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Antibody
2. Fragment crystallizable region
3. Heavy chain (blue) with one variable (VH) domain followed by a constant domain (CH1), a hinge region, and two more constant (CH2 and CH3) domains.
4. Light chain (green) with one variable (VL) and one constant (CL) domain
5. Antigen binding site (paratope)
6. Hinge regions
Antibodies (also called immunoglobulins) are large Y-shaped proteins that can stick to the surface of bacteria and viruses. 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 humoral immunity.[4][5]
Each antibody is different. They are all designed to attack only one kind of antigen (in practice, 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]
- ↑ 1.0 1.1 Janeway C.A. Jr.; et al. (2001). Immunobiology (5th ed.). Garland Publishing. ISBN 0-8153-3642-X. (electronic full text via NCBI Bookshelf).
- ↑ Litman G.W.; et al. (1993). "Phylogenetic diversification of immunoglobulin genes and the antibody repertoire". Mol. Biol. Evol. 10 (1): 60–72. doi:10.1093/oxfordjournals.molbev.a040000. 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.
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