Adaptive Immunity and MHC Complexes
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Questions and Answers

What is a critical outcome of the site-specific recombination process?

  • All DNA between the joined segments is lost. (correct)
  • Only the variable regions are lost.
  • All DNA segments are preserved.
  • Episomes are retained in the nucleus.

What structural classification does the BCR fall under?

  • Heterotetramer (correct)
  • Homotetramer
  • Dimer
  • Monomer

In which phase of the cell cycle does V-D-J recombination occur?

  • Throughout the M phase
  • In the G0-G1 phase (correct)
  • In the G2 phase
  • During the S phase

Which components are involved in the initial step of the V-D-J recombination process?

<p>D and J segments (A)</p> Signup and view all the answers

Which components make up the co-receptor for the BCR?

<p>Igα and Igβ (C)</p> Signup and view all the answers

What is the role of alternative splicing in the maturation of RNA?

<p>It brings the V-D-J segments close to the constant portion. (A)</p> Signup and view all the answers

How are the heavy and light chains of the BCR synthesized?

<p>Independently from different genes (A)</p> Signup and view all the answers

What characterizes the timing of V-D-J recombination?

<p>It is regulated to occur in immature T and B cells. (D)</p> Signup and view all the answers

What role does the ITAM domain play in the BCR signaling process?

<p>It initiates signal transduction when the BCR binds an antigen (A)</p> Signup and view all the answers

What structure is formed from the DNA that is removed during site-specific recombination?

<p>It is degraded as an episome. (C)</p> Signup and view all the answers

What occurs during the maturation of T and B cells?

<p>Receptors are expressed without any prior antigen exposure (B)</p> Signup and view all the answers

What best describes the V-D-J recombination process?

<p>It is tissue-specific, occurring only in B and T cells. (D)</p> Signup and view all the answers

What is the main component of the BCR responsible for binding to specific antigens?

<p>Extracellular portion (D)</p> Signup and view all the answers

During the process of V-D-J recombination, how are the segments brought close to each other?

<p>By the action of specific proteins. (A)</p> Signup and view all the answers

Which statement is true regarding the surface receptor expression in T and B cells?

<p>Receptors appear prior to antigen exposure (D)</p> Signup and view all the answers

What is the significance of the BCR being unable to transduce signals independently?

<p>It maintains signaling specificity (C)</p> Signup and view all the answers

What is the role of sphingosine I phosphate (S1P) receptors in T lymphocytes?

<p>Regulate lymphocyte exit from lymphoid tissue. (D)</p> Signup and view all the answers

How does the presence of interferon type I (IFN I) affect T lymphocyte S1P receptors?

<p>It inhibits the expression of S1P receptors after lymphocyte activation. (B)</p> Signup and view all the answers

What happens to naive T lymphocytes when they enter the lymph nodes?

<p>They internalize their S1P receptors. (A)</p> Signup and view all the answers

What occurs when T cells encounter a specific antigen in the lymph nodes?

<p>They reduce their ability to exit the lymph nodes. (B)</p> Signup and view all the answers

What is the fate of activated T cells after they fully differentiate?

<p>They express S1P receptors and migrate out of lymph nodes. (C)</p> Signup and view all the answers

How frequently do lymphocytes check secondary lymphoid organs for antigens?

<p>Daily. (A)</p> Signup and view all the answers

What is the consequence of a T cell not recognizing any antigen within the lymph nodes?

<p>It will remain in the lymph nodes without activation. (C)</p> Signup and view all the answers

What is the primary function of sphingosine as a lipid in the lymphatic system?

<p>To serve as a chemoattractant factor for lymphocytes. (D)</p> Signup and view all the answers

What does V-D-J recombination achieve in the process of T cell receptor formation?

<p>It randomly selects one segment from each variable, diversity, and joining region. (A)</p> Signup and view all the answers

In contrast to the β chain, how does the δ chain differ in its variable region segments?

<p>The δ chain has fewer segments than the β chain. (B)</p> Signup and view all the answers

Which statement about the diversity of T cell receptors is true?

<p>The diversity in receptors is limited by the number of DNA segments available. (D)</p> Signup and view all the answers

Which regions must be combined to create a functional exon for the β chain?

