Autoimmunity as a trigger for structural bone damage in rheumatoid arthritis

Bone loss is a central feature of rheumatoid arthritis (RA). It is considered to represent a sign of irreversible structural damage triggered by chronic inflammation. Recent evidence, however, suggests that autoantibodies are an important and earlier driver for bone damage in RA. This article summarizes current evidence for the role of RA-related autoantibodies in mediating bone loss. Rheumatoid factor and antibodies recognizing modified (citrullinated) proteins are the central features of autoimmunity in RA patients. Despite being used as diagnostic markers for many years, ascertaining the differentiation of RA from other forms of inflammatory arthritides, the role of these antibodies as pathogenic players has long been unrecognized. Recently, several pieces of evidence suggested that bone-resorbing osteoclasts are highly responsive to RA-related autoantibodies, providing a novel link between autoimmunity and bone. These developments have allowed unraveling the underlying mechanisms, which are responsible for the well-known clinical observation that RA-related autoantibodies are associated with a more severe disease course. At present, rheumatoid factor and antibodies recognizing citrullinated proteins are considered as potent osteoclast inducers and triggers for bone loss in arthritis.