The lipid A moiety of Porphyromonas gingivalis lipopolysaccharide specifically mediates the activation of C3H/HeJ mice.

The lipid A preparation isolated from Porphyromonas gingivalis was found to induce splenocyte mitogenicity and TNF-alpha release from peritoneal macrophages in LPS-unresponsive C3H/HeJ mice to the same extent as in LPS-responsive mice. In order to clarify whether the activation of C3H/HeJ mice was specifically caused by the lipid A and not by contaminating protein, two strategies were employed. The lipid A fraction from P. gingivalis was subjected to either hydrochloric acid or alkaline treatment to eliminate either glycosylated phosphate or O-acylated fatty acids from the lipid A structure, and the biologic activities of the derivatives were compared in both LPS-responsive and unresponsive C3H/HeJ mice. De-1-O-phosphorylated P. gingivalis lipid A showed partial loss, and de-O-acylated lipid A complete loss of splenocyte mitogenic and TNF-alpha-inductive activities from peritoneal macrophages in both LPS-responsive and unresponsive mice. The relative activities of the intact and treated lipid A compounds in splenocyte mitogenicity and TNF-alpha-inductive activity in macrophages were similar to the relative activities of these preparations in Limulus gelation activities. The LPS-specific antagonist, succinylated lipid A precursor, inhibited P. gingivalis lipid A-mediated splenocyte mitogenicity and TNF-alpha induction in macrophages in a similar manner in LPS-responsive and unresponsive mice. These results strongly suggest that the activation of LPS-unresponsive C3H/HeJ mice by P. gingivalis lipid A was specifically mediated by the lipid A portion and not by contaminating protein. The characteristic action of P. gingivalis lipid A on LPS-unresponsive C3H/HeJ mice was thought to reflect the unique chemical properties of this compound.