OSTEOCLASTS ARE NOT THE MAJOR SOURCE OF INTERLEUKIN-6 IN MOUSE PARIETAL BONES

Interleukin-6 (IL-6) is produced by bone cells and has been shown to s timulate the proliferation of osteoclast progenitors. Which cells in b one produce IL-6 is controversial. This article tests the hypothesis t hat tartrate-resistant acid phosphatase-positive osteoclasts (TRAP + O C) in neonatal mouse parietal bones are the major source of IL-6. Bone s were preincubated with indomethacin to decrease the number of TRAP OC and the amount of IL-6 produced. Incubation with parathyroid hormo ne or prostaglandin E(2) increased the number of TRAP + OC and the amo unt of IL-6 produced. Calcitonin and 17 beta-estradiol inhibited this increase in TRAP + OC but had no effect on IL-6 production. 1,25-dihyd roxy-vitamin D-3 also stimulated an increase in TRAP + OC number but d id not cause increased IL-6 production. Both the endocranial and ectoc ranial membranes of these bones produced large amounts of IL-6. TRAP a ctivity in extracts of endocranial membranes was 14-fold that of the e ctocranial membrane and, histochemically, some TRAP + cells could be d etected here. However, the ectocranial membranes produced more IL-6 th an the endocranial membranes. We conclude that TRAP + OC are not a maj or source of IL-6 in this system.