The cells of the immune system generate a large variety of binding sites
which differ in their binding specificities and can therefore react
specifically with a large variety of ligands. These binding sites are
part of receptor molecules, enabling the system to react to the universe
of antigens. The classical antigen receptor is the antibody molecule,
and accord- ingly the first session of this colloquium deals with a
classical sub- ject, namely antibody structure. Dramatic recent advances
in this field make it possible to interrelate primary and
three-dimensional struc- ture both to each other and to function, i.e.
the binding of antigen and possible reactions occurring in the antibody
molecule upon antigen binding. The latter point is of particular
interest since it may be relevant not only for effector functions of
antibodies such as the binding of complement, but also for the
triggering of a lymphocyte through its antibody receptor for antigen.