A crucial role of B cells in the pathogenesis of IIM is evidenced by the relative effectiveness of B cell directed therapies such as rituximab in the treatment of IIMs [65,66,67], the endomysial production of B cell activating factor (BAFF), the presence of B cells and plasma cells in muscle tissue, antibody production, and endomysial B cell-maturation in part within the muscle itself [68,69]. The gene discussed is TNFSF13B; the disease is acquired idiopathic inflammatory myopathy.