Immounoglobulins (antibodies) are the glycoproteins involved in immune response. They possess ability to recognize antigens and bind them. Immunoglobulins could be found as in plasma, as linked to lymphocytes cellular membrane. The molecule is comprised of two identical s.c. light chains and two heavy chains, linked by disulphide bridges [1].
The characteristic feature of the antibodies is the highly variable sequence pattern, recognizing and specifically binding to the exposed antigen. Due to this feature immune system could react to the broad range of allogenic agents.
Variable regions are located at N-termini region of the heavy (VH) and light (VL) chains. Together with two other constant regions CH1 and CL (of the heavy and light chains, respectively) they form one of two FAB fragments (antigen binding fragment). The third molecule component is presented by invariable CH2 and CH3 domains of the heavy chains. This latter is called Fc-fragment (crystallizable fragment) and is involved in interaction with cell surface, complement system, also as in antibodies transportation [2].
Immunoglobulins are separated in 5 subclasses: IgG, IgA, IgM, IgD and IgE. The classes distinguish by localization, prevalence, role and participation timing in immune response. In addition, they are different by the structure and shape, especially in non-variable part [3].
IgG are the most common human immunoglobulins bearing 75% share of all plasma immunoglobulins and have several functions f.e. being the start trigger for complement system (proteolytic plasma enzymes cascade, involved in antigen degradation in blood). IgG class is split in for subdivisions according to their biochemical features including affinity to complement system proteins and concentration in plasma [4]. Structurally they differ the most in hinge area — the pattern between Fab and Fc fragments [5].
The model presented provides the view of the common IgG1 protein. Light chains are shown in red, heavy are in grey, disulphides linking chains one to other are in yellow, oligosaccharide is in dark grey.
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 Immunoglobulin images distributed with the licence. End user licence agreement.
Cast:
Project director, 3D vizualizator: Konstantinov Ivan
Designer: Hlebny Ivan
Flash-technologist: Grishaev Max
Article author: Stephanov Yuri (translated from the Russian by Varvara Melikhova)
1. Meulenbroek A.J., Zeijlemaker W.P. Human IgG Subclasses: Useful diagnostic markers for immunocompetence. Published by Sanquin formerly CLB (Centraal Laboratorium van de Bloedtransfusiedienst) Plesmanlaan 125, 1066 CX Amsterdam, The Netherlands. CLB (1996)
2. Stitis, D.P., J.D. Stobo, J.V. Wells: «Basic and Clinical Immunology» 7th edition, Appleton and Lange (1991)
3. Koolman J., Rohm K-H. Taschenatlas der Biochemie, Georg Thieme Verlag Stuttgart, New York (1998)
4. Spiegelberg H.L.: «Biological activities of Igs of different classes and subclasses». Adv.Immunol.19, 259 (1974) 
5. Burton, D.R., L. Gregory and L. Jefferis:«Aspects of the Molecular Structure of the IgG subclasses». Monograph. Allergy 19,7 (1986) |
