Regulating activated peripheral T and B cells bySle1 and possibly other genes. The size of this compartment is also controlled by activation-induced cell death (AICD) through Fas, wild-type Sle3, or other apoptosis-mediating receptors. Factors favoring the accumulation of cells (designated “+”) lead to the entry of additional cells into the lymphoid pool (left arrow). Those genes promoting reduction in cell numbers (designated “–”) result in a smaller pool (right arrow).