Immunoglobulin IgG

Variable regions are located at the N-terminal region of the heavy (VH) and light (VL) chains. Together with the two other constant regions of the heavy and light chains, CH1 and CL, respectively, these regions form one of two Fab fragments (antigen binding fragment). The third component of the molecule is called the Fc-fragment (crystallizable fragment) and is comprised of the invariable CH2 and CH3 domains of the heavy chains. This latter portion of the antibody is involved in interaction with the cell surface, the complement system, and in antibody transportation [2]. Immunoglobulins are separated into 5 subclasses, IgG, IgA, IgM, IgD and IgE. The classes are distinguished by their localization, prevalence, role and participation in the immune response. In addition, immunoglobulins differ in their structure and shape, especially in the non-variable portion of the antibody [3]. IgGs, the most common human immunoglobulins, represent 75% of all plasma immunoglobulins and have several functions including triggering the complement system (the proteolytic plasma enzyme cascade involved in antigen degradation in the blood). Members of the IgG class of immunoglobulins can be subdivided according to their biochemical features, which include their affinity for complement system proteins and their concentration in the plasma [4]. Structurally, IgGs differ most in the hinge area (the section between the Fab and Fc fragments) [5]. The model presented provides a view of the common IgG1 protein. Light chains are shown in red, heavy chains are in grey, disulphide bridges linking the chains are in yellow, and the oligosaccharide is in dark grey.