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?

<p>They induce an absence of a specific immune reaction. (A)</p> Signup and view all the answers

How are antigens classified according to origin?

<p>By their biological species source. (A)</p> Signup and view all the answers

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

<p>Heterophilic antigen (D)</p> Signup and view all the answers

What distinguishes a strong immunogen from a weak immunogen?

<p>The ability to produce immunological memory. (A)</p> Signup and view all the answers

An autoantigen is best defined as:

<p>A normal protein recognized by the immune system in autoimmune diseases. (B)</p> Signup and view all the answers

Which type of cell recognizes non-degraded soluble antigens?

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

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

<p>They present antigenic peptides to T cells. (B)</p> Signup and view all the answers

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

<p>Nucleic acids require a carrier to elicit antibody response. (C)</p> Signup and view all the answers

What type of epitopes do T lymphocytes specifically recognize?

<p>Internal linear peptides (A)</p> Signup and view all the answers

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

<p>They can be presented by soluble antigens. (C)</p> Signup and view all the answers

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

<p>They both use specific receptors to bind to antigens. (D)</p> Signup and view all the answers

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

<p>B cells can recognize soluble antigens; T cells require MHC and internal peptides. (A)</p> Signup and view all the answers

Why are pure lipids considered non-immunogenic?

<p>They have no antigenic determinants. (C)</p> Signup and view all the answers

What is the primary role of HLA molecules?

<p>To present endogenous and exogenous antigens (D)</p> Signup and view all the answers

Which cells predominantly express MHC class I molecules?

<p>All nucleated cells and platelets (A)</p> Signup and view all the answers

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

<p>It prevents premature binding of peptides (B)</p> Signup and view all the answers

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

<p>Through the assembly with TAP and tapasin (B)</p> Signup and view all the answers

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

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

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

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

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

<p>Non-covalent interaction (C)</p> Signup and view all the answers

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

<p>B lymphocytes and macrophages (C)</p> Signup and view all the answers

What is the main function of histocompatibility molecules?

<p>To play a role in graft rejection between incompatible subjects (C)</p> Signup and view all the answers

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

<p>Class I region (D)</p> Signup and view all the answers

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

<p>Thymus-dependent antigens (B)</p> Signup and view all the answers

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

<p>Alpha chain (D)</p> Signup and view all the answers

What defines alloantigens?

<p>Antigens found in different members of the same species (B)</p> Signup and view all the answers

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

<p>Beta 2-microglobulin (D)</p> Signup and view all the answers

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

<p>Class II region (A)</p> Signup and view all the answers

Which of the following statements best describes antigenic determinants?

<p>They interact with B and T lymphocyte receptors. (C)</p> Signup and view all the answers

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

<p>Interaction with CD8 molecules (D)</p> Signup and view all the answers

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

<p>Thymus-independent antigens (C)</p> 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?

<p>C3 (C)</p> Signup and view all the answers

What is indicated by polyclonal antiserum?

<p>Response to multiple epitopes (B)</p> Signup and view all the answers

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

<p>Fibrous extracellular domain (D)</p> Signup and view all the answers

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

<p>Conformational determinants (A)</p> Signup and view all the answers

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

<p>They are typically polysaccharides. (A)</p> Signup and view all the answers

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

<p>Specific immune response (C)</p> Signup and view all the answers

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

<p>Inhibits the role of HLA-DM in antigen processing (A)</p> Signup and view all the answers

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

<p>APCs (Antigen-Presenting Cells) (B)</p> Signup and view all the answers

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

<p>MHC class I (D)</p> Signup and view all the answers

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

<p>Class I consists of an a chain and b2 microglobulin, while class II consists of an a chain and b chain. (D)</p> Signup and view all the answers

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

<p>TH cells (CD4+) (D)</p> Signup and view all the answers

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

<p>The cytoplasmic tail of ζ (B)</p> Signup and view all the answers

How are antigenic peptides in the endocytic processing pathway generated?

<p>By the degradation of exogenous proteins in acidic compartments (C)</p> 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?

<p>HLA-DP (C)</p> Signup and view all the answers

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

<p>It enhances the stability of the MHC-peptide complex. (C)</p> Signup and view all the answers

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

<p>It promotes the dissociation of CLIP from MHC class II molecules. (A)</p> Signup and view all the answers

Flashcards

MHC (Major Histocompatibility Complex)

A complex region on human chromosome 6 containing genes that code for proteins crucial in immune responses and tissue compatibility.

MHC Class I Region

A region on the MHC that contains genes coding for proteins involved in presenting antigens to cytotoxic T lymphocytes.

MHC Class II Region

A region on the MHC that contains genes coding for proteins involved in presenting antigens to helper T lymphocytes.

MHC Class III Region

A region on the MHC containing genes for proteins that are involved in the immune response but not directly in antigen presentation.

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Alpha Chain

The main protein of MHC Class I, a transmembrane glycoprotein with three extracellular domains, a transmembrane region, and a short cytoplasmic tail.

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Beta 2-Microglobulin

A small protein that binds to the alpha chain in MHC class I, encoded on chromosome 15.

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a3 Domain

A region on the alpha chain of MHC Class I that interacts with the CD8 molecule on cytotoxic T lymphocytes.

