Page 526 - Veterinary Immunology, 10th Edition

antigen, the B cell will not be stimulated and will die. In contrast,
VetBooks.ir those B cells whose receptors bind antigen with a high affinity

survive and proliferate (Fig. 17.10). Thus as B cells respond to an
antigen, successive cycles of mutation and selection of the highest

affinity receptors eventually generate populations of B cells
producing very-high-affinity antibodies.

FIG. 17.10 The selection of somatic mutants. Spontaneous
mutation during the expansion of a B cell clone results in the
development of cells with antigen receptors that differ in their affinity
for antigen. Cells that bind antigen strongly will be more intensely
stimulated than cells that bind it weakly. As a result of this selection
pressure, the B cell population gradually increases its binding
affinity during the course of an antibody response.

Somatic mutation does not begin until after B cells have switched
from making immunoglobulin M (IgM) to making either IgG or

IgA. This suggests that the mutation mechanism is not activated
until after a responding B cell had committed to utilizing a specific
heavy chain V gene. As a result, the affinity of IgM antibodies does

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