Cellular Immunity Overview

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Questions and Answers

What is the primary role of CD28 in T cell activation?

  • Promoting T cell activation by interacting with B7 on APCs (correct)
  • Inhibiting T cell activation by binding to B7 on antigen-presenting cells (APCs)
  • Directing T cell differentiation towards TH1 or TH2 subtypes
  • Inducing apoptosis in target cells

What happens when CTLA-4 binds to B7 on APCs?

  • T cell activation is enhanced, leading to a stronger immune response.
  • The T cell differentiates into a TH2 subtype, promoting humoral immunity.
  • The T cell differentiates into a TH1 subtype, promoting cell-mediated immunity.
  • The T cell becomes anergic, meaning it is inactivated and unable to respond to antigens. (correct)

Which cytokine is critical for the activation of the TH1 response?

  • IL-10
  • IL-12 (correct)
  • IL-4
  • IL-5

Which of the following is NOT a characteristic of TH1 cells?

<p>Production of IgG and IgE antibodies (A)</p> Signup and view all the answers

What is the main function of TH1 responses?

<p>Eliminating intracellular pathogens and fungi through cell-mediated immunity (C)</p> Signup and view all the answers

Which of the following cytokines are associated with TH2 responses?

<p>IL-4, IL-5, IL-6, IL-10 (B)</p> Signup and view all the answers

Which of the following is a consequence of an exaggerated TH2 response in the context of intracellular infections?

<p>Suppression of the protective TH1 response (C)</p> Signup and view all the answers

What is the primary role of TH2 responses in the immune system?

<p>Promoting antibody production for targeting extracellular pathogens (C)</p> Signup and view all the answers

How does the interaction between CD40L on T cells and CD40 on APCs influence the immune response?

<p>It stimulates the production of cytokines that regulate the function of macrophages, DCs, and B cells. (B)</p> Signup and view all the answers

Which of the following statements is TRUE about the relationship between TH1 and TH2 cytokines?

<p>TH1 cytokines suppress the production of TH2 cytokines. (D)</p> Signup and view all the answers

What is the primary function of cytotoxic T lymphocytes (CTLs)?

<p>To eliminate virally infected and tumor cells (D)</p> Signup and view all the answers

How are CTLs activated to initiate their response?

<p>When CD8 T cells encounter antigen-presenting dendritic cells and TH1 cytokines (A)</p> Signup and view all the answers

What role does perforin play in the function of CTLs?

<p>It forms pores in the target cell membrane to induce apoptosis (A)</p> Signup and view all the answers

Which statement best describes NKT cells?

<p>They release significant amounts of IL-4 and IFN-γ (C)</p> Signup and view all the answers

Which component of the immune response is specifically responsible for programmed cell death in target cells during CTL activity?

<p>Granzymes released by CTLs (D)</p> Signup and view all the answers

What role do adhesion molecules primarily play in T cell responses?

<p>They tighten interactions between T cells and target cells. (C)</p> Signup and view all the answers

Which of the following is critical for the activation of CD4 helper T cells?

<p>Interaction between TCR and class II MHC molecules with antigenic peptides (C)</p> Signup and view all the answers

What is the consequence of T cell activation without the necessary co-stimulatory signal?

<p>Partial activation leading to anergy or apoptosis (B)</p> Signup and view all the answers

Which of the following accurately describes leukocyte function-associated antigen-1 (LFA-1)?

<p>It interacts with intercellular adhesion molecules on target cells. (D)</p> Signup and view all the answers

What is one of the mechanisms for eliminating self-reactive T cells in the thymus?

<p>Inducing apoptosis during partial activation without co-stimulation (C)</p> Signup and view all the answers

What is the primary cytokine produced by TH17 cells?

<p>IL-17 (A)</p> Signup and view all the answers

Which T cell subset is primarily involved in the protection against autoimmune responses?

<p>Treg (B)</p> Signup and view all the answers

What role do T follicular helper cells (Tfh) play in the immune response?

