With age, this B cell hyperactivity leads to autoimmunity, as evidenced by the display of multiple autoimmune phenotypes in 6-month-old Blk+/− mice, including increased numbers of MZ and B1 B cells, detection of B cells with an activated surface phenotype, and production of a low but significant level of serum anti-nuclear antibodies (ANAs) [17]. This evidence concerns the gene BLK and Autoimmunity.