<p>A segment from the variable, diversity, and joining regions. (B)</p> Signup and view all the answers

What role do stromal and epithelial thymic cells play in T cell receptor development?

<p>They influence the opening of chromatin in specific regions. (C)</p> Signup and view all the answers

Why might the γ-δ receptor have less diversity compared to the α-β receptor?

<p>It has fewer available DNA segments for recombination. (A)</p> Signup and view all the answers

What structural feature distinguishes the α chain from the δ chain?

<p>The α chain has a greater variety of segments in its joining region. (D)</p> Signup and view all the answers

How many different types of segments make up the diversity region of the β chain?

<p>2 segments (D)</p> Signup and view all the answers

What is the origin of B1 cells during development?

<p>Fetal liver hematopoietic stem cells (C)</p> Signup and view all the answers

Which surface immunoglobulin is associated with follicular B cells?

<p>IgM (A), IgD (D)</p> Signup and view all the answers

What is the function of the chemokine receptor CCR7 in naive lymphocytes?

<p>Guides naive lymphocyte recirculation (C)</p> Signup and view all the answers

Which statement is true regarding B1 cells after birth?

<p>Their levels decline after the first day of life (B)</p> Signup and view all the answers

What role does L-Selectin play in lymphocyte recirculation?

<p>Adhesion to endothelial cells (B)</p> Signup and view all the answers

Which of the following describes the function of sphingosine 1-phosphate receptor in T cells?

<p>Mediates exit from lymphoid organs (C)</p> Signup and view all the answers

What type of cells are formed in secondary lymphoid organs from immature B cells?

<p>Follicular B cells or marginal zone B cells (B)</p> Signup and view all the answers

What is commonly true about the immunoglobulins expressed on the surface of B cells?

<p>They express either IgG or IgM (C)</p> Signup and view all the answers

What is the primary function of TCR receptors on T lymphocytes?

<p>To interact with the HLA complex along with peptides (D)</p> Signup and view all the answers

Which types of receptors are NOT found on B cells?

<p>TCR receptors (D)</p> Signup and view all the answers

Which cellular component is NOT essential for signaling transduction in T lymphocytes?

<p>Adhesion molecules (D)</p> Signup and view all the answers

What role do cytokine and chemokine receptors play in lymphocytes?

<p>To help lymphocytes navigate to the site of infection (B)</p> Signup and view all the answers

Which of the following is a significant difference between T cells and B cells?

<p>B cells bind antigens without the need for MHC presentation (C)</p> Signup and view all the answers

What is the function of adhesion molecules in T lymphocytes?

<p>To facilitate interaction with antigen presenting cells (D)</p> Signup and view all the answers

What is the main purpose of the recombination of genes coding for antigen receptors in lymphocytes?

<p>To allow binding to multiple pathogens (B)</p> Signup and view all the answers

Which of the following correctly describes CD4 and CD8 co-receptors on T lymphocytes?

<p>They are involved in the interaction with the MHC complex (C)</p> Signup and view all the answers

Flashcards

Lymphocytes

Adaptive immunity cells that recognize and bind specific antigens through their unique receptors.

How do lymphocytes create diverse receptors?

These cells use a special process to recombine genes, creating many diverse antigen receptor combinations.

What is the purpose of TCR (T cell receptor)?

Important for interacting with major histocompatibility complex (MHC) molecules and presented peptides.

What are Adhesion molecules?

These molecules help T cells adhere to antigen-presenting cells (APCs), facilitating communication and activation.

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What is the function of Fate Receptors?

These receptors help determine the fate of a lymphocyte, such as whether it becomes activated, differentiates, or undergoes apoptosis.

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What is the function of BCR (B cell receptor)?

These receptors bind antigens without MHC presentation, allowing direct recognition of pathogens.

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What is the role of B cells in antigen presentation?

B cells can present peptides like T cells, allowing them to participate in antigen presentation.

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Why are Cytokine receptors important for lymphocytes?

Cytokine receptors help lymphocytes respond to signals from other immune cells, including expansion or activation.

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What is sphingosine 1-phosphate (S1P)?

A lipid signaling molecule that is abundant in the blood and acts as a chemoattractant for lymphocytes.

