O-antigenic determinants in Salmonella species of serogroup C1 are expressed in distinct immunochemical populations of chains

Abstract

The O-antigenic specificities found among salmonellae of serogroup C1 are O:61,7, O:62,7, O:61,62,7 and O:6,7,14, as defined by classical serology. Factor O:7 is the group-wide determinant while factors O:61, O:62 and O:14 are found in some strains but not others. Strains of the O:62,7 specificity are subject to lysogenic conversion by phages 61 and 14 to the O:61,7 and O:6,7,14 specificities, respectively. To further delineate antigenic complexity and serological relationships among strains of this serogroup monoclonal antibodies (mAbs) were generated against the O:61,62,7 polysaccharide of Salmonella thompson. Five mAbs of either the O:61, or the O:62 specificities did not bind O:6,7,14 strains or LPS, showing that the O:6 determinant in these strains is neither O:61, nor O:62. Thus antigenic conversion of O:62,7 strains by phage 14 is accompanied by addition of O:14 as well as loss of O:62 Three mAbs which demonstrated group-wide reactivity, and were thus specific for O:7, recognized clearly separable epitopes hereby defined as sub-specificities, O:71 O:72 and O:73 Immunoblotting of mAbs against electrophoretically resolved LPS showed that factors O:61 and O:62 are expressed only in LPS molecules of high molecular mass whereas O:72 and O:73 are expressed only in relatively low-molecular-mass chains. These results are consistent with the expression of different antigenic determinants in structurally distinct subpopulations of O chains. The implication of the existence of distinct subpopulation of chains is that the published structure of the O:6,7 repeat unit is not fully representative of the O-antigenic structure of this group.