T he etiology of autoimmunity in humans remains poorly defined, and animal models provide a unique opportunity to study potential autoimmune mechanisms. A novel model of autoimmune inflammatory arthritis results from a point mutation in the ζ-associated–protein of 70 kDa (ZAP-70), which causes abnormal thymic T cell selection and survival of autoreactive clones. Although the resulting clinical and pathologic abnormalities are clearly T cell–dependent, macrophage and fibroblast cytokines such as IL-1 and TNF-α are required for full expression of the disease. The studies of Hata et al. raise the intriguing possibility that traditional proinflammatory cytokine networks represent common effector mechanisms in inflammatory joint diseases such as rheumatoid arthritis. Hence, effective therapeutic interventions can target either unique etiologic pathways related to adaptive immune responses or shared terminal mechanisms.