Comparison of the capacity of two lipid A precursor molecules to express the local Shwartzman phenomenon

It has been shown recently that a Salmonella lipid A precursor molecule (Ia) and its synthetic counterpart are inactive in expressing the local Shwartzman reaction in both homologous and heterologous systems in combination with lipid A. Precursor Ia contains a bisphosphoryl-beta-1,6-glucosamine disaccharide substituted by 4 mol of (D)-3-hydroxytetradecanoyl residues. Escherichia coli lipid A, on the other hand, which contains two additional non-hydroxylated acyl residues in the form of two 3-acyloxyacyl units, is highly active. We have recently isolated a lipid A precursor molecule (Ib) with the same basic structure as precursor Ia, which contains, however, one additional non-hydroxylated (hexadecanoic) fatty acid forming one 3-acyloxyacyl residue. A comparison of precursor Ia and Ib in homologous and cross-reacting Shwartzman systems confirmed that precursor Ia completely lacked the capacity to prepare the skin for, or to elicit, the Shwartzman reaction. In contrast, precursor Ib was strongly active in inducing the local Shwartzman reaction both when administered intradermally as a preparatory agent and when administered intravenously as a provocatory agent. The results indicate that the additional presence of at least one fatty acid either as such or as an acyloxyacyl residue (as in precursor Ib) is a prerequisite for the ability of the molecule to induce the local Shwartzman phenomenon.