Antigen Presentation Quiz

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Questions and Answers

What is the first step in the processing of endocytosed antigens for MHC class II-associated presentation?

Transport of MHC class II molecules to the Golgi apparatus

Uptake of extracellular proteins into vesicular compartments of APCs (correct)

Expression of peptide-class II complexes on the APC surface

Association of processed peptides with MHC class II molecules

Which type of immune cell is primarily responsible for internalizing antigen using the BCR?

Dendritic cell

B lymphocyte (correct)

Macrophage

T lymphocyte

What role do cathepsins play in antigen processing?

They assist in the synthesis of MHC molecules in the ER

They are critical for the degradation of internalized proteins (correct)

They bind peptides to MHC class II molecules

They transport peptides to the APC surface

What happens to MHC class II molecules after they are synthesized in the endoplasmic reticulum?

They are transported to endosomes with an invariant chain Signup and view all the answers

Which type of antigen presents MHC class II-associated peptides after uptake primarily occurs through endocytosis?

Exogenous proteins from extracellular sources Signup and view all the answers

What occurs during the association phase of processed peptides with MHC class II molecules?

Invariant chain dissociates allowing peptide binding Signup and view all the answers

What length are peptides typically generated from the degradation of proteins in endosomal compartments for MHC class II binding?

14-20 amino acids long Signup and view all the answers

Which pathway primarily generates peptides for MHC class I-associated presentation?

Cytosolic protein degradation via the proteasome Signup and view all the answers

What is the primary role of antigen-presenting cells (APCs) in the immune response?

To convert protein antigens to peptides and present them to T-cells Signup and view all the answers

What process allows dendritic cells to present antigens from infected cells to CD8+ T cells?

Antigen cross-presentation Signup and view all the answers

What role does the proteasome play in antigen processing?

It degrades proteins into peptides for MHC loading Signup and view all the answers

What occurs during the endocytosis of antigens by dendritic cells?

Antigens are processed and presented on MHC class II Signup and view all the answers

Which component is essential for the assembly of peptide-MHC class I complexes?

Transport proteins in the endoplasmic reticulum Signup and view all the answers

What molecule is primarily responsible for presenting antigens to CD4+ T lymphocytes in MHC class II presentation?

Dendritic cells Signup and view all the answers

Which of the following cells are classified as professional antigen presenting cells (APCs)?

B lymphocytes Signup and view all the answers

In antigen processing, what is the purpose of endocytosis?

To acquire antigens from the extracellular environment for processing Signup and view all the answers

How do peptide-MHC class I complexes assemble?

Peptides are transported to the endoplasmic reticulum to bind with MHC class I Signup and view all the answers

What role does the proteasome play in peptide transport during antigen processing?

It cleaves proteins into peptides that can be transported to MHC class I Signup and view all the answers

Which cell types present antigens to differentiated CD4+ T lymphocytes during the effector phase?

Macrophages Signup and view all the answers

Which of the following best describes the function of non-professional antigen presenting cells?

They process antigen but do not initiate T cell responses Signup and view all the answers

What is the main difference between MHC class I and MHC class II molecules in terms of the types of T lymphocytes they interact with?

MHC class I interacts primarily with CD8+ T lymphocytes, while MHC class II interacts with CD4+ T lymphocytes Signup and view all the answers

What is the primary function of antigen presenting cells in the immune response?

To process and present antigens to T lymphocytes for activation Signup and view all the answers

Which of the following cells is NOT considered an antigen presenting cell?

Erythrocytes Signup and view all the answers

What is the primary function of the proteasome in antigen processing?

Degradation of cytosolic proteins into peptides Signup and view all the answers

Which T-cell type recognizes peptides presented by MHC class II molecules?

CD4+ T-cells Signup and view all the answers

What role do APCs (Antigen-Presenting Cells) play in the immune response?

Engulf soluble antigens and present them via MHC class II Signup and view all the answers

How are peptides transported from the cytosol to the endoplasmic reticulum (ER)?

Through TAP (transporter associated with antigen presentation) Signup and view all the answers

What is required for the correct recognition of antigens by T-cell receptors (TCR)?

MHC context for peptide binding Signup and view all the answers

What type of antigens do CD8+ T-cells specifically recognize?

Endogenously synthesized proteins presented by MHC class I Signup and view all the answers

What characterizes the recognition of antigens by γδ T-cell receptors?

MHC-independent recognition Signup and view all the answers

What is the role of anchor residues in peptide binding to MHC molecules?

Stabilize the association between peptide and MHC Signup and view all the answers

How do MHC class I molecules differ in their antigen presentation compared to MHC class II molecules?

