Antibodies have two Fab portions and a
single Fc portion. The end of each Fab portion includes a binding site which binds to the antigen.
11
See the figure above. The Fc portion interacts with other elements of the immune system. In
general, antibodies bind strongly with a particular portion of the antigen, called the antigenic
determinant or epitope of the antigen. An antigen may have several different epitopes or repeated12
13 14
epitopes. Epitopes have a particular shape recognized by the binding site of the antibody.
Antibodies are specific to the particular epitopes with which they bind, rather than the antigen. 15
When a pathogen is introduced into a body, the body’s immune response produces a mixture
16
of different ?heterogenous” antibodies binding with different epitopes of the antigen. In 1975,
Köhler and Milstein, developed an in vitro technique for providing large quantities of homogeneous
antibodies. The antibodies produced by the Köhler and Milstein technique are now referred to as17
monoclonal antibodies. The heterogenous mixtures of antibodies came to be known as polyclonal18
antibodies.
11
IMMU, p. 1.6.
12
IMMU, p. 1.7.
13
IMMU, p. 1.7.
14
IMMU, p. 1.8.
15
IMMU, p. 1.7.
16
FUND, pp. 421-22.
17
Köhler, G. et al., ?Continuous cultures of fused cells secreting antibody of predefined specificity,”
256 Nature 495-97 (1975). .
18
FUND, p. 455.
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