Page 524 - Veterinary Immunology, 10th Edition

VetBooks.ir Somatic Mutation

Recombination cannot account for all the sequence variability seen
in immunoglobulin V regions. For example, there are three

hypervariable areas (CDRs) within a V region (Fig. 17.9). One of
these, CDR3, is located around position 96 and is generated by
recombination between V and J genes. However, CDR1 and CDR2
are located far from V-J or V-D-J splice sites. Other mechanisms of
generating antibody variability must therefore exist (Box 17.1). In

fact, gene recombination is only the first step in generating
antibody diversity. It is followed by somatic mutation that
generates antibodies that bind much more strongly and specifically

to antigens.

FIG. 17.9 The major difference between the variable regions of the
TCR and immunoglobulins is in the formation of CDRs.
Immunoglobulins have three CDRs. CDR1 and CDR2 are
generated by somatic mutation. CDR3 is generated by gene
conversion. This option is not available to the TCR, in which
somatic mutation is stringently avoided to prevent self-reactivity.

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