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Questions and Answers

What molecular weight range is generally associated with poor immunogens?

  • 70,000 - 90,000 Da
  • 30,000 - 50,000 Da
  • 5,000 - 10,000 Da (correct)
  • 100,000 - 150,000 Da

Which type of immunogen is more immunogenic due to its insolubility?

  • Soluble immunogen
  • Native immunogen
  • Denatured immunogen
  • Particulate immunogen (correct)

What type of antigen requires the assistance of T cells for antibody production?

  • Auto-antigen
  • B-cell antigen
  • T-independent antigen
  • T-dependent antigen (correct)

Which characteristic contributes most to the immunogenicity of a protein?

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

What defines a hapten in immunology?

<p>A partial antigen that needs a carrier for immune response (A)</p> Signup and view all the answers

Which type of antigen is characterized by the non-specific activation of T-cells?

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

Which type of antigen is specifically recognized by individuals with autoimmune diseases?

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

What enhances the immunogenicity of an immunogen in terms of its degradation?

<p>Easily phagocytized characteristics (A)</p> Signup and view all the answers

Which characteristic is indicative of a good immunogen's stability?

<p>Resistance to pH changes (B)</p> Signup and view all the answers

What type of antigen provokes hypersensitivity reactions in sensitized individuals?

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

Which of the following correctly identifies the main characteristic of T-independent antigens?

<p>They consist primarily of polysaccharides and stimulate B cells directly. (D)</p> Signup and view all the answers

What class of antigens is recognized by T cytotoxic cells (CD8+) in normal cell metabolism?

<p>Endogenous antigens (D)</p> Signup and view all the answers

Which antigens are associated with autoimmune diseases due to a misdirected immune response?

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

Which type of antigen is unique to tumor cells and is the result of tumor-specific mutations?

<p>Tumor-specific antigens (TSAs) (B)</p> Signup and view all the answers

What is the typical immunogenicity of nucleic acids in isolation?

<p>Poorly immunogenic unless combined with proteins. (B)</p> Signup and view all the answers

Which type of antigens are primarily presented by Antigen Presenting Cells (APCs) using MHC class II molecules?

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

Which of the following statements accurately describes the immunogenic nature of lipids?

<p>Lipids are non-immunogenic and act solely as haptens. (A)</p> Signup and view all the answers

What sequence correctly describes the role of MHC class I molecules in antigen presentation?

<p>They present endogenous antigens to T cytotoxic cells. (B)</p> Signup and view all the answers

In general, which molecule type is considered the best immunogen?

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

What is the primary role of T helper cells in response to exogenous antigens?

<p>To activate B cells for antibody production. (C)</p> Signup and view all the answers

What distinguishes an immunogen from an antigen?

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

Which statement about epitopes is correct?

<p>Epitopes are known as antigenic determinants. (B)</p> Signup and view all the answers

What is the primary factor that influences the degree of immunogenicity?

<p>The molecular weight of the immunogen. (C)</p> Signup and view all the answers

Which of the following statements about haptens is true?

<p>Haptens require binding to larger molecules to become immunogenic. (A)</p> Signup and view all the answers

What is antigenicity?

<p>The ability of an antigen to bind specifically to immune response products. (D)</p> Signup and view all the answers

Which is a true statement regarding immunogens?

<p>Immunogens must be non-self to be recognized by the immune system. (B)</p> Signup and view all the answers

Which property is NOT relevant to defining an immunogen?

<p>Type of antibody binding affinity. (B)</p> Signup and view all the answers

Why might a large molecular weight immunogen be more effective?

<p>It can provoke a stronger immune response than smaller molecules. (C)</p> Signup and view all the answers

What does not factor into the immunogenicity of an antigen?

<p>Its ability to bind to TCR/MHC complexes. (C)</p> Signup and view all the answers

What type of antigens are expressed at lower levels on healthy cells but are recognizable by cytotoxic T lymphocytes?

<p>Tumor-associated antigens (D)</p> Signup and view all the answers

Which of the following best defines an incomplete antigen or hapten?

<p>A substance that requires a larger molecule to induce antibodies (B)</p> Signup and view all the answers

What is the primary role of adjuvants in vaccination?

<p>Enhancing the immunogenicity of an antigen (B)</p> Signup and view all the answers

Aluminum potassium sulfate (alum) acts primarily by:

<p>Prolonging the persistence of the antigen in the body (D)</p> Signup and view all the answers

Freund’s complete adjuvant is characterized by which of the following components?

