Role for innate immunity in rheumatoid arthritis.

Innate immunity is the first line of defense against pathogenic microorganisms (bacteria, viruses, fungi, and parasites). After a long period of neglect, innate immunity is again recognized as a key mechanism not only in preventing invasion of the body by microorganisms, but also in contributing to the pathogenesis of autoimmune and inflammatory diseases by deviating the immune response or promoting the emergence of a regulatory response. The many factors involved in innate immunity often act in parallel or in alternation to generate adaptive immune responses. Innate immune responses are specific for groups of molecules or macromolecules found in components of microorganisms, usually the cell wall. The cellular and protein effectors of innate immunity are found in the rheumatoid synovium, and an increasing body of evidence indicates that they are directly involved in joint inflammation and in destruction of the joint cartilage and bone. In addition, they may have regulatory effects on inflammation and immunity. Whether innate immune mechanisms are causes or consequences of inflammation, and whether they regulate or amplify adaptive immune responses, they constitute a target of choice for new antiinflammatory and immunoregulating treatment strategies.