Immunology - Lecture 8

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Questions and Answers

What is the primary role of MHC molecules in antigen presentation?

To process soluble antigens for T cell recognition

To display host cell-associated antigens for T cells (correct)

To recognize and destroy invasive pathogens

To initiate T cell division in lymphoid organs

Which type of antigen do T cells primarily recognize?

Radiolabeled antigens

Lipid-based antigens in cell membranes

Soluble antigens circulating in the blood

Peptide antigens displayed by MHC molecules (correct)

Which compartments are primarily involved in antigen processing for T cell recognition?

Cytosol and various membrane-bound compartments (correct)

Nucleus and endoplasmic reticulum

Cytosol and mitochondria

Golgi apparatus and lysosomes

What is meant by 'MHC restriction' in T cell activation?

T cells can only recognize antigens presented by certain types of MHC molecules Signup and view all the answers

Naive T cells circulate constantly through which type of lymphoid organs?

Secondary (peripheral) lymphoid organs Signup and view all the answers

What role does the endoplasmic reticulum aminopeptidase associated with antigen processing (ERAAP) play in peptide processing?

It trims long peptides to bind to MHC class I. Signup and view all the answers

Which of the following statements is true regarding the peptide loading complex (PLC)?

It includes calreticulin, tapasin, ERp57, and TAP. Signup and view all the answers

What initiates the increased expression of ERAP1?

Interferon-gamma stimulation Signup and view all the answers

What is the function of HLA-DM in the context of MHC class II molecules?

It facilitates loading of antigenic peptides onto MHC class II. Signup and view all the answers

Which mechanism best describes how peptides are acquired by MHC class I molecules?

Peptides are acquired from cytosolic protein degradation. Signup and view all the answers

What occurs to new MHC class II molecules before they reach acidic intracellular vesicles?

They are directed by the invariant chain. Signup and view all the answers

What is one of the key functions of CD4 T cells recognizing peptide: MHC class II complexes?

Aiding in B cell antibody production. Signup and view all the answers

In which location do MHC class II molecules acquire their peptides?

In acidified intracellular vesicles. Signup and view all the answers

What is the primary purpose of MHC polymorphism in a population?

To prevent susceptibility to new or mutated pathogens Signup and view all the answers

Which of the following properties of MHC polymorphism affects T-cell recognition?

Peptide binding range Signup and view all the answers

Which molecules mainly present non-peptide antigens?

Specialized MHC class I molecules Signup and view all the answers

What role do anchor residues play in relation to MHC molecules?

They assist in peptide binding to MHC molecules Signup and view all the answers

What does the term promiscuous binding site refer to in MHC molecules?

The capacity to bind various peptides actively Signup and view all the answers

Which of the following is an example of non-peptide antigen?

Metabolites Signup and view all the answers

What is the role of cross-presentation in dendritic cells?

It facilitates the activation of T cells against non-infectious antigens Signup and view all the answers

The interaction between TCR and MHC is primarily influenced by which factor?

Peptide conformation Signup and view all the answers

What is the primary function of MHC molecules?

To bind peptide fragments and display them for T cell recognition Signup and view all the answers

How does the genetic encoding of MHC contribute to its diversity?

It is polygenic and contains several MHC class I and II genes Signup and view all the answers

Which statement best describes MHC gene polymorphism?

MHC genes have many alternative forms or alleles Signup and view all the answers

What is a haplotype in the context of MHC genes?

A set of MHC alleles inherited from one parent Signup and view all the answers

Which consequence is NOT typically associated with MHC-mediated immune responses?

Inhibition of T cell activation Signup and view all the answers

What is the role of codominance in MHC gene expression?

Both inherited alleles are expressed simultaneously Signup and view all the answers

What does the term 'polymorphic' imply regarding MHC genes?

They have an infinite number of derivatives at a point Signup and view all the answers

Which of the following statements is true regarding MHC class I and II molecules?

They display peptide fragments from different classes of pathogens Signup and view all the answers

What is the role of vesicular compartments in cells?

