From Big Medical Encyclopedia

VI-ANTIGEN — capsular polisakharidny antigen of nek-ry enterobakteriya: Salmonella typhi, Escherichia coli, Citrobacter (Paracolobactrum ballerup). It is applied to serodiagnosis, treatment and prevention of a typhoid. For the first time Vi-antigen is described in 1934 by Felix and Pitt (A. Felix, R. Pitt), to-rye considered that it defines virulence of S. typhi, and called it antigen of virulence (from here and its name — «Vi-antigen»). The capsular arrangement of Vi-antigen is confirmed by serological researches, according to the Crimea Vi-positive strains are not agglutinated by O-serums. Elektronnomikroskopichesky researches showed that Vi-antibodies, marked paraaminofenilmerkuratsetaty, are found on a surface of the whole cell of S. typhi of Tu2 in the form of granules with a diameter no more than 10 — 12 nanometers (100 — 120 And). Discrete character of an arrangement of marked antibodies reflects, apparently, topography of antigenic determinants of Vi-antigen (S. M. Sobolev and soavt., 1966). Vi-antigen — N-atseti-lirovannoy polymer aminohexuronic to - you, a base unit to-rogo is 2-amino-2-dezoksi-D-galacturonic to - that. Polymer is characterized by the expressed positive specific rotation and is steady against oxidation by periodate that indicates existence of alpha (1-3) bonds. Experiences with methylation of the Vi-antigen isolated from E. coli 5396/38 showed that in polymer there is a communication 1 - 4. The main component of the isolated Vi-antigen has a pier. weight more than 1 000 000. Drug is steady against acid hydrolysis and termostabilen. At hydrolysis concentrated salt to - that an exit of polysaccharide makes 80%, and this material identified as a hydrochloride D-aminogalakturo-new to - you can be crystallized with a small exit. Vi-antigen is emitted from bacteria with extraction by isotonic solution of sodium chloride or distilled water. Subjecting to vigorous stirring at 3000 fluctuations in 1 min. a dense suspension of cells of S. typhi of Tu2, it is possible to receive the capsular fraction containing a large amount of Vi-antigen. Purification of Vi-antigen of impurity of O-antigen is made by several methods. Webster (M. of E. Webster) et al. (1953, 1954) offered fractionation of extract ethanol and hydrolysis acetic to - that. At the same time O-antigen collapses, and resistant Vi-antigen keeps the properties. The method Webster was modified and adapted for production of Vi-antigen (N. B. Holchev, D. D. Yefimov, 1965). The method of purification of Vi-antigen with extraction of 60% is described by ethanol at t ° 37 ° and a repeated peressazhdeniye at t ° 0 — 5 ° tsetavlony [E. E. Baker and soavt., 1959, 1960]. Vi-antigen is purified by also paper electrophoresis or adsorption on a column with a formalinizirovanny stroma of erythrocytes. The Vi-antigen isolated by method Webster from S. typhi, P. ballerup and E. coli contains nek-ry impurity of O-antigen, serological is active, and drugs, having identical antigenic specificity, differ on viscosity a little. Polymeric drug of Vi-antigen more antigenen for mice, but less antigenen for rabbits. So, protective activity of homogeneous high-polymeric Vi-antigen is 40 times higher, than depolimerizovanny and deacetylated. At immunization of people depolimerizovanny and deacetylated antigen observes products of specific antibodies, to-rye react with native Vi-antigen. At a depolymerization and deacetylation its protective activity [Landi (M. of Landy) and soavt decreases., 1963]. Protective activity of Vi-antigen depends on number of the acetyl groups which are contained in it. The Vi-antigens received by Baker's method or by means of an electrophoresis from Vi-positive strains, also do not differ on chemical structure, physical. to properties and biol, activities. However D. D. Yefimov (1964, 1965) notes nek-ry serological distinctions between S. typhi Vi-antigen Tu2 and ballerup Vi-antigen P.

The role of Vi-antigen as receptor of a phage is for the first time shown in 1936 by several researchers [Kreygi, Brandon (J. Craigie, To. Brandon), etc.]. It is established that ability of the isolated Vi-antigen to brake activity of a Vi-phage depends on presence at antigen of O-acetyl groups. At an immunoelectrophoretic research of different drugs of Vi-antigen two fractions differing on mobility and a pier are revealed. to weight, but identical on antigenic specificity. The receptor of a Vi-phage contains in slowly moving fraction. Heterogeneity of the isolated Vi-antigen is shown by analytical ultracentrifugation and gel filtering. Synthesis of Vi-antigen in a bacterial cell is determined by two genes: To ViB connected with Vi-inl-purA-pyrB and Vi A localized near a his-0-antigenic locus — the 04 or 09 factor.

Vi-positive strains of S. typhi are more virulent for the person, than Vi-negative, however this situation relatively. Vi-negative strains, napr, a strain of T-5501, etc. are described [by A. Standfast, 1960], S. typhi, to-rye were virulent for the person and laboratory animals. The isolated Vi-antigen is used for preparation of an erythrocyte Vi-diagnosticum. The vaccines prepared from a Vi-positive strain (e.g., Tu2-4446), protect mice against intraperitoneal infection with both a Vi-positive, and Vi-negative strain, however vaccines from a Vi-negative strain do not protect mice against infection with a Vi-positive strain. Immunization of people against typhoid (see) it is made or the killed corpuscular vaccines consisting of a Vi-positive strain or the drugs consisting of the soluble antigenic S. typhi complexes and containing Vi - the anti-gen. M. P. Pokrovsk (1965) with soavt, the spirit corpuscular typroid vaccine enriched with the isolated Vi-antigen is offered. However the role of Vi-antigen in formation of specific immunity against a typhoid is finally not found out from people.

See also Vi-typroid phage , Diagnosticums .

Bibliography: Petrosyan E. A. Complex antigens of tifo-paratyphoid group of bacteria, M., 1961; Samsonova V. S., etc. Fractionation of drugs of S. typhi Vi-antigen by method of a gelfiltration on G-200 sephadex, Zhurn, mikr., epid, and immun., No. 10, page 3, 1973, bibliogr.; Stanislavsky E. S. Bacterial structures and their antigenicity, M., 1971; Esposito V. T. a. F e e 1 e at J. Page of Isolation of Vi antigen from Escherichia coli by a new method, Infect. Immunol., v. 1, p. 69, 1970; Landy M. Bacterial endotoxins, Tex. Rep. Biol. Med., v. 20, p. 1, 1962; Landy M., Sanderson R. P. a. Jackson A. L. Humoral and cellular aspects of the immune response to the somatic antigen of Salmonella enteritidis, J. exp. Med., v. 122, p. 483, 1965; Wong K. H., Feeley J. C. a. Pittman M. Effect of a Vi degrading enzyme on potency of typhoid vaccines in mice, J. infect. Dis., v. 125, p. 360, 1972; Wong K. H. a. o. Vi antigen from Salmonella typhosa and immunity against typhoid fever, Infect. Immunol., v. 9, p. 348, 1974.

E. S. Stanislavsky.