Antibody
Antibodies (also called immunoglobulins) are large Y-shaped proteins. They are found in the blood or other body fluids of vertebrates. Antibodies are the key element in the adaptive immune system.
The antibody recognizes a unique part of the foreign target called an antigen.[1][2] Each tip of the "Y" of an antibody contains a structure (like a lock) that fits one particular key-like structure on an antigen. This binds the two structures together.
Using this binding mechanism, an antibody can tag a microbe or an infected cell for attack by other parts of the immune system, or can neutralize its target directly.[3] The production of antibodies is the main function of the humoral immune system.[4][5]
Each antibody is different. They are all designed to attack only one kind of antigen (in practise, this means virus or bacteria). For instance, an antibody designed to destroy smallpox is unable to hit the Bubonic plague or the common cold.
Though the general structure of all antibodies is very similar, that small region at the tip of the protein is extremely variable. This allows millions of antibodies with different tip structures to exist. Each of these variants can bind to a different antigen.[1] This enormous diversity of antibodies allows the immune system to recognize an equally wide variety of antigens.[6]
[change] Immunoglobulin diversity
There are a vast number of microbe strains, and so vertebrates need millions of different antibodies.[7] Actually, humans generate about 10 billion different antibodies, each capable of binding a distinct antigen site.[8]
This must be done with a very much smaller number of genes: the total human genome has only about 20,000 genes.
Several complex genetic mechanisms have evolved. These allow vertebrate B cells to generate a huge pool of antibodies from a relatively small number of antibody genes.[9]
The variety of antibodies is got by combining segments from a pool of genes in many different ways. Then, hyper-mutations occur in the binding site area of the antibody gene. This creates further diversity.[10][11]
[change] Other websites
[change] References
- ↑ 1.0 1.1 Janeway C.A. Jr. et al. (2001). Immunobiology. (5th ed.). Garland Publishing. (electronic full text via NCBI Bookshelf) ISBN 0-8153-3642-X.
- ↑ Litman G.W. et al. (January 1993). "Phylogenetic diversification of immunoglobulin genes and the antibody repertoire". Mol. Biol. Evol. 10 (1): 60–72. PMID 8450761.
- ↑ For example, by blocking a part of a microbe that is essential for its invasion and survival.
- ↑ The system which produces antibodies in the blood plasma. Another system, cellular immunity, is done in the tissues by cells.
- ↑ Pier GB, Lyczak JB, Wetzler LM (2004). Immunology, infection, and immunity. ASM Press. ISBN 1-55581-246-5.
- ↑ Rhoades RA, Pflanzer RG (2002). Human Physiology (4th ed.). Thomson Learning. ISBN 978-0-534-42174-8.
- ↑ Mian I, Bradwell A, Olson A (1991). "Structure, function and properties of antibody binding sites". J Mol Biol 217 (1): 133–51. doi:10.1016/0022-2836(91)90617-F. PMID 1988675.
- ↑ Fanning LJ, Connor AM, Wu GE (1996). "Development of the immunoglobulin repertoire". Clin. Immunol. Immunopathol. 79 (1): 1–14. doi:10.1006/clin.1996.0044. PMID 8612345.
- ↑ Nemazee D (2006). "Receptor editing in lymphocyte development and central tolerance". Nat Rev Immunol 6 (10): 728–40. doi:10.1038/nri1939. PMID 16998507.
- ↑ Market E & Papavasiliou FN (2003). "V(D)J recombination and the evolution of the adaptive immune system". PLoS Biol. 1 (1): E16. doi:10.1371/journal.pbio.0000016. PMC 212695. PMID 14551913.
- ↑ Diaz M & Casali P (2002). "Somatic immunoglobulin hypermutation". Curr Opin Immunol 14 (2): 235–40. doi:10.1016/S0952-7915(02)00327-8. PMID 11869898.
