IL-4, but not vitamin D-3, induces monoblastic cell line UG3 to differentiate into multinucleated giant cells on osteoclast lineage

The formation of multinucleated giant cells (MGCs) from monocytes/macrophag es is controlled by various cytokines, the roles of which are not fully und erstood. Both interleukin (IL)-4 and 1 alpha,25(OH)(2) vitamin D-3 (D-3) ar e known to induce MGC formation from monocytes/macrophages. D-3 is also kno wn as a stimulator of osteoclast formation in the presence of stroma cells, and 1L-4 as an inhibitor. Previously, we showed that IL-4-induced MCCs fro m monocytes/macrophages expressed tartrate resistant acid phosphatase (TRAP ) activity and hydroxyapatite-resorptive activity in the presence of M-CSF without stroma cells. In this study, we examined the effects of D-3 and/or IL-4 on MGC formation and the characteristics of these MGCs using a monobla stic cell line (UG3), to elucidate the involvement of these factors in oste oclast development without stroma cells. D-3-induced MGCs showed none of th e markers of osteoclasts, such as TRAP activity, calcitonin receptor (cal-R ) expression, hydroxyapatite-resorptive activity, and bone-resorptive activ ity. A low concentration of D-3 synergistically stimulated IL-4-induced TRA P-positive MGC formation whereas a high concentration of D-3 inhibited it. When IL-4 was added on day 7 of the 2-week culture with D-3, TRAP positivit y reached maximum. On the other hand, delayed addition of D-3 on day 7 of c ulture did not increase the TRAP positivity. Although the fusion rate incre ased during the first week of the 2-week culture in the presence of D-3, it increased further in the second week following the addition of IL-4 on day 7. Furthermore, IL-4-induced, or 1L-4- and D-3-induced MCCs differentiated into functional osteoclasts with bone-resorptive activity following cocult ure with osteoblastic cells, whereas D-3-induced MGCs did not acquire bone- resorptive activity even after coculture with osteoblastic cells in the pre sence of D-3. These findings suggest that IL-4 initiates osteoclast develop ment of UG3 cells, although stroma cells were necessary for development of functional osteoclasts. On the other hand, D-3 had only a "supportive" effe ct on this differentiation. IL-4 and direct contact with stroma cells may r egulate different stages in the multistep process of osteoclastogenesis of UC3 cells. (C) 2000 Wiley-Liss, Inc.