Kuby Immunology: MHC and Antigen Presentation

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Questions and Answers

How do the peptide-binding characteristics of MHC class I molecules differ from those of MHC class II molecules?

MHC class I molecules have peptide-binding clefts that are closed at both ends. (correct)
MHC class I molecules present peptides with anchor residues distributed along the length of the peptide.
MHC class I molecules generally bind larger peptides than MHC class II molecules.
MHC class I molecules have peptide-binding clefts that are open at both ends.

What is the predominant role of the TAP complex in antigen processing?

It facilitates the transport of peptides from the endoplasmic reticulum to the cytosol.
It transports peptides from the cytosol into the endoplasmic reticulum for MHC class I loading. (correct)
It prevents MHC class II molecules from binding to peptides in the endoplasmic reticulum.
It loads peptides onto MHC class II molecules within endocytic vesicles.

Which of the following best describes the function of the invariant chain (Ii) in MHC class II antigen presentation?

It promotes the loading of antigenic peptides onto MHC class I molecules in the ER.
It stabilizes the interaction between the T-cell receptor and the MHC class II molecule.
It facilitates the assembly of MHC class I molecules with $\beta_2$-microglobulin.
It prevents MHC class II molecules from binding peptides in the endoplasmic reticulum and directs MHC class II molecules to endocytic compartments. (correct)

How does the binding of a superantigen to MHC class II molecules and T-cell receptors differ from that of a conventional peptide antigen?

Superantigens bind to the MHC class II molecule and the T-cell receptor outside of the peptide-binding groove. (A) Signup and view all the answers

What is the significance of the polygenic nature of MHC genes in the context of immune responses?

It increases the likelihood that an individual will be able to present a wide variety of antigens. (B) Signup and view all the answers

Which cellular process is directly inhibited by the presence of the CLIP (Class II-associated Invariant chain Peptide) molecule?

The binding of antigenic peptides to MHC class II molecules within endosomes. (C) Signup and view all the answers

Which of the following statements accurately compares the structure of MHC class I and MHC class II molecules?

MHC class I molecules consist of one transmembrane glycoprotein paired with $\beta_2$-microglobulin, whereas MHC class II molecules consist of two transmembrane glycoproteins. (B) Signup and view all the answers

What is the primary consequence of a genetic defect that impairs the function of the TAP transporter?

Impaired presentation of cytosolic antigens via MHC class I molecules. (B) Signup and view all the answers

Which cellular compartment is the primary site for the loading of peptide antigens onto MHC class II molecules?

Lysosomes and endosomes. (B) Signup and view all the answers

What is the role of calreticulin and tapasin in MHC class I antigen presentation?

To stabilize the MHC class I molecule and facilitate peptide loading in the ER. (D) Signup and view all the answers

The diversity of T-cell receptors (TCRs) is generated through somatic recombination of gene segments. Which of the following gene segments are rearranged to form the variable region of the TCR $\beta$ chain?

V, D, and J segments. (B) Signup and view all the answers

In T-cell development, what is the significance of positive selection?

It ensures that T cells can recognize and respond to antigens presented by MHC molecules. (C) Signup and view all the answers

Which of the following statements best describes the role of CD3 molecules in T-cell activation?

CD3 molecules are transmembrane signaling components of the T-cell receptor complex. (B) Signup and view all the answers

What is the function of the immunological synapse formed between a T cell and an antigen-presenting cell (APC)?

To concentrate signaling molecules and adhesion factors for efficient T-cell activation. (C) Signup and view all the answers

Which of the following is an immediate early event in T-cell activation following T-cell receptor engagement?

Phosphorylation of ITAMs on CD3 molecules by Lck kinase. (B) Signup and view all the answers

How does the mechanism of action differ between CTLA-4 and CD28 in regulating T-cell activation?

CTLA-4 delivers an inhibitory signal by outcompeting CD28 for B7 binding on antigen-presenting cells. (D) Signup and view all the answers

What is the outcome of T-cell anergy when a T cell recognizes its cognate antigen on an APC that lacks co-stimulatory molecules?

