Opsonin


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Related to Opsonin: opsonization, Cytokines

opsonin

[′äp·sə·nən]
(immunology)
A substance in blood serum that renders bacteria more susceptible to phagocytosis by leukocytes.

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

References in periodicals archive ?
Anne's; and in fifteen minutes I'll give you his opsonin index in figures.
Purification and characterization of a humoral opsonin from the solitary urochordate Syela clava.
This bacterium inhibits the chemotaxis of neutrophils, suppresses the opsonins (both complement and immunoglobulin) and phagocytes, could rapidly react to abrupt changes in ROS (Lavoie et al.
1983) Binding and phagocytosis of sialidase-treated rat erythrocytes by a mechanism independent of opsonins.
Humoral factors are able to recognize foreign antigens, acting as surface phagocyte receptors and regulating the migration and concentration of hemocyte opsonins (Anderson & Beaven 2001, Yang et al.
This reduction of bacterial load by using autologous plasma along with leucocytes is attributed through supplementation of plasma derived opsonins and particularly components of complement systems in uterine lumen (Asbury, 1984).
12) Although most antibodies function as opsonins and accelerate platelet clearance by phagocytic cells, occasional antibodies bind to epitopes on crucial regions of these GPs and impair platelet function.
18 The acute phase proteins regulate immune responses, function as mediators and inhibitors of inflamma-tion, act as transport proteins for products generated during the inflammatory process (the haem-binding protein hemopexin, and haptoglobin), function as opsonins, activate complement, bind cellular rem-nants like nuclear fractions9,18, scavenge free haemo-globin and radicals, modulate the host's immune response, prevent apoptosis and / or play an active role in tissue repair and tissue remodeling.
Further, injection of decoys of nanoparticle can be used to eliminate plasma opsonins and reduce uptake of the nanoparticles.
Opsonization is a process that facilitates phagocytosis by the deposition of opsonins such as antibodies or complement fragments that coat the surface of foreign particles.
However as the hydrophobicity of the surface reduces the affinity of the protein to the surface also reduces, and bigger opsonins will attach to the surface.
1) Opsonins ("nature's antibiotics") and protective nutritives that inihibit pathogens produced by an abundance of healthy probiotic microflora.