Antigen Presenting Cells and Dendritic Cells
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Questions and Answers

What characterizes effector cells in the immune response?

  • They only function in the bloodstream without tissue involvement.
  • They present antigens to other immune cells.
  • They actively engage in immune defenses after encountering antigens. (correct)
  • They are long-lived and store memory of antigens.

    • Which statement accurately describes professional antigen-presenting cells (APCs)?

  • They primarily provide signals to activate naïve T cells. (correct)
  • They require additional signals to activate effector B cells.
  • They are less effective at displaying antigens compared to non-professional APCs.
  • They can only present antigens during times of infection.

    • What is the role of Major Histocompatibility Complex (MHC) in antigen presentation?

  • MHC is responsible for activating B cells without T cell assistance.
  • MHC molecules destroy pathogens before they are presented.
  • MHC molecules help to attach antigens to the surface of APCs. (correct)
  • MHC facilitates the death of effector cells after antigen elimination.

    • Which type of immune cells are classified as naïve lymphocytes?

    <p>B-lymphocytes and T-lymphocytes that have not yet encountered foreign invaders.</p> Signup and view all the answers

    How do non-professional APCs differ from professional APCs?

    <p>Non-professional APCs can only present antigens in specific situations.</p> Signup and view all the answers

    What is the primary role of dendritic cells in the immune response?

    <p>Serving as a bridge between antigens and T cell activation</p> Signup and view all the answers

    Which surface receptors do dendritic cells express upon activation?

    <p>Receptors for chemokines</p> Signup and view all the answers

    What triggers the activation of dendritic cells?

    <p>Cytokines and Toll-like receptors</p> Signup and view all the answers

    What happens to dendritic cells after they become activated?

    <p>They lose adhesiveness and migrate</p> Signup and view all the answers

    What inflammatory cytokines are produced by activated dendritic cells?

    <p>Tumor Necrosis Factor and Interleukin-1</p> Signup and view all the answers

    Where are dendritic cells typically found in the body?

    <p>In lymphoid organs and epithelial tissues</p> Signup and view all the answers

    Which type of dendritic cells migrate and are involved in B cell maturation?

    <p>Germinal center dendritic cells</p> Signup and view all the answers

    What is the significance of chemokines in the function of dendritic cells?

    <p>They guide dendritic cells to lymph nodes</p> Signup and view all the answers

    What is the primary role of dendritic cells during migration to lymph nodes?

    <p>They undergo maturation into antigen-presenting cells.</p> Signup and view all the answers

    Which type of antigens do MHC class I molecules primarily present?

    <p>Intracellular and extracellular antigens</p> Signup and view all the answers

    What is a critical function of professional antigen-presenting cells (APCs) like dendritic cells?

    <p>Efficient internalization of antigens through phagocytosis and endocytosis</p> Signup and view all the answers

    How do dendritic cells interact with T cells after maturation?

    <p>By presenting antigens via MHC and expressing co-stimulatory molecules</p> Signup and view all the answers

    What triggers the expression of MHC class II molecules on professional APCs?

    <p>Induced by cytokines and bacterial infection</p> Signup and view all the answers

    Which cells are considered professional antigen-presenting cells?

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

    Where are antigen-presenting cells primarily located in the body?

    <p>In connective and lymphoid tissues, and body cavities</p> Signup and view all the answers

    Which co-stimulatory molecules are typically expressed by antigen-presenting cells?

    <p>B7 molecules</p> Signup and view all the answers

    Which type of dendritic cells are specifically involved in capturing antigens from the skin and mucous surfaces?

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

    What is the primary role of follicular dendritic cells (FDCs)?

    <p>Assisting in B cell maturation and antibody production</p> Signup and view all the answers

    Which type of dendritic cells is rich in MHC class II molecules?

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

    Which characteristic is true about follicular dendritic cells (FDCs)?

    <p>They lack MHC class II molecules.</p> Signup and view all the answers

    What is the primary function of dendritic cells when they interact with T cells?

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

    Which of the following is NOT a characteristic of interdigitating cells?

    <p>They do not interact with B cells.</p> Signup and view all the answers

    Which of the following types of cells is considered a professional antigen-presenting cell (APC)?

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

    How do germinal center dendritic cells assist in B cell function?

    <p>By helping form memory B cells.</p> Signup and view all the answers

    What occurs when tissues are damaged and antigens are released?

    <p>The immune system mistakenly attacks the damaged tissues.</p> Signup and view all the answers

    What is molecular mimicry in the context of autoimmunity?

    <p>Foreign antigens resemble the body's own proteins, leading to self-attack.</p> Signup and view all the answers

    How can an alteration in antigen processing affect the immune system?

    <p>It might lead to the immune system attacking normal cells.</p> Signup and view all the answers

    Which factor does NOT contribute to the development of autoimmunity?

    <p>Over stimulation of adaptive immunity.</p> Signup and view all the answers

    What role do lymphocyte abnormalities play in autoimmunity?

    <p>They can lead to self-reactivity and autoimmunity.</p> Signup and view all the answers

    What may happen due to the failure of central tolerance mechanisms?