The T cell becomes unresponsive to subsequent antigen stimulation, even with co-stimulation. (A) Signup and view all the answers

Superantigens can activate a large proportion of T cells, leading to excessive cytokine production. What region of the T-cell receptor do superantigens bind to?

The variable region of the TCR $\beta$ chain. (B) Signup and view all the answers

Which of the following is a key function of IL-2 (Interleukin-2) in T-cell activation?

It promotes T-cell proliferation and survival. (C) Signup and view all the answers

What is the primary function of negative selection during T-cell development in the thymus?

To eliminate T cells that strongly react to self-antigens, preventing autoimmunity. (D) Signup and view all the answers

What is the role of the co-stimulatory molecule B7 in T-cell activation?

It interacts with CD28 on the T cell to provide a signal required for T-cell activation. (D) Signup and view all the answers

In the context of T-cell activation, what is the function of ZAP-70?

It phosphorylates downstream signaling molecules, leading to T-cell activation. (A) Signup and view all the answers

How does the process of positive selection in T-cell development ensures self-MHC restriction?

By promoting the survival of T cells that can recognize and bind to self-MHC molecules. (A) Signup and view all the answers

What is the role of Lck kinase in T-cell receptor signaling?

It phosphorylates the ITAMs on the CD3 molecules. (B) Signup and view all the answers

What describes the distribution and function of adhesion molecules, such as LFA-1 and ICAM-1, in T-cell activation?

They stabilize the interaction between the T cell and the antigen-presenting cell. (B) Signup and view all the answers

Which of the following is the primary mechanism by which T cells undergo apoptosis?

Activation of the Fas/FasL pathway. (A) Signup and view all the answers

How are the genetic rearrangements that contribute to T-cell receptor diversity mediated?

By V(D)J recombinase. (B) Signup and view all the answers

What would be the most likely outcome if a genetic mutation disabled the expression of MHC class II molecules?

Impaired activation of CD4+ T cells. (A) Signup and view all the answers

Which of the following best explains how a dendritic cell initiates T-cell activation?

By presenting antigenic peptides on MHC molecules and providing co-stimulatory signals. (D) Signup and view all the answers

What is the significance of the ITAMs (immunoreceptor tyrosine-based activation motifs) in T-cell activation?

They serve as docking sites for signaling molecules, initiating downstream signaling pathways. (D) Signup and view all the answers

How does a fixed antigen-presenting cell (APC) – one lacking co-stimulatory molecules – influence T-cell activation?

It induces T-cell anergy. (A) Signup and view all the answers

Given its role in T-cell activation, what direct effect would a drug that inhibits the interaction between CD28 and B7 have?

Inhibited T-cell proliferation. (D) Signup and view all the answers

Which process is directly associated with the release of cytochrome c from the mitochondria during T cell apoptosis?

Formation of the apoptosome. (B) Signup and view all the answers

What is the primary significance of the observation that T cells in G0 state before activation?

Allows for controlled responses and prevents uncontrolled proliferation. (B) Signup and view all the answers

Which of the following surface interactions is required for T cell activation?

TCR and peptide-MHC. (B) Signup and view all the answers

How does negative selection impact T-cell development and overall immune function?

Eliminates self-reactive T cells, preventing autoimmune responses. (C) Signup and view all the answers

Which component of the T-cell receptor complex is directly responsible for transducing the activation signal into the cell?

Costimulatory signals. (B) Signup and view all the answers

Which of the following outcomes can happen to a T-cell presented with antigen in the absence of sufficient co-stimulation?

Anergy development. (A) Signup and view all the answers

Flashcards

Major Histocompatibility Complex (MHC)

A complex of genes encoding MHC class I and II molecules, and proteins involved in antigen processing.

MHC class I function

Present peptides derived from intracellular pathogens to T cells.