Preparation and biological properties of a chemically modified Escherichia coli endotoxin of high immunogenic potency and low toxicity.

The chemical basis of the toxic and immunogenic properties of endotoxins from enteric gramnegative bacilli has been the subject of intensive investigation. Recent methods of purification yielded biologically active preparations which were essentially free of dissociable protein and consisted of complex phosphorylated lipopolysaccharides containing firmly bound peptides (1, 2). Chemical degradation destroyed toxicity, liberating complex phosphoglycolipds and a haptenic polysaccharide endowed with serological specificity (1, 3-7). It was concluded that the lipid was essential for toxicity, whereas the polysaccharide merely functioned as a water-soluble carrier (7, 8). This concept was supported by the successful restoration of toxicity upon artificial recombination of the lipid with unrelated proteins (9, 10). These findings suggested the possibility of preparing a nontoxic antigen by chemical dissociation of the lipid from the native endotoxin complex. In the past, all attempts to separate the toxic from the antigenic properties failed, since the hydrolytic methods employed lacked the required selectivity and invariably destroyed the antigenic properties more rapidly than the toxicity (1, 2). The use of nonhydrolytic reagents of greater specificity, on the other hand, appeared to offer a more promising approach. In the present study, the selective reduction of toxicity was accomplished by the treatment of a Boivin antigen from Escherichia coli with LiAlH4. The data presented show that the resulting product retained the immunogenic potency and serologic activity of the original complex.