108 Questions
What are antibodies?
Antigen-binding proteins present on the B-cell membrane and secreted by plasma cells
How does the immune system usually respond to complex antigens?
By producing antibodies to several epitopes on the antigen
What are the outputs of B cells in response to complex antigens?
Monoclonal antibodies, each specifically binding a single antigenic determinant
Where do antibodies reside?
In the serum
What are antibodies also commonly referred to as?
Immunoglobulin (Ig)
Which fraction of the blood contains red blood cells, leukocytes, and platelets?
Cellular fraction
What is the common structure of antibody molecules?
Two identical light chains and two identical heavy chains
What type of chains make up the structure of antibody molecules?
Light and heavy chains
How many peptide chains make up the structure of antibody molecules?
Four peptide chains
What type of bond links each light chain to a heavy chain in the antibody structure?
Disulfide bond
What gives segmental flexibility to the immunoglobulin?
Hinge region rich in proline and cysteine residues
What forms the basic four-chain antibody structure?
(H-L)2, a dimer of dimers
What is the composition of the antigen-binding site of the antibody molecule?
Complementarity-determining regions (CDRs) on both light and heavy chains
Which region of the immunoglobulin molecule differs from one antibody to another?
Variable (V) region
How many amino acids typically make up the amino-terminal variable (V) region in each heavy and light chain of an immunoglobulin molecule?
100–110 amino acids
What is the composition of the constant (C) region in heavy chain of an antibody molecule?
Three or four Ig domains
Which region of the antibody molecule mediates most of the biological functions of antibodies?
Heavy chain C region
Where are the membrane-bound antibodies in the plasma membranes of B lymphocytes attached?
Heavy chain C region
How many sub isotypes of α heavy chains are there in humans?
Two
How many distinct classes and subclasses can antibody molecules be divided into based on differences in the structure of their heavy constant chain (HC) regions?
8
How many sub isotypes of ϒ heavy chains are there in humans?
Four
What do hypervariable regions correspond to in antibody-antigen interaction?
Complementarity-determining regions (CDRs)
Where do smaller antigens fit in the variable regions of antibodies?
Pockets
How do larger antigens interact with the variable region of antibodies?
Flatter regions
What is opsonization?
The promotion of phagocytosis of antigens by macrophages and neutrophils
What initiates the signal-transduction pathway resulting in the phagocytosis of the antigen-antibody complex?
Crosslinking of the FcR by binding to an array of antibody
What are protein molecules called that can bind the constant region of Ig molecules and are present on the surfaces of macrophages and neutrophils?
Fc receptors (FcR)
Which immunoglobulin subclasses can activate the complement system in humans?
IgM and most IgG subclasses
What is the protein fragment produced as an important byproduct of the complement activation pathway?
C3b
What allows erythrocytes to deliver antigen-antibody complexes to the liver or spleen for removal?
Binding of antigen-antibody complexes by C3b receptors
Which cell type can direct the cytotoxic activities against target cells in antibody-dependent cell-mediated cytotoxicity (ADCC)?
Natural killer (NK) cells
What is the role of the antibody in antibody-dependent cell-mediated cytotoxicity (ADCC)?
Acts as a newly acquired receptor enabling the attacking cell to recognize and kill the target cell
What type of cells have Fc receptors that can link with antibody bound to target cells in antibody-dependent cell-mediated cytotoxicity (ADCC)?
Natural killer (NK) cells
Which process is responsible for the movement of immunoglobulin across epithelial layers?
Transcytosis
Which antibody species is the major one that undergoes transcytosis in humans and mice?
IgA
What type of transcytosis is a form of passive immunization?
Transcytosis of IgG from mother to fetus
What is the main function of Fc receptors (FcR) in relation to antibodies?
Facilitate the movement of antibodies across cell membranes and transfer of IgG from mother to fetus
Which cell types can passively acquire antibodies through Fc receptors?
B and T lymphocytes, neutrophils, mast cells, eosinophils, macrophages, natural killer cells
What is the specific affinity of Fc receptors (FcR) in relation to the antibody molecule?
Affinity for the Fc portion of the antibody molecule
Which IgG subclass readily crosses the placenta and plays a role in protecting the developing fetus?
IgG1
Which IgG subclass is the most effective complement activator?
IgG3
Which IgG subclass binds with high affinity to Fc receptors on phagocytic cells and mediates opsonization?
IgG1
Is IgG the most abundant class in serum, constituting about 80% of the total serum immunoglobulin?
True
Do IgG1, IgG3, and IgG4 readily cross the placenta and play an important role in protecting the developing fetus?
True
Is IgG4 able to activate complement at all?
False
Is IgM the first immunoglobulin class produced in a primary response to an antigen?
True
Does IgM have a higher valency than the other isotypes due to its pentameric structure with 10 antigen-binding sites?
True
Is IgM the first immunoglobulin to be synthesized by the neonate?
True
Is IgM more efficient than IgG at activating complement?
True
Is IgM found in very low concentrations in the intercellular tissue fluids due to its large size?
True
Does IgM require less IgM than IgG to neutralize viral infectivity?
True
Where is Immunoglobulin A (IgA) predominantly found?
Breast milk, saliva, tears, and mucus of the bronchial, genitourinary, and digestive tracts
What is the daily production of secretory IgA compared to other immunoglobulin classes?
