Bone destroying cells (red) flourish in the presence (top) of the IL-17 cytokine.
Autoimmune arthritis, such as rheumatoid arthritis, is a T cell–driven disease, in which bones are destroyed by hyperactive bone-resorbing osteoclasts. Activated T cells have long been implicated in arthritic inflammation and the resulting bone destruction, but exactly which type of T cell is responsible has never been confirmed. T helper (Th)-1 cells, the cells that promote cellular immunity, have received the lion's share of the blame. Yet Th1's signature cytokine, IFNγ, actually inhibits bone resorption by osteoclasts.
The study by Sato et al. helps resolve this paradox by putting the blame for inflammatory bone destruction on a recently described T cell subset called Th17....
