Ch 5 Book Questions Flashcards
Detection of antibodies specific for a particular microbe is commonly used as evidence of prior infection by that microbe. To obtain these antibodies, blood is collected into tubes and allowed to clot. Antibodies are found in the fraction of the blood that remains fluid after clotting. What is this fluid fraction called?
a. Plasma
b. Serum
c. Lymph
d. Water
e. Urine
b. Serum
Clots form from the cellular elements of blood, including platelets, and a meshwork of cross-linked coagulation proteins. The acellular fluid phase that is left after clotting is called serum, which contains most of the soluble protein elements of whole blood, except clotting factors. Plasma is the acellular fluid fraction of unclotted blood, and apart from coagulation proteins that form the clot, it contains all of the soluble protein components of whole blood, including antibodies. Lymph is extracellular fluid derived from blood; it may contain antibodies. Urine is the fluid filtrate of blood exclusively produced and excreted by the kidneys. It normally does not contain antibodies.
Monoclonal antibodies used as drugs or diagnostic reagents are characterized by all of the following EXCEPT:
a. Single antigen specificity
b. Production by a B cell hybridoma
c. Single isotype
d. Monovalent, with one antigen-binding site
e. Known antigen specificity
d. Monovalent, with one antigen-binding site
Monoclonal antibodies are, by definition, identical antibodies of a single isotype and antigen specificity, produced by a single clone of cells. They are usually produced in vitro by clonal B cell hybridomas and are structurally normal, with at least two antigen-binding sites and a known specificity. Tumors of B lymphocytes (e.g., myelomas) may produce monoclonal antibodies, usually of unknown specificity, or often single chains of antibody molecules.
Which one of the following is a correct description of the basic symmetric core structure of an IgG antibody?
a. One heavy chain and two light chains
b. One constant domain and one variable domain.
c. Two heavy chains and one light chain
d. Two heavy chains and two light chains
e. One heavy chain and one light chain
d. Two heavy chains and two light chains
Two γ heavy chains are covalently linked to each other, and each heavy chain is covalently linked to one light chain (κ or λ). IgM molecules contain 5 covalently linked copies of the basic IgM core structure, and IgA contain two copies. Each IgG heavy chain has one variable domain and three constant domains, and each light chain has one variable domain and one constant domain.
An antigen-binding site of an IgG antibody molecule is composed of which of the following?
a. Twelve hypervariable loops, three each on two heavy chains and two light chains
b. Three hypervariable loops on a light chain
c. Three hypervariable loops on a heavy chain
d. Six hypervariable loops, three each on one heavy chain and one light chain
e. Six hypervariable loops, three each on two heavy chains
d. Six hypervariable loops, three each on one heavy chain and one light chain
An IgG molecule has two antigen binding sites. Each one is composed of six hypervariable loops, three that extend from the variable domains of a heavy chain and three that extend from the variable domains of the covalently linked light chain.
Which of the following properties of antibodies is not related to isotype?
a. Ability to activate complement
b. Ability to act as an opsonin for phagocytosis of antigens
c. Antigen specificity
d. Ability to be transported into the lumen of the gut
e. Ability to activate mast cells
c. Antigen specificity
Antigen specificity is determined by the variable regions of the heavy and light chains, and not the isotype, which is defined by the structure of the constant region of the heavy chain. The other properties listed are all related to one or another istoype, whose Fc regions (part of the heavy chain constant region) interact with different kinds of Fc receptors on cells or with complement proteins.
IgG has a longer half life in the blood than most other plasma proteins. This property is important for maintaining protection against pathogens, and has lead to the design of drugs with long half lives because they contain the part of IgG responsible for the long half life. Which of the following is the basis for prolonged IgG half life?
a. Binding of C1q to the IgG Fc region
b. Binding of the IgG Fc region to the poly Ig receptor on gut epithelial cells
c. Binding of the IgG variable regions to ubiquitous blood antigens
d. Binding of the J chain to the IgG joining region
e. Binding of the IgG Fc region to the neonatal Fc receptor (FcRn)
e. Binding of the IgG Fc region to the neonatal Fc receptor (FcRn)
IgG molecules are internalized by endothelial cells and macrophages, and bind the FcRn in the membrane of endosomes. FcRn sequesters the IgG molecules, shunting them away from lysosomal degradation, and releases them back into the circulation.