<p>They support B cell antibody production. (B)</p> Signup and view all the answers

What cytokines are produced by Treg cells to control T cell responses?

<p>IL-10 and TGF-β (B)</p> Signup and view all the answers

TH17 responses are particularly associated with which type of diseases?

<p>Cell-mediated autoimmune inflammatory diseases (C)</p> Signup and view all the answers

What distinguishes Th9 cells from other CD4+ T cells?

<p>They are induced by TGF-β and IL-4. (C)</p> Signup and view all the answers

Where are T follicular helper cells primarily located?

<p>Spleen, tonsil, and lymph nodes (D)</p> Signup and view all the answers

How do Tfh cells assist B cells during the immune response?

<p>Through interaction with CD40 ligand. (A)</p> Signup and view all the answers

What is the function of the CD3 complex?

<p>To act as the signal transduction unit for the TCR (B)</p> Signup and view all the answers

Which of the following is NOT a characteristic of the TCR complex?

<p>The TCR complex is found on all T cells and is not unique to specific T cell clones. (D)</p> Signup and view all the answers

What is the role of CD4 and CD8 proteins in T cell activation?

<p>To enhance the interaction of the TCR with the antigen-presenting MHC molecule. (B)</p> Signup and view all the answers

Which of the following statements about CD4 and CD8 is TRUE?

<p>CD4 binds to class II MHC molecules and CD8 binds to class I MHC molecules. (C)</p> Signup and view all the answers

Which of the following proteins is NOT considered an accessory molecule on T cells?

<p>IL-12R (C)</p> Signup and view all the answers

What is the primary function of CD45RA and CD45RO?

<p>To distinguish between native and memory T cells. (D)</p> Signup and view all the answers

Which of the following molecules is involved in promoting tighter interactions between T cells and APCs?

<p>CD154 (C)</p> Signup and view all the answers

What is the estimated capacity of the TCR repertoire in terms of recognizing different epitopes?

<p>10^15 (A)</p> Signup and view all the answers

Flashcards

FasL

A ligand that interacts with Fas receptors, important in apoptotic signaling.

Adhesion Molecules

Proteins that strengthen T cell interaction with APCs or target cells.

TCR-MHC Interaction

Binding between T cell receptors and MHC peptides that initiates T cell activation.

Co-stimulation

Additional signal required for T cell activation through CD28 binding on T cells.

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Anergy

State of unresponsiveness in T cells due to lack of co-stimulation.

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TCR complex

Combination of TCR (antigen recognition) and CD3 (cell activation) that determines T cell response.

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TCR structure

Each TCR molecule consists of two different polypeptide chains: one constant and one variable region.

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TCR repertoire

The diversity of TCRs allows recognition of approximately 10^15 distinct epitopes.

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CD3 complex

Signal transduction unit for TCR found on all T cells, made of γ, δ, ε, and ξ chains.

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CD4 co-receptor

Binds to class II MHC molecules on antigen-presenting cells (APCs) to enhance TCR signaling.

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CD8 co-receptor

Binds to class I MHC molecules on APCs and target cells, aiding cytotoxic T cell response.

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Accessory molecules

Additional receptors on T cells that promote activation and enhance interactions with APCs.

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CD45RA/CD45RO

CD45RA is found on native T cells, while CD45RO is found on memory T cells, indicating their state.

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CD8 T Cytotoxic Cells

T cells important for eliminating infected and tumor cells.

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Activation of CTLs

CD8 T cells are activated by antigen-presenting cells and cytokines.

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Granules in CTLs

Contain perforin and granzymes for killing target cells.

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NKT Cells

Hybrid cells between NK and T cells, releasing IL-4 and IFN-Ï’.

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Function of Perforin

Forms pores in target cell membranes to induce apoptosis.

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TH17 Cells

A type of CD4+ T helper cell producing IL-17, involved in antibacterial and antifungal responses.

