ANTIGENIC VARIATION 717 



d antigen, this antigen was lost and replaced by a new antigen j, which had never been 

 met with in typhoid bacilli under natural conditions. Similarly, the b, z^j antigens of 

 Salm. schleissheim may be replaced by a new antigen, Z5. In both these organisms, 

 which are monophasic, the antigen appearing in the induced phase belongs to the series, 

 a, b, c . . . commonly found in Phase 1. Bruner and Edwards (1941a), however, were 

 able to induce in the monophasic Sabn. paratyphi A a second phase containing the 1,5... 

 antigens, which are characteristic of the group series of antigens of Phase 2. An even 

 more remarkable series of induced variations was recorded by Edwards and Bruner (1939) 

 in Salm. abortus-equi. This organism exists normally only in Phase 2, in which it possesses 

 the antigens e, n, x . . . By growth in appropriate sera a Phase 1 , containing the antigen a, 

 was induced, and a Phase 3, containing the antigen Z5. All three phases were reversible. 

 It is by no means always easy to decide whether a new phase that appears as the result 

 of growth in immune serum is to be regarded as an artificial phase or as the alternative 

 phase of an organism that is generally, though not invariably, monophasic. Legitimate 

 difference of opinion may exist on this point. For example, Salm. cholerce-suis var kuJizen- 

 dorf was for many years regarded as a well-estabUshed monophasic type occurring in the 

 group phase. When it was found, however, by Bruner and Edwards (1939) that a specific 

 phase could be induced containing the same antigen c as Salm. cholerce-suis, it was decided 

 to omit the kunzendorf type from the Kauilmann- White scheme on the ground that it 

 was merely a group phase variant of the parent strain. 



Variation in the Vi antigen. — There is a type of variation that concerns the Vi antigen 

 (seep. 1525). The Hand antigens remain unaffected. Kauffmann (1935rt) found that 

 typhoid bacilli might exist in three forms : (1) the V form, which contains the full quota 

 of Vi antigen and is inagglutinable by serum ; (2) the VW form, which contains some 

 Vi antigen but not enough to inhibit O agglutinability ; and (3) the W form, which con- 

 tains no Vi antigen and is fully agglutinable by O serum. A similar variation in the 

 Vi antigen may be observed in Salm. paratyphi C and Salm. ballerup. The V -> W 

 variation appears to be irreversible (Craigie and Brandon 19366). 



Variations in the antigens. — In some strains containing two or more components, 

 some colonies may be found in which one of the components is missing or developed to 

 only a sUght extent. The two antigenic components most likely to be affected are I 

 and XII. Within the same strain there are I ++, I + and I± colonies, the tendency 

 being for the I + + to pass over to the I ± type. The XII antigen is complex, con- 

 taining XIIj, Xllg, and XII3 fractions. According to Kauffmann (1941), it is the Xllg 

 fraction that is most likely to be lost or weakened. A rather different type of variation 

 is noticed in organisms, like Salm. paratyphi B and Salm. typhi-murium, containing the 

 IV. V antigenic components. In some strains the V antigen is missing, not merely from 

 certain colonies but from the whole strain. Strains of Salm. paratyphi B showing this 

 so-called loss variation seem to be commoner in carriers than in acute cases ; and strains 

 of Salm. typhi-murivm showing the same loss variation are, according to Edwards and 

 Bruner (1940a), usually derived — at least in the United States — from pigeons. 



The OH -> variation. — Flagellated strains may occasionally give rise to variants 

 that contain only the antigen. As a rule, this type of variation is irreversible. Some 

 strains, like Salm. gallinarum and Salm. pullorum, are permanently non-flageUated. The 

 OH -> O variation cannot readily be induced m the laboratory. The production of 

 forms by growth on phenoUzed agar is not a true impressed variation, since there is 

 a rapid reversion to the normal flagellated form when the organisms are inoculated on to 

 ordinary media. 



The smooth -^ rough variation. — This type of variation has already been described 

 at sufficient length in Chapter 9. So far as the Salmonella group is concerned, it consists 

 essentially in a loss of the normal smooth somatic antigen, with the appearance of a new, 

 rough antigen, having far less specific properties than the smooth antigen and conferring 

 on the bacilU a sensitivity to salt solution which renders them unstable in suspension. 



