Membrane-bound CD40 ligand on T cells from mice injected with lipopolysaccharide accelerates lipopolysaccharide-induced osteoclastogenesis.

BACKGROUND AND OBJECTIVE

T cells infiltrate the inflammatory site of periodontitis and consequently stimulate the loss of periodontal bone. We previously reported that T cells from lipopolysaccharide (LPS)-injected mice (LPS-T cells) accelerated osteoclastogenesis in the presence of LPS. Ηowever, the detailed mechanism of this acceleration is still unclear. In this study, we analyzed the mechanism of osteoclastogenesis accelerated by LPS-T cells.

MATERIAL AND METHODS

We examined the mechanism of osteoclastogenesis acceleration. First, to determine the effect of cell-to-cell contact, we co-cultured T cells and bone marrow macrophages, prestimulated with RANKL for 48 h (R-BMMs), in the presence of LPS for 24 h, in a Transwell. Second, to determine the effect of CD40 ligand (CD40L), we co-cultured T cells and R-BMMs in the presence of LPS and anti-CD40L immunoglobulin. Third, we examined the effect of recombinant mouse CD40L (rCD40L) in the presence of LPS in vitro and in vivo. Lastly, we examined the expression of membrane-bound CD40L (mCD40L) by fluorescence-activated cell sorting (FACS).

RESULTS

Blocking cell-to-cell contact between LPS-T cells and R-BMMs completely inhibited the acceleration of osteoclastogenesis. Anti-CD40L immunoglobulin also completely inhibited the acceleration of osteoclastogenesis. Moreover, rCD40L accelerated osteoclastogenesis in the presence of LPS in vitro and in vivo. Finally, the expression of mCD40L on LPS-T cells was higher than that on T cells isolated from mice not injected with LPS.

CONCLUSION

The results demonstrate that CD40L accelerates osteoclastogenesis in the presence of RANKL and LPS. The results also suggest that mCD40L on LPS-T cells accelerates osteoclastogenesis.