Page 39 - Veterinary Immunology, 10th Edition

antibodies produced in response to tetanus toxin bind only to
VetBooks.ir tetanus toxin. When the antibodies bind, they “neutralize” the toxin

so that it is no longer toxic. In this way antibodies protect animals
against lethal tetanus.

The time course of the antibody response to tetanus toxin can be
examined by taking blood from a horse at intervals after injection of
a low dose of the toxin. The blood is allowed to clot and the clear
serum removed. The amount of antibody in the serum may be

estimated by measuring its ability to neutralize a standard amount
of toxin. Following a single injection of toxin into an unexposed
horse, no antibody is detectable for several days (Fig. 1.7). This lag
period lasts for about 1 week as responding B cell populations grow

and begin to produce antibodies. When antibodies eventually
appear their levels climb to reach a peak by 10 to 20 days before
declining and disappearing within a few weeks. The amount of
antibody formed, and therefore the amount of protection conferred,

during this first or primary response is relatively small since there
are few antibody-producing B cells. However, memory B cells are
produced in large numbers.

FIG. 1.7 The characteristic time course of the adaptive immune
response to an antigen as measured by serum antibody levels.
Note the differences between a primary and a secondary immune
response. These are the reasons why the adaptive immune
responses are so successful.

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