can be presented by HLA-1?

  • Cross-migration
  • Autophagy leading to presentation on HLA-2
  • Antigens leaking out of endosomes into the cytosol (correct)
  • Phagocytosis into the cytosol

    • What is the function of cross-presentation in antigen presenting cells?

    <p>Simultaneously activating both Thelper and cytotoxic T cells</p> Signup and view all the answers

    After a peptide-bound HLA-2 is expressed on the cell surface, what happens next?

    <p>It binds with CD4+ T-cells</p> Signup and view all the answers

    What is the primary role of dendritic cells in cross-presentation?

    <p>Being the best at cross-presentation</p> Signup and view all the answers

    What is the major CD that distinguishes a Helper T-cell from a cytotoxic T-cell?

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

    What is the co-receptor for a cytotoxic T cell?

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

    Which molecule interacts with CD28 on T-cells for co-stimulatory activation?

    <p>CD80</p> Signup and view all the answers

    Which cells have the capacity to up-regulate CD80/86 after they are activated by an encounter with a pathogen?

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

    Which type of HLA is involved in the endogenous antigen presentation pathway?

    <p>HLA-1</p> Signup and view all the answers

    When is the antigen loaded onto the HLA protein in the exogenous antigen presentation pathway?

    <p>After being engulfed by the antigen-presenting cell</p> Signup and view all the answers

    How are cytotoxic T cells activated?

    <p>By direct recognition of antigens displayed on MHC class I molecules</p> Signup and view all the answers

    What types of cells might present the HLA bound antigen in the endogenous antigen presentation pathway?

    <p>All nucleated cells</p> Signup and view all the answers

    What distinguishes foreign antigens from self antigens for T-cells?

    <p>The binding affinity to HLA proteins</p> Signup and view all the answers

    Why can HLA proteins present a wide variety of antigens to a wide variety of lymphocytes?

    <p>They are not bound particularly tightly to antigens</p> Signup and view all the answers

    How is an HLA class II molecule loaded with antigen?

    <p>Via the exogenous pathway in endocytic compartments</p> Signup and view all the answers

    Under what circumstances can exogenous antigens be presented by HLA class I molecules?

    <p>During antigen crosspresentation in endocytic compartments</p> Signup and view all the answers

    What ensures that a cytosolic antigen isn’t loaded onto an HLA-2 in the rough endoplasmic reticulum?

    <p>HLA-DM assisting with loading onto HLA-2</p> Signup and view all the answers

    In the endogenous pathway of HLA-1 expression, where is the source of the antigenic peptide?

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

    What is responsible for loading the antigenic peptide onto the HLA-1 protein in the endogenous pathway?

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

    What happens to the loaded HLA-1 in the endogenous pathway?

    <p>It is expressed on the cell surface</p> Signup and view all the answers

    What is the source of the antigenic peptide in the exogenous pathway of HLA-2 expression?

    <p>Extracellular space</p> Signup and view all the answers

    Where are HLA-2 bound peptides transported to in the exogenous pathway?

    <p>Endoplasmic reticulum</p> Signup and view all the answers

    What happens to the loaded HLA-2 in the exogenous pathway?

    <p>It is expressed on the cell surface</p> Signup and view all the answers

    What is the main difference between antigens in endogenous and exogenous pathways?

    <p>Source of antigens: Cytosol for endogenous, extracellular space for exogenous</p> Signup and view all the answers

    Where is the does the antigen bind on an HLA-1 molecule?

    <p>Between Alpha-1 and Alpha-2 Subunits</p> Signup and view all the answers

    CD8 binds to the alpha-3 subunit of HLA_1

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

    Where is the does the antigen bind on an HLA-2 molecule?

    <p>Between Alpha-1 and Beta 1 subunits</p> Signup and view all the answers

    Which of the following cells always express high levels of HLA-2?

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

    B-cells always express HLA-2 at low levels

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

    ___________ needs to be up-regulated in concurrence with HLA-2 expression (think of a process not a molecule)

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

    Which of the following will prevent an exogenous antigen from loading onto an HLA-1?

    <p>Invariant chain</p> Signup and view all the answers

    The chopped version of the invariant chain is known as _______

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

    Dendritic cells are the only APC that always express CD80/86

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

    cSMAC includes the binding between TCR and an HLA only

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

    What is the effect of paracrine signaling between APC and T-cells?

    <p>It will affect polarization of T cell</p> Signup and view all the answers

    Study Notes

    HLA Expression and Antigen Presentation

    • HLA-2 can be expressed by antigen presenting cells, including dendritic cells, macrophages, and B cells.
    • HLA-1 presents extracellular antigens, which are typically derived from outside the cell.
    • Exogenous antigens are presented by HLA-1 through a process called cross-presentation, where antigen presenting cells can take up extracellular antigens and present them to CD8+ cytotoxic T cells.

    Antigen Presentation Process

    • After a peptide binds to HLA-2 and is expressed on the cell surface, it engages T cells, initiating an immune response.
    • Dendritic cells play a crucial role in cross-presentation by capturing antigens from outside and presenting them in a way that activates both CD4+ helper and CD8+ cytotoxic T cells.
    • Helper T cells can be distinguished from cytotoxic T cells by the expression of CD4.
    • The co-receptor for cytotoxic T cells is CD8.

    Co-Stimulatory Activation

    • CD28 on T cells interacts with CD80/CD86 on antigen presenting cells for necessary co-stimulatory signals.
    • Antigen presenting cells can up-regulate CD80/CD86 in response to pathogen encounters.

    Antigen Presentation Pathways

    • HLA class I is involved in the endogenous antigen presentation pathway.
    • In the exogenous pathway, antigens are loaded onto HLA class II molecules after being processed and transported into the endosomal/lysosomal compartments.
    • Cytotoxic T cells require antigen presentation via HLA-1 for activation and recognition of infected cells.

    Antigen Sources and Recognition

    • Endogenous pathway utilizes intracellular sources for antigenic peptides, typically from proteins synthesized within the cell.
    • Exogenous pathway utilizes processed antigens derived from the external environment.
    • T cells differentiate self antigens from foreign antigens through specific recognition by their receptors; self-antigens are usually presented by HLA without activating T cells.

    HLA and Antigen Binding

    • HLA proteins can present a diverse range of antigens due to their polymorphic nature and ability to bind various peptide sequences.
    • Antigens bind to the α1 and α2 subunits of HLA-1, while HLA-2 accommodates antigen binding to the β1 and α1 subunits.

    Special Notes on HLA and Co-Expression

    • B cells consistently express low levels of HLA-2, which can be up-regulated upon activation.
    • A fragment of the invariant chain prevents exogenous antigens from loading onto HLA-1.
    • Dendritic cells uniquely express high levels of CD80/CD86, essential for effective T cell activation.

    cSMAC and Signaling

    • cSMAC, or central supramolecular activation cluster, involves binding between T cell receptors (TCR) and HLA molecules, fostering signal transduction during immune responses.
    • Paracrine signaling between antigen presenting cells and T cells enhances T cell proliferation and activation, leading to a robust immune response.

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    Related Documents

    BMS150_PHL3.04_W23_Antigen Presentation_STUDENT.pdf

    Description

    Test your understanding of T-cell activation and co-receptors with this quiz. Explore the roles of antigen presenting cells, T-cell receptors, HLA-2 molecules, and CD4 co-receptors in the immune response.

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