Antigens
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Questions and Answers

What is an antigen?

Molecules or pieces of molecules that bind to antibodies, MHC molecules or lymphocyte receptors (TCR and BCR)

What is antigenicity?

Antigens that are capable of binding products of the immune response that they induced (e.g. lymphocytes or antibodies)

Which of the following correctly defines immunogenicity?

  • The ability of an antigen to bind MHC molecules
  • They ability of an antigen to stimulate the production of antibodies
  • The ability of an antigen to induce an immune response (correct)
  • The ability of an antigen to remain non-degradable in tissues

    • What is the main difference between immunogenicity and haptens?

    <p>Immunogenicity can induce an immune response by themselves, whereas haptens cannot</p> Signup and view all the answers

    What are the two subcategories of antigens?

    <p>The two subcategories of antigens are immunogens and haptens</p> Signup and view all the answers

    What are the two cardinal features of antigens?

    <p>Immunogenicity and antigenicity</p> Signup and view all the answers

    Which of the following is a type of antigen that can directly stimulate B cells without the help of T cells?

    <p>T-independent antigens</p> Signup and view all the answers

    Which of the following is a characteristic of T-independent antigens?

    <p>They have a polymeric structure with repeated antigenic determinants</p> Signup and view all the answers

    What is the primary feature of superantigens?

    <p>They activate a large number of T cells non-specifically</p> Signup and view all the answers

    Which of the following molecules are most likely to serve as autoantigens in autoimmunity?

    <p>Altered self-antigens</p> Signup and view all the answers

    Haptens are considered incomplete antigens because:

    <p>They cannot induce an immune response on their own</p> Signup and view all the answers

    Which of the following factors is least likely to affect the immunogenicity of an antigen?

    <p>The age of the antigen</p> Signup and view all the answers

    Which type of antigen is most likely to stimulate a polyclonal activation of lymphocytes?

    <p>Superantigens</p> Signup and view all the answers

    Which of the following characteristics is true for most protein antigens?

    <p>They are primarily T-dependent antigens</p> Signup and view all the answers

    What role do adjuvants play in vaccine formulations?

    <p>They enhance the immune response to an antigen</p> Signup and view all the answers

    Which type of antigen is most likely to require a carrier protein to induce an immune response?

    <p>Haptens</p> Signup and view all the answers

    What characteristic makes particulate antigens more immunogenic than soluble antigens?

    <p>They are more easily phagocytosed and processed by antigen-presenting cells</p> Signup and view all the answers

    Which of the following routes of antigen administration is rarely used for vaccines?

    <p>Intravenous</p> Signup and view all the answers

    Why are denatured antigens more immunogenic than their native counterparts?

    <p>Denaturation exposes more antigenic determinants</p> Signup and view all the answers

    Which of the following is NOT an example of an exogenous antigen?

    <p>Tumor antigen</p> Signup and view all the answers

    Which of the following is a structural characteristic of T-dependent antigens?

    <p>They require the presence of helper T cells for activation of B cells</p> Signup and view all the answers

    How do superantigens differ from regular antigens in T cell activation?

    <p>They bind to the variable domain of the β-chain of TCRs</p> Signup and view all the answers

    Which of the following is the most immunogenic macromolecule?

    <p>Proteins</p> Signup and view all the answers

    Which of the following would be classified as an endogenous antigen?

    <p>Self-antigen altered during tumorigenesis</p> Signup and view all the answers

    Autoantigens differ from foreign antigens in that:

    <p>Autoantigens are derived from endogenous molecules</p> Signup and view all the answers

    Which of the following is a key property of antigens that influences their immunogenicity?

    <p>Foreignness</p> Signup and view all the answers

    A polysaccharide vaccine is most likely to act as a:

    <p>T-independent antigen</p> Signup and view all the answers

    Which type of antigenic determinant is most likely to activate a polyclonal response?

    <p>Superantigen</p> Signup and view all the answers

    Which of the following would decrease the immunogenicity of an antigen?

    <p>Small molecular size</p> Signup and view all the answers

    What happens when a hapten binds to a larger carrier molecule?

    <p>It can induce an immune response</p> Signup and view all the answers

    Which of the following factors increases the likelihood that an antigen will induce an immune response?

    <p>High complexity</p> Signup and view all the answers

    Which type of antigen is derived from microbial agents and is responsible for activating the immune system in infections?

