Chapter 4:
1. Indicate
whether each of the following statements is true or false. If you think a
statement is false,
explain why.
a. A rabbit
immunized with human IgG3 will produce antibody that will react with all
subclasses of IgG in
humans.
b. All immunoglobulin molecules on the surface of a given B cell have the same idiotype.
c. All immunoglobulin molecules on the surface of a given B cell have the same isotype.
d. All myeloma protein molecules derived from a single myeloma clone have the same idiotype and allotype.
e. Although IgA is
the major antibody species that undergoes transcytosis, polymeric IgM, but not
monomeric IgA, can also undergo transcytosis.
f.. The hypervariable regions make significant contact with the epitope.
g. IgG functions more effectively than IgM in bacterial agglutination.
h. Although
monoclonal antibodies are often preferred for research and diagnostic purposes,
both
monoclonal and polyclonal antibodies can be highly specific.
i. All isotypes are normally found in each individual of a species.
j. The heavy-chain variable region (VH) is twice as long as the light-chain variable region (VL)
2. You are an energetic immunology student who has isolated protein X, which you believe is a new isotype of human immunoglobulin.
a. What structural features would protein X have to have in order to be classified as an immunoglobulin?
b. You prepare rabbit antisera to whole human IgG, human k chain, and human g chain. Assuming protein X is, in fact, a new immunoglobulin isotype, to which of these antisera would it bind? Why?
c. Devise an experimental procedure for preparing an antiserum that is specific for protein X.
3. According to the clonal selection theory, all the immunoglobulin molecules on a single B cell have the same antigenic specificity. Explain why the presence of both IgM and IgD on the same B cell does not violate the unispecificity implied by clonal selection.
4. IgG, which contains g heavy chains, developed much more recently during evolution than IgM, which contains m heavy chains. Describe two advantages and two disadvantages that IgG has in comparison with IgM.
5. Although the five immunoglobulin isotypes share many common structural features, the differences in their structures affect their biological activities.
a. Draw a schematic diagram of a typical IgG molecule and label each of the following parts: H chains, L chains interchain disulfide bonds, intrachain disulfide bonds, hinge, Fab, Fc, and all the domains. Indicate which domains are involved in antigen binding.
b. How would you have to modify the diagram of IgG to depict an IgA molecule isolated from saliva?
c. How would you have to modify the diagram of IgG to depict serum IgM?
6. Fill out the accompanying table relating to the properties of IgG molecules and their various parts. Insert a (+) if the molecule or part exhibits the property; a (-) if it does not; and a (+/-) if it does so only weakly.
Whole H L
Property IgG chain chain Fab F(ab'), Fc
Binds antigen
Bivalent antigen
binding
Binds to Fc
receptors
Fixed complement
in presence
of antigen
Has V domains
Has C domains
7. Write YES or NO in the accompanying table to indicate whether the rabbit antisera listed at the top react with the mouse antibody components listed at the left.
g Chain k Chain IgG Fab IgG Fc J Chain
fragment fragment
Mouse g chain
Mouse k chain
Mouse IgM
whole
Mouse IgM Fc
fragment
8. The characteristic structure of immunoglobulin domains, termed the immunoglobulin fold, also occurs in the numerous membrane proteins belonging to the immunoglobulin superfamily.
a. Describe the typical features that define the immunoglobulin-fold domain structure.
b. Consider proteins that belong to the immunoglobulin superfamily. What do all of these proteins have in cornmon? Describe two different Ig superfamily members that bind antigen. Identify four different Ig superfamily members that do not bind antigen.
9. Where are the CDR regions located on an antibody molecule and what are their functions?
10. An
investigator wanted to make a rabbit antiserum specific for mouse IgG. She
injected a rabbit with
purified mouse IgG and obtained an antiserum that reacted
strongly with mouse IgG. To her dismay,
however, the antiserum also reacted with each of the other
mouse isotypes. Explain why she got this
result. How could she make the rabbit antiserum
specific for mouse IgG?
11. For each immunoglobulin isotype (a-e) select the description(s) listed below (1-12) that describe that isotype. Each description may be used once, more than once, or not at all; more than one description may apply to some isotypes.
Isotypes
_____ a. IgA
_____ b. IgD _____ c. IgE _____ d. IgG
_____ e. IgM
(1) Secreted form is a pentamer of the basic H2L2 unit
(2) Binds to Fc receptors on mast cells
(3) Multimeric forms have a J chain
(4) Present on the surface of mature, unprimed B cells
(5) The most abundant isotype in serum
(6) Major antibody in secretions such as saliva, tears, and breast milk
(7) Present on the surface of immature B cells
(8) The first serum antibody made in a primary immune response
(9) Plays an important role in immediate hypersensitivity
(10) Plays primary role in protecting against pathogens that invade through the gut or respiratory mucosa
(11) Multimeric forms may contain a secretary component
(12) Least abundant isotype in serum
12. Describe four distinct roles played by Fc receptors. In what ways is signal transduction from Fc receptors similar to signal transduction from the B-cell receptor?