T cell Development (Immune System - Osmosis)
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Questions and Answers

What is the primary function of the innate immune response?

  • To enhance memory of previous infections
  • To generate a diverse set of lymphocytes
  • To provide immediate, non-specific protection against invaders (correct)
  • To develop specific responses to unique antigens

    • Why is the adaptive immune response considered to have memory?

  • It is activated instantly upon infection
  • It can remember all past infections without any exposure
  • It speeds up responses upon subsequent encounters with the same pathogen (correct)
  • It involves both B and T cells regardless of pathogen type

    • Where do T cells complete their development?

  • Spleen
  • Lymph nodes
  • Bone marrow
  • Thymus (correct)

    • What does lymphopoiesis aim to achieve?

    <p>To generate diverse lymphocytes and eliminate self-reactive ones</p> Signup and view all the answers

    What happens to the thymus as one ages?

    <p>It undergoes involution, leading to decreased T cell production</p> Signup and view all the answers

    What is the main distinction between the innate and adaptive immune responses?

    <p>The innate response cannot differentiate between pathogens</p> Signup and view all the answers

    How are B cells matured after their initial development?

    <p>They mature in the spleen after initial development in the bone marrow</p> Signup and view all the answers

    What are the key cells of the adaptive immune response?

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

    What is the primary purpose of positive selection in T cell development?

    <p>To allow T cells to recognize and bind to MHC molecules.</p> Signup and view all the answers

    What role does the autoimmune regulator gene AIRE play in negative selection?

    <p>It enables the expression of various self-antigens by thymic epithelial cells.</p> Signup and view all the answers

    What determines whether a DP T cell downregulates CD4 or CD8?

    <p>The binding strength between T cell receptors and MHC molecules.</p> Signup and view all the answers

    After successful positive selection, what type of T cell does a DP cell become?

    <p>A single positive naive T cell.</p> Signup and view all the answers

    In the context of T cell development, what process occurs after the rearrangement of the beta chain?

    <p>Combination of the beta chain with the invariant pre-T alpha chain.</p> Signup and view all the answers

    What is the function of the T cell receptor (TCR) in relation to peptides and MHC?

    <p>To recognize and bind both peptides from protein antigens and MHC.</p> Signup and view all the answers

    Which type of cells are responsible for presenting antigens to mature T cells in secondary lymphoid organs?

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

    What is the immediate fate of a DP cell that binds strongly to a self-antigen during negative selection?

    <p>It undergoes apoptosis.</p> Signup and view all the answers

    Which chain rearrangement occurs first during T cell development?

    <p>Beta chain rearrangement.</p> Signup and view all the answers

    How does the thymus contribute to T cell development?

    <p>It provides a unique environment for both positive and negative selection.</p> Signup and view all the answers

    What is the role of MHC molecules in T cell development?

    <p>They present peptide antigens to T cell receptors.</p> Signup and view all the answers

    During which stage is a T cell considered to be double negative?

    <p>When it does not express CD3, CD4, or CD8.</p> Signup and view all the answers

    What signifies the transition of a DN1 cell to a DN2 cell?

    <p>The expression of Rag-1 and Rag-2 enzymes.</p> Signup and view all the answers

    Which chain of the T cell receptor is assembled first?

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

    What is the significance of allelic exclusion during T cell development?

    <p>To prevent expression of multiple T cell receptors.</p> Signup and view all the answers

    What happens to a T cell that fails to express a functional T cell receptor?

    <p>It dies as a quality control mechanism.</p> Signup and view all the answers

    What is the function of interleukin 7 (IL-7) in T cell maturation?

    <p>To stimulate the proliferation of T cells.</p> Signup and view all the answers

    Which proteins are critical for the recombination of the T cell receptor gene segments?

    <p>Rag-1 and Rag-2.</p> Signup and view all the answers

    How many variable gene segments are typically present in the alpha chain of a T cell receptor?

    <p>70-80</p> Signup and view all the answers

    At what stage does a T cell express both CD4 and CD8 on its surface?

    <p>Double positive stage</p> Signup and view all the answers

    What is the primary function of the invariant pre-T alpha chain?

    <p>To assist the beta chain in gaining surface expression.</p> Signup and view all the answers

    Which of the following stages involves rearranging the alpha chain after the beta chain is formed?

    <p>DP stage</p> Signup and view all the answers

    Which combination represents a unique structure of a T cell receptor?

    <p>A combination of unique V, D, and J gene segments.</p> Signup and view all the answers

    Which cells are involved in antigen presentation to developing T cells?

    <p>Epithelial cells and dendritic cells.</p> Signup and view all the answers

    At which developmental stage is a T cell primarily focused on creating a functional receptor?

    <p>DN3 stage</p> Signup and view all the answers

    What is the main function of RAG1 and RAG2 during T cell maturation?

    <p>Initiating V(D)J recombination to create TCR diversity</p> Signup and view all the answers

    At which stages are RAG1 and RAG2 predominantly active in T cell development?

    <p>DN2 and DN3 stages</p> Signup and view all the answers

    Which of the following accurately describes the checkpoints in T cell development involving RAG1 and RAG2?