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What role do S1P receptors play in lymphocyte trafficking?

S1P receptors expressed on lymphocytes regulate their entry and exit from lymphoid tissues like lymph nodes.

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How do naive T cells exit a lymph node?

When a naive T cell enters a lymph node, it re-expresses S1P receptors, allowing it to exit the lymph node upon encountering S1P in the blood.

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Why do activated T cells stay in the lymph node?

After activation by antigen, T cells are prevented from exiting the lymph node as their S1P receptor expression is downregulated.

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How do activated T cells eventually exit the lymph node?

T cells re-express S1P receptors after differentiation, allowing them to migrate out of the lymph node.

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What inhibits S1P receptor expression in activated T cells?

Type I interferon (IFN I), along with CD69, inhibits S1P receptor expression on activated T cells.

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Why is inhibiting S1P receptor expression important for activated T cells?

This process prevents premature exit from the lymph node, ensuring sufficient time for a proper immune response.

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How does S1P play a crucial role in lymphocyte trafficking?

This complex process of S1P-mediated trafficking ensures that lymphocytes are directed to the right places at the right time for an effective immune response.

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B1 cells

A type of B cell originating from fetal liver hematopoietic stem cells, characterized by the presence of IgM and CD5 on its surface.

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L-Selectin

A key receptor expressed on naive T cells mediating adhesion to high endothelial vessels, crucial for T cell recirculation.

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CCR7 Chemokine

A specific type of chemokine recognized by the CCR7 receptor, guiding naive lymphocytes and dendritic cells towards lymphoid organs.

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Sphingosin I Phosphate Receptor

A molecule expressed on T cells, responsible for guiding their exit from lymphoid organs, ensuring continuous recirculation.

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Lymphocyte Recirculation

The process of lymphocytes circulating through the body, constantly interacting with lymph nodes and other lymphoid organs, enabling immune surveillance.

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CCR7 Receptor

A crucial receptor expressed on naive T cells, triggering the movement of cells towards lymphoid organs in response to specific chemokines like CCR7.

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High Endothelial Vessel

The type of blood vessel found in lymphoid organs, specialized for adhesion and homing of lymphocytes, aided by molecules like L-Selectin.

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Recirculation Signals

Signals that regulate lymphocyte recirculation, ensuring constant monitoring of the body and efficient immune responses.

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What is the BCR?

The B-cell receptor (BCR) is a protein complex found on the surface of B lymphocytes. It is responsible for recognizing and binding to specific antigens, initiating an immune response.

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What are the components of the BCR?

The BCR is made up of two identical heavy chains and two identical light chains. These chains are coded by separate genes and synthesized independently.

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What are the structural regions of the BCR?

The BCR has three main regions: an extracellular portion that binds to antigens, a transmembrane portion that anchors it to the cell membrane, and a short cytoplasmic tail that interacts with intracellular signaling pathways.

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How does the BCR initiate an immune response?

The BCR itself cannot signal for an immune response. It requires a co-receptor, called Igα and Igβ, which contain an ITAM domain. When the antigen binds to the BCR, the co-receptor triggers the initiation of the signal cascade.

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What happens when antigen binds to the BCR complex?

The BCR, Igα, and Igβ form a complex that can trigger an immune response upon antigen binding. This complex is essential for B cell activation and subsequent antibody production.

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When does the BCR develop on a B cell?

The BCR and its co-receptors are expressed on B cells before they encounter any specific antigen. This ensures that the B cell repertoire is diverse and ready to respond to a wide range of pathogens.

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Is the BCR changeable once it develops on a B cell?

The BCR on a mature B cell is fixed and does not change throughout its lifetime. This ensures that the B cell maintains its specificity for a particular antigen throughout its life.

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How do B cells generate such a diverse repertoire of BCRs?

The generation of a huge repertoire of BCRs is achieved through a process called V(D)J recombination, which occurs during B cell development. This process allows for a vast diversity of BCRs, ensuring that the immune system can respond to an enormous variety of potential threats.

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What is V(D)J recombination?

The process of rearranging DNA segments within the TCR gene to create unique receptors.

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What is the TCR (T cell receptor)?

A type of lymphocyte receptor with a variable, diversity, and joining region that allows for a broad range of antigen recognition.

