Immunology 2nd Year, Chapter 4

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Questions and Answers

What does immunogenicity refer to?

The ability of a substance to cause immune tolerance.

The capacity of an antigen to be coupled with haptens.

The ability to induce a humoral and/or cell-mediated immune response. (correct)

The specific recognition of molecules by the immune system.

Which statement is true about antigens and immunogens?

All antigens are immunogens.

Immunogens can be antigens but not vice versa. (correct)

Only haptens are considered antigens.

Antigens cannot stimulate an immune response.

What are haptens?

Strong immunogens that elicit a robust immune response.

Low molecular weight substances unable to produce antibodies independently. (correct)

Antigens that react with B cells only.

Substances that cause immune tolerance.

What is the primary characteristic of tolerogens?

They induce an absence of a specific immune reaction. Signup and view all the answers

How are antigens classified according to origin?

By their biological species source. Signup and view all the answers

Which type of antigen displays cross-reactivity across different species?

Heterophilic antigen Signup and view all the answers

What distinguishes a strong immunogen from a weak immunogen?

The ability to produce immunological memory. Signup and view all the answers

An autoantigen is best defined as:

A normal protein recognized by the immune system in autoimmune diseases. Signup and view all the answers

Which type of cell recognizes non-degraded soluble antigens?

B lymphocytes Signup and view all the answers

What is the role of MHC molecules in T lymphocyte activation?

They present antigenic peptides to T cells. Signup and view all the answers

Which of the following statements is true regarding the immunogenicity of nucleic acids?

Nucleic acids require a carrier to elicit antibody response. Signup and view all the answers

What type of epitopes do T lymphocytes specifically recognize?

Internal linear peptides Signup and view all the answers

Which of the following is NOT a characteristic of T cell epitopes?

They can be presented by soluble antigens. Signup and view all the answers

In terms of antigen recognition, what do both B and T lymphocytes have in common?

They both use specific receptors to bind to antigens. Signup and view all the answers

What distinguishes the recognition of B cell epitopes from T cell epitopes?

B cells can recognize soluble antigens; T cells require MHC and internal peptides. Signup and view all the answers

Why are pure lipids considered non-immunogenic?

They have no antigenic determinants. Signup and view all the answers

What is the primary role of HLA molecules?

To present endogenous and exogenous antigens Signup and view all the answers

Which cells predominantly express MHC class I molecules?

All nucleated cells and platelets Signup and view all the answers

What does the invariant chain do in relation to MHC class II?

It prevents premature binding of peptides Signup and view all the answers

How is the MHC class I molecule stabilized before peptide binding?

Through the assembly with TAP and tapasin Signup and view all the answers

What remains in the binding groove of MHC class II after digestion of the invariant chain?

CLIP Signup and view all the answers

Which of the following pathways do MHC class II molecules use for antigen presentation?

Endocytic pathway Signup and view all the answers

What interaction occurs between the alpha and beta chains in MHC class II molecules?

Non-covalent interaction Signup and view all the answers

Which cell types are considered antigen-presenting cells that express MHC class II?

B lymphocytes and macrophages Signup and view all the answers

What is the main function of histocompatibility molecules?

To play a role in graft rejection between incompatible subjects Signup and view all the answers

Which region of the MHC is located on the telomeric end of chromosome 6?

Class I region Signup and view all the answers

What type of antigens require the assistance of T cells for B cell activation?

Thymus-dependent antigens Signup and view all the answers

What type of chain complex is primarily found in MHC class I molecules?

Alpha chain Signup and view all the answers

What defines alloantigens?

Antigens found in different members of the same species Signup and view all the answers

Which component is encoded on chromosome 15 in MHC class I molecules?

Beta 2-microglobulin Signup and view all the answers

Which class of MHC molecules contains genes responsible for antigenic presentation?

Class II region Signup and view all the answers

Which of the following statements best describes antigenic determinants?

They interact with B and T lymphocyte receptors. Signup and view all the answers

What type of interactions does the MHC class I a3 domain facilitate?

Interaction with CD8 molecules Signup and view all the answers

Which type of antigens can activate B cells without the help of T cells?

Thymus-independent antigens Signup and view all the answers

Which of the following genes is involved in the immune response but is found in the MHC class III region?

C3 Signup and view all the answers

What is indicated by polyclonal antiserum?

Response to multiple epitopes Signup and view all the answers

Which structural feature is NOT associated with the alpha chain of MHC class I molecules?

Fibrous extracellular domain Signup and view all the answers

Which type of antigenic determinants are characterized by the physical structure of the molecule?

Conformational determinants Signup and view all the answers

Which of the following best describes the nature of thymus-independent antigens?

They are typically polysaccharides. Signup and view all the answers

What type of immune response is primarily associated with specific antigenic determinants on carbohydrates?

Specific immune response Signup and view all the answers

What is the primary role of HLA-DO in class II antigen processing?

Inhibits the role of HLA-DM in antigen processing Signup and view all the answers

Which cell type primarily presents exogenous antigens loaded on MHC class II molecules?

APCs (Antigen-Presenting Cells) Signup and view all the answers

Proteins synthesized in the cytosol are associated with which class of MHC molecules?

MHC class I Signup and view all the answers

What is the main structural difference between MHC class I and class II molecules?

