Chapter: Genetics and Molecular Biology: Generating Genetic Diversity: Antibodies
Class Switching of Heavy Chains
Class Switching of Heavy Chains
As mentioned before, the first detectable antibody
synthesized in response to an antigen is IgM. Later, the other classes, IgM,
IgD, IgG, IgE, and IgA can be detected. Remarkably, myelomas in culture also
can switch the class of antibody they are synthesizing, but without changing
Since the class of an
antibody is determined solely by the constant region of the heavy chain, class
switching must be generated by a change in the C segment that is connected to
the V, D, and J segments.
As mentioned above, following the J segment, the
chromosome contains a series of C region segments beginning with the one coding
for the M class of immunoglobulin. This array of eight C region segments is
spread over 200 Kb of DNA and possesses an order consistent with the sequence
of class switching that has been observed. Class switching replaces one of the
downstream C regions for the M constant region by deleting intervening DNA.
Hence, the intervening sequence between the J and C region and sites ahead of
the other C region genes contain signals used in the generation of the
deletions that produce class switching.
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