112 INTRODUCTION TO IMMUNOCHEAIICAL SPECIFICITY 



^. schottinuclleri, contains a side chain terminating in glucose as 

 well as one terminating in rhamnose. 



Similar studies carried out by Staub et al. on antisera to .S". sclioff- 

 muelleri (containing antigens 4, 5, and 12) showed that abequose in- 

 hibited the precipitation of PsPtB and especially of PsPtBox- This 

 showed that abequose is the terminal unit of either antigen 4 or 5. 

 Since abequose and antigen 4 are found in all Salmonella of group B, 

 but antigen 5 is lacking in some members of this group, Staub et al. 

 concluded that abequose plays no role in antigen 5. This was con- 

 firmed by the observation that the precipitation of an extract of 

 S. typhimurimn, which contains no 5 antigen, is inhibited by abequose 

 and by the finding that when all the antibody precipitable by an ex- 

 tract of this 5". typJiiniuriitui was removed from the anti-PsPtB 

 serum, the action of the serum on PsPtB was not inhibited by the 

 abequose. 



Staub et al. (1959) suggest that the dideoxyhexoses may play an 

 especially important role in the specificity of the Salmonella antigens, 

 not only because they are always terminal, but because the two hydro- 

 phobic CH2-groups they contain are able to approach much closer 

 to the corresponding surface of the antibody than the hydrophilic 

 CHOH-groups, thus strengthening the van der Waals forces between 

 the antigenic determinants and the antibody (see Chapter 9). 



Cross-Reactions 



As a result of extensive studies similar to those just outlined, Staub 

 et al. concluded that although distinct Salmonella antigens generally 

 have different terminal sugars, this is not always the case. For in- 

 stance, abequose occurs at the extremity of both antigens 4 and 8, 

 and glucose at the extremity of antigens 1 and 12. It seems reasonable 

 to conclude that in such cases the next-to-terminal sugar is difTerent, 

 or attached in a different way. In order to test this idea, the authors 

 carried out quantitative cross-reactions with a number of polysac- 

 charides. Some of their results are shown in Table 8-6. 



From the precipitation observed with the galactomannans of gum 

 ghatti, lucerne, and clover, Staub concluded that the Salmonella an- 

 tigen 4 has structural similarities with these polysaccharides ; for. 

 whenever the antibodies to antigen 4 were removed, precipitation of 



