Primary interactions between antigens and antibodies involve all of the following
If an IgG antibody preparation specific for hen egg lysosome (HEL) is treated with
papain to generate Fab fragments, which of the following statements concerning the
avidity of such fragments is true?
Western assays used to test serum samples for the presence of antibodies to infectious
agents, such as HIV, are particularly useful as diagnostic assays because
The major difference between transgenic mice and knockout mice is that
SCID mice have a genetic defect that prevents development of functional
Which of the following statements regarding B cell hybridomas is false?
An ELISA designed to test for the presence of serum antibody for a new strain of
pathogenic bacteria is under development. Initially, a monoclonal antibody specific
for a single epitope of the organism was used both to sensitize the wells of the ELISA
plate and as the enzyme-labeled detecting antibody in a conventional sandwich
ELISA. The ELISA failed to detect the antigen despite the use of a wide range of
antibody concentrations. What is the most probable cause of this problem?
The indirect Coombs' test (anti-immunoglobulin test) typically uses:
Answers To Review Questions
1. A No covalent bonds are involved in the interaction between antibody and antigen. The binding forces are relatively weak and include van der Waals forces, hydrophobic forces, and electrostatic forces. A very close fit between an epitope and the antibody is required.
2. A Avidity denotes the overall binding energy between antigens and multivalent antigens. Since the valency of the Fab fragments is one as compared with the HEL-specific IgG molecule, which has a valence of 2 (due to the presence of two Fab regions), the avidity of the fragments will be lower. Choice E is incorrect since the affinity of the Fab fragments will be the same as each of the Fab regions of the intact IgG molecule.
3. B In Western assays, electrophoretic separation techniques are used to resolve the molecular mass of a given antigen or mixtures of antigens. Since antibody responses to infectious agents generate polyclonal responses by virtue of the complex antigenic determinants expressed by such agents, Western assays can confirm the presence of these antibodies, which react with the electrophoretically separated antigens of known molecular weights.
4. C Cloned foreign genes from either the same or other species are introduced into mice to generate a transgenic strain. Integration is random and occurs in both somatic and germ line cells. Choice D is incorrect because sometimes knockout mice do not have a phenotype unique caused by the replacement of a functional gene with one that is nonfunctional, probably due to the activity of redundant or compensatory mechanisms.
5. B SCID mice possess an autosomal recessive mutation that causes a disorder in which B and T cells fail to develop. Like their human counterparts, SCID mice are compromised with respect to lymphoid defense mechanisms. Pluripotential stem cells present in SCID mice can give rise to other hematopoietic lineages, including cells in the myeloid lineage and NK cells.
6. B The method used to generate B cell hybridomas employs the fusion of B cells (e.g., from the spleen and lymph nodes) harvested from immunized mice with a selected population of malignant plasma cells unable to secrete immunoglobulin. Antigen-specific B cells are not cloned first and then fused with such plasma cells.
7. C In a sandwich ELISA, an antibody (often monoclonal) is used to coat ELISA wells followed by blocking with a nonspecific protein to saturate any unbound sites. The antigen is then added, followed by the addition of a second antigen-specific antibody that is enzyme- labeled. A polyclonal, antigen-specific antibody is often used as the enzyme-labeled reagent. This is done because the epitope detected by the coating antibody (a monoclonal antibody in this case) may be blocked by that antibody, thus preventing its access if the same monoclonal were used as the enzyme-labeled detecting antibody.
8. D The indirect Coombs test is generally used to detect the presence in a patient's serum of antibodies that react with antigens expressed on red blood cells (see Figure 5.2).
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