They are involved in endocytosis and secretion. Signup and view all the answers

What is required for peptides derived from the cytosol to be loaded onto MHC I molecules?

Transport into the endoplasmic reticulum. Signup and view all the answers

What is cross-presentation of antigen primarily facilitated by?

Antigen presenting cells, mostly dendritic cells. Signup and view all the answers

What is the function of the ubiquitin-proteasome system?

To tag proteins for degradation. Signup and view all the answers

How are proteins in the cytosol primarily delivered into the proteasome for degradation?

By the ubiquitin-proteasome system. Signup and view all the answers

What triggers ubiquitination of a target protein?

Attachment of a chain of ubiquitin molecules. Signup and view all the answers

What is the role of TAP-1 and TAP-2 in antigen processing?

They transport peptides into the endoplasmic reticulum. Signup and view all the answers

What is the result of the activation of naïve CD8 T-cells via cross-presentation?

The differentiation into activated CD8 T-cells. Signup and view all the answers

Which of the following is a component of the proteasome responsible for peptide generation?

19S regulatory caps. Signup and view all the answers

What type of antigens do autophagy pathways primarily deliver for MHC II presentation?

Endogenous and self-cytosolic proteins. Signup and view all the answers

Study Notes

Antigen Presentation

Antigens are captured and displayed in secondary lymphoid organs, where naive T cells circulate.
T cells recognize cell-associated antigens.
MHC (major histocompatibility complex) molecules display antigens for CD4+ and CD8+ T cells.
Most T cells recognize short peptides.
MHC restriction: CD4+ and CD8+ T cell receptors are specific for peptide antigens presented by MHC molecules.

Antigen Processing

Antigen processing generates peptides from native proteins.
Cytosol and vesicular compartments are the main intracellular compartments for antigen processing.
Peptides derived from the cytosol are transported to the ER and loaded onto MHC I.
Direct presentation: Somatic and immune cells present antigens via MHC I.
Cross-presentation: DCs present exogenous antigens via MHC I to CD8 T cells.
Autophagy: Delivers cytosolic antigens for presentation by MHC II.
Protein degradation: The proteasome breaks down proteins into short peptides in the cytosol.

The Ubiquitin-Proteasome System

Ubiquitination: Proteins are tagged for degradation by a chain of ubiquitin molecules.
Proteasome: A multi-catalytic protease complex containing a 20S catalytic core and 19S regulatory caps.
Ubiquitin chains are recognized by the 19S cap, the protein is unfolded, and degraded into peptides by proteasomes.

MHC Class I Antigen Presentation

TAP-1 and TAP-2 transport peptides from the cytosol into the ER.
ERAAP (ER aminopeptidase) trims peptides that are too long to bind MHC I.
Peptide loading complex (PLC): Contains calreticulin, tapasin, ERp57, and TAP.

MHC Class II Antigen Presentation

Peptides are generated in acidified endocytic vesicles.
Invariant chain: directs newly synthesized MHC II molecules to acidic vesicles.
CLIP (class II-associated invariant chain peptide) binds to MHC II.
HLA-DM facilitates the exchange of CLIP with antigenic peptides.

MHC Diversity and Peptide Binding

MHC genes are polygenic, polymorphic, and codominant.
Haplotype: All alleles of MHC class I and II genes inherited from one parent.
MHC polymorphism allows different individuals to present a wider range of peptides.

T-cell Recognition of Antigens

MHC restriction: T-cell receptors recognize peptide-MHC complexes.
MHC polymorphism affects peptide binding and TCR-MHC interactions.

Non-Peptide Antigen Presentation

Specialized MHC molecules (non-classical class I, CD1 family, MR1) present non-peptide antigens to NK cells and unconventional T cells.
Non-peptide antigens include small lipids, metabolites, and small molecules.

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Description

Explore the intricate mechanisms of antigen presentation and processing in the immune system. This quiz covers the roles of MHC molecules, T cells, and various pathways involved in presenting antigens to naive T cells. Test your understanding of how antigens are processed to elicit immune responses.