    <p>Exogenous antigens</p> Signup and view all the answers

    Which antigen type is most closely associated with autoimmunity?

    <p>Autoantigen</p> Signup and view all the answers

    Which of the following factors might influence whether a particular antigen will be recognized as immunogenic in different individuals?

    <p>Genetic differences in MHC molecules</p> Signup and view all the answers

    Which of the following routes of vaccine administration might be used to prevent respiratory infections?

    <p>Intranasal</p> Signup and view all the answers

    Why do proteins tend to be highly immunogenic compared to other macromolecules?

    <p>They have greater molecular complexity</p> Signup and view all the answers

    Which of the following best describes a superantigen's interaction with T cells?

    <p>It induces activation by binding to the variable domain of the β-chain of TCR</p> Signup and view all the answers

    Which of the following is a characteristic of T-independent antigens?

    <p>They have a polymeric structure with repeated antigenic determinants</p> Signup and view all the answers

    What is the primary feature of superantigens?

    <p>They activate a large number of T cells non-specifically</p> Signup and view all the answers

    Which of the following molecules are most likely to serve as autoantigens in autoimmunity?

    <p>Altered self-antigens</p> Signup and view all the answers

    Haptens are considered incomplete antigens because:

    <p>They cannot induce an immune response on their own</p> Signup and view all the answers

    Which of the following factors is least likely to affect the immunogenicity of an antigen?

    <p>The age of the antigen</p> Signup and view all the answers

    Which type of antigen is most likely to stimulate a polyclonal activation of lymphocytes?

    <p>Superantigens</p> Signup and view all the answers

    Which of the following characteristics is true for most protein antigens?

    <p>They are primarily T-dependent antigens</p> Signup and view all the answers

    What role do adjuvants play in vaccine formulations?

    <p>They enhance the immune response to an antigen</p> Signup and view all the answers

    Which type of antigen is most likely to require a carrier protein to induce an immune response?

    <p>Haptens</p> Signup and view all the answers

    What characteristic makes particulate antigens more immunogenic than soluble antigens?

    <p>They are more easily phagocytosed and processed by antigen-presenting cells</p> Signup and view all the answers

    Which of the following routes of antigen administration is rarely used for vaccines?

    <p>Intravenous</p> Signup and view all the answers

    Why are denatured antigens more immunogenic than their native counterparts?

    <p>Denaturation exposes more antigenic determinants</p> Signup and view all the answers

    Which of the following is NOT an example of an exogenous antigen?

    <p>Tumor antigen</p> Signup and view all the answers

    Which of the following is a structural characteristic of T-dependent antigens?

    <p>They require the presence of helper T cells for activation of B cells</p> Signup and view all the answers

    How do superantigens differ from regular antigens in T cell activation?

    <p>They bind to the variable domain of the β-chain of TCRs</p> Signup and view all the answers

    Which of the following is the most immunogenic macromolecule?

    <p>Proteins</p> Signup and view all the answers

    Which of the following would be classified as an endogenous antigen?

    <p>Self-antigen altered during tumorigenesis</p> Signup and view all the answers

    Autoantigens differ from foreign antigens in that:

    <p>Autoantigens are derived from endogenous molecules</p> Signup and view all the answers

    Which of the following is a key property of antigens that influences their immunogenicity?

    <p>Foreignness</p> Signup and view all the answers

    A polysaccharide vaccine is most likely to act as a:

    <p>T-independent antigen</p> Signup and view all the answers

    Which type of antigenic determinant is most likely to activate a polyclonal response?

    <p>Superantigen</p> Signup and view all the answers

    Which of the following would decrease the immunogenicity of an antigen?

    <p>Small molecular size</p> Signup and view all the answers

    What happens when a hapten binds to a larger carrier molecule?

    <p>It can induce an immune response</p> Signup and view all the answers

    Which of the following factors increases the likelihood that an antigen will induce an immune response?

    <p>High complexity</p> Signup and view all the answers

    Which type of antigen is derived from microbial agents and is responsible for activating the immune system in infections?

    <p>Exogenous antigens</p> Signup and view all the answers

    What is a common characteristic of T-independent antigens?

    <p>They consist of repeating units</p> Signup and view all the answers

    Which antigen type is most closely associated with autoimmunity?

