Antibodies against core and O antigen epitopes of Escherichia coli O83 in rabbit antisera and in commercial human immunoglobulin.

An unexpected serological cross-reaction was detected between two common Escherichia coli O antigens: O83 and O6. It was found that the cross-reacting antibodies were induced by common core epitopes not exposed in naturally occurring smooth strains. Smooth O6 strains would, however, after prolonged immunization of rabbits provoke production of precipitating antibodies against this common core epitope. Routine rabbit O antisera of smooth test strains O1 to O171 did not contain antibodies to the core epitope. Core antisera could readily be produced with an R mutant of the O6 strain. Extracts or Lipopolysaccharides (LPS) of several of the E. coli commonly found in the normal intestine and in extraintestinal diseases would only precipitate in antisera containing anti-core epitope anti-bodies after treatment with deoxycholate or sodium dodecyl sulfate. Other E. coli such as J5 (O111), used extensively for production of antisera intended for protection against endotoxemia, did not react with antibodies against this common core epitope. Another unexpected observation was that normal commercial human immunoglobulin contained precipitating IgG antibodies to the E. coli O83 antigen commonly found in strains from neonatal meningitis and other extraintestinal infections. Significant amounts of precipitating anti-LPS antibodies against other common O antigens (O2, O4, O6, O75 etc.) could not be detected in normal immunoglobulin.