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Graft Rejection

A mechanism by which the immune system identifies and rejects foreign tissue.

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Alloantigens

Antigens found on different individuals within the same species.

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T-dependent Antigens

Antigens that require T cells to activate B cells for antibody production.

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T-independent Antigens

Antigens that can activate B cells directly, without the help of T cells.

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Antigenic Determinants

Specific regions on an antigen that bind to receptors on immune cells, such as antibodies or T cell receptors.

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Antigenicity

The ability of an antigen to trigger an immune response.

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Sequential Determinants

Antigenic determinants formed by a linear sequence of amino acids in a protein.

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Conformational Determinants

Antigenic determinants formed by the 3D structure of a protein.

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Polysaccharide Antigens

Polysaccharides that can trigger immune responses without the help of T cells.

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Antigenic Determinants of Lipids

Pure lipids, by themselves, do not trigger an immune response (not immunogenic).

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Antigenic Determinants of Nucleic Acids

Nucleic acids alone do not usually cause an immune response. However, they can become immunogenic when combined with a carrier molecule and an adjuvant (helper molecule).

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B and T Cell Epitope Recognition

B cells and T cells recognize different parts (epitopes) of the same antigen molecule.

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B Cell Antigen Recognition

B cells recognize antigens directly, whether they are soluble or on the cell surface.

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T Cell Antigen Recognition

T cells only recognize antigens that are broken down into smaller pieces (peptides) and presented by MHC molecules on the surface of other cells.

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T Cell Epitopes

These epitopes are linear and internal, meaning they exist within the protein and not on the outside.

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MHC Molecules

MHC molecules are cell surface proteins that present antigen fragments to T cells. In humans, they are called HLA molecules.

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TCR/Ag/MHC Complex

T cells recognize antigens only when presented by MHC molecules.

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MHC Class II Structure

Two polypeptide chains, alpha and beta, linked by non-covalent bonds. These chains form an antigen-binding cavity for presenting processed antigens.

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MHC Class II Localization

MHC Class II molecules are expressed primarily on antigen-presenting cells (APCs) such as B lymphocytes, macrophages, and dendritic cells.

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MHC Class II Function

MHC Class II molecules present processed antigens derived from exogenous sources, such as bacteria or viruses, that have been taken up by the cell.

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Endogenous Antigen Presentation

The process by which MHC Class I molecules bind to and present peptides derived from proteins synthesized within the cell (endogenous antigens).

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HLA-DM

A non-classical MHC Class II molecule that is involved in the exchange of antigenic peptides for CLIP, a fragment of the invariant chain, in the MHC Class II binding groove.

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Tapasin

A protein that binds to newly synthesized MHC Class I molecules and aids in their proper folding and assembly with beta2-microglobulin and peptides.

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Invariant Chain

The invariant chain, a protein that binds to MHC Class II molecules in the ER, prevents premature binding of peptides and helps direct the complex to endosomal compartments.

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Exogenous Antigen Presentation Pathway

The endocytic pathway is the process by which cells take in exogenous antigens, break them down into peptides, and present them on MHC Class II molecules.

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Immunogenicity

The ability of a substance to induce a humoral (antibody) and/or cell-mediated immune response. This means the substance can trigger the body's immune system to fight against it.

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Antigen

Any molecule that can be recognized by the immune system, even if it doesn't trigger an immune response. For example, human albumin or glucose.

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Hapten

Small molecules that are not capable of stimulating an immune response on their own. They can become immunogenic if they attach to a larger molecule (carrier) that can then be recognized by the immune system.

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Tolerogen

Substances that cause immune tolerance, meaning the immune system doesn't react to them under specific conditions. This tolerance is specific to the host.

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Strong Immunogen

Antigens that trigger a strong immune response, leading to a significant antibody production and/or strong T cell activation.

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Weak Immunogen

Antigens that induce a weaker immune response compared to strong immunogens. They may still trigger some immune response, but it's less pronounced.

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Heterophilic Antigen

Antigens found in diverse species, including humans and bacteria, that can cross-react with each other. They have similar structures that can be recognized by the immune system of different species.

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CLIP

A peptide fragment derived from the invariant chain (Ii) that initially binds to MHC class II molecules.

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Exogenous Antigens

Antigens that are taken up by cells through endocytosis and processed within intracellular vesicles.

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T Cell Receptor (TCR)

Components of the adaptive immune system that recognize and respond to specific antigens presented by MHC molecules, leading to T cell activation.

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Antigen Presenting Cell (APC)

A specialized type of immune cell that presents antigens to T cells, initiating an immune response.

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MHC Class I

A highly polymorphic cell surface protein expressed on all nucleated cells that presents processed peptides from intracellular proteins to CD8+ cytotoxic T cells (CTLs).

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MHC Class II

A highly polymorphic cell surface protein expressed mainly on APCs that presents processed peptides from extracellular proteins to CD4+ helper T cells.

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Polymorphism of MHC Molecules

MHC molecules are characterized by polymorphism, meaning they have multiple variations within the population, enabling diverse antigen recognition.

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CD4+ Helper T Cells

A type of T cell that recognizes MHC class II-peptide complexes and activates other immune cells, like B cells, to eliminate the antigen.

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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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Immunology 2nd Year/1st Semester Chapter 4 PDF

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.

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