<p>Mineral oil, emulsifier, and killed mycobacteria (A)</p> Signup and view all the answers

Which of the following adjuvants is the only one approved for clinical use in the United States?

<p>Aluminum potassium sulfate (alum) (D)</p> Signup and view all the answers

What is a notable effect of Freund’s adjuvant when injected?

<p>It induces chronic inflammation and scar tissue formation (C)</p> Signup and view all the answers

The precise mechanism of action of adjuvants is:

<p>Uncertain but believed to increase immune cell attraction (A)</p> Signup and view all the answers

In the context of immunology, which process is primarily initiated by complete antigens?

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

Why might adjuvants be necessary for certain vaccines?

<p>To boost the immune response when antigens are low in quantity (C)</p> Signup and view all the answers

Flashcards

Antigen

A substance that can bind to antibodies or T cell receptors.

Immunogen

A type of antigen that can trigger an immune response.

Epitope

The specific part of an antigen that is recognized by antibodies or T cell receptors.

Antigenicity

The ability of an antigen to bind to antibodies or T cell receptors.

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Immunogenicity

The ability of an antigen to trigger an immune response.

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Foreignness

One of the factors affecting immunogenicity. An immunogen must be recognized as foreign by the immune system in order to trigger a response.

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Molecular weight

One of the factors affecting immunogenicity. Generally, larger molecules are better at triggering an immune response.

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Hapten

Smaller molecules that can bind to antibodies but cannot trigger an immune response by themselves.

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Carrier molecules

Haptens become immunogenic when attached to larger carrier molecules.

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Good Immunogen

Antigen with high molecular weight and specific characteristics that readily stimulate immune cells to produce a strong immune response.

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Insoluble Immunogen

An antigen that is poorly soluble in solutions.

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Degradable Immunogen

An antigen that is readily broken down and processed by immune cells.

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Allergen

An antigen that causes an exaggerated immune response, leading to allergy.

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Superantigen

An antigen that specifically activates T-cells, leading to a widespread immune response.

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Tolerogen

An antigen that induces the immune system to tolerate a specific substance, suppressing an immune response.

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T-independent antigen

Antigens that directly stimulate B cells without the need for T cell help.

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Protein antigens

The most common type of immunogen, usually proteins or modified proteins.

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Polysaccharide antigens

These complex carbohydrates can often trigger an immune response.

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Nucleic Acid antigens

Typically, nucleic acids are poor at triggering the immune system alone.

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Lipid antigens

These molecules are generally not immunogenic by themselves, but can become immunogenic when combined with other molecules.

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Exogenous antigens

Antigens that originate from outside the body, like bacteria or viruses.

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Endogenous antigens

Antigens produced within the body, such as those from intracellular bacteria or viruses.

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Autoantigens

Antigens normally present in the body, but mistakenly targeted by the immune system in autoimmune diseases.

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Tumor antigens

Antigens expressed specifically on tumor cells.

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Tumor-specific antigens (TSAs)

Antigens found only on tumor cells, likely resulting from tumor-specific mutations.

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Tumor Associated Antigens (TAAs)

Antigens expressed at lower levels on normal cells but can trigger immune responses against tumor cells.

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Complete Antigen

A substance that can trigger antibody formation and cause a specific reaction with the produced antibody.

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Incomplete Antigen (Hapten)

A substance that cannot trigger an antibody formation on its own but can do so if combined with a carrier molecule.

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Adjuvants

Substances that enhance the immunogenicity of an antigen when mixed and injected together.

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Aluminum potassium sulfate (alum)

A commonly used adjuvant that prolongs antigen persistence by creating a slower release of the antigen.

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Freund's complete adjuvant

An adjuvant made of mineral oil, emulsifier, and killed mycobacteria, used for experimental purposes but not in humans due to its side effects.

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Aluminum Salts

The only adjuvants approved for clinical use in the United States, used to increase the size of the antigen and prevent rapid escape from tissues.

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Mechanism of Adjuvants

The precise mechanism of how adjuvants enhance immune response is still under research. However, it is believed to involve various mechanisms including a local inflammatory response.

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Cytotoxic T lymphocytes (CTL)

A type of immune response where the body destroys cells with antigens it recognizes as foreign.

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Study Notes

Antigens

  • Antigens are foreign substances that induce the production of specific antibodies or activate specific immune cells. They specifically interact with immune response products.
  • Immunogens are foreign substances inducing a specific immune response (humoral or cell-mediated). All immunogens are antigens, but not all antigens are immunogens.
  • Epitopes are the parts of an antigen that are recognized and bound by antibodies (Ab) or T cell receptor/Major Histocompatibility Complex (TCR/MHC) complexes (also called antigenic determinants).

