Interleukin-7 production by B lymphocytes affects the T cell-dependent osteoclast formation in an in vitro model derived from human periodontitis patients.

Periodontitis is characterized by irreversible destruction of alveolar bone and connective tissue attachment in the periodontium. We recently reported that T cells support the osteoclastogenesis by the overproduction of nuclear factor-kappa-B-ligand (RANKL) and Tumor Necrosis Factor-alpha (TNF-alpha) in an in vitro osteoclastogenesis model from periodontitis patients (Pp). It is known that IL-7 stimulates the production of osteoclastogenic factors by T cells and IL-6 potentiates IL-7 expression. Thus, we studied the involvement of IL-6 and IL-7 in the T cell regulation of osteoclast (OC) formation, in an in vitro osteoclastogenesis model from Pp. We demonstrated high levels of IL-7 in both the media collected from PBMC cultures of Pp and the sera of the same patients. We also demonstrated that freshly isolated B cells from PBMCs of Pp were the source of IL-7 in our model. B cells, in fact, overexpressed IL-7 at mRNA and protein levels, and this production was up-regulated by IL-6. Moreover, the OC formation decreased in the presence of anti-IL-6 and IL-7 functional antibodies in PBMC cultures from Pp. These data suggest that B cells could be responsible for the T cell-dependent osteoclastogenesis in periodontitis through the involvement of IL-6 and IL-7.