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How many segments make up the TCR β chain?

The β chain of TCR has more than 50 variable segments, 2 diversity segments, and around a dozen joining segments.

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How many segments make up the TCR α chain?

The α chain of TCR has more than 45 variable segments and over 50 joining segments.

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Why does the γ-δ TCR have less diversity than the α-β TCR?

The δ chain of TCR has fewer variable, diversity, and joining segments compared to the β chain, resulting in less diversity.

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Why is the β chain often the first TCR chain to recombine?

The β chain is typically the first to undergo rearrangement, influenced by signals from stromal and epithelial cells.

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What's the main purpose of V(D)J recombination?

Rearranging DNA segments to create unique TCRs allowing for a diverse range of antigen recognition.

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How does the TCR variable region form?

The TCR variable region is determined by segments from the variable (V), diversity (D), and joining (J) genes.

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V(D)J Recombination

The process of rearranging DNA segments within the V, D, and J regions of B and T cell receptor genes to create a diverse repertoire of receptors.

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How does V(D)J Recombination work?

Randomly chosen segments from the V, D, and J regions are joined together, with the DNA between them being lost.

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Why is V(D)J Recombination important?

This process ensures that each B or T cell expresses a unique receptor, enabling recognition of a vast array of antigens.

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What happens after V(D)J Recombination?

The segment joining the V, D, and J regions is brought closer to the constant region of the gene through alternative splicing of the RNA transcript.

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Where does V(D)J Recombination happen?

This process occurs specifically in B and T cells, demonstrating its crucial role in the development of adaptive immunity.

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When does V(D)J Recombination occur?

V(D)J recombination only occurs in immature B and T cells when they are differentiating into mature cells.

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How is the cell cycle related to V(D)J recombination?

V(D)J recombination takes place during the G0-G1 phase of the cell cycle, when the cells are not actively replicating their DNA.

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Why is cell cycle phase specific for V(D)J recombination?

This ensures that DNA replication does not interfere with the recombination process, preventing errors.

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Study Notes

Adaptive Immunity

  • The innate immune system is the first line of defense against pathogens
  • It activates immediately upon pathogen entry
  • If pathogens are numerous, inflammation occurs, and the adaptive immune response is activated
  • The adaptive immune system comprises lymphocytes (T and B cells)
  • Lymphocytes have specific receptors (TCR and BCR) that identify unique pathogen-derived peptides presented on MHC complexes
  • Allows for a more potent response to pathogens compared to the innate system
  • This response is specific to the pathogen involved

MHC Complexes

  • MHC complexes present peptides to circulating cells
  • Allow identification of intracellular pathogens
  • Two types of MHC complexes: class I and class II
  • Class I MHC presents intracellular peptides to cytotoxic T cells
  • Class II MHC presents extracellular peptides to helper T cells

Pathogen Detection

  • Some pathogens can enter and replicate inside cells
  • The adaptive immune system has evolved to detect pathogens inside cells as well as those that remain outside cells
  • The MHC complex is crucial for this as it's how the adaptive immune system recognizes any pathogen
  • Peptides from the pathogen compete with peptides from normal endogenous proteins

T Cell Activation

  • T cells have receptors (TCR) that bind peptides presented by MHC complexes
  • Activation occurs when a T cell's TCR recognizes a peptide and the cell becomes strictly connected
  • The activation of T cells initiates various effects, such as the release of perforin and/or granzyme
  • Cytokine release activates other cells that are involved in the adaptive immunity
  • The CD8 cells kill infected cells, differently from the CD4 cells which help in activating a humoral response

Adaptive Immune Response Features

  • Recognition of specific peptides, enabling a tailored response to each pathogen
  • Clonal expansion of cells with the receptor: Only the cells that recognize the peptide expand and differentiate to form effector cells
  • Development of memory cells, providing long-term protection against reinfection. Memory cells are extremely important for vaccination strategies.

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Adaptive Immune Cells PDF

Description

Test your understanding of adaptive immunity and the role of MHC complexes in pathogen detection. This quiz covers the basics of lymphocyte function, the types of MHC complexes, and their crucial roles in the immune response. Challenge yourself with questions that explore how the adaptive system responds to various pathogens.

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