[Osteoimmunology: an integrated vision of immune and bone systems]

Study of dysregulations of the immune system resulting in abnormal bone homeostasis has led to the emergence of the field of osteoimmunology. Among the interactions between the immune system and bone, several signaling molecules and pathways previously identified in immune cells have been shown to be key players in the osteoclast, the bone resorbing cell. Osteoclast differentiation requires two signaling pathways: the RANK/RANKL pathway and the signal initiated by the ITAM-harboring adaptor proteins DAP12 and FcRgamma. Until recently, it was unclear how RANK and ITAM signals merge to cooperatively stimulate activation of NFATc1, the master transcription factor in osteoclastogenesis. A recent study from H. Takayanagi's group has shown that the tyrosine kinases Btk and Tec form a multiprotein complex with adaptor molecules such as BLNK, that is able to integrate these two signaling pathways and thus stimulate osteoclastogenesis. Taken together, these new data open novel clinical perspectives especially for osteoarticular inflammatory diseases.