Page 331 - The Veterinary Laboratory and Field Manual 3rd Edition

chapter 6

Serology and immunology

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

6.1 Introduction of the principles of immunology, especially in
relation to the tests that are carried out in the
Serology is the branch of laboratory medicine diagnostic laboratory. In this chapter, we will
that studies blood serum for evidence of infec- present an overview of the immune response
tion, particularly antibody-mediated immune along with the laboratory tests most commonly
response by evaluating antigen–antibody reac- used at the district and regional level.
tions in vitro. It includes the study of antibodies
(or antigens) present in serum, although anti-
bodies can also be detected in other body fluids the immune response
such as cerebrospinal fluid, saliva, milk and so
on. A serology technician typically carries out In simple terms, the immune response in
techniques involving antigen–antibody reactions animals can be divided into ‘specific’ and ‘non-
that are highlighted and measured in different specific’ components (Figure 6.1a) and these
ways (for example, agar gel immunodiffusion, two arms of the immune system are linked
precipitation or agglutination tests, comple- (Figure 6.1b). The ‘non-specific’ response refers
ment fixation and so on). Serology, using paired to a general defence against all invaders, which
sera taken over a 1–2 week period (during acute is also called the ‘natural’ or ‘innate’ immune
phase and convalescent period) can be used to response and is potent, quick to respond (hours
detect current infections (that is, if a rising anti- to days), broadly effective and lacks memory.
body titre can be demonstrated) and can also be The components involved in the non-specific
used to indicate historical exposure to specific immune system include the intact skin surface,
antigens. intact mucous membranes and surface mucus,
The broader study of immunology includes which often contains immunoglobulin (IgA).
serology as well as the evaluation of the cell-medi- Non-specific macrophage engulfment of for-
ated immune response (for example, as detected eign material is also an important component
in delayed-type hypersensitivity skin tests such along with the process of inflammation, which
as the tuberculin test). Research into the cause involves heat, and the release of chemical media-
and treatment of cancer and immune-related tors to attract phagocytic cells (see Figures 6.2a
diseases in humans and animals has improved and 6.2b). Recent discoveries show that natural
our understanding of the cell-mediated immune killer (NK) cells, type 1 interferon (IFN) and
response. Laboratory technicians and veteri- pathogen recognizing receptors such as toll-like
nary staff should have a basic understanding receptors (TLRs) are also essential contributors

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