Inflammatory Reactions in Extraoral Tissues in Mice after Intragingival Injection of Lipopolysaccharide

Intragingival (ig) injection into mice of lipopolysaccharide (LPS) from Prevotella intermedia or Escherichia coli elevated the activity of the histamine-forming enzyme, histidine decarboxylase (HDC), in the mandible, liver, lung, and spleen, with a time course similar to that seen with intravenous (iv) injection. The effect of i.g. injection was less than that of i.v. injection but similar to that of intraperitoneal (ip) injection. The i.g. injection also increased hepatic serotonin, reflecting platelet accumulation. In galactosamine-treated mice, the minimum ig dose of LPS needed to induce lethal hepatitis was very small (less than that needed by ip injection). These results support the idea that the LPS produced in oral tissues may be transported easily to extraoral tissues and, in some cases, may cause inflammatory or immune responses. It also may influence the pathogenesis of some systemic diseases.