Prostaglandin E2 stimulates the production of interleukin-6 by neonatal mouse parietal bones

The pleiotropic cytokine interleukin-6 (IL-6) is thought to be involved in bone homeostasis. A number of bone resorbing agents have been shown to induce the release of IL-6 from bone. We wished to determine whether prostaglandin E₂ (PGE₂), which is a mediator of bone resorption, can elicit the production of IL-6. IL-6 was measured by the proliferative response of B9 hybridoma cells and could be completely neutralised by an anti-IL-6 antibody. Parietal bones from neonatal mice were maintained in culture in the presence of indomethacin (10⁻⁶ M) with or without PGE₂. The time course and dose-response to PGE₂ of IL-6 production were determined. After 6 h in culture, 10⁻⁸ M PGE₂ produced significantly more IL-6 than the controls (P < 0.005). PGE₂ (10⁻⁶ M) stimulated the production of a mean of 12.8 ng/ml IL-6 over 6 h. Preincubating bones with indomethacin for 20 h prior to a 6 h culture with indomethacin led to a lowering of the production of IL-6 (mean 1.8 ng/ml) compared to bones cultured without the preincubation period (5.8 ng/ml). When the indomethacin preincubation period was used, a significant increase in IL-6 production was found with 10⁻⁹ M PGE₂ (P < 0.005), and 10⁻⁶ M PGE₂ caused the production of 39.9 ng/ml IL-6 over 6 h. Stripping endocranial and ectocranial membranes from bones demonstrated the membranes to be the major site of IL-6 production. However, intact bones were required for maximal stimulated IL-6 production.