Immunoblot analysis of the R-form lipopolysaccharide from Salmonella S forms

Lipopolysaccharide (LPS) preparations from Salmonella S-form bacteria contain, in addition to S-form LPS, variable amounts of R-form material, lacking the O-specific polysaccharide. In the present study, we investigated the R-form LPS present in 22 LPS preparations derived from different Salmonella S-form strains belonging to 8 serological groups. The R-form part of the LPSs was separated by SDS-polyacrylamide gel electrophoresis and its antigen specificity analyzed by subsequent immunoblotting using Salmonella R-antisera (anti-Ra, -Rb1, -Rb2, -Rc). The results show that different R-determinants were present in one and the same LPS preparation. The pattern of reaction varied considerably among individual strains. This variation was also present among strains of the same serogroup. Approximately one half of the R-form LPSs exhibited a weak or no reaction with Ra antiserum. In contrast, almost all R-form LPSs showed a significant reaction with Rb1 antiserum. The electrophoretic mobility of the R-form material was very similar, exhibiting only minor differences among the different LPS preparations. In most cases, migration was similar to that of authentic Salmonella Ra-LPS; in some cases, the migration was somewhat faster resembling that of Rb1-LPS.