Immunogens and Antigens Overview
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Questions and Answers

What is the primary function of adjuvants in vaccines?

  • Increasing blood flow
  • Enhancing fever response
  • Prolonging antigen persistence (correct)
  • Neutralization of toxins

Which antibody class is known for its ability to cross the placenta?

  • IgG (correct)
  • IgD
  • IgM
  • IgA

What is the main characteristic of hypervariable regions in antibodies?

  • They are responsible for binding complement
  • They provide flexibility and structure
  • They are highly variable in amino acid sequence (correct)
  • They are identical in all antibody types

Which immunoglobulin is primarily found in secretions such as tears and saliva?

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

Which of the following statements about IgM is true?

<p>It is the first antibody produced after infection. (D)</p> Signup and view all the answers

What is the function of Antibody-Dependent Cell-Mediated Cytotoxicity (ADCC)?

<p>Involves the destruction of infected cells by immune cells (C)</p> Signup and view all the answers

What role does IgE play in the immune system?

<p>Mediator of Type I hypersensitivity reactions (A)</p> Signup and view all the answers

Which of the following is NOT a function of antibodies?

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

Freund's complete adjuvant is specifically used in which type of setting?

<p>Animal experimentation (D)</p> Signup and view all the answers

Which of the following describes the structure of antibodies?

<p>Has both secreted and membrane-bound forms (D)</p> Signup and view all the answers

What is the primary factor that distinguishes immunogens from antigens?

<p>Immunogens can induce an immune response. (C)</p> Signup and view all the answers

Which molecular weight range is typically considered immunogenic?

<blockquote> <p>6kD (D)</p> </blockquote> Signup and view all the answers

What characteristic do homopolymers of amino acids exhibit regarding immunogenicity?

<p>They are not immunogenic. (B)</p> Signup and view all the answers

How does the dosage of an immunogen affect the immune response?

<p>Insufficient doses may lead to tolerance. (A)</p> Signup and view all the answers

Which of the following statements about haptens is true?

<p>Haptens require a carrier to become immunogenic. (A)</p> Signup and view all the answers

Which class of antigens is associated with being very immunogenic?

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

What does cross-reactivity refer to in the context of antibodies?

<p>An antibody's reaction with closely related antigens. (C)</p> Signup and view all the answers

What is the role of an adjuvant in immunology?

<p>An adjuvant enhances immunogenicity when mixed with an immunogen. (A)</p> Signup and view all the answers

Which factor does NOT contribute to the immunogenicity of a substance?

<p>Solubility of the substance (D)</p> Signup and view all the answers

Which statement about nucleic acids and immunogenicity is accurate?

<p>Nucleic acids are not immunogenic. (B)</p> Signup and view all the answers

What is a unique characteristic of aluminum hydroxide as an adjuvant?

<p>It is the only adjuvant with FDA approval for human use. (A)</p> Signup and view all the answers

Which of the following best describes the role of hypervariable regions in antibodies?

<p>They are responsible for antigen-binding diversity. (D)</p> Signup and view all the answers

What is a primary function of IgA in the immune system?

<p>Providing immunity in respiratory and mucosal surfaces. (B)</p> Signup and view all the answers

Which IgG subclass is primarily known for opsonization?

<p>IgG1 (A)</p> Signup and view all the answers

Which statement accurately differentiates immunogens from antigens?

<p>All immunogens are antigens, but not all antigens are immunogens. (D)</p> Signup and view all the answers

What distinguishes the immunological response of IgM from other immunoglobulins?

<p>IgM is always the first antibody class produced after exposure. (C)</p> Signup and view all the answers

Which of the following immunoglobulin classes mediates Type I hypersensitivity reactions?

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

What is the significance of molecular weight in determining immunogenicity?

<blockquote> <p>6 kD are generally immunogenic, while &lt; 1 kD are not. (D)</p> </blockquote> Signup and view all the answers

Which property must a substance possess to enhance its immunogenicity as an adjuvant?

<p>Enhance the response to an immunogen. (D)</p> Signup and view all the answers

Which of the following statements about antibody-dependent cell-mediated cytotoxicity (ADCC) is incorrect?

<p>ADCC involves the complement system. (D)</p> Signup and view all the answers

What defines haptens in relation to immunogenicity?

<p>They require conjugation with an immunogenic compound to become immunogenic. (D)</p> Signup and view all the answers

Which immune function is NOT primarily associated with antibodies?

<p>Directly killing of viral pathogens (C)</p> Signup and view all the answers

Which major class of antigens is typically associated with high immunogenicity?

