Page 1438 - Veterinary Immunology, 10th Edition

direct measure of the therapeutic efficacy of an antiserum, they are
VetBooks.ir also subject to great experimental variation because of differences

among animals. Animals differ in their susceptibility to infection
and in a number of other factors, such as the rate of absorption of

antiserum, the level of activity of the mononuclear phagocyte
system, and the half-life of the passively administered
immunoglobulin. As in neutralization tests, meaningful results can
be obtained only if large numbers of animals are employed and if

the challenge dose is carefully standardized. It is usual to use a dose
of organisms or toxin containing a known number of LD or ID .
50
50
Similarly, the protective effect of an antiserum may be expressed in
PD , the dose required to protect 50% of a group of animals.
50

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