MHC class I presents endogenous antigens while class II presents exogenous antigens Signup and view all the answers

What is the consequence of the self MHC restriction in T-cell recognition?

Peptides must be bound to the MHC molecules of the same individual for recognition Signup and view all the answers

Study Notes

### Antigen Presentation

The process of antigen presentation involves antigen processing, a process where APCs (Antigen Presenting cells) break down an antigen into peptides and display them on MHC (Major Histocompatibility Complex) molecules on their surface.

### Professional Antigen Presenting Cells (APCs)

Dendritic cells, macrophages, and B lymphocytes are the professional APCs.
Dendritic cells are critical for initiating T-cell responses by presenting antigens to naïve CD4+ and CD8+ T lymphocytes in the peripheral lymphoid organs.
Macrophages present antigens to differentiated CD4+ T lymphocytes during the effector phase of cell-mediated immunity.
B lymphocytes present antigens to helper T-cells (CD4+) during humoral immune response.

### Antigen Processing

The pathways of antigen processing convert protein antigens into peptides and load them into MHC molecules.
Protein antigens present in acidic vesicular compartments of APCs generate MHC class II-associated peptides, whereas antigens present in the cytosol generate MHC class I-associated peptides.

### MHC Class II Antigen Processing

Uptake: APCs internalize extracellular proteins using receptors.
Processing: Internalized proteins are degraded in endosomes and lysosomes into peptides, typically 14-20 amino acids long.
MHC Class II Assembly: α and β chains of MHC class II molecules are synthesized in the endoplasmic reticulum (ER) and associate with the invariant chain (Ii) before moving to endosomes.
Peptide Loading: In endosomes, Ii is removed, and processed peptides bind to MHC class II molecules.
Surface Expression: MHC class II-peptide complexes are transported to the cell surface for recognition by CD4+ T lymphocytes.

### MHC Class I Antigen Processing

Protein Source: Cytosolic proteins, including those from viruses or intracellular microbes, are processed.
Proteasomal Degradation: Proteins in the cytosol are ubiquitinated and degraded by the proteasome into peptides.
Peptide Transport: Peptides are transported to the ER lumen by the transporter associated with antigen presentation (TAP).
MHC Class I Assembly: Peptides bind to MHC class I molecules in the lumen of the ER.
Surface Expression: MHC class I-peptide complexes move through the Golgi apparatus and are expressed on the cell surface for recognition by CD8+ T lymphocytes.

### Co-stimulation

Co-stimulatory signals are essential for full T-cell activation.
Signal 1: Antigenic peptide bound to MHC engages the TCR-CD3 complex on the T cell.
Signal 2: Co-stimulatory molecules, such as CD28 on T-cells, interact with the B7 family (CD80/CD86) on APCs.

### Regulation of co-stimulation

Microbial products enhance antigen presentation by APCs.
Toll-like receptors on APCs recognize microbes and induce expression of MHC molecules, co-stimulators, and cytokines that stimulate or recruit T-cells.

### Cross-presentation

Dendritic cells can ingest infected cells and tumor cells and present antigens from these cells to CD8+ T cells through the MHC class I pathway, a process called cross-presentation or cross-priming.

### The T-cell Receptor (TCR)

The TCR is a surface molecule found on T-cells.
It recognizes antigen presented in the correct MHC context.
Two types of TCRs exist: αβ TCR and γδ TCR.
The αβ TCR is found on most T lymphocytes and recognizes antigen in an MHC-dependent manner.
The γδ TCR is found in mucosal surfaces and recognizes antigen in an MHC-independent manner.

### The CD3 Complex

The CD3 complex is closely associated with the TCR.
It is made of four invariant proteins (γ, δ, ε, and ξ) and does not contribute to the specificity of the TCR.
The CD3 complex is required for TCR surface expression during T-cell development.
It transduces activation signals to the cell nucleus following TCR antigen interaction.

### Antigen Recognition by T Lymphocytes

Most T lymphocytes recognize only peptides.
They are specific for defined amino acid sequences in peptides.
They recognize only a few key residues (anchor residues) in the peptide sequence.
Peptides are recognized by T-cells only when bound to MHC within the appropriate MHC background.
CD4+ T-cells are restricted to MHC class II, whereas CD8+ T-cells are restricted to MHC class I.

### B-cell Receptor (BCR)

The BCR does not interact with MHC molecules.
B-cells can recognize soluble antigens as well as cell-surface antigens.
They recognize peptides, proteins, nucleic acids, polysaccharides, and lipids.

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Description

Test your knowledge on the process of antigen presentation, including the roles of antigen presenting cells like dendritic cells, macrophages, and B lymphocytes. This quiz covers antigen processing pathways and their importance in T-cell responses and immunity.