Page 339 - The Veterinary Laboratory and Field Manual 3rd Edition

308 Susan C. Cork, M. Faizal Abdul Careem and M. Sarjoon Abdul-Cader

Primary antibody response (or organism), that is, because IgM is produced
early and declines rapidly, detection of antigen
The primary antibody response is the first anti- specific IgM indicates recent exposure (acute
body response seen following exposure to a new disease). A rising titre of IgG in serum samples
antigenic challenge (Figure 6.5). The first type collected 2 to 3 weeks apart also indicates recent
of antibody detectable after initial exposure to exposure and possibly current active infection.
the antigen is predominantly IgM, which usu- Sero-conversion is the term used when antibody
ally appears 3 to 4 days after exposure. IgG is becomes detectable in the serum of an animal
detectable one to 2 weeks after antigen exposure which previously tested negative.
and decreases over a period of months or years The secondary antibody response or anam-
(depending on the antigen involved). In con- nestic ‘booster’ response is the response seen
trast, the IgM titre (concentration) quickly peaks after re-exposure to an antigen (Figure 6.5). This
and then declines rapidly over a few weeks. is what provides protective immunity in a vac-
Detection and measurement of IgM can provide cination regimen. In this case, because immune
information about the time frame in which an cells ‘remember’ the antigen, the IgM and IgG
individual animal was exposed to an antigen levels rise immediately (within 2 or 3 days)

Figure 6.5 Serum antibody concentrations following primary and secondary infections. The initial IgM
response follows the IgG response. The magnitude of the secondary response is greater and the time
taken for the response to occur is shorter. See also Plate 30. Source: M. Sarjoon Abdul-Cader, University
of Calgary, Canada.

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