Osteoprotegerin

Rankel, which stands for Receptor Activator of Nuclear Factor Kappa B Ligand, helps form osteoclasts, the cells that break bone down.

Osteoprotegerin acts as a decoy that soaks up Rankel and limits its effect.

This system controls bone breakdown, but it also overlaps with the immune system because many immune cells use related signals.

Chronic inflammation can ramp up osteoclast activity and cause bone loss.