    <p>Autoantigen</p> Signup and view all the answers

    Which of the following factors might influence whether a particular antigen will be recognized as immunogenic in different individuals?

    <p>Genetic differences in MHC molecules</p> Signup and view all the answers

    Which of the following routes of vaccine administration might be used to prevent respiratory infections?

    <p>Intranasal</p> Signup and view all the answers

    Why do proteins tend to be highly immunogenic compared to other macromolecules?

    <p>They have greater molecular complexity</p> Signup and view all the answers

    Which of the following best describes a superantigen's interaction with T cells?

    <p>It induces activation by binding to the variable domain of the β-chain of TCR</p> Signup and view all the answers

    Study Notes

    T-Independent Antigens

    • T-independent antigens have a polymeric structure with repeated antigenic determinants.
    • They don't need help from CD4+ T cells to activate B cells.

    Superantigens

    • Superantigens activate a large number of T cells nonspecifically.
    • They bind to the variable domain of the β-chain of TCRs, bypassing normal antigen presentation.

    Autoantigens

    • Autoantigens are altered self-antigens that are mistakenly recognized as foreign by the immune system.
    • They are often involved in autoimmune diseases.

    Haptens

    • Haptens are small molecules that cannot induce an immune response on their own.
    • They need to bind to a larger carrier molecule to become immunogenic.

    Immunogenicity

    • The foreignness of an antigen is a key factor determining its immunogenicity.
    • The size and complexity of an antigen also play a role in its immunogenicity.
    • Adjuvants enhance the immune response to an antigen.

    Antigen Types

    • T-dependent antigens require helper T cells for activation of B cells.
    • Exogenous antigens are derived from microbial agents and are responsible for activating the immune system in infections.

    Factors Affecting Immunogenicity

    • Genetic differences in MHC molecules can influence whether an antigen is recognized as immunogenic.
    • The route of administration can affect the immunogenicity of an antigen.

    Vaccine Administration

    • Intranasal administration is used to prevent respiratory infections.

    Protein Immunogenicity

    • Proteins are highly immunogenic due to their greater molecular complexity.

    Superantigen vs. Regular Antigen

    • Superantigens bind to the variable domain of the β-chain of TCR, unlike regular antigens which require specific MHC-peptide complex recognition.

    T-Independent Antigens

    • T-independent antigens are characterized by their polymeric structure with repeated antigenic determinants which allows direct stimulation of B cells without requiring the involvement of T cells.

    Superantigens

    • Superantigens bind to MHC molecules and TCRs, resulting in the non-specific activation of a large number of T cells.
    • This non-specific activation leads to a massive release of cytokines—a phenomenon associated with autoimmune disorders.

    Autoantigens

    • Autoantigens are self-antigens that are mistakenly identified as foreign by the immune system, leading to autoimmune responses.
    • These self-antigens can be altered from their normal state, such as in the case of tumor antigens, and are thus recognized as foreign by the immune system.

    Haptens

    • Haptens are small molecules that are not immunogenic on their own but can become immunogenic when they bind to larger carrier molecules.
    • This binding creates a new antigenic determinant, thus triggering an immune response.

    Immunogenicity

    • The immunogenicity of an antigen is influenced by its size, foreignness, and route of administration.
    • The age of the antigen is not a significant factor in determining its immunogenicity.

    Antigen Types

    • T-dependent antigens are typically proteins and require the involvement of helper T cells for B cell activation.
    • T-independent antigens are predominantly polysaccharides and can activate B cells directly.
    • Haptens are small molecules that are not immunogenic on their own and require a carrier molecule to become immunogenic.
    • Superantigens are potent activators of T cells and typically bind to the variable domain of the β-chain of TCRs.
    • Endogenous antigens are derived from within the body, such as tumor antigens or self-antigens that have been altered during tumorigenesis.
    • Exogenous antigens are derived from external sources, such as bacteria, viruses, or allergens.

    Adjuvants

    • Adjuvants enhance the immune response to an antigen by promoting antigen persistence, increasing antigen uptake by antigen-presenting cells (APCs), and stimulating the production of cytokines.

    Immunogenicity Factors

    • The foreignness of an antigen is a key determinant of its immunogenicity.
    • The complexity of an antigen increases its immunogenicity as more diverse epitopes are available for recognition by the immune system.
    • The size of an antigen is also a factor that can modulate immunogenicity with larger antigens tending to be more immunogenic than smaller ones, with a significant exception being very large molecules that may not be efficiently processed by the immune system.

