Judy H. Cho, M.D., and Peter K. Gregersen, M.D.
The major autoimmune diseases, including rheumatoid arthritis, systemic lupus erythematosus, multiple sclerosis, type 1 diabetes mellitus, psoriasis, and inflammatory bowel disease, share epidemiologic, clinical, and therapeutic features. In each of these diseases, chronic and often intermittent inflammation contributes over time to the destruction of target organs that house inciting antigens or are the sites of immune-complex deposition. For some of these disorders, such as inflammatory bowel disease, the contribution of autoimmune mechanisms is questioned, but the overlap of genetic associations that have been identified during the past 5 years suggests a shared immune pathogenesis. At the same time, genetic data also support some distinct pathways of pathogenesis for the various disorders.
Although the adaptive immune system has long been a focus of attention, innate immune mechanisms are now viewed as being central to the pathogenesis of these disorders. In addition, the concept of quantitative thresholds for immune-cell signaling has emerged in the past decade as a potential way of understanding how multiple genetic factors of relatively small effect may combine to create a state of susceptibility to autoimmune activation. The new genetic findings have also emphasized that the identification of the environmental components that interact with host genetic factors will be critical in developing a deeper understanding of autoimmunity, as well as new approaches to prevention and treatment.