Immune protection against enterotoxinogenic E. coli: search for synergy between antibodies to enterotoxin and somatic antigens.

The protective effect against intestinal challenge with enterotoxinogenic (ent+) E. coli of enterotoxin antibodies alone and in combination with various antibacterial antibodies has been studied in rabbits. Both antibodies against E. coli heat-labile enterotoxin (LT) and cholera toxin were equally effective against different serotypes of ent+ E. coli. Antiserum to purified homologous E. coli lipopolysaccharide (LPS) as well as to cross-reactive LPS structures (Re LPS and Common antigen) contained protective antibodies which increased the protection obtained with anti-enterotoxin. Antiserum to whole bacteria acted synergistically with anti-LT against homologous and sometimes also against heterologous E. coli. This synergy remained after complete absorption of the LPS antibodies from the antibacterial serum.