Opsonin

Opsonin
Action of opsonins; a phagocytic cell recognises the opsonin on the surface of an antigen

An opsonin is any molecule that targets an antigen for an immune response. However, the term is usually used in reference to molecules that act as a binding enhancer for the process of phagocytosis, especially antibodies, which coat the negatively-charged molecules on the membrane. Molecules that activate the complement system are also considered opsonins. Phagocytic cells do not have an FC receptor for IgM, making IgM ineffective in assisting phagocytosis. However, IgM is extremely efficient at activating complement and is, therefore, considered an opsonin. Opsonins can also refer to molecules that target a cell for destruction through the action of Natural Killer cells. Only opsonins that enhance phagocytic activity will be further described in this article.

Contents

Mechanism

Both the membrane of a phagocytosing cell and its target have a negative charge (zeta-potential), making it difficult for the two cells to come close together. Once the opsonins attach to the target, the negative charged is masked. Take note that the negative charge of the target doesn't disappear. The opsonin simply overrides the charge, making it easier for white blood cells (phagocytic cells), to undergo phagocytosis. During the process of opsonization (also, opsonisation), antigens are bound by antibody or complement molecules. Phagocytic cells express receptors, CR1 and Fc receptors, that bind opsonin molecules, C3b and antibody, respectively. With the antigen coated in these molecules, binding of the antigen to the phagocyte is greatly enhanced. In fact, most phagocytic binding cannot occur without opsonization of the antigen.

Furthermore, opsonization of the antigen and subsequent binding to an activated phagocyte will cause increased expression of complement receptors on neighboring phagocytes.

Examples

Examples of opsonin molecules include:

  • Antibodies: IgG and IgM
  • Components of the complement system: C3b, C4b, and iC3b
  • Mannose-binding lectin (initiates the formation of C3b)

The most important are IgG and C3b.[1][broken citation]

See also

The example of opsonine is the lectin pathway. It is a type of the complement system. Mannan-binding lectin proteins play a major role in activation of this pathway. Opsonin belongs to the same family as C1q, a family called the collectins.

References

  1. ^ Immunology at MCG 1/phagocyt

External links



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Look at other dictionaries:

  • opsonin — opsònīn m <G opsonína> DEFINICIJA fiziol. antitijelo koje kao dio krvne tekućine omogućuje bijelim krvnim zrncima uništavanje mikroba koji su prodrli u organizam, na čemu se temelji cijepljenje ETIMOLOGIJA grč. ópson: hrana + in …   Hrvatski jezični portal

  • opsonin — [äp′sə nin] n. [obs. opson(ium), relish (< L < Gr opsōnion, food, provisions < opsōnein, to buy food < opson, meat or any food eaten with bread < o , together with + * psōn, food, bread, akin to psōmos, mouthful) + IN1] a substance …   English World dictionary

  • opsonin — noun Etymology: Latin opsonare to buy provisions, cater (from Greek opsōnein) + English 1 in more at oligopsony Date: 1903 any of various proteins (as antibodies or complement) that bind to foreign particles and cells (as bacteria) making them… …   New Collegiate Dictionary

  • Opsonin — Opsonine sind im Körper vorkommende Proteine, die einen Teil der Immunantwort darstellen. Opsonine können entweder Antikörper oder Komplementfaktoren sein, die die Verknüpfung von Phagozyten an Bakterienzellen oder andere Mikroorganismen… …   Deutsch Wikipedia

  • opsonin — Substance that binds to the surface of a particle and enhances the uptake of the particle by a phagocyte. Probably the most important in mammals derive from complement (C3b or C3bi) or immunoglobulins (which are bound through the Fc receptor) …   Dictionary of molecular biology

  • opsonin — opsonoid, adj. /op seuh nin/, n. Immunol. a constituent of normal or immune blood serum that makes invading bacteria more susceptible to the destructive action of the phagocytes. [1900 05; < L opson(ium) victuals ( < Gk opsonía, deriv. of… …   Universalium

  • opsonin — noun Any antibody that causes an invading species to be more susceptible to phagocytosis …   Wiktionary

  • opsonin — Any blood serum protein that binds to antigens, enhancing phagocytosis ( e.g., C3b of the complement system, specific antibodies). [G. opson, boiled meat, provisions, fr. hepso, to boil, + in] common o. SYN: normal o.. immune o …   Medical dictionary

  • Opsonin — Op|so|nin [griech. ópson = Fleisch, Speise; ↑ in (3)], das; s, e: veralteter Name für ↑ Fibronectine, deren Anbindung an eingedrungene Bakterien oder Zellen man als Opsonierung bezeichnete. * * * Op|so|nin, das; s, e <meist Pl.> [zu griech …   Universal-Lexikon

  • Opsonin — Op|so|nin 〈n.; Gen.: s, Pl.: e; Med.; meist Pl.〉 körpereigener Stoff, der sich zur Infektionsabwehr an die eingedrungenen Bakterien, Pilze u. Ä. anlagert …   Lexikalische Deutsches Wörterbuch

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