Greater than any other immunoglobulin class
Where are IgA-secreting plasma cells concentrated?
Along mucous membrane surfaces
What prevents the attachment of pathogens to mucosal cells?
Secretory IgA binding to surface antigens
What does breast milk contain that helps protect newborns against infection?
Secretory IgA
Which molecule in breast milk plays a key role in protecting newborns against infection?
Secretory IgA
What is the role of the J chain in secretory IgA?
Linking at least two IgA molecules together
Where does secretory IgA serve an important effector function?
Mucous membrane surfaces
What plays an important role in maintaining the health of newborns due to the incomplete immune system of infants?
Breastfeeding
What is the main function of IgE antibodies?
Mediate immediate hypersensitivity reactions
Where does IgE bind in the body?
Fc receptors on blood basophils and tissue mast cells
What was the basis for the first biological assay for IgE activity?
P-K reaction
What is the main function of IgE antibodies?
Mediate immediate hypersensitivity reactions
What does IgE bind to in the body?
Fc receptors on blood basophils and tissue mast cells
What was the basis for the first biological assay for IgE activity?
P-K reaction (Prausnitz and Kustner reaction)
Is allergen cross-linkage of receptor-bound IgE on mast cells responsible for causing release of substances that mediate allergic manifestations?
True
Does degranulation of mast cells release substances that mediate allergic manifestations?
True
Is the release of substances (blue dots) from mast cells responsible for mediating allergic manifestations?
True
What was the basis for the discovery of Immunoglobulin D (IgD)?
Failure to react with anti-isotype antisera against known isotypes
Which immunoglobulin is expressed as a major membrane-bound form by mature B cells?
IgD
What is the current status of the role of IgD in the physiology of B cells?
Under investigation
Which of the following is a member of the immunoglobulin superfamily?
Poly-Ig receptor
Which protein is associated with class I MHC molecules?
β2-microglobulin
Which of the following is a T-cell accessory protein?
CD28
What is the composition of the B-cell receptor (BCR)?
Membrane-bound immunoglobulin (mIg) and disulfide-linked heterodimers called Ig- α /Ig-β
What is the length of the cytoplasmic tail in the Ig- α chain of the B-cell receptor (BCR)?
61 amino acids
What is the function of the cytoplasmic tails in both Ig- α and Ig- β chains?
Interact with intracellular signaling molecules
What are the three major categories of antigenic determinants on immunoglobulin molecules?
Isotypic determinants, Allotypic determinants, Idiotypic determinants
Where are the idiotypic determinants located in the antibody molecule?
Characteristic portions of the antibody molecule
What are the three major categories of antigenic determinants on immunoglobulin molecules?
Isotypic determinants, Allotypic determinants, Idiotypic determinants
What collectively defines each heavy-chain class and subclass and each light-chain type and subtype within a species?
Isotypic determinants
What will be recognized as foreign when an antibody from one species is injected into another species?
Isotypic determinants
What are encoded by separate constant region genes, with all members of a species carrying the same constant-region genes?
Isotypes
What are allotypic determinants?
Subtle amino acid differences encoded by multiple alleles for some genes
When can antibodies to allotypic determinants be produced in response to paternal allotypic determinants?
During pregnancy
What can give rise to antibodies to allotypic determinants?
Pregnancy and blood transfusion
Where are idiotope sequences located?
Both in the antigen-binding site and outside of it
What is each individual antigenic determinant of the variable region referred to as?
Idiotope
In which region may an idiotope comprise variable-region sequences outside of the antigen-binding site?
Framework region
What type of differences occur in the constant region from one species to another when it comes to immunoglobulins?
Isotypic differences
Which type of differences occur in the variable regions and can differ even on antibodies of the same isotype?
Idiotypic differences
What term is used for the differences (alleles) that occur in some individuals with respect to immunoglobulins?
Allotypic differences
What type of antibodies are derived from a single clone and specific for a single epitope?
Monoclonal antibodies
What is the advantage of a polyclonal antibody response for an organism in vivo?
Facilitates localization, phagocytosis, and complement-mediated lysis of antigen
What is the primary function of monoclonal antibodies?
Research, diagnostic, and therapeutic purposes
What is a hybridoma?
A hybrid cell resulting from the fusion of a B cell and a myeloma cell
What are the properties of hybridoma cells?
They possess immortal-growth properties and secrete large quantities of monoclonal antibody
Why was the work by Kohler and Milstein significant?
It provided immunologists with a powerful and versatile research tool
Why are monoclonal antibodies useful in clinical applications?
They are highly specific and uniform
What are the clinical uses of monoclonal antibodies?
Diagnostic reagents (e.g. cancer metastasis)
What is a key advantage of monoclonal antibodies in terms of production?
They can be produced in large quantities
What is the target of adalimumab (Humira)?
TNF
Which cell type is targeted by rituximab (Rituxan)?
Lymphomal B cells
What is the term for human monoclonal antibodies drugs, indicated by the suffix (-umab)?
Monoclonal antibodies drugs
Monoclonal antibodies drugs can be indicated by the suffix (-umab)?
True
Adalimumab, known as Humira, targets TNF to reduce inflammation?
True
Rituximab, known as Rituxan, targets CD20 found on lymphomal B cells?
True
Test your knowledge about the diversity and specificity of antibodies, including their production by B cells and the binding to antigenic determinants. Learn about the complex immune response and the generation of monoclonal antibodies.
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