[Status of the osteoclast-activating system in cosmonauts after long-duration missions to the International Space Station].

The results of studying the system of osteoprotegerin/ receptor activator of nuclear factor kappa-B ligand (OPG/RANKL) in 22 cosmonauts after long-duration (124 to 199 days) ISS missions are presented. Immediately on return to 1 g, changes were observed in OPG and RANKL serum levels and the ability to produce unstimulated and stimulated PGA of peripheral blood mononuclear cells in vitro. Individual variability of these changes was noticed. Our findings suggest that the cytokine OPG/RANKL-system is involved in bone remodeling in members of long-duration space missions.