Enhanced osteoclastogenesis in 4-1BB-deficient mice caused by reduced interleukin-10

Enhanced osteoclastogenesis was observed in bone marrow-derived macrophage cells from 4-1BB-deficient mice than in those from wildtype mice. 4-1BB and 4-1BB ligand interaction may play a role at a certain stage of osteoclast formation through increased level of IL-10, a negative regulator of osteoclastogenesis. Introduction: 4-1BB is an inducible T-cell costimulatory molecule and a member of the TNF receptor family. The expression pattern of 4-1BB and 4-1BB ligand (4-1BBL) has suggested that 4-1BB plays a role not only in various responses related to innate immunity but also in bone metabolism. Materials and Methods: Osteoclast formation was evaluated in bone marrow-derived macrophage cells (BMMs) from wildtype and 4-1BB-deficient (4-1BB(-/-)) mice. Expression of interleukin-10 (IL-10) during osteoclast formation was analyzed at the mRNA and protein levels. Results: Expression of IL-10 was higher in RANKL-stimulated wildtype BMMs than 4-1BB(-/-) BMMs. When 4-1BBL was stimulated with 4-1BB-Fc fusion protein, the expression of IL-10 in BMMs increased. Neutralization of IL-10 was not as effective in preventing inhibition by IL-10 of osteoclast differentiation in 4-1BB(-/-) BMM as in wildtype BMMs. When IL-10 was added to the culture medium, osteoclast formation was inhibited more efficiently in the 4-1BB(-/-) BMMs than in the wildtype BMMs. Conclusions: Interaction of 4-1BB and 4-1BBL stimulates IL-10 production through 4-1BBL signaling. 4-1BBL plays a role at a certain stage of osteoclast formation, and IL-10 may mediate this effect. The elevated level of osteoclastogenesis in 4-1BB(-/-) BMMs may thus be caused, in part, by a lower level of IL-10.