    Antigen Route of Administration

    • Intranasal administration is a suitable route for vaccine administration for respiratory infections because it allows for the induction of mucosal immunity.
    • The intravenous route of vaccine administration is rarely used as it can trigger systemic immune responses.

    Protein Antigens

    • Protein antigens are typically T-dependent antigens, meaning they require the assistance of helper T cells to activate B cells.
    • Proteins have a high degree of molecular complexity which makes them highly immunogenic.
    • They contain multiple epitopes which can be recognized by diverse T cells.

    Polysaccharide Antigens

    • Polysaccharide antigens are typically T-independent antigens, meaning they can activate B cells directly without the help of T cells.
    • Polysaccharides have a repetitive structure with repeating antigenic determinants which allows them to directly bind to B cell receptors and stimulate antibody production.

    Superantigens vs. Regular Antigens

    • Superantigens bypass the normal antigen processing pathway and directly bind to the variable domain of the β-chain of TCRs.
    • This interaction results in the activation of a large number of T cells, leading to a massive release of cytokines.
    • In contrast, regular antigens stimulate a specific immune response by presenting processed antigen fragments to specific T cells.

    Immunogenic Molecules

    • Proteins are generally the most immunogenic macromolecules, owing to their high complexity and diversity of epitopes.
    • Lipids, nucleic acids, and polysaccharides are less immunogenic and in some cases might require carrier molecules to elicit an immune response.

    Endogenous vs. Exogenous Antigens

    • Endogenous antigens are derived from within the body and are encountered when cells undergo processes like tumorigenesis (for example, altered self antigens).
    • Exogenous antigens are derived from external sources such as pathogens or environmental agents.

    Autoantigens vs. Foreign Antigens

    • Autoantigens are self-antigens that are mistakenly identified as foreign by the immune system.
    • These self-antigens can be derived from normal body components but are altered or presented in a manner that triggers an immune response.
    • Foreign antigens, on the other hand, are derived from pathogens or other non-self sources and are easily recognized by the immune system.

    Factors In uencing Immunogenicity

    • The genetic background of an individual can influence the immunogenicity of an antigen.
    • This is because MHC molecules are highly polymorphic, and different individuals may express different MHC alleles.
    • These variations in MHC molecules can influence antigen presentation and T cell recognition.

    Vaccine Administration

    • Intramuscular administration is a common route for vaccines, particularly for protein-based vaccines.
    • It allows for the delivery of the antigen to antigen-presenting cells and induces a strong immune response.

    Denaturation

    • The denaturation of an antigen can expose more antigenic determinants by breaking down the 3-dimensional structure of the protein, increasing its immunogenicity.
    • This process can be used to enhance the immunogenicity of certain antigens.

    Exogenous Antigens

    • Exogenous antigens are crucial for mounting a protective immune response against invading pathogens.
    • These antigens are processed by antigen-presenting cells (APCs) and presented to T cells.

    T-Independent Antigens

    • The repetitive structure of T-independent antigens allows for direct interaction with B cells and activation without requiring T cell help.

    Autoimmunity

    • Autoimmunity arises when the immune system mistakenly targets self-antigens as foreign.
    • The underlying mechanisms can involve the breakdown of tolerance, genetic predisposition, or environmental factors.

    Immunogenic Factors: MHC and Genetic Diversity

    • MHC molecules play a crucial role in antigen presentation to T cells.
    • Genetic variation in MHC alleles can significantly influence an individual's immune response to specific antigens.
    • This diversity in MHC molecules contributes to the highly personalized nature of the immune system.

    Vaccination Strategies

    • The route of administration is tailored to the type of infection and the desired immune response.
    • For example, intranasal administration is used for respiratory infections to induce mucosal immunity.

    Protein Immunogenicity

    • The complex structure of proteins allows for a greater diversity of antigenic determinants.
    • This richness in epitopes makes proteins highly immunogenic.

    Superantigen Mechanism

    • Superantigens bind to both the MHC molecule and the TCR, bypassing the normal antigen processing steps.
    • This non-specific activation of a large number of T cells leads to an uncontrolled release of cytokines.
    • The consequences of this can be severe, including immune dysregulation and tissue damage.

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