6.1 5.6.1 General remarks

Antibodies exist in a number of different formats. The most frequently used format is an immunoglobulin G (IgG), which is a large, Y-shaped protein composed of two identical light chains and two identical heavy chains, both containing variable and constant domains. Antibodies bind specifically to antigen targets via the antigen binding region which contains complementarity-determining regions (CDRs). In the case of an IgG, the antigen binding region consists of a heavy and light chain variable domain, each variable domain having three CDRs.

Other immunoglobulin structures are also known, such as heavy-chain-only antibodies that consist of only two identical heavy chains (with variable and constant domains) and the antigen-binding region consists of a single variable domain with only three CDRs.

Furthermore, knowledge of the structure-function relationships of parts of the antibody has allowed for the creation of antibody derivatives for a multitude of applications. These include antibody fragments, bispecific or multispecific antibodies and antibody fusion products.

In general, antibodies can be defined by (but are not limited to):

(a)their own structure (amino acid sequences); 

(b)nucleic acid sequences encoding the antibody; 

(c)reference to the target antigen; 

(d)target antigen and further functional features; 

(e)functional and structural features; 

(f)the production process; 

(g)the epitope;

(g)(h) the hybridoma producing the antibody.