ANTIGENIC AND IMMUNOGENIC DIFFERENCES IN LIPOPOLYSACCHARIDES OF ESCHERICHIA-COLI J5 VACCINE STRAINS OF DIFFERENT ORIGINS

Escherichia coli strain J5 mutants of various origins have often been used as vaccines for induction of cross-reactive, cross-protective ant ibodies directed against the lipopolysaccharide (LPS) core region. The antigenic composition of LPS from J5 strains of different origin, i.e . strains J5(U), J5(UK), J5(2877) and J5(a), was investigated using mo noclonal antibodies (mAbs) reactive only with LPS of a given chemotype , i.e. one specific for the incomplete E. coli core of the Rc chemotyp e, a second mAb reactive only with the E. coli R3 complete core, and a third specific for the O-antigen of E. coli serovar 0111. The LPS of strains J5(U) and J5(a) is almost exclusively composed of LPS of the R c chemotype, LPS of the J5(UK) strain is composed of Rc LPS and R3 com plete core, while LPS of the J5(2877) strain contains Rc, R3 complete core and O-antigen. Growth of the bacteria in medium supplemented with galactose led to increased expression of complete core. The immune re sponses to the various strains were investigated. Antiserum to the J5 strain expressing the largest amount of R3 core [J5(UK)] had much high er anti-R3 LPS antibody titres compared to antiserum to the other stra ins. mAb 53, representative of the anti-R3 response to J5 strains cont aining complete core, bound to those E. coli LPS expressing the R3 cor e. Thus, the R3 LPS, present in some J5 vaccine strains is at least pa rtially responsible for some of the cross-reactivities exhibited by so me anti-J5 antisera. The present findings may explain some of the disc repant outcomes reported for cross-protection studies with J5 antisera , where J5 strains of various origins grown under different culture co nditions have been used as vaccines and where LPS or bacteria expressi ng various core types have been used for challenge.