The rough mutants of Gram-negative bacteria are widely used to induce protective antisera but the nature of the target epitope for such antibodies is not precisely defined. Endotoxin is one of several antigens present on the surface of bacterial cells, which are able to elicit specific antibodies. We studied the specificity of antibodies produced against a conjugate of E. coli J5 endotoxin core oligosaccharide with tetanus toxoid. The use of chemically defined antigen for immunisation excludes the possibility of production of antibodies against other cell surface antigens. A comparison of this monospecific anti-endotoxin serum with antiserum against E. coli J5 whole cells was performed in order to distinguish the role that endotoxin core oligosaccharide plays in the interaction with humoral host defences from that of other potentially important Gram-negative bacterial surface antigens. The reactivity of both sera with smooth and rough lipopolysaccharides was determined in ELISA, immunoblotting and by flow cytometry. Both antisera reacted with similar specificity with most lipopolysaccharides of identical or related core type. Less distinct reactions with endotoxins of the antibacterial serum in comparison with the anti-conjugate serum were found in all serological tests. LPS of E. coli O100 that showed the strongest reactions with both sera was used to stimulate IL-6, TNFα and nitric oxide production by the J-774A.1 cell line. Both sera were used to inhibit that stimulation and no inhibitory effects of the examined sera in comparison with non-immune serum were observed.
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