    <p>Self-reactive lymphocytes persist and may attack the body.</p> Signup and view all the answers

    Which of the following describes polyclonal lymphocyte activation?

    <p>Non-specific activation, including self-reactive lymphocytes.</p> Signup and view all the answers

    How can chronic inflammation lead to autoimmunity?

    <p>By disrupting immune system’s tolerance to self-antigens.</p> Signup and view all the answers

    Study Notes

    Antigen Presenting Cells (APCs)

    • APCs are immune cells that display antigens on their surface, alerting other immune cells to an infection.

    • APCs can be divided into two groups:

      • Professional APCs: These are cells specialized for presenting antigens, including dendritic cells, macrophages, and B cells. They are highly efficient at antigen presentation and activating naive T cells.
      • Non-professional APCs: These cells can also present antigens but only under specific circumstances, such as during an infection. They are less effective at antigen presentation compared to professional APCs.

    • Professional APCs are important because they:

      • Display antigens on their surface for T cells to recognize.
      • Provide signals necessary to fully activate naive T cells.

    Types of Dendritic Cells

    • Langerhans cells: Found in the skin and mucosal epithelium. Capture antigens from these surfaces and migrate to lymph nodes to trigger an immune response.

    • Interdigitating cells: Dendritic cells that travel to lymphoid tissues (like lymph nodes) and interact with T cells. They help activate T cells by presenting antigens.

    • Follicular dendritic cells (FDCs): Found in the primary and secondary follicles of B cell areas in lymph nodes and the spleen. Present antigens to B cells to aid in antibody production.

    • Germinal center dendritic cells (GCDC): Found within germinal centers. Assist in B cell maturation and the selection of high-affinity antibodies, forming memory B cells.

    Dendritic Cell Migration and Maturation

    • When dendritic cells encounter an antigen, they activate and undergo various changes:

      • Loss of adhesiveness to the epithelial tissue.
      • Expression of specific surface receptors that respond to chemokines.
      • Migration to lymph nodes guided by chemokines.

    • As dendritic cells mature, they express MHC and co-stimulatory molecules for efficient interaction and activation of T cells.

    MHC Expression in Professional APCs

    • Macrophages: MHC-II expression is induced by bacteria and/or cytokines. MHC-I is expressed at low levels.

    • Dendritic Cells: MHC-II is expressed constantly and at high levels. MHC-I is expressed at low levels but is induced by bacteria and/or cytokines.

    • B Cells: MHC-II is always expressed and is further induced upon activation. MHC-I is constantly expressed at low levels.

    Antigen Presentation by Professional APCs

    • Macrophages: Process both intracellular and extracellular antigens. Antigens are presented via MHC-II (extracellular antigens) and MHC-I (intracellular).

    • Dendritic Cells: Process extracellular antigens. Antigens are presented via MHC-II.

    • B Cells: Process extracellular antigens that bind to specific immunoglobulin receptors. Antigens are presented via MHC-II.

    Co-stimulation

    • Co-stimulatory molecules (like B7 expression) are necessary for full T cell activation. B7 expression is induced by bacteria and/or cytokines in macrophages. In dendritic cells, B7 is always expressed at high levels. B7 expression in B cells is induced upon activation.

    Location of Professional APCs

    • Macrophages: Found in connective tissues, lymphoid tissues, body cavities, and blood.

    • Dendritic Cells: Located in the connective tissue, epithelium, and lymphoid tissues.

    • B Cells: Found in lymphoid tissues and blood.

    Autoimmunity

    • Autoimmunity occurs when the immune system mistakenly attacks the body's own tissues and organs.

    • Mechanisms of autoimmunity:

      • Tissue damage: Damaged tissue releases antigens that are mistaken for foreign invaders.
      • Molecular changes: Self-proteins may undergo structural changes and be recognized as foreign.
      • Molecular mimicry: Foreign antigens resemble self-proteins, leading to cross-reactivity.
      • Alteration in antigen processing: Defects in antigen processing can lead to improper recognition of self-antigens.
      • Infection: Certain infections can disrupt tolerance to self-antigens.
      • Genetic factors: Specific genes can increase susceptibility to autoimmune diseases.

    • Other contributing factors:

      • Lymphocyte abnormalities: Abnormal B or T cells can contribute to autoimmunity.
      • Failure of central tolerance: Self-reactive lymphocytes fail to be eliminated in the thymus or bone marrow.
      • Overcome of peripheral tolerance: Mechanisms that suppress self-reactive lymphocytes fail.
      • Polyclonal lymphocyte activation: Non-specific activation of lymphocytes, potentially including self-reactive ones, can lead to autoimmunity.

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    Lecture 7 - Antigen Presenting Cells and Autoimmunity PDF

    Description

    Explore the essential roles of antigen presenting cells (APCs) in the immune response, including the distinction between professional and non-professional APCs. Gain insights into the specific types of dendritic cells, such as Langerhans cells, and their functions in triggering immunity. Test your understanding of these key concepts in immunology.

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