Class I consists of an a chain and b2 microglobulin, while class II consists of an a chain and b chain. Signup and view all the answers

Which T cells are primarily presented with antigens by MHC class II molecules?

TH cells (CD4+) Signup and view all the answers

Which component of the T cell receptor complex is responsible for signal transduction?

The cytoplasmic tail of ζ Signup and view all the answers

How are antigenic peptides in the endocytic processing pathway generated?

By the degradation of exogenous proteins in acidic compartments Signup and view all the answers

Which of the following MHC class I genes is not part of the HLA-A, -B, and -C clusters?

HLA-DP Signup and view all the answers

What role does the peptide anchor residue play in MHC molecules?

It enhances the stability of the MHC-peptide complex. Signup and view all the answers

Which of the following statements accurately describes the role of HLA-DM?

It promotes the dissociation of CLIP from MHC class II molecules. Signup and view all the answers

Study Notes

Immunology 2nd Year / 1st Semester, Chapter 4

Antigen: A substance that elicits an immune response.
Immunogenicity: The ability of a substance to induce a humoral and/or cell-mediated immune response.
Antigens vs. Immunogens: All immunogens are antigens, but not all antigens are immunogens. Immunogens stimulate an immune response, while antigens are simply recognized by the immune system. Examples include human albumin-glucose (does not stimulate an immune response) and haptens.
Haptens: Small molecules that are not immunogenic by themselves but become immunogenic when coupled to a larger carrier molecule (e.g., a protein).
Tolerogens: Substances that induce immune tolerance by preventing a reaction to a particular immune stimulus under given conditions. This tolerance is usually specific to the host.
Antigen Classification by Strength: Strong immunogens induce a strong immune response, weak immunogens a weaker one, and haptens are not immunogenic by themselves however can induce an immune response if attached to a carrier. Examples of haptens include gold, copper, nickel, and certain medicinal substances.
Antigen Classification by Nature: Can be soluble (unfigured) or particulate (figured).
Antigen Classification by Origin: Includes heterophilic (cross-reacting antigens across species), heterologous (or xenoantigens, identical antigens across species), autoantigens (normal components of the body recognized as foreign by the immune system in certain diseases like autoimmune disorders), and alloantigens (antigens that vary between individuals of the same species, e.g., blood type antigens).
Thymus-dependent Antigens: Require T cell help for B cell activation. These are frequently proteins.
Thymus-independent Antigens: Can induce B cell proliferation and antibody production without T cell help. Usually polysaccharides.
Antigenic Sites (Epitopes): Specific regions on an antigen recognized by the immune system (e.g., B cell receptors and T cell receptors). An immunogen has multiple epitopes that can elicit an antibody response
Concept of Anitgenic Determinant: Antigenicity is determined by the presence of specific antigens, which are sites on an antigen that can interact with B and T Lymphocyte receptors.
Antigenic determinants of Carbohydrates: certain carbohydrate components may have immunogenic power.
Antigenic determinants of Proteins: Sequential Determinants may consist of a single amino acid or a chain of amino acids. Conformational determinants depend on the conformation of the area of the molecule.
Antigenic determinants of Nucleic Acids: Do not typically have immunogenic power (by themselves), but when combined with a carrier in presence of Freund's adjuvant anti-DNA and anti-RNA antibodies can be made.
Antigenic determinants of pure lipids: Do not have immunogenic power on their own.
Two types of Antigen-specific Receptors: B cells and T cells recognize different epitopes (antigenic sites) on the same antigen molecule
Epitope Recognition: B lymphocytes recognize non-degraded soluble antigens (BCR). T lymphocytes recognize epitopes presented on MHC complexes (a specialized compound)
Antigenic Recognition (B lymphocytes): Recognize macromolecules or small substances, either soluble or attached to cells.
Antigenic Recognition (T lymphocytes): Recognise peptides presented by specialized molecules like MHC molecules.
Properties of T cell epitopes: These are tertiary complex and need MHC molecules for recognition. They usually are proteins.
Major Histocompatibility Complex (MHC): Group of genes encoding surface proteins crucial for immune recognition and response.
MHC Classification: Structurally MHC I and II, and are located on chromosomes that are characterized by certain polypeptide chain features
MHC Class I localization: Expressed on most nucleated cells and platelets
MHC Class II localization: Highly restricted, primarily on antigen-presenting cells (APCs) like macrophages, B cells, and dendritic cells.
Function of MHC Molecules: Crucial for presenting endogenous and exogenous antigens (either proteins or material coming from inside or outside the cell, respectively)
Endogenous Antigens: Produced within the cell. The cytosolic pathway describes their presentation to cytotoxic T cells.
Exogenous Antigens: Produced externally and are internalized by the cell. The endocytic pathway presents them to helper T cells.
T-cell receptor complex (TCR-CD3): A complex on the surface of T cells used to recognize and bind to specific antigens. The TCR molecule is composed of two chains (alpha and beta), and interacts with associated proteins.
Double Recognition: TCRs recognize both the peptide and the MHC molecule as combined recognition.

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Description

This quiz covers key concepts from Chapter 4 of Immunology, focusing on antigens and immunogenicity. Learn the differences between antigens, immunogens, haptens, and tolerogens, as well as their classifications. Test your knowledge on these fundamental immunological principles.