W1-13 Antigen and antibody

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Questions and Answers

Which of the following best defines an adjuvant?

  • A molecule that binds to an antibody and modifies its activity
  • A substance that enhances the body's immune response to an antigen (correct)
  • An enzyme that breaks down antibodies into smaller fragments
  • A protein that helps in the transport of antigens across cell membranes

What is the primary function of an epitope?

  • To regulate B-cell maturation
  • To bind specifically to an antibody or T-cell receptor (correct)
  • To trigger apoptosis in infected cells
  • To induce T-cell activation

What are the products of papain and pepsin digestion of IgG?

  • Three fragments with different antigenic specificities
  • Four smaller fragments with different effector functions
  • Two identical fragments with antigen-binding activity
  • One Fc fragment and two Fab fragments (correct)

Which of the following best describes the structure of an antibody molecule?

<p>Two heavy chains and two light chains linked by disulfide bonds (C)</p> Signup and view all the answers

Which isotype of antibody is primarily responsible for mucosal immunity?

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

What are the necessary characteristics that enable an antigen to drive an immune response?

<p>Ability to be recognized by the immune system and induce an immune response (B)</p> Signup and view all the answers

Which molecule is responsible for displaying peptides to T cells?

<p>Major Histocompatibility Complex (MHC) molecules (B)</p> Signup and view all the answers

What is the role of adjuvants in enhancing the immune response to an antigen?

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

What is the term for the portions of an antigen that bind the recognition molecules of the immune system?

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

What are haptens?

<p>Small molecules that are non-immunogenic (A)</p> Signup and view all the answers

What is the first phase of removal for intravenously injected antigen from the circulation?

<p>Phase of equilibration (D)</p> Signup and view all the answers

What is the role of plasma cells in the adaptive immune response?

<p>Secretion of antibodies (B)</p> Signup and view all the answers

How is the specificity of antibodies determined?

<p>Amino acid sequence of the antigen-binding site (D)</p> Signup and view all the answers

What determines the specificity of antibodies produced by single B cells?

<p>Random gene rearrangement of immunoglobulin gene segments (B)</p> Signup and view all the answers

How many functional V gene segments are there for the heavy chain in B cells?

<p>Up to 65 functional V gene segments (A)</p> Signup and view all the answers

What is the modern definition of an antigen?

<p>A molecule that is recognized by the immune system (B)</p> Signup and view all the answers

Which of the following properties makes proteins the best antigens?

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

What type of molecules usually must be conjugated to a larger macromolecule to be antigenic?

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

Which phase involves the distribution of antigen between vascular and the extravascular compartments?

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

What triggers phagocytosis and allows recognition of the Fc portion of antibodies?

<p>Fc Receptors (D)</p> Signup and view all the answers

What is responsible for creating the antigen recognition site through gene segment rearrangements?

<p>RAG-1 and RAG-2 (B)</p> Signup and view all the answers

What mediates the generation of junctional diversity by adding or deleting nucleotides to create a joint?

<p>&quot;TdT enzyme&quot; (B)</p> Signup and view all the answers

What enzyme is responsible for cleaving IgG into 2 Fab and Fc portions?

<p>&quot;Papain&quot; (D)</p> Signup and view all the answers

Which type of variation refers to variations in the variable region, particularly hypervariable region?

<p>&quot;Idiotypic variation&quot; (A)</p> Signup and view all the answers

Which characteristic defines the specificity of an antibody in terms of which antigen it will bind?

<p>&quot;Idiotype&quot; (D)</p> Signup and view all the answers

What does "Isotype" define in terms of antibody function?

<p>The constant sequence in immunoglobulin (C)</p> Signup and view all the answers

What is responsible for defining the function of an antibody in terms of its contribution to the immune response?

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

What process results in the addition of random nucleotides into the antigen-binding region of the BCR and further modifies the avidity and affinity of antibody molecules?

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

Which enzyme cleaves the antibody molecule into 3 fragments: 2 identical Fab fragments and one Fc fragment?

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

What do the hypervariable regions within both the VH and VL chains form when the antibody molecule assembles into its three-dimensional structure?

<p>Loops at the surface of the molecule that interact with antigens (A)</p> Signup and view all the answers

Which enzyme cuts the antibody molecule on the carboxyl-terminal side of the disulfide bonds, producing the F(ab’)2 fragment?

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

What determines the effector function of the antibody molecule?

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

What determines an antibody's tissue distribution and effector function?

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

What term refers to genetic differences between individuals within a species involving different alleles at a given locus?

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

Which region provides the structural framework for the hypervariable regions of an antibody?

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

What do public idiotypes refer to?

<p>Idiotypes shared between different B-cell clones (B)</p> Signup and view all the answers

What adds additional diversity to the immunoglobulin genes during B cell development?

<p>Somatic hypermutation (D)</p> Signup and view all the answers

Which enzyme is involved in enzymatic cleavage of the IgG molecule to yield three fragments?

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

Which term refers to variations in the variable domain, particularly in the hypervariable region (CDR) that determine antigen binding specificity?

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

Which antibody is the 'early' antibody secreted in an immune response?

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

What is the main function of IgA antibodies?

<p>Neutralizing pathogens along mucosal surfaces (D)</p> Signup and view all the answers

Which antibody subclass can readily cross the human placenta, providing protection for the developing fetus?

