In rheumatoid arthritis, T cells activation enhances osteoclast differentiation and bone destruction through receptor activator of NF-kappaB ligand (RANKL) . Recent study revealed the importance of interleukin-17 (IL-17) -producing helper T cell subset (Th17) in bone destruction. The emerging field of osteoimmunology will be of great importance not only to the better understanding of osteoclast differentiation and activation but also to the regulation of inflammation-associated bone destruction.