Page 337 - The Veterinary Laboratory and Field Manual 3rd Edition

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

Figure 6.4(a) The structures of
classes of antibodies. The IgG
molecule is made of two identical
‘heavy’ chains (H) and two identical
‘light’ chains (L). The main body of
the heavy chains is variable in each
antibody class but the light chains
tend to be antigenically similar in
each class. The ends of both light
and heavy chains are composed of a
variable sequence of amino acids (A–C
and B–D), this is the antibody-antigen
binding site. Source: M. Sarjoon Abdul-
Cader, University of Calgary, Canada.

IgG but it is the functional equivalent to mam- Antibodies are proteins produced by plasma
malian IgG. cells which themselves are derived from ‘B’ cells
In mammals, IgA, IgD, IgE, IgG and IgM and secreted into body fluids in response to anti-
are recognized. In simple terms, IgG provides gen exposure. Immunoglobulins circulating in
long lasting immunity; IgM is part of the pri- the blood make up approximately 15% of serum
mary antibody response and is a short-lasting protein.
antibody with a large molecular weight; IgA is Antibodies combine specifically with the anti-
present in secretions (respiratory tract, tears, gen that stimulated their production. The high
saliva, milk and so on) and IgE is produced in degree of specificity of antibody for its respective
allergic reactions and is commonly associated antigen is its most important characteristic and
with immunity to helminth parasites. The func- forms the basis for all antigen – antibody reac-
tion of IgD is not fully understood but it has tions whether they occur in vivo, as a defence
been shown to be active on B-lymphocytes as mechanism in the host, or in vitro in a serological
an antigen receptor. IgD has also been shown test performed in the laboratory.
to activate basophils and mast cells to produce Specific antibodies are named by placing the
antimicrobial factors. prefix ‘anti’ before the antigen with which the

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