<p>Proteins and Glycoproteins. (B)</p> Signup and view all the answers

What is one of the primary roles of adjuvants in vaccine formulations?

<p>They slow the release of antigens. (A)</p> Signup and view all the answers

How does chemical complexity affect the immunogenicity of a substance?

<p>Higher complexity increases potential for immunogenicity. (C)</p> Signup and view all the answers

Which comment about the distribution of antibody isotypes is FALSE?

<p>IgG is largely absent in plasma. (A)</p> Signup and view all the answers

What is a key factor in antigen processing that influences immunogenicity?

<p>Stability for antigen presentation. (C)</p> Signup and view all the answers

What does cross-reactivity imply concerning antibodies?

<p>Antibodies often bind with closely related antigens. (B)</p> Signup and view all the answers

Which requirement is NOT necessary for a substance to be considered an immunogen?

<p>It must induce tolerance. (D)</p> Signup and view all the answers

What type of antigens are polysaccharides typically associated with?

<p>Immunogenic only as part of glycoproteins. (C)</p> Signup and view all the answers

Flashcards

Immunogen

A substance capable of inducing an immune response.

Antigen

A substance that can bind specifically to antibodies or T cells.

Immunogenicity

The ability of a substance to induce an immune response.

Hapten

A low molecular weight substance that is not immunogenic on its own but can become immunogenic when conjugated to a carrier molecule.

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Antigen Processing

The breakdown and presentation of antigens to the immune cells.

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Epitopes

Specific regions on an antigen recognized by lymphocytes.

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Adjuvant

A substance that enhances the immunogenicity of an antigen.

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Cross-reactivity

The ability of an antibody to react with antigens other than the one it was elicited against.

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Immunogenicity factors: Foreignness

The more foreign, the stronger the response

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Major Antigens Classes

Proteins, Glycoproteins are among the most potent immunogens; carbohydrates (polysaccharides) are also good immunogens, but only as part of glycoproteins; lipids are rarely immunogenic; Nucleic Acids are generally non-immunogenic.

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Aluminum hydroxide/phosphate

The only FDA-approved adjuvant for human use.

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Freund's complete adjuvant

An adjuvant used in animal studies, oil-based, with killed bacteria.

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Antibody

A protein produced by plasma cells that helps fight infection.

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Antibody Structure

Antibodies have a variable and constant region, for antigen binding and function respectively

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Hypervariable regions

Highly variable regions of antibodies that bind to specific antigens.

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IgG

A major antibody class found in blood; crosses placenta; opsonizes bacteria and viruses.

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IgA

Antibody class abundant in secretions like tears and saliva.

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IgM

The first antibody produced in response to infection, effective in complement fixation.

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IgE

Antibody mediating allergic reactions and parasitic infections.

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What makes something immunogenic?

To be immunogenic, a substance must be foreign, have a certain size and chemical complexity. It must be degradable and be administered in the right dosage.

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What's an autoimmune disease?

When the immune system wrongly attacks the body's own tissues.

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What is the difference between an immunogen and an antigen?

All immunogens are antigens, but not all antigens are immunogens. Immunogens are capable of inducing an immune response, while antigens simply bind to antibodies or T cells, they do not necessarily trigger an immune response.

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What's the importance of antigen processing?

Antigen processing is necessary for the presentation of antigens to immune cells. This process involves breaking down the antigen into smaller pieces that can be recognized by lymphocytes. It's a crucial step in the immune response.

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What are the requirements for a successful immune response?

For a successful immune response, the antigen must be foreign to the body, a sufficient size, chemically complex and susceptible to degradation. It also needs to be administered in the correct dosage.

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What are adjuvants?

Substances added to vaccines that help boost the immune response to the antigen. They can prolong the persistence of the antigen, cause inflammation and attract immune cells, and improve antigen uptake.

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What is the only FDA-approved adjuvant for humans?

Aluminum hydroxide (or phosphate) is the only adjuvant approved for human use.

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What is the adjuvant used in animal studies?

Freund's complete adjuvant is commonly used in animal studies. It's an oil-in-water emulsion containing killed mycobacteria.

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What are antibodies?

Proteins produced by plasma cells (B lymphocytes) that specifically bind to antigens. They are found both as secreted proteins and membrane-bound receptors on B cells.

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Why do we need antibodies?

Antibodies play a crucial role in fighting infections by neutralizing toxins, immobilising bacteria or parasites, activating complement, opsonizing pathogens, and triggering antibody-dependent cell-mediated cytotoxicity (ADCC).

