The Significance of the Vi Antigen

Abstract

Typhoid fever is still a public health problem of considerable importance in many parts of the world. Any contribution to our fund of knowledge concerning the etiologic agent (applicable to diagnosis, prophylaxis, and therapy) is, therefore, to be welcomed as a possible basis for better control of the disease. The discovery by Felix and Pitt in 1934 (30, 31) of a hitherto undescribed antigenic component of the organism responsible for the disease was a step in this direction. Up to that time Eberthella typhosa was known to contain at least two heat-stable antigens in the somatic fraction and one specific antigen in the flagellar fraction. The toxic manifestations of typhoid fever were commonly thought to be due to the endotoxins contained in the somatic fraction. An additional property of the organisms, virulence (at least for mice), was now described as being associated with the presence of the new-found component, and it was accordingly named "Vi". It was this concept of the antigen being a virulence antigen which gave such pronounced impetus to renewed study of the typhoid organism; for the implications concerning severity of attack and immunity were quickly seen. The purpose of this review is to take bearings on how much progress has been made as a result of the studies thus stimulated, and to call attention to places where a strengthening of evidence would be desirable.Occurrence. Almost all freshly isolated typhoid cultures have been shown to contain the Vi antigen (29,46,20,1,66,57). In addition, it has been found sporadically in some of the Hirschfeld paratyphoid C strains (46), in a species of Salmonella designated as "ballerup" (49), and in a few cultures of the coli group (48).Strains of Eberthella typhosa which possess the antigen do not differ noticeably in cultural reactions (including fermentative ability) from those which lack it, although Giovanardi (36) reports that colonies of the Vi-containing form are somewhat more opaque than those of the forms not containing it.Properties. The antigen has been precipitated from protein-free trichloracetic acid extracts by uranyl salts (13, 59). Freeman and Anderson (34) were unable to repeat this separation from the 0 complex and hence are not convinced that the Vi properties may be ascribed to a compound separable from the 0 fraction. However, Henderson (43) demonstrated at least part of the Vi substance free from any of the smooth 0 substance in anhydrous diethylene glycol extracts of rough Vi-containing forms.Acetone extracts containing Vi and 0 fractions show a precipitation reaction with phosphotungstic acid in 5% sulphuric acid and with neutral lead acetate, uranium acetate, mercuric acetate and aluminum sulphate, whereas extracts containing only the 0 fraction fail to show precipitates with these reagents (65). The antigen is probably situated for the most part near the surface of the 43 on July 6, 2020 by guest

An outbreak of typhoid fever in the Middle East

“…However, the major weight of evidence presented by other workers is in favour of the reliability of such tests in the exclusion ofnon-carriers. This was first suggested by Felix et al (1935), and supported later by Pijper & Crocker (1937, 1938, Felix (1938), Bhatnagar (1938, Bensted (1940), Almon & Stovall (1940), Almon (1943, and others; although Horgan & Drysdale (1940), and Davis (1940), were less favourably disposed to the test because they found occasional Vi negative carriers, and were able to demonstrate raised Vi titres in subjects from whom the typhoid bacillus could not be isolated. A large-scale survey of this type in Egypt would certainly be of great value, for there is little doubt that the number of typhoid carriers among the 'fellahin' must be high.…”

ANTIGENIC ANALYSIS OF CELL STRUCTURES ISOLATED FROMBACILLUS MEGATERIUM

“…These and subsequent results (table 3) also indicated that the capsular polypeptide is not an integral component of the cell wall or of other cell components. However, antiserum to cell walls (but not to wall polypeptide or, of course, the haptenic polysaccharide) reacted in high titer with encapsulated cells, allowing either of two interpretations: (a) Complete penetration of the capsule by antibody to cell walls is a first possi-1959] VENNES AND GERHARDT bility but seems unlikely, on the basis of findings by Schiutze (1932) and Almon (1943) that the presence of capsular material in other organisms prevents the reaction of antibody to somatic antigens, and by Tomesik (Spooner and Stocker, 1956) that incomplete penetration by capsular antibody is seen in capsules of B. megaterium.…”