Immunotherapy for Infectious Diseases

Production of Igs and MAbs Targeting Infectious Diseases 65
Fig. 1. The basic structure of IgG. The variable regions of heavy and light chains are on the
amino-terminal end of the peptide chains. The constant region of IgG is divided into three structurally
discrete regions: C H1, C H2, and C H3. These globular regions are stabilized by disulfide
bonds and are called domains. The variable domain binds to the antigen; the constant regions
are responsible for different effector mechanisms.
Antibodies: Structure and Function
Constant Region
Immunoglobulins consist of two identical heavy-chain/light-chain heterodimers. The
constant region of the heavy chain determines the class affiliation. Figure 1 shows a
schematic diagram of an IgG1 molecule with the different peptide regions, carbohydrate
moieties, and disulfide bonds. The carboxy-terminal half of the light chain (C L;
constant light chain) is constant except for certain allotypic and isotypic variations,
whereas the amino-terminal half shows sequence variability and is known as V L (variable
light chain). The two subtypes of light chains (C� and C�) can be combined with
any heavy chain type (� �, �, �, or �) and are bound to one heavy chain via an
intramolecular cystein-derived SH-group. Every light chain has two intrachain disulfide
bonds, forming so-called loops, one in the variable and one in the constant region.
The constant part of the heavy chains �, �, and � can be divided into three domains,
each generating loops spanning about 60–70 amino acids (C�1, C�2, and C�3). Thus,