Immunogen Characteristics

  • Foreignness: Immunogens must be recognized as non-self by the immune system. A greater phylogenetic distance between species leads to a greater chance of immunogenicity.
  • Molecular Weight: There's a strong correlation between molecular weight and immunogenicity. Higher molecular weight generally means greater immunogenicity. Large molecules (100,000 Da) are effective immunogens, while smaller ones (5-10,000 Da) are generally poor immunogens.
  • Chemical Nature and Stability: The immunogen's chemical structure must be stable in various conditions (temperature, pH, and biological solutions). Chemical complexity, particularly the makeup of amino acids in a molecule, correlates with increased immunogenicity. More complex structures are better immunogens.
  • Physical Form: Insoluble (particulate) immunogens are more immunogenic than soluble ones. Denatured immunogens are more immunogenic than their native forms.
  • Degradability: Easily phagocytized immunogens are generally more immunogenic. This is because phagocytosis leads to processing and presentation of the antigen to T helper cells by antigen-presenting cells (APCs).

Other Antigen Types

  • Hapten (partial or incomplete antigen): These are low-molecular-weight foreign substances incapable of inducing an immune response on their own. They require combination with a larger molecule (like a protein) to elicit an immune response.
  • Allergen: An antigen that provokes a hypersensitivity reaction (allergy) in sensitized individuals.
  • Superantigen: An antigen that causes non-specific activation of T cells, leading to polyclonal T cell activation and massive cytokine release.
  • Tolerogen: An antigen, usually in a soluble form, that induces immunological tolerance.
  • Autoantigen (self-antigen): A normal protein or protein complex (or DNA/RNA) recognized by the immune system of patients with autoimmune diseases. Under normal conditions, these would not be targeted by the immune system.
  • Alloantigen (isoantigen): Antigens found in different members of the same species (e.g., blood type antigens like A and B).
  • Heterophile antigens: Identical antigens found in cells and tissues of different species (e.g., cross-reacting microbial antigens).
  • T-dependent antigen: Antigens needing T cell assistance to induce antibody formation.
  • T-independent antigen: (Usually polysaccharides) that directly stimulate B cells.

Antigen Chemical Nature

  • Proteins: The majority of immunogens are proteins or protein-molecule conjugates (e.g., glycoproteins, lipoproteins). Generally very good immunogens.
  • Polysaccharides: Polysaccharides and lipopolysaccharides are generally good immunogens.
  • Nucleic acids: Nucleic acids are usually poor immunogens.
  • Lipids: Lipids are typically non-immunogenic and may act as haptens; they only become immunogenic when combined with proteins or polysaccharides.

Antigen Origin

  • Exogenous antigens: Antigens that enter the body from the outside (e.g., bacterial structures, toxins, viruses, fungi, parasites).
  • Endogenous antigens: Antigens generated within normal cells (e.g., from normal cell metabolism, viral or intracellular bacterial infection).
  • Autoantigens (self-antigens): Normal proteins/complexes recognized by the immune system in autoimmune diseases.
  • Tumor antigens: Antigens presented by MHC class I or II molecules on tumor cells; those unique to the tumor cells are termed tumour specific antigens (TSAs). Tumor-associated antigens (TAAs) are also present on normal cells though at lower levels.

Antigen Presentation

  • Antigens are presented by antigen-presenting cells (APCs), such as macrophages, B cells, and dendritic cells.
  • APCs present processed fragments to T helper cells (CD4+) using MHC class II molecules.
  • Endogenous antigens are presented by MHC class I molecules to cytotoxic T cells (CD8+).

Adjuvants

  • Adjuvants are substances mixed with an antigen to enhance its immunogenicity, often used when the antigen has low immunogenicity or limited amounts are available.
  • Adjuvants boost the immune response by stimulating local inflammation, attracting more immune cells to the injection site, and prolonging antigen persistence.
  • Examples include aluminum salts (used in many vaccinations, like hepatitis B) or Freund's complete adjuvant (with mineral oil and killed mycobacteria).

Mechanism of Adjuvants

  • Precise mechanism remains somewhat unclear.
  • It may include increasing the number of cells involved in antibody production, ensuring more efficient antigen processing, prolonging antigen duration in the body, and stimulating antibody synthesis and release.

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