Introduction to the field

Since the elucidation of the structure of antibodies, it has been recognized that immunoglobulins (Ig) are bifunctional molecules which assemble the products of several genes, allowing the almost infinite diversity of antigen recognition and a large array of effector and regulatory functions. Families of V genes encode the variable regions of Ig heavy (H) and light (L) chains whereas a set of C genes encodes the H and L constant regions which define Ig isotypes. Associations of the variable regions form the antigen-binding site while the C terminal constant regions form the Fc part of the Ig molecule and bear the sites for functional activities. The use of proteolytic enzymes has allowed separation of the Fc region from the rest of the molecule. An Fc-less Ig is a pure antigen-binding unit (and has therefore be called F(ab) when monovalent and F(ab)′ 2 when divalent) whereas intact molecules, after binding to antigen, exert multiple effector and regulatory functions [1,2].