1. IgM is the first antibody isotype secreted following activation of a naive B
ID: 219488 • Letter: 1
Question
1. IgM is the first antibody isotype
secreted following activation of a naive B cell. IgM is
found at high concentrations in the serum, and is found
as a very high molecular weight complex. This high
molecular weight complex is composed of:
A. A single IgM monomer plus monomers of IgA and IgG
B. A single IgM monomer bound to several non-immunoglobulin serum proteins
C. A single IgM monomer bound to serum complement components
D. A pentamer of IgM monomers
E. Two dimers of IgM plus IgD forming a tetrameric
complex
2. Some pathogenic microorganisms encode proteins, such as the
Staphylococcus
Protein A, that bind to immunoglobulin
constant
region
domains with high affinity. These microbial proteins provide a
benefit to the microorganism by:
A. Preventing antibodies bound to the microbe from binding to Fc receptors on phagocytes
B. Blocking the binding of anti-microbial antibodies to the pathogen
surface
C. Cleaving the antibody into fragments that separate the antigen-binding region from the effector function
D. Inducing aggregation of the anti-microbial antibodies by multivalent binding to the pathogen-derived protein
E. Preventing the antibody from neutralizing the pathogen
3. True/False: The generation of a complete coding sequence for an antibody heavy chain involves a lymphocyte-restricted process of DNA rearrangement that links V, D,
and J gene segments together to form the exon that
encodes the heavy chain V region. A similar type of DNA rearrangement is also utilized for the simultaneous expression of IgM and IgD antibodies by the same B cell.
Explanation / Answer
1. D. A pentamer of IgM monomers
2. A. Preventing antibodies bound to the microbe from binding to Fc receptors on phagocytes
3. true
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