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

Which immunoglobulin binds to high affinity receptors on mast cells and plays a major role in allergic reactions?

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

What is the main function of IgE antibodies in triggering mast cells to release their granule contents?

<p>Triggering allergic reactions (A)</p> Signup and view all the answers

Which antibody is expressed on the surface of B cells and acts as the B cell receptor for antigen?

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

What influences the activated B cell to switch to a particular antibody isotype?

<p>Cytokines produced by activated CD4 T cells (A)</p> Signup and view all the answers

Which antibody is the first to be secreted in immune response?

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

What is the main function of IgA?

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

Where is IgE found bound in tissues?

<p>On Fc receptors on mast cells (D)</p> Signup and view all the answers

What are the characteristics of a typical antigen that provoke an immune response?

<p>Complexity, foreignness, and solubility (C)</p> Signup and view all the answers

What is the property of an immunogen that differentiates it from an antigen?

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

What contributes to the immunogenicity of an antigen?

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

Where is IgM found?

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

What does IgG trigger?

<p>Opsonization of pathogens (B)</p> Signup and view all the answers

What is the main function of IgD?

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

Flashcards

Antigen

Any molecule that can be recognized by the immune system.

Immunogen

An antigen capable of triggering an immune response.

Epitope

The specific part of an antigen that binds to the antigen recognition molecule.

Equilibration Phase

The first stage of antigen elimination where the antigen spreads throughout the body.

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Catabolic Phase

The phase where innate immune cells break down the antigen.

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Immune Elimination Phase

The phase where antibodies bind to the antigen and form immune complexes.

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Antibody

Proteins secreted by B cells that bind to antigens.

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Immunoglobulin

The B cell receptor, responsible for recognizing antigens.

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Adjuvant

A chemical that enhances the immune response to an antigen.

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Antibody Structure

The basic structure of an antibody, consisting of two Fab fragments and one Fc fragment.

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Opsonization

The ability of antibodies to trigger phagocytosis of antigen-antibody complexes by macrophages.

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Fc Receptors

Receptors on immune cells that recognize and bind the Fc portion of antibodies.

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Antibody Diversity

The process of generating a diverse repertoire of antibodies from a limited number of genes.

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IgM

The first antibody secreted during an immune response, it is a pentamer.

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IgG

The most abundant antibody in serum, it is a monomer.

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IgA

The major antibody in mucosal secretions, it can be a monomer or dimer.

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IgE

The antibody involved in allergic reactions, it is a monomer.

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IgD

An antibody found on the surface of naive B cells, its secreted form has no known function.

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Cell Differentiation

The process by which a cell becomes specialized to perform a specific function.

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Cell Proliferation

The process by which cells divide and create more cells.

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Macrophages

Antigen-presenting cells that engulf antigens and present them to T cells.

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Lymphocytes

White blood cells that are responsible for the adaptive immune response.

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B cells

A type of lymphocyte that produces antibodies.

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Cytotoxic T cells

A type of lymphocyte that directly kills infected cells.

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Helper T cells

A type of lymphocyte that helps activate other immune cells.

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Adaptive Immune Response

A type of immune response that is specific to a particular antigen.

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Innate Immune Response

A type of immune response that is non-specific and always present.

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Ligand

A molecule that binds to a specific target molecule.

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Phagocytosis

The process in which a cell engulfs and digests another cell.

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Study Notes

  • Ross University School of Medicine: overview of student outcomes in Immunology and Medical Microbiology
  • Professor Raymond F Adebiyi: topic - Antigen and Antibody: Structure and Function
  • Learning objectives: 1-8

Antigens and Immunogens:

  • Antigen: a molecule recognized by the immune system, induces an immune response
  • Immunogen: an antigen that provokes an immune response
  • Immunogens are antigens but not all antigens are immunogens
  • Antigens vs Immunogens: immunogens are antigens that induce an immune response
  • Factors influencing immunogenicity: dose, route
  • Adjuvants: chemical substances that enhance immune response to an antigen
  • Epitopes: portion of antigen that binds the antigen recognition molecule

Phases of Antigen Elimination:

  • Equilibration Phase: distribution of antigen between vascular and extravascular compartments
  • Catabolic Phase: elimination of antigen by innate cells
  • Immune Elimination Phase: formation of antigen-antibody immune complex
  • The appearance of free antibody in serum

Antibody:

  • Secreted by B cells
  • Immunoglobulin: B cell receptor
  • Basic structure: two Fab fragments and one Fc fragment
  • Antibodies trigger phagocytosis
  • Fc receptors allow recognition of the Fc portion of antibodies
  • Generation of antibody diversity: combinatorial and junctional diversity
  • Papain and pepsin digestion of IgG: Fab and Fc fragments

Five Isotypes:

  • IgM: first antibody secreted, pentamer, bound by J chain, activates classical complement
  • IgG: second antibody secreted, monomer, activates classical complement, opsonization, neutralization, ADCC
  • IgA: secreted as monomer and dimer, secretory component facilitates transport across epithelium, neutralization
  • IgE: secreted as monomer, binds to high affinity Fcε receptors, efficiently triggers degranulation (important in allergy)
  • IgD: expressed on surface of naïve B cells, secreted form has no known function

Tissue distribution and biological functions (effector functions) of each class.

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