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Cytokines

Proteins like IL-17 and TNF-α produced by TH17 cells that mediate inflammation.

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Immunoprivileged Sites

Areas like the eye where immune responses are controlled to protect tissues.

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Treg Cells

CD4+ CD25+ antigen-specific suppressor cells that prevent autoimmunity.

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TGF-β

Transforming growth factor beta, a cytokine produced by Tregs that regulates immune responses.

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T Follicular Helper Cells (Tfh)

A specialized subset of CD4+ T cells aiding B cells in antibody production.

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IL-21

A cytokine produced by Tfh cells that drives B cell proliferation.

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Th9 Cells

New subset of CD4+ T cells that produce IL-9, involved in various immune-related diseases.

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CTLA-4 binding

Binding of CTLA-4 to B7 leads to T cell anergy.

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Antigen presentation

Process where APCs present antigens to T cells, activating them.

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CD4 T cells

A type of T cell that helps activate B cells and other immune cells.

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TH1 response

Immune response that activates cellular defense against infections.

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Cytokines role

Signaling proteins that determine the function of immune cells.

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Fas ligand function

Promotes apoptosis in target cells through Fas protein interaction.

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TH2 response

Later immune response using antibodies for systemic defense.

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Ig class switching

B cells change antibody types due to TH2 cytokines.

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TH1 / TH2 balance

The equilibrium between TH1 and TH2 responses in the immune system.

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TH2 and allergies

TH2 responses promote IgE production, linking to allergic reactions.

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Study Notes

Cellular Immunity

  • Cellular immunity is a crucial part of the body's defense system.
  • Specific T cell receptors (TCRs) recognize and respond to specific antigens.
  • TCRs have variable and constant regions, like antibodies.
  • The TCR repertoire is vast, capable of recognizing a huge number of antigens (estimated 10^15 distinct epitopes).
  • The CD3 complex assists the TCR in signaling and activating the T cell.
  • Each T cell clone expresses a unique TCR.
  • The CD3 complex is composed of various polypeptide chains.
  • The CD3 complex is vital in triggering the T cell response.
  • The CD3 complex activates specific transcription factors in the nucleus to activate the T cell.
  • Activation leads to the production of various cytokines (IL-2, IL-12) and their corresponding receptors.
  • T cell activation involves multiple signaling pathways.
  • Different types of T helper (TH) cells exist with specific functions concerning cytokines and inflammatory reactions.
  • TH1 cells are critical for intracellular pathogen elimination.
  • TH2 cells are responsible for humoral responses, particularly antibody production.
  • TH17 cells defend against extracellular pathogens.
  • Regulatory T cells (Tregs) help control immune responses and prevent autoimmunity.
  • NKT cells are hybrid cells bridging NK and T cell functions and are central to initial immune responses to infections.
  • Different cellular activities and response mechanisms depend on specific cytokines secreted.

T Cell Activation

  • T cell activation needs two signals:
    • Antigen recognition (TCR binding to MHC).
    • Co-stimulation (e.g., CD28 interacting with B7).
  • Lack of co-stimulation leads to T cell anergy or apoptosis.
  • CD4 and CD8 proteins are co-receptors facilitating TCR-MHC interaction for improved responsiveness.

TH Cell Activation

  • Activation involves binding of MHC molecules to the TCR which leads to ITAM phosphorylation by Lck.
  • ZAP-70 binds phosphorylated -chain ITAMs and is phosphorylated by Lck.
  • CD4 and CD8 cells bind MHC class I or II on target cells and activate specific T helper cells.
  • Co-stimulation molecules (e.g., CD28, CTLA-4) are necessary during T cell activation.

Adhesion Molecules

  • Adhesion molecules (e.g., LFA-1, ICAMs) strengthen interactions between T cells and antigen presenting cells (APCs) to support activation.
  • Co-stimulation and adhesion molecules affect cellular activation.

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