55 Questions
Which of the following best defines an adjuvant?
A substance that enhances the body's immune response to an antigen
What is the primary function of an epitope?
To bind specifically to an antibody or T-cell receptor
What are the products of papain and pepsin digestion of IgG?
One Fc fragment and two Fab fragments
Which of the following best describes the structure of an antibody molecule?
Two heavy chains and two light chains linked by disulfide bonds
Which isotype of antibody is primarily responsible for mucosal immunity?
IgA
What are the necessary characteristics that enable an antigen to drive an immune response?
Ability to be recognized by the immune system and induce an immune response
Which molecule is responsible for displaying peptides to T cells?
Major Histocompatibility Complex (MHC) molecules
What is the role of adjuvants in enhancing the immune response to an antigen?
Prolonging the persistence of the antigen
What is the term for the portions of an antigen that bind the recognition molecules of the immune system?
Epitopes
What are haptens?
Small molecules that are non-immunogenic
What is the first phase of removal for intravenously injected antigen from the circulation?
Phase of equilibration
What is the role of plasma cells in the adaptive immune response?
Secretion of antibodies
How is the specificity of antibodies determined?
Amino acid sequence of the antigen-binding site
What determines the specificity of antibodies produced by single B cells?
Random gene rearrangement of immunoglobulin gene segments
How many functional V gene segments are there for the heavy chain in B cells?
Up to 65 functional V gene segments
What is the modern definition of an antigen?
A molecule that is recognized by the immune system
Which of the following properties makes proteins the best antigens?
Complex nature
What type of molecules usually must be conjugated to a larger macromolecule to be antigenic?
Small molecules
Which phase involves the distribution of antigen between vascular and the extravascular compartments?
Equilibration Phase
What triggers phagocytosis and allows recognition of the Fc portion of antibodies?
Fc Receptors
What is responsible for creating the antigen recognition site through gene segment rearrangements?
RAG-1 and RAG-2
What mediates the generation of junctional diversity by adding or deleting nucleotides to create a joint?
"TdT enzyme"
What enzyme is responsible for cleaving IgG into 2 Fab and Fc portions?
"Papain"
Which type of variation refers to variations in the variable region, particularly hypervariable region?
"Idiotypic variation"
Which characteristic defines the specificity of an antibody in terms of which antigen it will bind?
"Idiotype"
What does "Isotype" define in terms of antibody function?
The constant sequence in immunoglobulin
What is responsible for defining the function of an antibody in terms of its contribution to the immune response?
Isotypic difference
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?
Somatic hypermutation
Which enzyme cleaves the antibody molecule into 3 fragments: 2 identical Fab fragments and one Fc fragment?
Pepsin
What do the hypervariable regions within both the VH and VL chains form when the antibody molecule assembles into its three-dimensional structure?
Loops at the surface of the molecule that interact with antigens
Which enzyme cuts the antibody molecule on the carboxyl-terminal side of the disulfide bonds, producing the F(ab’)2 fragment?
Pepsin
What determines the effector function of the antibody molecule?
Isotypic variation
What determines an antibody's tissue distribution and effector function?
Heavy chain classes
What term refers to genetic differences between individuals within a species involving different alleles at a given locus?
Allotypic variations
Which region provides the structural framework for the hypervariable regions of an antibody?
Framework regions
What do public idiotypes refer to?
Idiotypes shared between different B-cell clones
What adds additional diversity to the immunoglobulin genes during B cell development?
Somatic hypermutation
Which enzyme is involved in enzymatic cleavage of the IgG molecule to yield three fragments?
Papain
Which term refers to variations in the variable domain, particularly in the hypervariable region (CDR) that determine antigen binding specificity?
Idiotypic variation
Which antibody is the 'early' antibody secreted in an immune response?
IgM
What is the main function of IgA antibodies?
Neutralizing pathogens along mucosal surfaces
Which antibody subclass can readily cross the human placenta, providing protection for the developing fetus?
IgG1
Which immunoglobulin binds to high affinity receptors on mast cells and plays a major role in allergic reactions?
IgE
What is the main function of IgE antibodies in triggering mast cells to release their granule contents?
Triggering allergic reactions
Which antibody is expressed on the surface of B cells and acts as the B cell receptor for antigen?
IgD
What influences the activated B cell to switch to a particular antibody isotype?
Cytokines produced by activated CD4 T cells
Which antibody is the first to be secreted in immune response?
IgM
What is the main function of IgA?
Neutralization
Where is IgE found bound in tissues?
On Fc receptors on mast cells
What are the characteristics of a typical antigen that provoke an immune response?
Complexity, foreignness, and solubility
What is the property of an immunogen that differentiates it from an antigen?
Immunogenicity
What contributes to the immunogenicity of an antigen?
Dose and foreignness
Where is IgM found?
In blood
What does IgG trigger?
Opsonization of pathogens
What is the main function of IgD?
Neutralization
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.
Test your knowledge about the impact of different routes of administration on the immune response. Understand how materials introduced via the digestive tract differ from those introduced parenterally in terms of immune system recognition and response.
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