    <p>They play a vital role in the successful recombination of the TCRβ chain at the DN3 stage</p> Signup and view all the answers

    What occurs immediately after RAG1 and RAG2 introduce double-strand breaks in the DNA?

    <p>Repair and recombination of TCR segments by other proteins take place</p> Signup and view all the answers

    Which phases are included in the double-negative (DN) stage of T cell development?

    <p>DN1, DN2, DN3, and DN4</p> Signup and view all the answers

    Which of the following best explains the importance of TCR diversity generated by V(D)J recombination?

    <p>It enables the adaptive immune system to respond to a broad spectrum of pathogens</p> Signup and view all the answers

    What role do RAG1 and RAG2 specifically play in TCR gene rearrangement?

    <p>They recognize specific DNA sequences and induce double-strand breaks</p> Signup and view all the answers

    What is the consequence of unsuccessful TCRβ chain recombination in thymocytes?

    <p>The cell may undergo apoptosis</p> Signup and view all the answers

    Study Notes

    Immune Response

    • Innate immune response is non-specific, but immediate.
    • Adaptive immune response is targeted for each invader, but takes time to activate.
    • Adaptive immunity has memory, which allows for quicker and stronger responses.

    Lymphopoiesis

    • Lymphopoiesis produces diverse lymphocytes, each with a unique antigen receptor.
    • It eliminates self-reactive lymphocytes to prevent autoimmune diseases.
    • Hematopoietic stem cells mature into common lymphoid progenitor cells.
    • Common lymphoid progenitors differentiate into B cells and T cells.

    B Cell Development

    • B cells develop in the bone marrow, maturing in the spleen.

    T Cell Development

    • T cells mature in the thymus, a fatty organ that shrinks with age, leading to decreased cell-mediated immunity.
    • Thymus has an outer cortex and inner medulla.
    • Epithelial cells and dendritic cells present antigens to developing T cells on MHC molecules.
    • T cell receptors (TCR) only bind peptide antigens when presented on MHC molecules.
    • TCRs are composed of an alpha chain and a beta chain, each made of V, D, and J gene segments.
    • Multiple V, D, and J segments allow for many unique combinations of TCRs.
    • T cell development occurs in three stages: Double negative, double positive, and single positive.

    Double Negative (DN) Stage

    • DN stage cells express neither CD4 nor CD8.
    • DN stage progresses through four steps: DN1, DN2, DN3, DN4.
    • DN2 cells express Rag-1 and Rag-2 enzymes, which initiate VDJ recombination.
    • VDJ recombinase rearranges D-J segments on both chromosomes, with only one chromosome successfully rearranging.
    • DN3 cells successfully join D and J segments.
    • DN4 cells attach V segments to D-J segments, forming a complete beta chain.

    Double Positive (DP) Stage

    • DP stage cells express both CD4 and CD8.
    • They rearrange the alpha chain while retaining the same beta chain.
    • DP cells undergo positive selection, ensuring they recognize MHC molecules.
    • Positive selection involves preserving T cells that recognize the individual's own MHC.
    • DP cells also undergo negative selection, eliminating self-reactive T cells.
    • AIRE (autoimmune regulator gene) allows thymic epithelial cells to express body-wide antigens for negative selection.

    Single Positive (SP) Stage

    • SP stage cells downregulate either CD4 or CD8.
    • CD4 downregulation leads to CD8+ T cells.
    • CD8 downregulation leads to CD4+ T cells.
    • SP stage cells are naive T cells, ready to encounter antigens in lymph nodes or spleen.
    • Mature T cells are released into the periphery, ready to respond to infections.

    Summary

    • T cell development in the thymus ensures the production of functional T cells that can recognize antigens and respond effectively to infections.
    • This process is a complex series of steps, involving gene rearrangement, selection, and maturation, ensuring the generation of a diverse yet safe repertoire of T cells.

    RAG1 and RAG2: Key Players in T Cell Development

    • RAG1 and RAG2 are crucial enzymes responsible for V(D)J recombination, a process that generates diversity in the T cell receptor (TCR).

    • V(D)J recombination rearranges the variable (V), diversity (D), and joining (J) segments of the TCR genes, creating unique receptors.

    • This diversity is essential for the adaptive immune system's ability to recognize a vast array of pathogens.

    The Double-Negative (DN) Stage

    • The DN stage of T cell development involves thymocytes that do not express the co-receptors CD4 or CD8.

    • The DN stage is divided into four phases: DN1, DN2, DN3, and DN4.

    • RAG1 and RAG2 are most active in the DN2 and DN3 stages, facilitating TCRβ chain recombination.

    Key Functions of RAG1 and RAG2

    • RAG1 and RAG2 recognize specific DNA sequences flanking the V, D, and J gene segments and introduce double-strand breaks.

    • Other proteins repair and recombine these segments to form a functional TCRβ chain.

    Checkpoints in T Cell Development

    • Successful TCRβ chain recombination, aided by RAG1 and RAG2, is a critical checkpoint at the DN3 stage.

    • If recombination is successful, the thymocyte continues development; otherwise, it may undergo apoptosis.

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    Description

    Test your knowledge on the basics of the immune response, including innate and adaptive immunity, lymphopoiesis, and the development of B and T cells. This quiz covers how the immune system functions and the importance of memory in adaptive immunity.

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