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What are the main functions of the different regions of an antibody?

The variable region binds specifically to the antigen, while the constant region determines the antibody's effector function and class.

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Why are hypervariable regions important?

Hypervariable regions (also known as complementarity determining regions or CDRs) are highly variable amino acid sequences within the variable regions. They are responsible for the antibody's unique antigen-binding specificity.

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What are the five major classes of antibodies?

The five main classes of antibodies are IgM, IgG, IgA, IgD, and IgE. Each class has a unique structure and function.

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Which antibody is the first to be produced in response to infection?

IgM is the first antibody produced after an infection or immunization. This means it is often detectable before IgG is present.

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Which antibody is important for mucosal immunity?

IgA is present in high amounts in secretions like tears, saliva, and mucus, providing protection on respiratory and mucosal surfaces.

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Study Notes

Immunogens and Antigens

  • Immunogens induce an immune response; antigens bind to antibodies or T cells.
  • All immunogens are antigens, but not all antigens are immunogens.
  • Requirements for Immunogenicity:
    • Foreignness: Substances not recognized as "self" (exceptions exist in autoimmune diseases). More foreign = more immunogenic.
    • Size: Generally, molecules larger than 6 kDa are immunogenic; smaller than 1 kDa are typically not (e.g., penicillin, aspirin).
    • Chemical Complexity: Homopolymers of amino acids are not immunogenic.
    • Degradability: Susceptible to enzymatic degradation is important for antigen presentation.
    • Dosage: Insufficient doses can cause tolerance; repeated administrations may be needed for an adequate immune response.

Hapten

  • Low molecular weight (antigen but not immunogen).
  • Non-immunogenic alone.
  • Requires conjugation with an immunogenic compound (carrier) to become immunogenic.

Epitopes Recognized by Lymphocytes

  • Surface antigens
  • Peptides

Major Classes of Antigens

  • Carbohydrates (polysaccharides): Immunogenic as part of glycoproteins.
  • Lipids: Rarely immunogenic.
  • Nucleic Acids: Not immunogenic, except in some diseases (e.g., systemic lupus erythematosus – SLE).
  • Proteins, Glycoproteins: Highly immunogenic.

Cross-reactivity

  • Ability of an antibody targeting one antigen to react with a second, related antigen.
  • Often occurs with closely related antigens due to shared epitopes.

Adjuvant

  • Enhances immunogenicity of an immunogen.
  • Mechanism of action:
    • Physically prolongs antigen persistence/slows release.
    • Induces local inflammation and immune cell proliferation.
    • Improves compound uptake and processing by immune cells.
  • Examples:
    • Humans: Aluminum hydroxide (or phosphate) – FDA-approved.
    • Animals: Freund's complete adjuvant (oil-in-water emulsion with killed mycobacteria).

Function & Structure of Antibodies

  • Antibodies: Globular proteins produced by plasma cells (B lymphocytes). Exist as secreted and membrane-bound forms, forming B cell receptors.
  • Functions: Neutralize toxins/viruses, immobilize bacteria/parasites, activate complement, initiate opsonization, and mediate antibody-dependent cell-mediated cytotoxicity (ADCC).

Antibody Structure

  • Antigen binding: Occurs through hypervariable regions.
  • Fc: The fragment of an antibody that interacts with other molecules

Hypervariable Regions

  • Highly variable amino acid sequences.
  • Present in three locations in both light and heavy chains.

Five Major Classes of Antibodies

  • Different classes with specific functions and distributions.

Distribution of Antibody Isotypes in Body Fluids and Secretions

  • Different isotypes (IgM, IgG, IgA, IgE) have different roles and distributions in body fluids and secretions.

IgG

  • Four subclasses (IgG1, IgG2, IgG3, IgG4).
  • Crosses the placenta.
  • Involved in opsonization, ADCC, complement activation, and toxin/viral neutralization.

IgM

  • First antibody class produced during infection/immunization.
  • Highly efficient in complement activation.

IgA

  • Predominantly found in secretions (tears, saliva, mucus).
  • Important first line defense in the respiratory and mucosal systems.
  • Exhibits antibacterial and antiviral activity.

IgE

  • Mediates Type I hypersensitivity reactions.
  • Levels rise during parasitic infections.

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Description

This quiz explores the key concepts of immunogens and antigens, including their characteristics and requirements for immunogenicity. It also covers haptens and their role in eliciting immune responses. Perfect for students studying immunology and related fields.

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