Opsonin


Also found in: Dictionary, Thesaurus, Medical, Wikipedia.
Related to Opsonin: opsonization, Cytokines

opsonin

[′äp·sə·nən]
(immunology)
A substance in blood serum that renders bacteria more susceptible to phagocytosis by leukocytes.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.
The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.

Opsonin

 

a type of antibody. Opsonins are immunoglobulins of the G class (IgG) and are largely responsible for the body’s resistance to bacteria, viruses, and tumors (seeIMMUNOGLOBULINS).

The British scientists A. Wright and S. Douglas introduced the term “opsonin” in 1903 to denote humoral factors in the blood that facilitate and stimulate the phagocytosis of bacteria by leukocytes. The cytophil portion of the opsonin molecule has an affinity for the plasma membrane of phagocytes. When opsonins combine with bacterial or viral antigens or with foreign macromolecules, the cytophil portion becomes exposed and attached to the surface of a phagocyte. An opsonin promotes the adhesion reaction and the absorption and destruction of a particle by reducing the energy of the surface interaction between the leukocyte and the object of phagocytosis. This reduction of energy can be accomplished, for example, by decreasing the repulsive electrostatic forces between the leukocyte and the foreign body.

Immunoglobulins of the M class (IgM) can also act as opsonins in the presence of complement (seeCOMPLEMENT). The first five components of complement greatly enhance the ability of IgG to act as an opsonin. In addition to humoral antibodies, cytophil antibodies that are fixed on certain phagocytes are opsonins. Like complement, fibrin and a polypeptide that is released by lymphocytes upon contact with certain antigens act as nonspecific opsonins. Although insects do not have immunoglobulins or phagocytes with IgG receptors, the hemolymph of insects does contain specific opsonin proteins.

Opsonins are responsible for selectivity, an important property of the phagocytic reaction. Because of opsonins, a phagocyte recognizes and attacks only foreign substances, not its own macromolecules. Some bacterial substances, for example, polysaccharides of pneumococci and meningococci and proteins of streptococci, are able to suppress the phagocytic activity of leukocytes. Antibodies to these suppressor substances perform the function of opsonins. Virulent strains of staphylococci and Escherichia coli release a specific protein that can block the cytophil portion of an opsonin, thereby inhibiting phagocytosis. Along with complement, thrombocytes, and phagocytes, opsonins neutralize foreign substances and microbes.

A. N. MATS

The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.
References in periodicals archive ?
B., but Shaw was not about to concede that Ridgeon's opsonin treatment was any less ridiculous in its way than the removal of something Walpole calls the "nuciform sac."
Humoral opsonin) from the colonial ascidian Batryllus schlosseri as a member of the galectin family.
MBL is a liver-derived complement-activating opsonin that recognizes repetitive sugar structures present on a variety of microorganisms.
Winkelstein JA, Smith MR, Shin HS (1975) The role of C3 as an opsonin in the early stages of infection.
In addition, MBL can also function as an opsonin to facilitate phagocytosis of bacteria, virus, and fungi [3].
cordata might have also activated the complement factors via the alternative pathway, which acts as opsonin leading to enhancement of phagocytosis.
i) The presence of ketosis leads to diminution of opsonin content, depression of antibody titre of the blood and interference with the action of INH in Tuberculosis bacilli.
So far, many efforts have been done to yield stealth products by modification of the surface properties of nanocarriers with polymers that prevent opsonin interactions [25] and subsequent phagocyte clearance [26-28].
Albumin also decreased opsonin binding to PEGylated liposomes and improved the therapeutic activity of doxorubicin-loaded liposomes against sarcoma.
PEGylation is routinely used to mask the surface charge effectively camouflaging the nanoparticle from opsonin proteins and significantly extending the half-life of the nanoparticle in the circulation.
Acting as an opsonin for gram-positive bacteria to aid in their phagocytosis, CRP increases late during the onset of sepsis.
This was first shown in vitro, demonstrating that extracellular Gal-3 acts as an opsonin for the phagocytosis of apoptotic neutrophils by macrophages [60].